Paul G asks:
"[W]hat is the best way to protect a
speaker from destruction if the amp is sufficiently powerful, and you
have no control over volume? It happens.... the kids have fun with
your stereo, the grounds come loose on the inputs (huge buzz), the
system oscillates, etc."

I don't know if you want to design and build your own stuff from
scratch, Paul, or merely want to buy a plug-in protector. If you can
solder, here's a halfway house in a couple items to protect your
loudspeakers from switch-on pops and from DC.

Velleman K4700 Loudspeaker protection kit, stereo with switch-on delay

Velleman K4701 Loudspeaker DC-protection, mono

The reason I've identified them is that I have a QUAD 405 MkII which
occasionally eats an ESL-63, which soon gets expensive, and it is
tricky rebuilding them because here is no way to solder except over
the fragile panels... So an audiophile's fancy turns to ripping out
the 405's inadequate clamp circuit and replacing it with industrial
strength protection.

The reason I choose Velleman is I've built some of their kits,
including the multimeter I've used for years and a 100W PP tube amp,
and found their stuff first class, head and shoulders above the
competition (well, in most cases there is no competition, because the
other guys make crap); in the end Velleman is worth the premium price.

Andre Jute
I just listen to one channel at a time. You do have to listen twice.
Adequate stereo separation. -- Al Marcy

In article , Andre Jute wrote:
Paul G asks:
"[W]hat is the best way to protect a
speaker from destruction if the amp is sufficiently powerful, and you
have no control over volume? It happens.... the kids have fun with
your stereo, the grounds come loose on the inputs (huge buzz), the
system oscillates, etc."

I don't know if you want to design and build your own stuff from
scratch, Paul, or merely want to buy a plug-in protector. If you can
solder, here's a halfway house in a couple items to protect your
loudspeakers from switch-on pops and from DC.

Velleman K4700 Loudspeaker protection kit, stereo with switch-on delay

Velleman K4701 Loudspeaker DC-protection, mono

The reason I've identified them is that I have a QUAD 405 MkII which
occasionally eats an ESL-63, which soon gets expensive, and it is
tricky rebuilding them because here is no way to solder except over
the fragile panels... So an audiophile's fancy turns to ripping out
the 405's inadequate clamp circuit and replacing it with industrial
strength protection.

The reason I choose Velleman is I've built some of their kits,
including the multimeter I've used for years and a 100W PP tube amp,
and found their stuff first class, head and shoulders above the
competition (well, in most cases there is no competition, because the
other guys make crap); in the end Velleman is worth the premium price.

Andre Jute
I just listen to one channel at a time. You do have to listen twice.
Adequate stereo separation. -- Al Marcy

For a solid state amp, I usually put in a fuse on the speaker lines,
only if I feel its necessary. The fuse is not a sure thing, and you have to
use the right value. It can save speakers some of the time.
The Velleman devices have nothing to do with over volume, unless the
overvolume cause a shift in average DC offset.

greg

On Fri, 10 Sep 2010 14:00:49 GMT, (GregS)
wrote:

In article , Andre Jute wrote:
Paul G asks:
"[W]hat is the best way to protect a
speaker from destruction if the amp is sufficiently powerful, and you
have no control over volume? It happens.... the kids have fun with
your stereo, the grounds come loose on the inputs (huge buzz), the
system oscillates, etc."

I don't know if you want to design and build your own stuff from
scratch, Paul, or merely want to buy a plug-in protector. If you can
solder, here's a halfway house in a couple items to protect your
loudspeakers from switch-on pops and from DC.

Velleman K4700 Loudspeaker protection kit, stereo with switch-on delay

Velleman K4701 Loudspeaker DC-protection, mono

The reason I've identified them is that I have a QUAD 405 MkII which
occasionally eats an ESL-63, which soon gets expensive, and it is
tricky rebuilding them because here is no way to solder except over
the fragile panels... So an audiophile's fancy turns to ripping out
the 405's inadequate clamp circuit and replacing it with industrial
strength protection.

The reason I choose Velleman is I've built some of their kits,
including the multimeter I've used for years and a 100W PP tube amp,
and found their stuff first class, head and shoulders above the
competition (well, in most cases there is no competition, because the
other guys make crap); in the end Velleman is worth the premium price.

