Acoustical Treatments Master Thread - Page 22 - AVS Forum
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post #631 of 10416 Old 11-23-2005, 12:33 PM
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Norm,

> should I place panels behind the screen, behind the speakers? Where would you put them on the side walls ... Can anyone help me sort this out? I definitely need bass traps. <<br />
Yep, all rooms need bass traps. There's a lot of advice about bass traps and panel placement in my Acoustics FAQ:

www.ethanwiner.com/acoustics.html

--Ethan

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post #632 of 10416 Old 11-23-2005, 04:05 PM
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Originally Posted by RicosRevenge View Post

myfipie... I raced offshore powerboats on the APBA Pro-Series circuit. I have a 34' Eliminator V-bottom with twin 500 HP Mercs in Factory 2 class, she ran 96.5 MPH on radar. I love going fast on the water (Top speed 165 MPH in a 46' Skater cat with twin 1400 hp Sterlings).

Thanks for not lighting me up on my lay-person's description. I find that there are many times when the incredible knowledge on this forum can overpower the novice. If I was given a more direct approach, it would have taken me MUCH less time to track down the stuff I needed. BobGold's co-efficient charts are key!

Well 6 knotts is really fast to me!!! ha h aha

I got to tell you that sometimes we get so lost in the science that people get plan turned off to acoustics, throw up there hands and say for get it, in fear of doing it wrong.. Really the only thing you can do wrong is do nothing at all.
We all owe a lot to Bob!!

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post #633 of 10416 Old 11-24-2005, 08:30 PM
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I have a question for you HT gurus. Forgive my newbie-ness.
Why do so many folks use GoM fabric on their walls? I can understand its use when its hiding speakers, but what purpose does it serve on the wall? An accoustically transparent material seems like it would do nothing for sound. Hopefully someone can set me straight. Thanks.


Marc
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post #634 of 10416 Old 11-24-2005, 08:58 PM
 
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because usually there is absorbing material behind it, or diffusors or other acoustical devices and speakers and whatnot. It's mainly for aesthetics, and to be transparent to any of the aforementioned devices that would be behind it.
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post #635 of 10416 Old 11-25-2005, 04:53 AM
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Exactly. The idea is not no have to worry about the look of what's behind. Whether it's a full covered wall of batting/duct liner or scattered treatments so you don't have to worry about aesthetics of patterns and spacing - the cloth does the trick.

I am serious...and don't call me Shirley.
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post #636 of 10416 Old 11-25-2005, 07:26 AM
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In the same vein, I need advice on two things;

1. What other fabrics besides GOM can I use? Names would be nice.

2. I can't find OC 703 anywhere. Mind you I have only checked HD and Rona?
Where should I look?

Thanks
John
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post #637 of 10416 Old 11-25-2005, 09:19 AM
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My understanding is that OC is going to get harder and harder to find... If you want to build yourself you may want to contact Bryan about getting some.. BTW Bryan I got the notice that OC is going up 9%..

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post #638 of 10416 Old 11-25-2005, 10:11 AM
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John- I see you're in Canada as well (I'm in winnipeg). I phoned a few places too- and actually had luck with a local building supply store this week. They had no issues ordering in 703. The only catch was that I had to buy a minimum of 12 2x4 sheets of it. Kind of pricey though- they wanted cdn$18 per sheet. So my advice is to phone local places. If they carry OC product, they should be able to get it in.
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post #639 of 10416 Old 11-25-2005, 03:58 PM
 
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fiberglass board like OC 703/705 is more industrial/commercial insulation you usually wont find it at HD or similar. Look in the yellow pages for insulation supply places, hvac supply etc and call and ask for rigid fiberglass board such as OC 703, they'll know what you're talking about shouldn't take you long. If you're on the boonies obviously you'll probably need to find places near civilization, but shouldn't be hard to find, there are other brands than OC its all the same stuff and bout the same price so they'll know what you mean. BTW it's usually used for big HVAC ducting and such, but any competent commercial supply guy will know exactly what you're talking about.
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post #640 of 10416 Old 11-28-2005, 01:27 PM
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Can anyone direct me to someone in San Diego who sells any of the accepted 1" absorption materials listed on this thread? I'm coming up with absolutely nothing so far. Thanks.
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post #641 of 10416 Old 12-03-2005, 07:38 AM
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Hi-

