Confusion over absorbtion numbers for 703/705 (Rod?)

Posted: Tue Jun 17, 2008 6:29 am

I'm in the middle of constructing my new studio, and as I was reviewing the information in Rod's book "Home Recording Studio: Build It Like the Pros," I noticed a contradiction. It's mentioned that when using fiberglass panels, placing them with spacing from the wall will give better performance, especially in the lower frequencies, but on page 171 in the book, Table 9.2 actually shows that at 125hz when the panels are placed directly on a hard surface, they actually perform better than to place them with 16" of air space away from the hard surface. doesn't that go against all the common wisdom we've seen on the subject? Shouldn't having that air space give better performance in absorbtion--especially in the lower frequencies?

A second question I have is this--if I were to put fiberglass panels in the wall/wall corners, I should be getting even better performance if I were to fill the wall/wall space behind the panels with even more absorbtion material such as rockwool or soft (not stuff) fiberglass, right? Also by doing that I'm assuming I can absorb down to even lower frequencies (hopefully as low as below 40hz)?

Right now my plan is to make a bunch of 4" thick fiberglass panels and place them in all the standard places (reflection points on either side of listening position, on ceiling, behind monitors, behind the listening position...etc), all with 4 or 6 inches of air space, and then also place as many as I can at wall/ceiling, wall/floor, wall/wall corners and stuff the air spaces with soft absorbtion material. The floor will be wood so the space is not completely dead.

How does that sound?

Posted: Tue Jun 17, 2008 7:26 am

Luna,

I hate generalities - because they never present the right picture.

Your claim is not really the case. for example - at 1" and 2" thick - both 703 and 705 out-perform the A mounting by far when mounted away from the wall.

yet at 3" and 4" the opposite is true.

Now - as far as my claims in the book - I stated

"It also gives you a place to mount the stand-off brackets, which will keep this away from your wall, giving you greater sound attenuation."

This related to the specific example I was indicating in the book - which was clearly 2" - which outperformed the A mounting when mounted off the wall.

I see no contradiction.

I do not see where I made a blanket statement that an "E" mounting was always better than an "A" mounting at lower frequencies.

Sincerely,

Rod
2nd -

Posted: Wed Jun 18, 2008 2:51 am

Rod, thank you so much for responding. Often when we read books we wish that we could ask the author questions, and now I can! Very Happy

I was really only confused because the general information that's been spread everywhere is that putting an air space behind the panels will always work better. That's always the problem with generalizations, isn't it? It's just like the people who blindly repeat that putting your monitors on the Auralex foam pads will automatically make them sound better because of the decoupling. I had to learn the hard way that it's a load of BS. The weight of the monitors play a huge part in making that work, and unless you use steel plates to add weight to your monitors (if they aren't heavy enough), using the foam pads will actually make your monitors sound worse--muddy bass with no definition.

So it appears to me for my needs, I should stick to 4" panels and just stick them directly on the wall and not worry about it.

Posted: Wed Jun 18, 2008 8:53 am

Luna,

that is not what I said - nor is it what I would do.

I would install them about 4" to 6" off the wall (not the 16" used for type "E" mounting) and enjoy the improved performance.

I was speaking above in response to your (not so accurate) quote of something I was supposed to have said in my book.

I was then comparing ONLY the Type "A" to "E" results.

Sincerely,

Rod

Posted: Wed Jun 18, 2008 10:03 am

Gotcha. 4" thick panels with 4~6 inches of air space.

Thanks Rod!

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