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Old 12th September 2008, 07:03 AM   #21
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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?
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Old 12th September 2008, 05:14 PM   #22
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Quote:
Originally posted by craigwalsh
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.
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.)
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Old 12th September 2008, 05:49 PM   #23
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Default 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...
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Old 12th September 2008, 05:54 PM   #24
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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.
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Old 12th September 2008, 06:54 PM   #25
MartinQ is offline MartinQ  Canada
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So where are we at with $$$/litre champions? Are we shooting for best tapped-horn driver, bandpass driver, or either one?
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Old 12th September 2008, 07:10 PM   #26
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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.
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Old 12th September 2008, 07:25 PM   #27
MartinQ is offline MartinQ  Canada
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Here's what tops my list so far.
Attached Images
File Type: gif driver displacement leaderboard - 2008-09-12-r01.gif (11.0 KB, 577 views)
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Old 12th September 2008, 07:29 PM   #28
MartinQ is offline MartinQ  Canada
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The only thing skewed in that list is that the MJ18 price has shipping included, but is at the qty 4+ price.

The Tempest-X is priced each and not at the 4-pack price ($173 each).
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Old 12th September 2008, 07:38 PM   #29
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I spent a few minutes coming up with a mini-matterhorn using the NHT eights. At $12 a piece, you could pick up sixteen of them and a 2400 watt amp for about $600. Imagine four of these mini-matterhorns, each with four eights, doing home theater duty. Kind of compelling huh?
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Old 12th September 2008, 07:59 PM   #30
MartinQ is offline MartinQ  Canada
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OK, I updated my leaderboard and fixed a few things. Some of the drivers were incorrect and some NHT inventory was only showing a QTY of 1.
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File Type: gif driver displacement leaderboard - 2008-09-12-r03.gif (12.8 KB, 527 views)
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