On Thu, 25 Dec 2003 09:31:58 -0500, "Arny Krueger"
wrote:

"Stewart Pinkerton" wrote in message


On Wed, 24 Dec 2003 17:28:39 -0600, "Rusty Boudreaux"
wrote:

"Stewart Pinkerton" wrote in message
...
Well, unless you have the box on springs, it will also be due to
mechanical coupling. IME, ceilings are not so strongly built as
floors!

Not so. With identical opposing drivers the mechanical forces
cancel. It's not like a box sub trying to walk it's way across
the floor.

That's certainly the logical way to minimise box rattle.

IME it's a working plan. You may see both Nousaine and I referring to a
pair of subwoofers engineered and built by our friend Dave Clark. He went
this route and it just works.

It certainly should work, if you carefully align the driver
centrelines and have the drivers perfectly parallel. I canna' change
the laws o' physics (Newton's 2nd in this case), cap'n! :-)

Tom Nousaine's IB has eight TC Sounds 15s (23.4mm Xmax) and he
has been unable to test maximum SPL at 10 Hz with a 5000 watt amp
due to his windows not being up to the task. To quote Tom,
"vinyl double windows twist in frame severely".

Yup, I'm familiar with his weapon of house destruction!

Last time I was there the house was still standing and seemed to be
suffering minimal damage. It seems to be a fairly ordinary modern box with
normal to-code wood frame structure and drywall. A tad flimsy compared to
mine, but if I had my druthers...

Yes, I'm expecting very good bass drive, as my room has a concrete
slab floor and 13" brick and block walls. Even the ceiling is heavily
joisted, so it shouldn't absorb *too* much bass, according to LspCAD.

The poor sealed box has the problem due to
lack of displacement. If you're hitting Xsus with an IB then a
typical sealed box would have long since hit it's limit . A
sealed box of Tempests with equivalent displacement requires over
1000 liters for a Butterworth alignment. I'd rather have a small
discrete hole in my ceiling than a massive expensive box in the
room.

You can still have the box in the loft space, and a Linkwitz transform
equaliser will give you any alignment you want. A small box doesn't
have to mean a high Qts in 2003/4. I guess I'm just hedging my bets.
Besides, SWMBO doesn't want a hole in the ceiling!

Slits work and are pretty inconspicious. It's all a matter of hydraulics.

Well, pneumatics and aerodynamics, but I know what you mean! :-)

My main concern is to keep the hole close to the room corner, to
maximise 1/8 space gain. OTOH, I can see how a long slit might be
useful in smoothing the response across the room. Decisions,
decisions........................
--

Stewart Pinkerton | Music is Art - Audio is Engineering