There are always what one might call "practical limitations" to speakers. The DV12 and the SV9 are not subwoofers. They can produce a fair amount of bass, but the woofers also plays midrange, which all woofers do more easily and efficiently than they make bass. To put that another way, for the same amount of power input, any woofer will make much more midrange than bass. Most people listening to dance music want more bass than midrange, which is what necessitates subwoofers.
To give an idea of how much the demand for bass is above midrange, and the relative ease with which midrange can be made, the ratio can be as high as 4:1 of subwoofers to tops. Trying to get a level of bass that's close to what's desired in modern music from a single 12" or single 9" top cabinet is going to push that top's driver past its limits.
Two high-powered 12" tops could be used with 6 or 8 single 18" subwoofers and the tops would easily keep up. They will definitely "outrun" a single 15" sub. If the DV12 or SV9 cabinet is being run in full-range mode with heavy bass music, it may be that it's giving all it can and that's the limit. In this case, the speaker will make a popping sound, indicating that it has exceeded its performance abilities and should be turned down, and ideally paired with a subwoofer (or two).
This issue is only present in the absence of sufficient bass output, so providing the system with sufficient low-frequency output for your genres and output needs will fix this problem.