It is well known that loudspeakers are quite good at protecting fuses.
Confused about underpower/overpower amp and speakers? What gets damaged?
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Gavin Pursinger
Well-known member
I have noticed that also...but CUE button sh... does happen. Driverack 260 peakstop limiter is helpful...cannot get some JBL factory cones for some old friends...You are correct of course...just trying to help...thx
Speaker protection is a quite complex subject. As JR mentioned, there is no easy answer.
There are indeed two major failure causes: overexcursion and thermal
For TMI:
The difficulty with thermal protection is that the voice-coil temperature evolves according to four different time-constants, one for the thermal path between voice-coil and pole pieces, the second between pole pieces and chassis, the third between chassis and inside the box, the 4th one for the path between inside the box and outside. The two latter are very long (minutes and hours), so are difficult to model with common analog methods. And there is an unknown, the ambient temperature. In order to provide correct simulation, a temp probe is requested. Some digital processors actually provide an accurate temperature simulation.Now, what does the processor do with this information? Does it shut the system when max temp is attained? I don't think it's acceptable for PA. So there are different takes on the subject, with various actions when approaching max temperature.
Of course this is meant to protect the voice-coil, but actually there are some elements that suffer from excessive temp, such as glue, magnets and the small portions of wire that connect the voice-coil, which often act as fuse.
Now, regarding over-excursion, there are different approaches from different manufacturers. Except some very crude designs using simple level limiting (actually what the Drive rack does), most use some kind of modelling excursion vs. signal and reduce signal when a limit is reached (or approached).
The big issue there is that the X vs. signal transfer function varies with temperature and humidity, and age of teh speaker components, so actually, implementing a very accurate simulation is useless because the main parameters vary significantly between the start of the show and its end. It takes a lot of experimentation to predict how these parameters change and how to include these variations in a "one size fits all" protection scheme.
Some designers have worked on temperature probes inside the speakers and accelerometers on the diaphragms, but these solutions are only suited for powered boxes, and actually have not given much better results.
In addition to that, multiway speakers would require to have selective processing in order to support the different drivers.
To resume: Not only a complex subject, but it shows that it's almost impossible to provide protection for all the failure modes.
Speaker protection has been the subject of the last 15 years of my professional career. I designed the protection schemes that are used in Linea Research and Powersoft amps. I can't claim they are 100% foolproof, but I think they do a pretty good job. Of course, the best speaker protection system is defeated if the user makes a silly mistake, such as selecting the wrong preset...
There are indeed two major failure causes: overexcursion and thermal
For TMI:
The difficulty with thermal protection is that the voice-coil temperature evolves according to four different time-constants, one for the thermal path between voice-coil and pole pieces, the second between pole pieces and chassis, the third between chassis and inside the box, the 4th one for the path between inside the box and outside. The two latter are very long (minutes and hours), so are difficult to model with common analog methods. And there is an unknown, the ambient temperature. In order to provide correct simulation, a temp probe is requested. Some digital processors actually provide an accurate temperature simulation.Now, what does the processor do with this information? Does it shut the system when max temp is attained? I don't think it's acceptable for PA. So there are different takes on the subject, with various actions when approaching max temperature.
Of course this is meant to protect the voice-coil, but actually there are some elements that suffer from excessive temp, such as glue, magnets and the small portions of wire that connect the voice-coil, which often act as fuse.
Now, regarding over-excursion, there are different approaches from different manufacturers. Except some very crude designs using simple level limiting (actually what the Drive rack does), most use some kind of modelling excursion vs. signal and reduce signal when a limit is reached (or approached).
The big issue there is that the X vs. signal transfer function varies with temperature and humidity, and age of teh speaker components, so actually, implementing a very accurate simulation is useless because the main parameters vary significantly between the start of the show and its end. It takes a lot of experimentation to predict how these parameters change and how to include these variations in a "one size fits all" protection scheme.
