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Natural Science Forum / Physics / Acoustics / April 2005low frequency street sweeper how do I mitigate the sound?
Skip to the end for the question if you don't feel like reading the whole set-up. I live in an urban downtown district, and the builder had the bad idea of putting the bedroom at the front of the building. I live on the second floor, and my bedroom has a 10' x 10' window facing the street. Our building is a fancy loft-type building. We have 16" of poured concrete on the floor, substantial sound deadening materials in the walls and the ceilings. But lots of windows. I never hear my neighbors, but I hear the noise from the street quite easily. Even though the windows are supposed to be "quiet". The ceiling is 14'. We installed a mezzanine in the bedroom which bisected this distance, and our bed is beneath it. The mezannine is attached to two heavily sound proof walls, with the other two sides open (facing the street). Our ceiling in the bedroom is 7' high. It is basically a sheet of drywall, hanging on welded steel supports which are attached to .25" metal sheets. At 5 a.m. every day the street sweeper comes by, and spends about 20 minutes cleaning the street. I would guess the hz is around 60 hz and the noise is about 80db. (not sure. It's loud and low) It's a Tymco 600 sweeper. I'm about 25'-35' from the sweeper when he goes by. Right whenI fall back asleep the leaf blower guys come by at about 6:30 a.m. and keep going until 7:30 a.m. The current solution, which works great, is that I got an air mattress and sleep in my master bedroom closet. The headboard is on the other side of one of the closet walls, and that wall is standard drywall (but of course, all my clothes are hanging in front of it). So I feel confident that enclosing the mezzanine may work, since my closet is so nice and quiet, and my head is literally only 2' away from where it would be lying were I to be able to sleep in my actual bedroom. I am taking a multi-pronged approach: 1) working with the city to reduce the noise (ha!) 2) running one of those rinky-dink Brookstone wave machines in the room 3) enclosing the mezzanine. 4) looking at other ways to mitigate the noise, such as doing something to the exterior of the building, or some sort of active noise control. Because of the way the building is designed, my mezzanine enclosure can't be more than 6" thick. I am installing doors which will roll along the steel beams so that I can get in and out. The doors can't be much more than 3" thick. Right now the plan is that the walls will have soundproof panels on either side, with insulation and regular studs. The rolling doors will be made of soundproof panels which sandwich a foam material. The main issue, is what materials should I use? So far, I like the looks of these two: http://www.glacierbay.com/insulation_ultradb.asp http://www.quietsolution.com/ Is this the way to go? Or should I do a bunch of lead sheets, or what? I don't want to waste money installing something that won't make the room any quieter. Should I stagger the studs? Should I avoid studs? Should I be thinking along other lines? Any help would be appreciated. Julia [snip] >Any help would be appreciated. I don't want this to sound like a blow-off, but I really think you need to hire a consultant. Seems like you've got an upscale place, and you're about to embark on something that's not going to be cheap. I expect that you will get some very good technical advice here - some of the best consultants in the world hang out in this group. But take those answers as education and get someone local to look at your place and make measurements to see what you're really dealing with. Ken Plotkin Julia, Heed Ken's message. You can throw a whole lot of money at the problem and accomplish absolutely nothing. You need good data and someone who can advise you as to proper solutions. If in the US, look at http://ncac.com To find someone near you. Dave > Because of the way the building is designed, my mezzanine enclosure > can't be more than 6" thick. I am installing doors which will roll [quoted text clipped - 3 lines] > studs. The rolling doors will be made of soundproof panels which > sandwich a foam material. Somehow, you need to get a two-layer system with an air gap between the layers. "Storm windows" work this way, where the air gap is a few inches. But in your case, it likely needs to be an entire wall. That's why your closet works well. > The main issue, is what materials should I use? So far, I like the > looks of these two: For walls; a few layers of drywall. For windows; panes of glass 1/4" thick and greater. Plastic foam, especially the hard stuff is useless. Soft foam works, but it is a fire hazard. Fiberglass batt (R-11. R-13, etc.) for filling voids is better. > Is this the way to go? Or should I do a bunch of lead sheets, Lead sheets would be in place of extra