Acoustical Treatments Master Thread - Page 14

Will the spray glue on the GOM and 703 wreck any of the acoustic capabilities of either?

Is it necessary to glue the two together?

I was hopping to be able to just use staples but I've read that most seem to spray glue on both materials and I am concerned that it might cause a reflection instead of absorption????


Husker

Well.. I finally picked up some OC 703, and I'm still waiting on my GOM fabric samples.. so I can't make my panels and bass traps yet.. but for the heck of it, I decided to place some on the wall and behind my screen anyway... Now I wish I could do a simple A/B, panels off panels on quickly ... but with DVD's I'm very familiar with I noted the following...

1. Significant dialouge improvement from center channel (B&W Matrix HTM), I had to turn the level down 2 levels (had it +3 compared to front channels)

2. Surround speakers much more defined, and localized. Example, when listening to Bugs life.. I heard the ambient rear surround channels much more distincly..

3. The room just sounds much more dead... don't know how else to say it, it's just not alive as it used to be...

I haven't done a frequency response comparison of the room yet... I only use test tones and Rat Shack SPL meter...

Overall, the sound is just more defined, and I can better tell from what speaker the sound is coming from.. I woudl say that's the biggest difference. I couldn't play anything too loud to tell any bass differences...

I'm not sure that this would be a good idea.

For one thing, you'd have to seal your screen to a box. Also, the very low frequency absorption wouldn't be great because of the hole size and hole/area ratio of the screen.

Having said that, here is the predicted 0-incidence response (transfer matrix method) of a 0.4 mm thick Stewart microperf screen covering a 1-foot deep box completely filled with uncompressed fiberglass batt.



Not a bad broad-band absorber, though I wouldn't call it a bass trap.

- Terry

Please...

Husker

A thick enough layer of spray glue could create some high frequency reflection. I'd avoid glue if possible, or confine it to the edges.

Hi Terry,

Kevin's question was in regard to a non-perforated screen.

Neverthess, very interesting information.

Thanks.

Larry

krasmuzik,

Sorry, I misread your posting. You asked about a non-perforated screen. I'll do the calculations for this, and get back to you.

- Terry

Here it is.

Identical to the earlier device I posted, but the screen does not have the perforations.

- Terry

JM INSUL-SHIELD question.

Trying to buy and must buy a "unit" ie 48 pieces regardless of size. (I will use 2x4)

I assume I need the" knitted faced" but they come in densities ranging from 1.5 to 6.0 lbs/sq ft.

Which density do I need for lower 48 inch side walls and complete front wall? The theater is 12x20x9 ft.

Yes I have read the entire thread but after 18 months of house building I am in overload.

Bob,

> Which density do I need <<br />
703 at 3 pcf is pretty much the standard for mid and high frequencies. Denser 705 at 6 pcf is better for bass trapping when using thicker panels mounted straddling the corners. And you really do need that too.

--Ethan

Density

Is the spec 3 lbs/cubic ft OR 3lbs/square foot as my supplier told me. Big difference ie 2x4=8 sqft x 3 = 24 lbs for one sheet. ??

Anyone using a different density?

3 lb/cu ft. If it were by the SQ FT, then you'd have different ratings for different thicknesses (1", 2", 4", etc.)

Some people use 6lb for bass trapping purposes. 3lb is a more genral purpose, all around good density for bass absorbtion, reflection points, etc.

bpape

OK then I should use 3 lb/cuft for entire front wall and lower 4' of both side walls?

mooney,

I put 1" OC 703, on my front wall ( behind my screen and velvet curtains), and put 1" OC 703 at my reflection points. I didn't put anything upto ear level, since I'm not doing the room from scratch, so only the reflection points. I'm doing these treatments after the fact.

Intially, I had only treated my reflection points, and I really liked the difference, as I posted above. This weekend, after also treating my wall behind my screen ( 1" OC 703 beghind screen and light duty velvet curtatins), I don't know.. I'm having 2nd thoughts, I have to try it without because it may be too dead.. Maybe the light duty velvet curtains were enough.. and for me the refletion points will suffice.. I just hate to take it all down again... to see what it sounds like without an treatment on my front wall....

