It was a commercial b.s.
In fact, just speakers with heavy mobile mobile assembly and flexible suspension, that have a resonance frequency so low that you can put them in a relatively little box and still have an acceptable cut-off frequency... in the same time than a non acceptable low efficiency.
You cannot rely on the air to center your membrane and are obliged to have at least a little hole in a closed enclosure: Think about atmospheric pressure changes..
Speaker designers. They all seem to think so. Click on this --->
Loudspeaker and Headphone Handbook - Google Books
Cost is not a problem...… have you seen the prices many speakers sell for ? OMG! Dont need to lift a car though.
-THx-RNMarsh
The gap field is assymetrical front to back by design.
The vc coupling to the magnetic structure is assymetrical by design.
The permeability of the iron at the gap surface is assymetrical by design.
The eddy losses in the iron gap surfaces caused by the vc audio currents are assymetrical by design.
It almost appears that there is some kind of trend here, although I can't seem to get a handle on what that might be...
Jn
I would argue: by necessity on all four counts, not by design. Although by design also happens, especially non-linearity in the suspension....oh, you didn't mention that one.
We might have a misunderstanding here: I was referring to the air trapped between the two cones in George's experiment. This is the medium that couples the two oscillating cones together, apart from the slight coupling through the two metal structures in contact.
Regards,
Braca
If you "need" to use the exact same assymetrical magnetic design, then yes, it can be construed as a necessity. But recall, the design everyone falls into is over a century old, figured out by someone who does not have our level of knowledge. They also did not have access to cheap titanium nor carbon fiber composites nor magnetic FEA.
If you detail to a really good magnetic designer what the problems are that you wish to avoid, you might be surprised.
Jn
Ps. As to the air coupling the two speakers... Remember, PV=nrT.. The expansion/contraction of air is non linear. With drivers bolted face to face the ratio of air moved to air trapped is higher than if it was two drivers in a box or tube of length. For work to be done on the slave driver, there has to be rarefaction and compression which is inherently non linear. Also, it is very very sensitive to air leaks at the lower frequencies.
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Overarching books are not meant to freeze technology in time. It is simply a guide to what is known at the time.
If you felt that way, you would not have been bustin our chops to think outside the box.
Think servosub.. Stick to a book, it never would have happened.
Jn
Why not use a laser ( or other optical device) mounted in the driver basket to track cone montion(same technology as laser distance measuring devices). Refine the technilogy to the shorter distance involved and sample often enough to make it useful. Then you have to mount nothing on the cone or mess with the coil at all.
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What is inherently different going on in a piston chamber? I have measured microphones at 350Hz and highish SPL doing 0.1% THD. I thought at low frequencies the thermal properties of the gas start to contribute nonlinearity.
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He said distortion occurred at around 1/2Fs or lower. This indicates suspension nonlinearity and/or Bl(x) nonlinearity.
Couldn't we estimate how much compression is occurring if we know the Vas of the drivers and the approximate volume enclosed between the cones? Vas would tell us the relative compliance of the speaker and enclosed air. Then we only need to know the excursion of one speaker to know the excursion of the other and the level of compression of the air.
Couldn't we estimate how much compression is occurring if we know the Vas of the drivers and the approximate volume enclosed between the cones? Vas would tell us the relative compliance of the speaker and enclosed air. Then we only need to know the excursion of one speaker to know the excursion of the other and the level of compression of the air.
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Exactly.
There is a single situation when the compression and expansion follow the same line, i.e. are reversible, and it takes place when the entropy stays constant, which is here not the case.
The difference between the wave propagation velocities of the compression and rarefaction waves are rather small in this case. Assuming the SPL of approx. 95dB (1Pa,rms) in the volume enclosed by the two cones, the Earnshaw's formula of 1860 gives a difference of 0.0025% between the respective wave propagation velocities (sorry I can't quote a reference for this formula, it appears to be used in special literature only).
Wave interactions may produce higher or lower peak pressures, but would not give rise to dramatic changes of the above figure.
However, leakage may even give rise to a sort of Helmholtz resonator being created at the respective location, which can produce a non-negligible modification of the frequency response.
Regards,
Braca
Earnshaw's paper is available at JSTOR:JSTOR: Access Check
JOURNAL ARTICLE
On the Mathematical Theory of Sound
S. Earnshaw
Philosophical Transactions of the Royal Society of London
Vol. 150 (1860), pp. 133-148
Published by: Royal Society
Stable URL: On the Mathematical Theory of Sound on JSTOR
Page Count: 16
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Quite easy to do. We measure sub micron vibration using lasers, prices have come down a lot. The last one was only 60,000 dollars. I guess quantity buys could get it down into the 30 to 40K range.
I use renishaw absolutes as well, 40 nanometer typical resolution, but also use 10 and 5 nanometer ones. I think speed resolution is fast enough for woofers, Biss-C is pretty fast with short well terminated cables. Quadrature interpolators can be fast as well, but are incrementals.
Jn
Specifications : IL series | KEYENCE America On eBay for pretty reasonable. Build your own Klippel analyzer. . . . .1% linearity. The problem with the interferometer measurement systems is that they are not really linear as much as digital, counting wavelengths. And expensive. Plus the temperature and humidity of the air alters the accuracy (if you need that sub-light wavelength accuracy).
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