To me comparing the requirements of four drivers to that of a single driver makes no sense. I completely miss the point.
To end the debate, I should rather have stated that the maximum power compression achievable in a sealed enclosure would normally be higher than for a dipole.
For me it is far more interesting to consider headroom and BL(x)/K(x) linearity for home audio bass systems. As long as the driver have a descent sized motor system I don't pay so much attention to power compression.
For me it is far more interesting to consider headroom and BL(x)/K(x) linearity for home audio bass systems. As long as the driver have a descent sized motor system I don't pay so much attention to power compression.
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r
I was only talking about thermal compression, not passing Xmax ( that's similar to limiting, bad limiting).
I'm not sure what the rest means. You say thermal compression time constants can aproach signal time constants. From which side, are they usually slower or faster. My guess is slower and so it effects the envelope like a compressor. Do you have any numbers for these time constants? And the only ones that matter are the voice coils cummalative ones. ( which include the magnet etc.)
I understand what your getting at but I think your use of linear/nonlinear is confusing. If I ride a fader very quickly to even out levels is this linear? I don't think so, not in the physics definition. Compression is the same thing. The Vo/Vi is constantly slewing, how can this be linear.
Its all about how fast one changes the amplitude of the signal. If it happens in ms. then yes, its nonlinear, but you can't "gain ride" a fader that fast. Even electronic compressors tend to act much slower than this.
The thermal time constants in a driver are, of course, generally slower than the signal. A 100 Hz tone has a time constant of 1/100 sec. or 10 ms. Generally slower than this is too slow to be consider nonlinear. Faster than this and frequencies will be modified in a nonlinear manner, but it would need to be down to about 1 ms. to actually be nonlinear over a significant bandwidth.
The time constants for a typical 1" tweeter come in at about a few ms., compression drivers many times this, Woofers well above 10's of ms. to 100's depending on voice coil size, etc. The dominate factor is the volume of copper in the voice coil. The more copper the slower the dominate effect.
Actually doubling power for every 3db, take for example a B&C 8Pe21 in my horn it is 106 db with 2.8 volt at 3 feet. Put that same driver on a board and it's around 90 so 16db. The same SPL requires around 32 times the power for the same SPL. So instead of 64 watts to work at 120 db it takes a mere 2048 watts as a dipole (disregard x max LOL.) The same driver at the same SPL will be into thermal distress at 120 db in the dipole (2000 watts) where in a horn it's just breezing. I imagine it will take more than 2000 watts due to compression. Mybe it would catch fire? 
Distorted?
Distorted?Hello,
Is this also true for the JBL M2 drivers? I replaced QUAD ESL 989 with them. The M2 seem very fast and high resolving powers. Little compression of any cause.... great dynamics. [using the recommended Crown iT5000HD amplifiers... bi-amp'ed]
THx-RNMarsh
I mostly agree with this. The more I think about the power levels involved while listening and the visible excursion I tend to doubt my experience is based on thermally or mechanically induced compression of the driver. I'm still going to measure it to be sure. I've ordered a pair of UM18-22 that I may experiment with in a dipole configuration in the coming months. I'm pretty sure at my modest listening levels that driver compression won't be an issue with such drivers. Ultimately I'll probably throw them in a sealed box and call it a day
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A good place for everybody to start is very very simple. Just watch your music on a real time analyzer, such as free REW.
You will see instantaneously how much oomph you have at each frequency in a beautiful display. Most folks will be surprised to find their favourite music that sounds like it has a lot of real deep bass is really just at 80 Hz and pitiful little below 40 and then briefly.
Even if you have a big collection of organ music (as I happen to have), very hard to find recordings with notes under 35 Hz.
As organ builders have known for centuries, your brain inserts fundamental tone if the partials are played. Yes, you hear it (except for golden-eared people who think they never hear or see illusions).
I can't speak for all the wonderful things that have ever been recorded, but for music without too much cooking in the studio, that's the story.
Ben
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What I proposed as a plausible cause for your experience is also related to electro magnetism. The non-linearities are not necessarily limited to xmax, although drivers will normally tend to increase their non-linearities when the voice coil starts leaving the gap. There can be huge variations between manufacturers and model types both within and outside xmax, depending on motor principles, geometry, soft parts and tolerances in the assembly. Seas does show Klippel measurements for their L26ROY in their application note. Its performance is very descent within xmax (appr. 20% loss in BL at xmax).I mostly agree with this. The more I think about the power levels involved while listening and the visible excursion I tend to doubt my experience is based on thermally or mechanically induced compression of the driver. I'm still going to measure it to be sure. I've ordered a pair of UM18-22 that I may experiment with in a dipole configuration in the coming months. I'm pretty sure at my modest listening levels that driver compression won't be an issue with such drivers. Ultimately I'll probably throw them in a sealed box and call it a day
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If you are going to measure these non-linearities or their effects, you need a suitable measurements method. Standard measurement software does not have a method for this, at least not that I know of. Frequency response measurements at different SPL will not give you the answer. A method could may be to play a part of a record where you normally experience this harshness and read out the signal amplitude (scope) and compare/overlay this exact same sequence at different SPL. At least you may demonstrate the effects, if any, of non-linearities this way.
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A lot of this chatter is loose, even mythological talk about compression.
Here's a very challenging article by Floyd Toole that may well hold the key to the sorts of hearing effects people are bandying about in comparing the imagined differences in "compression" between dipoles in rooms versus conventional speakers in rooms. Toole core topic is dispersion and how dispersion angle (and the timing of reflections) at different frequencies affects the sound. It is a critique of simple adherence to freq response and sims. This is real science, if you have the fortitude to read it through.
http://www.aes.org/tmpFiles/elib/20160909/17839.pdf
Ben
Here's a very challenging article by Floyd Toole that may well hold the key to the sorts of hearing effects people are bandying about in comparing the imagined differences in "compression" between dipoles in rooms versus conventional speakers in rooms. Toole core topic is dispersion and how dispersion angle (and the timing of reflections) at different frequencies affects the sound. It is a critique of simple adherence to freq response and sims. This is real science, if you have the fortitude to read it through.
http://www.aes.org/tmpFiles/elib/20160909/17839.pdf
Ben
Ben, thanks for sharing but the results are 404 file not found. This is also a way fro me to subscribe because this is one of the better threads I have read through. A lot of audio-myths have been dispelled, and that pleases me.
http://www.aes.org/tmpFiles/elib/20160910/17839.pdf
Hope it works for everybody.
"Disruptive" and important message in this fine article is that room EQ is a faulty idea. Read it and see.
Very sorry. AES truly a mine-field or obstacle maze to getting their handful of free articles, like this one. Not nice of them but all academic publishers under the same profit-driven pressure.
Ben
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