I finally got through this thread and am well on my way to reading Ethan's FAQ. It is still not clear to me what might happen to bi-polar speakers if you treat the front wall. I am okay the thought of removing the first reflection from the speakers I have, but I'd like to hear from people that have heard them. Has anyone done this?
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post #642 of 10416 Old 12-03-2005, 09:11 AM
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Quote:
Originally Posted by Tweakophyte View Post

I finally got through this thread and am well on my way to reading Ethan's FAQ.

Congratulations...

HH
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post #643 of 10416 Old 12-04-2005, 02:43 PM
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Originally Posted by HuskerHarley View Post

Congratulations...

HH

At least I have pics of MY HT online... :P
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post #644 of 10416 Old 12-04-2005, 02:57 PM
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I have a few more...

- What does putting in a broadband bass absorber do for total output? I understand it will tame my peaks (and reduce smearing). Will my max SPL drop a few db? Will it just flatten the response but allow the SPL to flow? (Let's assume I EQ'd my peaks out with regards to max SPL... make sense?)

- It's pretty easy to understand how absorbtion will reduce a peak. How does it effect a null? For converstation, assume both a dip and a deep drop.

- What are some good ways to treat a null with bass traps? Would you only trap a portion of the room (i.e. one wall with the room dimension causing the null)?

- I am considering broadband bass traps in certain corners of my room. Only one corner allows for floor to ceiling (soffit) treatment using the 2' hypotenuse 703 method I have read about. How effective would it be do only do from the floor to half way up? I might go from 2' to 1' to smaller (so I can make it all the way up). Any comments on that?

- My current surrounds are bi-polar and would be located close to any corner bass trap I might construct. Is it advisable to use a semi-reflective surface on a portion of the trap so I can keep the surround non-locatable?

PS... pics of my HT in the link in my sig...

Thanks!
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post #645 of 10416 Old 12-05-2005, 12:13 PM
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Quote:
Originally Posted by Tweakophyte View Post

I have a few more...

- What does putting in a broadband bass absorber do for total output? I understand it will tame my peaks (and reduce smearing). Will my max SPL drop a few db?

Hi,

Over at Siegfried Linkwitz's web site there's a discussion of how to calculate Amplifier power needed to sustain a Reference Level if you know the type of speaker, the volume of your room, the Reverberation Time of your room, the efficiency of your speakers and the reference level desired.

As mentioned above the amount of amplifier power needed to sustain a particular sound pressure level depends on a number of factors, including the overall Reverberation Time of the room. So depending on how much the broadband bass absorber decreases Reverberation Time there could be a measurable effect on power requirements, and therefore maximum SPL level.

For example, when I used Mr. Linkwitz's method to calculate the per channel requirements of my home theater it came out to about 152 watts to sustain a 100 dB sound pressure level from one of my main speakers based on my room's Reverberation Time of 230 ms. If my room had a Reverberation Time at twice that duration (460 ms) the required power would only be about 76 watts to maintain a 100 dB sound pressure level.

However, while my power requirements might be reduced if I removed half of my absorption, the increase in Reverberation Time would adversely impact the sound quality for multi-channel listening, which depending on whose formula you use, should ideally be roughly 230 ms for my room size.

Larry
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post #646 of 10416 Old 12-05-2005, 12:31 PM
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After reading this thread, it is obvious to me that no matter what I would do to treat a room, it would be wrong.

Is there not a good book or two out there with full intructions or specifications on how to build a quality (not nerd-prefect) HT of varying sizes? Maybe THX Specs or the like.

