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Listed below are some of the more common questions that Fhrx Studio's is asked during day to day operations.
- Store related questions.
- Why should I employ Fhrx Studio's to install my system?
- Do you mail order equipment?
- How does your 'rewards' scheme work?
- Do you offer gift vouchers?
- Audio / Visual related questions.
- What's the best system I can get for XXXX dollars?
- Should I use a blocking capacitor on my midrange speakers?
- How can I destroy my speakers?
- What is severe clipping?
- What is distortion?
- How much power can my new speakers handle?
- Do I need the biggest amp possible?
- How loud will my speakers play?
- What brand of amplifier would you recommend?
- What is the optimum enclosure for my new subwoofer?
- Should I use sound deadening, diffusers or fibrefill inside my enclosure?
- What is the ideal box size for my midrange speakers?
- What crossover frequency should I use between my subwoofer and my 6" or 5" midbass drivers?
- Should I use an active crossover or a passive crossover?
- Where should I place my tweeters for best performance?
- What speaker pods and door trims can I get for different budgets?
- I've heard people recommend against 6x9's. What are the pros and cons?
- When I turn my music up, my headlights dim. How come?
- My system "pops "when I turn it off. How do I stop it?
- How do I tell if my speakers are in or out of phase?
- How do I use my faders and balance settings to make my system sound better?
- Can my car stereo really hurt my ears?
- Is there a place I can talk to someone about this stuff?
- What are the different amplifier classes all about?
- What amplifier specs should I look out for?
- Can you simply explain Ohms and resistance?
- Which way should I aim my subwoofer?
- What is the highest sound pressure level (SPL) we can achieve?
- How do I set my gains?
- What do all the Theile / Small parameters stand for?
- Do I really need sound deadening in my doors?
- Should I upgrade the speakers in the rear of my car?
- Are the expensive cables really worth it?
- Do my subwoofers need separate chambers within their enclosure?
- What grille can I get to protect my subwoofer?
- What are the frequencies of sound?
- Can you explain batteries, capacitors and cycles?
- Is there a website that lists all manufacturers?
- Should I upgrade my earths?
- What subwoofer enclsoure can I get for different budgets?
- How does 'Qtc' effect my bass?
- Door installation guides. We put these on forums so you might have to join to view them.
- How to install midrange speakers into an Holden Astra door.
- How to install midrange speakers into an Integra door.
- How to install midrange speakers into a Mazda 3 door.
- How to install midrange speakers into a Mazda 323 / Astina door.
- How to install midrange speakers into a Mini door.
- How to install midrange speakers into a Nissan Pulsar door.
- How to install midrange speakers into a Nissan Skyline door.
- How to install midrange speakers into a Subaru WRX door.
- How to install midrange speakers into a Toyota Supra door.
Why should I employ Fhrx Studio's to install my system?
With many people being burned by shoddy workmanship and corner cutting, we strive to produce the best install possible for any desired budget. For info about us and more reasons to come see us for your next install, Click here.
Yes we certainly do! We're always more than happy to take orders via email and phone. Payment can be made by either credit card, cheque, cash or direct debit (internet transfer). Upon clearance / receipt of payment you're issued with a receipt. Items are shipped via Australia Post and are registered and insured.
We are also more than happy to ship to New Zealand. Note; due to some of our agreements with certain distributors and companies we are forbidden to ship certain brands overseas. If in doubt, please ask as these conditions constantly change.
How does your 'rewards' scheme work?
Put simply, we're more than happy to reward friends and customers that get us additional work. If you get us a job or if your name is mentioned as the referrer for a job that comes in the door, we'll rebate you 3% of that particular job total. It is as simply as that. For example; if your best mate gets $10000 worth of work done with Fhrx Studios and names you as the referrer, then you'll get $300 cash back.
We certainly do. If you're stuck for ideas on what present to give a friend or relative how about giving them a Fhrx Studio's gift voucher? We can supply gift vouchers for any value and can even post them fully wrapped to people if that suits you better.
What's the best system I can get for XXXX dollars?
We're constantly asked what the best systems are for various budgets. The short answer is that there is no right or wrong
answer to this question. Everyones ears and tastes are different so the best thing to do is audition as many products as possible
and chose based on what you like the most. Listed below are various product most commonly chosen by our customers. These are also
amoung the products that win the most competitions in Australia. However, there are a few things to remember:
Should I use a capacitor on my higher frequency speakers?
Remember midranges and tweeters are not designed to play subsonic (in the case of midrange) and midrange (in the case
of tweeters) frequencies. Therefore, many midranges and tweeters benefit from a capacitor wired in to prevent lower range
signals travelling to them. On the larger midranges you can go without them but more often than not the midrange speaker
naturally rolls off.
How can I destroy my speakers?
When asked how one can destroy speakers we reply by explaining there is only three real ways. The first is thermally and this
is the most commonly occurring. Breaking the equation down further there are only two ways to thermally destroy a speaker
(and crossover in the case of split systems); over powering and under powering. Over powering the speaker with way too much
power will cause the voice coil wire (which is receiving more current through it then its rated too) to melt and short on the
magnet. This is simple enough to understand so if you have a 200 watt subwoofer then you don't feed it 2000 watts. However much
more dangerous is under powering the speaker because the end result will be the same but it happens in a slightly slower and
sneakier way.
In audio systems where you hear speakers 'distorting', it's not the speaker that is causing the struggle, it's the
amplifier. Speakers are quite simple devices and don't discriminate. They cannot tell the difference between harmonic sound and
rough distorted noise and simply reproduce whatever wave signal is given to them regardless of what it may sound like. When you
ask the amplifier to do its job (by turning the volume up) it takes a comparatively small sound wave and amplifies it before
sending this bigger signal to the speakers. If you ask your amplifier to produce more than it's capable of it will attempt to
achieve this request but the output sound wave becomes rough and distorted as the amplifier reaches its power output threshold.
Pushing it beyond this point causes the amplifier to begin clipping. When a woofer is driven hard by a high power amplifier there
is a significant amount of current flowing through the voice coil. The voice coil has resistance and therefore a voltage drop
across it occurs. This means that there may be a great amount of power being dissipated in the form of heat within the voice
coil. When a speaker is driven with clean power the cone moves back and forth a great deal. You'll notice many speakers have
perimeter vents in the basket and pole vents in the back. The speakers movement forces air to flow in through these perimeter
vents and into the magnetic gap (the area where the voice coil lives and moves) before flowing out the pole vent (and hopefully
taking the heat with it). When the cone moves forward out of the basket, the area that's under the dust cap and around the voice
coil increases in volume. This pulls cool air into the magnetic gap. When the woofer moves the other direction, the chamber size
is reduced and the hot air is forced out of the pole vent. This air flow cools the voice coil.
