# Room absorption test with Rockwool and REW 5.18

2116 Views 6 Replies 2 Participants Last post by  Wayne A. Pflughaupt
4
I have a kind of dice living room (5,4m (width) x 5,04m (length) x 3,7m (high) with a lot of hard reflections. And a wife that don’t like to convert it to a studio
I did some tests with rockwool solids in the corners to create a DIY bass trap with a global absorption. The result however is not very satisfactory. It doesn’t seem to make much difference.
In the REW picture the response with- (green) and without absorption (red). The blue areas are the real annoying super loud waves I found with the build in wave generator at my sofa.
What do you think? For me it seems that my parametric equalizer is much more effective (in the lower sections), although the effect depends very much on where you sit :/

Tips and comments about the absorption or the REW interpretation are welcome!

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Judging from the graph (and pictures) it’s the main speakers, with no subwoofer? Part of the problem likely is the two speakers interfering with each other.

Briefly, when the sound from a speaker hits a boundary, reflects back and “meets” the original signal out of phase, there will be a “suck out” or “null” at a specific frequency. There are formulas that can calculate the exact frequency.

If you employ two large speakers with good extension, the half-way point between them is going to behave acoustically like a boundary. Thus, two full-range speakers placed 12-feet apart will exhibit a null at about 56 Hz. If either or both of those woofers are also about 6 feet from another boundary, the null will be reinforced accordingly. Two full-range speakers placed 9-feet apart will have a bass null at about 75 Hz, the same as they would have if one or both were 4.5 feet from a wall or two walls.

This can be a major dilemma for spaced full-range speakers. The solution is surprisingly simple: a mono sub, located in a corner. A subwoofer positioned that way is so close to three major room boundaries that any notches it generates will be well above its crossover-controlled operating range.

In addition, the main speakers, now high-pass filtered at, say, 80 Hz, will not generate any significant bass signals at low enough to interfere with the subwoofer.

From that point you can smooth any anomalies in frequency response that the sub might have with parametric equalization.

Regards,
Wayne
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Thanks Wayne, that’s a very new point of view for me. So basically you suggest that it's not the dice hard room that cause the biggest problems, but rather the 2.0 system? I can understand that a sub does not interfere with the main speakers. In my case the crossover must me above 120Hz (the 3 main problem areas). So I can take the absorption away? Not necessary and not helpful?
And how about the standing waves of the sub? Not a problem when placed in the corner?
I wouldn’t worry about how things look ~ 120 Hz until you get the sub up and running. Things could look different, and if you’re luck, “better.”

Standing waves – otherwise known as peaks in response. Parametric EQ can deal with them

Regards,
Wayne
Thanks again Wayne. I will try a sub placed in the corner (although I don't really understand the theory why this is the best place).
You didn't react to my absorption experiment. Do you have any opinion about that?
Well, it looks like it didn’t work. No opinion of mine will change that.

Or, are you looking for an opinion as to why it didn’t work?

Regards,
Wayne
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