Fuse in series with loudspeaker
Svante
with the loudspeaker. It is a nice thought, since the drivers in a
system could be individually fused. Tweeters would love that :-) . But
I have also heard that this would induce distorsion since the metal in
the fuse would have to become heated (otherwise it would never melt)
and thus possibly inducing a signal dependent resistance in series
with the speaker.
Is this a problem, or is it a too small effect?
Sofie
"Svante" <svante_g...@hotmail.com> wrote in message
Svante:
It is a much, much smaller effect that a burnt out voice coil in an
expensive driver.
This is not an issue unless you think you can hear the difference.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
.
.
.
.
Rich Andrews
news:93d2ebc6.04021...@posting.google.com:
Ask yourself a question or two. Which is cheaper to replace. A fuse or a
driver or two? Even if there was a difference in the sound, (which there
isn't BTW), wouldn't that safety factor be worth it?
r
--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.
Barry Mann
A fuse is not a perfect protector for a loudspeaker, but it is better
than nothing. The problem is in picking the correct value. The maximum
power your speaker can handle is frequency dependent, but the fuse
response does not vary much over the audio band. If you use only one
fuse per channel, a fuse that will not blow due to woofer current draw
will not offer much protection for the tweeter.
In most cases, for home use, it's the tweeters that get toasted. Many
manufacturers, announced or not, are now adding automatic reset
protective devices in the tweeter section of the crossover. We've found
them to be very effective. Check with your speaker manufacturer to see
if your speakers are already protected.
Some users can hear the fuses, others cannot. Your milage may vary.
One very easy way to try things out is to purchase an "inline fuse
holder" (as the name implies it's just a fuseholder with wires
attached). It's not usually a stereo store item, try electronic parts
supply houses or automotive supply shops. Splice a fuse holder into
each of your speaker lines. Note that you will be able to hear poor
splices.
I usually use fuses as an educational device. For dim, macho customers
I'll recommend a fuse that is slightly smaller than optimum. This will
afford somewhat better protection, but since it will blow aggressively,
the customer will learn to keep things down to a dull roar. "Smart" dim
wits figure this out and use a larger fuse. In one case I found a slug
of 1/4" brass rod where the fuse used to be.
The best protective device is one that would track voice coil
temperature, keeping it with in safe limits. A recent paper in the AES
Journal describes a model for calculating voice coil temperature. I've
seen some manufacturers use what is essentially an analog computer to
track voice coil temperature and mute or disconnect the tweeter when
threatened. Unfortunately, the relay used in this type of circuit often
fails after a few years.
-----------------------------------------------------------
spam: u...@ftc.gov
wordgame:123(abc):<14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13> (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------
Tim Schwartz
For what it is worth, I use fuses on all of my speakers. I suggest
only 'fast blow' type, and as small a value as you can get away with. I
have found that a 2 amp fuse is fine for my listening habits. I figured
this out by starting with a 1 amp fuse that I blew a couple time a
month, so I then tried a 1.5A which still blew when I was listening as
loud as I ever do. The 2 amp fuses almost never blow, once or twice a
year at most, and that I can live with. I have not noticed a
deterioration of sound quality.
The fuse value that will work for you depends on your amplifier power,
speaker efficiency, and listening habits. I suggest starting small and
working up by 1 or half amp values from a starting point of your
choice. If they never blow, then go lower.
Regards,
Tim Schwartz
Bristol Electronics
Arny Krueger
news:40335C71...@worldnet.att.net
> Hello all,
>
> For what it is worth, I use fuses on all of my speakers. I suggest
> only 'fast blow' type, and as small a value as you can get away with.
> I have found that a 2 amp fuse is fine for my listening habits. I
> figured this out by starting with a 1 amp fuse that I blew a couple
> time a month, so I then tried a 1.5A which still blew when I was
> listening as loud as I ever do. The 2 amp fuses almost never blow,
> once or twice a year at most, and that I can live with. I have not
> noticed a deterioration of sound quality.
That's exactly the technique I use, and it seems to work.
> The fuse value that will work for you depends on your amplifier power,
> speaker efficiency, and listening habits. I suggest starting small
> and working up by 1 or half amp values from a starting point of your
> choice. If they never blow, then go lower.