drywall layers, if appropriate. > I don't want to waste money installing something that won't make the > room any quieter. Should I stagger the studs? Should I avoid studs? > Should I be thinking along other lines? This is a complex 3-dimensional problem, and a picture is worth a thousand words... Angelo Campanella  Signature--------- www.CampanellaAcoustics.com --------- "Every day, we perform on the stage that we set yesterday." AJC. > Skip to the end for the question if you don't feel like reading the > whole set-up. [quoted text clipped - 52 lines] > http://www.glacierbay.com/insulation_ultradb.asp > http://www.quietsolution.com/ If you must deal with this, try high density vinyl sheeting, it's made for this. It weighs about a pound per square foot and sandwiched between two sheets of sheetrock, you get excellent isolation. > Is this the way to go? Or should I do a bunch of lead sheets, or what? > I don't want to waste money installing something that won't make the > room any quieter. Should I stagger the studs? Should I avoid studs? > Should I be thinking along other lines? > > Any help would be appreciated. I would suggest talking to others in your neighborhood to see if the noise is bothering them too, there's real power in numbers, especially when they're all registered voters. Then talk to an attorney, try to find one with a record of "fighting city hall". The city shouldn't be operatinng noisy equipment during hours when most folks are sleeping. If others in your building aren't bothered by the noise, it may be that your apartment is in a resonant area of the building and the noise is worse there. In that case, talk to the building manager or owner about fixing the problem or getting you moved to a quieter apartmant. Isolation from lF doesn't come cheap, so I'd suggesting exhausting all other possibilities first. The possibilities include getting the city to either add noise reduction to the equipment or changing the hours of operation to the daytime, or if the problem is your apartment, getting the building owners to fix the problem at their expense. >> Skip to the end for the question if you don't feel like reading the >> whole set-up. >> >> I live in an urban downtown district, and the builder had the bad idea >> of putting the bedroom at the front of the building. I live on the >> second floor, and my bedroom has a 10' x 10' window facing the street. You have not told us anything about the design of the windows. A first step to consider is improvement of the windows. However, if the sound truly is concentrated at 60 Hz you have to be very careful. Typical acoustical window designs are designed to block higher frequencies. They may be especially weak around 60 Hz. You really need someone who understands the problems of dealing with low frequencies. >> Our building is a fancy loft-type building. We have 16" of poured >> concrete on the floor, substantial sound deadening materials in the >> walls and the ceilings. But lots of windows. I never hear my >> neighbors, but I hear the noise from the street quite easily. Even >> though the windows are supposed to be "quiet". As I said, you may have special windows, but they may be especially weak right at the frequency of the sound. SNIP >> I am taking a multi-pronged approach: >> [quoted text clipped - 16 lines] >> >> http://www.glacierbay.com/insulation_ultradb.asp Not heavy enough to do much good at 60 Hz. >> http://www.quietsolution.com/ Has some advantages for higher frequencies, but you can get the mass you need for 60 hz less expensively with plain gypsum. > If you must deal with this, try high density vinyl sheeting, it's made for > this. It weighs about a pound per square foot and sandwiched between two > sheets of sheetrock, you get excellent isolation. Vinyl has its place, but this is not one of them. You are only adding an extra pound of weight that can be added less expensively with thicker gypsum. All the vinyl does in a sandwich like this is fill in the coincidence dip which is not the problem described. The coincidence dip problem can be solved other ways less expensively if necessary. >> Any help would be appreciated. Blocking a low frequency noise requires weight. You can get some benefit by separating that weight into two (an not more than two usually) layers with a large airspace between them. However, this will create a resonance situation that will be weak at some frequency. You have to make sure that weakness does not correspond to the frequency of concern. I'm only a novice in this field but I'd like to know wether or not you think that perhaps the low frequency might be caused by internal structure as well as your window "problem." I have heard it said that studs (in regards to framing) have the ablility to carry low frequency waves; could it be the framing around the window causing the noise to amplify through the glass? |
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