Microperf. Screens-Audio Reflection and Speaker Setup - AVS Forum
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Old 11-13-2012, 12:59 PM - Thread Starter
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So I got to really dialing in my setup last night and noticed some things. At the moment I have 2x4x2thick acoustic panels strategically placed along all the side walls, front and rear wall as well. room is 11x29 with the setup all tucked into the 11 foot wide section, before it opens up on the right side to a bar area that is about 5x5. Seating area is about 11 feet back from the mains. My screen is a Stewart Firehawk Microperf screen that is hanging from the ceiling about 3 feet from the front wall and all the speakers are located either behind it, or in the sub's case, below it. It is kind of a floating screen type design, at least for the time being.

At this point in time I have my av123 LS6's right almost up against the screen, but I have room to scoot them back to about 18" away if that is preferred. I can't really do that and definitively test whether that is better placement or not as it would require movement of ALL of the acoustic panels anywhere near the front of the screen. I would like to get everyone's experience here with microperf screens and where they placed their speakers after testing for flattest response.

The other problem I am running into is it seems I am getting some high frequency bounce from the left side, but not the right. All upper level percussion (symbols and all) seem to ALL come from the left side so either the screen is causing this bounce, but only on the left side, OR I am getting some HF reflection off the front or side wall that I haven't been getting previously behind the speaker. I have seen where people have just deadened everything on the front wall behind their screen with some type of material... What is that stuff? I could easily re-purpose the panels I have to other areas if I could just line the front wall floor to ceiling with something instead! It would probably be more effective anyways smile.gif The other option is the ole false wall to cover all those reflections, but I move speakers around and reposition too often that this honestly makes me nervous.

I would love to hear everyone's thoughts. Thanks in advance!

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Old 11-13-2012, 01:41 PM
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Quote:
Originally Posted by beastaudio View Post

So I got to really dialing in my setup last night and noticed some things. At the moment I have 2x4x2thick acoustic panels strategically placed along all the side walls, front and rear wall as well. room is 11x29 with the setup all tucked into the 11 foot wide section, before it opens up on the right side to a bar area that is about 5x5. Seating area is about 11 feet back from the mains. My screen is a Stewart Firehawk Microperf screen that is hanging from the ceiling about 3 feet from the front wall and all the speakers are located either behind it, or in the sub's case, below it. It is kind of a floating screen type design, at least for the time being.

At this point in time I have my av123 LS6's right almost up against the screen, but I have room to scoot them back to about 18" away if that is preferred. I can't really do that and definitively test whether that is better placement or not as it would require movement of ALL of the acoustic panels anywhere near the front of the screen. I would like to get everyone's experience here with microperf screens and where they placed their speakers after testing for flattest response.

The other problem I am running into is it seems I am getting some high frequency bounce from the left side, but not the right. All upper level percussion (symbols and all) seem to ALL come from the left side so either the screen is causing this bounce, but only on the left side, OR I am getting some HF reflection off the front or side wall that I haven't been getting previously behind the speaker. I have seen where people have just deadened everything on the front wall behind their screen with some type of material... What is that stuff? I could easily re-purpose the panels I have to other areas if I could just line the front wall floor to ceiling with something instead! It would probably be more effective anyways smile.gif The other option is the ole false wall to cover all those reflections, but I move speakers around and reposition too often that this honestly makes me nervous.

I would love to hear everyone's thoughts. Thanks in advance!

My thoughts are that microperf screens are supposed to be approximately sonically transparent. Any sonic effects they have are primarily restricted to the highest octave or two. They may cause transmission losses at very high frequenceis, but I would not expect them to have much effect on the effects of sort of absorbing panels that you are talking about.

It shouldn't matter how far the speakers are from the screen.

IME if you hang a screen like this in front of some architectural feature that causes a bounce echo, it will have negligible effects one way or the other.
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Old 11-13-2012, 03:14 PM
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Originally Posted by beastaudio View Post

I have seen where people have just deadened everything on the front wall behind their screen with some type of material... What is that stuff? I could easily re-purpose the panels I have to other areas if I could just line the front wall floor to ceiling with something instead!

Perhaps it's not for all rooms, however I reall like a full front wall assault via broad-band absorption. As thick as one can get away with, and as one gets real thick a move to loose fluffy is more effective than rigid. That's good, ... it's cheaper.