Yup. It also helps to look at the *final* value you settle on. If it is too
large, which might be something like a 3 amp fuse in series with a small
tweeter, it's probably predicting the early demise of the driver.
Svante
> In <93d2ebc6.04021...@posting.google.com>, on 02/17/04
> at 02:44 PM, svante_g...@hotmail.com (Svante) said:
>
> >I see every now and then people talking about putting fuses in series
> >with the loudspeaker. It is a nice thought, since the drivers in a
> >system could be individually fused. Tweeters would love that :-) . But
> >I have also heard that this would induce distorsion since the metal in
> >the fuse would have to become heated (otherwise it would never melt)
> >and thus possibly inducing a signal dependent resistance in series
> >with the speaker.
>
> >Is this a problem, or is it a too small effect?
>
> A fuse is not a perfect protector for a loudspeaker, but it is better
> than nothing. The problem is in picking the correct value. The maximum
> power your speaker can handle is frequency dependent, but the fuse
> response does not vary much over the audio band. If you use only one
> fuse per channel, a fuse that will not blow due to woofer current draw
> will not offer much protection for the tweeter.
But the power in the voice coil resistance would be I^2*R, right? IMO
opinion that is what would melt a voice coil. So a fuse in series with
each *driver* (not the entire system) would do a pretty good job? What
would be mismatched is probably the thermal time constant (the fuse
will melt first, which is good, due to a shorter thermal time
constant).
> In most cases, for home use, it's the tweeters that get toasted. Many
> manufacturers, announced or not, are now adding automatic reset
> protective devices in the tweeter section of the crossover. We've found
> them to be very effective. Check with your speaker manufacturer to see
> if your speakers are already protected.
They're not, I built them myself... :-)
> Some users can hear the fuses, others cannot. Your milage may vary.
Mmm... Some claim to hear cables, so I am not surprised. But the fuse
effect is possibly larger than the cable effect, since there is a
piece of wire that actually is near melting at full power. The
question is how much larger. I think I'll do an experiment. A power
amplifier, a tone generator, a 8 ohm resistor and a 1 amp fuse.
Measure the voltage over the resistance and see if there is any
distorsion. If so does it increase with power. Hmm...
> I usually use fuses as an educational device. For dim, macho customers
> I'll recommend a fuse that is slightly smaller than optimum. This will
> afford somewhat better protection, but since it will blow aggressively,
> the customer will learn to keep things down to a dull roar. "Smart" dim
> wits figure this out and use a larger fuse. In one case I found a slug
> of 1/4" brass rod where the fuse used to be.
I *love* your pedagogy! :-)
> The best protective device is one that would track voice coil
> temperature, keeping it with in safe limits. A recent paper in the AES
> Journal describes a model for calculating voice coil temperature. I've
> seen some manufacturers use what is essentially an analog computer to
> track voice coil temperature and mute or disconnect the tweeter when
> threatened.
Mmm, such an analog computer would be a fuse, right? It is a piece of
wire that takes the same amount of current as the voice coil, so the
(steady state) temperature of the fuse wire should follow the (steady
state) temperature of the voice coil. So when the coil is near
meltdown the fuse will be too, and melt, if the margins are right. The
only hard thing would be to match the thermal time constants of the
fuse/coil.
> Unfortunately, the relay used in this type of circuit often
> fails after a few years.
Yes, it's a pity that mercury is poisonous.
Bob Urz
The best protection circuit ever made is the one between your ears.
If its malfunctioning, your in trouble.
Bob
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
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Barry Mann
at 06:03 AM, svante_g...@hotmail.com (Svante) said:
[ ... ]
>> A fuse is not a perfect protector for a loudspeaker, but it is better
>> than nothing. The problem is in picking the correct value. The maximum
>> power your speaker can handle is frequency dependent, but the fuse
>> response does not vary much over the audio band. If you use only one
>> fuse per channel, a fuse that will not blow due to woofer current draw
>> will not offer much protection for the tweeter.
>But the power in the voice coil resistance would be I^2*R, right? IMO
>opinion that is what would melt a voice coil. So a fuse in series with
>each *driver* (not the entire system) would do a pretty good job? What
>would be mismatched is probably the thermal time constant (the fuse
>will melt first, which is good, due to a shorter thermal time
>constant).
