treating reflections from rear surrounds

[thothsong]

When I look at ETC charts for my rear surrounds, a primary first reflection point is my 75" TV. Does anyone bother trying to deal with this? Experimentally, it seems I can treat it by placing a narrow free-standing panel forward of the speaker, such that it blocks the line to the TV, but narrow enough that it doesn't block the line to my MLP. But placement is tricky, because the hard side of the panel introduces a new reflection point for the other rear surround. And it looks pretty funky.

 

[VinceHoffman]

How far are the surrounds from the TV screen @thothsong? Next how far is the TV screen from your ears at the MLP?

 

[thothsong]

In terms of the reflection path, it's ~11' from surround to screen and ~8' from screen to ears.

 

[VinceHoffman]

Well there @thothsong, I don't really see that particular reflection being much of a problem from a psychoacoustics point of view. The direct sound from those surround speakers must be arriving at your ears in about 4-5 milliseconds. The reflection of the same speakers from the TV screen up front should be arriving at the MLP around the 18 millisecond mark. The difference of 13-14 milliseconds is well outside the 0-to-6 millisecond window of image/soundstage confusion you should be concerned about. I wouldn't lose too much sleep over that one. If you're gonna obsess to that degree its time for a projector and motorized acoustically transparent screen. Then you can fully acoustically treat your front wall too!

 

[thothsong]

Thanks for the response. Yes, the delay is ~13.7ms. I was going by the Master Handbook of Acoustics, "For a home listening room or other small room, delays in the 0- to 20-msec range are significant". The reflection from the TV is down only 7 dB.

 

[VinceHoffman]

Thanks for the response. Yes, the delay is ~13.7ms. I was going by the Master Handbook of Acoustics, "For a home listening room or other small room, delays in the 0- to 20-msec range are significant". The reflection from the TV is down only 7 dB.

Well once the arrival time difference between the direct sound and the primary reflection exceeds 6 milliseconds, the ear-brain is supposed to be able to identify the reflection as an echo and disregard it with regards to source localization. I suppose you could perform an impromptue experiment to confirm this.

Temporarily disconnected all loudspeakers except your rear surrounds. Choose and play a surround-heavy clip from a movie soundtrack or better yet a multi-channel music DVD-A or SACD music disc with strong rear channel directional cues. Then listen to that clip repeatedly while alternating between the TV uncovered and temporarily covering ot with some surplus broadband absorptive panels. I suspect the result will be that it sounds better covered but I also suspect image localization will be ok regardless.

 

[thothsong]

As a practical matter, I've decided it's too clunky to try to treat. I was mostly interested in whether anyone else has ever tried to deal with similar. Thanks again for the responses.

 

[ddude003]

I used to put a wide band absorber directly on/infront of a TV when listening to stereo... And it did improve the soundstage for stereo music... And I would take it off to watch TV/Movies... I could tell the difference... Now I have a 103 inch CLR3 screen for my UST projector which seems like an even larger/better wide band absorber...

 

[VinceHoffman]

I used to put a wide band absorber directly on/infront of a TV when listening to stereo... And it did improve the soundstage for stereo music... And I would take it off to watch TV/Movies... I could tell the difference... Now I have a 103 inch CLR3 screen for my UST projector which seems like an even larger/better wide band absorber...

I'm totally with you on your past observation about the benefits of broadband trapping your TV screen while listening to music. However I'm pretty dubious about your second anecdotal observation with regards to your Elite CLR3 projection screen.

Unless the screen material is specifically designed to be acoustically transparent, it will be airtight. In which case I'd expect it to manifest the same sort of acoustic behavior as a sheet of thick plastic "drop cloth" @ddude003. Above about 500Hz the stretched-smooth screen material behaves like a low-pass filter. Above 500Hz or so, the screen would become as acoustically reflective as the wall behind it. So while you could treat the wall behind the screen with an 8"-12" thick layer of porous fiber for low frequency absorption, don't expect to achieve broadband absorption.

 

[ddude003]

Having removed the TV, adding the Elite CLR3 screen, re-measuring, re-adjusting speakers, and going with "new" math style Room Correction DSP... Hard to pin down the exact cause... I do know that the bare wall did not sound as good... I am no expert on projection screens... This screen is a PVC type of material with an interesting lenticular type of design that bends and/or absorbs light depending on the direction the light comes from... I imagine that it would have some affect on sound as well... Maybe some diffusion?