Yeah, I like the black hole approach to my front wall eek.gifcool.gif

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Old 11-13-2012, 03:57 PM
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no first hand experience, but I heard that with perforated screens, it is important to keep speakers at least 1 foot away from the screen . that was one of the reasons why I went with a woven screen.

I cannot imagine, however, that the close positioning can explain the HF boost on one side you were describing. is there any way you can check if the problem goes away with the screen removed?
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Old 11-13-2012, 07:23 PM
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Originally Posted by zheka View Post

no first hand experience, but I heard that with perforated screens, it is important to keep speakers at least 1 foot away from the screen . that was one of the reasons why I went with a woven screen.
I cannot imagine, however, that the close positioning can explain the HF boost on one side you were describing. is there any way you can check if the problem goes away with the screen removed?

+1 ... I've seen the 1 foot recommendation many times from multiple sources.

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Old 11-13-2012, 09:38 PM
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Originally Posted by FOH View Post

Perhaps it's not for all rooms, however I reall like a full front wall assault via broad-band absorption. As thick as one can get away with, and as one gets real thick a move to loose fluffy is more effective than rigid. That's good, ... it's cheaper.
Yeah, I like the black hole approach to my front wall eek.gifcool.gif

I concur with this approach, at least in a dedicated room. The wall behind my proscenium where the screen is mounted is covered with black cloth acoustical panels ranging from 1" to 4" in depth. The 1" panels are directly behind the LCR speakers, which are behind a Stewart StudioTek 1.3 Microperf. My Synthesis® calibrator placed the mains right behind the screen, with about a half a foot to the wall behind.

The sidewalls have just one absorber and two diffusers each, then three absorbers and four diffusers on the back wall.

My three front speakers are horns on top and direct radiators on the bottom, so they're different than your LS6s. I can't predict what impact that difference might make in how well this approach may or may not help you. However, I will write that you should think about diffusion as well as absorption.

In an experiment, you can have someone hold extra absorption on the left side and move it systematically along the wall to see if there's any attenuation of the reflection problem.

It could also be coming off the ceiling.. oh no!eek.gif but unless there's a physical difference from one side of the ceiling to the other, that's less likely.

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Old 11-14-2012, 07:59 AM - Thread Starter
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Originally Posted by zheka View Post

no first hand experience, but I heard that with perforated screens, it is important to keep speakers at least 1 foot away from the screen . that was one of the reasons why I went with a woven screen.
I cannot imagine, however, that the close positioning can explain the HF boost on one side you were describing. is there any way you can check if the problem goes away with the screen removed?

Hindsight, eh... I did get a heck of a good deal on the stewart tho. Thanks for the pointer, ill give it a shot tonight. Yes, I can removed the screen from the clips easily, and didnt notice this phenomenon for the first few nights when I had the screen down. SO either I am getting a bounce from the screen or screen border, or speaker placement has shifted enough from tinkering that everything is just in a bad spot. I will continue to tweak and update as I make progress (hopefully)

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I concur with this approach, at least in a dedicated room. The wall behind my proscenium where the screen is mounted is covered with black cloth acoustical panels ranging from 1" to 4" in depth. The 1" panels are directly behind the LCR speakers, which are behind a Stewart StudioTek 1.3 Microperf. My Synthesis® calibrator placed the mains right behind the screen, with about a half a foot to the wall behind.
The sidewalls have just one absorber and two diffusers each, then three absorbers and four diffusers on the back wall.
My three front speakers are horns on top and direct radiators on the bottom, so they're different than your LS6s. I can't predict what impact that difference might make in how well this approach may or may not help you. However, I will write that you should think about diffusion as well as absorption.
In an experiment, you can have someone hold extra absorption on the left side and move it systematically along the wall to see if there's any attenuation of the reflection problem.
It could also be coming off the ceiling.. oh no!eek.gif but unless there's a physical difference from one side of the ceiling to the other, that's less likely.

I dont have any good diffusion panels, just mostly 2x4 absorption. The ceiling is a definitely possibility but with it being a drop ceiling, I need something nice and light to put there as the panels would be too heavy. Any pointers for some nice cheap diffusion panels that I could run floor to ceiling perhaps at the first reflection points and ceiling?

FOH,

I really think I am going to give this a shot too. not only will it help with the acoustics, but it will kill any ambient light behind the screen...at least even more than it already is smile.gif even with all the lights full on, I have to put on a headlamp to do ANYTHING behind the screen :nice:

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Old 11-14-2012, 09:20 AM
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Above a drop ceiling is an ideal place for some serious bass trapping effectiveness. Merely fill it with the loose-fluffy stuff.