There are amplitude and frequency effects. High amplitude bass notes
(forcing large cone excursions) enhance cooling a bit. And the driver
construction details effect the cooling somewhat.
>> In most cases, for home use, it's the tweeters that get toasted. Many
>> manufacturers, announced or not, are now adding automatic reset
>> protective devices in the tweeter section of the crossover. We've found
>> them to be very effective. Check with your speaker manufacturer to see
>> if your speakers are already protected.
>They're not, I built them myself... :-)
Then a fuse per driver would be better than a single fuse per channel.
>> Some users can hear the fuses, others cannot. Your milage may vary.
>Mmm... Some claim to hear cables, so I am not surprised. But the fuse
>effect is possibly larger than the cable effect, since there is a
>piece of wire that actually is near melting at full power. The
>question is how much larger. I think I'll do an experiment. A power
>amplifier, a tone generator, a 8 ohm resistor and a 1 amp fuse.
>Measure the voltage over the resistance and see if there is any
>distorsion. If so does it increase with power. Hmm...
You are also inserting more connections. Connections are always a point
of mischief.
Be sure to test a range of fuses. Lower value fuses tend to have higher
resistance. Also, check to see how the fuse resistance changes with
temperature (of the fuse element).
>> I usually use fuses as an educational device. For dim, macho customers
>> I'll recommend a fuse that is slightly smaller than optimum. This will
>> afford somewhat better protection, but since it will blow aggressively,
>> the customer will learn to keep things down to a dull roar. "Smart" dim
>> wits figure this out and use a larger fuse. In one case I found a slug
>> of 1/4" brass rod where the fuse used to be.
>
>I *love* your pedagogy! :-)
>> The best protective device is one that would track voice coil
>> temperature, keeping it with in safe limits. A recent paper in the AES
>> Journal describes a model for calculating voice coil temperature. I've
>> seen some manufacturers use what is essentially an analog computer to
>> track voice coil temperature and mute or disconnect the tweeter when
>> threatened.
>Mmm, such an analog computer would be a fuse, right? It is a piece of
>wire that takes the same amount of current as the voice coil, so the
>(steady state) temperature of the fuse wire should follow the (steady
>state) temperature of the voice coil. So when the coil is near
>meltdown the fuse will be too, and melt, if the margins are right. The
>only hard thing would be to match the thermal time constants of the
>fuse/coil.
But, the fuse can't be frequency weighted. (True, you'll be using
different fuses for each driver.) Be sure to consider the effect of the
fuse resistance on your crossover.
So far I haven't encountered a speaker protection circuit that can foil
a determined user, but fuses are helpful.
[ ... ]
Sofie
"Barry Mann" <zz...@zzzz.zzz> wrote in message news:4032de09$2
>
> A fuse is not a perfect protector for a loudspeaker, but it is better
> than nothing. The problem is in picking the correct value. The
>
------------------
Barry Mann:
Yes, quite correct.
Furthermore the fuse is not "the foolproof answer" for protecting your
drivers from being driven harder that they can handle.... in my opinion,
the real usefulness of the fuse is to PROTECT the speaker voice coils from
being fryed if the amplifer has a catastofic power output stage failure and
the amp's protection circuitry doesn't activate or doesn't activate fast
enough thus preventing the amp's full DC power supply (high volts and amps)
rails from ending up on the speaker terminals.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Isaac Wingfield
svante_g...@hotmail.com (Svante) wrote:
There are some excellent amps that have a protection fuse inside the
feedback loop. That nicely deals with any nonlinearity due to heating,
but still gives protection to the woofer from a catastrophic event such
as an output device failure.
Tweeters have very low-mass wires, and generally do a fine job of
protecting your fuses, because they have a smaller time constant 8^}.
I have seen tweeter protection implemented with a pair of
appropriate-sized zener diodes in opposite polarity and in *series*,
placed across the tweeter. I think that should work, as their action
would be very fast. Near to the zener voltage, there would be some
nonlinearity.
Isaac
Barry Mann
at 05:19 AM, Isaac Wingfield <i...@witzend.com> said:
[ ... ]
>I have seen tweeter protection implemented with a pair of
>appropriate-sized zener diodes in opposite polarity and in *series*,
>placed across the tweeter. I think that should work, as their action
>would be very fast. Near to the zener voltage, there would be some
>nonlinearity.
