Installation manual

MYTHS, MAGIC AND FACTS
Subsonic filters and CLIPPING. The former are simply steep slope high pass filters with a
frequency range between 10 to 50Hz. Their only function is to filter out those frequencies
which lie below audibility. The woofer’s cone will not “flop” around as it does without the
use of the filter and because all the low frequency energy that we cannot hear is filtered
out, the amplifier runs more efficiently since it does not have to amplify all those inaudible
low frequencies. Remember one fact, ALL amplifiers are pretty dumb. They will amplify
anything you put into them (assuming the amplifier’s frequency response is wide enough)
and whether we can hear a particular frequency range is not the amplifier’s concern. Put
in an inaudible frequency and the amplifier dutifully does it’s thing. It does not care about
the load. This is why tweeters are easily burnt when amplifiers are clipping. The amplifier
generates high frequency harmonics and this energy is thrown to the unsuspecting
tweeter. When an amplifier is driven into clipping it basically generates a square wave.
This contains a large amount of energy but also due to the fact that the square wave sits
at a positive (or negative) state for a “long” period of time, the natural cooling effect of a
continuously moving cone/voice coil is inhibited and can lead to failure of a speaker.
Typically woofers are more tolerant of clipped power than mids and tweeters due to the
fact that they are more robust and that they do not respond to those high frequency
harmonics very well (but do not be fooled, woofers can be hurt by these harmonics even if
we cannot hear them). The inductive reactance is (2 x 3.14 x freq x inductance) and so
the higher the frequency the higher the inductive reactance of the speaker becomes.
However it’s DCR does not change with frequency.
A quick point about the term DCR (resistance at DC). I believe that this term was coined
because we all use a meter which operates with batteries and we measure the simple
resistance of a resistor or piece of wire with this meter. We take this measurement at a
frequency which is low enough so that if we increased the measurement time the result
would be the same. So using an ohm meter which works at say 50Hz would yield the
same result as long as the measured part has no AC reactive component.
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