Broadband absorber behind the speakers?

Did the person ever say why bass traps where not useful in a corner

I can't recall anyone off hand who's said "bass traps" weren't useful in a corner (all modes active in tri-corners). But I know Dennis Erskine (who does put "bass traps" in corners and other places) won't put a "Studio Tips Diagonal Corner Absorber" in a corner (he said that), because he doesn't like the absorbtion curve of that device for home theatre (I may be putting words in Dennis Erkines mouth), and he uses other techniques instead to accomplish the same goal (he definately does that).

Finally I'm back again. Some of you have mentioned that it's a danger to absorb too much highs with this kind of absorber. I'm aware of it and it's my plan to cover it with paper or plastic foil (or something else) to some extent. I have a measuring microphone so I can experiment a bit. Actually z60611 described it in his last posting on page 1. I want this absorber also as an alternative to baffling/soffeting. I thought that speakers are measured in a dead room and therefore reflections from this low frequency wrap around are neglected in it's frequency measurement. In other words, I thought it's a goal to get rid of this "wrap around" frequencies (many speakers have room EQs for this) - especially when they bounce back from the wall behind your speakers. I'm a bit confused now. 8)

> Ethan has his own manner to handle truth and context ... Ethan you really do believe yourself don't you? < Eric, in the US we have an expression "The pot is calling the kettle black." It definitely applies here.

JCR wrote:

The first thing I want to do is to cover all "first reflexion points" and add some basstraps (there is enough information about that in this forum) , but I also want to engage comb filtering and reflections from the wall behind my speakers (LEDE). So the idea is a broadband absorber between the speakers and the wall.

JCR, The front wall has first reflection points just like the side walls. And you're not going to significantly effect the "bass lift" from the front wall, even with 30cm of absorption. However, you will create a very odd sounding dead space in front of you that will probably be detrimental you good mix translation. If I were you, I would just put the front absorption in the areas around those first reflection points, and not cover the entire wall. This way you help reduce the lower midrange comb filtering effect from the front wall, but you don't create a total dead space.

Ethan Winer wrote:

As I see it, that's the third priority for treating. Some people have dipole speakers that send sound equally from the front and rear, so in that special case absorption on the front wall can be useful. Other than that, the first important places are the first reflection points on the side walls and ceiling (and floor). Second in importance is the rear wall behind you, especially if it's less than ten feet away. Then you could consider the front wall.

Ethan, I think you keep missing the point that normal (non-dipole) speakers radiate a significant amount of sound towards the rear of the speaker (towards the front wall) well up into the midrange. My Wall Bounce Calculator has been downloadable from this forum for quite a while. You should check it out. Thomas

Thomas, > I think you keep missing the point that normal (non-dipole) speakers radiate a significant amount of sound towards the rear of the speaker (towards the front wall) well up into the midrange. < I think the general rule of thumb is that once the output is 10 dB down, comb filtering is reduced to an "acceptable" level. Using your own speakers as an example, at what frequency is the rear radiation 10 dB down? Also, I am not opposed to using absorption on the front wall. It just seems to me far less important than the "primary" first reflection points, and also less important than rear wall reflections when the rear wall is relatively close. --Ethan

Ethan Winer wrote:

I think the general rule of thumb is that once the output is 10 dB down, comb filtering is reduced to an "acceptable" level. Using your own speakers as an example, at what frequency is the rear radiation 10 dB down?

About 500Hz. Though, I wouldn't call the potential +/- 3dB response anomalies "acceptable".

Thomas, > About 500Hz. Though, I wouldn't call the potential +/- 3dB response anomalies "acceptable". < I agree, and again I'm not opposed to anything that improves the response. Indeed, the main point of my Front Wall Absorption article is the avoid thin absorption. I cringe when I see people line their entire room with 703 only one inch thick. I still maintain that in the grand scheme of things, when someone has a finite budget for acoustic treatment or a wife that objects to a lot of panels, the front wall is third in the list of importance. :) --Ethan