An auto speaker tutorial

[Mike Pittinaro <mechimike@xxxxxxxxx>]

> I believe the one thing to be concerned about when
> replacing speakers is the 
> "ohmic-value". In order for the speaker to sound
> right,it must have the same ohmic-value as the ones 

Actually, the two most important characteristics of a
speaker (in terms of quantifiable measurements, at
least) are dB/1 watt (sensitivity) and frequency
spectrum.  A typical speaker has a sensitivity of
around 90 db/1 watt, that is, for one watt of input
(usually at a specific frequency, like 1kHz) it will
produce 90 dB of sound pressure.  You want your
speakers to have roughly equal sensitivity, so that
the sound will be balanced front and back (and
right-left)  Since its hard to determine what the
sensitivity of old speakers is, its best just to
replace them all.

Frequency spectrum is basically the range of audio
that the speaker can reproduce without distortion or
sound pressure drop off.  A good, full range auto
speaker should reproduce 40Hz to 16,000 Hz reliably. 
(the range of human hearing is 20Hz to 20,000Hz
roughly, but sounds above 16,000 and below 40 are
rare.  Also, your stock factory stereo probably can't
reproduce these frequencies anyway)

I had a problem once because I needed a set of 4"
speakers...I bought a set of 4" woofers from Radio
Shack, but they were woofers, and hence would not
reproduce above about 5,000 hertz.  The sound was very
deep, with no high end.  It wasn't the speakers'
fault, it was me for using the wrong speaker.  In
general, radio shack speakers are good for auto use. 
I particularly like their 5 1/4" dual cones and the
4x10 which fits nicely in the front center speaker
cutout of my Satellite.  I haven't experienced their
6x9's (yes, those are the size for the rear package
shelf, at least in my '67 Imp) but I imagine they
would be a good speaker.

Ohms are most important in terms of your radio unit,
and how much of a load it can drive.  Ohm values lower
than 4 are a real problem for most radios; I try to
stick with 8 ohm speakers for safety.  Lower Ohms
means higher current, for a given voltage. 
Voltage=Current*Resistance (V=IR) R=Resistance in Ohms.

=====
--Mike Pittinaro

'Tis Christmas again
Have a happy holiday
Imperially

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