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From: Phil Seakins
Subject: Re: Woofer repair
Organization: Phil Seakins
X-Newsreader: Forte Agent 1.92/32.572
Date: Mon, 25 Nov 2002 01:11:26 +1000
NNTP-Posting-Date: Mon, 25 Nov 2002 02:11:29 EST
On Thu, 21 Nov 2002 14:16:35 GMT, "Ban" wrote:
>> I have an old EPI 6" woofer that I'm looking at and putting it on my
>> function generator, the speaker distorts badly from around 40hz to
>> 120hz but fine at all freqs above and below.
>> I've never really indulged into the world of woofer construction and
>> repair other than knowing the basic principles.
>> There is no surround problem....there is a very small pinhole in the
>> cone I could fix....but what exactly is going on when a woofer won't
>> perform at a specific band of frequencies like that?
>> It will break up between 40 and 120 hz and also when I "move it"
>> manually between a certain range in it's travel.
>> There doesn't seem to be any impairment of the cone at all....nice and
>> smooth in when I move it back and forth.
>> And it breaks up straight out of the function generator so
>> it's not getting much power.
>your woofer seems ok to me, but not your knowledge...
>The function generator has probably 50 Ohms impedance. Now when the woofer
>has 5.5 Ohms DC-resistance, at low frequencies this is a 20dB divider, (at
>the woofer terminal there is only 1/10th of the open circuit voltage).
>With higher frequency there is the resonance of the woofer. At this point it
>might have without enclosure around 50 Ohms impedance, so you have now 5
>times the voltage across it than before.
>At higher frequencies the impedance goes down again to nearly the same point
>as the beginning.
>I advise a good book:
>Joe D'Appolito: "Measuring Loudspeakers"
I think "bansuri" suffers from too vivid an imagination. EBG, it
sounds like something is loose. Perhaps the voice coil former has
become partially detached from the main cone or one of the voice coil
lead-in wires has broken. The fact that it breaks up as you press on
the cone highlights this probability.
Try connecting a dry cell (a single C cell should do) to it then press
the cone in an out. If it crackles you've found your problem.
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