Hopefully, there is some form of current limiting between the zener's
and the power amplifier. Otherwise, when a diode turns on there will be
a brief struggle to see who has the most beef -- the amplifier or the
diode.
An advantage and disadvantage of the zener approach is that they are
fast.
An old approach is to insert an incandescent lamp in series with the
speaker. When cold, the lamp's resistance is very low. As the speaker
current increases, the lamp begins to turn on and the series resistance
increases dramatically, thus limiting the current. It's clever, but the
choice of lamp is somewhat limited and the switch point may not match
the speaker's needs very well. There are more modern devices, one trade
name is "Polyswitch," that are commonly used to protect tweeters. They
are available in a variety of sizes and their switching characteristics
are well suited for protecting tweeters.
Even though a Polyswitch provides very good protection, I've seen users
abuse their speakers to the point that they blow-up the tweeter and the
Polyswitch. It usually takes a few weeks to do this, but there is a
limit to the Polyswitch's good humor. One shortcomming to the
Polyswitch approach is that, when the limit is reached, the tweeter
output is reduced. Some customers interpret this as a need to turn
things up a bit to compensate for the loss of trebble. Once the
situation reaches that point, it's a downward spiral.
Sofie
"Isaac Wingfield" <i...@witzend.com> wrote in message
news:isw-14E0DA.2...@netnews.comcast.net...
> There are some excellent amps that have a protection fuse inside the
> feedback loop. That nicely deals with any nonlinearity due to heating,
> but still gives protection to the woofer from a catastrophic event such
> as an output device failure.
>
> Tweeters have very low-mass wires, and generally do a fine job of
> protecting your fuses, because they have a smaller time constant 8^}.
.
>
> Isaac
----------------------
Isaac Wingfield:
The good news about tweeters and mid-range is that the speaker's cross-over
network will usually have a capacitor in series with the driver and thus
protecting it from long term DC ........ while thumps can still get
through, usually tweeters fail from being over-driven... particularly with
distortion artifacts if the amp is driven into distortion or is just too
powerful for the speaker. As you indicated in your posting, the fuse
in-line from the amp to the speaker is primarily there to protect the woofer
from catastrophic amp failure since it's voice coil is "directly" (no
capacitor, maybe an inductor) connected to the amp.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-----------------------
.
.
.
.
Svante
> effect is possibly larger than the cable effect, since there is a
> piece of wire that actually is near melting at full power. The
> question is how much larger. I think I'll do an experiment. A power
> amplifier, a tone generator, a 8 ohm resistor and a 1 amp fuse.
> Measure the voltage over the resistance and see if there is any
> distorsion. If so does it increase with power. Hmm...
OK, so I did the experiment. It did not turn out quite as I wanted it
due to the equipment I got hold of, but it gives a rough idea about
the magnitude of these effects.
I hooked up the computer to an amplifier and a 500mA quickblow fuse in
series with 3.3 ohms. I meanured the voltage across the *fuse* (this
should reveal any distortion products even more). At 1kHz it turns out
that the 3rd harmonic is 60 dB down (0.1% distortion). In the feeding
signal it is 80 dB down, so there is a slight increase in the
distortion, but not very much to worry about. Across the resistor, the
distortion should be lower, presumably somewhere around 0.03%.
However, the resistance of the fuse increases with the current through
it, and just before it blows, the resistance was about 0.9 ohms. If I
connect a cold fuse to the multimeter it reads about 0.2-0.3 ohms.
This fits well with the melting point of silver which is some 960
degrees celsius, or four times the room temperature, measured in
kelvin. Since resistance is proportional to absolute temperature, the
resistance *should* increase by a factor four just before meltdown.
I also tried the same thing at 10 Hz, lower frequency should provoke a
higher distortion since the temperature more easily can follow the
fluctuations of the voltage. However, the amplifier I got hold of
appeared to have a problem with delivering the signal at these low
frequencies, the third harmonic is now 50 dB down, with the fuse
shorted. The most I can say is that the distortion is *less than*
-50dB or 0.3%. The resistance increase was the same as for 1kHz.
