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Discussion Starter · #1 ·
Hello,

In general, is it better to apply acoustic (say 703) panels on the top half or bottom half of a wall in a HT room?


I'm sure that the full wall is preferred but I would like to know if there is an optimal location. My feeling is the top 1/2 but I think I've read that the panels should be on the lower 1/2.


Anybody?

Thanks,

Doug
 

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Quote:
Originally Posted by dougc11 /forum/post/0


Hello,

In general, is it better to apply acoustic (say 703) panels on the top half or bottom half of a wall in a HT room?


I'm sure that the full wall is preferred but I would like to know if there is an optimal location. My feeling is the top 1/2 but I think I've read that the panels should be on the lower 1/2.


Anybody?

Thanks,

Doug

Actually, the middle half.
This will assure that side wall early reflections are covered.


- Terry
 

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They should be applied from ear level down, which is the bottom half. I've heard some people say that you should also do the top half from the front of the room to the first reflection point, which is what I did.
 

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Quote:
Originally Posted by koach /forum/post/0


They should be applied from ear level down, which is the bottom half.

If any of your front speaker tweeters are above ear level, this oft quoted "rule of thumb" does not work.


- Terry
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by Terry Montlick /forum/post/0


If any of your front speaker tweeters are above ear level, this oft quoted "rule of thumb" does not work.


- Terry


So, it appears that two factors are involved: where the sound is coming from height wise from the speaker, and your ear height relative to the sound bouncing off walls. If a front speaker was mounted 1 foot from the ceiling then having 'high' mounted panels would be important, but that would only partially solve the issue because the ear would/might be getting reflections off a reflective wall. Does this, ahem, 'sound' right?


If that is the case , is the optimal solution ear height speakers and panels that are basically at the midpoint of one's ear (1/2 above and 1/2 below)?
 

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Quote:
Originally Posted by Terry Montlick /forum/post/0


If any of your front speaker tweeters are above ear level, this oft quoted "rule of thumb" does not work.


- Terry

True, this was assuming the speakers were placed at the proper height.
 

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Quote:
Originally Posted by dougc11 /forum/post/0


So, it appears that two factors are involved: where the sound is coming from height wise from the speaker, and your ear height relative to the sound bouncing off walls. If a front speaker was mounted 1 foot from the ceiling then having 'high' mounted panels would be important, but that would only partially solve the issue because the ear would/might be getting reflections off a reflective wall. Does this, ahem, 'sound' right?


If that is the case , is the optimal solution ear height speakers and panels that are basically at the midpoint of one's ear (1/2 above and 1/2 below)?

There are other factors that make for an optimal solution. How much overall absorption do you need? How much diffusion? What is the directivity of the speakers? Where and how large is the listening area? How important is it to make the sound quality uniformly good over the entire listening area vs. just the prime seats? If the room is for music listening too, how much and what type of music?


This is what custom home theater acoustics is all about! I only have the "optimal" solution after I have built a 3D model of the room, run several test cases with my ray tracing software, plus applied a lot of experience to the problem.


It is why all "rules of thumb" have limited utility. They work in many situations, but not all.


- Terry
 

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Discussion Starter · #9 ·
Thanks.


Sounds like you can't go wrong by buying some 703 panels and sitting in the viewing area and just testing it out.


In a general set up where are the usual 'first reflection' points?


-Doug
 

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Ethan, I *believe* (though am not 100% sure) that this methodology was adopted because this is the way Dennis Erskine designs his HT rooms.


The important part that is missing is that Dennis follows this treatment up with tuned resonant panel traps to target the bass modes. A lay person does not usually have the tools to design these traps and so end up implementing a partial solution.


I agree with you - lining the room with thin, flimsy 1" Linacoustic does absolutely nothing for the bass frequencies, which are at least as important as first reflections if not moreso.


Andy K.
 

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I'm pretty sure Dennis has also said that 1st reflections are not ALWAYS a bad thing too. Depending on the off axis response of the speakers and the timing and volume of the reflections, they can widen the front sound stage and add spaciousness without adversely affecting imaging. I'd personally like to hear this talked about a little more....


Dan
 

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Reflections in general that have a >20ms delay before reaching your ear are subjectively pleasing because they fill out the sound and add ambience.


First reflections (ie. reflections that bounce off only one surface before reaching your ear), unless your room is very large, will typicially be much less than 20ms of delay and so should be cancelled by treatments.


If you have a very directional speaker, its possible the first reflections will be less of an issue, but I dont think you could ever say they would be desirable.


Andy K.
 

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I generally use "early reflections" instead of "1st reflections." This is the more commonly used term in acoustics.


Here's the EBU Technical document 3276 definition:


2.2. Early reflections

Early reflections are defined as reflections from boundary surfaces or other surfaces in the room which reach the listening area within the first 15 ms after the arrival of the direct sound. The levels of these reflections should be at least 10 dB below the level of the direct sound for all frequencies in the range 1 kHz to 8 kHz.


The "10 dB down" is a good rule of thumb, though that's a simplification of a complex psychoacoustic phenomenon. Alpha Certification® uses a more precise metric.


Weak early reflections (or later reflections), the kind provided by diffusive surfaces or sufficiently attenuated off-axis speaker response, can definitely enhance the spaciousness of the sound stage. You don't necessarily want to kill all such reflections. But it is hard to completely kill off anything (darn dB log scale!
), so this is often not an issue.


- Terry
 

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High, low, middle of wall?? Well pull out a mirror, sit in your listening spot and have someone run the mirror down each side wall. When you can see the speaker then that is where the panels would go.


Glenn
 

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Ethan,


You are certainly correct about the fundamental connection between perception of comb filtering from early reflections and the problem of sound localization in the presence of early reflections. Sound localization at low frequencies is controlled by interaural time difference (ITD), while at high frequencies it relies on interaural intensity difference (IID). IID for high frequencies must be significantly cued by comb filtering. Sound at 2 kHz and above is critical to the sensitivity of the image shift phenomenon of early reflections. If you band limit the early reflections to lower than this frequency, the image shifting threshold gets worse.


As usual, the devil is in the details.
Experiments have shown the detection threshold for sound coloration from early reflections to be consistently lower than that for spatial shifting effects. And they both change with the type of sound and the number of milliseconds of delay. However the 10 dB down rule for early reflections and the 3-to-1 rule (9 dB down) to avoid comb filtering derive from the same principle, and are both quite serviceable under most conditions.


Once again, we agree much more than we disagree.



- Terry
 
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