How Choose Speaker Fuse?
Theodore R. Goodman
I'm building a speaker, and I don't know what fuse value to use.
The lowest-power component of the speaker is the woofer, rated at 60W RMS,
85W peak.
What sort of ampere rating do I want? Should it be a slow or fast
fuse?
Kurt Strain
: I'm building a speaker, and I don't know what fuse value to use.
: The lowest-power component of the speaker is the woofer, rated at 60W RMS,
: 85W peak.
: What sort of ampere rating do I want? Should it be a slow or fast
: fuse?
Consider not using a fuse. None of the best speakers I've auditioned had them,
and it would be nice to protect specially modified selected drivers costing
about $300 apiece.
The last speaker I had that used a fuse was an inexpensive pair of B&W's.
I fried the tweeters with a low power Dynaco tube amp. The fuses remained
blissfully intact.
Even the B&W 801 with it's enormous power handling capability used to have a
special protection circuit. I believe they have now discontinued its use.
I modified my old B&W's by shorting the fuse. It resulted in improved
performance. I know it served little useful purpose. For DC problems,
you probably have a fuse in your amp's output. That should be enough for
practical purposes.
If you must have a fuse for this driver, a typical one might be a 2-amp fast
blow. Slow blow fuses are not protecting anything. A 1-amp fuse is probably
more prudent being the average loud music only puts out maybe a couple of
watts on average, much more for brief peaks, too brief to blow the fuse.
But a 1-amp might blow too soon for you so stock up. My old amp's speaker
fuses are 2-amps, I think.
Morpheus
Thus spake Theodore R. Goodman (tgo...@eis.calstate.edu)...
>
> I'm building a speaker, and I don't know what fuse value to use.
> The lowest-power component of the speaker is the woofer, rated at 60W RMS,
> 85W peak.
> What sort of ampere rating do I want? Should it be a slow or fast
> fuse?
>
A=SQRT(P/i)
where A is the fuse amperage
SQRT is a Square root
P is the power of the woofer in Watts
i is the impedance of the woofer in ohms
Then go to Radio Shack and get the fast-blow 1 1/4"x1/4" fuse that has the
value from the above equation, or the next value below it. Using this system
I've cranked Amps way too big for my speakers and blown 4 or 5 fuses but
I have yet to blow a woofer on a fused speaker.
I hope this helps.
By the way I still need plans for a mixer and an equalizer :)
Breton Bienvenue
V023...@ubvms.cc.buffalo.edu
Suny At Buffalo
Bertram Walsh
>The last speaker I had that used a fuse was an inexpensive pair of
>B&W's. I fried the tweeters with a low power Dynaco tube amp. The
>fuses remained blissfully intact.
Curious. My old-but-still-good B&W DM6's have 2.5A main fuses and 315
mA fuses for the tweeters. An inadvertent attempt of mine to fry the
tweeters took out their fuses right away (but not the 2.5As), saving
the tweeters. I lose one or two pairs of 2.5As a year to bad power-
line transients and I figure that on some of those occasions I would
have lost the woofers or midrange had the speakers not been fused.
>Even the B&W 801 with it's enormous power handling capability used to
>have a special protection circuit. I believe they have now
>discontinued its use.
Curiouser. Never mind the enormous power-handling capability; consi-
der the price of a pair of the speakers.
>I modified my old B&W's by shorting the fuse. It resulted in
>improved performance. I know it served little useful purpose. For DC
>problems, you probably have a fuse in your amp's output. That should
>be enough for practical purposes.
Suus cuique mos, I guess. How greatly was the performance improved,
and in what way?
>If you must have a fuse for this driver, a typical one might be a
>2-amp fast blow.
Ted Goodman (original poster) said his woofer had an 85W peak wattage
rating. I^2 R (assuming 8 ohms) says that's about 3.26A. Why not
then a 3A fuse (fast-blow, of course), which would protect a little
below the rated peak wattage? If the fuse really does degrade the
sound, the higher-current fuse presumably has less resistance and thus
presumably less undesirable effect.
Bertram Walsh | "A Walzer von Strauss is ma
Dep't of Mathematics | liaba wia a Symphonie von
Rutgers University | Brahms."
New Brunswick NJ 08903-2101 USA | -- A. Bruckner