Room Acoustics - Isolation & Noise Control - CEDIA Seminar 4

Audioholics · Jan 25, 2005

<A href="http://www.audioholics.com/techtips/roomacoustics/RoomIsolationNoiseControl.php"><IMG alt="CEDIA logo" hspace=10 src="http://www.audioholics.com/images/cedia_logo.jpg" align=left border=0></A>Patrick Hart is rounding the bend on completing his reports on several key CEDIA seminars. This latest one, “Room Acoustics: Isolation & Noise Control” is taught by Steve Haas of SH! Acoustics and dispels some of the myths associated with making a quiet, isolated theater room while presenting some very solid information on how to control the inevitable noise leakage of dinosaur foot falls and anti-aircraft guns in the rest of your home’s living space. This is something that can be a really good idea if you expect to get optimal use out of your home theater space. As always, we want you to remember that the sound of that signal at your ears is 50% the direct sound from the speakers and 50% the sound generated by the room. The four classes reviewed to date from the Electronic Systems Designer track are: 
<OL>
<LI><A href="http://www.audioholics.com/techtips/roomacoustics/hometheatercalibration.php">“High Performance Home Theater Calibration”</A> taught by Anthony Grimani </LI>
<LI>“<A href="http://www.audioholics.com/techtips/roomacoustics/Acoustics101THX.php">Acoustics 101</A>” taught by John Dahl</LI>
<LI>“<A href="http://www.audioholics.com/techtips/roomacoustics/roomacoustictreatments.php">Room Acoustics: Acoustics Treatment</A>” taught by Anthony Grimani 
<LI>“<A href="http://www.audioholics.com/techtips/roomacoustics/RoomIsolationNoiseControl.php">Room Acoustics: Isolation and Noise Control</A>” taught by Steve Haas Coming Soon: </LI>
<LI>“Room Acoustics: The Room and Loudspeaker System” taught by Dr. Floyd Toole</LI></OL>
[Read: Room Acoustics: Isolation & Noise Control]

Rip Van Woofer · Jan 25, 2005

Good stuff. I'd just like to mention that a cheap DIY alternative to the ceiling isolation springs is...rope! Lots of pieces of rope fastened by means of eyescrews at both ends. Emphasis on "lots", lest the whole thing come crashing down on you! Rope is a natural low frequency barrier according to both Siegfried Linkwitz and Dr. Earl Geddes (author of a very good self-published book on HT design and construction). Dr. Geddes is an acoustical consultant and speaker designer with lots of AES papers to his credit. He hosted a meeting of the local audio club and I saw (and heard) his basement HT constructed with his techniques. Minimal sound in the rest of the house even when the Talking Heads "Stop Making Sense" DVD was playing at gutshaking levels.

Geddes also advocates that spray foam insulation (like Great Stuff) to isolate HT structures from the existing structure. Says that used in quantity it is sufficiently strong to partially anchor the walls. He also uses it to hang the doorframes.

Another duct isolation technique I've heard about is to replace the "feeder" ducts (my term) branching to individual rooms from the main duct with insulated flexible ducting. It's typically a fiberglass wool tube sandwiched in plastic sheeting, maybe with a wire coil reinforcement. In my house the "feeders" are 6" dia. round sheet metal and easily replaced. I plan to do it at least for the rooms closest to the basement HT.

As music rather than HT is my thang I'm going to forego the floating floor in my basement setup. And even if I do eventually go to HT the movies me and mrs. enjoy tend not to be heavy sfx-laden spectaculars. A vibrating floor would add nothing to the sly humor of a film like "Sideways", for example.

The Geddes book is "Premium Home Theater Design and Construction" Should be available thru Amazon. Only caveat I have is that he has a bit of a 'designer's agenda' regarding speakers. He is of the opinion that HT speakers should have "controlled directivity" or narrow dispersion and his room acoustics suggestions are tailored to that type of speaker (basically less absorption, more diffusion, and a generally "live" room). It's a reasonable and widely held position but there are other equally qualified people who disagree - so not entirely settled IMO and I sure don't have the training to argue either side. Again, my intended speakers are wide dispersion types just because I like 'em, and I suspect that the narrow dispersion model is most applicable to cinema sound (having to do with dialogue localization and delivering max SPL). He and I had a brief email exchange on the subject and I could just about hear him gnashing his teeth!

Question: What are some typical brand names for the duct lining material? Not something I've seen at Home Depot.