The increased resistance would IMO be the only reason to avoid using
ordinary fuses in series with the loudspeaker (regarding the
audibility). The distortion is low compared to other sources,
especially near the maximum output level of the speaker. A series
resistance of 1 ohm may alter the frequency response slightly of the
speaker, and thus make the fuse "audible". The difference will however
be small, and not certainly for the worse.
One more thing I learned. The fuse broke at about 1 ampére, even
though it was rated 500mA. I recall knowing this some time in the
past, but had forgotten about it. Fuses can take more than they
"state".
Opinions?
Sofie
> though it was rated 500mA. I recall knowing this some time in the
> past, but had forgotten about it. Fuses can take more than they
> "state".
>
> Opinions?
Svante:
Usually most brands and most types of Fast Blow fuses are specified by the
manufacturer to take 200% of rating for NO MORE than 5 seconds while the
Slow Blow version can take 200% of rating of AT LEAST 5 seconds and upwards
to 60 seconds or more.
Obviously higher amperage surges can take them out faster.
For purposes of protecting speaker voice coils from being fried by
malfunctioning amplifier circuitry..... the absolute value of the fuse is
not that critical...... usually a fast blow fuse rated between 2 to 5 amps
will do the trick for most home applications.
An old rule of thumb used while I was in the pro-audio installation
business, and not necessarily derived by a specific formula for specific
speakers and amplifier impedances... was 1 amp per 25 watts..... just a
rule of thumb in most applications... of course these values can be juggled
by the purist and the knit-pickers with their slide rules and scientific
calculators. A lot will depend of course on the installation and
listening habits..... peak watts produced, heavy thumping bass, etc. .....
as I said, not that critical....and as long as there is a fuse in there, it
will probably and hopefully melt before the woofer voice coil if the
amplifier fails.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
---------------------
.
.
.
.
Isaac Wingfield
zz...@zzzz.zzz (Barry Mann) wrote:
> In <isw-14E0DA.2...@netnews.comcast.net>, on 02/19/04
> at 05:19 AM, Isaac Wingfield <i...@witzend.com> said:
>
> [ ... ]
>
> >I have seen tweeter protection implemented with a pair of
> >appropriate-sized zener diodes in opposite polarity and in *series*,
> >placed across the tweeter. I think that should work, as their action
> >would be very fast. Near to the zener voltage, there would be some
> >nonlinearity.
>
> Hopefully, there is some form of current limiting between the zener's
> and the power amplifier. Otherwise, when a diode turns on there will be
> a brief struggle to see who has the most beef -- the amplifier or the
> diode.
The series capacitor in the crossover prevents DC from flowing, so the
only risk to the tweeter is from high-frequency transients. If 5 or 10
watt zeners are used, there's no problem.
> An advantage and disadvantage of the zener approach is that they are
> fast.
The advantage is clear. What is the disadvantage?
> An old approach is to insert an incandescent lamp in series with the
> speaker. When cold, the lamp's resistance is very low. As the speaker
> current increases, the lamp begins to turn on and the series resistance
> increases dramatically, thus limiting the current. It's clever, but the
> choice of lamp is somewhat limited and the switch point may not match
> the speaker's needs very well.
Also, it's rather nonlinear at levels far below those where it provides
any actual protection. Worse than a fuse, I suspect.
>There are more modern devices, one trade
> name is "Polyswitch," that are commonly used to protect tweeters. They
> are available in a variety of sizes and their switching characteristics
> are well suited for protecting tweeters.
I suspect the reason those are used in commercial speakers is that they
are less expensive than good zeners. I don't think they are superior, or
even equivalent, in terms of their actual performance.
Isaac
Isaac Wingfield
svante_g...@hotmail.com (Svante) wrote:
The time constant of the nonlinearity of a fuse is too long to show up
during a cycle of any audible frequency. It'll manifest as a higher
resistance during loud passages -- the effect will be like "turning down
the volume" a bit at hight levels. Whether or not it is noticeable is
another issue.
> The increased resistance would IMO be the only reason to avoid using
> ordinary fuses in series with the loudspeaker (regarding the
> audibility). The distortion is low compared to other sources,
> especially near the maximum output level of the speaker. A series
> resistance of 1 ohm may alter the frequency response slightly of the
> speaker, and thus make the fuse "audible". The difference will however
> be small, and not certainly for the worse.