When a relatively low powered amplifier is driven into clipping (to the point of full square wave sometimes) the voltage
delivered to the voice coil no longer resembles a sine wave because the amplifier clips the top and bottom of the wave off
(because it's beyond what it can do). While this output is clipped (the flat spot on the top of the wave) the voice coil in
your speaker is not moving but instead remains almost stationary at this time with high current still running through it. Because
the voice coil is not moving it is not being cooled sufficiently (remember the coil is driven by a linear motor therefore the
more voltage applied to the voice coil, the further it moves). In the image above you see that at points A, B, D, E, F and H
the voltage is changing causing the voice coil to move in the gap and therefore pull in fresh cool air. At points C and G, the
voice coil is still moving a little but this is only due to momentum. This is not enough to cool efficiently and there is still
full current flowing through the voice coil. Since the displacement of the voice coil (and the relating airflow around it) is no
longer proportional to the heat being generated, the voice coil will overheat. This excess heat (just as with overpowering)
causes the voice coil to melt its insulation and the former to physically distort. Basically the whole motor burns apart as
adhesives start to fail. However before you stress too much it should be noted that many reputable manufacturers underrate
speakers so generally slight clipping isn't a problem. Severe clipping is more likely to cause a problem.
The second way to destroy a speaker is physically and this can also be broken down into two facets. The first physical facet
is what we call bell mouthing. This is where the voice coil and former are driven so hard they actually extend beyond their
normal range of motion and impact the back plate on the bottom of the speaker. This continual impacting causes the bottom of the
voice coil to bend out like the bottom of a bell and this eventually cause the coil and corner to become so physically disfigured
that it rubs on the magnet surrounding it and eventually comes to a complete halt. This isn't just restricted to subwoofers
either. Tweeters playing frequencies that are too low tend to suffer from this phenomenon too because they're not designed for
high excursion. The second facet of physically destroying a speaker is to punch way too much power into it fast and this causes
what us engineering types like to call critical structure failure. That is a technical way of saying you'll simply tear the
surround and/or spider(s) and pop the cone and motor assembly right off the frame. To 'blow the guts out of the speaker' is
the more Aussie way of saying it. This is commonly witnessed during sound pressure level competition because the drivers are
being pushed to their absolute limits.
The third and final way to destroy a speaker is an age old enemy of technology; sunlight. Nothing breaks down and erodes foam
surrounds faster than sunlight (well except bugs like moths but you shouldn't have them living in your car). After only a few
months of direct sunlight your speaker surrounds will be significantly weakened and may eventually begin cracking or simply tear
all together. Butyl rubber surrounds are more resistant to sunlight but eventually all materials succumb to the mighty sun. The
best thing to do with shelf speakers is place some grille cloth over the factory grilles. This helps in resisting ultra-violet
rays from the sun penetrating through to the speaker.
These are the three main causes of most damaged speakers. The end result is the same with all three methods but you tend to get
a lot more warning with thermal or sunlight damage. Physically speaking though; if you're pushing your speaker way beyond what
its rating dictates you'll get very little warning before your speakers starts to smoke or literally explodes.
What is severe clipping?
Now that you know about clipping (see above) we move to severe clipping (a.k.a square wave). It always amazes me when I
hear some idiot driving down the road and the audio is clearly distorted (you know what I mean). Many people drive their
amplifiers into what could be called a square wave output (white line below). When an amplifier is pushed that hard, it is
actually possible to drive the speaker with twice as much power as the amplifier can cleanly produce into the speaker. As
you can see below, the yellow sine wave is the maximum 'clean' output that the amp can produce. When an amplifier is pushed
way too hard, the signal will eventually look like the white line. The effective voltage of the white line is ~1.414 x the
yellow line. This means the total power driven into the speaker by the clipped (square wave) signal is double the power
delivered by the 'clean' signal (yellow line). This means that the power is double but the cooling of the voice coil will
not increase in proportion with the power increase (since the voice coil isn't moving as much as it needs to be for the
given power dissipation). This will lead to the voice coil overheating. If we compared the output of a 100 watt amp (the one
that's clipping) to a 200 watt amp, the 200 watt amplifier would be able to push the speaker as much as 40% farther than
the 100 watt amp (depending on the frequency of the signal). This extra travel (in each direction from its point of rest)
would result in added airflow around the voice coil.
Note: The RMS voltage of a pure sine wave is equal to the peak voltage multiplied by 0.707. The RMS voltage of a pure
square wave it equal to the peak voltage. For 2 waveforms with equal amplitude (as shown above), the RMS voltage of the
square wave is 1.414 times the voltage of the sine wave. If we use the example of the 100 watt amp which can produce a
sine wave of 20 volts RMS, we can see that the output power at hard clipping is double the power it can produce cleanly.
What is distortion?
Well, to get a little more complicated, distortion is any departure from a true and accurate reproduction of the
original waveform. It can include Noise, Clipping Distortion, Harmonic, and Intermodulation Distortion. These last two forms
are fairly common in loudspeaker reproduction and can be reduced but not entirely eliminated in the existing technology.
It would be fair to say that modern amplifier design fairly eliminates nearly all forms of inherent perceived distortion,
leaving only that caused by inappropriate user settings and overloading.
Distortion is the name given to anything that alters a pure input signal in any way other than changing its size.
The most common forms of distortion are unwanted components or artifacts added to the original signal, including random
and hum-related noise. Distortion measures a system's linearity - or nonlinearity. Anything unwanted added to the input
signal changes its shape (skews, flattens, spikes, alters symmetry or asymmetry). A spectral analysis of the output
shows these unwanted components. If a circuit is perfect, it does not add distortion of any kind. The spectrum of the
output shows only the original signal - nothing else - no added components, no added noise - nothing but the original
signal.
It's rather amusing to see amplifier manufacturers making great claims about the advantage of the extra .001 %
Distortion they've wrung out of their products, while most speakers are considered very good if they can keep such
distortions below 5 %. It's true that the reduction of any distortion anywhere is a positive contribution to the goal
of high fidelity, but the disparity between the two technologies in this regard points up the largely subjective nature
of many such claimed advantages.
Here are some of the definitions:
How much power can my new speakers handle?
If you've read the FAQ above you'll already know that you're better off with too much power than not enough. That's no
to say however that speakers cannot be damaged by too much power; they can!
All speakers have a rated power handling level and this comes in handy as a rough guide to know how much power
to feed your speakers. A speaker's general power rating tells you how much A.C. power can be dissipated in the speaker's
voice coil without damaging the speaker. The realistic way to rate a speaker is to give the rating as continuous
RMS watts. Many speakers are advertised as "150watt" or "100watt" speakers and you may be forgiven for thinking that
the 150watt speakers are better and will play louder than the speakers rated at 100watts. The first thing you should
realise is that speaker ratings are often exaggerated for marketing reasons. Check to see if the rating is in RMS or peak
watts and are the speaker ratings for maximum or continuous power. Most car audio speakers (with the exception of some
subwoofers) are rated in peak power or music power. Only a few speakers (generally the higher quality speakers) are rated
in RMS watts. While peak power is a legitimate way to rate speakers (as long as the manufacturer tells you that the power
rating is in peak watts), it can be deceptive.
When talking peak vs RMS, you know that peak power is 2*RMS power. If a speaker is actually capable of handling 150 watts
of peak power it would only be rated to handle 75 watts RMS. If a speaker is rated to handle 150 watts 'music power' it
may mean that the speaker will take only very short bursts of power approaching 150 watts RMS. Even if there are two
speakers from different manufacturers which have the same power ratings, one of the manufacturers may be more conservative
in their ratings than the other manufacturer. The more conservatively rated speaker would be more likely to handle its
rated power. The bottom line is beware of power ratings on speakers. Knowing that some manufacturers are somewhat optimistic
with their power ratings will help you to make better decisions when buying speakers.
