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Sep 29, 2004

The journal Nature will be publishing an article on the source of a natural “hum” (NPR, New Scientist, Google News) present in the ground. The NPR article mentions that the earth vibrates at a rate of 1 cycle over 300 seconds which corresponds to a frequency of 3 milliHertz - not something you’re likely to measure with an accelerometer.

The source of the hum is apparently wave activity caused by seasonal storms in the north and south Pacific during the winter seasons in the respective hemispheres.


I got a response from a reader regarding his experience with Bose’s Personal Amplification System:

I only just now read your 3 APR 04 and 20 OCT 03 blogs on the Bose L1 line system PA. I’ve been fascinated with this system since I first saw it at a Guitar Center store. I’m a jazz vocalist/guitarist and not terribly concerned with frequencies below 80Hz ( the lowest E on the guitar ). The Bose sounds excellent with acoustic guitar/ voice without the bass modules connected.

We did some A-B testing (with/without a bass module plugged in) and discovered this: If you have program material (guitar, in our case) going through the system, and unplug the bass module, there is about a one second period during which the sound from the column is very tinny (lacking bass). Once the system detects the absence of the bass module, the EQ is adjusted to compensate, and it sounds good again. There is _extremely_ heavy EQ going on here.

He went on to note (as I did) that the PAS look like Bose’s earlier PA column speakers. Kinda emphasizes the point that the speaker itself is nothing new, but the application is novel.

I’m not surprised about the heavy EQ, Bose’s self-powered speakers use a lot of equalization to compensate for deficiencies in the speaker drivers. Whether this is a good or bad think I’ll leave for you to decide.


Peter Hotton of the Boston Globe (via since the original article is only available for a fee) addresses a reader’s concern that excessive ‘stomping’ can cause damage to a home. Short answer: it’s nothing to worry about.

It brings up a point that we consultants have to make time and again when it comes to vibration analysis. It can be understandably scary when some source (be it train, plane, industrial or construction) causes perceptible vibration in your home, but that doesn’t automatically mean that the vibration will cause damage.

Really, it’s true.

With the exception of extreme cases (nearby blasting, vibratory rollers at your porch, impact pile driving right outside your window), you don’t have any more reason to worry about most vibration sources causing damage to your home than, say, an angry teenager slamming his bedroom door.

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Sep 23, 2004

It was inevitable: we all now THX offers certification for cinemas, studios, home theater equipment and car audio systems. Now, THX has announced certification for high-end home theaters.

The Home Theater certification requires THX-certified components (of course). Much like the THX TAP and audio/video component specs, I’m sure the home theater specs won’t be publicly available. However enough pieces of the spec usually find their way onto the ‘net so that you can get a general idea of the end goal.

[via Home Theater Blog]


The 117th AES Convention has scheduled a wide variety of workshops. One workshop of note is Field Recording in the Wild which focuses on the recording of natural sounds despite “rapidly disappearing natural soundscapes.”

[Digital Pro Sound News via Peter Cook’s Audio blog]


Roland Piquepaille reports that Dust Networks’ “Smart Dust” wireless communication nodes have hit the market. As a measurement guy, this is a technology that excites me — low-cost, low-power, interconnected sensors that can be deployed over large areas to collect massive amounts of data.

Of course, once you add $1,000 precision microphones to the mix, the system is no longer “low-cost,” but you don’t necessarily need precision mics everywhere. Use $5,000-$10,000 precision measurement systems at primary locations, and supplement them with “dust motes.” Add $20 Radio Shack mics (which I’ve used in place of B&K 1/4-inch in Naval research to great success, trust me they’re good mics!) and you’ve got a lot a measurement capability for not much money.

It’s all about using technology to reduce the costs of measurements. A lot of people don’t think it can be done, but they’re wrong. It can be done. I’ve done it. I’m doing it.


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Sep 06, 2004

I updated the frequency-weighting article with some information on some freely available Matlab scripts that can be used to build digital A- and C-weighting filters.

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Sep 05, 2004

Wired Magazine reports on medical journal article that states that loud bass can callapse a lung. The article doesn’t give a lot of details, but you gotta believe that if this was true under normal common circumstances, we’d have seen this before. I guess I need to read the Thorax article. offers an online hearing test you can take using your web browser, your computer, and headphones. Obviously this won’t be a calibrated test, but I suppose it could be useful on a relative basis.

I took the online test - the results weren’t anywhere near the results from any of the audiograms I’ve taken over the past couple of years. YMMV.


Professor Russell of Kettering University has posted animations of various acoustics and vibration concepts. In addition to the usual animations of sound propagation and cancellation, he also has animations of concepts such as refraction and Doppler effects. The Doppler demo is especially helpful in visualize sonic booms.

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