Hi Everyone,
I just realized I may be making a Yuuuuge mistake.
My understanding about compression in a driver was that there were two reasons for it (within their normal range):
1 - Thermal
2 - Suspension / motor non-linearities.
Am I wrong?
I ask because a couple of sites i've read recently attribute it all to thermal effects.
Thanks,
E
I just realized I may be making a Yuuuuge mistake.
My understanding about compression in a driver was that there were two reasons for it (within their normal range):
1 - Thermal
2 - Suspension / motor non-linearities.
Am I wrong?
I ask because a couple of sites i've read recently attribute it all to thermal effects.
Thanks,
E
Compression is due to the movement of a diaphragm against the air, hence the name 'compression driver'.
Heat is built up when too much DC is present either from voltage or square waves on the output stage and that will distort the air movement slightly just before the coil burns up.
Non linearity in the suspension, I find hard to see as it is basically a spring and air pressure.
Heat is built up when too much DC is present either from voltage or square waves on the output stage and that will distort the air movement slightly just before the coil burns up.
Non linearity in the suspension, I find hard to see as it is basically a spring and air pressure.
I think short term compression is primarily BL and compliance curve related. John K did a study which shows that short term thermal modulation does not happen. The thermal time constants are simply too long.
Longer term thermal compression which alters the sensitivity of a driver or alters the balance between woofer and tweeter OTOH is real.
Matter of taste, if one calls 1/x^(2n+1) part of voice coil excursion due to motor and suspension limitations distortion, limitation or compression. Recording engineers tend to call it compression, live mixers limitation, and device designers distortion.
Thermal time constants of electro-magneto-acoustic transducers are not that long, maybe around 2s. Thermal compression of pulses may happen in certain designs or with certain sources. Recent hifi standard of combining heat-isolating voice coil former and -resistant glue nourish this possibility.
Thermal time constants of electro-magneto-acoustic transducers are not that long, maybe around 2s. Thermal compression of pulses may happen in certain designs or with certain sources. Recent hifi standard of combining heat-isolating voice coil former and -resistant glue nourish this possibility.
Well, clearly I needed to define my terms better. Here's what I meant:
Measure FR at 1m for 70 dB at 1 kHz.
Measure FR again at 90 db at 1 kHz.
Compare FR.
That is the compression I'm talking about. Clearly thermal effects matter and can occur sub-cycle, but does it dominate everything else?
Best,
E
Measure FR at 1m for 70 dB at 1 kHz.
Measure FR again at 90 db at 1 kHz.
Compare FR.
That is the compression I'm talking about. Clearly thermal effects matter and can occur sub-cycle, but does it dominate everything else?
Best,
E
Thermal compression raises the resistance of the voice coil, but to reach it with a sine wave, moreover music signal you need effort. Mechanical xmax is different, it is the real maximum of power your driver can take before the former to hit the top pole plate. Usually, above xlinear the BL curve will shift rapidly causing nonlinear distortion which depends on the motor design, if rought - distortion will increase dramatically. This happens because the voice coil leaves the gap. But there is another one. When current is applied to the voice coil, its own magneitc field would interact with the permament magnet flux and cause nonlinearities, this can be seen as another type of "compression". A highly saturated motor can deal with it.
What you speak of, regarding the changes in FR, is caused by the flux modulation, increaed air resistance of air in front of the cone as it gets compressed and the suspension non-linear behaviour.
What you speak of, regarding the changes in FR, is caused by the flux modulation, increaed air resistance of air in front of the cone as it gets compressed and the suspension non-linear behaviour.
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Well, in hifi, yes. In PA, no. With limiters in place and rising gain you're increasing the rms by far. The limiter compresses ofcourse but the thermal compression of the driver will rise nonetheless.
Where the compression starts depends pretty much on the construction of the driver. The higher the compression ratio the sooner you'll reach the nonlinearities of the air or get more or less flex in the diaphragm and suspension, all three ofcourse introduce compression, distortion and possibly resonances.