First, let me apologize for my ignorance. I have tried to read this thread along with a bunch of articles on the web such as Audioholics, etc. I am trying to figure out how to acoustically treat my new home theater. I'm not stupid, honestly, but for some reason I just can't seem to figure out all this acoustical business. My new home theater is fairly big: 26x15x8. I don't have the furniture in yet, but it will be leather, which won't help acoustics much. I would like to improve the acoustics of the room for use with multi-channel sound.

My questions/concerns:

1. Can someone point me to a source that can help a beginner out with what is needed from a practical standpoint? I find the science/physics of sound interesting, but I don't really get it. I need a source of practical how-to information on how to treat the room. I need information on placement of panels, number of panels, reflection points, bass traps, materials, etc. In the end, all I want is to have a great-sounding theater.

2. I would prefer not to cover the entire surface of every wall. I have sconces already installed so that may also pose an obstacle. Further, I want to make sure that whatever is installed is aesthetically pleasing.

3. I don't want to spend thousands of dollars. Are there places out there that sell completed panels/bass traps at a reasonable price? I am willing to do some work myself to make them, but I am confused by all the different terminology and materials discussed.

Any help is appreciated!

Thanks,

Jonathan Schmidt

jschmidt

contact homeacoustics.net to find an audio calibrator in your area. They know the science and are familiar with treatment solutions.

Thanks, Krasmuzik. The nearest engineer is about an hour and a half away. (I live in a rural area.) I'll give him a call, but I'm worried about the cost of hiring someone like that. But, I suppose if I want it done right, I'll need the help.

If anyone else has any other suggestions, I would appreciate it.

Jonathan,

> it will be leather, which won't help acoustics much. <<br />
Actually, a leather couch in the right place can help to absorb bass. However, it won't do much at mid and high frequencies. Moreover, the best place for acoustic treatment is where the reflections originate, which is the walls and optionally the floor and ceiling.

> I need information on placement of panels, number of panels, reflection points, bass traps, materials, etc. <<br />
See the Acoustics FAQ, second in the list on my Articles page:

www.ethanwiner.com/articles.html

> I would prefer not to cover the entire surface of every wall. <<br />
Nor should you!

> Are there places out there that sell completed panels/bass traps at a reasonable price? <<br />
Yes.

--Ethan

jschmidt

HAA is to Audio techs much like ISF is to Video techs. They are not expensive acoustic engineers - they just have been trained on acoustic science so they stay away from audiophile voodoo that some AV places participate in. So they should give you bang for the buck solutions - maybe even just moving stuff around the room, or a list of things to get at industrial warehouses.. Most calibrators realize their market is limited to how far they can travel - I just did a three hour trip last weekend!

Of course there are several acoustic engineers and acoustic treatment companies that hang out in this thread who would be willing to help you.

Well, I got the estimate back from the place I was referred to by HAA. I'm not a good judge of whether ehtier pricing is reasonable, but it is definitely a LOT more than I was thinking. To start, they recommended the following:

* Seating and speaker placement modelling - $695
* Modelling of first order reflection points - $695
* Modelling of reverberation control (where to put the accoustical treatment and what size) - $1500

Mind you that this does not include any on-site visit. I would have to provide them with all measurements of the room. This also does not provide any actual accoustical treatment. Only provides a mapping of where the speakers and seats need to go along with a diagram of where the accoustical treatment needs to be applied.

I don't know about you guys, but spending nearly $3000 for no actual sound improvement to the room is not my idea of value.

Thanks, Ethan for the very informative article! When it comes to actually putting up some accoustical treatment, I will get some OC from my local HVAC company. I have a call into them to see if they can special order from 705-FRK. It's not something that they normally use for ducts. Instead, they typically use Enduragold, which does not appear to have the accoustical properties needed. Your article helped a ton!

Now I just need to find a cheaper way to figure out the first order reflection points to at least make sure those are covered... without spending $3000.

That's pretty easy, unless somebody wants to sell you a $3000 mirror. All you need is one other person and a mirror. Do a search on the forum - their are a number of discussions on the mirror method for finding the first reflection points.

- Terry

Jonathan,


Yikes, you can get all that for free on the Articles page of my company's web site!

