Ask Slashdot: Hacking Urban Noise?

b1tbkt writes "I live at the corner of one of the busiest intersections in my city (pop. 350k). Although I've replaced all windows, insulated, and caulked every square inch of the place, the fire trucks and cars with obnoxious stereos still regularly intrude on my home office. Most of the noise comes in through the windows. I'm considering mounting an oblong parabolic reflector in the ceiling above the windows with a steady feed of white or brownian noise directed into it (e.g., via a small speaker placed within the reflector) to create a 'wall' of sound that would act as a buffer to the outside world. Active noise cancellation would be nice, too, but that's probably more than I want to take on. I don't see any products on the market for this sort of thing. Does anyone have any experiences to share with similar homebrew noise remediation efforts?"

Comments

Heavy drape

[Anonymous Coward]

Have curtains made from the kind of heavy drape they use in studios. Check out how people deal with acoustic treatment in home studio builds. For instance the gearslutz.com "studio building/acoustics" subforum has many threads to geek out on.

Mass

[Anonymous Coward]

Although there are dozens of vendors selling what sound like promising solutions, there is only one solution that really works: more mass. Think of it as a physics problem.. sound waves energy transmitted through the air that cause parts of the structure (including the structure above and below) and environment (e.g. the air around you) to vibrate at a particular resonance. The only way to stop the noise is to stop the vibration. A popular option is to use double drywall with something like rockwool insulation between the studs. You can get away with either 2 x 1/2" drywall or 2 x 5/8" drywall with a small furring strip in between without sacrificing too much living space. Look into Green Glue as an additional way to dampen vibrations in that setup. You can also go for a detached wall or "room within a room," but that starts to get expensive to do right.

If you want to look at a "serious" solution ($$$$), you should try to find a sound mitigation contractor in your area. They can survey the room during different times of day and determine what the best solution is for your situation.

More details needed

[arth1]

How and what, exactly, have you insulated, and where is your domicile in relation to the street?

Do you have sound dampening mats on the ceiling? If not, bear in mind that most houses and apartments are above street level, and most of the sound will be reflected off the ceiling. A layer of sound dampening material there should have the largest effect.

If you live low to the ground, sound insulating the walls that can see the street, rather than just outside walls would have a similar effect.

A few strategically placed plants or sound dividers - think cubicle walls but far less intrusive - can also help.

If you must go with a noise generator (which I don't recommend), try pink noise instead of white. The sounds from the street you try to mask out are going to be mostly low frequency, and white noise will mainly add more sound energy in the higher end of the spectrum.

Re:More details needed

[davegravy]

How and what, exactly, have you insulated, and where is your domicile in relation to the street?

Do you have sound dampening mats on the ceiling? If not, bear in mind that most houses and apartments are above street level, and most of the sound will be reflected off the ceiling. A layer of sound dampening material there should have the largest effect.

If you live low to the ground, sound insulating the walls that can see the street, rather than just outside walls would have a similar effect.

There are two components to the noise intrusion - the direct field and the reverberant field. Adding absorptive finishes to the room will help reduce the reverberant field, which in a best case scenario will buy you 3dB (i.e a barely noticeable improvement). Short improving the isolation (i.e windows and exterior partition construction) there isn't anything you can do about the direct field.

A few strategically placed plants or sound dividers - think cubicle walls but far less intrusive - can also help.

Massive barriers can help in outdoor noise propagation scenarios. In this type of situation, the outdoor noise is impacting the exterior facade, causing it to vibrate, and is re-radiating sound in the interior of the OP's space. This means that the source of sound is a large area, not a point source. The sound is effectively coming from "everywhere", and so you don't get the same kind of path length difference attenuation from barriers like you do when you have a point source that is far from the receiver. This is exascerbated by the fact that the intrusion is low frequency which diffracts around corners far more than higher frequency sound.

Plants are not massive enough to be of any significant help. To put things into perspective, a dense forest that's 100m in depth will only attenuate sound 2-3dB, and that's mostly a high frequency reduction.

If you must go with a noise generator (which I don't recommend), try pink noise instead of white. The sounds from the street you try to mask out are going to be mostly low frequency, and white noise will mainly add more sound energy in the higher end of the spectrum.

White noise will add equal sound energy across the spectrum. Pink noise will add more energy in the lower frequencies. We don't typically recommend noise masking for low frequency intrusions into offices and other facilities we consult on because the masking is generally perceived to be more annoying than the original problem. It's best used when there is a speech privacy problem in large open offices because there isn't ENOUGH background noise.

Upgrading your window would typically be recommended, but will only do a little for low frequency. Note that in glazed assemblies, the framing is the weak point. STC 35 is where most frames will top out (even though the glazing will advertise higher STCs into the 50s). If you want a really solid window construction you need an isolated frame assembly which is two frames in series that do not touch each other and which are isolated from the surrounding structure using 3mm thick neoprene gaskets. Each frame supports a separate pane of glass. The inside perimeter should be lined with glass-fibre to prevent standing waves in the cavity.
Overall thickness of the glazing might be 2-3"

Wall of sound won't work

[Chalnoth]

It will do literally nothing. Sound waves simply add. You can't get rid of sound waves by adding a bunch of random sound waves. The sound waves you don't want will pass right through. Now, if you simply have a white noise generator in your house, so that the ambient volume is higher, that may make it so that your ears have a harder time picking out specific sounds, which will, in turn, make it easier to ignore them.

Barring that, noise cancelling headphones or double-pane windows, as others have mentioned, are going to be your best bets. And double-pane windows are good for heating/cooling anyway.

As an aside, I'm also rather skeptical that noise cancellation for the entire apartment could ever be practical. The problem is the waveform bouncing off the various walls and other features of the apartment is going to be too complex to accurately measure or cancel. And then what about the sounds you do want to hear?

Re:are the windows..

[grub]

We put all triple-pane in our house (Winnipeg, Canada) 5 years ago. We noticed the street noise almost disappear. (Not to mention the winter heating bills dropped by ~30%+)
Cost a pretty penny, about $13K for the whole house, but man was it worth it.