Subwoofer damping

Ooops - I was logged in on an sick friend's account (at his request - he has trouble typing now and wanted me to post an ad for him) and forgot to log off before posting. The post just above should have been under username "Audiokinesis".

Duke

I actually wasn't thinking that your amp was clipping . . . I was speculating (as have a few others) that it's the subwoofer drivers themselves that are overloading.

If the drivers are exposed on the bottom, and there are four ports, then I was wrong . . . this IS a reflex enclosure . . . and it's alarmingly big. That is to say, by conventional practices, the guy who designed it maybe didn't know what he was doing? It's probably a minimum of 19 cubic feet or so internal volume, even subtracting for internal bracing, driver magnets and baskets, etc.

For comparison, the JBL 2235 was a 15" of the era with a low Q and low Fs (i.e. might be similar to your drivers in concept) and a pair of them work well in a reflex cabinet of less than 8 cubic feet. If I was to install a pair of 2235s in a cabinet similar to yours, I would expect it to behave much as you describe, with uncontrolled cone excursion at certain frequencies.

So I would do your research on this thing's background and design to try to determine if it indeed CAN work correctly. If it's a one-off piece, then you need to figure out EXACTLY which drivers you have, and see what their common configurations were. And even if you do determine that it's intelligently engineered . . . the drivers themselves could be shot. I'm assuming you would recognize rotted foam surrounds, but another very common issue in older, downward-firing systems is spiders that have lost their springiness and have started to sag (like so many other things do with age, when they are called upon to defy gravity).

No amount of stuffing, or electronic compensation, can make it right if you have worn-out drivers in an ill-conceived enclosure.

Kirkus thanks for your thoughts. I havent talked to the designer in a year but I will have to see if I can contact him. He definately is capable as a designer and audio engineer. He designed me sattelites and their crossovers along with my mono block amps. They are incredible speakers.

I guess I'll have to inspect this. I know for sure Scanspeak made the drivers. I will report back as things progress.

I am going to replace the current crossover. Probably with a NHT X2 as it looks to be the best fit for my system.

Thanks
Roger

Kirkus....I pulled the vents out...they were really tight. Things are not what they seem as far as the internal cabinet size. The HDF walls are 1-5/8 thick all around. It looks to have 2 chambers with a space about 10 inches high above the top of the chamber were there is wool stuffed in. One side has less wool than the other. There is thick padding on most surfaces. So I would say each woofer chamber is about 7 cu ft or a little less. I felt underneath and the rubber suspension feels fine. I probably overdrove the drivers as the present crossover does'nt provide a low pass filter and I have listened and there is alot more energy(frequency) being passed to the sub than is needed. So I will add a little wool and try the NHT crossover when it get's delivered....go from there.

Roger

the present crossover does'nt provide a low pass filter

IMHO, whay you may need is a "high pass filter" to prevent ultra LF reaching the drivers...I'd cut everything below 30 Hz....I don't think you have a "subwoofer" in the modern sense - I think you have something that was intened and designed to enhance bass reprodution in a large space like a club - it probably works best from 40 to 100 Hz.