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Bass management -- the trick of putting absorbers at a front null

Very interesting discussion with Anthony Grimani. He advocates both traps and multiple subs and goes through the basics and tactics of bass management.

What's of interest to me is a "trick" he mentions -- putting an absorber panel at null between the listening position and the front wall. This, he says, can help even out the bass and take the place of the brute (and impractical) physics of trying to absorb the standing wave with absurdly thick absorbers.

He mentions it very soon after this point (which provides some context): https://youtu.be/QYpAbv7gKrs?t=1853

Has anyone tried this? Any details or outcomes you can share will be welcome.

P.S. He mentions Todd Welti, who did a Ph.D. thesis on using multiple subs. He's now with Harman. There is a paper by Welti, here: "Low-Frequency Optimization Using Multiple Subwoofers" https://www.semanticscholar.org/paper/Low-Frequency-Optimization-Using-Multiple-Welti-Devantier/00da...

This looks interesting, too: "How Many Subwoofers are Enough"
https://www.semanticscholar.org/paper/How-Many-Subwoofers-are-Enough-Welti/96b772af4ea937d8028c2f845...
128x128hilde45
rego
378 posts
 
The idea is that a frictional absorber necessarily is placed away from a wall ... not always very practical.
Angled corner traps work a bit differently (angle of incidence ... ?) with angled (design dependent) half filled corner type trap.
Something to remember is that the illustration (flat 2D) references only left / right / up / down and no depth ...
@hilde45, if all those traps are piling up and not being used I can take one or two.
hilde45's avatar
hilde45 OP
5,165 posts
 
Thanks, Rego. I will message you if I am buried under traps! When you say, "The idea is that a frictional absorber necessarily is placed away from a wall ... not always very practical."

I know that frictional absorbers are placed away from walls -- to gain the extra absorption from a distance to the wall roughly equal to the width of the traps, if I remember right. 

But Grimani is suggesting something different than this. He is suggesting placing them very very far from the wall in order to capitalize on a null endemic to the room's modes. That is an application utilizing a different phenomenon, no?
erik_squires
16,446 posts
 
By the way, in terms of having multiple subs, I'm thinking less of this as a solution as I've played around with the Room EQ Wizard's room simulator.

Try it out, but it basically lets you set up a rectangular room with speakers and a sub so you can try out different placements.  Based on those simulations, I'm not sure if multiple subs really does all that. I'm not claiming expertise, I'm just saying that the evening out effect is not as good as I thought.
hilde45's avatar
hilde45 OP
5,165 posts
 
Thanks, Erik. I'll take a look, but the problem is that my room's irregular shape and non-hermetic situation makes it impossible to put into these room simulators. I use REW a lot but it's as much a systematic try-and-see and try-and-listen approach.
rego
378 posts
 
Again the idea for placement as in the video diagram at a null position uses the idea of equalization of relative high to low pressure areas with a velocity.

That is an application utilizing a different phenomenon, no?

Yes-but a same phenomenon as any frictional absorber with the variables being frequency and absorption band.
My emphasis would be to acknowledge the 3D environment being helpful with placement.
The example (diagram presented in video) uses 50 Hz as the frequency range and appears to position the panel perpendicular to the wall and parallel to the end wall (assuming a rectangular plan) illustrating the idea that can work to ’level’ an imbalance at a narrow frequency range.
A narrow band (mid-high frequency absorption) frictional panel could be placed parallel to a side wall, perpendicular, and any angle from 0 deg to 180 deg.

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