Originally Posted by femi
Why do you think the paper cone of the FV18 will have more low-bass then the FV25?
I didn't say that the paper cone FV18 would have more low-bass (SPL) than the FV25HP. I said that, based on user reports at least, it would have more low-bass TR. Tactile response is not the same thing as loudness. And, those low-bass tactile sensations can really enhance the special effects in movies. I think that it is partly the low-bass SPL that Hop is after, and partly the low-bass TR. The FV25 will have far more low-bass SPL than he has now, while the FV18 (with the paper cone) will have both more low-bass SPL and
more low-bass TR. Win-win!
To me, an even better question is why does the paper cone FV18 have more low-bass TR than the metal cone version? And, I don't know that anyone has suggested a viable answer for that yet. Here is what I know--or at least believe that I know. Ported subs, in general, can produce more particle velocity, which we feel as tactile sensations, within about an octave of their port tune. I believe that is due to a combination of factors, including increased air moving through the ports, an increasingly out-of-phase condition between the driver and the ports as the subwoofer approaches its tuning point, and increased ringing.
That out-of-phase condition was pretty well demonstrated a couple of years ago on the Nearfield Ported MBM thread, when some people deliberately ran their ported mid-bass modules out-of-phase, with no increase in SPL, and achieved significant increases in mid-bass TR. I don't really see a role for THD (total harmonic distortion) in low-bass TR, and Ray's graphs certainly don't demonstrate a correlation between THD and TR. According to his distortion test results, the V1801's demonstrated far more ULF distortion than the other two subwoofers, but produced the least
amount of ULF TR.
But, so far, I can't think of a good explanation for why the paper cone driver would allow the FV18 to have more low-bass TR than other ported Rythmik subwoofers. As I understand it, the paper cone is more flexible than the metal cone, and it produces approximately 3db more SPL in the mid-bass range than the one that Data-Bass measured. But, additional headroom doesn't translate into additional low-bass TR.
If it did, the FV18 with the metal cone should have more low-bass TR than PSA ported subwoofers, and the FV25HP should have more low-bass TR than the paper cone FV18. And, anecdotally at least, that is not the case. (It is also not the case with people who are able to produce very high low-bass SPL's with multiple sealed subs. The low-bass TR still lags, compared to that of ported subs.)
So, at this point, I am having to attribute the increase in low-bass TR as an unintended, and unexplained consequence, of the development of the paper cone for the FV18. FWIW, I think that subwoofer design involves both art and science, with final results sometimes surprising the designer. There are several recent examples of that, including the newer model JTR Cap 2400 and the PSA S7201.