Quote:
| brucek wrote:
Any normal ported design would have a subsonic filter protecting it, but because these LLT's are tuned so low, the theory (as I understand it), is that the electronics will roll off the power to the driver by the nature of their own poor low end response. |
That is one form. Available headroom and amp limiting is another. If we were using something like an average commercial 12" ported sub that happened to be tuned as low as a LLT, max headroom would be considerably less than the high excursion 15 or 18" drivers most of us use. It would be far easier to completely tax and bring to bottoming such a commercial sub without a highpass. And keep in mind that in Ilkka's model, that's probably at full power. If you model a 15" driver LLT tuned to 15hz and include something like a 1st order 10hz highpass to account for electronics rolloff, try lowering the power to obtain more common levels, as one's demands on a sub aren't always gonna be ~113db or so
With the common RL-p15 LLT design for instance, if we take a look at 400 watts, which equates to an average ~109db levels, max excursion is never reached, let alone xmech. In Rodny's case, with 4 drivers, I wouldn't waste 1 second worrying.
Additionally, if an amp is rated for ~1000 watts and the design is made to keep the driver pretty much within xmech with 1000 watts, amp limiting comes into play. It's not that the amp can't pump out any more than 1000 watts, but the clipping lights should be activated when it's taxed that much and you should be able to hear distress from the sub. If you notice that amp clipping is even a semi common occurrence, you need to build another sub to both keep you better protected and eliminate compression.
You bring all these things together and you have protection to the point where bottoming just hasn't been an issue.
Quote:
| willy-be wrote:
The choice of an infrasonic Fb, in and of itself affords no special protection to a vented alignment. |
Sure it does. If we have two subs in roughly the same size enclosure with the same power, one with a 14hz tune and one with a 25hz tune, and neither with a highpass, which is more likely to bottom with low bass movies? Powerful 10-20hz bass is much more common than powerful single digits bass.
Quote:
| willy-be wrote:
If the electronics pass frequencies below Fb to the driver it will unload. So it's a bit naive to claim these designs need no supplementary protection. |
Again, we get back to headroom. Was Rodny's ported sub bottoming at 7hz at 80db? With 4 ported drivers, he can achieve ~122db in room from about 10hz on up without ever exceeding xmech at any frequency....probably even louder than that.