Bass traps for asymmetrical set-up in L-shaped apartment? - Page 4 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #31 of 48 Old 08-28-11, 04:14 PM Thread Starter
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Doing a full range sweep seems to have made a big difference and I think I'm getting a proper looking ETC's now. I think had also read that it was easier to limit the sweeps to 300Hz, so I guess that's why I was doing it.

Here's some new graphs. Please let me know what you think.

I was also wondering if disconnecting the speakers is the only recommended way to make these measurements. Is there any reason why I can't disconnect the input for right or left, or just use the balance control? Disconnecting the speakers is the least convenient way for me, so I would prefer one of those other methods as I continue my testing.
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Bass traps for asymmetrical set-up in L-shaped apartment?-left-etc-aug28.jpg  

Bass traps for asymmetrical set-up in L-shaped apartment?-waterfall-left-aug28.jpg  

Bass traps for asymmetrical set-up in L-shaped apartment?-spl-left-aug28.jpg  

Bass traps for asymmetrical set-up in L-shaped apartment?-etc-right-aug28.jpg  

Bass traps for asymmetrical set-up in L-shaped apartment?-waterfall-right-aug28.jpg  

Bass traps for asymmetrical set-up in L-shaped apartment?-spl-right-aug28.jpg  


Last edited by streetcore; 08-28-11 at 04:24 PM.
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post #32 of 48 Old 08-29-11, 08:54 AM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Using a balance control or disconnecting a channel from the source can certainly also work.

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post #33 of 48 Old 08-29-11, 10:07 AM Thread Starter
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

I did some more testing last night, and I'm starting to understand how to use the Impulse measurements to identify the various reflection points. By taking some measurements and experimenting with a piece of 3" upholstery foam and heavy blankets to treat the right speaker reflection points on the floor, back of the door and ceiling. I could easily see how the Impulse response changed when each reflection point was treated.

Below is the right speaker Impulse with no treatments. The three spikes after the initial spike at 0 correspond to the floor, back of door and ceiling. The next picture shows the Impulse with foam on the ceiling and blankets on the back of the door, and you can see a drop in the second and third spike.

However, I'm still not sure where to start with the proper acoustic panels and/or bass traps. If we forget about aesthetic concerns for now, what would you guys suggest? Would a Super Chunk in the right corner and some panels at the reflection points be a good place to start?

Thanks again for your patience and assistance while I work through this.
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Bass traps for asymmetrical set-up in L-shaped apartment?-etc-right-no-treatments.jpg  

Bass traps for asymmetrical set-up in L-shaped apartment?-etc-right-treatments.jpg  


Last edited by streetcore; 08-29-11 at 10:13 AM.
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post #34 of 48 Old 08-29-11, 10:13 AM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Yes. That would be a good place to start in addition to right next to the speaker. Impulse response can be very useful in terms of finding specific reflections but will not show you boundary interactions.

Once you individually measure the left and right channels, you'll see pretty quickly the difference due to the boundary proximity.

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post #35 of 48 Old 08-29-11, 04:12 PM Thread Starter
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

What do you think if I treated the corner like the picture below? It's basically a Studiotips Corner Absorber plus a 3" panel with a 1" air gap on the side wall beside the speaker. Rather than wrapping each panel in fabric, I was thinking about a screen that would sit in front of the insulation. It might look neater and require less fabric.
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post #36 of 48 Old 08-29-11, 05:15 PM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

You could certainly do that and it will help a good deal with the difference in boundary gain between the 2 speakers and also likely address at least some of the near wall reflections on that side. Not going to fix all the issues but it's a good starting point.

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post #37 of 48 Old 08-29-11, 06:08 PM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

A couple of comments...

As your primary concern is modal behavior, you would do well to address the modes first.

Regarding the proposed traps, you might consider a Superchunk style corner trap using the 'cheap pink fluffy stuff" and utilizing several pieces of plastic orchard bird netting to create several partitions that will act to support the material such that it will not compress as much over time.

Also note that a 3 inch panel mounted adjacent to a wall will not act as a bass trap. in fact, a 3 " panel with a 3" gap, utilizing Rockwool, will only exhibit an ~.3 absorption coefficient at 100 Hz! In fact, a 4 inch panel with a 4" gap is about the 'smallest' you want to use for a broadband (mid and higher) absorptive panel.

To be effective below 100 Hz, you need to go with at least a 6" panel with a 6" gap ([email protected] Hz and [email protected] Hz).

