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AudioAcoustics

Serving the Acoustics Community Since 1994

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November
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Nov 25, 2007

A few quick hits before I jet off to Chicago:


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Nov 18, 2007

From the San Jose Mercury News:

The Santa Clara Valley Transit Authority is warning residents near certain stretches of light rail track to be prepared for loud noise as tracks are ground and smoothed starting Thursday night.

..

Completion of the grinding will considerably reduce track noise and extend the life of both tracks and light rail vehicles.

Sometimes you gotta break some eggs to make an omelet.

(But seriously, the long-term gains are worth the short-term noise impacts.)


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Nov 11, 2007

I’ve been staying away from the Blu-ray vs. HD-DVD debate simply because the whole debacle has been so frustrating for consumers. While it’s still too early to declare a winner, two recent events have got me wondering if we may be moving toward an endgame:

Of course Blu-ray still has a trick up its sleeve: namely the Sony Playstation 3. But with prices on HD-DVD players falling much faster than Blu-ray, I think that this might be the beginning of the end. We’ll see.


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Nov 02, 2007

Seems like yesterday when I was writing about getting acoustical experts involved in matters of residential sound insulation - oh wait, it was.

Now comes an article from the Staten Island Advance that asserts “[t]here are easy ways to contain sound at home and keep the neighbors from complaining:”

If noise is absorbed into, say, soft surfaces with plenty of surface area, such as a medium to dense fabric like draperies, the sounds die, because they cannot bounce off them. So soft surfaces contain sound and work to minimize transmission of noise to other rooms.

Umm, no.

The author is making one of the common mistakes that many laypeople make: confusing sound insulation (i.e. sound proofing) with sound treatment (i.e. room treatment).

Room treatment (bass traps, absorption, diffusion) is all about the effect of the acoustics within the room. Room treatment changes room acoustics properties like reverberation time (echoes/reflections), standing wave amplitudes, and speech intelligibility. Room treatment can reduce interior noise levels, but substantial absorption over a large area is required to significantly reduce noise levels. However a relatively small amount of absorption can cause a perceived reduction in noise levels by reducing reverberation - humans will perceive two sounds (such as a direct sound and a reflected sound) arriving at nearly the same time as one louder sound rather than two separate quieter sounds.

Sound-proofing/sound-insulation (double-walls, double-studs, resilient channel, “QuietRock”, mass-loaded vinyl, etc) is all about reducing sound outside the room. If you want to listen to your favorite action/sci-fi/sports program at full volume without waking up the kids in the next room, or you want your neighbors to stop complaining about your barking dog, you need sound insulation. Doing things like adding egg-crate foam to the walls or heavy curtains to the windows will change the acoustics within the room, but not outside the room.

Think about an open window or door: it makes an ideal sound “absorber” since it reflects 0% of sound waves, but it makes a lousy sound insulator since it allows 100% of sound to be transmitted from one room to the outside. If you have have a totally enclosed room with a loud noise source (say a rock band or table saw) and you remove one of the exterior walls, the sound level in the room will be reduced but the sound level outside the room will increase substaintially.

I suspect that the curtains the author installed hasn’t reduced the noise level at the neighbors’ apartments. Yet the article implies that the treatment was a success because the neighbors have not complained. So, why the disconnect?

My guess: the landlord/friend/author likely told the neighbors that “soundproofing” was installed. The neighbors still hear the barking, but they know that the dog’s owner has installed noise mitigation. As a result, either the neighbors decided to cut the owner a break since they know the owner has tried to solve the problem, or their knowledge of the mitigation efforts (which they assumed was installed by someone with expertise) leads them to genuinely believe that the noise they’re hearing has been reduced. Plus, there is the fact that rambunctious puppy tend to mellow with age, and it may be that the puppy is barking less and less as it grows older.

There’s another lesson in here about non-experts trying to apply acoustic knowledge acquired for a regulatory purposes, usually through specialized training courses (like the one I’ll be assisting in later this month) or internet research. These types of courses and learning methods are not designed to turn laypeople into experts. We give these types of training courses to help non-experts intelligently read and interpret our guidance. When it gets time to implement your project, hire someone that knows what they’re doing.

I’ve been doing acoustical engineering on a professional basis for 13 years now and I’m still learning something new everyday. A non-expert isn’t going to crack the profession after a couple of days of reading Wikipedia or taking a 3-day course.


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Nov 01, 2007

A group of graduate students from the Penn State acoustics program has been measuring the sound levels of crowd noise at Nittany Lions football games. One purpose of this work is to make calibrated recordings that can be piped in to football practices to simulate loud crowds.

This is the kind of game planning you can do when your university has a top-notch football program and a top-notch acoustics program. Of course you can put Purdue and the University of Miami in that same category.


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This piece from the Northwestern Midell Washington Program is focused on airport noise, but it does a good job describing the negative effects of noise on people.

Unfortunately many people think we can all “get used” to noisy environments without realizing that long-term noise exposure can cause problems with concentration and learning not to mention sleep disruption and serious medical problems.


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It wasn’t enough to build a top-of-the-line home theater system. The owners wanted to make sure that the homeowner could watch his high-octane action movies in their full sonic glory without disturbing family members in other rooms. As a result, the custom home theater was designed to incorporate sound insulating techniques where possible.

The article is written in lay terms so the exact construction methods aren’t detailed, but it looks like the home theater uses mass-loaded vinyl, double-walled construction, resilient channel, and a floating floor. One thing that’s not clear from the article is whether proper room treatment was applied, but the pictures show a blend of hard walls and absorptive panels on the ceiling and walls, so it appears the room acoustics were given at least minimal attention.

This project is a good example of why you want to get an acoustical expert involved before the contractor breaks out the hammer. While it does cost money up front to design and build the sound insulation at the beginning of a project, it will cost a lot more (and by more, I mean “an order of magnitude more”) to have to rip out everything you just built to retrofit the room after the fact.


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