>
> One more thing I learned. The fuse broke at about 1 ampére, even
> though it was rated 500mA. I recall knowing this some time in the
> past, but had forgotten about it. Fuses can take more than they
> "state".
If a fuse is expected to hold *forever* at its rated current, it's not
going to blow any too fast at only a 100% overload. To get anything like
"fast" action, you'll need to provide about 10X rated current.
There's a special variety of low-current fuse called an "instrument
fuse" with a very low time constant that's intended to protect
D'Arsonval meters. They are not cheap.
Isaac
TonyP
"Arny Krueger" <ar...@hotpop.com> wrote in message
news:atSdnQIty-2...@comcast.com...
too
> large, which might be something like a 3 amp fuse in series with a small
> tweeter, it's probably predicting the early demise of the driver.
Even the 2A is going to be too much for a tweeter alone, so if you fuse each
driver separately you just use a smaller fuse for the tweeter. 1A will
probably be more than sufficient for the average 8 ohm, 1" dome. Better to
use a polyswitch though.
TonyP.
Arny Krueger
> The time constant of the nonlinearity of a fuse is too long to show
> up during a cycle of any audible frequency.
The classic Greiner JAES article found a fair amount of nonlinear
distortion using typical-valued quick blow fuses and test signals in the
audio range.
Amplifier·Loudspeaker Interfacing 637611 bytes (CD aes4)
Author(s): Greiner, R. A.
Publication: JAES Volume 28 Number 5 pp. 310·315; May 1980
Abstract: Loudspeaker cables are investigated to determine if they exhibit
transmission-line characteristics. Lumped representations of cables are
suggested with consideration of the effects cable parameters might have on
the audio signal being transmitted. Interaction of the cable with the
amplifier, the loudspeaker, and other elements which may be part of the
amplifier·cable·loudspeaker circuit are treated.
>It'll manifest as a higher
> resistance during loud passages -- the effect will be like "turning
> down the volume" a bit at high levels.
That, too.
>Whether or not it is noticeable is another issue.
The Greiner article found 0.5 to 4% nonlinear distortion using 20 & 5000 Hz
test tones, in fuses in the 2-5 amp range. Power levels were just below
observed burn out of the fuse.
The article also pointed out that multiway speaker systems with fuses for
each driver tended to minimize these effects for pretty obvious reasons.
normanstrong
> "Isaac Wingfield" <i...@witzend.com> wrote in message
> news:isw-110295.2...@netnews.comcast.net
>
> > The time constant of the nonlinearity of a fuse is too long to
show
> > up during a cycle of any audible frequency.
>
> The classic Greiner JAES article found a fair amount of nonlinear
> distortion using typical-valued quick blow fuses and test signals in
the
> audio range.
>
> Amplifier·Loudspeaker Interfacing 637611 bytes (CD aes4)
> Author(s): Greiner, R. A.
> Publication: JAES Volume 28 Number 5 pp. 310·315; May 1980
>
> Abstract: Loudspeaker cables are investigated to determine if they
exhibit
> transmission-line characteristics. Lumped representations of cables
are
> suggested with consideration of the effects cable parameters might
have on
> the audio signal being transmitted. Interaction of the cable with
the
> amplifier, the loudspeaker, and other elements which may be part of
the
> amplifier·cable·loudspeaker circuit are treated.
Has anyone come across a loudspeaker protected by a positive tempco
resistor? These devices go from very low resistance to almost open
circuit over a very narrow temperature range.
Norm Strong
Svante
> news:isw-110295.2...@netnews.comcast.net
>
> > The time constant of the nonlinearity of a fuse is too long to show
> > up during a cycle of any audible frequency.
>
> The classic Greiner JAES article found a fair amount of nonlinear
> distortion using typical-valued quick blow fuses and test signals in the
> audio range.
>
> Amplifier·Loudspeaker Interfacing 637611 bytes (CD aes4)
> Author(s): Greiner, R. A.
> Publication: JAES Volume 28 Number 5 pp. 310·315; May 1980
Thanks, I'll have a look at this. I had the feeling that this must
have been examined by someone.
