Xref: utzoo rec.audio:14461 sci.electronics:7352
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From: ingoldsb@ctycal.COM (Terry Ingoldsby)
Newsgroups: rec.audio,sci.electronics
Subject: Re: Question re: Speaker Fuse Sizing
Summary: Put a resistor in parallel
Message-ID: <426@ctycal.UUCP>
Date: 1 Aug 89 19:00:36 GMT
References: <30238@ucbvax.BERKELEY.EDU>
Organization: The City of Calgary, Ab
Lines: 37

In article <30238@ucbvax.BERKELEY.EDU>, jbier@janus.berkeley.edu (Jeff Bier) writes:
> The JBL's are rated for 120 watts continuous power.
> 
> In the past few months, two tweeters on the JBL's have been
> blown, apparently in the same way, but at different times.
> 
> I want to place fuses on the speakers to prevent this from
> happening again.  Given that the speakers' power rating is
> probably assuming some kind of broadband (music) signal, can
> anyone give me a reliable method for selecting a fuse size
> small enough to protect the tweeters, and large enough so

I seem to recall that tweeters are usually rated at about 1/10
the power of the woofers in most systems.  You can figure it
out from that.  (In other words, only 10% of the energy in
music occurs above 5 KHz).  If you decide to fuse all the
speakers (including the woofer), put a 100 ohm resistor in
parallel with fuse so that if it blows the fuse the amp will
still have a load.  

Since fuses are cheap compared to tweeters, why not start
small and gradually increase the value until the fuses just
stop blowing at maximum listening values.

If you are really serious about this, there are a number of
active circuits (ie. with semiconductors, power supplies) that
are much more effective than fuses.  

By the way, driving an amp too hard (so that it clips) sends
lots of high energy high frequency harmonics straight to
the tweeters.  Thus an underpowered amp (in a given application)
is good at blowing even high power speaker systems.

-- 
  Terry Ingoldsby                       ctycal!ingoldsb@calgary.UUCP
  Land Information Systems                           or
  The City of Calgary         ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsb