D I O... P A P E R
INSIGHTS ABOUT SUBWOOFERS
the past 30 years in this country, there has been a trend in
audio to go for convenience first and high fidelity second.
This has resulted in the DOWN SIZING of speaker cabinets to
increase the marketability. While this generated a garden of
cute little speakers (little being the key word) it has done
little for efficiency or fidelity. What suffers the most when
you down size a speaker-- bass response. After a period of time
the market got tired of clinging to the “loudness control” on
their receivers and demanded some real bass. And so was born
the sub woofer, a cabinet designed to play only low bass.
DOES ONE WORK?
sub woofer works by typically playing frequencies between 20
cycles and 100 cycles. The “bookshelf” or “small tower” speakers
in this country are commonly only going down to between 40 and
60 cycles. That leaves at minimum an entire octave of music
missing from your listening experience. To fill in the octave
of missing information a sub woofer is used.
common question, why only one sub woofer cabinet, when we all
know there are two channels? Well, it is an issue of localization.
The pure objective of a sub woofer is to make your present speakers
sound like they have bass, NOT to sit over in the corner and
draw attention to itself as it booms away. So, you would think
that you would need two, and would almost have to set your speakers
on top of them, right? Wrong!
frequencies have different distances between wave fronts. For
example, a 1000 Hz tone generates sequential waves spaced around
11 inches apart. The higher the frequency, the shorter the distance
gets. The human ear was designed and shaped the way it is, to
triangulate these frequencies and tell the brain where the source
is located. That way you know which direction to run when you
hear a noise in the middle of the night.
the noise you heard were lower than 100 Hz, you would really
panic, because not only would you feel the noise, but it would
come from all around you. You ears would not be able to locate
the source because you don’t have a fat enough head! The lower
frequency wave fronts are spaced farther apart than the distance
between your ears, so instead of reflecting off your head and
ears, the wave front simply passes through your head.
kind of Low frequencies that you are looking for out of a sub
are in the neighborhood of 40 feet long. So, a sub placed anywhere
in the listening room will create bass that is impossible to
there are about a million possible exceptions to that statement,
but lets just go with it for now.)
can start to see why only one sub is needed to create the illusion
of bass coming from both speakers. Because of the large size
and length of low frequency wave fronts, most recordings have
a natural side effect of being recorded with monaural bass anyway.
WAYS PEOPLE USE SUBS
is the most important thing to understand, and the reason I
wrote this paper, so if nothing else, please try to grasp this.
high fidelity application of a sub woofer is very different
from the common application of a sub woofer. In high fidelity
playback systems the desired goal is to reproduce all frequencies
at the same pressure, i.e. flat response. If a pair of high
fidelity speakers have a response that rolls off at 40 cycles
then the application of the sub woofer would be to start at
40 cycles and play on down to 20 cycles. It would be exactly
matched in volume with the high fidelity speakers. The result
of this would be flat response, in so much as you would never
be able to “HEAR” the sub woofer. In fact, since you high fidelity
speakers go down to 40 cycles, and 90% of all recorded music
lies in the band between 40 and 20,000 cycles-- your basic impression
of the sub woofer would be that it doesn't seem to be doing
common application of a sub woofer is far from high fidelity
because of two things: The user turns up the volume to a level
greater than his speakers, and turns up the crossover frequency
to 90, 120, even 150 cycles. He does this because he is waiting
to hear the sub work, and that is what it takes to get it to
draw attention to itself. In this application, the response
of the speakers are altered by overlapping them with a thick
veil of bass.
common application being the default application of most buyers
of sub woofers has create from a high fidelity point of view,
a ridiculous trend for DOWN SIZING sub woofers as well! Just
as down sizing normal speakers killed the low bass, down sizing
sub woofers has done exactly the same thing, kill the low bass.
You will find that the majority of smaller sub woofers only
go down to 30 or 40 cycles. That rather dictates which application
you’ll be applying doesn’t it?
most asked question about sub woofers, no doubt, is where to
put the thing. In the high fidelity application, between your
two speakers. In the common application, in a corner of the
room wherever it’s convenient.
between the two... possibly a lot; possibly none. It depends
on the quality of the sub woofer and the odds that where you
placed it will remain in phase with your speakers. To have the
luxury of placing a sub anywhere in the room you want, and create
no fidelity issues, is to have an active crossover with sophisticated
time alignment adjustments to make sure that the overlapped
wave fronts between your speakers and the sub woofer are in
perfect time (Phase).
the sub is located between your speakers, the chances for phasing
problems are different for each frequency. This is where lots
of experimentation comes in. In a larger listening room, when
the sub is placed on the rear wall without any kind of electronics
to correct phase, you will find that reversing the phase of
the sub by swapping the positive and negative on the woofer
terminals will create a closer phase alignment with your speakers
and more bass.
more than one sub woofer to your system, and locating the two
on different walls can create a phasing disaster and you
will more than likely have less bass than you did with just
one sub woofer.
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2007 2008 by Steve Deckert