Barry Mann
>> Hopefully, there is some form of current limiting between the zener's
>> and the power amplifier. Otherwise, when a diode turns on there will be
>> a brief struggle to see who has the most beef -- the amplifier or the
>> diode.
>The series capacitor in the crossover prevents DC from flowing, so the
> only risk to the tweeter is from high-frequency transients. If 5 or
>10 watt zeners are used, there's no problem.
>> An advantage and disadvantage of the zener approach is that they are
>> fast.
>The advantage is clear. What is the disadvantage?
The zeners have a very sharp knee. The real enemy of the driver is
heat. Within reason, as long as the voice coil temperature remains
below the critical point, you can push the driver as hard as you want.
The zeners will limit the dynamics somewhat.
>> An old approach is to insert an incandescent lamp in series with the
>> speaker. When cold, the lamp's resistance is very low. As the speaker
>> current increases, the lamp begins to turn on and the series resistance
>> increases dramatically, thus limiting the current. It's clever, but the
>> choice of lamp is somewhat limited and the switch point may not match
>> the speaker's needs very well.
>Also, it's rather nonlinear at levels far below those where it
>provides any actual protection. Worse than a fuse, I suspect.
But, lamps are cheap and available.
>>There are more modern devices, one trade
>> name is "Polyswitch," that are commonly used to protect tweeters. They
>> are available in a variety of sizes and their switching characteristics
>> are well suited for protecting tweeters.
>I suspect the reason those are used in commercial speakers is that
>they are less expensive than good zeners. I don't think they are
>superior, or even equivalent, in terms of their actual performance.
I've found that, good protection or not, if the protection is "in your
face", customers don't like that and the protection is often defeated
by the customer and/or the product fares poorly in the word of mouth
network. The product could be technically robust, but fail in the
marketplace.
Barry Mann
at 06:02 PM, "normanstrong" <norman...@comcast.net> said:
[ ... ]
>Has anyone come across a loudspeaker protected by a positive tempco
>resistor? These devices go from very low resistance to almost open
>circuit over a very narrow temperature range.
In many respects that's what Polyswitches are. You can think of them as
a positive tempco resistor with a heater built-in. The heater gives
them a sharper knee. Their thermal mass also slows down the reset.
Peter Larsen
> A fuse is not a perfect protector for a loudspeaker, but it is
> better than nothing. The problem is in picking the correct value.
ValueS, acoustic research had some "dual" fuses on the marker some 20+
years ago, some kind of fast-slow combination, came with recommendation
of which to use with what AR speaker. I wonder what happened to that
product, it was a neat concept in my understanding of this.
Kind regards
Peter Larsen
--
*******************************************
* My site is at: http://www.muyiovatki.dk *
*******************************************
Peter Larsen
> I see every now and then people talking about putting fuses in series
> with the loudspeaker.
It is completely safe, the loudspeaker will protect the fuse from
damage.
> It is a nice thought, since the drivers in a
> system could be individually fused. Tweeters would love that :-) . But
> I have also heard that this would induce distorsion since the metal in
> the fuse would have to become heated (otherwise it would never melt)
> and thus possibly inducing a signal dependent resistance in series
> with the speaker.
> Is this a problem, or is it a too small effect?
The likely issues are: fuse impedance should possibly be included in the
cross-over math and the the additional contact surfaces and their
ability to degrade sound by corroding.
gregs
>In <aZrZb.353292$I06.3753091@attbi_s01>, on 02/20/04
> at 06:02 PM, "normanstrong" <norman...@comcast.net> said:
>
>
>[ ... ]
>
>>Has anyone come across a loudspeaker protected by a positive tempco
>>resistor? These devices go from very low resistance to almost open
>>circuit over a very narrow temperature range.
>
>In many respects that's what Polyswitches are. You can think of them as
>a positive tempco resistor with a heater built-in. The heater gives
>them a sharper knee. Their thermal mass also slows down the reset.
The turn on time is also slow. Might also mean they have less audible effect at lower volumes.
The right value is critical for it to protect.
greg
gregs
>Svante wrote:
>
>> I see every now and then people talking about putting fuses in series
>> with the loudspeaker.
>
>It is completely safe, the loudspeaker will protect the fuse from
>damage.
