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

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Feb 22, 2007

Mary Ellen Eagan, HMMH’s President, recently gave a presentation at the Transportation Research Board’s annual meeting on Using Supplemental Metrics to Communicate Aircraft Noise Effects. The PowerPoint presentation is probably a bit dense for the layperson, but I’d like to point out a statement in her presentation summary:

The effects of aviation will continue to be a constraint to aviation growth unless we start communicating in a way that reflects the way people live.

Now Mel’s presentation was specific to aviation noise, so with apologies, let me revise the statement:

The effects of noise will continue to be a constraint to growth unless we start communicating its effects in a way that reflects the way people live.

I’m focusing on this statement, because Mary Ellen’s presentation addressed something that we acoustical engineers rarely consider - most lay people don’t have a clue as to what we’re talking about! I can talk about noise impact in terms of 10 dB above ambient levels, or exceedances of 65 dBA EPA criteria, “pure tones” or any number of technical terms. While they make perfect sense to those of us in the industry, it’s clear from experience that lay people have difficulty figuring out how these numbers apply to their day-to-day lives.

Mary Ellen’s paper gives examples of an airport noise analysis where impacts are quantified not based on the typical FAA “DNL 65 dB” criteria, but based on real-world effects like sleep awakenings and classroom disruptions. Noise control engineers have for some time known that excessive noise levels correlate to quantifiable adverse effects, but this tends to get lost in all the numbers that get tossed around in the typical capital project. As a result, most of the public don’t really know what “noise” is, or believe that it’s purely a subjective matter.

Instead of saying “this new power plant will raise ambient sound levels by 13 dBA,” what if we said “40% of residents within a 2 block radius of this power plant won’t sleep” - meaning that the project will effectively lead to increase in drunk driving? Or maybe “this new highway will cause MCAS scores at an adjacent school to decline by 15%”? These are real-world effects that people can identify with.

…and I suppose an anciliary effect would be an increase in billable work for me ;)

I think it’s worth thinking about. The problem is that this thinking requires a re-evaluation of noise analysis procedures and lots of research to tie acoustical characteristics with readily observable effects - all of which costs money that no one will want to spend. I expect will see more and more of this type of analysis at the Federal level, but it will still be difficult to get this done at the municipal and community level where money and technical expertise are difficult to find (but that’s another post).

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I do home theater consultations, although my work consists mainly of recommending equipment, system setup, acoustical room measurements, and audio calibrations. I am frequently asked to perform custom installations for high-end home theaters; unfortunately I’ve had to turn down these projects because I am not a licensed contractor.

About a year ago, I met Stanley Kowalski of FloDesign through HiddenTech. I just recently found out that Stan is also a licensed Construction Supervisor in Massachusetts, and works with a qualified crew through SK3 Engineering Inc. Among other projects, his crew is currently hard at work renovating FloDesign’s new headquarters, which will have office space as well as shop/lab space for their prototyping and experimental acitivities. When Stan heard about some of the work I’ve had to turn down, he offered to team with me for these projects.

So I’m pleased to announce that Cross·Spectrum Labs, in conjunction with SK3 Engineering, is now offering full service acoustical design and custom installation services in Massachusetts. Up until now, all I could do was help design your home theater or provide recommendations for residential/commercial noise insultation. Now we can help you actually implement and install acoustical treatment, in-wall speakers, custom cabinetry, and anything else that you may need.

How does this compare with the installation services offered by the big-box stores? Well frankly, it doesn’t. If you’re perfectly happy with 128 kb/s MP3’s, and you’re just looking to buy a $500 home-theater-in-a-box, then you’ll do fine with Circuit City or Tweeter. On the other hand, if you really care about audio, and are willing to invest accordingly, we can help. I know audio. I understand the theoretical and practical aspects of room characteristics like reverberation time, envelopment, modal density; sound insulation, and noise criteria. I understand why audiophiles seek out brand names like Thiel, Wilson, B&W, and Adire. The pursuit of perfect audio is why I got into this business in the first place, and I want to put that passion to work for you. We can help you to create your perfect audio environment.

Feel free to contact me if you have any questions.

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Speaking of additional capabilities: I’ve been doing microphone characterization measurements for some time now. What I haven’t publicized is that I’ve expanded the measurements services I offer to better meet the needs of microphone manufacturers and OEMs. In addition to on-axis free-field measurements, I can also measure:

Pricing for microphone frequency response measurements only remains $50 per mic. Pricing for everything is $75. À la carte pricing usually ranges from $50-$75 per mic, and volume discounts are available. Please inquire for further details. Volume discounts are available. All prices include return shipping via USPS Priority Mail service.


Like all my measurements, I probably give too much information - for example, the Fat Head II’s impedance plot looks pretty ugly, but since no one else plots their mic’s wide-band impedance response, there’s nothing to compare it to. Of course the output impedance for most ribbon mics vary widely across a wide frequency range. Unfortunately, most manufacturers only give values at a single frequency, which can make an apples-to-apples comparison difficult.

In any event, I can help you navigate these pitfalls so you (and your customers) can have a fair and accurate picture of what your microphone can do.

As explained on my mic measurements page, I perform my measurements using quasi-anechoic techniques. I have had some requests to make full anechoic measurements. All I can say right now is that I’m working on it - stay tuned.

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