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Jul 02, 2006

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As the weather turns warm, and people start to open their windows, it seems that the thoughts of urban residents turn to a singular concern – neighborhood noise. Specifically: noise from boomcars.

Throughout this past spring, many cities and towns have been pushing for noise ordinances to clamp down on noisy car audio systems and motorcycles. I can sympathize, people want to be able to enjoy life outdoors without being drowned out by 50 Cent or loud exhaust. However there is one provocative tactic that is being pursued by several localities in an attempt to control car audio noise: banning the sale and/or installation of specific car audio components, such as subwoofers over xx-inches in diameter, or amplifiers with a power rating of more than XX watts.

Dumbest. Idea. Ever.

(And I’ve done work for the Federal government, so that should say something.)

Several cities have considered this. St. Louis is the first city, to my knowledge, that attempted to ban audio components (an attempt that was quickly defeated). Officials in other cities, including my home town have discussed it, and it seems that Buffalo is the latest city to evaluate the idea.

Everyone is talking about it — so why is it a stupid idea?

Because, contrary to lay belief, audio systems are not easily defined and categorized. The St.Louis legislation attempted to reduce bass noise by limiting the size and number of speakers and enclosures, limitations that can easily be overcome using a variety of acoustical techniques such as multiple smaller drivers, bandpass/transmission line tubes and free-air mounting techniques that use the trunk or cabin as the “box.” Not to mention that a subwoofer doesn’t have to be a conventional “speaker” at all, thanks to advances in servo technology and inertial mass transducers.

The amplifier power restrictions are unenforceable because of the laws of physics, namely Ohm’s Law. In the case of audio amplifiers, Ohm’s law says that the power output is inversely proportional to the impedance of the speaker. So an amp that puts out 150 watts into an 8-ohm speaker will put 300 watts into a 4-ohm speaker. So the same amp could be illegal for one install, but legal (and louder, if a more sensitive speaker is used) in another installation. Who is going to be the final arbitrator of the power rating? This is a problem the FTC has struggled with in recent years. Are local town officials going to succeed where engineering professionals have failed?

Such limits are impractical – they will either be ineffective, unenforceable, or they will have unintended consequences. For example, the aforementioned St. Louis legislation states that any motor vehicle with “more than 10 speakers” is prohibited. Let’s look at my 1998 Passat. The baseline audio systems has 8 speakers (one tweeter and one midwoofer on each of 4 doors). At first glance, that would appear to be okay… but, in addition to the audio system speakers, my car also has 3 horn drivers (2 for the “honk-honk” horn in the engine bay, and 1 for the alarm system in the trunk), and at least 1 piezoelectric speaker for the low-fuel/low-coolant/low-wiper fluid alarms. I’m sure the legislation wasn’t looking to regulate the internal alarm speakers, but there is nothing in the ordinance that explicitly excludes such an interpretation.

The biggest problem I have with these proposals is the implicit assumption that “big speakers + audio amplifier = booming bass.” I’m not an naive; I’m know that most teens who are buying this stuff want exactly that. However, there are lots of people that are using high fidelity equipment for its intended purpose: namely, high-quality audio. My car audio system adds a 12-inch subwoofer and 300-watt amplifier to the base audio system. At first glance, this would seem to be the text-book “boom” system that activists find so infuriating. A closer look shows that I made some design decisions in my system that adversely affect the sensitivity in exchange for low-frequency extension. As a result, my car audio system will generate very clean bass below 30 Hz, although it doesn’t get particularly loud. Yet audio system-limits would punish me based not on the output of the audio, but simply by the characteristics of the components I choose to install.

I’m all for municipalities working to limit noise (hey, it’s part of how I make my living), but to be effective, they need to do it by enforcing quantitative criteria, not by making uninformed judgments of the components. But so long as these legislators don’t want to consult with acoustical experts, we’re going to continue to see these asinine proposals.

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