Honestly, the amount of varying opinions and minute details in this thread seems very piecemeal to me.
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post #647 of 10416 Old 12-05-2005, 12:33 PM
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Quote:
Originally Posted by LarryChanin View Post

Hi,



As mentioned above the amount of amplifier power needed to sustain a particular sound pressure level depends on a number of factors, including the overall Reverberation Time of the room. So depending on how much the broadband bass absorber decreases Reverberation Time there could be a measurable effect on power requirements, and therefore maximum SPL level.

For example, when I used Mr. Linkwitz's method to calculate the per channel requirements of my home theater it came out to about 152 watts to sustain a 100 dB sound pressure level from one of my main speakers based on my room's Reverberation Time of 230 ms.

Larry

Wouldn't it just have been a hell of a lot easier to use a dB meter and turn it up until you reached 100dB's? Save your pencil lead maybe?
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post #648 of 10416 Old 12-06-2005, 06:31 AM
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Larry-

EDIT
[strikethrough]
Thanks for the link... I am too tired for math in the morning, but it looks like a reduction in ring time equates to a reduction in power requirement. Did I miss a section on the SPL being absorbed by traps?

Now I wonder if the reduction in ring time offsets the absorbed sound? ...check my math (if you like)... like I said, I am generally too tired to think in the morning. [/strikethrough]

...no more math before coffee
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post #649 of 10416 Old 12-06-2005, 06:48 AM
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Quote:
Originally Posted by Tweakophyte View Post

Larry-

Thanks for the link... I am too tired for math in the morning, but it looks like a reduction in ring time equates to a reduction in power requirement.

No. 'Fraid its the other way around. A reduction in reverberation time results in an increase in power requirement. That's because increased reverberation provides more sound energy storage in the room. An amplifier doesn't need to put out as much power to excite the room to a particular sound level. The downside, however, is a reduction in clarity of transient sound.

Regards,
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post #650 of 10416 Old 12-06-2005, 07:02 AM
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Tweaks,

> Did I miss a section on the SPL being absorbed by traps? <<br />
Terry is of course correct - adding absorption to a room reduces the overall level if for no other reason than it reduces the energy from reflections. But...

At bass frequencies adding absorption generally increases the level because deep nulls, which are very common throughout a room, are raised.

--Ethan

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post #651 of 10416 Old 12-06-2005, 07:04 AM
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Quote:
Originally Posted by Terry Montlick View Post

No. 'Fraid its the other way around. A reduction in reverberation time results in an increase in power requirement. That's because increased reverberation provides more sound energy storage in the room. An amplifier doesn't need to put out as much power to excite the room to a particular sound level. The downside, however, is a reduction in clarity of transient sound.

Regards,
Terry

No more math before coffee!


That was more intutive anyway.
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post #652 of 10416 Old 12-06-2005, 07:10 AM
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Quote:
Originally Posted by Ethan Winer View Post

Tweaks,

> Did I miss a section on the SPL being absorbed by traps? <<br />
Terry is of course correct - adding absorption to a room reduces the overall level if for no other reason than it reduces the energy from reflections. But...

At bass frequencies adding absorption generally increases the level because deep nulls, which are very common throughout a room, are raised.

--Ethan

So that explains it... trapping reduces peaks (and overall output) but increases nulls by absorbing the cancellations. (...again... too tired to think in the morning).

Is there any simple math or rules I might use? My concern is I am going to improve my room so much that I'll need (... REALLY need) another sub. My Ultra is doing pretty well right now...
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post #653 of 10416 Old 12-06-2005, 07:14 AM
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Tweak,

> My concern is I am going to improve my room so much that I'll need (... REALLY need) another sub. <<br />
I'd say that's unlikely. If anything, adding a lot of bass traps will give you more output. And the sub will also not have to work as hard thereby lowering distortion. My living room HT is pretty large at 25 by 16 with an 11 foot peak ceiling. I have an original 11-inch cube Carver Sunfire subwoofer and 38 traps. I get a huge amount of very deep bass in this room, even from that tiny sub.