AFMG Reflex simulations curves are available for the above.


As far as the ETC...

I am not sure how much you want to go into this, as it can quickly become a extended discussion of the theoretical and conceptual underpinnings that are quite different than that with which most are familiar. We can certainly do it, but its not worth it if no one is interested and if we just get comments from folks saying that their 'brain hurts'.

Stated quickly, the ETC can indeed identify each reflection, provide information about the nature of the reflected energy, and provide specific detail not only about its precise path, but also identify the precise location of boundary incidence!

In other words, it can tell you precisely where to place treatment material appropriate to your desired response model. And it can verify its effectiveness.

Below is a very quick perusal of one the ETC responses annotated generally.
If you are serious in following up and determining the paths and specific points of boundary incidence for each anomalous reflection, let me know - and post the mdat files.

Also, I will provide a synopsis of the manner in which the reflections can be identified and also resolved into their paths and walked back to their boundary incidence locations. (As soon as I figure out the interface sufficiently to attach a PDF...)



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post #38 of 48 Old 08-29-11, 06:14 PM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Here is the description of the basic steps to identify, determine path and incident points of an indirect signal, be it a reflection or diffraction.
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post #39 of 48 Old 08-29-11, 07:46 PM Thread Starter
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

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SAC wrote: View Post
Regarding the proposed traps, you might consider a Superchunk style corner trap using the 'cheap pink fluffy stuff" and utilizing several pieces of plastic orchard bird netting to create several partitions that will act to support the material such that it will not compress as much over time.

Also note that a 3 inch panel mounted adjacent to a wall will not act as a bass trap. in fact, a 3 " panel with a 3" gap, utilizing Rockwool, will only exhibit an ~.3 absorption coefficient at 100 Hz! In fact, a 4 inch panel with a 4" gap is about the 'smallest' you want to use for a broadband (mid and higher) absorptive panel.

To be effective below 100 Hz, you need to go with at least a 6" panel with a 6" gap ([email protected] Hz and [email protected] Hz).
So there's seems to be some consensus that a Superchunk in the right corner is a good start, but the effectiveness of any further treatment of the wall beside the right speaker is still questionable.

If I was going to use a 4 to 6" thick panel of OC703 with a 4 to 6" gap, could I skip the Superchunk and just fill that 4'x8' side wall with the panel from the back wall to the door? Something like the picture below might suit my aesthetic concerns better, and be easier to build, than separate corner and side panels, especially if then need to be so thick.

Thanks again for the incredibly detailed response. I'll take some more time to read and digest the ETC info.
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post #40 of 48 Old 08-29-11, 08:07 PM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

A few suggestions that are not only more effective, but much less expensive.

For the corner bass trap, stop messing with expensive OC703 panels and the additional complexity of complex multi-element face frames and simply make a Superchunk corner trap that straddles the entire space that you are imagining being treated with a corner trap and adjacent panels.





The additional space that is filled by the resultant hypotenuse is negligible in terms of room use, but substantial in terms of bass absorption.

And fill the entire corner region with cheap fluffed 'pink fluffy stuff' available at any home improvement store. Just provide a few horizontal layers of plastic orchard bird netting (cheap at any nursery supply or Wal-Mart in season) dividing the Superchunk into sever 2-3' compartments. You can fill these with fluffed 'pink fluffy stuff' and the netting will minimize the insulation settling and compressing due to gravity as the mass will be less in each compartment and it will not all press on the lower portions.

This will outperform the Superchink made with the more expensive lower performing semi rigid OC703.

{Part of the reason the corner placement will outperform the planar application is that some of the energy reflects ;laterally off the wall surface and is directed 'sideways' through the absorbent material, effectively increasing the reactive area whereby the energy interacts with the absorptive material. In other words, porous traps are velocity based devices. Velocity goes to zero near a boundary, so by moving the absorbent material further out from the wall, you lower the effective frequency that corresponds to the maximum velocity quarter wave spacing, and then you also further increase the amount of interaction by having some if the energy be redirected off the wall as it travels 'sideways' over a longer path through the absorbent material, thus increasing the energy dissipation.}

And its MUCH simpler to construct as well! A case where the easier cheaper alternative outperforms the more expensive and complex variation.

Last edited by SAC; 08-30-11 at 11:59 AM. Reason: "face complex multi-element frames" to "complex multi-element face frames" ;-)
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