"Stewart Pinkerton" wrote in message
...
Besides, SWMBO doesn't want a hole in the ceiling!

You do raise an interesting point, however, as I'm having
trouble
running the numbers as tpo how small the hole in the ceiling
can be
before it causes problems with either port noise or turning the
manifold into a reflex cabinet. Any advice on that mattter from
your
own experience?

There are two things to consider. Manifold cross sectional area
and opening size.

In a nutshell, if the manifold's cross sectional area and opening
is less than the driver's summed Sd, then it becomes a bandpass
design with a fairly low tuned low pass filter. Once the Sd/area
rises above about 3:1 you can start getting harmonic distortion.
The opening L:W ratio should be less than about 1.3:1 to keep
slit diffraction from nonlinear loading of the drivers and to
average out internal standing waves.

However, my opening is 16"x16" or only 1/2 the total Sd. It's a
huge hole but my ceiling is 12 feet up and painted black (front
projection theater) so the hole is essentially invisible even
with the lights on. Even at obscene levels I hear no port noise
and it doesn't seem to affect the frequency response or add
harmonics (ECM8000 measurement mic).

One IB forum member is using two 4"x10" HVAC floor vents with two
Dayton 15" drivers due to wife factors. Even without considering
the grill obstruction this is less than 1/3 Sd so would seem bad.
However, he won't stop gushing about how great it is. He has
some pictures of his manifold/vents he
http://users.rcn.com/mjrjunk/

Do you have Thiele Small numbers for the AV15? I might take you
up on
that if I can't source them any other way. As you say,
displacement is
everything at LF.

The AV15s were going for $165 USD during preorder but that's over
and they're now $205. Still a great bargain for IB but a little
more pricey.

http://www.stryke.com/AVseries.html
Fs: 22.39 Hz
Qms: 5.293
Qes: .517
Qts: .471
Vas: 140.1L
2.95 ohm
Z: 4 ohm
(dual 2ohm)
BL: 16.84 Tm
Cms: .143 mm/N
Mms: 353g
Rms: 9.391kg/s
Le: 3.5mH
Pe: 500W cont.
2.83V: 91.15dB
Xmax: 23 mm
Xsus: 30 mm
Sd: 830 sq cm
Vd: 3.8 L