Reducing Low Frequency transmissions through residential walls 1

[Umhoefer]

I found a need to reduce the amount of low frequency (subwoofer produced) audio waves that get transmitted through my townhouse walls into my neighbors house. He has the same problem, so we would like to know if there is a somewhat affordable way of acousticly deadening the connecting wall without tearing open the wall or creating a eyesore. As always any help/ideas anyone contributes are very appreciated. If it helps the wall between the living rooms is about 20ft wide by 25ft tall(Valted ceiling). The speakers are moved away from the corners and the low frequencies are cutt down at the sorce but sound still travels through.

 

[MikeyP]

The simple answer is to increase the mass of the dividing wall. However, there is a limit to the effectiveness of this: As you put more and more mass on to the wall, there comes a point where the transmission of vibration along paths other than directly through the wall become important(for example - sound/vibrations from your sub excites vibrations in your floor which pass along the joists to his floor and are re-radiated as sound in his room). Adding extra mass will then become irrelevant. Low frequency sounds are often the hardest to block.

There are people on the Usenet group alt.sci.physics.acoustics who answer this sort of question all the time. I suggest you try posting there as well.

M

 

[butelja]

MikeyP brings up good points. The way wall mass is often increased is to use multiple layers of drywall. Also, staggered stud construction with internal insulation is very helpful. Whatever you do to the wall, making it airtight via caulking and/or drywall taping is vital. The following link shows comparative information on many types of wall construction:

http://www.saecollege.de/reference_material/pages/STC Chart.htm

Also, as MikeyP mentioned, too good a wall will reveal other transmission paths and re-radiation on the other side. For critical applications (recording studios), an entire isolated room within a room is used, with all floors, walls, and ceilings isolated. This is very costly and complex.

 

Two large air conditioning units were installed accross my street by a school. This cause high frequency noises and low frequency vibration 50 Ft away at our house. Can this problem be corrected and if not can it be a health hazard.

 

[acoustician]

In addition to increasing the number of layers of drywall, another scheme that we use is to build a double wall providing a 1" airgap between wall. Walls additionally should be full height to reduce the chance of flanking above. Flanking below may be a problem as well. Even with a double wall you are looking at most a 60 maybe 65 dB reduction if there aren't any other shortcuts for noise to travel through. This means that the sound will still be perceptable.

 

[Paulism]

You may want to consider a damped inter-layer wall construction. Using multiple layers of sheetrock will reduce the level of airborne sound energy simply because of the increased mass in front of the sound, however it's similiar to using a vibration dampers to reduce airborne sound, not the right product. Some manufacturers offer acrylic adhesive film in rolls that can be bonded directly to the existing layer of sheetrock, this is followed by another layer of sheetrock. The adhesive film will create a slight airspring which may yield results up to 10db of reduction through the wall. This method won't take up much space in the room, only the thickness of the 2nd layer of sheetrock.

 

[Umhoefer]

Paulism,
What you recomend sounds like a product i've seen used on cars called Dynamat. However this product is very expensive, is the material you refer to commonly refered to by it's commercial name. Example; soem people i know still refer to coppiers as Xerox machines after the brand that made them popular. Everyones tips have opened up alot of ideas for me. Thanks for the help.

Thanks Again.

G.Umhoefer

 

[Paulism]

The material is not Dynamat. That product is an asphalt based vibration damping sheet material. The acrylic adhesive itself is an entirely different product all together. It does not damp vibration beacuse it does not have the mass nor the energy conversion caracteristics of viscoelastic damping products. It's strictly a decoupler.
Regards,
Paul

 

[Umhoefer]

Thanks for clearing that up. As you can tell this is definitely not my field of expertise. Thanks again for the assistance

Sincerely,

G. Umhoefer

 

[kareny]

My husband and I are having a problem very similar to nicolefili. We live in an apartment building where there is a forced air and heating unit placed in the center of each apartment in a closet. The outdoor unit of the air conditioners for four apartments is at the base of the wall of our bedroom outdoors (we are on the second floor). We have been experiencing vibration and low-frequency sound which affects my husband to the point of sleep loss, nausea and headaches. We have been trying to solve this problem, but no one seems to understand what we're talking about. Our bed actually vibrates despite the shock absorbent pads that we have placed under it and the foam we have placed between the box spring and the top mattress and on top of the mattress. We are getting really frustrated with this and don't know where to turn. We would like to have the apartment tested, but have no idea of where to find someone with the kind of instrument that would measure low-frequency noise and vibration. Would contacting a local university or an engineering firm be useful? Should we check with the local government? Our "landlords" have been helpful only to the point of checking to make sure that the machines are running properly. Because no one else has complained of the problem, they don't seem to think it's worth the money to check it out for us. If anyone has any information that might be of use to us, please let us know. Thank you!