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

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post #1 of 48 Old 08-22-11, 03:12 PM Thread Starter
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Bass traps for asymmetrical set-up in L-shaped apartment?

Hi,

This is my first post here and I'm hoping to get some advice regarding bass traps or acoustic treatments for my apartment. It's a rented space, and it's not very big, so I want them to be as unobtrusive as possible. My setup is 2-channel only and I've already purchased Jim Smith's book "Get Better Sound" and have achieved some benefits from his setup tips. I've also purchased a Behringer ECM8000 mic and have tested the room with REW. Based on the results I was able to further optimize my speaker and listening positions. I've attached a pic of the best graph I was able to achieve by moving the speakers and mic position, and I'm wondering if I can improve on this with some DIY bass traps.

I've been doing some thinking about it, and cutting out cardboard templates, and I think I could make some 24" tri-corner traps that would be fairly easy to install in the positions shown in the Sketchup drawing below. I was also thinking I might be able to put a soffit style panel across the upper rear wall over the desk, and perhaps install some downlights to dress it up a bit. I may also try building some bass-trap planter boxes similar to the ones offered by RealTraps.

Any thoughts on these ideas? Anything else I should consider since the room is L-shaped and my set up is asymmetrical? Right now I have blinds and thin curtains over the large windows, and I was also wondering if I would be better off starting with some heavy curtains or blinds instead of bass traps.

Thanks very much and any advice would be much appreciated.
Attached Thumbnails
Bass traps for asymmetrical set-up in L-shaped apartment?-rew-measurement-2.jpg  

Bass traps for asymmetrical set-up in L-shaped apartment?-room-layout-forward.jpg  

Bass traps for asymmetrical set-up in L-shaped apartment?-room-layout-rear.jpg  


Last edited by streetcore; 08-22-11 at 03:25 PM.
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post #2 of 48 Old 08-22-11, 03:48 PM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

While those locations will help address excess bass ringing in the room, in my opinion, the front right corner is a prime location for bass absorption. The right speaker is much more boundary and somewhat corner loaded than the left which is going to cause it to sound much richer and fuller than the other one. You'll also want to address the early reflections off that right wall which are going to be more intense and arrive earlier in time than the ones off the opposite wall.

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post #3 of 48 Old 08-22-11, 05:00 PM Thread Starter
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

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While those locations will help address excess bass ringing in the room, in my opinion, the front right corner is a prime location for bass absorption. The right speaker is much more boundary and somewhat corner loaded than the left which is going to cause it to sound much richer and fuller than the other one. You'll also want to address the early reflections off that right wall which are going to be more intense and arrive earlier in time than the ones off the opposite wall.

Bryan
Thanks for your response. Actually, my first thought was to fill that right corner with a SuperChunk or Studiotips Corner Absorber trap, but I thought it might be better to distribute the absorption around the room a bit. It sounds like it might be better to completely fill that right corner first.
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post #4 of 48 Old 08-23-11, 07:13 AM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

You will get some benefit in decay time by spreading things out. That said, that corner and the close right wall still need to be done. Then you can maybe do the upper rear corners.

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post #5 of 48 Old 08-23-11, 09:52 AM Thread Starter
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Thanks again for your advice. I had a mirror out last night and with my current setup the first reflection point on the right wall is in the seam between the door and the wall where the door is hinged. So treating that point is going be difficult. I may be able to move the speakers forward and my seat back to put the reflection point on the back of the door, but I don't think I have the room and I'm not sure I want to hang a panel on the door. Maybe I'll start with the right corner for now and see what happens.

Cheers,

Andrew
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post #6 of 48 Old 08-23-11, 12:56 PM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Even without getting at the reflection area, having a panel directly beside the speaker will help minimize the uneven boundary loading.

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post #7 of 48 Old 08-23-11, 01:13 PM Thread Starter
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

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Even without getting at the reflection area, having a panel directly beside the speaker will help minimize the uneven boundary loading.

Bryan
That would be much easier, and not too obtrusive. I really don't want to fill the corner with a superchunk, but would be willing to put a tri-corner in the upper right, and a 2'x4' panel on the right wall beside the speaker. Would you recommend 4" thick with FRK facing out for both of them?
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post #8 of 48 Old 08-23-11, 02:34 PM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Brian is trying to help you, but I fear your concern for aesthetics has already significantly limited your options.

Let me summarize:

First, your choice of speaker placement lacks Left-Right symmetry.

The significance of this is that the imaging, localization is pretty much hosed unless you can effectively establish that.

Brian has politely suggested a partition and bass traps.

But realize that this reflective partition will necessarily need to be large. It must be large enough to be larger than the wavelengths down to about 400 Hz (at least 3 ft by 3 ft per each pathway) and large enough to cover the multiple reflective pathways affecting the seating area.

This is further complicated by the fact that you will have to make this boundary perform similarly to the other side boundary – while also surgically controlling the high gain, early arriving reflections. Thus you will be selectively applying absorption to the reflective boundary. A mirror is not sufficient to determine this complex amalgam of behaviors. You NEED to use the ETC response to identify specific reflections and to adjust gain to both effectively control the various reflections as well as to create acoustical symmetry. And don’t’ forget the ceiling!

