Acoustical Treatments Master Thread - Page 13 - AVS Forum
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post #361 of 10493 Old 02-03-2005, 03:21 PM
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It could be a nasty feature of the sound card mic/line input - I use the ETF mixer which is supposed to bypass everything - but you can never be sure. ETF only cancels out frequency response errors with the feedback channel- but can never know if there is auto/nonlinear gain on both channels.

Yes indeed the waterfall plots have a waterline - just makes it easier to see the mountains without all the garbage on the ocean floor.

I sure hope it is the case the delta dBETF = dBSPL - but I have not seen any tests that (dis)prove that. Maybe this only occurs with SPL calibration in ETF.

For doing reverb/modal decay and Sabine calculations that would be important - but for just doing continuous measurements to see relative impact of a panel should not matter as long as you are aware of the dB shift to max peak=100dB.

But this max=100dB feature can get you into trouble - suppose you build a resonator to target a peak mode as some on here have been attempting. In reality the resonator could be successful at killing the peak - but now some other peak is at max=100dB - leaving you scratching your head - as that peak was not there before! Even though in reality the peak SPL dropped from 100dB to 80dB.

I have not checked continuous mode to see if it scales up to max 100dB. It seems it could use differences between readings to make better relative scales - at least within the same ETF session - so that you have max=100dB only once per session rather than per graph. But that would require that successive runs be able to show >100dB. Then the user would have to watch out for the continuous graph scale changing - which could itself be misleading.


So I still think it is worth doing the SPL calibration!
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post #362 of 10493 Old 02-04-2005, 12:38 PM
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Bob,

> The minimum on the ETF5 waterfall charts is always 70db.
> The maximum on the ETF5 waterfall charts is always 100db

Not so! When displaying a waterfall graph, click the icon at the lower far-left of the window and you can set both limits to anything you want. That's why I suggested yesterday that maybe I should display my Density graphs again setting a new lower bottom limit to better see more of the decay.

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post #363 of 10493 Old 02-04-2005, 12:40 PM
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Kras,

> suppose you build a resonator to target a peak mode as some on here have been attempting. In reality the resonator could be successful at killing the peak - but now some other peak is at max=100dB - leaving you scratching your head <<br />
I agree with that completely. But again, my goal was to see the change in decay rate versus frequency, not changes in absolute level.

I promise the next time I do a test like this I'll either do it your way, or run it both ways. Okay?

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post #364 of 10493 Old 02-05-2005, 01:25 AM
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Quote:


Originally posted by Ethan Winer
Bob,

> The minimum on the ETF5 waterfall charts is always 70db.
> The maximum on the ETF5 waterfall charts is always 100db

Not so! When displaying a waterfall graph, click the icon at the lower far-left of the window and you can set both limits to anything you want. That's why I suggested yesterday that maybe I should display my Density graphs again setting a new lower bottom limit to better see more of the decay.

--Ethan

that would be very interesting, Ethan.

also, are there any other means of presenting the data? like a frequency-filtered (filter between two of the nulls) "o-scope" view that would let you see the decay over time at a given frequency?

Understanding sound isolation
That link may be helpful
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post #365 of 10493 Old 02-05-2005, 05:41 AM
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My God Brian - don't you ever sleep!?

I am serious...and don't call me Shirley.
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post #366 of 10493 Old 02-05-2005, 09:54 AM
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Brian,

> a frequency-filtered (filter between two of the nulls) "o-scope" view <<br />
No, ETF offers only a few fixed ranges. If it did allow setting any arbitrary upper and limit limits, that would solve the problem I mentioned to you this morning in alt.sci.physics.acoustics, about some peaks being hidden behind others.

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post #367 of 10493 Old 02-05-2005, 08:09 PM
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Ethan,

i guess the possible analogy with assessing mechanical damping via individual modes and peeking at absorber performance via individual modes has kind of intrigued me through all this discussion.

i understand if you're not interested, but you can mail me at brianravnaas@audioalloy.com, and if you don't mind emailing the files (i'm sure they are huge) i'll take an hour and try to process them on some equipment here at the lab. ASCII files or .wav files, if they are possibilities.

just a thought, and just for my own curiosity.

Brian

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post #368 of 10493 Old 02-06-2005, 09:12 AM
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Brian,

> if you don't mind emailing the files (i'm sure they are huge) i'll take an hour and try to process them on some equipment here at the lab. ASCII files or .wav files, if they are possibilities. <<br />
The 13 files I have are native ETF data files, and each is about 790 KB. If you have ETF I'll be glad to send them to you so you can do whatever analysis you'd like. But if you don't have ETF these files will be of no use.

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post #369 of 10493 Old 02-07-2005, 01:40 AM
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Quote:


Originally posted by Ethan Winer
Brian,

The 13 files I have are native ETF data files, and each is about 790 KB. If you have ETF I'll be glad to send them to you so you can do whatever analysis you'd like. But if you don't have ETF these files will be of no use.

