Originally Posted by chucky7
My best guess is the Cap 4000ULF should have a HPF @ 7Hz, or 2/3 octave lower than its port tune. A 20Hz tuned sub would have HPF @ 13Hz or so.
The Lone Survivor - Helicopter scene is so far the most demanding scene for my Cap 4000ULF, due to the hot 6Hz signal.
Originally Posted by Madaeel
Chucky I don't think a HPF is that far below a ported subs tune. Using your example that's like saying a sub like the V1801 has a HPF around 13hz. The port compression would be monumental and the driver would unload way before 13hz. Again we're talking about a sub tuned to 10hz. The excursion requirements skyrocket since the octaves are so much smaller so it can be dangerous quick. 6hz is almost 4x the excursion below the subs tune. Any ported ID sub is already suffering from port compression as it has to make some sacrifices and at 6hz would be extreme. I'd bet Jeff will share the info with you though. Like you said that 6hz note in the Chinook scene is extremely hot though so it might play some of it at a much lower level then intended or it's harmonics. Without Speclab it's impossible to say really but I highly doubt it. It's just the physics of ported subs. Though the 4K is not your typical ported sub...
It seems to me that the ratio would not be a constant, to begin with. The difference between 2/3 of an octave with a 20Hz port tune, and 2/3 with a 10Hz port tune, would be substantial. I imagine that designers determine the best location for a HPF through a combination of intuition and trial-and-error. But, if anything, I would expect the HPF to be only a few decibels below the port tune, even with a 20Hz tuning point.
On the other hand, let's say that the HPF for the Cap 4000ULF is at about 8Hz, instead of 7Hz. With enough room gain (which at 6Hz could be substantial) I could see the subwoofer still putting-out some significant SPL with the right material. There is something that I think we may be overlooking anyway, though, when we talk about "hearing" the Chinook at 6Hz. Whales might hear the Chinook (even at very low volume levels) but I don't believe that any humans would, even at very high volume levels. We could feel the tactile energy, though, and we could hear harmonics of that fundamental frequency, with the right subwoofer(s). That would make it seem as if we were hearing 6Hz.
That is a point that I think was lost in an earlier post by @beastaudio
. It wasn't just whether the sub was producing meaningful SPL, at a particular frequency, that made the floor buckle upstairs. It was whether the very low-frequency was still making the drivers move rapidly in-and-out, producing particle velocity, which made things shake upstairs, even if there weren't much sound associated with that. Beastaudio was talking about low-frequency tactile response, not low-frequency sound pressure, and they are produced by different mechanisms.
FWIW, I think that under the right conditions, a Cap 4000ULF could produce either meaningful SPL well below 10Hz (with enough room gain), or it could produce significant low-frequency TR, as long as there was still some serious cone excursion occurring.