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post #654 of 10416 Old 12-06-2005, 07:39 AM
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Quote:
Originally Posted by Ethan Winer View Post

Tweaks,

> Did I miss a section on the SPL being absorbed by traps? <<br />
Terry is of course correct - adding absorption to a room reduces the overall level if for no other reason than it reduces the energy from reflections. But...

At bass frequencies adding absorption generally increases the level because deep nulls, which are very common throughout a room, are raised.

--Ethan

Okay, let's go to the videotape, and see if this matches our recent experiment!

Here are the mean dB sound levels for the average of all seven positions, as taken directly from the spreadsheet:

79.1 dB - empty room
78.8 dB - 2 Mondo traps
78.7 dB - 4 Mondo traps
77.8 dB - 17 Mondo traps

Looks to me like the bass sound level decreased with increased absorption. However this effect was not huge -- only 1.3 dB going from empty room to 17 Mondo traps. It is hardly worth worrying about.

Regards,
Terry

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post #655 of 10416 Old 12-06-2005, 07:48 PM
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Tweakophyte:

Quote:


What does putting in a broadband bass absorber do for total output? I understand it will tame my peaks (and reduce smearing). Will my max SPL drop a few db? Will it just flatten the response but allow the SPL to flow? (Let's assume I EQ'd my peaks out with regards to max SPL... make sense?)

Absorbtion reduces the height of modal peaks, and reduces the depth of modal nulls.

Absorbtion also reduces the sound pressure level of a steady noise, according to the formula:
reduction in SPL = 10 log (a2 / a1)
where a1 is the absorbtion in sabins of the before room, and
a2 is the absorbtion in sabins of the room after additional treatment.

As you add absorbtion you will turn your volume knob up to achieve the same SPL.
You can keep adding absorbtion until your speakers start distorting, or melt and fail completely.

Quote:


- What are some good ways to treat a null with bass traps? Would you only trap a portion of the room (i.e. one wall with the room dimension causing the null)?

Have one.

Absorbers damp a mode. They treat both peaks and nulls of that mode.


Quote:


- I am considering broadband bass traps in certain corners of my room. Only one corner allows for floor to ceiling (soffit) treatment using the 2' hypotenuse 703 method I have read about. How effective would it be do only do from the floor to half way up?

It would be a little more than half as many sabins.

An amateur built the Ark. Titanic was built by professionals. Of course Noah took a little advice.
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post #656 of 10416 Old 12-06-2005, 10:11 PM
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Quote:
Originally Posted by dallas27 View Post

Wouldn't it just have been a hell of a lot easier to use a dB meter and turn it up until you reached 100dB's? Save your pencil lead maybe?

Hi Dallas,

Either I'm missing the humor in your posting, or you are missing the point. Since I didn't see any of those cute smilely faces etc., in your posting indicating your response was tongue-in-cheek, I'll assume that you're serious.

Tweakophyte asked whether adding a broadband bass trap would effect his maximum SPL, not how far should he twirl his dial to reach a given SPL dB. My calculation was intended to demonstrate that there could be a significant difference in power required to reach a given SPL if the total absorption of a room were to change significantly.

I appreciate your concern, but with today's computers not a lot of expensive pencil lead was harmed in the making of these calculations.

Seriously, I had recently gone through the exercise to calculate the how much amplifier power I would need to sustain reference levels in my home theater when playing some of the more energetic action movies. It was virtually no additional effort to substitute another value for Reverberation Time. On the other hand, ripping out half of my insulation to empirically demonstrate the differences, now that would have been an effort.

Larry
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post #657 of 10416 Old 12-07-2005, 06:33 AM
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Bpape gave me this info from another area:
Quote:


If you're looking at answers about the bipolar surrounds then the answer is that yes - it will absorb some of the mids and highs depending on if they're angled or not will determine how much to a certain extent.

