Yes, the Lowther drivers are an excellent example of paper fatiguing due to flex, i.e. the so-call hundreds of hours they typically take to 'break-in', though I view it as once broken in they are actually worn out and need replacing.
Paper PA drivers were (some still are?) chemically treated during the moulding process to both make it durable as well as have/maintain a specific tone WRT its break-up modes BW, so when properly done it can hold up quite well over decades of abuse as proved by measuring old cinema sound (mid) bass horn drivers.
GM
There's actually a reason I started reading this thread. I was wondering if a JBL 2241H tuned to 20 Hz in a relatively small enclosure would work "well" if I used EQ to flatten/trailer the response.
Yes, it probably would, but when EQing, you make vent sensitivity that much more. You'll want an awfully capable high pass filter if you're boosting, immediately below tuning your excursion will go through the roof if it's still boosted there.
Probably, if sealed. For simple vented it's not a good plan tuning below ~0.7*Fs or ~24-25 Hz based on published Fs and will need some form of steep high pass to protect it below Fb in some apps and of course Caveat Emptor applies for running out of linear excursion above Fb, so will be relatively severely power limited if there's not a lot of room gain.
GM
I was thinking of going sealed actually, since this subwoofer (might use two) will go with my computer speakers 😀 But I wasn't sure if this was a good idea with these drivers
You might take a look at this concept, the "double integrator" circuit. Something like this is used in products from Bag-End. It's for sealed box systems only:
Sub-Woofer Controller
The idea is this:
If you put a driver in a "small" sealed box (here small means Vb<<Vas), the response can be characterized by a relatively high Fb (box tuning), below which the frequency response falls at 12dB/octave. The circuit boosts the power at 12dB/octave to lift the bass and restore flat passband response. For every octave you need 12dB of boost, so practically speaker you can only extend the response about 2.5 octaves before power requirements get to be way too large to be useful.
If you do some modeling, you will find that you can indeed get some impressive bass from this kind of system. On the other hand, when the volume of the box is not very large compared to the total displacement of the cone (at low frequencies), distortion will result from non-linear effects resulting from differences in the air pressure on each side of the cone during the "out of box" and "in to box" motions of the cone. Sigfried Linkwitz has a spreadsheet on his site that can be used to calculate the percent distortion that would result just from this effect (you will get more from other driver non-linearities, too). So even if you can put a huge driver in a small box and apply lots and lots of power, you may not get "high quality" (e.g. low distortion) bass.
-Charlie
2.5octaves is way too high a target for extension of the low frequency bandwidth.
+18dB to +20dB is in my view too much equalisation. +30dB for 2.5octaves is simply unreachable. If upper bass and mid is ticking over at 100mW and peaks of +12dB pass through the system then the +30dB of low bass equalisation would need 100W for the quiet moments and 1600W capability for the transients. If you need +20dB overhead for louder transients we are upto 10kW.
I suggest no more than +10dB of LF equalisation.
+18dB to +20dB is in my view too much equalisation. +30dB for 2.5octaves is simply unreachable. If upper bass and mid is ticking over at 100mW and peaks of +12dB pass through the system then the +30dB of low bass equalisation would need 100W for the quiet moments and 1600W capability for the transients. If you need +20dB overhead for louder transients we are upto 10kW.
I suggest no more than +10dB of LF equalisation.
Yes, I can't argue with what you are saying, but you are being conservative and I was trying to give the absolute limit that you could push to...
Also, the power that is needed depends on other factors to some degree. For instance, the efficiency of the driver is important to consider. For instance, you can use an 18" pro driver that has 10mm Xmax and 98dB/1W SPL. Moreover, the power spectrum is source dependent and most music really does not have all that much power in the subsonic range (below 20Hz) so even if you boost +30dB so your driver is flat to, say, 10Hz the 10Hz-20Hz octave may not really need the full power that you might expect. OTOH, if you are using this to make really loud special effect sounds, like from Jurrasic park or whatever movie soundtrack that has content down to the single Hertz, then you have another story altogether!
-Charlie
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