A quick word on amplifiers and speakers. Many people ask us "Can my speakers handle this amplifier or will this
amplifier blow my speakers?" The simple answer is that any speaker can be driven by any amplifier. The only time that
issues arise is when the person operating the system becomes careless. Sadly most people drive their amplifiers well into
clipping. See above for explanations on clipping.
Do I need the biggest amp possible?
The answer to this question depends on factors such as how loud you like to listen, what speakers you're using and
what your budget is. Remember we always say that the bigger the amplifier the better because the larger the amplifier, the
less work it must perform to successfully drive the speakers. Larger amps keep their THD low, their efficiency and control
level high and they stay cooler. It's better to have a larger amplifier doing minimal work than to wring the neck out of
your smaller one. Remember though that too much power can also damage speakers so the gains MUST be set correctly.
How loud will my speakers play?
Look up the sensitivity rating of the speaker, which is expressed in dB/watt/meter. For example a speaker
with a 89dB sensitivity will produce 89dB of sound 1 meter (39") from the speaker with a 1 watt input. For
every doubling of power input the SPL (volume) increases by 3dB. So in this case, assuming a 100 watt power
handling spec:
Power input (watts)
So, theoretically, the SPL limit of this speaker would be somewhere between 107dB and 110dB.
What brand of amplifier would you recommend?
There are literally thousands of amplifiers to choose from out there. This is where an installers experience comes in
handy. Serious installers will listen to your demands and then recommend an amplifier that best suits your desires.
Beware of "bargain" amps though as cheap amplifiers are exactly that and you'll often have problems not
too long down the track. Too much power for too little money generally means that corners have been cut somewhere in
quality of construction or service back-up. Aim for about $2-$3 per watt for quality.
What is the optimum enclosure for my new subwoofer?
Most subwoofers come with recommended enclosure volumes in the owner's manuals. More often than not this enclosure volume
is safe allowing for the most 'home user error'. Specialized shops however use complete manual's and specialised computer
programs to carefully design enclosures for specific applications based on the subwoofers paramters. The following is a
very basic crash course on box types (this topic gets very in depth).
Sealed Ported Bandpass Obviouly the same thing be accomplished by placing a low pass crossover on the subwoofer system but a bandpass enclosure
can produce significant performance benefits in terms of efficiency and/or deep bass extension that would not be possible
in conventional designs of equal size. By adjusting the volumes of the front and rear chambers and the tuning of the port
or ports, significant performance trade-offs can be created. When box parameters are adjusted for a narrower bandwidth the
efficiency of the subwoofer system within that bandwidth increases and can reach gains of up to 8dB and sometimes even
higher. As box parameters are adjusted for wider bandwidths, very impressive low-frequency extension can be produced from
extremely compact enclosures at the expense of efficiency and good transient response. Intermediate bandwidths can also be
designed which create a compromise between all these characteristics. As if that is not confusing enough, within each
bandwidth range the designer can also manipulate box parameters to shift the range of operation up or down the sub-bass
range which also has an effect on efficiency. As you can see, bandpass enclosures can have very different sound
characteristics based on the designer's choice of box parameters. As such, it is not always possible to make blanket
statements as to the performance benefits and drawbacks of bandpass enclosures in general.
One characteristic of bandpass enclosures which is universal is that they exert greater control over cone motion over a
wider frequency band than conventional designs. Due to controlled, rapidly changing air pressure on either side of the
woofer, the woofer is capable of producing high levels of acoustic output without physically moving very much. This means
that the woofer is less likely to encounter excursion limits in the main part of the sub-bass range. However, just because
the cone isn't moving as much doesn't mean that the speaker's motor assembly isn't still trying to drive the cone hard; it
just means that the speaker cone is encountering resistance to motion. This resistance can be very hard on speakers,
especially when SPL heads are playing their music. The conflict between the force generated by the motor assembly and the
air pressure in the enclosure can impose extreme stress on the glue joints and suspensions of the woofers. You can
literally tear a speaker apart in a bandpass enclosure if you apply too much power. Because the speaker is not moving as
much and because noises are masked by the front chamber, it is also very difficult to hear when a woofer is in serious
trouble. Many people have been known to crank bandpass enclosures up and blow the speaker to bits within a few minutes
because they did not realize that the speaker was dying a horrible death. Choosing the right amount of power and carefully
setting amplifier gains is very important in order to ensure long term reliability.
Bandpass enclosures can be divided into two basic types; single and dual reflex. In a single reflex design, the rear
chamber is sealed and the front chamber is ported. In a dual reflex design, both front and rear chambers are ported into
the listening area. A variation of the dual reflex and single reflex, known as "series-tuned," has a port which connects
the rear and front chambers. The differences between single reflex and dual reflex bandpasses are similar to the
differences between sealed and ported enclosures. A single reflex typically exhibits a shallower low-frequency roll off
rate (e.g. 12dB/octave) and better transient response. A dual reflex is more efficient and controls cone motion over a
wider range but typically has a sharper (e.g 18-24dB/octave) low frequency roll off. Because of the difference in
low-frequency roll off rates, a dual reflex usually has to be larger in size to produce the same low frequency extension
as a single reflex design.
Compared to more conventional enclosure designs, bandpass enclosures are very complex to design and build. The rules
governing the performance of bandpass enclosures leave no room for error. Slight volume miscalculations or sloppy
construction can turn a good design into a poor performing box. Integrating the proper size port or ports can be extremely
challenging and often renders designs that looked great on paper completely impractical. The design of these boxes should
definitely be left to people with extensive enclosure building experience.
Should I use sound deadening, diffusers or fibrefill inside my enclosure?
The debate on whether to use sound deadening material, diffuser panels and fibrefill inside an enclosure has been around
for a long time. However, this debate needs to be broken down into two areas because you're actually addressing two separate
issues when asking about these materials. The first issue is regarding standing waves and the second is regarding the
delaying of sound waves and the smoothing of resonance. Well start with standing wave issue first.
Standing waves Sound delaying and resonance smoothing What is the ideal box size for my midrange speakers?
Assuming your 3" / 4" / 5.25" / 6" / 6.5" speakers are midrange drivers and not subwoofers (Focal make a 5.25" subwoofer for
example), you shouldn't need to make a sealed enclosure for it. In most cases (but not all) there is no need to build sealed
enclosures for these midrange drivers because their suspension (the spider and surround) is designed to operate in an infinate
baffle situation such as a door or rear deck of a car. In other words, most midranges are free-air drivers. However, it's always
best to consult the manual for your new speakers if you're not sure.
What crossover frequency should I use between my subwoofer and
my 6" or 5" midbass drivers?
There's no quick and easy answer to this question, It all depends on the car and the overall design of the
system. Generally speaking you don't want your subwoofers to go much higher than 80-100Hz. Typically when you set
your subwoofer crossover point you will use that as a starting point for your high-pass on your mid/bass drivers.
Sometimes you will need to increase the crossover frequency and sometimes you will need to lower it. It is basically
all a matter of personal preference and the acoustics of your car. Electronic crossovers make it very easy to try
a variety of crossover frequencies to see what works best for you and your car.
Should I use an active crossover or a passive crossover?