--Ethan

i've got no ETF, so i guess for now i can't do anything.

Brian

Understanding sound isolation
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post #370 of 10493 Old 02-11-2005, 08:40 AM
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I have been reading through this thread and although I have gleaned a ton of great information, I don't think this question ever got answered definitively (pg.3 of the thread). I have seen one response saying it doesn't matter if you treat above ear level at all (its only for aesthetics) and another which says it is part of the sound characteristics of the room. Which is it? I would love to just paint that part of it and be done.

Quote:


Originally posted by smithb
I really could you use some advice based on the following questions:

-----------------------------------------------------------------------------------------
I am very interested in an answer to "gjlowe" question:

"if you put a ledge molding instead of chair rail around the walls, do you even need treatment on the upper half?"

My plan is to treat the whole lower half (ear level and below) of the room as suggested (except full treatment on front wall). However, I have read mix messges on the value of using cloth covered batting on the top. Some say it is for acoustical purposes and some say that it just pushes the upper wall out to meet the treatments of the bottom half. I personally would like to just paint the top half and build a ledge in the chair rail to save money if batting doesn't add any additional value. So which is it?

What is the rule about hanging pictures on the upper walls?

Some treat the lower half of columns and others do not. Is there a reason to go one way or the other?

I see many putting heavy curtains along the front wall which looks very nice. What impacts does this cause on the front wall treatment? No impact or cancel it out?

Finally, do people treat the wall area behind the screen?

Thanks for any feedback.
-----------------------------------------------------------------------------------------

Any response from the experts would certainly be appreciated: Dennis or Eric?


Craig

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post #371 of 10493 Old 02-11-2005, 08:58 AM
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strange_brew,

Batting is definitely not just for aesthetics. It provides significant sound absorption.

Whether or not you need it depends on your room. There is no "one size fits all" in room acoustics.

For example, suppose your front speakers are mounted high up, and the first reflection points between speakers and ear are above the level of the fiberglass treatment. Then you definitely want to put up polyester batting (or additional fiberglass) to absorb these reflections.

On the other hand, if the fiberglass itself provides the right amount of absorption for correct reverberation times, adding batting may over-absorb high frequencies.

The only way to know is to test and/or computer model your room.

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post #372 of 10493 Old 02-11-2005, 09:14 AM
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Thanks Terry.

Then I'm guessing that in most cases it must be required from the number of theaters (particularly DE designs) that include it. I suppose that answers another of the questions that has been bothering me as well - when I look at many of the professionally designed theaters (again, mostly DE designs), it looks to me like the lower "insulshield" portion is lower than ear level? Or maybe its just hard to tell from the screenshots I have seen.

To be honest I glossed over much of the thread that dealt with computer modelling the rooms since what I gathered (particularly from Dennis' posts) is that it just depends too much on people, furniture etc... as those things become a large portion of the volume of the room. And I don't know that i'm up for trying to Ray Trace my room. Obviously this is where the value of hiring a pro designer comes in, but if by mimicking rooms similar to mine I can get 80% of the way there, I'll probably be happy.

Craig.

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post #373 of 10493 Old 02-11-2005, 10:25 AM
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Craig,

> I have seen one response saying it doesn't matter if you treat above ear level at all <<br />
See my first reply in this thread:

http://www.avsforum.com/avs-vb/showt...hreadid=507497

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post #374 of 10493 Old 02-11-2005, 04:26 PM
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Thanks Ethan. I think I'll follow the crowd on this one and go with the Polyester batting and GOM.

Craig

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post #375 of 10493 Old 02-21-2005, 09:52 PM
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Hello,

I have been reading and learning a lot. Thank you very much for all your time you put into this.

Here are two pictures of my dedicated home theater that is in the beginnings of construction by me. I am interested in your thoughts about my design? I have some options right now while under construction.

1) Most dedicated home theaters I see pictures of have the front speakers close to the screen. Am I making this more difficult by trying to have the speakers far forward for an equilateral triangle? Complicates #2 below.

2) As it stands now, I would have to go behind the speaker to access the equipment. AV equipment can be moved toward the screen more and not have a corner trap. Or back and then move the speaker toward the screen. Thoughts on this.

3) Are the rear surrounds placed in the room properly with the door and walkway to the seating? Door can be moved only back. If I move it back further is there any advantage?