--Ethan

For $3K you could buy a boat-load of Ethan's traps.

All this depends if you value your money more than your time. Everyone on here is always happy to educate - but you have to be willing to make the investment in time to learn. If you consider that calibration is normally charged at a higher rate than the guys pulling the wire - say $100/hr instead of $75/hr -their fees are not that unreasonable considering contractor overhead is usually 3x take-home pay. It probably takes half the time quoted - but you have to leave room for the back and forth on the design and multiple redos. You could look into Dennis and Terry on this forum to find out what they charge for design/calibration as they both work nationally.

* Seating and speaker placement modelling (1 day)

Good resources for this are Harman Kardon white papers, RPG Room Sizer/Optimizer, and CARA. To be most effective you will need to know the directivity and crossover data for your drivers.

* Modelling of first order reflection points (1 day)

Two people and a mirror, as already suggested. Don't forget to check all reflective surfaces - any soffits, ceilings, floors, stages, proscenium, columns, etc. This needs done in every seat for every front speaker. RPG Room Optimizer will do this for a rectangular room. You also need to know how much reflection to cut, and how much to keep (how deep - how long - how wide - in space and time)

* Modelling of reverberation control (where to put the accoustical treatment and what size) (2 days)

Here is where it gets difficult. You have to know the frequency absorption curves of your material and how much total to use in the room, to achieve what reverb time. Absorption varies depending on how much the edges are exposed and how far it is from the wall. SpreadSheets or CARA are useful tools for this.

BasementBob has been an avid collector of absorption data - his website is a good start. Don't forget that your carpet, chairs, risers, walls, stage, etc. all have variant absorption curves, as well as people.


Finally, what you were not quoted was calibration& verification of the design. This involves taking impulse or sweep measurements of the room. ETF5 is a popular program for this - mostly because it is free, unless you expect to save your work for later analysis or use a calibrated mike/preamp, or use useful special features.

What the HAA tech should have told you is they have a 50pt design checklist they can use on your room - this is always a good start with a site visit or floorplan review, and should be done for a much more nominal fee. If you have some fatal flaws in your room - you may want to fix those before pursuing treatment.

I currently charge $95/hr for everything - acoustical device design, custom theater design, measurement, calibration, computer simulation from 3D DXF files using professional ray-tracing software, etc. Also 1/2 that rate for actual travel time. And of course, there's the Great Food Discount if you live in someplace like New Orleans.

- Terry

...I charge extra for New Orleans. That way I have more to spend on food.

Okay, we can buy each other oysters at the Acme Oyster House.

Regards,
Terry

For what its worth, I tried to engage every single listed HAA contractor in the Southern Ontario area to do room measurements, treatment suggestion and followup and every single one denied me. They all wanted to only handle turnkey HT setups (ie. designing & building the entire space from scratch).

I dont know if this is typical of all HAA certified contractors.

Andy K.

kromkamp

I think that is typical of most CEDIA contractors, which tend to ignore the DIY marketplace. ISF indicates if calibrations are available with installations only or if calibrator is independent. Sounds like something HAA should do as well!

www.rivesaudio.com
They have packages from basic planning for DIY up to full design & CAD work and after-install calibration/tweaking. They do not sell treatments, so they show how to DIY home build them in the sample drawings I saw. The pro-AV company I work for has signed on as a local delaer so we can use their services for commerical installations where acoustic treatment and/or sound control isolation planning are needed, but their bread and butter is 2-channel high end rooms and home theater. I was referred by Dennis since he was at the time also only doing turnkey design of the full system (that may still be the case; not sure.) Being an AV designer myself, I did not need the system wiring and site planning help, only the acoustic modeling and tweaking. If I can ever find a contractor to build out my room, I am going to become a Rives customer as well. The way it works, the local dealer has a test kit to come out and measure the room before and after. That data, along with answers about the room, aesthitcs, and system equipment is sent to Rives designers, who generate the plans for a DIYer or GC to build. Then after the room is built to plans and the treatments added, the room is measured again and any necessary tweaks are suggested.

PM me if you are in the DC area and are interested in learning more. As I said, my employer does not install home theater, but we can probably do the measurements for a Rives design sale locally.