Active crossovers are ones that effect the signal before it is sent to the speaker. Passive crossovers sit near the
speaker and filter out certain signals coming towards the speaker. Using either you'll achieve the same aural result but
it's a lot easier to adjust an active one.
I've heard people recommend against 6x9's. What are the pros and cons?
It seems there are few debates in the known world larger than the one concerning the humble 6x9" speaker. Now depending
on which side you're on (as there seems to be no middle ground these days), 6x9's are either a little nuisance that you'd
rather have sitting far in the rear of the car or better still, on the road behind the car, or you cannot even contemplate
a life without them.
Lets begin with some basics. 6x9's are oval shaped speakers aptly named because they measure 6 inches by 9 inches. There
are slightly different versions measuring 7x10, 4x6 and 6x8 on the market but let us concentrate on the daddy of the group.
6x9's are more often than not three or four way drivers (that is; three or four speakers in one unit) and comprise of a 6x9
woofer, smaller mid-bass (or two) woofer and a tweeter mounted on a bridge over the main woofer. They are commonplace in
many different factory audio systems right over the world.
But I have heard so many conflicting opinions… Lets look at the cons first. But they must have some pro's. Expense. Time. Space. Money. Say it how you will, 6x9's are a hell of a lot cheaper than lashing out on a large external
amplifier, sub enclosure, subwoofer and splits. And they will take up a lot less room too incidentally. At the end of the
day 6x9's make an excellent addition to budget systems and make terrific factory upgrades because they do a little of
everything quite acceptably. They are very good drivers for beginners and people looking for a little more of everything
but lets be realistic, they won't keep the staunch audio buffs satisfied for long.
When I turn my music up, my headlights dim. How come?
Your headlights dim because your audio system has caused a drop in the available voltage level of power
for your car's other, less necessary accessories (headlights, engine, etc.). Voltage drops can be
caused by an accessory's large current demand, like an amp struggling to produce a loud bass note. Get
your battery and alternator checked. A low battery can overload an alternator, drawing power away from
your system. If everything checks out okay, you could be making such large demands on your electrical
system that an upgraded alternator may be necessary. A "stiffening" capacitor can also be installed. A
stiffening capacitor is like an extra power supply for your electrical system; it keeps a small reserve
of 12V power. See your installer. If your car won't start after you play the stereo for a long time w
ith the engine off, try paralleling another battery into your system. Another reason this happens is because the battery
negative to body has not been upgraded. Remember whatever positive cables you add to your battery, the equal negative must
also be upgraded.
My system "pops "when I turn it off. How do I stop it?
As you power-down, transient signals in the processor sometimes find their way into the signal
path. The amp transmits them to the speakers, and POP! Add some "turn off delay" to your head unit.
See your manual, or your installer. Or, read this: You can add delay by adding a 1N4004 diode in
series with the processor's turn-on lead, with the striped side towards the equalizer. Then add a
capacitor in parallel, the (+) side of the cap to the striped (processor) side of the diode; the (-)
side of the cap to ground (not the radio or eq chassis, connect it directly to the car chassis).
Fiddle with the cap value to get the amount of delay you need before the eq shuts off; not too long,
just long enough to make sure the amp is off before the eq powers down (220 - 1000 uF). Make sure the
cap is a polarized electrolytic, 16V or higher, and remember that the diode introduces a 0.7V drop on
the remote wire, which can cause the processor to power down before the rest of the system. There will
be a quiz.
How do I tell if my speakers are in or out of phase?
If your speakers are out of phase, imaging will be vague and bass output will be reduced. To ensure
that your speakers are hooked up in phase, check to make sure that the positive and negative leads are
connected the same way to both your speakers and your receiver or amp. Make sure red is connected to
red, black to black, etc. Check for correct phasing... With a 9-volt battery. Disconnect the speaker
wire from the amp. Touch the wire you think is negative to the negative battery terminal (the big one).
Touch the positive wire to the positive battery terminal (the other one). If your speakers are wired
in phase, the speaker cone will move "out" and stay there. If they are out of phase, the driver cone
will move "in" and stay there. (This won't help you for tweeters, only midranges and woofers. So when
you're wiring your tweeters, be careful. Do it right the first time.) Phasing is never absolute in car
audio situations, since speakers are rarely facing the same directions. Phasing differences mostly
affect bass. Is your system lacking bass? Try changing the phase on your sub system. 90% of the time,
that's the key to more bass!
How do I use my faders and balance settings to make my system sound better?
Proper setting of your front-to-rear fader and left/right balance controls is important for optimum
staging and imaging in your system. Too much sound in the rear of the car (sometimes called "rear
fill") will often eliminate staging altogether, forcing sound away from the front of the car, while
too little rear fill will sound dull. Too much sound on one side of the car or the other will add an
unrealistic element to the imaging. To adjust fade and balance, play a tape or CD you are familiar
with and turn the rear speakers on full with the fade control. Listen to the rear speakers, and then
slowly turn the fade up in the front speakers just until you can't tell the rear speakers are playing
anymore, then ease off a tad. You're probably close to optimum setting when the front staging is such
that the rear speakers provide little more than ambiance and space to the sound. Test it by going full
on the front speakers (without losing the position you just attained). You'll hear an immediate loss
of spaciousness in the sound with the rear speakers faded all the way down. Return to your optimum
setting. Setting the balance is more difficult, so it's always a good idea to leave the balance fader
at the "12 o'clock" position. That's as close to equal as you're going to be able to hear with your
own ears.
Can my car stereo really hurt my ears?
It most certainly can. Prolonged exposure to sound pressure levels above 85dB will cause permanent hearing damage.
Professional audio competitions specify the use of hearing protection devices for their contests,
especially at higher volume levels. You can test the dB level of your car stereo with a Sound Pressure
Level Meter (available at electronics stores). If you're disoriented and your hearing is sort of
muffled after you've been listening to your car stereo, or you hear ringing in your ears, then turn it
down! If you have to shout at the person in the passenger seat, and you're not angry with them, then
it's a good bet that your stereo is too loud. For the sake of your hearing, turn it down.
Is there a place I can talk to someone about this stuff?
Sure is. Marty and Co and thousands of other car audio enthusiasts are often found in the audio section of
the Fast Fours Forums. Click here
to go there. There are also many technical articles on Car Audio
Australia, Aus Car Audio and
Elite Car Audio.
What are the different amplifier classes all about?
All sound is a sinosoidial waveform in that it has alternating peaks and valleys. The center point of each wave is the
zero, or switching point that separates the positive (top) from the negative (bottom) portion of each wave.
When a tube or transistor amplifier operates in Class A, the output tubes or transistors amplify the entire waveform
without splitting it into positive and negative halves. Class A amps usually provide lower, often imperceptable distortion,
but at the expense of reduced power output.
In Class AB, used in the overwhelming majority of amplifier designs, the signal is split into two halves, positive and
negative, and each half is sent to a tube or transistor circuit for amplification. Both sides work in tandem, and the two
halves are recombined at the output section to reconstruct the whole signal. This technique increases the amount of power
that can be applied, but increases distortion.
