Woke up this morning with this odd idea on my mind :
How about making an L-pad using NTC and PTC thermistors tuned to the thermal properties of the loudspeaker's VC/motor system to compensate for loudspeaker voice-coil heating?
As VC temperature fluctuations cause a loudspeaker's Re to wander, dynamics are impacted by varying degrees of power compression, and the tuning of passive crossover networks becomes compromised. Perhaps this could fix both problems.
If you wanted to get a little crazy, you could even tune the thermistors to supply a touch of artificial dynamic expansion.
The obvious penalty, of course, would be the loss of sensitivity that comes with use of any L-pad, but if your application needs an L-pad anyway, this added functionality might make sense.
Anyone ever heard of this being done? A cursory search revealed nothing.
Bill
How about making an L-pad using NTC and PTC thermistors tuned to the thermal properties of the loudspeaker's VC/motor system to compensate for loudspeaker voice-coil heating?
As VC temperature fluctuations cause a loudspeaker's Re to wander, dynamics are impacted by varying degrees of power compression, and the tuning of passive crossover networks becomes compromised. Perhaps this could fix both problems.
If you wanted to get a little crazy, you could even tune the thermistors to supply a touch of artificial dynamic expansion.
The obvious penalty, of course, would be the loss of sensitivity that comes with use of any L-pad, but if your application needs an L-pad anyway, this added functionality might make sense.
Anyone ever heard of this being done? A cursory search revealed nothing.
Bill
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So how are you going to find components with dynamic properties, time constants and stuff to match the voice coil heating process? I think in analog this will prove extremely difficult.
O.t.o.h, using current measurements on the speaker and some proper DSP, it should be possible to determine the change in impedance due to the temperature rise and compensate for it. I think the difficult part of it would be mapping the change in impedance to some kind of 'dynamic eq' or multiband compressor to get the proper power-compression-to-frequency curve.
O.t.o.h, using current measurements on the speaker and some proper DSP, it should be possible to determine the change in impedance due to the temperature rise and compensate for it. I think the difficult part of it would be mapping the change in impedance to some kind of 'dynamic eq' or multiband compressor to get the proper power-compression-to-frequency curve.
That may adjust for crossover values but the voice coil resistance will still fluctuate. How about a water cooled magnet structrue?
Don't use any passive crossovers and use all fully variable active crossovers and muliple amp channels.
Don't use any passive crossovers and use all fully variable active crossovers and muliple amp channels.
Yeah, that probably wouldn't be trivial.
However, IIRC, some other threads here seemed to indicate that instantaneous heating effects were less important than longer-term temperatures. Maybe you could sink the thermistors to the motor structure.
And the thermistors compensate for that by raising the voltage on the voice coil as temps rise.
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the BeoLab 5 active loudspeaker has voice coil heating nonllinear compensation internally in dsp
good thermal modeling may be a little complicated:
http://www.klippel.de/pubs/Klippel papers/Nonlinear_Modeling_of_Heat_Transfer_03.pdf
good thermal modeling may be a little complicated:
http://www.klippel.de/pubs/Klippel papers/Nonlinear_Modeling_of_Heat_Transfer_03.pdf
Why odd... (do you mean the heat component - Thermistor, not electrical?)
PTC's are widely used in the industry. I've one in my vintage Mordaunt-Short's. Some CD's have them (Selenium). Following some engineers, Hommero S. Silva from Selenium compressors and limiters work better and Wayne Parham from PiSpeakers they are not fast enough to stop the problem. In fact you will have to test and burn a series of CD's in lab to achieve max. input.
Advanced PTC™ Horn Protection makes its debut in the élite series.
PTC Calculator www.lautsprechershop.de
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I'm familiar with their use in protection circuits, but I'm sorta turning that inside out by suggesting an arrangement that reduces voltage to the VC when cold and allows more when hot.
Good thinking in theory. When the VC heats up, send it more power. hmmm but on second thought sounds like the beginnings of thermal runaway.
Thanks!
Seems to me, since it's basically just an L-pad with a twist, when it opens up, it can only add back the proportion of the voltage it normally diverts/dissipates. So maybe 3db or less in a typical application. That limits what it can do, but it also means thermal runaway can't really get going too much.
My thinking, not that it's a good idea, would consist of mounting the thermistor in contact with the VC assembly and using it to control the amplifier gain. Say as part of Rf.
You really do want to see it burst into flames, don't you? :0
If sampling actual VC heat is the goal, then maybe an optical system like those IR thermometers aimed right at the VC winding is the logical conclusion...
but of course now we've leaped from talking about two passive components to talking about a whole servo feedback can o worms.
If sampling actual VC heat is the goal, then maybe an optical system like those IR thermometers aimed right at the VC winding is the logical conclusion...
but of course now we've leaped from talking about two passive components to talking about a whole servo feedback can o worms.
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