To answer these questions more fully, I know you will need the RT60 and the sound adjustment ideas. I am working on the RT60 calculation and so far it looks like this:

Preliminary results from Chris Whealy's 2004__V 2.61

1.5? Ductboard with Foil facing NRC =.90
Frequency___________125Hz___________250Hz___________500Hz___ ________1KHz___________2KHz___________4KHz
Sabine_______ _ _ _ _ ___0.43___________ __0.43__________ _ _ 0.27______ _ _ _____0.21__ _________0.23________ ___0.21
_
1? Ductboard with Matt facing NRC =.70
Frequency___________125Hz___________250Hz___________500Hz___ ________1KHz___________2KHz___________4KHz
Sabine___________ _ _ _ _0.45___________ _ _0.56___________ _ 0.36_______ _ _ ____0.26___________0.23_________ ___0.21

Room details:
I currently have the 1.5" and 1" ductboard.
Room size 88.25" H x 139.75" W x 235"L (in basement). Room Volume 1,677 ft3
Fabric covered Insulation on Lower 48? side wall coverage and entire front wall
Upper side walls and back is painted
Ceiling and walls are basic 1/2" drywall, no insulation in Ceiling, walls have R-13 in standard wood studs.
Carpet is a shag with a 1/2" pad over concrete
Seating is one large cloth pillow back sofa 110" x 36" (4 seats) plus two ottomans (18" x 31")
Door is a can be either hollow or solid core?
AV equipment will have a glass door over the front of it (approximately 60" x 18")
Screen is 96" wide and is Gatorfoam painted.
Projector AE700, ceiling mounted

Thanks for your help,

Kevin

 

top down view.pdf 23.6708984375k . file
Attached Files
File Type: pdf top down view.pdf (23.7 KB, 10 views)
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post #376 of 10493 Old 02-21-2005, 10:01 PM
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Here is the speaker firing diagrams to go along with the top down view in previous post.

Thanks, Kevin
LL
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post #377 of 10493 Old 03-03-2005, 06:46 PM
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Question regarding OC703 on my front wall.

My plans include covering the front wall with OC703. I'll have a false wall about 30" out from that covered in black GOM FR701 fabric. My L/C/R speakers and my sub will be behind this false wall. My RPTV will be recessed into this false wall.

Should I cover the OC 703 on the wall to keep the fiberglass from possibly becoming airbourne inside this false wall area? I've never seen OC703, so I don't know if this is a valid concern or not.

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post #378 of 10493 Old 03-03-2005, 08:26 PM
 
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It's fairly well-contained as far as fiberglass goes, fluffy insulation seems to let loose a lot more fibers, it seems that the fiberboard tends to release fibers mainly with physical contact, so you should still wear gloves. I have an MD in the family, so I definitely made sure to cover all the fiberglass to keep from breathing it in, but if you have a false wall covered in fabric, I think that barrier is relatively effective for that unless there is a lot of air blowing around in there.

I'm really not qualified to know, but my common sense tells me that you'd at least avoid having bare fiberglass in areas where people are, or where there are air vents and such.
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post #379 of 10493 Old 03-04-2005, 09:40 PM
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I haven't tried 703 nor linacoustic, but with Roxul's rigid rockwool I found that when I carried some around with my bare hands that eventually my hands started to feel prickly and turned red. Nevertheless I'd say the effect was much less than I've had on exposed arms (holes in workshirt near buttons at wrists) and neck when I've worked with fluffy insulation insulating a house and attic. Also some little pieces (1/4") and dust fell off when the Roxul panels were moved or bumped. Thereafter I handled it with rubber gloves and a jumpsuit.

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post #380 of 10493 Old 03-05-2005, 09:44 AM
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Quote:


Originally posted by Toeside
Question regarding OC703 on my front wall.

My plans include covering the front wall with OC703. I'll have a false wall about 30" out from that covered in black GOM FR701 fabric. My L/C/R speakers and my sub will be behind this false wall. My RPTV will be recessed into this false wall.

Should I cover the OC 703 on the wall to keep the fiberglass from possibly becoming airbourne inside this false wall area? I've never seen OC703, so I don't know if this is a valid concern or not.

Hi,

I used coated Insulshield behind my fabric false wall and I've never experienced any problems with airborne fiberglass. As Chris cautions, there were no air vents behind the false wall.

Larry
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post #381 of 10493 Old 03-05-2005, 09:53 AM
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I don't have any vents where my false wall will be, so that's not a concern.

However, I am concerned with the air movement caused by the sub that will be behind the fabric wall.

I think I'll try to find insulshield locally (there's a place to get OC703). If I go the OC703 route, maybe I'll cover it with fabric to be safe.

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post #382 of 10493 Old 03-05-2005, 05:37 PM
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Quote:


Originally posted by Toeside
I don't have any vents where my false wall will be, so that's not a concern.

However, I am concerned with the air movement caused by the sub that will be behind the fabric wall.

I think I'll try to find insulshield locally (there's a place to get OC703). If I go the OC703 route, maybe I'll cover it with fabric to be safe.

