Those of us wishing to build subs for pro-sound applications also need to consider sensitivity. While I think this issue of displacement vs. cost is cool, it's clear that the large xmax drivers often suffer in efficiency. For example, the DIYCable Shiva-X 12" driver has an amazing xmax, and thus displacement. Unfortunately, its rated at around 84 db/1M/1W. That means that while it is unlikely to go beyond xmax before hitting its thermal limit (400W), the maximum acoustic output is going to fall short of other drivers with greater sensitivity but reduced xmax. I wonder if it might be possible to build in that sensitivity into that calculation.
I also wonder if it might not be possible to apply servo technology to tame the high excursion as the low frequency cutoff is approached? My very limited understanding of how tapped horns work suggests that such excursion is a factor of diminished acoustic damping in that range (and at roughly double its frequency). Would limiting excursion in those frequencies reduce acoustic output?
I also wonder if it might not be possible to apply servo technology to tame the high excursion as the low frequency cutoff is approached? My very limited understanding of how tapped horns work suggests that such excursion is a factor of diminished acoustic damping in that range (and at roughly double its frequency). Would limiting excursion in those frequencies reduce acoustic output?
craigwalsh said:
Here's a question for you:
Let's say you have two 12 inch drivers. One has a sensitivity of 97db and an xmax of 11mm. The other has a sensitivity of 84db and an xmax of 12mm. If the cone area of the two woofers is identical, which woofer will deliver more output? The one with a sensitivity of 84db or the one with the sensitivity of 97db? (Ignore thermal compression for the moment.)
hmm...
A trick question?
If *all* else is equal then the xMax will/must determine the maximum output, though this is presuming the enclosure, signal bandwidth and power available allow xMax to be the limiting factor...
Stuart
PS Jack just lowered the price of the 12" AR subs on his website...
A trick question?
If *all* else is equal then the xMax will/must determine the maximum output, though this is presuming the enclosure, signal bandwidth and power available allow xMax to be the limiting factor...
Stuart
PS Jack just lowered the price of the 12" AR subs on his website...
Stuart got it right 
People get hung up on efficiency, even though amplifiers are ridiculously cheap these days.
If you have two woofers with equivalent cone size, the one with the higher XMAX will deliver more output, even if the efficiencies are dramatically different.
It seems counter-intuitive but true. In fact, one of the strangest tapped horns that I simmed ran out of xmax with LESS than ONE watt!!! It used a Galaxy Audio woofer, which has VERY high efficiency combined with a low xmax.
People get hung up on efficiency, even though amplifiers are ridiculously cheap these days.
If you have two woofers with equivalent cone size, the one with the higher XMAX will deliver more output, even if the efficiencies are dramatically different.
It seems counter-intuitive but true. In fact, one of the strangest tapped horns that I simmed ran out of xmax with LESS than ONE watt!!! It used a Galaxy Audio woofer, which has VERY high efficiency combined with a low xmax.
Those NHT woofers are almost impossible to beat. As for box option, I'm open to either. I'd prefer to do a tapped horn, for the sake of novelty. But I'm leaning towards a Diyma12 in a bandpass, since it appears to offer the best combination of output and power handling.
The guy who designed them puts them up on ebay occasionally for $100, and I already have a pair sitting here.
The guy who designed them puts them up on ebay occasionally for $100, and I already have a pair sitting here.
Patrick Bateman said:
Patrick: You are correct about which one has more maximum output, so long as they are within their power limits. The higher sensitivity drivers tend to be limited by xmax, whereas the higher xmax units like the Shiva-X are limited by power rating, at least from what I can tell in Hornresp. Thus, their performance is relatively on par for a given TH alignment. So, from what I've gathered, you end up with similar output from a given box (with different limitations). Perhaps I'm looking at this wrong, because I'm a newbie to all this. But the more sensitive box will require less wattage. While I agree amps are cheap, finding a good source of AC is not always that easy (depending on venue of course), and being able to get more output per watt is intuitively more pleasing from an engineering standpoint.
Even so, it's nice to find large x-max drivers to compare in Hornresp. Have you looked at the P-Audio SD21 yet? It's very expensive, but would certainly win hands down on displacement.
MartinQ said:
Martin:
Yeah, I read the xmax value wrong on the USSpeaker site. I thought it was 31.7 mm p2p. A big difference from reality (5.9 mm). I need to understand a bit more about those specs I guess. Even so, in a large (1000l!) TH, this speaker can put out some pretty mean low bass. In this respect, there is another 21" driver, roughly the same price, from B&C (21SW150). I modeled it at 135 dB at it's peak excursion (~15 mm) at roughly 1000W into 1/2 space. At a little over 5L, this driver doesn't have the displacement as the Maelstrom. But I've modeled both in HR, and this driver gives more peak output within its power and displacement limits. Plus, in this large TH, it gets down to around 25Hz without a hiccup. A true UberSub.
Now, I agree this isn't going to win this contest with respect to price, as it comes in at over 2X the price of the Maelstrom. It would also require a HUGE sub volume. I totally got the point of this thread. But, the great thing about this thread is that you all have identified some very potent subs with great excursion ratings. For prosound applications, a more expensive driver isn't that big of a deal if it can get the job done. The price/performance ratio is still way below those for standard commercial subs out there.
Also, thanks for including efficiencies in your list.
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