There's an entire variety of quality ceiling tile products too, but more bucks than simply insulating. Either way, the bass trapping would be good an inexpensive.

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Old 11-14-2012, 09:35 AM - Thread Starter
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For sure, the only problem is there is a lot of HVAC and can lighting to wrap around, and my bass response is essentially +/- 5db's across the range. Not too bad smile.gif

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Old 11-14-2012, 02:04 PM
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Bass traps do help with freq response, however they also work in the time domain. Subjectively, they can significantly tighten up the bass response, creating a well delineated pitch definition, and increased note to note clarity.

Addressing LF room response in the time domain, via LF damping/trapping, is something most every room can use more of. It's both, easily measurable, and clearly audible.

Best of luck

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Old 11-14-2012, 02:18 PM - Thread Starter
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Originally Posted by FOH View Post

Bass traps do help with freq response, however they also work in the time domain. Subjectively, they can significantly tighten up the bass response, creating a well delineated pitch definition, and increased note to note clarity.
Addressing LF room response in the time domain, via LF damping/trapping, is something most every room can use more of. It's both, easily measurable, and clearly audible.
Best of luck

without a doubt. My lack of usable corners in my room is one problem, but I need to tackle what is happening with the mains first and foremost as it is much more noticeable.

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Old 11-15-2012, 05:53 AM
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without a doubt. My lack of usable corners in my room is one problem, but I need to tackle what is happening with the mains first and foremost as it is much more noticeable.

You're right, I understand that entirely.

btw; love the big, comfy, overstuffed seating cool.gif

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Old 11-15-2012, 11:33 AM
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You speakers should be no closer than 6" from a microperf screen.

I would be very careful about over treating your room acoustically. There are specifications for these things and measurements should be taken to see where you really are. The following attachment shows a room similar to what you are describing that you did. It is possible to have a room be both too live and too dead acoustically.

Dolby Room Acoustics Rating.pdf 128k .pdf file
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File Type: pdf Dolby Room Acoustics Rating.pdf (127.7 KB, 14 views)
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Old 11-15-2012, 12:06 PM - Thread Starter
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actually, The further i backed the speakers away from the screen, the more the top end from about 5-10khz would drop pretty drastically. I ended up bringing them both all the way back up, while watching the room sweeps on OM and adjusted the right speaker to almost face straight out, and the additional dip I saw from 5-10 I got almost perfectly flat. I will try and post what I ended up with, but I still have some work to do. I did notice I am still getting some decent bounce from the couch, and I think that is another part of why the left speaker sounds a little brighter, as I sight in the far right seat of the couch. It is microfiber so this was a little surprising to me!

Regardless, progress was made, but still a little more to go.

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Old 11-15-2012, 12:55 PM
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The other problem with close placement in a heavy increase in comb filtering.

You also need to conform to SMPTE-222M when looking at high frequencies and good microphones are required for that.
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Old 11-15-2012, 01:05 PM - Thread Starter
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The other problem with close placement in a heavy increase in comb filtering.
You also need to conform to SMPTE-222M when looking at high frequencies and good microphones are required for that.

Yep, that is what required the adjustment of the speaker to accommodate for the comb filtering, but even still playing a single source i.e. left and then right speakers, the upper octaves performed better closer to the screen. This may have also been a product of ALL the treatments are placed with the speaker position needing to be closer to the screen. Nothing matches up properly if I move them further back. So in reality, the dip in the upper octaves was more than likely a first order reflection that could have dropped the overall response, rather than the screen actually being the issue at all.

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Old 11-19-2012, 01:22 AM
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Are you using the Stewart processor? It helps flatten the frequency response in the upper ranges.

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Old 11-19-2012, 07:41 AM - Thread Starter
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Are you using the Stewart processor? It helps flatten the frequency response in the upper ranges.
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Nope, but that wouldnt have anything to do with the L/R speakers, it is just for the center correct?

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Old 11-19-2012, 06:22 PM
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Nope, but that wouldnt have anything to do with the L/R speakers, it is just for the center correct?

My understanding is that it is available single channel for any of the speakers located behind the screen. If that is your fronts then you'd get one for each L/R.

Did you read the .pdf on the the woven vs. microperf on Stewart's website. There are freq. response graphs that show this difference (corrected vs. uncorrected).

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