no, there is no poly fill or any other dampening inside the box. It sounds great....until it bottoms. The thing is, is that when I got it all together it was awesome at first, very loud, and lots of output, then it seemed as it got broke in, it started bottoming in low lfe scenes in movies, don't have an issue with music even pushing it with bass heavy stuff. The gain is at 1/2 and if I have the receiver turned up past -15db it will do it, sucks because I like it around 0db for movies. you would think if they sell this as a kit with a 500w amp, the driver should not have a problem even at max gain?
I'm not so lazy this morning and I have looked at the design.
First of all I was struck by their published simulation. I have never seen a passive radiator sub have a response like that. That simulation is out of the back of the neck. Passive radiator subs ALWAYS have a rapid fall of response below the F3 point.
The next issue is the driver, which has the correct parameters for a sealed sub, except it does not have enough xmax for the required Eq.
Your driver is a high Qts high compliance driver. These types of drivers bottom easily in ported and ABR alignments and are easily damaged, because as you have found they bottom at the drop of a hat.
I have simulated your driver and played with it. I have modeled your box and others. Your box size is suboptimal and so is the ABR. The impedance curve shows significant misalignment. However this alignment was done with intent to help mitigate the bottoming of the driver and running out of xmax.
I modeled your 20" cube with that driver and ABR with a total mass of 135 GM.
There is a 6db peak at 40 Hz to give a false bass impression, then the response drops off like a stone and is 3 db down at 33 Hz and is 33db down at 20 Hz.
However the driver only reaches xmax, the bottoming point, at 20 Hz with a drive of 350 watts. How CSS claim this driver can handle 500 watts is boyond me. It is rated as a 350 watt driver/700 watts peak. Forget the peak, it is a 350 watt driver, period.
So the Bash amp has the power to destroy those drivers and because of the T/S parameters it will, if pushed.
CSS have added a boost below F3, a small one but it compounds the felony and will run the driver out of xmax sooner.
The cabinet should be loosely filled with Polyfill by my model.
I think you have damaged that driver. So the question is how to stop it happening again.
I think the subsonic filter at 18.7 Hz is far too low to prevent damage to that driver. Since the response falls off like a brick wall below 33 Hz, raising the subsonic filter to 30 Hz will protect your driver and not alter the performance.
This is not a sub with a deep reach, it does however reach half way into the last octave.
I note on their site that they say they are developing a horn design for that sub driver. I wish them luck, as the T/S parameters of that driver are totally inappropriate for a horn design. In my view that outfit are far from the brightest bulbs on the block, as you have already found out.