As to a comment regarding your questions: A 2'x4' panel would not be large enough to control 'well controlled' distribution down to 400 Hz where the wavelength is ~2'8". And not having a reflective surface there is already equivalent to having an absorber there! You just have no idea regarding what the energy is doing and how it correlates to the other boundary surface! You need an ETC response for each speaker to discover what is actually happening! that will determine the exact nature of the boundary, be it reflective, absorptive or a combination of the two.

Much of this could be alleviated if the room were rearranged for optimal sound quality by relocating the speakers to the end of one of the alcoves, providing a degree of symmetry… And then using the ETC to surgically treat the side walls and ceiling as necessary.



The other major fly in to ointment is room modes. You have what is known as a coupled space. You will effectively have modes that are conditioned by 3 regions: Each of the side alcoves, and also by the entire space. Compounding this is the similarity in the dimensions of each space! They will sum. Prediction is beyond the already severally restricted generally available tools.

The only way to determine the distribution of these modes is to measure and map the space.
I appreciate your reluctance to employ obtrusive bass trapping. But as you are opting to go the porous route, you don’t have much choice. Tri- corner traps are very cool looking, but they will not be extremely effective, especially anticipating the degree of trapping you will require. Also, while a straddled panel may be more convenient to make, they are not as effective as SuperChunk style, where you benefit from more porous material. And you are going to need more coverage area to be effective.

One additional ‘trick’ you can use is to use adjoining spaces as bass ‘sinks’ and to, where possible, leave the doors open and allow the energy to be distributed into a larger volume. Just realize that in doing so this will modify the modal distribution as well, so you will need to explore these options and measure and map the space in order to determine the best options – hoping that such manipulation will not place your listening position in a null.

And again with regards to your question: Right now you have lots of uncontrolled reflections about which you have no idea what is happening. And considering the limited volume of bass traps, I would not worry about FRK facing at this point - especially as it is hard to predict just where and how such reflection would be directed and at what gain. Again, ETC measurements made with simple panel template mock-ups would provide much needed information that would quickly and accurately determine the effect of the use of a reflective FRK surface...

Again, I would suggest that you use the waterfall response and determine the precise behavior involved. And then use this as guide for determining the optimal treatment, rather than simply estimating you needs based upon aesthetic concerns without any idea of what are the real problems.

Dependent upon the results, you may want to seriously consider some of the tuned Modex modules (RPG), placed in high pressure regions determined by modal mapping of the space.

But, as always, the choices are yours. Simple measurements will reduce the range of reasonable options from 'unlimited', to a more manageable range conditioned by the actual behavior. If you need any assistance, please don’t hesitate to holler. (But also realize that positing ‘what ifs’ without actual measurements of actual behavior will necessarily receive an indeterminate answer! Good luck!

Last edited by SAC; 08-23-11 at 03:07 PM.
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post #9 of 48 Old 08-23-11, 04:09 PM Thread Starter
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

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Brian is trying to help you, but I fear your concern for aesthetics has already significantly limited your options.
I am very appreciative of Brian's assistance, and I certainly hope I didn't say anything that would suggest otherwise. Unfortunately, this is not a dedicated listening room or home studio, so I do have to take the aesthetics of any acoustic treatments into consideration. Due to the placement of doors and windows, and the lack of electrical outlets on some walls, I also have very few options for equipment placement. So it's certainly a less than ideal situation, but it's one I have to live with for now.

Quote:
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Brian has politely suggested a partition and bass traps

But realize that this reflective partition will necessarily need to be large. It must be large enough to be larger than the wavelengths down to about 400 Hz (at least 3 ft by 3 ft per each pathway) and large enough to cover the multiple reflective pathways affecting the seating area... A 2'x4' panel would not be large enough to control 'well controlled' distribution down to 400 Hz where the wavelength is ~2'8"
The wall beside the right speaker is 4' wide from the rear corner to the door. I understand it's almost impossible to give definitive answers, but should I consider covering most of that wall, if not the whole thing, with 4" thick panels?

I'm generally pretty happy with the sound I'm getting and the imaging, but sometimes I find the bass pretty boomy, which is why I started looking into bass traps. Adjusting my listening position and the speakers has made a difference, but I thought some room treatments would also be worth considering, as long as they didn't take over the apartment and make it look like a recording studio.

I definitely appreciate the advice both of you have provided and it's given me lots to think about. I was all set to rush out and buy some insulation a few days ago, but I think I'm going to slow down and spend some more time learning about the various options.

Thanks again,

Andrew
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post #10 of 48 Old 08-23-11, 04:30 PM
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Re: Bass traps for asymmetrical set-up in L-shaped apartment?

Please take the time to make a few measurements (waterfalls and ETCs).
This step can significantly bring what may seem to be a pretty overwhelming issue down to a manageable task.

These will tell you exactly what is going on and will provide an inventory of behaviors you would want to focus on treating.
Armed with such information, not only will the many possibilities be reduced to a few realities, the options for effectively treating them can be better assessed. Many of the most egregious issues can often be treated rather easily and surgically - without the need to rebuild the entire house!

Then you can explore the best options for each, maximizing their effectiveness while complimenting your home to the greatest extent possible.

And the effects of incremental changes can be quickly and objectively assessed.

I know many are scared by the thought of measurements, but they are actually quite easily done and WILL make your options more defined.

Last edited by SAC; 08-23-11 at 04:50 PM.
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