Can fusing be hazardous?

[SteveS]

I found this on the JBL site:

Should I fuse my speakers? JBL does not recommend fusing loudspeakers. A fuse may blow with a signal that would not damage the speaker, but it can also pass a signal that can damage the speaker. To protect your system, JBL advises using adequate, clean amplifier power and watch for amplifier clipping. Add a limiter to your system to electronically limit any potentially damaging transients. Some JBL Professional speaker systems include SonicGuard™, a system that actively protects drivers from excess power.

How can a fuse pass a signal that could damage a speaker?

[dynaco_dan]

>I found this on the JBL site:

>

>Should I fuse my speakers? JBL does not recommend fusing

>loudspeakers. A fuse may blow with a signal that would not

>damage the speaker, but it can also pass a signal that can

>damage the speaker. To protect your system, JBL advises using

>adequate, clean amplifier power and watch for amplifier

>clipping. Add a limiter to your system to electronically limit

>any potentially damaging transients. Some JBL Professional

>speaker systems include SonicGuard™, a system that actively

>protects drivers from excess power.

>

>How can a fuse pass a signal that could damage a speaker?

Hi Steve;

The file you copied to your page does not open.

Yes, you should fuse your speakers!

Now that I have said that, if your speakers have another means of self protection, the manufacturers have already done the engineering for you.

I can't comment on JBL's, "SonicGuard", I know nothing about it.

We can only talk about fusing our older classic speakers with the ways and means at hand.

Unless a member or manufacturer designs something solid state that will replace our recommended fuses, which can happen, and then a fuse can eliminated, maybe.

[soundminded]

Using a fuse or circuit breaker to protect an electrical device (including wire) from carrying so much current it would be damaged or destroyed is common to many if not most electrical circuits. The principles are pretty straightforward. What isn't is the data from the manufacturer you would need to properly fuse your loudspeaker.

In principle, every electrical device has a maximum time/current curve, that is the amount of current it can safely handle for a given period of time. So a transformer or motor which might handle a few hundred amps during a brief startup period might only handle a few dozen amps while operating continuously. This is usually plotted on log/log paper so that it is easy to see. The art of protecting these devices is to select the right upstream series element which can be easily and cheaply replaced such as a fuse or reset such as a circuit breaker. The protective device also has a time/current curve beyond which it is intended to open the circuit by melting in the case of a fuse element or activating a solenoid operated switch in the case of a circuit breaker. Choosing the right one is merely a process of choosing one whose time/current curve is to the left and below (less current for a given time) than the device to be protected. If you can't find one device which meets this criteria, then two or more in series might be required such as a slow blow at a lower amperage and a fast blow at a higher amperage. Because loudspeakers handle different frequencies and their impedence is frequency dependent, it is possible that the maximum safe current is a matter of frequency as well. Therefore, it is safest to select fuses for the worst case. It is better to have a fuse blow at too low an amperage than to have the driver damaged because the fuse didn't blow being rated at too high an amperage. There's an old joke among TV repair technicians that a three hundred dollar picture tube protected a ten cent fuse. So that is how choosing the wrong fuse or combination of fuses will allow a speaker to be damaged. And of course, each driver has different limits than others in the same system so for the best protection meaning the most power available for each individual driver, it would be best if each is fused separately. BTW, the impedence of the fuse itself is so low in comparison to the rest of the circuit that it has no audible effect on performance, words to the contrary of some "audiophiles" notwithstanding.

[dynaco_dan]

>Using a fuse or circuit breaker to protect an electrical

>device (including wire) from carrying so much current it would

>be damaged or destroyed is common to many if not most

>electrical circuits. The principles are pretty

>straightforward. What isn't is the data from the manufacturer

>you would need to properly fuse your loudspeaker.

>

>In principle, every electrical device has a maximum

>time/current curve, that is the amount of current it can

>safely handle for a given period of time. So a transformer or

>motor which might handle a few hundred amps during a brief

>startup period might only handle a few dozen amps while

>operating continuously. This is usually plotted on log/log

>paper so that it is easy to see. The art of protecting these

>devices is to select the right upstream series element which

>can be easily and cheaply replaced such as a fuse or reset

>such as a circuit breaker. The protective device also has a

>time/current curve beyond which it is intended to open the

>circuit by melting in the case of a fuse element or activating

>a solenoid operated switch in the case of a circuit breaker.

>Choosing the right one is merely a process of choosing one

>whose time/current curve is to the left and below (less

>current for a given time) than the device to be protected. If

>you can't find one device which meets this criteria, then two

>or more in series might be required such as a slow blow at a

>lower amperage and a fast blow at a higher amperage. Because

>loudspeakers handle different frequencies and their impedence

>is frequency dependent, it is possible that the maximum safe

>current is a matter of frequency as well. Therefore, it is

>safest to select fuses for the worst case. It is better to

>have a fuse blow at too low an amperage than to have the

>driver damaged because the fuse didn't blow being rated at too

>high an amperage. There's an old joke among TV repair

>technicians that a three hundred dollar picture tube protected

>a ten cent fuse. So that is how choosing the wrong fuse or

>combination of fuses will allow a speaker to be damaged. And

>of course, each driver has different limits than others in the

>same system so for the best protection meaning the most power

>available for each individual driver, it would be best if each

>is fused separately.

BTW, the impedence of the fuse itself is

>so low in comparison to the rest of the circuit that it has no

>audible effect on performance, words to the contrary of some

>"audiophiles" notwithstanding.

Hi there;

Great write-up as usual.

The above information is maybe more formally worded than how I may have said it, but it is all absolutely true, except with my comment on the following regarding the ending sentence only.

It was well documented way back, perhaps back into the '60's, several decades ago anyways, about the damping factor being affected by the insertion of a resistive fuse.

There is no doubt, that there is a small resistance or added load, to the amplifiers circuit, but it was small and only mentioned on occassional writings.

The Audio Amatuer had an article or two on this subject, if I remember correctly.

It did have, in theory, and it was possible to measure the differences, with the knowledge and equipment at that time, the effects of inserting a fuse inline with a speaker.

I don't remember a lot about it, but that was even before, "magic cables".

As a sidenote, please refer to the writings of, AVA.COM, for critical comments on, "magic cables".

Capacitive, resistive and inductive, "magic cable", cable problems also.

The point is, that is factual information, but in the whole picture of things, all normal fast blow and slow blow fuses have a resistance, and that is a fact that can't be disputed.

Can we generally hear it?

Bypassing a fuse may be audible, my hearing isn't up that challenge anymore.

Someone with more technical skills and equipment, may want to persue the sound and measurement difference of inserting or not a fuse and type of fuse.

Do we ignore the facts and still fuse our speakers?

Yes we do, the overall loss or distortion of inserting a fuse, and any effect it has on the damping factor, far outways the sickening feeling of a $50 - $200.00 or even not available, tweeter, mid or woofer or all, biting the dust, or not.

Personal choice time.

What can we do to eliminate this loss or distortion?

Nothing, that I am aware of, at the present, with the state of the old technology fast blow and slow blow fuses.

Perhaps there maybe, just around the corner, a perfect safety valve, that has zero insertion loss and is electrically neutral.

At the present time, slow blow fuses, which, are slightly worse than fast blow fuses are our options.

This is really hair splitting, factual, but not worth the continuation of further discussion.

The reason I just made that statement, is, because it is too small a detail, in the whole picture of things, that we are unable to eliminate, at present.

The source, pre-amp, amplification, speaker cables, internal speaker wires, crossover components, the enclosures, the drivers themselves and of course our listening environment, also play a part as well.