Home studio use is the original intended application. It's connected to a pair of KRK RP5s (G2) via RCA cables and goes directly to my laptop (haven't got an audio interface yet). Though I also tested it on its own, without the monitors and used 2 different RCA to 3.5 mm Jack cables.
Of course before even thinking about what sub should I get the first thing I did was some research on how you should and should not treat this whole audio system thing, my first time after all. The first thing I did after hooking it up was to run a sine wave through and see how it sounds, I didn't even dare to put the volume on max, I was a bit too scared. Also I am aware that the sub is not designed to play frequencies anywhere below 28 Hz, the point of the video demonstration was just to show where the rattle occurs.
Therein lies your problem. There is a significant difference of the stress test of sine waves and music program. I would not think that a unit like that would perform well with sine waves, However for music program at modest volume it probably would not rattle.
It seems to me that unit is way oversold deigned to garner way over optimistic expectations. Studio use is a highly demanding application. That unit by virtue of size, and size of driver looks totally unfit for that purpose to me. I would expect, and predict, it would behave in the manner you describe.
You can try a return, but I would expect similar behaviour from its replacement.
I guess my best advice is to turn up your BS alarms to much higher sensitivity level, when dealing with advertising copy. One more tip. If you see specs like those where the spec. says it plays to 30 Hz, and there is no db level quoted in the spec, then run and do NOT press the buy button. The reason is that you don't know how many db down it is at 28 Hz. The ethical way to quote the spec, is to quote it at the -3db point. The way the spec, is written it could be 24 db down for all you know.
The point at which a sub is 3db down is important as it will roll off at 24db per octave below that point if it is ported and 12 db below that point if sealed. Although the sealed sub will have an innate f3 quite high and have its output extended by equalization, which requires a much more expensive driver with a missive motor system and suspension, driven by a powerful amp.
A ported sub can not be equalized. A driver in a ported sub rapidly decouples from the box loading below f3. If driver below f3 it will rattle as you describe, and if continued severe driver damage rapidly ensues. So it seems to me you have driven it with sine waves below f3. Manufacturers often, and should provide a high pass filter just below f3 to prevent driver bottoming and damage. However if you drive it with sine waves, you can drive it though the high pass filter and still cause damage.
I would surmise that sub spec, should actually be f3 40 Hz or 40 Hz -3db. It sounds to me that you drove with sine waves at frequencies where the driver has decoupled from the box. In which case it is not a sub and should have been described as a bass module.
