And I have said it as many times that above 50Hz has literally nothing to do with the suspension of the driver. The system compliance is dominated by the ENCLOSURE. Hoffman's Iron Law. You can't get around it. Below tuning in a vented box, there is virtually no compliance from the enclosure which is why it unloads. It takes very little power to drive the woofer to high excursions. That is what a highpass filter is for, also mistakenly called a subsonic or infrasonic filter. The point is to prevent the driver from over excursion. You argued with me over and over that a woofer should not need a highpass filter to protect from over excursion so I tried to explain it to you with models. I'll copy the basics here.
First, here is a graph of the AV12H in 2.5cf tuned to 33hz. The orange curve is with full range input to the driver. You can see with 1000W it is possible to exceed Xmax about 22-23hz. (with 1600W it will be much higher.) The idea is to take down excursion below tuning without affecting the output greatly above tuning. The 12db highpass (subsonic or infrasonic) with a Q of .7 will do this quite nicely. With the addition of the 30hz 12dB highpass you get the yellow curve.
This now keeps excursion well within limits. It now takes much more power to surpass the 23mm Xmax below tuning. Now, that assumes a 2nd order highpass with a Q of .7. Some amps have a higher Q filter above 1.0 that actually gives a bump and increases excursion over a limited range before lowering it. In that case it is a good idea to move it slightly higher to the same as your tuning frequency.
The other suggestion given was for a stiffer spider. This is not nearly as effective because the system is dominated by the enclosure and not the driver suspension. You need extreme changes in suspension stiffness to protect the driver below tuning. The following graph shows the original driver in green, suspension stiffness doubled in red and then 10x the suspension stiffness in the light gray.
You can see that doubling the suspension stiffness has very little effect until under 20hz. This is not in the area we are concerned with where we will run into the excursion limits of the driver. The light gray with 10x the suspension stiffness has more effect, but at the same time actually increases excursion from 28-30hz due to the raised Q of the driver. Excursion below that point is still coming very close to the 23mm Xmax. And now the Fs of the driver is moved all the way up to well over 50Hz.
Finally here is an image just showing the woofer alone in green, with 2x suspension stiffness in red, and with the 30hz 12dB highpass in yellow.
http://www.aespeakers.com/pics/AV12H_2.5cf_33hz_HP_vs_stiff_suspension.png[/ig]
This shows clearly that a highpass is much more effective at preventing over excursion from the driver than increasing suspension stiffness.
That all assumes that the driver doesn't have a bent up cone, torn spider, and surround ripped off. I just don't have the ability to see how a woofer will model under those circumstances.
John
