I teach physics at a technical college. I often guest lecture students in the architecture program on acoustics. As mentioned earlier, sound attenuates differently based on several parameters. One important parameter is the frequency of sound. Another important parameter is the material. When I am teaching these students, I quickly realize that there are so many materials and so many parameters that it is tough to “solve” challenging acoustics situations in a one hour lecture. As a scientist I tend to resort to theory … sometimes this helps. Sound is a vibration of molecules or atoms. There are approximately 10 to the 27th molecules/atoms in a room that appears to have nothing in it (air seems like emptiness). In other words there are a billion, billion, billion air molecules in a room. As mentioned, if you have a hole that is even small (1/8th of an inch) you have reduced the number of molecules to transmit sound to a mere 10 to the 21st, maybe. This is still a huge number of molecules! The best way to stop sound is to have no air between spaces (a vacuum). Astronauts, for instance, have to radio each other in outer space because there are so few molecules in space (close to a perfect vacuum). I offer no solutions, only ideas. I admire the people on this forum who have experience in actually creating sound proof/resitant rooms. If this helps, great, if not, well, I had fun sharing ideas.
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Unfortunately, it's hard to maintain a vacuum in an environment where things expand and contract frequently. That being said, high mass does a good job too and I'm sitting here wondering why I haven't thought to mention filling a wall cavity with sand. My uncle built a pair of speakers in the '50s, using mis-matched drivers. They sounded really good because he was also a technician at AC, before it was called Delco and he knew how to tune cabinets to match the driver's parameters, as well as measuring the parameters. He worked on some of the early Apollo guidance systems, along with some things he couldn't really talk about until quite a while after he retired.
I and others have often recommended the "box in a box" method and insulating well, in addition to decoupling one from the other as well as possible.
If you buy a book called "The Acoustics Handbook" by F.Alton Everest, read it before you use it as a teaching tool so you can correct the errors. Other than those, it's a good source of information.
Does this mean movies with noisy outer space explosions drive you crazy, since you know the theories behind sound?
E=MC² ± 3db
"I cut this piece four times and it's still too short."
Edited 5/2/2007 10:55 pm by highfigh
Thanks highfigh,
I like the sand idea. Newton defined mass in order to measure the misterious thing called inertia, the resistance to movement. High mass, by definition, resists movement of sound waves! The trick, as you say, is to "decouple" the high mass from the two rooms, the box within the box. Great idea, I will try that in my application.
I do not watch much Science Fiction because there is usually some violation of physics within the first few minutes of the show. Violating some basic physic law kind of ruins everything. The exception is when there is a good story behind the movie.
"I do not watch much Science Fiction because there is usually some violation of physics"What do you mean, "usually"? There's ALWAYS a violation of the laws of physics. When was the last time you saw a ship go from cruising speed to near-light speed without seeing everyone pancaked against the walls?
"I cut this piece four times and it's still too short."
Highfigh,
<<E=MC² ± 3db>>
Too funny!!
<<When was the last time you saw a ship go from cruising speed to near-light speed without seeing everyone pancaked against the walls?>>
That must be the ± 3db part...... ;-)
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Tschüß!<!----><!---->
<!----><!---->James<!----><!---->
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"I'm sorry, Dave, I'm afraid I can't do that...."
-- A.C. Clarke
I saw "E=MC² ± 3db" on the wall over a urinal at a bar that has live music, so I told the sound guy about it, thinking he would get a laugh. He said, and I quote, "I have no idea what that means". I walked off and said, "You're right, you don't". He's one of those "I never use an analyzer, I just use my ears" guys, whose ears have been abused to the point that I'm surprised he didn't say "huh?" when I told him about the graffiti.
"I cut this piece four times and it's still too short."
Ok, I just read this thread and find it very interesting.
I am getting ready to build a new shop. I have two concerns. 1) keep the sound of my tools from disturbing my neighbors, and 2) keep the sound from driving me nuts, i.e. from ricocheting around the shop and back to my ears.
I plan to spray in wet-cellulose insulation in the wall cavities, and cover the insides of the walls with 1/4" pegboard, top to bottom, on all walls. I figure this will absorb the sound waves like acoustical ceiling tile does and thus solve some of my #2 concern.
But this may not be the best solution for concern number 1. However, I have heard that the cellulose, which is recycled news papers, is an excellent sound deadening material. I do not want to spend a fortune on this shop, just be a good neighbor.
What do you guys think??
JDB
The way you want to do this should work fine but the direct sound from the machines to your ears will still damage them. Hearing protection should still be worn, regardless of the acoustics of the space. The pegboard and cellulose will absorb quite a bit, though.
