Treatments on frontwall SBIR

tjcinnamon

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I have towers that are 4' tall. I had some leftover fabric and built four 2'x2'x4" absorbers which I plan to put on the front wall behind the speaker. My question is how high/low do I put them? I was thinking about having one extend 15" above the speaker then 9" below and then I'm wondering do I put the other one above or below the speaker?

Based on pictures online what I've seen is people put them well below the speaker in addition to just above
 

ddude003

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You haven't given us much information to go on... Please describe your system (what speakers) and room (shape & dimensions) in a little more detail...
 

DanDan

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Small areas of absorption behind the speakers are most likely to make SBIR worse.
FWBIR Trap No Trap.png
 

AudiocRaver

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I believe that DanDan is correct, that the amount (area) of absorption you are talking about is unlikely to provide much, if any, positive benefit.

The optimal size and placement will depend on a lot of factors, and we might need to see a range of room measurements before we can provide meaningful suggestions.
 

natty

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I have towers that are 4' tall. I had some leftover fabric and built four 2'x2'x4" absorbers which I plan to put on the front wall behind the speaker. My question is how high/low do I put them? I was thinking about having one extend 15" above the speaker then 9" below and then I'm wondering do I put the other one above or below the speaker?

Based on pictures online what I've seen is people put them well below the speaker in addition to just above

There are simple SBIR calculators that help you see you need to keep you speaker VERY CLOSE to the front wall for a panel as thin as you are describing to have an impact: http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

Some speakers, in fact, will be too deep to be able to get close enough for the frequency range to get high enough for a panel that thin to really do the job.

In terms of precisely where behind the speaker to place the panel:

1. Measure your response at your seat without any panel there using REW.
2. Center the panel behind the midrange or (if a two way speaker) behind the woofer.
3. Measure the response again.
4. Adjust placement a few times, measuring each time, to see if you can do better.

Don't be surprised if most of the comb filtering you see if from SBIR off the side walls, floor, and ceiling, and not just the rear/front wall. Don't be surprised if you still see lots of room modes. In other words, even if you kill the SBIR, there are a half dozen other sources of boundary or room issues that will remain.
 

tjcinnamon

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There are simple SBIR calculators that help you see you need to keep you speaker VERY CLOSE to the front wall for a panel as thin as you are describing to have an impact: http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

Some speakers, in fact, will be too deep to be able to get close enough for the frequency range to get high enough for a panel that thin to really do the job.

In terms of precisely where behind the speaker to place the panel:

1. Measure your response at your seat without any panel there using REW.
2. Center the panel behind the midrange or (if a two way speaker) behind the woofer.
3. Measure the response again.
4. Adjust placement a few times, measuring each time, to see if you can do better.

Don't be surprised if most of the comb filtering you see if from SBIR off the side walls, floor, and ceiling, and not just the rear/front wall. Don't be surprised if you still see lots of room modes. In other words, even if you kill the SBIR, there are a half dozen other sources of boundary or room issues that will remain.
Small areas of absorption behind the speakers are most likely to make SBIR worse. View attachment 51597
I believe that DanDan is correct, that the amount (area) of absorption you are talking about is unlikely to provide much, if any, positive benefit.

The optimal size and placement will depend on a lot of factors, and we might need to see a range of room measurements before we can provide meaningful suggestions.
There are simple SBIR calculators that help you see you need to keep you speaker VERY CLOSE to the front wall for a panel as thin as you are describing to have an impact: http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

Some speakers, in fact, will be too deep to be able to get close enough for the frequency range to get high enough for a panel that thin to really do the job.

In terms of precisely where behind the speaker to place the panel:

1. Measure your response at your seat without any panel there using REW.
2. Center the panel behind the midrange or (if a two way speaker) behind the woofer.
3. Measure the response again.
4. Adjust placement a few times, measuring each time, to see if you can do better.

Don't be surprised if most of the comb filtering you see if from SBIR off the side walls, floor, and ceiling, and not just the rear/front wall. Don't be surprised if you still see lots of room modes. In other words, even if you kill the SBIR, there are a half dozen other sources of boundary or room issues that will remain.

This is very helpful!

My guess is they'd be better off on the side wall or the ceiling. I have a measurement mic with REW. I suppose I could just try them out on the ceiling and measure. Presumably, I'd post/look-at the frequency response and the decay times?
 
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natty

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Use the calculator.

If there is sbir off the ceiling it is likely so low a frequency that your traps would need to be four feet deep and not four inches deep. But if you are using bass management you may find there is no sbir on the ceiling, just room modes.

Those thin panels will be most effective for sbir on the closest wall, and again looking at the calculator, the speaker would need to be almost touching the panel assuming your speaker is not unusually large or small. If the speaker is further away, as you can see by the calculator, the frequency of the sbir gets too low for that panel to trap effectively.

And yes frequency response measurements are the objective means to view the impact.

But as DanDan’s comment suggests this might not be the most important thing in the room. You may want to share your measurements and take it from there.
 
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tjcinnamon

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Use the calculator.

If there is sbir off the ceiling it is likely so low a frequency that your traps would need to be four feet deep and not four inches deep. But if you are using bass management you may find there is no sbir on the ceiling, just room modes.

Those thin panels will be most effective for sbir on the closest wall, and again looking at the calculator, the speaker would need to be almost touching the panel assuming your speaker is not unusually large or small. If the speaker is further away, as you can see by the calculator, the frequency of the sbir gets too low for that panel to trap effectively.

