On Wed, 4 Feb 2004 20:33:45 +0000, Glenn Booth
wrote:

Hi Don,

Very interesting post.

In message , Don Pearce
writes
I've had subwoofers before, but I have always had to turn them off for
music, because they sound so dreadful. I know why this is - the bass
reflex design is so flabby that the whole thing just honks instead of
reproducing bass. The old test really showed this up; listening from a
distant part of the house, and hearing the booming of particular bass
notes.

This reflects my own experiences, to the point that I chose to live
without one.

So I decided to build my own, using a disused cupboard built under
some stairs. This is of brick construction and as solid as anything.
It is also about 80 cubic feet in volume. Having looked around for
drivers and finally got to the Adire Tempest (thank you Stewart) I
could see that this speaker, with its massive Vas would really benefit
from a sealed enclosure - which at 80 cubic feet amounts to an
infinite baffle.

Is the volume of the enclosure (erm, cupboard) important, or does it
simply have to be 'big enough'? I've looked at several of the web sites
that discuss infinite baffle systems, and they seem long on 'case
studies' but short on theory. I'm a dunce when it comes to cabinet
design.

Once the enclosure is a fair bit bigger than Vas, you get to a
situation of diminishing returns by going bigger still. I have gone
for the full cupboard size because it is so inconveniently placed as a
cupboard that I may as well.

Well it is finally built, and today I have been tuning it in to the
rest of the system. Easy! Got the polarity right, adjusted the cutoff
to 60Hz and set the level. It has blended in with the Sonus Fabers so
seamlessly that it is hard to tell when it is on, apart from the fact
that there are several new octaves available.

Did you choose 60Hz empirically, or was there a bunch of maths involved?

No maths, I just turned the frequency down until I couldn't hear the
sub producing "normal" bass, and that was about 60Hz.

Time for all to get building - a big infinite baffle sub will be a
revelation for those who hate the normal beasts as much as me.

I'm _very_ tempted, but now I'm full of questions. What are you driving
the Tempest with? What sort of crossover? Have you had to nail 2*4s
around the window frames? Has your liver liquified? Enquiring minds
(with under-stairs cupboards) want to know!

The driver is just the amplifier/filter panel stripped out of another
subwoofer. It is about 200 watts, and has a variable filter for
setting crossover frequency. As for my vitals - I don't go that loud
living in London. The neighbours would talk.

d

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