Andre Jute
I just listen to one channel at a time. You do have to listen twice.
Adequate stereo separation. -- Al Marcy

For a solid state amp, I usually put in a fuse on the speaker lines,
only if I feel its necessary. The fuse is not a sure thing, and you have to
use the right value. It can save speakers some of the time.
The Velleman devices have nothing to do with over volume, unless the
overvolume cause a shift in average DC offset.

greg

I looked over the schematic of the Velleman unit, although it has
no values shown for the components, it senses speaker voltage, thru a
2nd order lowpass filter, rectifies, filters, then thru to a
comparator and a relay circuit with a another lowpass filter that
gives a 6 sec. or so time delay. Judging from the electrolytics in the
1st 2nd order filter, it will only respond to very low frequencies and
DC.
The unit should protect the speakers from an amp that goes haywire
or blows the output transistors and puts a significant DC voltage to
the speakers.

It would not prevent your speakers from being damaged by too much
volume, and would be of no use with any amp that uses an output
transformer (no DC makes it to the secondary).

I think it is not effective to use a fuse or breaker in series with
the speaker. Those devices require energy to operate, and then must
divert some of the output power to get sufficiently hot. That puts a
resistance in series with the speakers, which may affect their
performance. Magnetic trip breakers would put a series inductance in
series.... that would mess up the treble response. Many of these
devices aren't linear, and could cause distortion. When the device
"trips" it may not switch cleanly (arcs or chatters). The sudden
open-circuit while at high volumes could cause a voltage transient
that could damage the amp if the output circuitry isn't properly
designed.
Even if you get something to work well, which speaker of the
2-or-3-way system are you protecting? They all have different thermal
behaviour, so you'd really need to monitor the voice coil temperature.
Even after that, you might worry about mechanical damage from the
excessive travel of the cone. That would depend a lot on the frequency
and speaker resonance. Looks like a very difficult problem.
I had thought if your speakers had a power rating way in excess of
the amp you'd be OK. But.... I've heard a story where some guy takes a
crappy little amp, runs it flat out (square waves or worse) and
destroys speakers that have a reasonable power rating. I'm not sure if
its an audio myth, but it was supposed to have ocurred when a
knowledgable customer challenged a salesman at a hifi store, claiming
the expensive powerful speaker could be damaged by the little
amplifier.
What all this means is you must carefully manage the volume
yourself, and be very careful with situations that could damage the
speaker, especially a fragile or expensive one. I don't think there is
a cheap simple technical solution.

Paul G.

Paul G. wrote in
:

snip

I've heard a story where some
guy takes a crappy little amp, runs it flat out (square
waves or worse) and destroys speakers that have a
reasonable power rating. I'm not sure if its an audio myth,
but it was supposed to have ocurred when a knowledgable
customer challenged a salesman at a hifi store, claiming
the expensive powerful speaker could be damaged by the
little amplifier.

I have heard similar, from technicians I used to work with. It
is the distorted nature of the sound waves that destroys the
speakers, not the volume (of course, volume CAN kill speakers as
well).

It is not coincidental that cheap crappy amps claim 5,000 PMPO
(about 15W/side) and deliver clipped non-sound, and THAT is what
will destroy a speaker. 20 W per side of QUALITY is all anyone
really needs, unless, as MANY people do, you own equipment to
appreciate IT, not the music it lets you hear.

A GREAT musician I used to go to music school with had a crap
little amp (with two volume controls and one tone control, built
circa 1970, Radio Shack branded...).

But he was a MUSICIAN and he cared about the MUSIC - he was not
a ****** who only cares about the fact that only 30 other people
in the world can afford a system like his - on which he (once or
twice a year) plays his ***3*** CD's (which came free with one
of his magazine subs).



--
Any mental activity is easy if it need not be subjected to
reality.

On Sep 10, 9:28*pm, Paul G. wrote:
On Fri, 10 Sep 2010 14:00:49 GMT, (GregS)
wrote:



In article , Andre Jute wrote:
Paul G asks:
"[W]hat is the best way to protect a
speaker from destruction if the amp is sufficiently powerful, and you
have no control over volume? It happens.... the kids have fun with
your stereo, the grounds come loose on the inputs (huge buzz), the
system oscillates, etc."

I don't know if you want to design and build your own stuff from
scratch, Paul, or merely want to buy a plug-in protector. If you can
solder, here's a halfway house in a couple items to protect your
loudspeakers from switch-on pops and from DC.

Velleman K4700 Loudspeaker protection kit, stereo with switch-on delay

Velleman K4701 Loudspeaker DC-protection, mono

The reason I've identified them is that I have a QUAD 405 MkII which
occasionally eats an ESL-63, which soon gets expensive, and it is
tricky rebuilding them because here is no way to solder except over
the fragile panels... So an audiophile's fancy turns to ripping out
the 405's inadequate clamp circuit and replacing it with industrial
strength protection.