And yes frequency response measurements are the objective means to view the impact.

But as DanDan’s comment suggests this might not be the most important thing in the room. You may want to share your measurements and take it from there.
Forgetting SBIR, isn't treating the ceiling's first reflection point a general approach?
 

BenToronto

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Cloth. Great. One way to dramatically improve sound is to hide your speakers with what in theatres is called scrim cloth, I think. Paul Klipsch used to insist his dealers demo with his speakers not visible.

Think I'm kidding?

BTW, easy to find synthetic cloth with almost no effect on sound. I've measured my large electrostatic panels using multiple plies covering to see the effect.

B.
 

ddude003

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The Arqen website has a wealth of information if you choose to learn... http://arqen.com/bass-traps-101/placement-guide/
BTY you haven't actually given us any additional information that some of us have asked you for... Did you really want help?
A "general approach" would be to treat 1/4 to 1/3 of all surface areas with bass and wide band absorbers...
 
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natty

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Forgetting SBIR, isn't treating the ceiling's first reflection point a general approach?

Sure. Depending on the speaker directivity and consistency of dispersion, attenuating the first reflections is a common practice.

The ceiling is a popular choice, especially since a panel like your can be hung a few inches off the ceiling, which makes them work over a wider range of frequencies, which is generally a good thing.

The wall behind your seats is another useful spot in most systems.

And for speakers with inconsistent dispersion the side walls are often a good place to treat as well.

How much and where depends a bit on the room, and a bit on the speakers, and measurements of rt60 can be useful for getting enough but not too much absorption into the room.

Probably worth sharing a diagram of your room layout, photo of the space, and the results of what measurements you have taken so far, if you want folks to make smarter more appropriate recommendations.
 

rcohen

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I'm always surprised that more acoustic treatment companies don't sell products targeted at front wall SBIR, since typical acoustic panels aren't well suited for it.
 

ddude003

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I am always surprised that so much time and effort is spent trying to get "a kit" to sound good and so little time and effort in getting "the room" to sound good...
 

natty

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I'm always surprised that more acoustic treatment companies don't sell products targeted at front wall SBIR, since typical acoustic panels aren't well suited for it.
Typical acoustic panels work GREAT for SBIR as long as they are THICK and truly broadband. And many places sell panels that work great for this.

TLDR:

Many do but few buyers are willing to put a six inch thick panel behind their speaker and back the speaker up to where it’s touching the panel…..unless they understand physics and have a congenial domestic situation:)
 
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rcohen

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Many do but few buyers are willing to put a six inch thick panel behind their speaker and back the speaker up to where it’s touching the panel…..unless they understand physics and have a congenial domestic situation:)
I haven't seen any products designed or marketed for absorbing SBIR. I imagine there are more ways to do it.
 

natty

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GIK sells six inch thick panels. I bought some and placed them behind my main speakers. To kill SBIR off that wall.

The same technology can be used for broadband absorption at first reflection points on the walls or ceiling or rear wall.

The same technology can be used for bass trapping (though not as deep as I would like) by placing them straddling corners (any of the twelve corners in a rectangular room).

Many other companies do the same (sell panels that work great for SBIR).

I assume the issue is that people don’t know how to use panels, not that they don’t exist and aren’t available?

The other ways to kill SBIR don't have to do with panels, but have to do with mounting the speaker in the wall, so that the speaker baffle and wall are in the same plane. But that's not really an acoustic product you can sell. That's a speaker design or mounting choice.
 
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ddude003

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@rcohen There are more than one ways to skin a cat... Grab a copy of Master Handbook of Acoustics by F. Alton Everest & Ken C. Pohlmann... You can probably find a old copy on the web somewhere as a pdf... Google is your frenemy...
 
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natty

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@rcohen There are more than one ways to skin a cat... Grab a copy of Master Handbook of Acoustics by F. Alton Everest & Ken C. Pohlmann... You can probably find a old copy on the web somewhere as a pdf... Google is your frenemy...
Great book.... but perhaps overkill if the OP is looking for a one off specific solution?
 

ddude003

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Front Speakers
Martin Logan ElectroMotion ESL
Center Channel Speaker
Martin Logan Motion C2
Surround Speakers
Martin Logan Motion 4
Surround Back Speakers
Martin Logan Motion 4 (yes, another set of these)
Subwoofers
Martin Logan Dynamo 700
Other Speakers or Equipment
Cifte 12AU7 NOS & Genalex Gold Lion Tubes in Pre
Video Display Device
Samsung The Premiere LSP7T UST Laser Projector
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Elite Screens Aeon CLR3 0.8 Gain 103-inch
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Netgear Nighthawk S8000 Streaming SwitchLumin U1 Mini Streamer/Transport
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QoBuz Studio Premier, Roon, Amazon Prime & Netflix
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Great book.... but perhaps overkill if the OP is looking for a one off specific solution?
Ah... Nothing better than a drink from the fire hose... Chapter 12-14 shows most types of absorbers and how/why they are built... A book to reference over and over as one builds on their curiosity of AV systems and the rooms/environments they play in...
 

natty

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Yeah I agree. A great reference.

The note I think about it the more I think the OP was commenting on marketing and not on whether solutions were easy to find if one knows what to look for? Because the solutions are easy to buy or build. But if you go looking for something called SBIR panels the results may be disappointing.
 
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