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Old 3rd July 2007, 08:20 AM   #1
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Default Designing a home theatre room

How would you design a home theatre room? Let's suppose it's a detached room separate from the house. How would you deal with room acoustics, room gain, room modes and sound isolation from a design point of view? What would you put in it?

In particular, how do you keep bass in the room with a sub bass horn?

Here's my take (for a generous budget) ... yes this is a theoretical project, one I'd like to have the budget one day to tackle (maybe a more modest version).

I'd build a room within a room, with a corridor all around. I'd have fun with the corridor, some kind of weird deconstructivist design with funky lighting and materials, and paintings/posters around like a gallery before you get into the theatre. The room would have carpet over a concrete floor and the walls and ceiling of the interior room would be plasterboard - double layer over staggered studs on each side of the timber framing. The idea is that this enclosure will act as one huge bass trap. I'd make the outside envelope whatever I can find that does the best job of keeping the bass in.

I'd keep the interior wall surfaces mostly bare, but with some paintings on canvas, and some artwork to act as diffusers and give a small amount of absorption. I prefer relatively live rooms, similar to what most living rooms are already.

Projector with dedicated fixed screen.

Home theatre computer with all music ripped to hard drive and set up so anyone can operate it with just one remote.

Speakers - open baffle mains and centre down to 80 Hz. Mains with WMTMW with pro drivers 18"/12" with CD on an oblate sphereoid waveguide. Yes, that's four 18" drivers to get down to 80 Hz!

Surround speakers - omni surrounds, probably something like a number of Linkwitz Plutos hanging from the ceiling, different heights each so they look like a feature like stalactites in a cave.

Sub - 14 - 80 Hz sub bass horn where the entire wall behind the screen is the horn mouth, driven by 8 x Rythmik Direct Servo kits.

Digital computer-based active crossover.

OUTCH (I just pinched myself - yep, it turns out, I was dreaming)
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Old 3rd July 2007, 11:54 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
do you need 4 18inchers to reproduce down to 80Hz?

I would expect 2 12inchers to get down there with adequate SPL.
Some would say a pair of 8inchers would do.

Why divorce the upper bass from the surround speakers?
I would use full rangers all around and roll them off electrically as the sub & bass roll in from a pair of dedicated LF amps & drivers.
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Old 3rd July 2007, 12:34 PM   #3
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AVS Forum has thousands of pages on home theater room construction. Including many pro designers.

http://www.avsforum.com/
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Old 3rd July 2007, 12:48 PM   #4
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Gentlemen, this has as much to do with need as drag racing has to do with fuel economy!
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Old 4th July 2007, 03:07 AM   #5
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Nobody wants to take the bait?

My only actual problem to solve here is how to keep bass in a room. Is it better to have very thick and solid concrete? Many layers of lighter construction with minimal mech connection? I have actually studied architectural acoustics at uni but we never covered how to deal with a sub bass horn! It was focused on more typical applications.

My guess is that the way to do it is have the room within the room, with the inner room with multiple layers of plasterboard. This will attenuate while giving some damping of modes. Then with what gets through, that can be contained within a more rigid concrete shell.
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Old 5th July 2007, 07:01 AM   #6
dangus is offline dangus  Canada
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I think you want the inner walls and ceiling to be single-layer drywall. That way they can flex which is supposed to reduce the standing waves. Then stiff/heavy outer walls supported by staggered studs so there's not mechanical connection from the inner walls. Maybe cinder-block filled with sand or something. Separate inner and outer doors, or one massive air-tight outer door. This room might double as a bomb shelter or bullet-proof refuge from home invaders.

As for bass, I'd consider getting a Bag End sub (or just the processor), then DIYing a bunch more compatible subs until there's some real usable single-digit output. But I'd also look at whether a more conventional 2nd-order sub would work with the room gain to get near-flat response down low. Put sub cabinet columns in each corner and maybe lining each wall until you can do over 130 dB at the seats.
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Old 5th July 2007, 07:39 AM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
over 130 dB at the seats
this is to reproduce faithfully the live event.

Which live event exposes the listener to such levels?
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Old 5th July 2007, 09:01 AM   #8
BHTX is offline BHTX  United States
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Quote:
Originally posted by paulspencer
Gentlemen, this has as much to do with need as drag racing has to do with fuel economy!
Quote:
Originally posted by AndrewT
Which live event exposes the listener to such levels?
Well, drag racing, for one.
...Top-fuel dragsters, mainly. 320+ MPH within around 4 seconds.
Blurry vision from insane SPL's, and stinch of fumes to the point of passing out...I love it!

Lots of stuff out there over 130dB

And besides...why not? 130dB at the listening position is fun. Well, at least for a very short period of time.

Edit: oh yeah, I'm in America.
..Sometimes I forget this insanely popular forum has so many members, and from so many countries.
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Old 5th July 2007, 01:41 PM   #9
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130 db ... how crazy that is depends on the frequency. Sine waves over 100 db at 3k and over is very irritating and unpleasant. I tested the first set of speakers I made as a teenager and measured 103 dB @ 3k and it drove me crazy! The same level at 20 Hz from a low distortion subwoofer seems as nothing. I've measured 120 dB right up close to my subs, yet it didn't seem to hit as hard as I've experienced in some rock concerts.
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Old 5th July 2007, 10:44 PM   #10
BHTX is offline BHTX  United States
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Quote:
Originally posted by paulspencer
I've measured 120 dB right up close to my subs, yet it didn't seem to hit as hard as I've experienced in some rock concerts.
A single 15" or 18" driver for professional touring applications can easily hit in the mid 130's or more when used in its recommended enclosure, although they can't do it at extremely low frequencies. Most PA bass cabinets start rolling off under 40Hz or so. But add to that single PA 'subwoofer' hitting the mid to upper 130's..a couple of dozen more identical cabinets operating simultaneously, as often used in concerts, and the reason for it seeming to 'hit' so hard becomes obvious.
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