The reason I choose Velleman is I've built some of their kits,
including the multimeter I've used for years and a 100W PP tube amp,
and found their stuff first class, head and shoulders above the
competition (well, in most cases there is no competition, because the
other guys make crap); in the end Velleman is worth the premium price.

Andre Jute
I just listen to one channel at a time. You do have to listen twice.
Adequate stereo separation. -- Al Marcy

For a solid state amp, I usually put in a fuse on the speaker lines,
only if I feel its necessary. The fuse is not a sure thing, and you have to
use the right value. It can save speakers some of the time.
The Velleman devices have nothing to do with over volume, unless the
overvolume cause a shift in average DC offset.

greg

(snip)

I've heard a story where some guy takes a
crappy little amp, runs it flat out (square waves or worse) and
destroys speakers that have a reasonable power rating. I'm not sure if
its an audio myth, but it was supposed to have ocurred when a
knowledgable customer challenged a salesman at a hifi store, claiming
the expensive powerful speaker could be damaged by the little
amplifier.

(snip)

Paul G.

I think it's only the tweeters that are wrecked by cheap, clipping
amplifiers
Cheers,
Roger

"Engineer" wrote

I think it's only the tweeters that are wrecked by cheap, clipping
amplifiers


It is. When an amplifier is driven into clipping the high-order harmonics
increase significantly and can damage the tweeter. This is no myth, it has
happened many times.

Bullet-proof speaker protection is difficult because a high amplitude short
duration overload can damage the speaker mechanically, whilst a sustained
high-level signal, well within the speaker's mechanical limits, can cause
thermal overload.

The answer is to always keep the volume setting below that at which audible
distortion is present!

David.

On 11/09/2010 09:46, David Looser wrote:
wrote

I think it's only the tweeters that are wrecked by cheap, clipping
amplifiers


It is. When an amplifier is driven into clipping the high-order harmonics
increase significantly and can damage the tweeter. This is no myth, it has
happened many times.


What's the symptom of the damage? As post below (Speaker Imbalance), I'm
suffering a 'quieter' HF unit. I'd have thought it's all or nothing?

Rob

"David Looser" wrote in
message
"Engineer" wrote

I think it's only the tweeters that are wrecked by
cheap, clipping amplifiers

It is. When an amplifier is driven into clipping the
high-order harmonics increase significantly and can
damage the tweeter. This is no myth, it has happened many
times.

This is at least partially a myth. The fact of the matter is that very few
people know exactly what happens when a tweeter fails because to know this,
you'd have to instrument the situation and sacrifice at least one tweeter.

The fact of the matter that there is a lot of music that actually has its
high frequency content *decreased* when it is clipped.

The one thing that is sure is that speakers fail when too much power is
applied to them for too long. One way to facilitate this is to use a larger
power amplifier.

Bullet-proof speaker protection is difficult because a
high amplitude short duration overload can damage the
speaker mechanically, whilst a sustained high-level
signal, well within the speaker's mechanical limits, can
cause thermal overload.

Agreed.

The answer is to always keep the volume setting below
that at which audible distortion is present!

Also agreed.

On 10/09/2010 08:47, Andre Jute wrote:
Paul G asks:
"[W]hat is the best way to protect a
speaker from destruction if the amp is sufficiently powerful, and you
have no control over volume? It happens.... the kids have fun with
your stereo, the grounds come loose on the inputs (huge buzz), the
system oscillates, etc."

I don't know if you want to design and build your own stuff from
scratch, Paul, or merely want to buy a plug-in protector. If you can
solder, here's a halfway house in a couple items to protect your
loudspeakers from switch-on pops and from DC.

Velleman K4700 Loudspeaker protection kit, stereo with switch-on delay

Velleman K4701 Loudspeaker DC-protection, mono

The reason I've identified them is that I have a QUAD 405 MkII which
occasionally eats an ESL-63, which soon gets expensive, and it is
tricky rebuilding them because here is no way to solder except over
the fragile panels... So an audiophile's fancy turns to ripping out
the 405's inadequate clamp circuit and replacing it with industrial
strength protection.

I would fit a sensor that detects the onset of ionization and instantly
shorts the input to ground with a triac.
And maybe a soft-clipping circuit that works a few dB below the shutdown
level.
I can't think why Peter Walker didn't think of doing it....

--
Eiron.