Class D or High Current operation is essentially rapid switching, hence the term switching power amplifier. Here the
output devices are rapidly switched on and off at least twice for each cycle. Theoretically, since the output devices are
either completely on or completely off they do not dissipate any power. If a device is on there is a large amount of
current flowing through it, but all the voltage is across the load, so the power dissipated by the device is zero; and
when the device is off, the voltage is large, but the current is zero. Consequently, class D operation (often, but not
always digital) is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast
switching times -- a product yet to be made; meanwhile designs do exist with efficiencies approaching 90%. Class D
design is increasingly popular for driving subwoofers, where maximum power is necessary, and slightly elevated levels of
distortion are easily tolerated.
What amplifier specs should I look out for?
Choosing an amplifier is about more than just watts. When speaking to anyone about achieving quality music in car audio
most people simply focus on the speakers rather than the amplifier. They often speak about speaker build quality and power
handling, enclosures, porting, fibrefill, loading and speaker cable. You don't really need to worry about the amplifier so
long as it's powerful enough right? Just like when you're considering the purchase of a new car; the only thing you need
to look at is the power output of the car alone right? Wrong.
When choosing an amplifier to power your speakers there are more stats than just power output you need to think about
before you splash a couple of grand on an amp that will sound like rubbish. For those among you dreading an upcoming
lecture on amplifier classes, resistors, capacitors, transistors, transformers and power supplies relax, I'll keep this to
plain English for the explanation of which stats to look out for. High power output is important but quality amplifiers are
not just about sheer power. Mining dump trucks have over 6000 horsepower but that doesn't make them spectacular performers.
Besides power there are certain other important figures that must be taken into consideration when choosing a suitable
amplifier. We'll go through a few of the more commonly found stats.
Damping Factor Slew Rate Total harmonic distortion Signal to noise ratio Stereo separation. Just a final few points to remember while you're looking at specs. You'll find many are followed by the term 'A weighted'. Put
very simply, 'weighting' is part of a compensation system that accounts for various factors (for example, one such factor is the
human ears' natural hearing curve). However; sadly some companies are guilty of using this weighting to make its amplifiers
figures appear more attractive. Loading is another issue to consider. Watch the impedance of speakers when choosing them because
while most amps are stable at low impedance levels, they're not overly efficient nor performing 100% when loaded down. Your cars
engine is 8000rpm stable but it's unwise to try and keep it there for long. By the same token many amps are 2 and 1 ohm stable but
this is for intermittent spikes (as music is dynamic it causes the speakers resistance to continuously change during playback),
not continous everyday running.
These are some of the more important figures to observe when buying amplifiers. It's not
simply just a matter of buying which ever amp outputs the most power. It's a matter of taking all the figures into
consideration and choosing which amplifier best suits your needs.
Can you simply explain Ohms and resistance?
Well lets see? Put simply, Ohms is the measurement of electrical resistance and system impedance. It is a measure of the
degree to which electrons are limited in both velocity and quantity in passing through a circuit. In Impedance
measurements, this takes into account, the mechanical resistance inherent in the motion of transducers. The standard is
usually 4 ohms for car audio and 8 ohms for home and commercial audio. Some specialty woofers may be rated at 2, 6, 12 or
even 16 ohms. You would have seen the 12 ohm JL's before no doubt.
Ohm's Law is the he mathematical relationship between voltage, current, and resistance. It is named after George Ohm,
it's discoverer. Ohm's law states that current volume in a conductor is directly proportional to the voltage flow across
it and inversely proportional to its resistance (assuming the temp remains constant). In general, this means that more voltage will produce more current, if
resistance stays the same, but higher resistance will cause current to decrease if voltage stays the same. In mathmatical
terms, V = I x R, where V is voltage, I is current, and R is resistance. Ohm's law is a description of electron behavior
upon which virtually all understanding of electronics is based.
Just for further background information, you might have heard all this called resistance of impedance so I'll give you
a little more info on those two things as well.
Regarding resistance, almost all conductors of electrons exhibit a property called resistance. Resistance impedes the
flow of current. It is measured in units called Ohms. With a water hose, resistance could be regarded as friction between
the water and the hose. A larger hose would create less friction and have a lower resistance than a smaller hose. It could also be a finger over the hose end. In
electrical circuits, small round cylinders with wires on either end are called resistors. These typically reduce the flow
of electrons to serve the specific requirements of the circuit elements, such as amplification or switching functions.
Finally, Impedance. The totality measured in Ohms of all electrical opposition to current flow: resistance, reactance,
capacitance, as well as all mechanical factors inhibiting the completion of energy transfer in a contained system. In
practical terms, this means that most Drivers are assigned a certain nominal impedance based on their DC voice coil
resistance and mechanical stiffness. For car audio this is usually 4 ohms; for home stereo, 8 ohms is the standard. Put
simply, your voice coil has a certain amount of copper winds in the voice coil(s). If you want a high resistance, triple
the amount of winds and the current suddenly has to do X amount more work to travel past the coil.
Which way should I aim my subwoofer?
The aiming of subwoofers has been quite a topic of speculation for years now in car audio. Through experimenting many
people have found that their subwoofers sound much better when aimed backwards. Many people realise that there seems to be
much more bass with the boot open than with the boot closed. We've heard a great deal of strange and utterly incorrect
theories to explain this phenomenon.
The main reason this phenomenon occurs is all about sound waves (direct and reflected) and more importantly the
cancellation of these waves. The diagrams below assist in showing the sine waves and their phase relationships between
the direct sound wave entering the car and the reflected wave that hits the back of the boot and reflects forward. Since
the reflection is bounced into the listening area one can treat them much the same as having two sources.
In the above picture the vertical black line at the left of the picture is the boot rear panel (the beaver panel the tail
lights are mounted on). This picture is an illustration of what happens when sound comes out of the front side of the
subwoofer enclosure. Sound travels forward into the car (the purple wave) and also backwards to reflect off of the back of
the boot (the red wave). Both the direct wave and reflected wave get to the listener but they are slightly out of phase
causing a variable amount of cancellation in the listening area. At this stage if you opened the boot the reflected wave
would disappear and not reflect back into the car, thus resulting in no cancellation.
In the picture above picture the speaker box has been aimed at the boot instead of the rear seat and you can clearly see the direct
and reflected waves are not nearly as much out of phase as in the first example. This resulting in much better bass
reproduction.
This picture above represents the subwoofer enclosure being moved to the rear of the trunk with the subwoofer aiming forward.
The waves are a little closer to being in phase with each other.
In this picture (above) we're aiming the rear mounted subwoofer enclosure at the rear so the direct and reflected wave are very
close to being in perfect phase from the start and hence they reinforcing each other quite well.
Note; these pictures are simulated using a 60Hz note with the rear of the box mounted approximately 3 feet from the back
of the boot. Keep in mind we're only discussing the direct and rear reflected sound in an effort to try to simplify this. The
reflecting sound waves in a car are much more complex than these drawings indicate but we must start simple before getting too
carried away. For example, remember that placing the subwoofer cone face too close to any panel can load it (resulting in a similar
effect to that achieved by a bandpass enclosure) but we'll worry about that another day. This explanation should be a nice
foundation for those of you who wish to study this phenomenon further. One other thing we should mention is that before people
comment that this cannot be true because the interior of cars being small in relation to bass wavelengths, the full wavelength does
not have to completely develop to be in or out of phase with its own reflected sound. The pictures above are showing a 60Hz
wavelength and the bounce distance to reflect back out of phase a complete 180 degrees is just over 4 foot. At higher frequencies
the distance is less (120Hz is 2.3ft for example). Remember, the key is to experiment and see what works best for you and your vehicle.
