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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...
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erik_squires
15,646 posts
 
I'm not sure what he calls absurdly thick absorbers.  I use soffit traps in the corners behind the speakers and find them very effective below 100 Hz.  In my current case I'm pretty sure I can't put big bass traps anywhere near the null locations.
I find that adding this is enough for a single sub with DSP correction. See my blog post about it here:
https://speakermakersjourney.blogspot.com/2021/03/how-to-equalize-subwoofer.html
hilde45's avatar
hilde45 OP
4,783 posts
 
He explains what he means in the clip or perhaps shortly before. Thanks for the link to your post. I'll take a look. 

erik_squires
15,646 posts
 
So I got to watch about half of that video.
While the idea of putting traps at high velocity/low pressure points makes sense to me, I think he underestimates the benefits of corner placed traps if well constructed and exaggerates the required size.

It is true that your average 4" thick fiberglass panel is completely ineffective < 100 Hz in the corners, but that doesn't mean you need 5' of fiberglass. :)  As I mentioned before, I've had very good luck with GIK Soffit traps in the corners for this.  See my blog post for an example of what I'm calling good results.

Fortunately, his theory is easy to test for yourself with the right tools.  As his graphs point out, if you correctly attack the problem the bass will immediately and obviously even out.  If it doesn't work, you can always use the panels elsewhere. :)

Best,
Erik
hilde45's avatar
hilde45 OP
4,783 posts
 
Thanks, Erik. Since I last posted about traps, etc. I was able to find someone locally who was literally giving away their traps to any local audiophile who was interested. I scored 14 traps in all, including stuff from GIK. I'm just not quite making a dent yet in some peaks and nulls, so I'm interested in additional tricks. 
erik_squires
15,646 posts
 
Hi hilde45
So, it is absolutely true that your traditional 2-3’ panels have a very hard time with this. If you look in the GIK site you can find specs which show how effective the panels are at different frequencies. Their absolute best bass traps are the Soffits.


Also, it IS true that without EQ you need massive traps, so the recipe is not just to rely on bass traps, but to rely on a combination of traps, placement of sub and listener AND EQ. Without the traps, the EQ wont work down low.
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