On Sun, 11 Jan 2004 22:49:14 -0000, "Wally"
wrote:

Stewart Pinkerton wrote:

Because sub design reduces to one single
factor - volume displacement. You can apply EQ to get as flat a
response as you want down to any frequency you want, but your max SPL
is limited by the volume displacement of the driver.

Or, to put it another way, one should seek to use drivers who's volume
displacement will deliver the required SPL.

Indeed, about 5 litres should do it for me.

An isobaric
arrangement allows you to use a half-size cabinet for the same
*unequalised* response, but you lose 6dB of SPL capability due to
having halved the radiating area. I intend to use a pair of Adire
Tempest 15" drivers with a 250 watt 'plate' amplifier,

Wossa plate amplifier? (Assuming it has nothing to do with american
anodes...)

An erudite little jest, but I was referring to amps which are built on
a flat metal plate, designed to be screwed to the back panel of a
subwoofer. You can get them from Wilmslow Audio, design3dw3 and
Madisound, among others.

... and this
arrangement will give me 109dB at 10Hz in-room, 115dB at 20Hz and
120dB from 30 Hz upwards. You simply can't move enough air with an
isobaric system!

A musician mate used to extoll the virtues of an Orange 2x15 cab - said it
had 'enough bass to shake the **** out of your arse'. I would suggest that
'enough' is a user dependant concept. :-)

Indeed yes, and at 5-10Hz it will have exactly this effect...... :-)

The only limitation is that if you use a small box, you'll need a more
powerful amplifier - there's an excellent 1000 watt device available
from Madisound for about 300 squids. Combine that with a pair of
Tempests on opposite faces of an 18" cube, and you can blow out your
windows for about £700!

Not only are new windows outwith my budget, I was hoping to keep the overall
spend about half a grand short of that. :-) (Ie, wood and an amplifier,
since I'm already awash with B139s.)

OK, but the old B139 can't actually shift much air. You'll find amps
on websites for the firms mentioned above. Wilmslow charge £150 for
their 200 watt jobby.
--

Stewart Pinkerton | Music is Art - Audio is Engineering