What is the highest sound pressure level (SPL) we can achieve?
Ever wondered just how loud or soft sound pressure can get? Or have you got no idea what all those dB readings you keep
hearing about actually compare too? Well click
here to find out.
How do I set my gains?
Contrary to popular belief, the amplifier gain control is not simply a volume knob that determines the maximum volume
that an amplifier can produce. As long as the head units signal (which runs down the RCA cords) has sufficient power the
amplifier is able to produce its maximum power output level. It's a matter of getting the full volume range of the head
unit to match the full output range of the amplifier(s). The gain controls do exactly that. They are also used to match
other amplifiers in the system (in the case of a multi-amp system). Not all head units have the same maximum preamp output
voltage. Some head units are capable of producing 9 volts on their preouts while others are only capable of 1.5 volts.
Please note that most head units will reach their maximum output level (and begin clipping - see above) just before the
volume control reaches the upper end of its range (usually at a point of 85-90% of its maximum range).
Assuming your amplifier is the right power for the speakers (around the same as their rating), the proceedure of setting
the gains is not overly difficult. First you set everything onto zero. All amplifier gains
should be turned right down and all head unit boosters (like the loudness button) should be off. Then turn your deck up
full volume and then back it off to about 85-90% (eg if your Alpine deck goes to 35, bring it up and then back off to 33-34).
Moving to the amplifier, slowly bring the gain up until the distorting becomes audible. Once it's audible, turn it back
ever so slightly and that is your gain set for that amp.
Now remember if your amplifier output is much higher than your speakers rating (e.g. running 50 watt speakers with a
500 watt amplifier) the amp will destroy the speakers long before it begins to distort at all. For this reason we strongly
recommend that unless you're a pro, you purchase the correct size power amplifier for your speakers. If you do have a larger
amplifier for superior control then you will need to get a pro to set the gains. It can be difficult to set the gains when
there is more power available than the speakers can handle.
In plain English, what you're doing is insuring the entire volume range of the head unit (e.g. 0-35 on Alpine head units)
matches the entire volume range of the amplifier. In multiple gain / mulitple amplifier situations, we usually recommend
setting the midrange amplifier first as it is easiest to hear distortion through midranges (human ears are most sensitive to
1000-2000hz).
What do all the Theile / Small parameters stand for?
This listing and explanation is from the "
the12volt.com" website.
As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and
0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle
applications. However, there are exceptions! The Eminence Kilomax 18 has a Qts of 0.56. This suggests a sealed enclosure, but
in reality it works extremely well in a ported enclosure. Please consider all the parameters when selecting loudspeakers. If
you are in any doubt, contact your Eminence representative for technical assistance."
Do I really need sound deadening?
Ever visited a cinema with no carpet on the walls? Ever wondered why most home theatre walls have curtains? Maybe you've seen
a car or jet test cell without diffusers on the walls? What about a radio studio or sound recording booth without diffusers? No?
Starting to notice a pattern? Sound deadening and diffusers are fundamental cornerstones (and arguably one of the most important
aspects) of any sound system. They're so important in fact, that they should be budgeted for long before the speakers themselves
are. However before we delve into the wonderful world of what sound deadening and diffusers actually do, let's first take a step
back and look at what sound actually is.
Simply put; sound is differing frequencies of pressure waves. Expanding that concept a little; when sound is created in a
medium (i.e. it cannot travel through a vacuum) it's in the form of a mechanical wave. This wave is the result of back and forth
vibration of the particles that make up this medium. As sound waves move through air the particles are displaced both right and
left as the energy of the sound wave passes through it. The motion of these particles is parallel to the direction of the energy
origin and this phenomenon is why we characterize sound waves in air as longitudinal waves. A speaker cone is designed to create
such a longitudinal wave. As the cone moves back and forth it pushes on neighbouring air particles. The forward motion of the
cone pushes air molecules horizontally to the left while the backward retraction of the cone creates a low pressure area allowing
the air particles to move back to the right. This movement creates regions in the air where the air particles are compressed
together and other regions where the air particles are spread apart. The high pressure regions are known as compressions and the
low pressure regions are known as rarefactions (note; not refractions - that's to do with light waves).
Wavelength (also known as path length or soundwave length) are common terms when talking speakers and physical sound.
Wavelength is the distance the aforementioned disturbance travels along the medium in one complete wave cycle. However at this
stage there is a small differentiating factor that should be explained and that's the difference between transverse and
longitudinal waves. For traverse waves this pattern occurs once every wave cycle and is commonly measured from one wave peak to
the next adjacent wave peak (or from one wave valley to the next adjacent wave valley). Since longitudinal waves do not contain
peaks and troughs, their wavelengths must be measured differently. A longitudinal wave consists of a repeating pattern of
compressions and rarefactions. Therefore the wavelength is commonly measured as the distance from one compression to the next
adjacent compression or the distance from one rarefaction to the next adjacent rarefaction.
When speakers move backwards and forwards they do so many times a second. Each time the cone does one complete movement
forward then backwards then back to the zero point it's known as a cycle or one hertz (a.k.a. 1Hz). If the speaker undertakes
one thousand of these cycles per second it is known to be playing 1000 hertz or 1 kilohertz (a.k.a. 1000Hz or 1kHz respectively).
Music is the repeating pattern of these high and low pressure regions in various frequency orders and certain patterns of
frequencies our ears interpret as harmonious. This harmony is simply the music you're listening too. The Pinna (the outer ear
skin section) catches these waves and directs them into our ear canal which houses our ear drum. The ear drum then mimics these
varying pressure waves and lets your brain know what its hearing.
Now you understand the basics of how sound physically works so let us move to the sound deadening itself. As speakers move in
alternating directions the sound emanates from both the front and rear of the cone. The front wave is heard by you while the rear
wave is what the sound deadening and diffusers deals with. With all due respect; your cars doors are glorified metal cans. They
echo and reverberate inside and the skins flex easily, causing bass to become blurred and muddy and even to cancel itself out all
together. I usually explain it by using the following analogy. Imagine you're seated in a boat in the middle of a crystal clear
flat lake. One hundred meters away there is another boat floating idle. If you start gently rocking you boat, waves emanate from
it. Pretty soon these waves reach the second boat and it also begins bobbing to mimic these waves. The problem is that as this
second boat rocks it not only reflects your waves back but also creates its own. Your doors are the same in that the metal skins
flex and create all matter of sound effects. These waves are only minutes or seconds out of phase (i.e. not even whole degrees)
to the active wave and the result is that your ears get bombarded by literally hundreds of sound waves that are not supposed to
be there. This creates an echoic effect and the end result is that the music sounds hollow and tinny. By adding sound deadening
you're adding mass to the doors skins (like swapping the second boat for a cement pier to our analogy). This combats flexing its
effects on internal sound waves.
