Wave absorption - Focal point

OK forgive my armchair engineering, I just have a question.

If you are going to completely absorb the backwave (in an attempt to reduce or just not deal with it), would it not make the most sense to place the speakers the price distance from the wall where backwave focuses into a line (the 30 degree arc like a kind of parabolic dish) and just absorb that line with a mad vengenance, possibly with some triangular wedge shaped absorbers? Would that not provide the maximum backwave absorbption for the least cost of treatment/surface area required?

Shoot holes!

I think I get what you're saying. My choice, as I have done when experimenting, is to have the sound panel directly behind the speaker. The sound panel has to be free standing and tall, as mine, 2' x 7'. This way, you are still able to position the speaker virtually anywhere with the sound panel following, as well as position the SP as close or far from the speaker for different results. To make a panel for this purpose on the wall and restrict speaker position options in relation to this may be to limiting for finding optimal response.
You can of course shape and size your panel as you seem fit for the job. An oversized concave shape may make more sense than just plain flat.

Actually, probably not. If the sound is focused on a narrow vertical band of the absorptive treatment, the absorption probably will not be as good as if it is somewhat spread out across a larger area of absorptive treatment. But I don't know how these physics really play out in a real world environment.

A couple of things to think about:

First of all, you need a panel that is capable of fairly uniform absorption of the entire frequency spectrum that the speaker emits (in the case of MLs, this is from about 250 hz. up to 20,000 hz.). Second, this absorptive panel should be mounted a few inches off of the wall, so that any sound which makes it through the panel will reflect off the wall and back through the panel, where it will be absorbed to the fullest extent.

Hopefully, Ethan or Jonfo will chime in on this thread with their expertise.

Try the Sumiko setup. Then come back and see if you have the same questions.

I have summit speakers in a large some what lively room. I will be installing one inch thick fiberglass panels across the whole front wall behind the speakers. They are full absorbtion panels which would be too much for this kind of speaker in my room enviroment. Directly behind the two speakers on top of these panels I will be placing thirty inch wide panels with less absorbtion so I still get the benifit of the rear wave with less reflection. This was the recomendation from an Audio/Video design group where I purchase most I my equipment. I believe ribbon speakers require some rear wave reflection. I cannot put the panels to the side wall, since I have a 16 foot sliding glass door.

AKM3, I’d agree with Rich that focusing is probably NOT what you want, as it narrows the field of absorption.
Now keep in mind that the lower the frequencies, the less this ‘focus’ thing matters, as the wavelengths get longer.

So I’d say position the speakers for best bass and imaging, and then place traps of sufficient width behind them. Of course, once you place traps, repositioning the speakers is probably in order again to find the right balance of imaging and bass.

Ron said:

I have summit speakers in a large some what lively room. I will be installing one inch thick fiberglass panels across the whole front wall behind the speakers. They are full absorbtion panels which would be too much for this kind of speaker in my room enviroment. Directly behind the two speakers on top of these panels I will be placing thirty inch wide panels with less absorbtion so I still get the benifit of the rear wave with less reflection. This was the recomendation from an Audio/Video design group where I purchase most I my equipment. I believe ribbon speakers require some rear wave reflection. I cannot put the panels to the side wall, since I have a 16 foot sliding glass door.

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Covering the front wall is a good thing, but beware that 1” fiberglass directly on the wall has very little mid-bass or bass absorption.
For the 30” wide panels placed directly behind the summits, I’d recommend offsetting them from the wall by 2 or 3”. Assuming they are not solid backed, to increase the mid-bass absorption.

Keep in mind, one of the challenges with a dipole radiating speaker is <400 hz cancellation as the rear wave cancels the front once the panel width is exceeded.

Also, your shops recommendations are behind the times (or only applicable to huge rooms) as the rear wave reflection is demonstrably deleterious to sound quality (comb filtering and imaging skew).

I keep using this analogy:

A dipole speaker placed 5’ out in the room, toed in so the rear wave bounces of the front wall and ricochets off the side wall (a 14’ path to the listener) is the same as placing two monopole speakers 14’ apart, one in front of the other and run out of phase. Not what most people do with their Wilson’s ;-)

Therefore mitigating the rear wave is something that dramatically cleans up the sound quality and frequency balance. But reasonable broad-band absorption is recommended.

As a data point, I have my front wall covered by six RealTraps MiniTraps HF (4” thick) offset from the wall by 3”, and have the side walls lined as well. I find that yields much better perceived and measured results.