Any 1/x^(2n+1) part of transmission function may be called compression, and in electro-magneto-acoustic transducers there are many reasons for such mathemathical parts. But thermal compression should become described foremost as compression, not as distortion, because it has a time constant (which is usually much longer than 1/2pi16Hz). Are you sure they do even exist?
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never heard an electrostat that didn't sound compressed. I had some of Sander's most efficient models, also DIY 32 square ft bass panels. They suck compared to a low compromise horn. dead lifeless sounding. better than the acoustat or quads but suck. Is that thermal?
Also all the direct radiators I have heard sound compressed, ie I had the big Dunlavy's (and many others including big line arrays) with 700 watt Classe' mono amps = dead. lifeless compressed. Is that thermal?
I'm not talking about loud playback here, the horns are much more dynamic and alive sounding at low levels too.
Also all the direct radiators I have heard sound compressed, ie I had the big Dunlavy's (and many others including big line arrays) with 700 watt Classe' mono amps = dead. lifeless compressed. Is that thermal?
I'm not talking about loud playback here, the horns are much more dynamic and alive sounding at low levels too.
how did this thread get so much hearsay without a link to real data?
https://www.klippel.de/know-how/literature.html
https://www.klippel.de/know-how/literature.html
Yeah, but in electro-acoustics we try to keep time and amplitude seperate and keep linear and non-linear distortion seperate. We call only a subset of a special case of distortions, which are time-variant, say mix up amplitude and time, now both depending on one another, compression. The rest of the set is expansion.
Hi Pooh!
That gets us way off topic. No, what you are listening to is probably more complex, and involves overall speaker balance and room interactions.
What I'm trying to get to occurs within 1 driver, in an anechoic chamber and is easy to measure. For a good idea, look at the charts at speakermeasurement.com where you will find compression charts.
Best,
E
That gets us way off topic. No, what you are listening to is probably more complex, and involves overall speaker balance and room interactions.
What I'm trying to get to occurs within 1 driver, in an anechoic chamber and is easy to measure. For a good idea, look at the charts at speakermeasurement.com where you will find compression charts.
Best,
E
There's an attempt to derail your thread, here. Defining your terms might help get useful answers.
Anyone that equates the performance of panel speakers to cones and domes isn't trying to sort this out.
Bill Fitz Maurice held an extensive, considered and cogent discourse on the topic back in 2005 over on Talk Bass. The abridged version: you're right - at highest power, BOTH the mechanical resistance of the ports and air volume of your room AND the heat in the motor steal power as waste heat.
I'll ascribe some of the less lucid answers to "translation errors" to be charitable.
The Klippel references cover the core principles, and the Talk Bass link explained it enough for an innumerate like myself to follow along.
To repeat, you're right - both heat and mechanical losses work against you.
https://www.google.com/amp/s/www.ta...ession-in-loudspeakers.198502/?amp=1125209333
Sent from my Nexus 6 using Tapatalk
Anyone that equates the performance of panel speakers to cones and domes isn't trying to sort this out.
Bill Fitz Maurice held an extensive, considered and cogent discourse on the topic back in 2005 over on Talk Bass. The abridged version: you're right - at highest power, BOTH the mechanical resistance of the ports and air volume of your room AND the heat in the motor steal power as waste heat.
I'll ascribe some of the less lucid answers to "translation errors" to be charitable.
The Klippel references cover the core principles, and the Talk Bass link explained it enough for an innumerate like myself to follow along.
To repeat, you're right - both heat and mechanical losses work against you.
https://www.google.com/amp/s/www.ta...ession-in-loudspeakers.198502/?amp=1125209333
Sent from my Nexus 6 using Tapatalk
That link does not work. Do they compare drivers in and out of horns for compression? Do they test for low signal level compression between direct radiators and horn loaded drivers? Do you have a link that works? I doubt a high end 88 db direct radiator woofer will have less compression than a 108 db sensitive bass horn.
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