Diffusers are absorbent pads that resemble foam or tiny egg cartons. These fight wave reflections and are placed directly
behind the speaker. Remembering back to our boat analogy with the cement pier (deadening) now in place; while extra waves are not
being created any more, the main waves will still be reflected. This is where the diffusers come in. We know from above that
sound waves have a certain lengths at any given frequency. Somewhere within these frequencies is the perfect distance for sound
emanating from the rear of the speaker cone to travel to the doors outer skin. This will then reflect and come flying back to
impact the cone and cancel the next cycle. The diffusers catch these sound waves and trap them much the same way that the paint
on stealth aircraft catches radar waves or submarines rubber skin traps sonar waves. The reason you need diffusers on top of the
deadening is that most sound deadening has a smooth skin and hence still reflects sound waves.
Another vitally important aspect of achieving good midbass is to seal the speaker into the door. In nature all elements take
the easiest path from origin to destination. Water is a good example of this phenomenon; you pour it out and it will run wherever
the easiest path is. Air is the same. When your speaker cone moves forward, it creates a high pressure cell right in front of the
speaker cone. If there is a high pressure cell in front of the cone then there will be a low pressure cell on the rear side of
the speaker cone. If the door is fully sound deadened and the speaker is sealed on using sealant of foam gasket, the high
pressure air will move out towards you with the end result being incredibly punchy and tight midbass from your doors. If there
is no sealing (say the speaker is simply screwed down to the metal) and contains air leaks everywhere, the high pressure air
simply takes the easiest path and moves around the edge of the speaker frame to behind the speaker where the low pressure cell
is. In simple terms, you get no bass.
Many cars come with deadening from the factory but it is usually an insufficient amount, often only being a few inches here
and there to minimise rattles during transit. Car manufacturers limit this deadening in order to keep production costs down. How
much deadening you end up installing depends on your budget but both the inner and outer skin of your front doors should be fully
deadened at least. You can always add more to the boot, floor and roof down the track.
In conclusion; for the serious sound enthusiast sound deadening is an absolute must. If you have a close look you'll notice
the cars that sound the best in every continent (especially the ones that win the sound offs) are chock full of deadening. Sound
deadening even helps factory speakers so get your self some today.
Note; wavelength image taken from A Review of the Universe - Structures, Evolutions, Observations, and Theories.
Should I upgrade the speakers in the rear of my car?
Think about a concert, opera or other similar performance; you don't sit with your back to the band or performance do you? It's
the same for your car audio system; seeing as you're seated at the front of the car and your ears face forwards we recommend you
leave the rear speakers factory and not bother to upgrade them. Instead, concentrate on the front speakers. The only time we
bother upgrading the rear speakers is if you either:
Hence the upgrading of the rear speakers will not present you with much benefit. This is why we have front 'stage' and
rear 'fill'. One thing to note though on the subject of rear fill is that this all comes down to personal preference. Some
people actually like the sound emanating from behind them so if this describes you then by all means upgrade the rear speakers.
From what you have read above you can now see why many demo and competition cars have their rear speakers turned down or
simply don't have them at all. What we instead recommend is that you spend all your money on the front speakers where you are
and get yourself some sound deadening (q.v.).
Are the expensive cables really worth it?
Now cables are one subject bound to start an argument at any audio gathering. Everybody has a different opinion on cables.
To us, cables are not just cables. The reason we recommend high quality cables is two fold. One reason is that the better
quality the cable, the more strands it usually has and hence more current carrying ability. Now this is not overly important at
all as you can simply buy a larger (lesser quality) cable if need be so we don't try and sell high quality cables based on that
argument alone. But consider this; when you think about it, you're paying just as much because you can get a better quality cable
of a smaller gauge that ends up being the same price as the larger one of lesser quality.
The other main reason is that better cable tends to have a much more uniformly extruded jacket. If you get a meter of
cheap cable and compare it to a meter of more expensive cable and chop it at 25mm intervals, you'll often find the cheap cables
come dangerously close to breaking out of the jacket every so often due to poor extrusion dies. Again not important if you plan
on having your system for three months but if those cables have to withstand literally years of abuse under carpet (water /
dirt / feet impacting them) then this does become an issue.
Moving onto the oxygen free argument, this is not overly important when referring to car audio cables as it will not make
an huge audible difference. However one interesting report that tends to generate quite polarised opinions is a text known as "The
Genesis report". This report really delves into the realm of high end cables. The best thing to do is to read it
here and make your own decision.
Do my subwoofers need separate chambers within their enclosure?
When running more than one subwoofer in an enclosure, you'll need to decide between using a common chamber (where all subwoofers
run in the same airspace) or a separate chamber enclosure (where each subwoofer has its own airspace). Common chamber enclosures
have no dividers between the subwoofers and the airspace inside the box is the internal volume for one subwoofer multiplied by the
number of subwoofers in the enclosure. Separate chamber enclosures are built in a way that sees every subwoofer isolated inside
the enclsoure in its own chamber.
Generally speaking, it's usually better to have each subwoofer running in its own isolated enclosure, especially in a sealed box.
We say this because if one of the subwoofers ceases working for any reason in a common chamber enclosure, it could cause the other
subwoofer(s) to unload and you could end up ruining the subwoofers that are still working. For example, if your subwoofer can only
handle a 0.88cf sealed enclosure and is running flat stick when it's brother dies, then all of a sudden that remaining subwoofer
is in a 1.6cf sealed enclosure.
Ported and bandpass enclosures are the only type of enclosures that we tend to recommend running with a common chamber. This is
because it allows you to have a single port (either slot, round or otherwise) acting as the port for all subwoofers in the box. This
will generally require less space than having separate ports in separate chambers for each subwoofers. The possibility of a good
subwoofer unloading when another fails is less likely in a ported box as well.
In conclusion; if you're running with a sealed box then we suggest it should have separate chambers for each subwoofer. If you're
running a ported subwoofer enclosure then it is quite okay to have either separate or common chambered enclosure. However, if you
have the space it is always best to design a multi-chambered enclsoure so each subwoofer is isolated in its own airspace.
What grille can I get to protect my subwoofer?
We get asked so often about what grilles are available to protect subwoofers that we actually decided to add it to the frequently
asked questions page! Below are some of the more common 12" grilles we employ here at Fhrx Studios. Other sizes vary depending on
grille type but you can get most in 8", 10" and 15".
$500 System
$1000 System
$2000 System
$3000 System
$5000 System
$10000 System
$20000 System
We continually update these lists so keep an eye on them.
Basically as far as sealed is concerned, the relationship between the characterisitics of the speaker being used and the
volume of air inside the enclosure dictates the how well the sub will sound. When the enclosure is bigger, the air spring
limits cone motion less and allows the system to play lower and with flatter overall response (lower Qtc) at the expense
of power handling. Problem is if you go too large you start to compromise efficiency in order to gain the additional low
frequency extension. On the other hand, making the enclosure smaller will cause the air spring to exert more control and
limits cone motion at low frequencies which increases power handling but does not let the system play as low and produces
a more peaked response (higher Qtc). For most half decent speakers there is a range of enclosure volumes that will produce
high quality sound. Changing the enclosure volume within that range can fine-tune the sound to best suit the tastes of the
listener. Of course other factors effect this but this is close enough.