"I cut this piece four times and it's still too short."
Hi JDB,I'm not certain that the results will be as you expect.The sprayed cellulose is probably a good start, but what is going to keep it in place? Consider putting up a layer of drywall (or two) for two reasons: one) to retain the sprayed insulation and two) cut down on noise transmission.You don't have to finish the drywall as you're going to put pegboard over it, but I would still consider it. I noticed a difference in how 'live' my garage sounded after I finished the drywall. I used a technique that put a decent amount of texture on the walls, and I suspect that helped change the nature of the sound reflection.From a sound absorbing point of view, I would think the pegboard is going to have a negligible effect. If I had to pick between drywall and pegboard, I would put up drywall or something else with a superior sound deadening ability.Glen
Thanks for your replies. I do use hearing protection (most of the time). As for keeping the cellulose in place, I think the pegboard would keep it there. When it is sprayed in "wet" it sticks to the walls and itself, just like it would if you wet a piece of news paper and stuck it to a wall. (they may even put a small amount of glue or something in it to help adhesion.My thought was that the holes in the pegboard would allow sound waves to enter and be captured there. I once put in regular ceiling tiles in the ceiling of a church activity room instead of acoustical tile that was in before the renovation. The tiles seemed to be made of the same type of material (very similar to cellulose), only the acoustical tiles have the little holes punched in them. And believe me, those little holes made a great difference that the musicians never let me forget. So I thought the pegboard with holes every inch, would do the same thing, and I could hang a tool anywhere I wanted to. But again, I still am not sure that it helps my neighbors. I may look at the “Quietrock”, but I figure it will be expensive.
Thanks.
The pegboard won't absorb the sound, it will do as the OP thinks it will, and let some pass by, to be absorbed by the cellulose. If you look at record jackets form the '50s and '60s, you'll see a lot of pegboard in recording studios, for this same reason and it works. A layer of rigid fiberglass insulation will increase the absorption in the mid-range region, too.
"I cut this piece four times and it's still too short."
there is usually some violation of physics within the first few minutes ..........
That's why I can never sit through an entire Dolly Parton concert.
A step up from sand would be concrete.Use the box in a box design, and pour concrete between the two box walls. THAT will cut down on noise transmission.Vacuum is the ideal, but very, very difficult to implement in reality due to the multitude of ways to damage the vacuum.One other suggestion I saw, but haven't had time to try, is sandwiching differing densities of material. Assuming a residential use, a layer or two of drywall is the top material and then use something more dense underneath such as homeosote (sp?) or concrete backerboard (durock, wonderboard, whatever). The idea is that the sound waves get deflected twice due to the differing densities. The second deflection should provide greater attenuation than just a single deflection.I haven't tried a hand at the calculations, but I can't say I was ever a big fan of wave theory while in school. :-)Glen
Concrete is definitely *not* a step up from sand. Sand is much better than concrete for deadening sound for the same reason you use a dead-blow hammer: reduced vibration.
this has been a point of debate among me and my fellow recording studio engineers for some time now. the pro physicists who specialize in acoustics seem to think that sand is not useful at all in deadening sound for studio construction and that concrete floor slabs no not transfer vibrations at all, provided that they're 2" in thickness or thicker, to the point where they say you'd be wasting money floating a room on a concrete slab floor. This may or may not be true. I'm not a physicist and I only have a rudimentary knowledge of acoustics. My knowledge comes from experience of having to isolate things for the use of recording. Trial and error, and a lot of reading.Frozen - if you've got some reading material you could point us to that would back your claim regarding sand vs. concrete, that would be great. I'm always looking for reasons to say "d'oh! i've been wrong about that all along"...-pete
Sorry, no reading material. I should also add that I have only classroom experience, so I defer to anyone with experience on actual buildings. I did take a course in acoustics 20+ years ago, where the two main principles for sound insulation were 1: isolate and 2: reduce transmission of vibration. The resilient channels for hanging drywall are used to isolate the mass of the drywall from the rigid structure of the building. Anything rigid like concrete will transmit a lot of noise, as I notice when I'm in a building when someone two floors away starts up a jack hammer. Sand and concrete both have mass, which is good, but sand can dissipate the vibrations. My brother is a contractor who recently built a house for an acoustical engineer, and the plans called for sand between the joists in some places. The project went well I understand, although they had to find and eliminate the source of every squeak!
Edited 5/3/2007 3:24 pm ET by Frozen
My shop used to be in a very large building that contained forty or more units the size of mine. (1500 sq. ft.) The whole place was on one large slab. Whenever someone dropped a heavy piece of metal anywhere, I would hear it. Now imagine if the building had been built on the beach using the insitu sand as a floor. I seriously doubt any noise would have been transmitted. (Actually if it was on the beach, there'd only be noise from cool drinks being opened, snoring, and maybe a vollyball game. Who'd want to work there?)
