Seattle Police are following through on a promise made last summer to ticket vehicles that are exceeding permissible noise levels, especially on Alki Beach or Golden Gardens where it's common to hear blaring speakers, blatting motorcycles, and roaring engines. Enforcement began May 10.
If your vehicle can be heard from over 75 feet away you could receive a $135 citation. For more information on the Municipal Code please follow this link.
Previously the issue was difficult to enforce since decibel levels descrease over distance and different sound frequencies are attenuated (blocked or absorbed) differently. Bass frequencies are longer wavelengths and tend to be transmitted a greater distance and can reverberate. Treble frequencies which are higher wavelengths tend to be reflected and are those that provide location information in stereo systems.
To enforce the law in the past Seattle Police had to be able to measure specific sound levels using decibel meters. Now the law permits more direct police discretion as to the determination of a violation. The new standard says, "Can be clearly heard by a person of normal hearing at least 75 feet away from the vehicle."
So, if your muffler is missing, your volume knob broken, or your testosterone level is just too high and only the thump of your speakers will help, you might be best served to take those issues outside the City of Seattle. Turn it down or get a ticket.