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Old 24th April 2012, 10:54 PM   #1
doggy is offline doggy  Canada
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Default X-max and coil overhang

What are the effects? sonic and mechanical of operating a speaker driver past the maximum allowed? I have a set of Fostex FE108ez in BLH that have been subjected to operation outside of X-max for many years and are still going strong.
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Old 24th April 2012, 11:24 PM   #2
kvholio is offline kvholio  Netherlands
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Assuming you mean driving it past the Linear Xmax, not mechanical Xmax,
it depends on the design of the driver.
Some fullrange drivers dont even tolerate being driven to Linear Xmax for prolonged periods.
Personally i think that if you regularly drive your loudspeakers at or beyond the linear Xmax, you need bigger loudspeakers.
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Old 25th April 2012, 12:31 AM   #3
doggy is offline doggy  Canada
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yes, maybe the FE168ez, but a little pricey, some fe126e I had did not last. maybe the sigma and surround design is a bit tougher, the cone is durable on the fe108ez. Going up in size some of the characteristics-speed may be lost.
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Old 25th April 2012, 11:01 AM   #4
T101 is offline T101  Bulgaria
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Quote:
Originally Posted by doggy View Post
yes, maybe the FE168ez, but a little pricey, some fe126e I had did not last. maybe the sigma and surround design is a bit tougher, the cone is durable on the fe108ez. Going up in size some of the characteristics-speed may be lost.
Look at parameters such as Qes, BL and Mms, this will give you an Idea of the impulse response and decay time. While all three parameters are important for impulse response, the decay time is mostly Qes, Qms (the lower, the better - low Qms means more energy is absorbed away from the system e.g. non resonant system) and damping factor dependant.

There are 12 inch drivers with such strong motors that make you blink on sudden passages in known tracks even though you expect it.

The problem with small drivers is that given the low Mms, the designers can't give them too strong motors, because Qes will fall, BL will be too much resulting in very low Qts irrespective of Qms and the bass response will be lost making the driver non fullrange but rather a midrange.

The heavier cones of bigger drivers such as 25-30-40 g. Mms of an '12 driver can tolerate much stronger motors without loosing bass performance, a strong motor also makes possible the use of softer suspension due to the greater damping. And there is a curious fact, while a small driver would experience cone breakup at frequencies in the treble region 6-10 Khz, a bigger driver will experience it at much lower frequencies and in the best case gradually. So while the small driver's motor is coupled to the full mass of the membrane for most of the octaves of the spectrum, the big driver motor gets gradually unloaded at higher frequencies, thus making the Mms to BL ratio (weight to power ratio) even more advantageous for reproducing of impulses and sharp signals.
IMHO amongst small drivers more can be found that mumble (less dynamic resolution) than amongst bigger drivers with strong motors.

Now on topic Driving a driver past x-max is nothing serious, it is a matter of inertia, higher compliance linear suspensions storing more energy (low Fs, higher Qms - soft spring, but spring rather than a pillow hanged on underwear sling) allow that. But as the coil leaves the gap, the force is reduced and the higher Qms (stored energy like in a spring) suspension overcomes the inertia easily and sends the membrane back. Many drivers operate like that without noticeable distortion.

Now for the horn enclosure. It is acoustic impedance, but the air in it has inertia too. If on certain frequencies the air in the passage moves together with the membrane, then it will drive it past x-max. Adding some damping on the walls of the horn after the throat of the compression chamber might be helpful or at least fun. Also wadding the front wall of the compression chamber.

Best regards!

Last edited by T101; 25th April 2012 at 11:04 AM.
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Old 25th April 2012, 04:39 PM   #5
doggy is offline doggy  Canada
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Very good informative reply! audio has been a life long obsession;I love my horns-true even with these outdated fe108ez, and confess that EnAbl has given these drivers a second life
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