Acoustical Treatments Master Thread - Page 11

Sorry to bump, but I could really use some advice. Does anyone have any thoughts on how badly the glass RP screen will impact acoustics, or ideas to help? I need to make a decision later this week on which direction to go:
keep the RP screen for the family room & drop down a custom motorized front screen in front of it for the new theater room side (original idea in my post.) That screen would be custom built much like a blackout shade, and rise/lower in side channels to block light from coming from behind.
Or I may move the RP screen into the theater and bag the dual room idea, if I can find enough room for an RP booth and seating area in the new space.
Option three is to just go front projection in the new room like most people do, and that would make for best acoutsics, but that would mean wasting the $700 RP screen and custom integration I have now (and paying extra to have it removed.)
So the real question is, will an RP screen w/ a front screen directly in front if it be horrible for the sound or is there some way to deal with it? What do you think?

Scott,

> does it matter that Rudee's room has a huge resonance specifically at 71 Hz, and also at 24 and 47 Hz, as compared to having resonances at some other frequency? <<br />
Yes and No. Yes, because good bass traps can succesfully target problems at 71 Hz and even at 47 Hz, but No because all frequencies need to be treated anyway. I pointed out the large resonance due to overlapping modes mainly to explain that even more bass trapping than usual is needed to make that room acceptable.

> Based on my understanding of your video on "Non-modal peaks and nulls in small rooms", it really doesn't matter what the resonances are related to a room's dimensions. <<br />
Yes, to a point. But when two or three dimensions are the same or related, the modal resonances are even more pronounced than usual. So you need more bass traps to make the room acceptable.

> So would Rudee's room be treated any differently than a room that had equally huge resonances at some other frequency? <<br />
Again, the main difference is that more bass traps than usual are needed.

> Would you treat a room differently if it has "huge" resonances at some particular frequency (like Rudee's), vs. a room that has more moderate resonances? <<br />
Again, only as far as how many traps are needed.

> if I place 8 - 10 traps in my room, does it matter if they are equally disbursed? <<br />
Not in the same sense as symmetry matters with speaker placement and listening position. The goals with bass trapping are 1) have enough of them, 2) put them across or at least near the corners, and 3) spread them evenly around the room as best you can. Exact symmetry is less important.

> if due to aesthetics or practicality, I can not put a trap in one particular corner, Can I double-up in another corner to compensate? <<br />
You'd be better off adding a trap to a new place, like a ceiling corner.

--Ethan

Rudee,

> to the trained eye are my numbers relfecting the bad things you say are happening to the lower frequencies in this size space? <<br />
The problem with those numbers is they show only part of the problem. You need to measure to at least 1 Hz resolution to really see what's going on. This graph, which I've posted here many times before, shows the response in a typical smallish room when measured at 1 Hz resolution:



Note the peak/dip pair at 110 and 122 Hz where the response varies a staggering 32 dB across a range smaller than one musical whole step. This activity is completely hidden if you measure at only 1/3 or 1/6 octave.

--Ethan

Mike,

> how badly the glass RP screen will impact acoustics <<br />
Unless your speakers are pointing directly at the glass it's probably not a problem. Otherwise it's just one more reflective surface out of many others in the room.

--Ethan

Thanks. The speakers will be forward of the screen and L/R off to the side a foot or two as well. I can treat the drywall surrounding the screen as well to try to help. Have not figured out the center yet- it will probably go above the screen tilted down slightly, or be just under the screen on a stand. Since the bottom of the screen will be only about 30" AFF high from the front row, I was thinking above may be better, but I would be glad for input here. It would be easier to mount it on a stand below & in front of the screen on the stage for sure. If I go above, I will have to build something out from the screen wall to hold it. Aesthetically, I was thinking it might look nice to have a center speaker bump out above the screen to hide the speaker, to mirror the curve of the stage below.
BTW Ethan- I was looking on your site, but the prices page takes me to the European site, which does not list prices. I am in the USA, so I think that is an error. Can you send me a link to get an idea about the cost of your traps?