To negate this (on the rear wall anyway and for surrounds), the bass absorbers in the corners could (maybe should depending on the room analysis and what it needs in terms of HT absorbtion - don't want to overdo the highs) be covered with a scrim of some sort. I have the FRK (just the facing) that you can attach via spray adhesive - or you can use kraft paper. This will reflect the highs and make the mid frequency absorbtion less efficient. Think of an absorbtion 'curve' that starts out at about 1.2 or so at 125Hz and gradually goes down after 250Hz to around .3 at 4kHz.

On the front wall, that's a bit trickier. Bipolar speakers in front present some challenges and issues. If it's just a rear tweeter, I'd scrim face just behind the tweeter - maybe 1 sq ft and leave the rest of the front wall soft to deal with surround reflections from the front. Whether or not you can scrim face the bass corner absorbers depends on how close your speakers are to the corners. Normally, I'd say leave the middle soft and scrim the top and bottoms. But, with the rear tweeter, you might not be able to do that - might have to scrim the whole thing - or just the middle foot or 2 for the rear tweeter.

Some people just treat bipoles in a room like a normal speaker and absorb the rear wave. While this gets rid of the anomolies generated by a bipolar design, it also can tend to skew the frequency response as those were voiced with that tweeter in the equation.

The cotton is a great product. It's class A fire retardant, non-shedding, non-itching, totally natural, etc. No gloves or long sleeves required to work with it. Cutting it is a bit of a trick but if you take your time and use a VERY sharp razor knife at a shallow angle and with multiple light strokes it's not too bad. This is for the thicker stuff. For the thinner 3lb and 6lb material, you can acutally use a good sharp pair of scissors (big ones) or can also use the knife as described above. I have people who cut it into triangles to stack up solid all the time.

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post #658 of 10416 Old 12-07-2005, 06:40 AM
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Some material cost/handling questions... With kids, I am concerned with contamination.

How many of you have worked with Cotton absorbers compared to the semi-rigid fiberglass (703)? How does the performance compare for say, a Mondo Trap? How is the cost?

Also, I have access to some excess (maybe 30-40ft) of Linacoustic. How is that to work with compared to the 703?

I am thinking about making some front-wall absorbers behind the mains, some mondo and semi-mondo (2' and 1' sides) traps in the back corners (and maybe front), and some treatment above the screen-wall. (see the pics in my gallery or my sig.)

Any comments?
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post #659 of 10416 Old 12-07-2005, 06:42 AM
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PS Ethan, Terry... I bumped your eq vs treatments thread...
nudge, nudge

...and thanks to all of you for you comments...
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post #660 of 10416 Old 12-07-2005, 08:12 AM
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Answers! And Questions?!?!

Hello people of the acoustic treament thread, I would like to give you some info on my experiecnes. I decided that using 703 wasnt gonna work for me becuase I didnt want to wrap all that stuff in fabric. So I went in the search for Black Acoustic Sound Board. I have found it. Available by Knauf, at a place is round rock TX called, General Insulation (they have a website). I found this loaction out by contacting Knauf directly from thier site, and I got an email back in a very short time.

I called this place, and they do not have it in thier Round Rock store, only in Dallas, but can get it to me, it sells in 4'X10'X1" sheets. It is 1 dollar per square foot, and only sells in 100 square foot sets. So I have to buy 200 or 300 square feet. That is the info, now here is the questions...

I wanted to use it on my front wall completly and my celing. The celing to make the celing black, and the front wall for front wall absorption, along with bass traps, I figured that I would do all of celing and wall, and corners, and that was 288 square feet. I was not sure how much this stuff was when I mad this decision. It will cost me $356.40 total for delivery and tax. I am not sure if I wanted to spend this much (was thinking $200). So I was thinking about cutting back to 200 square feet, which will allow the whole celing (to make it black) and some of the front wall and bass traps. The area is 16X12X8 rectangle, with the screen on the 12 foot wide wall. What would you do? Thanks for the replies.
Thedarksyde is offline  
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