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|24th January 2009, 15:06||#1|
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The World Below 100 Hz
But things change when we place a woofer inside a car. Things begin to change as the low frequency
wavelengths begin to exceed the physical dimensions of the car. Sound travels at around 1128 feet per
second, so the wavelength of 1128 Hz must be one foot. That means that the wavelength of 112.8 Hz
must be around 10 feet. Since the greatest interior dimension of a typical car is less than 10 feet, we can
now state that our ability to accurately localize on frequencies lower than 112.8 Hz is greatly diminished.
Believe it or not a few years ago there were a few car audio "engineers" who went around preaching that
low bass was impossible to achieve inside a car. Statements supporting such beliefs can easily be found in some of the industry magazines of the last few years. Their point was that since a complete wavelength
could not be reproduced, there could be no bass below say, 100 Hz.
The downfall of these "engineers" was the simple test of playing low frequency test tones over head-
phones. Since the greatest interior dimension between the headphone speaker and the ear was only
fractions of an inch, these "engineers" should only hear high frequencies in headphones, obviously they
were wrong. (This same group of "engineers" is currently involved in focusing and aiming woofers inside
What really happens to low frequencies inside a car is the same thing that happens inside headphones.
The bass becomes more a function of pressure variations rather than of waves. This means that the bass
won't reflect from windows. This means that the bass can't be focused. This means that bass, inside a
car, becomes little more than rapid changes in atmospheric pressure.
If you have a problem visualizing this phenomenon, think of the interior of a car as an inflated balloon.
Let's say that a fly lands somewhere on the perimeter of the balloon. If we press on the balloon with a
finger, the fly will notice the pressure difference. Does it matter where we press on the balloon? Of course
not. Does it matter where the fly lands on the balloon? Of course not. What happens if we use two fingers
to press on the balloon? The pressure will increase and the fly will quickly depart. What about if the fly
were inside of the balloon? Would it matter where he was located? Or even if he was flying around? Of
course not, the pressure would be identical everywhere.
For this reason, two 12" woofers can produce twice as much bass as one 12" woofer because twice as
much air is moved. More moving air increases the pressure variations and the woofers become simple
pistons. The low frequency pressure changes from each 12" woofer combine to yield an increase in bass.
The woofers are just big air pistons in the world below 100 Hz.
|24th January 2009, 15:32||#2|
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twice as much power only translates to a 3 db increase in loudness.
using the area would be a good measure of gauging bass.
cone area(assuming the entire surface is available - not usually true, some area is lost due to surrounds etc)
1 12" sub = 1.44 10" sub = 2.25 8" sub = 2.67 6x9 speakers = 4.4 6.5" speakers = 5.22 5.25" speakers = 9 4" speakers
|24th January 2009, 23:14||#3|
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