m II wrote:

As for those car stereo lunatics, I think they will all be deaf after a
few years. I can hear their bloody bass five cars away. How can the use
of headphones by a car driver be illegal when that megawatt idiocy is
allowed to continue?



mike


Well, since you've asked...


Many communities have passed ordinances, mostly for noise control,
making the use of such car stereo's illegal. The criteria are centered
on the distance from the vehicle that the sound is still audible. In
Aurora, if a car stereo is audible 50 feet from the vehicle (which would
be a little less than 5 cars away), the driver can be cited, and the
vehicle impounded.

Similar ordinances have been passed in a number of communities in and
around Chicago.

But that's only the tip of the Fletcher-Munson curve.

There has been legislative debate downstate, as well as in
communities around the state, about the long term safety concerns, not
unlike concerns surrounding headphones, of such high pressure sound
levels in cars while driving. Competition grade stereos have resulted in
permanent hearing loss from the extreme overpressure produced by huge
subwoofers firing into the cab. With the windows closed, the
overpressure produced by tight bass notes or kick drums can (and
frequently have) rupture ear drums. Where such debate stalls, is that
the safety aspects of driving with music playing are centered on the
ability to hear emergency vehicles, horns, tire screeches, and oncoming
traffic...all sounds with huge midrange components. Such sounds are
still audible though high bass content. One "expert" explaining to
legislators actually made the argument that a factory radio at high
levels is more isolating to ambient sounds than a customized vehicle's
twin aftermarket subwoofers. Not unlike (mandatory radio content,
here....) trying to hear the Liberty Net through the noise on Saturday
nights. If the stereo is on in the other room, and the bass is thumping,
you have less trouble hearing your RX-320's output, than you do if the
atmospheric noise is high. Why? Because the atmospherics and the LibNet
voices are competing for the same spectra, where the ear is most
sensitive...the bass is not. Take out the upper end on the atmospheric
noise, and intelligibility of voices is increased. Subwoofers in cars
are not competing for intelligibility with sirens, horns and the guy in
the car behind you accompanying his gesticulations with spontaneously
assembled language.

And there is another phenomenon at play. The truth is, that inside
the car, those subwoofers simply don't seem as loud to the driver, as
they do to YOU, sitting outside the car. Bear in mind that the guy in
the car 5 vehicles away with his windows open has actually created a
kind of two stage bandpass box for his subs...the enclosure in which
they're mounted is one, but the vehicle cab space into which they fire,
is actually another. And with a window open, when that over pressure
spews out, it does so through a crude bass port and becomes a wave
front. By the time it reaches you 5 cars away, that wave front is
defined, and has subtle directional components. Inside the cab, however,
it's merely overpressure that's uniformly impinging on the ears of the
driver without directional components.

These directional components, though very subtle, and often
consciously indistinct are at the very heart of how the mind processes
audio for the auditory sense. Humans here in stereo. The mind processes
in stereo. Without stereo field information, even highly defined audio
becomes indistinct, and can be lost in ambience. This is how you can
carry on a conversation in a crowded room. The mind allows focus on a
single voice among hundreds through recognition parameters...timbre,
tone, resonance as well as patterns of rhythm, and anomaly...and spatial
orientation. Using the stereo soundfield, the mind processes the subtle
phase differences from a single source, and locates it in space. So, in
a crowded room of hundreds of voices, one can identify and follow a
single voice by it's sound AND location.

Put your finger in one ear, take away that stereo spatiality
reference, and see how difficult it can become.

This phenomenon, btw, is what's behind the use of stereo detectors
in communication receivers. Military and commercial receivers have been
doing this for some time, because it makes it much easier for code
receivers to copy on crowded bands. Similar success has been realized in
SSB and AM modes.

Back to the issue, though...in the car, without the spatial
references, the mind finds the overpressures of bass to be less
objectionable, even less audible, than you do outside the car, with a
defined, and spatially locatable wavefront.

Literally, it's more irritating for you, because it's more difficult
for the mind to ignore.

And armed with expert testimony in this, the industry has stalled
legislation that would ban high powered stereos in cars, as was done
with headphones.

If you ever have the opportunity to drive a vehicle equipped with a
high watt stereo and big subs, you'll be surprised, at the end of the
drive, at how comfortable you are with the level, and how loud it is for
the rest of us outside the car.