I disagree. I've not played around with RPTVs which are smaller, but I will be including some movable thick curtains or panels for when I'm listening to music because my screen (FP, non-acoustically transparent) definitely damages the imaging and flattens the depth front/back.

ethan thanks so much for the further detail.
From the questions asked answered by you i can assume the following:
With the size of my room and the overall dimensions i have my work cut for me for getting this room treated to tame these ugly things- which is okay cause i'm at the point i'm ready to address the room.

I will go at it a bit blindly in the beginning and hopefully be able to devote more time to some of the room calc software as time permits.

-bass traps in corners- i can do both fronts and one rear fully and only a small top corner due to cabinets in the fourth corner. From what i gather i need heavy trapping- the denser the better?

-treat the whole front wall with a 1" oc 703 type material or linacoustic covered with a GOM or similiar material.

-treat the bottom half of the wall with a 1" oc 703 type material or linacoustic covered with a GOM or similiar material.

I could make a soffit trap using three sided wedges of compacted rigid fiberglass material wraped with GOM or simiar around the two side walls & rear if it would help do the trick in this room- Is there any chance this would be too much damping?

thanks much-
rudee

I have found a local place to purchase OC 703 or 705 & would like to see a detailed DIY Tutorial or guide that show's how to do EVERY step, especially how to cover with fabric.

I don't have the funds to hire some one to TEST my room for proper placement/location for the 703, so I will cover entire front wall and sides and rear to ear height.

Would it matter if I only covered from top of wall plates (electrical ect.) up to ear level (44"-48") for the sides & rear?

My room is 20'X14'5"X7'9" (LWH)

HH

I think once you get it you'll realize it's pretty easy to figure out. The two main ways that are used are a spray on glue and fabric right onto the fiberboard, or to make some kind of simple frame (or you can make it a spiffy elaborate frame if you so desire).

I just used a really cheapo frame idea, just a bunch of 1x4 boards nailed together, put the fiber board in there, and staple-gunned the fabric to it. I have no woodworking skills, so I went uber-simple. The only difficult thing was that home depot wood is total crap so the boards were warpy or would split, so I spent a few bucks for some little L brackets for a couple corners. Really easy.

Do you have pictures..

Did you make several frames and butt them side by side all the way around the 3 walls or did you leave gaps?

HH

HuskerHarley

Have a look at http://www.bobgolds.com/AbsorptionCoefficients.htm and scroll down about 85% of the way and click on all the links from
Jon Risch's Absorbers
through
Vshine's Wall Absorbers.
That should give you some ideas

Thanks for the link..

Lot's to digest there.

I get the impression that I don't need to cover entire front wall and not cover other 3 sides all the way around to ear height after looking through those sites...Very confusing based on info in this thread...

HH

HuskerHarley
This forum talks a lot about home theatre with 5.1 to 7.2 sound.
The links on my site include stereo for musicians.
I provided the links to show examples of manufacture of panels, not about placement, nor quantity.

By looking at the http://www.bobgolds.com/AbsorptionCoefficients.htm chart, should 703 2 FRK be the best solution for bass absorption but not overkill the high frequency?

I believe the general consensus is that 2" material provides too much absorption in the mid-bass range. To adequately absorb high frequencies, a certain % coverage of wall surfaces within the room is required. Using the 1" material results in the desired performance; using the same amount of 2" material would provide too much mid-bass absorption and using less 2" material would start to provide too little high frequency absorption. This is the way I understand it, but I'd like to hear confirmation from someone with more experience.

Do you mean 703 instead of 702? Owens Corning 702 is not a standard product.

The answer is "it depends."

There is mounting away from the wall, which is always better for low frequencies. There is faced (FRK) vs. unfaced, where faced with the facing mounted towards the room will reflect high frequencies but absorb low frequencies.

And there is also a grain of salt to be taken with any absorption coefficient chart. While these are nearly always made using certified laboratory data, there is also a fair amount of variation in measured absorption coefficients using the standard Reverberation Room method. There is significant variation from lab to lab, and even variation for samples measured in the same lab. So consider the coefficients good to only one decimal place, even though they are given for two!

- Terry

Carlton,
Seems like OC 703, FRK 2" even outperform the 703 1" plain on the midrange.
Terry,
Will you recommend the FRK (Foil reinforced kraft)? "This facing consists of an aluminum foil laminated to a kraft paper backing reinforced with a fiber glass scrim (yarn)"

Here's a chart I made to try to choose between the 1" and 2" OC's.

