Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83 based; site hound.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxj!houxm!hound!rfg From: rfg@hound.UUCP (R.GRANTGES) Newsgroups: net.audio Subject: Re: Speaker Fusing - While we're on the subject ... Message-ID: <826@hound.UUCP> Date: Fri, 11-Jan-85 13:56:10 EST Article-I.D.: hound.826 Posted: Fri Jan 11 13:56:10 1985 Date-Received: Sat, 12-Jan-85 07:12:56 EST References: <271@olivej.UUCP>, <10834@watmath.UUCP> Organization: AT&T Bell Labs, Holmdel NJ Lines: 63 [!] Oh boy! Here we go again on a subject that ought to produce a megabyte of traffic at least. That is because speaker fusing is both art and science and is controversial to boot. Some say - don't fuse at all because it introduces series resistance into your speaker lead (bad) and one that some claim is nonlinear (worse). Besides, they point out, by the time any self-respecting fuse will have acted, your speakers will have 'gone west.' Others, concerned about their investment, which is often as much or more than they have in all their equipment put together, say - Consider the possible sources of trouble. Many things could go wrong and fusing can help on some of them. For example, you could have a large sustained overload at a low frequency (say a ground connection comes off and you get 60 hertz hum at high level). This will eventually cook your woofers even with all the air they are blowing around. In this case you fuse for the maximum rated power of the woofer or (if its less) the amp (use the relation: power = I**2 R where R is resistance of the speaker (assume equal to the rated impedance (like 8 ohms)) so that I = squareroot of P/R). The result is usually a large current (e.g.4 amps is 128 watts in 8 ohms). Fuses with this sort of capacity generally have pretty low values of resistance and can be neglected if one takes care that the fuse clip connection itself does not introduce worse resistance. I never heard of "Monster Fuses", bet that will be the next big thing in Audio. Others, noting that this may help woofers but will blow hell out of ye average tweeter, may wish to fuse for the long term power rating of their tweeters, if they can find out what it is. When they do find out, they are generally depressed to discover it is only a few watts and so abandon this line.(Biamping can help here). Transients can blow out the spiders, surrounds, cones ,or what have you of any speaker regardless of fuses - if a big enuf transient can be generated. Speaker design is important also. For instance, horn loaded speakers can be pretty rugged. I know of a case where an Altec 800C (extremely sensitive, normal room volume from 100 milliwatts or less) was hit with a 100 volt step function (where millivolts were usually found in the preamp) due to an exploring screwdriver. This through a 35 watt tube amp in an apartment produced an explosion so loud the neighbors called the fire department. Person in bedroom fell out of bed. Building started to be evacuated. No damage to speaker. Lastly, there are other approaches. Best I know ofDavid Hafler's design in the late model amps under the Dyna name. I forget what it was called, but it was a circuit that you could set to some specified power level less than the amps maximum. If a signal exceeded the preset power level, the amps gain would be reduced to bring the power back in line. The time required to do this varied inversely with the magnitude of the overload. Hence, musical transients could use the amps full power, but real overloads get nipped in the bud. I use a Dyna Stereo 416 to drive Altec A-7's for sound reinforcement in outdoor theaters. This circuit makes it possible, since the tweeters blow at 15 watts or so and I keep hitting the speakers with 200 watt peaks (no fuses). A final word: People with big amplifiers shouldn't live in glass houses. -- "It's the thought, if any, that counts." Dick Grantges hound!rfg