I am uncertain the purpose of this thread, but I will contribute some bits of info for cogitation. 1) Back in the '60s there were some higher-priced loudspeakers the walls of which were chambers filled with sand. 2) When living & working in the Florida panhandle where the earth is sand as deep as you can dig, I worked in a building with a concrete slab floor which laid on the sand. Whenever a heavy truck would pass in front of the building, pounding the pavement as trucks are wont to do, the floor under my desk in the rear of the building would emit an earthquake-like rumble. The description comes from having experienced minor earthquakes elsewhere. 3) My guess is that sand is a better attenuator than concrete because the sound pressure is more directly transmitted through concrete whereas the granular nature of sand causes it to travel a much greater distance to get through a similar thickness of sand. I believe that the sand would be more isotropic (I believe that is the term (having a senior moment)) than the concrete also, a further source of attenuation.CadiddlehopperSorry, Sapwood. I meant to address this to ALL. -C.
Edited 5/3/2007 8:33 pm ET by cadiddlehopper
One difference is that concrete will actually transmit sound, whereas sand won't. Were the speakers called Wharfedale?
"I cut this piece four times and it's still too short."
"One difference is that concrete will actually transmit sound, whereas sand won't."Actually, it appeared that the sound was transmitted through sand since that and air was the only link from the pavement to the slab. Deep in the sand is a water table, but the sand is quite dry for some depth. I think that sand transmits sound but not nearly as efficiently as a solid or rigid material such as rock."Were the speakers called Wharfedale?"Yes, they were. The only ones I ever heard were pretty good, too.Cadiddlehopper
Wharfedale were the only production speakers I remember that used a sand jacket. The rest were all hobbyist speaker designs.
"I cut this piece four times and it's still too short."
Actually, the resilient channels attenuate the sound by having different resonant frequencies from the attached materials. They act as springs and when the incident sound hits a heavy drywall/heavy vinyl assembly, it moves the drywall and causes the metal channels to vibrate along with it, but because the resonant frequency is lower, it won't usually be transmitted. The energy lost is converted to heat, as in acoustic tiles, etc. Physically, the wall and framing aren't isolated, but acoustically, they are. Mass and total decoupling are the best ways to keep the STC (Sound Transmission Coefficient) low. Since air isn't as good at conducting sound as denser materials are, complete isolation is a good, cheap way to keep sounds from migrating to another area.
"I cut this piece four times and it's still too short."
"Actually, the resilient channels attenuate the sound by having different resonant frequencies from the attached materials."Resilient channels certainly will have different resonant frequencies than drywall, but I doubt that has anything to do with their performance. The springs on my van have a different resonant frequency than the body of the van, but that's not why they work. They decouple the body from the wheels and their resiliency absorbs much of the energy of the jolts from potholes. BruceT
But it's the shock absorbers that dampen the wheel movement, not the springs. The weight of the vehicle, unsprung weight, spring rate/compliance and damping factor of the shocks is what gives a good or bad ride. Basically, if sound moves something, there's going to be some energy loss. Some of the sound energy will be lost just through inertia and absorption, some through destructive interference. The act of the channels moving is dampening the sound energy and if they shared the resonant frequency, the walls would move uncontrollably if the sound was loud enough. Also, it's not the drywall's resonance, it's the sound's energy at specific frequencies that needs to be dampened. True, if the drywall is able to resonate freely, certain frequencies will make it dance.Sound moves faster through a dense medium so that needs to be considered, as well.
"I cut this piece four times and it's still too short."
I was just thinking about a thread in Breaktime about the home reno shows on TV. When I read your sand idea, I connected it with that thread and imagined some housewife taking the 10-pound sledge from the show host and popping a big hole in the wall, only to be swamped in sand!
Now THAT, I'd pay a buck to see.
Mike HennessyPittsburgh, PA
We are an architecture firm in Cincinnati and recently completed a home theater in Indianapolis and a large part of the success of the project is that it is acoustically isolated from the rest of the house. The separation happens in more than one way. The two biggest things to think of is mass and transmission/decoupling.
For mass, we used a staggered stud frame wall filled with sound insulation batts. The staggered stud frame wall is 2x6 bottom and top plate with 2x4 studs @ 8" o.c. staggered. One stud flushes out to the interior of the room, the next stud 8" away flushes out to the exterior of the room and so on. The net result is a frame wall 5 1/2" thick with studs at 16" o.c. on either face of the wall. This is the first step to decoupling. This minimizes the acoustic "bridge" through the wall to just the top and bottom plates. If you have the space to build the "box in a box" that is the best. The gap between the two frame walls can be what ever you want, preferably so that no elements from one wall touches the other.