A further note about Dr. Geddes and speaker design. A bit of a plug, actually. At the audio club meeting he ran a blind subjective test with two of his speaker designs (prototypes, one being a final production version with upgraded drivers) vs. two other good speakers. He is big on horn (aka waveguide) designs and has been doing a lot of serious work (see his AES papers) on the design of horns to eliminate their typical coloration. He is proceeding with production of his design. It was a big gloss black honker with a bass reflex woofer and horn tweet. Entire cabinet is constrained-layer fiberglass/foam composite; the horn is molded into the cabinet. I don't know if it will be under his own name/company or if the design will be licensed. But if you want clean high SPL sound and are into the controlled directivity thing, it would be worth looking out for! Projected price is low four figures per pair. I and others present were quite impressed.

Tsunamii · Jan 25, 2005

Thanks for the Article

I loved the article, I am getting ready to build a Theater room in my basement as soon as the addition is put on and this gave me lots to think about. I think I will use the AlphaResiliant Isolation Clips for the floating walls but also like the rope idea for the ceiling, thanks Rip Van Woofer, for giving cheaper alternatives!!!!

plhart · Jan 25, 2005

Good stuff. I'd just like to mention that a cheap DIY alternative to the ceiling isolation springs is...rope! Lots of pieces of rope fastened by means of eyescrews at both ends. Emphasis on "lots", lest the whole thing come crashing down on you! Rope is a natural low frequency barrier according to both Siegfried Linkwitz and Dr. Earl Geddes (author of a very good self-published book on HT design and construction).

The bitterness of poor quality remains long after the joy of a low price is forgotten.

I'm going to have to vehemently disagree with giving advice to our readers which could potentially cause great injury. Yes, rope could be made to work in holding a ceiling which weighs hundreds of pounds. But without a means to tension each piece of rope exactly equally over the entire surface of the ceiling one could most likely have a great deal of trouble in leveling the system initially, not to mention having it stay level (and not have certain pieces of rope which had more tension than their neighbor stretch) later on. Only a few springs, all of which have variable, tunable spring-rates as well as emergency failure stops probably would cost far less and be much easier to height-level.

Dr. Geddes is an acoustical consultant and speaker designer with lots of AES papers to his credit. He hosted a meeting of the local audio club and I saw (and heard) his basement HT constructed with his techniques. Minimal sound in the rest of the house even when the Talking Heads "Stop Making Sense" DVD was playing at gutshaking levels.

I'm aware of Dr. Geddes and his AES papers. Much but not all of what Earl has published is considered highly viable. I did buy his book about six months ago and agree with most of what he has to say.

Geddes also advocates that spray foam insulation (like Great Stuff) to isolate HT structures from the existing structure. Says that used in quantity it is sufficiently strong to partially anchor the walls. He also uses it to hang the doorframes.

Yep, could work but why not just use the isolation wall hangers available from www.kineticsnoise.com? This stuff isn't that expensive relative to the total cost of the materials and it is an engineered solution.

Another duct isolation technique I've heard about is to replace the "feeder" ducts (my term) branching to individual rooms from the main duct with insulated flexible ducting. It's typically a fiberglass wool tube sandwiched in plastic sheeting, maybe with a wire coil reinforcement. In my house the "feeders" are 6" dia. round sheet metal and easily replaced. I plan to do it at least for the rooms closest to the basement HT.

The examples given in the text show pre-existing steel duct-work. If you have the luxury of replacing this steel ductwork with the flexible ducting you suggest the cross sectional area of the replacement part should be the same as the square duct. If the replacement tubing has less square footage cross-sectional area the speed of the air through the duct will increase causing an increase in noise. So before just swapping one duct haphazardly for another we need to first calculate the deltas between the amount of dB decrease that will be attained in a smaller duct wherein the air is moving faster with the older square duct which can just have insulation added.

Rip Van Woofer · Jan 26, 2005

Patrick;

Thanks for your comments/corrections. I see your point about the rope; the possibility of a "cascading" failure caused by uneven tension is not one I'd considered. Better I (and others) should find out now than after hanging the ceiling! I suppose using turnbuckles would work....but by then maybe the springs would wind up being no more expensive, easier, and safer. Consider me chastised!

I'll check out the Kinetics Noise engineered hangers, too.

As for the ducting replacement, I wasn't clear on my intention. I was talking about replacing my existing steel 6" dia. round "feeder" or branching ducts with same inside diameter insulated flex duct. I would just insulate the square main (plenum?) ducts. Sound better? What's some brand names of the rigid duct insulation? It's not something I've seen at Home Depot.

In general, kids, this shows that being a moderator isn't necessarily a guarantee of expertise! Caveat lector applies in all cases regardless of the source.

EDIT: Just took a quick look at the Kinetics Noise Control site. Serious stuff that looks like it would make construction easier and quicker and give an excellent result that would justify the higher up front material costs. I've seen other resilient channel and their stuff looks far and away more robust. The downloadable PDF files of typical application/installation are invaluable. Like my dad used to say: Material is cheap, labor is expensive. Thank you again. Now, I hope they don't have large minimum order requirements...

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