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Feb 27, 2007

“A good lawnmower does not sound like a good refrigerator” - a very relevant quote from a presentation by Acentech’s David Bowen on sound quality

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NPR ran a story last week about the dangers that blind pedestrians face from quiet hybrid cars. Advocates for the blind are asking car makers to add “sound cues” to hybrid cars to provide audible warning to the blind.

Given that automobiles are one of the most significant noise sources in the country, the elimination of engine noise should be considered a good thing. Unfortunately, the law of unintended consequences has reared its ugly head.

Solutions? Well I don’t think adding a loudspeaker to the engine bay is going to make people happy. If I had to guess, I would say mounting a small sound source or loudspeaker low to the ground and facing to the fore and rear might be a good short term solution. By keeping the source low, Jersey barrier and parapets will make effective noise barriers while still allowing blind pedestrians in the immediate facility to hear the car. Maybe a broadband source similar to the BBS-TEK backup alarm?

Long-term, I think some sort of proximity-based warning device might make sense. But then again, what do I know?

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Feb 26, 2007

Today’s news event: Microsoft apparently sponsored another guerrilla marketing campaign that involved a using a “competition grade” car audio system to promote its Zune DAP by blasting tunes in a residential New York City neighborhood at 3am.

As might be expected, some of the residents in the affected neighborhood aren’t pleased. Of course I don’t know what’s worse - the fact they were blasting music at 3am, or the fact MS apparently chose to blast Justin Timberlake’s music at 3am.

[thanks Heather and Gizmodo]

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Feb 23, 2007

Last night’s BAS meeting was graciously hosted by Spearit Sound in Boston. The topic: a discussion by Jim Thiel and a demo of his latest creation - the Thiel CS3.7 loudspeaker.

Thiel makes high-end speakers, and the CS3.7 carries a high-end price tag - $9,900 per pair (as Jim put it, “It’s a great deal, you get two speakers!”). Unfortunately, the demo left me unimpressed.

It’s not that the speakers were bad, they sounded good, maybe even very good. But for that price tag, I was expecting greatness. What made the demo even more disappointing is that on the face of things, Thiel seems to have made all the right decisions - high stiffness driver cones, 1st-order cross-overs, neodymium magnets, coax tweeter/midrange driver, passive radiator, and so on. The brochure shows that the speaker has a flat frequency response. Ultimately, the sound was also flat.


On a positive note, I just discovered that Thiel has a blog that gives some insight into the manufacturing and support process.

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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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Feb 01, 2007

The big news in Boston today is the bomb scare yesterday caused by electronic advertisements placed on or near transportation structures by a ‘guerrilla’ marketing firm. The fallout has included various websites criticizing (or outright mocking) Boston authorities for their “foolish overreaction.”

As with many noise consultants, I often have to leave noise monitoring devices out in the field for days at a time. Often they are chained to telephone poles, trees, fences, etc for security. Through personal experience, as well as the experience of my colleagues, I’ve learned that if you set up an electronic device at or near a public area without informing anyone or providing contact info, there is a 100% chance that the bomb squad will get called in, and about a 95% chance your $5000 sound level meter will get blown up by said bomb squad.

I’m the first one to criticise the paranoid society we have become since September 11, but I can’t find any fault with the Boston authorities here. They didn’t evacuate the city, they didn’t call out the national guard, they didn’t round up all the Arabs - they closed some roads and bridges and investigated some unauthorized devices. The did their job and got down to the truth.

If there was any panic, the faults lies with the marketing firm and Turner Broadcasting who apparently couldn’t be bothered with attaching some identifying info to the devices.

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I have yet another microphone manufacturer that I have added to the client mix: Cascade Microphones of Olympia, WA. They sell inexpensive ribbon microphones, which, in my opinion, are good mics for their price. I recently performed frequency response, polar, noise floor, and output impedance measurements for several of their mics.

They are selling their X-15 stereo mic via their eBay store. The frequency curve they’re showing on the auction is generated using an exponential moving average. As can be seen on the full report for the X-15, I generate three separate data curves for my professional customers: narrow band (FFT), 1/3 octave band, and exponential moving average. I do this because there are no real standards in the prosumer space for microphone frequency response curves. As a result, some manufacturers play games with their specs. It’s not that the specs they give are wrong; they’re just, let’s say, “overly optimistic.”

The point of the three representations is to let you compare apples to apples. Unfortunately that tends to be a little difficult since most manufactures don’t tell you how they measured their mics. There are exceptions of course, Earthworks being most notable. So, if I generate a ragged narrow-band plot (the raggedness is caused by my 20ft by 15ft by 8ft quasi-anechoic measurement environment) and a potential customer tried to compare it with another manufacturer’s moving average or fast-sweep response, one might wrongly conclude that one mic is far superior than the other. In realty, the difference is in the measurement technique.

I just wanted to make people aware that whenever you’re comparing mic specs (even mine!), make sure you comparing the same thing. For example, it would be unfair to compare the X-15’s moving average response with the FFT response of one of the Crowley and Trip mics - remember to compare like with like.

For the record I will mention that when I as a customer am looking for a frequency response data, I tend to favor 1/3 octave band responses. Of course 1/3 octave band smoothing tends to suppress very narrow peaks and dips, but in my experience, the general trends that you’ll see on a 1/3 octave band correspond with what you’ll actually notice in the real world. The FFT measurements is also an indication of what will happen when you use the mic in a real room since most of us don’t record in anechoic spaces. I’m hoping that by giving folks all the facts (good, bad & ugly), customers can make informed decisions.

Please feel free to contact me if you have any questions about the data I generated for microphone distributors.

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