>
>> It is a nice thought, since the drivers in a
>> system could be individually fused. Tweeters would love that :-) . But
>> I have also heard that this would induce distorsion since the metal in
>> the fuse would have to become heated (otherwise it would never melt)
>> and thus possibly inducing a signal dependent resistance in series
>> with the speaker.
>
>> Is this a problem, or is it a too small effect?
>
>The likely issues are: fuse impedance should possibly be included in the
>cross-over math and the the additional contact surfaces and their
>ability to degrade sound by corroding.
Impedance is important, but using 1/2 A and higher, impedance is not
a factor. A 2 amp AGC has pretty low resistance. All connections in a system
shall be maintained over time with periodic maintenence!
greg
Svante
The 500mA fuse in my experiment had a resistance of about 0.9 ohms
just before melting. The resistance increases with temperature. If the
thread is of silver, the resistance should increase by a factor 4 just
before melting, based on the melting point of silver. The resistance
measured with a multimeter was 0.2-0.3 ohms (when the fuse was cold).
A resistance of 0.9 ohms could have *some* audible effect IMO, so in
some sense resistance is a (small) issue.
Karl Uppiano
The effect would be a form of audio compression. Voice coils also do this.
Fusing each driver separately helps, in much the same way as bi-wiring or
bi-amping sometimes helps.
John Fields
wrote:
>The 500mA fuse in my experiment had a resistance of about 0.9 ohms
>just before melting. The resistance increases with temperature. If the
>thread is of silver, the resistance should increase by a factor 4 just
>before melting, based on the melting point of silver. The resistance
>measured with a multimeter was 0.2-0.3 ohms (when the fuse was cold).
>A resistance of 0.9 ohms could have *some* audible effect IMO, so in
>some sense resistance is a (small) issue.
---
Why do you think the fusible material is silver?
--
John Fields
Svante
Erhh... I don't know. I've always thought it was. What is it?
Sofie
It is more like lead or tin or a combination of low melt point metals.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
"Svante" <svante_g...@hotmail.com> wrote in message
John Fields
wrote:
---
A zinc alloy, according to
http://www.littelfuse.com/PDFs/TechBriefs/TB98-004.pdf
but it seems to refer to their fuses with ribbon (instead of wire)
elements.
Just to check it out, if we look at silver with a melting point of 962°C
and an alpha (temperature coefficient of resistance) of 0.003819, we can
calculate the resistance at the melting point with
Rt = Rref ( 1 + (alpha (t - tref)))
Where
Rt is the resistance at the target temperature, in ohms
Rref is the resistance at the reference temperature (ambient), in ohms
alpha is 0.003819
t is the target temperature in degrees Celsius
tref is the reference temperature in degrees Celsius
If we split the difference between your 0.2-0.3 ohm cold resistance, we
get:
Rt = 0.25 ( 1 + (0.003819 (962 - 20))) ~ 1.5 ohms
which is quite a bit higher than your reported 0.9 ohms.
If we look at zinc, with a melting point of about 420°C and an alpha of
0.003847, we get:
Rt = 0.25 ( 1 + (0.003847 (420 - 20))) ~ 0.63 ohms
which is quite a bit lower, but since your fuse hadn't quite melted,
maybe in the ball park? Plus, they say it's a zinc _alloy_ ...
--
John Fields
Svante
Interesting... Then I wonder why I saw an increase to 0.9 ohms before
melting (incresed from 0.2-0.3 ohms). This would indicate a melting
point of some 600-1100 degrees celcius. I'll have to up look tin/lead
alloys.
Glenn Booth
In message <93d2ebc6.0402...@posting.google.com>, Svante
<svante_g...@hotmail.com> writes
>One more thing I learned. The fuse broke at about 1 ampére, even
>though it was rated 500mA. I recall knowing this some time in the
>past, but had forgotten about it. Fuses can take more than they
>"state".
During the first year of my EE degree we spent an afternoon doing
experiments on fuses and breakers. It was pretty educational... one
guy managed to put 38 Amps through a standard UK 13 amp mains fuse
before it blew. The average value around the class for these things was
in the high 20s (amps) before failure. We were winding on the current
slowly - I'm sure it would have been different with sudden increases in
current, but it was an eye opener, for sure.
--
Regards,
Glenn Booth