Hi,

I've got a decent size subwoofer and full range main speakers behind the fabric false wall, and still no problems.

Larry
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post #383 of 10493 Old 03-08-2005, 11:08 AM
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From this thread, it seems that curtains can help with high frequencies, but not really low frequencies. In my case, I plan to put a large front projector screen in front of an even larger set of picture windows. I could pull thick drapes across when using the room, but would the windows still severely damage the sound quality?

Is there anything I could do with other materials, while still having the option of seeing out the windows when I wasn't using the projector?

What about the idea of angling the windows a bit so that the reflections go to the sides instead of straight back to the viewer/listener?
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post #384 of 10493 Old 03-08-2005, 01:57 PM
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Quote:


Originally posted by Erikb
From this thread, it seems that curtains can help with high frequencies, but not really low frequencies. In my case, I plan to put a large front projector screen in front of an even larger set of picture windows. I could pull thick drapes across when using the room, but would the windows still severely damage the sound quality?

Cheap, wimpy curtains won't do much. But heavy velour drapes of 18 ounces per square yard, hung in loose folds, provide pretty good sound absorption:

absorption coefficients (from L.L. Beranek's "Acoustics")
0.14 at 125 hz
0.35 at 250 hz
0.55 at 500 hz
0.75 at 1000 hz
0.70 at 2000 hz
0.60 at 4000 hz

Theatrical supply houses stock this really heavy material. I use Georgia Stage -- www.gastage.com.

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post #385 of 10493 Old 03-09-2005, 10:56 AM
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Thanks, Terry. That was exactly what I was looking for.

Your reply also led me to find this book:

Noise and Vibration Control Engineering : Principles and Applications
by Leo L. Beranek

which has some great additional information (found using the "search inside this book" feature at Amazon).
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post #386 of 10493 Old 03-20-2005, 02:58 PM
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I have ordered some 1" OC 705 for my front wall. I will have enough to put some behind my screen, (92" Da-Lite HCCV, non-perforated). The screen is mounted 3" off the wall, so I could get some in there, but is it even worth doing if the screen is non-perf'd?

Also, what is the recommended mounting method for OC 705? It will be covered by burgundy velvet drapes, so it won't be seen.

Thanks,

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post #387 of 10493 Old 03-20-2005, 06:17 PM
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Quote:


Originally posted by craig john
I have ordered some 1" OC 705 for my front wall. I will have enough to put some behind my screen, (92" Da-Lite HCCV, non-perforated). The screen is mounted 3" off the wall, so I could get some in there, but is it even worth doing if the screen is non-perf'd?

Hi Craig,

If the screen is not micro-perforated, then it's not worth putting fiberglass behind. The solid screen would reflect frequencies above a few hundred hertz. But below this frequency, the absorption ability of even 3 inches of fiberglass falls off significantly. So you'd end up with an absorber peaking at a few hundred hertz.

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post #388 of 10493 Old 03-21-2005, 10:45 AM
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Quote:


Originally posted by Terry Montlick
If the screen is not micro-perforated, then it's not worth putting fiberglass behind. The solid screen would reflect frequencies above a few hundred hertz. But below this frequency, the absorption ability of even 3 inches of fiberglass falls off significantly. So you'd end up with an absorber peaking at a few hundred hertz.

Hi Terry,

What about a non-perforated screen that is 24" off of the wall?

I have my screen mounted across a recess that is 24" deep. There is 18" of space over and 22" of space under the screen for sound to get behind it.

Plan View

Front View

I have 1" of Insulshield covering the entire front wall, including the insides of the recess. I would like to add more insulation to improve the bass response, but I feared that it might make the room too dead at the mid and higher frequencies. I've attached a graph the Reverberation Time of the room, which you can see is fairly low.

However, I had not considered that the screen might reflect most of the mid and high frequencies traveling to the recess. Do you think adding 2-3 more inches of insulation in the recess behind the screen might make the room too dead. The recess is roughly 7' wide by 9' high. The room is 15' wide x 26' long (including the recess) x 10' high.

Thanks.

Larry
LL
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post #389 of 10493 Old 03-22-2005, 08:09 AM
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Originally posted by LarryChanin
I would like to add more insulation to improve the bass response, but I feared that it might make the room too dead at the mid and higher frequencies. I've attached a graph the Reverberation Time of the room, which you can see is fairly low.

However, I had not considered that the screen might reflect most of the mid and high frequencies traveling to the recess. Do you think adding 2-3 more inches of insulation in the recess behind the screen might make the room too dead.

It would be fine, Larry. It should only affect the low frequencies, because your screen is already reflecting the highs.

- Terry

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post #390 of 10493 Old 03-22-2005, 08:59 AM
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Terry

Have you done the calculation of vinyl movie screen (nonperf) over fiberglass as a membrane bass trap? One of the things on my list of things to do.
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