[audio] dumb ohm-age question (or square peg & round hole)

[peter at thescirocco.com (peter)]

Am I missing something...

"Sound" as it comes out of an amplifier, is varying or pulsating dc,
direct current, this is why one output is marked positive, and the other
minus or ground. ;) Try hooking up your speaker wires to an
oscilloscope, you will see it only goes in one direction, this looks
really cool btw.

The bass blockers I have, uses electrolytic caps, and just about every
crossover I own uses electrolytic capacitors.

Capacitors in series block the bass, and the capacitive reactance i.e.
the effective resistance of the capacitor, goes up as the frequency goes
down. Coils are the opposite...
It's been a while, but I think capacitive reactance is Xc = 1/2ñfC;
ñ=3.14 f=frequency and c=capacitance, (or Farads). Inductive reactance
is XL = 2ñfL, the resistance of the coil is directly proportional to the
frequency, and capacitive reactance is inversely proportional to
frequency.
You can use those formulas to design your own crossovers specs.

I think the capacitor needs to be in parallel across a circuit, or load,
to absorb current...

Peter
302.832.8989
http://thescirocco.com

-----Original Message-----
From: scirocco-l-bounces@scirocco.org
[mailto:scirocco-l-bounces@scirocco.org] On Behalf Of Allyn
Sent: Sunday, January 11, 2004 11:34 PM
To: John S. Lagnese; 'Mike'; 'Foxx (in a box)'; scirocco-l@scirocco.org
Subject: Re: [audio] dumb ohm-age question (or square peg & round hole)

well...

[electronics technician hat]

coils - in series - allow bass to pass (as opposed to trebble) - called
a
low-pass filter
the coil is an inductor, which opposes rapid changes in current. slow
changes (bass) can make it through.

caps - in series - allow trebble to pass (as opposed to bass) - called a
low-pass filter
the capacitor opposes rapid changes in voltage, thus acting like a short
to
rapid changes, which results in those rapid changes (trebble) being
passed
on to the speaker. slow changes (bass) only result in the capacitor
rapidly
charging/discharging, therefore absorbing the bass. another note here is
that its important to NEVER use electrolytic caps for this purpose, as
they
are polarity-based (where sound goes both + and -).

both of these methods are safe because in both cases, the filter
prevents
the signal from getting to the speaker. there are also such things as
capacitor-high-pass and indictor-low-pass filters, but these filters are
in
parallel with the input (from the amp), effectively shorting it out to
cause
the filter action. so... ALWAYS use the filters IN SERIES with the load
(speaker), or you risk total destriction of the amplifier.

[/important safety tip]

HTH
Allyn Malventano, ETC(SS), USN - who teaches crap like this every day :)


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