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AudioAcoustics

Serving the Acoustics Community Since 1994

Cross-Spectrum Acoustics Inc. offers Sound & Vibration Consulting Services

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Sep 18, 2005

ProSoundNews has a nice writeup on Crowley And Tripp Microphones (full disclosure: Soundwave Research Labs is a client of mine):

“Didi said that in 25 years, she’s never heard a microphone so dynamic and open,” explained Resta about their use of the Studio Vocalist. “She was astounded, and that’s more impressive than my bragging about it—she’s an amazing singer.”

I’ve previously written about my experience with the Proscenium microphone.

I performed the independent testing on the Crowley And Tripp Microphones (you can download the results here). I was asked to describe my testing process, so I’ll comment a bit below.

I have a variety of testing apparatus that I use to measure the performance of standard 1-inch, ½-inch, or ¼-inch microphones. There are lots of methods that can be used to measure the performance of microphones such as the the reciprocity method (described in ANSI S1.10-1966), acoustical calibrators, or electrostatic actuators. However, the shape and figure-of-eight directivity of the Crowley and Tripp microphones make these methods impractical.

As a result, I settled on the “substitution” method to test the Crowley and Tripp mics (in fact I generally use the substitution method to measure mics that don’t have the standard 1-, ½-, or ¼-inch diameters - that is to say, pretty much any non-measurement microphone).

I use a reference microphone to measure the output (a maximum length sequence, MLS) of a full-range driver mounted in a large baffle. The reference microphone (usually my TerraSonde or ACO Pacific ½-inch mic) has been calibrated by a NIST-traceable calibration lab. I then substitute the device-under-test (DUT) in the same position, and measure the same test signal. By subtracting the DUT curve from the (known) reference curve, I can compute the frequency response for the DUT.

The low-frequency response of ribbon microphones will change based on the distance between the microphone and the noise source. Specifically, the low-frequency response of ribbon mics will increase as the mic moves closer to the sound source (the “proximity effect”). I performed the mic measurement at a distance of 25-inches to obtain the “flat” curve for the tested microphones.

Given that these mics are used for audio recordings, as opposed to audio measurements, the mics themselves are basically musical instruments and will be positioned according to the tastes of the musicians and engineers. The point of using a 25-inch reference distance is to demonstrate that the mics can have a flat frequency response, if desired. In practice, you will see (and hear) a more pronounced bass boost if you use close-miked techniques. If I have a chance, perhaps I’ll do some close-in frequency response measurements to better demonstrate the proximity effect of Crowley and Tripp Microphones.

That’s the measurement procedure in a nutshell. Comments, questions, and suggestions are welcome.

Bob, Chris and Hugh from Soundwave Research Labs will be showing off their mics at AES; I’ll be there as well. Hope to see you there!

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Sep 15, 2005

Two new acoustics-related blogs I found today:


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Sep 13, 2005

People have started to realize that MP3 players can cause hearing loss. This is one of those that’s obvious to me but, then again, I do this stuff for a living.

The problem is that there’s no real solution to the problem (other than turning down the volume). Portable audio players have to be able to drive a wide variety of headphones, so that even low-sensitivity headphones can output acceptable sound levels. That, of course, means that high-sensitivity headphones will get loud.

Just use some common sense – keep the volume at a reasonable level (if your ears are ringing, or you can’t understand speech from someone speaking with a raised voice, it’s probably too loud) or try to limit the amount of time you listen to music at high volumes. Once you lose your hearing, you never get it back.


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The CEDIA 2005 Expo concluded this past weekend. I was planning to go, but I got roped into was invited to present a paper at Noise-Con 2005, and I only have budget for one out-of-state tradeshow this year (although I may sneak down to AES in NYC next month).

[BTW, searchable database of papers to be presented at the 2005 Noise-Con/ASA meeting can be found here.]

Anyhow, one CEDIA announcement caught my eye: Dolby Introduces Dolby TrueHD, Lossless Audio for High Definition Discs“With Dolby TrueHD, home theater viewers will experience audio performance equal to the highest-resolution studio masters currently available.”

HD combined with a losslessly compressed audio? Yum.

[from Peter Cook]


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A non-CEDIA announcement that caught my eye: a DIY DVD burner and harddrive recording unit. Just add your own harddrive.

[from Gizmodo]


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A couple of MIT tidbits:


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Sep 05, 2005

Remember Doug Chiang’s Star Wars-themed home theater?

Well, here’s a home theater based around Raiders of the Lost Ark, complete with actual props from the movies.


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Here’s a review of the X-woofer, a “wearable woofer” that’s worn around the neck. Good idea in principle, if not in execution.

[from Engadget]


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Using sound to improve aircraft performance at low speeds: “A Qantas aerospace engineer has found a way to make small planes safer and more efficient by turning their wings into flying speakers that can beat out a tune.”

More info here.


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First is was the Kokomo Hum, now it’s the Ohio Scream: “An unusual and noisy mystery has people in a small town north of Middletown on edge, worried and asking questions.”

Maybe it’s time to give Jim Cowan a call?


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Another step in the preservation of “Natural Quiet”: A man speaks up for silence

“In claiming one small inch for the sounds of the natural world, without intrusion from the racket of man, Hempton, 52, hopes to preserve the quiet of miles of wilderness backcountry in Olympic National Park.”


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From the New York Times:

While scientific literacy has doubled over the past two decades, only 20 to 25 percent of Americans are “scientifically savvy and alert,” he said in an interview. Most of the rest “don’t have a clue.” At a time when science permeates debates on everything from global warming to stem cell research, he said, people’s inability to understand basic scientific concepts undermines their ability to take part in the democratic process.

I can sympathize, this is something I encounter more and more as I try to explain acoustical concepts to lay people – for example, people don’t understand concepts like decibels and A-weighting so they dismiss these metrics even though they can be very effective at predicting annoyance from noise.

But in the end, as a consultant, it’s my job to help people to understand these things. But sometimes I wish it was just a bit easier.


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Brad’s Audio Blog has info on a new DIY line array loudspeaker kit.

Interesting design – the array consists of a pair of woofers and a tweeter mounted in a D’Appolito configuration which, in turn, is flanked by a ported woofer array.


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Here’s a tutorial for DIY Tube Traps.


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