But instead of helping, I think I'm jut more confused because I still don't know how much is too much and how little is too little.

703 plain 1" (pink line) is what I was origninally looking at, and it still looks fine in comparison...

It's only too much or too little in comparison to a furnished room full of people. You can't decide just based on these numbers. You have to know what your room needs, where it will be applied, etc.

I am not sure if his is covered elsewhere in the forum but I plan to use the GOM fabric on the 703 and used speay adhesive and works fine,I also plan to use the same fabric on the upper part of wall (above 2 panels of 703 ) my question- what method have those of you who have applied this fabric to the wall applied it I wastold I should use the same spay adhesive, but definitely not wall paper paste, any help is appreicated
Peter

I am not sure if this is covered elsewhere in the forum but I plan to use the GOM fabric on the 703 and used speay adhesive and works fine,I also plan to use the same fabric on the upper part of wall (above 2 panels of 703 ) my question- what method have those of you who have applied this fabric to the wall applied it I wastold I should use the same spay adhesive, but definitely not wall paper paste, any help is appreicated
Peter

I was so surprised by the mighty 703. It really works. Now I can enjoy the deep bass that I'm longing for and it allows my 12 sub to do its work. Thanks you all(including OC).

ptwood, will you let me know how you do it(GOM) once you figured it out?

I hae another question, I have seen recommendation to put the adsoring 703 style panels on lower portion of walls, I was planning to just do GOM glued to walls above but found pictures and references to use a poly batting material above and cover this with GOM, can anyone comment on what this does
Thx for any help, if this is way to go then won't ned to glue
Thx

I hae another question, I have seen recommendation to put the adsoring 703 style panels on lower portion of walls, I was planning to just do GOM glued to walls above but found pictures and references to use a poly batting material above and cover this with GOM, can anyone comment on what this does
Thx for any help, if this is way to go then won't ned to glue
Thx

Polyester batting provides additional sound absorption, though not as much as 703 for the equivalent area.

- Terry

Thank you Terry I appreciate your reply, would you suggest just going ahead using the batting in addition to the 703 (top portion of the wall and about 2 panels of 703 hung horizontally) or shall I check room and go from there,
also I have soffitts (6-7 inches vertical 18 inches, horizontal) all around the room as well as columns on the side and rear walls holding the surround speakers should these be filled with insulation (mineral wool, fiberglass batts...?) any suggestions
Thank you
Peter

DIY VS REAL TRAPS

Besides the obvious difference in cost between REAL TRAPS and DIY OC 703 designed Traps.

Do they both deliver what were after?

I want to save money but I'm not sure if the DIY route would deliver what the REAL TRAPS promise to deliver, are the REAL TRAPS using the same insulation or do they have something special inside to separate them from the DIY versions.

In my situation money matters but I don't want to waste it doing a DIY that won't deliver what I'm after...

Convince me that DIY is as good as REAL TRAPS or just a few percentage points away from being as good.

HH

The article Room Acoustics: Acoustic Treatments- Absorption is quite interesting. But the following statement get me all confuse. Maybe they use something more sophisticate than the OC703.
Note that 1 acoustical panels only work down to 1000Hz which is above most of the primary vocal frequencies and thus just about useless in affecting vocal intelligibility. Two inch material gets down to 500Hz or so and 4 down to 250Hz.
http://www.audioholics.com/techtips/...reatments3.php

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Adam

Hi Adam,

It's not the material (703) but the way in which it is mounted which makes a huge difference in bass absorption. That article assumed you were mounting the absorber right against the wall ("A" mounting). If it is spaced away from the wall, the extra depth provides a very effective way to absorb the longer, low-frequency wavelengths. Ditto for corner mounting, which gives a continuous range of depths.

- Terry

I'll let Ethan describe exactly how the RealTraps are put together since it's his product.

Also understand that the recommended mounting for RealTraps is @ 45 degrees across a corner or at a tri-corner. They can be mounted other places but will not yield the bass absorbtion in that confiburation.

Standard 703 will also yield good bass trapping when placed @ 45 degrees across a corner.