Archived from groups: rec.audio.pro (More info?)
"Mike Rivers"
Phil Allison
>
> > [the crossover network] - it has a 10
> > dB peak in the output at 1.4 kHz ?? I notice that the wood surface
next
> > to a 33 ohm, 10 watt resistor is scorched - this resistor is in
parallel
> > with an inductor so has to be disconnected to do a test - it tests
OPEN !!
> So I replace the resistor and the response is now as expected. But how
did
> > it ever burn out like that ??
> >
> > Running a 1.4 kHz sine wave into the x-over with NO load connected
provides
> > the answer - when driven at even moderate power levels at or near 1.5
kHz,
> > the 33 ohm resistor starts to SMOKE !! With no load the x-over
becomes a
> > series resonant circuit that *magnifies* the drive voltage by several
times
> > at 1.5 kHz so that 33 ohm resistor cops about 10 times more power than
it
> > ever would normally.
>
>
> It would help to have a schematic for reference.
** Help who ? Not you that is for sure.
> The first question
> that came to mind was "how can you have a circuit with the load
> disconnected,
** Errr - happens whenever the diaphragm fails open.
> but then I thought about variations in crossovers. I've
> seen crossover designs which have a series L-C circuit
** With no load a basic LC (ie 12dB/oct ) crossover becomes a *series
resonant circuit*.
The input Z drops to near zero ohms at the resonant frequency while the
input voltage is magnified a great many times at the output.
> What did the peak look like with the speaker connected and the
> resistor disconnected?
** Errr - as stated above it was 10 dB.
>
> But the real question is, why did the tweeter blow in the first place?
** Separate issue entirely.
The original diaphragm had lasted for many years of live PA work and so did
the replacement after the resistor change.
............ Phil
"Mike Rivers"
Phil Allison
>
> > [the crossover network] - it has a 10
> > dB peak in the output at 1.4 kHz ?? I notice that the wood surface
next
> > to a 33 ohm, 10 watt resistor is scorched - this resistor is in
parallel
> > with an inductor so has to be disconnected to do a test - it tests
OPEN !!
> So I replace the resistor and the response is now as expected. But how
did
> > it ever burn out like that ??
> >
> > Running a 1.4 kHz sine wave into the x-over with NO load connected
provides
> > the answer - when driven at even moderate power levels at or near 1.5
kHz,
> > the 33 ohm resistor starts to SMOKE !! With no load the x-over
becomes a
> > series resonant circuit that *magnifies* the drive voltage by several
times
> > at 1.5 kHz so that 33 ohm resistor cops about 10 times more power than
it
> > ever would normally.
>
>
> It would help to have a schematic for reference.
** Help who ? Not you that is for sure.
> The first question
> that came to mind was "how can you have a circuit with the load
> disconnected,
** Errr - happens whenever the diaphragm fails open.
> but then I thought about variations in crossovers. I've
> seen crossover designs which have a series L-C circuit
** With no load a basic LC (ie 12dB/oct ) crossover becomes a *series
resonant circuit*.
The input Z drops to near zero ohms at the resonant frequency while the
input voltage is magnified a great many times at the output.
> What did the peak look like with the speaker connected and the
> resistor disconnected?
** Errr - as stated above it was 10 dB.
>
> But the real question is, why did the tweeter blow in the first place?
** Separate issue entirely.
The original diaphragm had lasted for many years of live PA work and so did
the replacement after the resistor change.
............ Phil
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