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Originally posted by John Ashman
a) As I understand it, NHT's subs are both low-Q AND flat, generally +/- 1.5dB or less. |
Sorry. Those two things are mutually exclusive. The flattest bass extension from from a Q=.707, known as a maximally flat tuning. Lower Q tunings (such as infinite baffle designs and very large sealed enclosures) roll off the bass gradually, but starting at a higher frequency.
The NHT Evolution subwoofer's enclosure is not large enough for two 12 inch drivers to be a low-Q tuning. With about 1 cubic foot of enclosure per driver, I would say that the actual tuning of the drivers is probably a fairly high Q tuning (>.9).
What they are then doing is equalizing the bottom end response to achieve something like maximally flat tuning (Q=.7) down to about 30 Hz and then using a very very steep subsonic filter at around 25 Hz to keep from destroying the drivers. I would guess that they are using as much as 8 dB of bass boost at 30 Hz. The dual drivers allow them to do this, since excursion is the limiting factor with this kind of EQ.
This is a good approach, although they might actually get even better performance by moving the -3dB point a little higher and not using the subsonic filter. This would reduce overall output a bit, but a gradual roll-off extending even deeper may be a prefered approach.
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c) "good vented subwoofer" is almost an oxymoron in my book. There are some, but not very many in my experience. You have to accept that everything coming out of the port is musically unrelated to the original signal and is purely for "effect". |
I wouldn't agree with that at all. It is quite possible to tune a vented subwoofer for very impressive, dare I say "musical" performance with no peak at all. This kind of tuning looks very much like a low-Q sealed enclosure. Just look at the way many British companies use vented enclosures in their speakers.
Any output from the vented tuning is most certainly related to the musical signal, since the musical signal is the only energy being input into the subwoofer. The output may well be under-damped, just as a high-Q sealed enclosure tuning may be under-damped. It is, of course, possible to tune a vented enclosure with a huge peak, but I don't really see that happening with most good subwoofers when I model drivers and enclosures. Most companies seem to be doing about the same thing that NHT is doing -- using low bass EQ to achieve a "better" -3dB point on spec sheet and then using a steep subsonic filter to protect the driver. It's a perfectly valid approach.
My pont is this. There is nothing in a two PSB subwoofer system that would inherently lead to "boomy" bass. It is far more likely that "boomy" bass is the result of either a room resonace OR a bass management/subwoofer level calibration issue. I would suggest that the number one cause of "boomy" bass is excessive subwoofer levels -- not the design of the subwoofer.
The reason I bring this up is that throwing money at different subwoofers isn't going to solve a problem if the problem is the result of poor system configuration or calibration.