jmsellens@watmath.UUCP (John M Sellens) (01/11/85)
The original article didn't ask, but I will. How does one go about
determining what size of fuse to put on your speakers? I've been
wondering about this for a while now, but I've never seen any ideas
on the topic.
Anybody care to enlighten me?
Much obliged!
John Sellens
UUCP: {decvax|utzoo|ihnp4|allegra|clyde}!watmath!jmsellens
CSNET: jmsellens%watmath@waterloo.csnet
ARPA: jmsellens%watmath%waterloo.csnet@csnet-relay.arparfg@hound.UUCP (R.GRANTGES) (01/11/85)
[!] 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 of <was> David 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
pmr@drutx.UUCP (Rastocny) (01/13/85)
<> I agree with Dick on the subject of fuses. There are two camps: those that fuse and those that do not. I belong to the latter camp. My power amp, except for the line, has no fuse. Fuses are nonlinear resistors when they become warm, like when your music is played loud. And since most people I know buy a stereo to play their music loud, they listen to this nonlinear fuse in combination with their music. So what does a fuse sound like? That's a good question. I have never set up a deliberate listening session to observe a fuses effects. I removed my fuses in the process of beefing up the supply and output device wiring. I am a firm believer in the KISS principle and believe that fuses are NOT as simple as they appear to be on the surface. I also believe that the average person with a receiver and speaker selector switch in series with the speakers will never notice the effects of removing the fuse without first removing the selector switch. Fuses can hide in all sorts of places: Hafler puts them on the wiring between the main supply filters and the PC boards for each channel AND on the line (5 fuses total on the supply). Then they fuse each of the speaker leads (2 more, for a total of 7). Is all this fusing necessary? Yes and no. Some engineers believe in making an amplifier user-mistake proof (people may short leads out and try to plug is interconnect cables with the amplifier on and speakers connected, etc.). All of this degrades the sound in some way. So what happens when you defeat the most of the fuses and speaker protection circuitry (leaving only the line fuse) and something goes wrong with the amplifier? The worst thing that could happen if you don't make the above mistakes is that an output device or bridge may die and take the main fuse out. Before the fuse goes, it may send a large enough DC pulse to the woofer to take out its voice coil and possibly those of the other drivers. The line fuse may not react fast enough to the surge and the surge may take some of the traces on the pc board. So why do I risk it? I feel that it's a small risk. Life is made up of many risks and compromises. Without taking some risks, you never get anywhere. In the case of fidelity, you never know what you're missing until you take the fuses out and see if it makes a difference. I know that when I finished the wiring and fuse mod I made on my amp, the system sounded TOTALLY different. How much of this difference the removal of the fuses contributed is not known. One other thing to remember is that a fuse cannot degrade the sound any more than the other pieces of equipment in the reproductive chain already have. My chain is highly already refined (esoteric wires, cables, internal speaker wiring, etc.). Those of you with receivers will probably never hear the benefits of removing fuses. Those of you with higher end equipment probably will. I'd go for it. After all, I enjoy listening to music, not fuses. Yours for higher fidelity, Phil Rastocny AT&T-ISL ihnp4!drutx!pmr
herbie@watdcsu.UUCP (Herb Chong [DCS]) (01/13/85)
I might mention at this point that there are some speaker
manufacturers, notably B&W and KEF, that use electronic protection of
the drivers. They have electronics inside the speaker that measure and
approximate the power handling capabilities of the drivers and activate
relays when that capacity is exceeded. I know that MY relays in MY B&W
DM7Mk2's do not have as many problems as fuses and, although not
perfect, protect my speakers far better than fuses while affecting the
sound far less. I agree with Phil's statement that speaker selector
switches are the pits. I have a $1200 integrated amplifier that had
arcing across the contacts until I changed them to heavy duty 15amp
microswitches. I believe that the disadvantages of fused speakers
outweigh the advantages.
Herb Chong...
I'm user-friendly -- I don't byte, I nybble....
UUCP: {decvax|utzoo|ihnp4|allegra|clyde}!watmath!water!watdcsu!herbie
CSNET: herbie%watdcsu@waterloo.csnet
ARPA: herbie%watdcsu%waterloo.csnet@csnet-relay.arpa
NETNORTH, BITNET: herbie@watdcs, herbie@watdcsu