Depending on the sound you desire, you tune a port to a certain frequency to achieve better bass response around that
frequency. The tuning of the port there must be done using careful calculations which take into consideration the
enclosure volume, the resonance of the port and the Thiele / Small parameters of the sub into consideration. Using these
we attempt to delay the rear output wave of the speaker just enough so that when it comes out of the port it is close to
being in phase with the wave being produced by the front of the sub. So with that in mind, you can see how, by altering
the port length and diamter, we tuned the port to a certain frequency. The reason ported enclosures are generally considered
louder is that when we utilise the work of the rear of the cone we gain double the bass, or 3dB over a broad range of
frequencies. Again there are other things to consider and explain like the sub unloading below the port tuning but that
is another thing...
With bandpass enclosures the woofer no longer plays directly into the listening area. Instead the entire output of the
subwoofer system is produced through the port or series of ports. In a conventional sealed or ported enclosure the
low-frequency extension is controlled by the interaction of the speaker and the enclosure design but the high frequency
response is a result of the speaker's natural frequency response capability unless limited by a crossover. In a bandpass
enclosure the front of the speaker fires into a chamber which is tuned by a port. This ported front chamber acts as a
low-pass filter which acoustically limits the high frequency response of the subwoofer system. The name "bandpass" is
really pretty descriptive in that it refers to the fact that the enclosure will only allow a certain frequency "band"
to "pass" into the listening environment.
Standing waves cause violent response fluctuations inside the enclosure but for a standing wave to exist the distance between
parallel boundaries (the enclosure walls) must be half the wavelength of the frequency at which the standing wave exists.
Considering that sub-bass waves vary from 17.19 meters (@ 20 Hz) to 3.44 meters (@ 100 Hz) the generation of a standing wave
is going to be impossible in an enclosure designed to fit in your average sedan or hatchback. People often install sound
deadening and diffuser panels unnecessarily inside their enclosures to combat these standing wave issues (this is also the
reason why some people are reluctant to employ certain square enclosure shapes). As you can see above though; in reality, due
to the small dimensions of most car audio subwoofer enclosures, there is little chance of generating standing waves in the
enclosure.
Sound delay and resonance smoothing is another matter altogether and this is where the fibrefill comes in. Fibrefill is often
employed in enclosures that are a little too small (usually due to space restrictions within the vehicle). Damping material is
primarily used to fool a subwoofers suspension into 'seeing' a larger enclosure than it actually lives in. The other primary use
for fibrefill is to smooth over little resonances, peaks and dips inside the enclosure itself. Just as a side note; if you're
planning on using fibrefill inside a ported enclosure, make sure it is not getting to close to the internal port mouth.
Full door trim.
Now you might have heard hi-fi buffs recommending against using 6x9's in high end audio systems whilst recommending them for
every other type of system. There are actually numerous pro's and con's of 6x9's and there are reasons why they're avoided
for high budget systems and targeted for low budget systems and factory upgrades.
The first issue is the actual cone size. The large woofer cone is a different width to length so it is obviously uneven.
When viewed under a microscope the woofer cone can physically distort quite dramatically and hence, disastrously so far as
sound quality is concerned. They tend to distort more than round or square speakers where kinetic forces are evenly exerted
across the cone surface. Another big problem faced by 6x9's is one similarly faced by co-axials. The woofer is seated
directly underneath the midrange and tweeter. While this doesn't bother the average tweeter because they're sealed in most
cases, it can cause great stress and problems for the midrange which is trying to play a higher frequency than the pounding
a woofer underneath. More often than not midrange clarity tends to suffer and can sound blurred as the woofer underneath
wins every time. Simply put, 6x9s are not dedicated drivers. They do not offer the same freedom for fine tuning nor do they
faithfully reproduce sound like separate components do. They do their job competently but will never match a separate
subwoofer for bass reproduction, or separate woofer for mid-bass reproduction or tweeter for high end reproduction because
these drivers are dedicated to reproducing their own little part of the sound spectrum and they do it well. Components can
also be mounted separately to help with staging and imaging.
They do. As stated above the cone on a 6x9 is exactly that, which incidentally is nearly the same surface area as an 8"
subwoofer. With their relatively high power handling, the 6x9 can punch out quite a bit of bass and they can even be run
in enclosures to enhance this ability. Another big bonus of the 6x9 is their power handling ability and efficiency. They
can be run off the smallest internal (head unit) amplifier to the largest external units. Because of this ability they
make terrific upgrades to factory systems where a little more bass is required. On that note, they will also fit into many
factory locations without the need to cut anything up.
Damping factor describes an amplifiers ability to control a woofer cone. It's the ratio of rated load impedance to the
internal impedance of an amplifier. The higher the damping factor the more efficiently an amplifier can control unwanted
movement of the speaker coil. High damping factor is crucial for subwoofers and the higher the damping factor the better.
It is debatable if anything over 50 is audible. Damping factor is calculated by dividing the speaker impedance by the output
impedance of the amplifier. In other words the damping factor will decrease as the speakers impedance decreases. This
means an amp optimised at 4 ohms will provide tighter bass than when they're running at 2 ohms. A lower damping factor
will leave bass notes sounding soft and undefined, regardless of the amplifiers power output. You can see by this that a
smaller 100 watt amplifier with a high damping factor can often sound better than one twice it's size with a low damping
factor.
Sometimes referred to as damping factor for tweeters, the slew rate describes the amplifiers ability to accurately control
fast direction changes of a speaker cone or dome. Have you even turned your stereo up to discover that your cymbals sound
like someone throwing a brick through a glass window? That's because the amplifier simply wasn't fast enough to accurately
reproduce the high frequency ring of the symbols. Measured in volts per microsecond, a low slew rate softens the definition
of a sound signal which blurs transients and causes the sound to appear muddy. A high slew rate means the amp responses
faster which ultimately results in crystal clear highs.
THD is the measurement of the how much the amplifier can distort the sound signal through the introduction of added
harmonics or overtones. THD figures are usually given as percentages and a THD figure below 1% are generally inaudible to
most people. However, distortion is a cumulative phenomenon so if your head unit, eq, crossover and amplifier are all rated
at less than 1%THD each, together they could produce 5%THD which may well be noticeable to most of you.
Noise leaking into the sound signal is an ever present problem in car audio. The Signal to noise ratio is a measurement of
noise level in the amplifier compared to the level of the signal. A higher S/N ratio signifies a greater difference which
is better. Technically speaking, it's the ratio expressed in dB of signal power at a reference point in a circuit to the
noise information that would exist if the signal were removed (the noise floor). The maximum signal to noise ratio of the
amp can be seen as a measure of realistic fidelity. This ratio is how much absolute noise it produces compared to the
highest signal voltage it can pass without distortion. Many companies combat noise by utilising balanced line systems.
Separation is not spoken about much but this refers to the amplifiers ability to maintain the separation between the right
and left channels. This is essentially what allows an amplifier to reproduce an accurate sound stage. Each individual
instrument is after all, are recorded in it's own location in the sound stage and you should be able to hear this in the
same way when it's played in your car.
The reason is this; the Pinna (also called the auricle) is the visible part of the outer ear. It collects pressure waves
(differing frequencies of pressure that we interpret as music / sounds) that the membrane captures from in front of it and
directs this sound into the outer ear canal. It's important to remember too that each pinna individually is responsible for
determining height while the two ears together determine width. Sound coming from being the pinna, unless the frequency or
volume fluctuations are significant, will not be accurately collected accurately.