On the interior side of the wall (the home theater) we next installed resilient channels at 4" from the top and bottom of the wall and spaced at 24" o.c. horizontally in between. It is important that the attachment strip is at the BOTTOM the channel. This helps to minimize the point of contact of the channel to the stud. Next, sheet up the first layer of drywall at 5/8" thick. After it is taped and bedded, we installed a sheet of 40 mil impregnated vinyl around the perimeter of the room staggering the seams in the vinyl from the seams of the drywall. Then lay up the second layer of drywall, this time 1/2" thick again staggering the seams of the drywall from the seams in the vinyl. The reason for the differing drywall thickness is to stop different frequencies/wavelengths from passing through. Two layers of the same thickness is not nearly as effective.
The ceiling is constructed in much the same way. The resilient channel is attached to the bottom of the joists, rafters, trusses, etc. then drywall, vinyl, drywall. We actually used spring dampers for the home theater that hung the ceiling from the floor joists of the family room above, but those are not too cheap. I can provide the contact for getting the dampers and impregnated vinyl to those interested. The floor for the theater was built up on sleepers over a concrete slab.
The weak points are any penetrations through this envelope such as recessed electric outlets and light fixtures which we were able to deal with without compromising the envelope. The biggest breach is the door into the space, which we used a 2 1/4" thick solid core door with acoustic head and jamb gaskets door sweep.
We metered the family room above the theater during a explosive chase scene that barely registered 20 dB at its peak, a moderate whisper.
The wall finish of room for the woodworkers out there is predominately American Cherry with ebonized maple accents and Carpathian Elm burl inlays at select areas. The clients are big fans of Beidermeier furniture and art deco which shows up in the design. See attached photo or go to our website http://www.rwaarchitects.com.
Great looking theater, and I like your methods. The only thing that I think would help, and you may have done, only failed to mention would be to caulk between floor and plates, and between top plates, and deadwood, cripples and king-stud etc.Beyond what you have described, I wonder what special features to use in the HVAC?I was through Nashville when my brother Wood was setting up a sound-room in his office. Wood is a singer - songwriter - producer, and the room was to be used mainly for recording demo's. I was trying to suggest ways to get some air in, and a return that didn't make any noise like the turbulent hiss from a grill, and or traveling on the air from other rooms through the ducts.
Hi Keith and thanks!We did in fact caulk, but only where the gyp board was held off the floor and the perimeter of the hung ceiling plane which was below level of the top plates. It was pointless to do more than that in our situation because of the joist cavities change in wall direction with respect to joist direction, etc.There is a separate, dedicated HVAC system for this theater which made it much easier to deal with the issues you brought up. A good HVAC contractor would be able to address your brother's concerns and is more qualified to answer. Now, having said that, the air handler must be properly sized to handle both the heating and usually more important cooling loads. That is in conjunction with the proper duct and register size. For ducting, round ducts produce less turbulence, and limit the amount of turns in the duct on the supply side. Turns that sweep in a larger radius also help to reduce turbulence. Under NO circumstances should flex duct be used! All of the supply lines to the theater were insulated as well.On the return side, making sure that the grille is properly sized is the first step and after that is less restrictive. We did make a 180 degree switchback leg where it returns to the air handler which is more helpful if the air handler supplies more zones than just the one you are trying to isolate. In this case, we didn't want the any noise from the A/V equipment coming back into the theater.There are sound insulating baffles that can be utilized in-line for shared-zone units but we've never had to specify one because we push for a separate, dedicated system. Again, a good HVAC contractor in the Nashville area would be a good source. I'm sure they've had to deal with this before.Hope this helps!
Mark
I wish you had mentioned the difference between attenuation and wetting; a lot of people seem to think that wetting(dampening) sound will solve a noise problem...
To All, Below the line is the pasted text from Qualified Remodeler Magazine. I have no affiliation with them or the drywall mfg.; just passing on useful info.
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Arlington, Texas (The dash in Dallas-Fort Worth)
Practice...'till you can do it right the first time.
Traditionally a thin layer of lead sheet (about 1/16" thick)was put between a double stud wall or even between the studs and the plaster and lathe to deaden sound between units in a multiple unit dwelling. It worked by both transmitting sound poorly due to its softness and by the dramatic change in acoustic impedance (the acoustic equivalent of the index of refraction in light) at the lead/air interface. The difference was so great that the bulk of the sound was reflected back into the noisy space.
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