Will O'Brien wrote:
> When you get into deep bass the speaker has to move back and forth
> very fast or the sound may be distorted. In a sealed enclosure the air
> acts as a spring force against the speaker. Therefore it cannot move as
> fast. This decrease in speed cn distort hard hitting bass.
This just really isn't true.
The speed of the cone is governed by the note it is playing and
the amplitude it is playing at.
If the speaker is "slowed down" the way you seem to be saying,
then it would change the note being played, which really doesn't
happen. If the speaker is "slowed down" limiting excursion, all
that is lost is volume.
> The opposite is also true in the full rage boxes.
However, all are full range boxes. I think you have a few
bits twiddled.
The porting is not a function of how many speakers you have
in the box. My low-end computer speakers are ported and they have
ONE speaker in the box.
Porting uses the inertia of a column of air in the port to
make the equivalent volume of the box larger than it really
is.
(think of the air in the port having inertia like the air
in your exhaust ports, which allows that really lumpy cam to
have so much overlap and use the exhaust scavenging to draw
in through the intake)
A box has to be large enough that the compression wave in
the box (speaker going in) doesn't reflect back and cause
cone breakup and decreased excursion. You can either do this
with a giant box, an infinite baffle (speaker on the rear
bulkhead) or using ports.
If you notice a pattern that most "three speaker" units have
ports, it's probably because the units are aiming to produce
a low powerful bass, having a ported woofer works towards that
goal. The smaller speakers generally sacrifice the extreme
bottom end for cost and size, and the port is simply not
necessary for the frequency ranges involved: the box is large
enough.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
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