towers placed "in-wall"

[tparmer]

Hi all, looking for some reco's on how to go about placing my B&W DM603s (to be purchased soon) below my video screen in the wall. I have a false wall built that is deep enough to accomodate towers. I'm loosing the spousal approval battle of having towers set out in the room and was initially planning on placing three LCR600s behind the screen. Have you seen the price of true acoustically transparent screens lately? Here are the details:

false wall built across entire front of room, floor to ceiling (12' w X 8' h) 15" deep with an opening behind where the screen will be placed. There are three specific places where front speakers can be placed between the studs in this false wall. I have planned on keeping the space between the false wall and actual wall completely open to allow the speakers to breathe (and will damp thoroughly with materials).

Aside from making sure the front of the speakers are flush with the front of the studs and I use the proper materials to make "grill panels, " what else do I need to do to cover my bases and not totally compromise the sound quality for asthetics? Thanks for your help.

 

[WmAx]

That speaker, as most, was specifically designed to operate away from a boundary. One main problem you will experience is with frequency response. The speakers will likely have baffle step compensation -- a shelf filter essentially reducing the upper mid/high frequency range in order to compensate for the change in radiation space as midrange frequency wavelengths begin to exceed the width(in air) of the speaker baffles. Normally, the lower midrange-bass frequencies would be too low in amplitude if this filter was not used due to this normal change from half-space radiation to full-space radiation and the sound would be 'thin' as a consequence. However, you will probably expereiene the opposite problem since this filter is most likely present and designed to operate away from boundaries. Since you are mounting this flush with the wall the response will be elevated in the lowermidrange-bass band by about 3-4dB(typical compensation used). You will need to insert a shelf filter to the line level feeds to the front amplifiers if possible. If you are using a reciever, hopefullly it has front channel bypass loops to the front channel amplifiers.

I recommend making the fit 'tight' for the speaker having only small gaps in the flush front and speaker front or alternatively using generous amounts of foam behind the 'wall grills' around the speaker flush/wall flush in order to prevent significant effects of of the uppermidrange/treble in a large open gap/cavity.

It may also prove benefecial to install a thick open felt around the tweeter, extending to or past the edge of the speaker cabinets. You may have some re-radiation diffraction problems as the high frequencies reflect off of these non-linear surfaces/gaps -- even relatively small ones. The felt will help to dampen the reflected high frequencies so that they are of smaller amplitud -- thus less effect. A sheet of 1"-1.5" non desnse filter material with high coefficient for high frequencies would also work -- and be more effective. Look for a material with a visibly open but small fiber structure with high randomization/factures in the fibers. You could even use sheet of low density fiberglass with the fiberglass fibers exposed to the front side -- but then you have to make provisions to make this safe by installing a grill cloth over the fiberglass....

I could go on and on -- but's that's enough for now.

-Chris

Hi all, looking for some reco's on how to go about placing my B&W DM603s (to be purchased soon) below my video screen in the wall. I have a false wall built that is deep enough to accomodate towers. I'm loosing the spousal approval battle of having towers set out in the room and was initially planning on placing three LCR600s behind the screen. Have you seen the price of true acoustically transparent screens lately? Here are the details:

false wall built across entire front of room, floor to ceiling (12' w X 8' h) 15" deep with an opening behind where the screen will be placed. There are three specific places where front speakers can be placed between the studs in this false wall. I have planned on keeping the space between the false wall and actual wall completely open to allow the speakers to breathe (and will damp thoroughly with materials).

Aside from making sure the front of the speakers are flush with the front of the studs and I use the proper materials to make "grill panels, " what else do I need to do to cover my bases and not totally compromise the sound quality for asthetics? Thanks for your help.

 

[tparmer]

Thanks for the info. Glad you responded as my inclination would have been to allow as much "free space" around and behind the speaker as possible. I'll fix that issue post-haste. Thanks again.

PS any recommendation on bi-wiring or not from Marantz SR7500 to B&W DM603s?

 

[gregz]

I couldn't agree with Chris more.

You may have some re-radiation diffraction problems as the high frequencies reflect off of these non-linear surfaces

This would be my biggest concern.

The stunt Bose used when they first unveiled their Acoustimass system was to place their speakers away from any nearby walls, just as in a normal room setup, but then veil everything with a very large acoustic screen.

Harmon International conducts their in-house testing by hiding their speakers in a similar manner. The trick is to use minimal or no framing in the screen, so that it is a non-factor in the sound.

If you can do this, you'll avoid both the image robbing diffraction AND the bass transfer functions that Chris warned you about, which is the way I would go because each brute force "fix" you introduce has the potential to degrade either your tone balance, phase, imaging, or all of the above.

 

[gregz]

tparmer, looks like we posted at the same time!

To clarify, I believe it's an all or nothing proposition. Unless you plan to dedicate the entire false wall to show nothing but the TV screen (no stud framing, hence no shelves, in-wall cabinets, or anything else useful), you're better off going all the way and implementing the fixes Chris described.

The wife factor revisited!

P.S.

As far as the price of acoustically transparent cloth, have I got good news for you! Years back when I was a broke college student, I obtained not just one but two 4x8 dry erase boards for a mere pittance. It turns out that the boards that cost hundreds of dollars for small versions were quite cheap when the label said "Mobile Home Interior Wall Panel." Not just similar, it was identical. Same turned out to be true for many re-packaged items, not the least of which is "acoustically transparent grille cloth."

Get thee to Jo-Anne Fabrics, or some simlar place, and you'll find a plethora of thin, almost transparent (depending upon which side the light's on) material for around $2 per yard. Bring a sample of grille cloth to compare.

If any shred of doubt exists in your mind, you can stretch it across a Hula Hoop (or any large loom that won't diffract sound) and have your wife hold it in front of the right speaker alternately whith you blindfolded. Compare a sample of the expensive grille cloth to your chosen fabric in a blind test, with your wife holding each in random order for periods of 1 minute. Don't have her say a single word, and see if you can tell any difference whatsoever, especially if she skips a sequence.

 

[tparmer]

you guys are good! Thanks for help. While it great fun laying out a new dedicated room and buying ALL new gear-it is overwhelming at the same time. Thanksa again and happy listening/viewng.