Some designers have worked on temperature probes inside the speakers and accelerometers on the diaphragms, but these solutions are only suited for powered boxes, and actually have not given much better results.
In addition to that, multiway speakers would require to have selective processing in order to support the different drivers.
To resume: Not only a complex subject, but it shows that it's almost impossible to provide protection for all the failure modes.
Speaker protection has been the subject of the last 15 years of my professional career. I designed the protection schemes that are used in Linea Research and Powersoft amps. I can't claim they are 100% foolproof, but I think they do a pretty good job. Of course, the best speaker protection system is defeated if the user makes a silly mistake, such as selecting the wrong preset...
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Back when I was still thinking about solutions for this, I speculated about imputing VC temperature from the VC resistance. As It heats up that resistance rises so when driven with a constant voltage the current draw drops. This might be used inside powered speakers with specific knowledge about the drivers and ability to measure V and I.
JR
JR
Indeed, Powersoft amps in particular include continuous DC resistance monitoring, but it is seldom used for critical applications because of all the uncertainties regarding cables, contact resistance, and intempestive disconnections.
Again it is more suitable for powered boxes than conventional separate amp/speakers.
yes, most amps that sense resistance are used to crudely detect failed loudspeaker drivers in large distributed systems.
JR
JR
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david moran
Member
lots of sensible (meaning true) responses here, unlike almost any other audio site
amp misbehavior and passage of dc (obvs) will harm speakers quickly
speaker overdriving, sure, eventually
clipping never, unless it results in the above; the harmonics simply do not have enough energy. Fully studied 40 and more years ago (Allison), and since. This falsehood refuses to die.
amp misbehavior and passage of dc (obvs) will harm speakers quickly
speaker overdriving, sure, eventually
clipping never, unless it results in the above; the harmonics simply do not have enough energy. Fully studied 40 and more years ago (Allison), and since. This falsehood refuses to die.
Back in the 80's I wrote a magazine column called "audio mythology"... the old myths refuse to die and are still kicking around today.
JR
david moran
Member
cool
I forget who besides Roy Allison was an early debunker of the clipping myth (his moreover was a sidebar about power needs in general, arcanely technical for lay consumption)
what mag was your column in?
I forget who besides Roy Allison was an early debunker of the clipping myth (his moreover was a sidebar about power needs in general, arcanely technical for lay consumption)
what mag was your column in?
I wrote "Audio Mythology"*** for Record Engineer/Producer magazine for a couple years back in the 80s. It was fun to debunk some of the widespread myths. I upset some people in the industry, but when they wrote letters to editor complaining about me, I got to answer them...
After I started working at Peavey I got a little too busy to drop everything to crank out my articles, and I felt a little conflicted about not being arm's length from a major audio company.
JR
*** I suspect there are copies of my old columns floating around the interwebs...
PS; After I stopped writing the column, Dennis Bohn from Rane ASSumed I was an old gray hair who died of old age... Bohn's eulogy
Brian Roth
Well-known member
John....
https://worldradiohistory.com/Archive-All-Audio/Recording_Engineer_Producer.htm
What years so we can all enjoy your musings? I'd love to read them again in 2023; I used to receive that mag Back In The Daze <g>, but alas, I sent my paper copies to recycling when I moved 10-ish years ago.
The Worldradiohistory.com site has many scans of vintage magazines, including all the years I wrote regular articles for Modern Recording magazine....mid/late 70's into early 80's.
Bri
https://worldradiohistory.com/Archive-All-Audio/Recording_Engineer_Producer.htm
What years so we can all enjoy your musings? I'd love to read them again in 2023; I used to receive that mag Back In The Daze <g>, but alas, I sent my paper copies to recycling when I moved 10-ish years ago.
The Worldradiohistory.com site has many scans of vintage magazines, including all the years I wrote regular articles for Modern Recording magazine....mid/late 70's into early 80's.
Bri
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