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Old 15th November 2011, 07:50 PM   #21
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Quote:
Originally Posted by just a guy View Post
Ok, so you are saying that if you have 2 drivers in the same type of enclosure and the drivers are identical but one has more xmax, that the one with more displacement will win?

Ok, I fully agree, that much is almost too obvious to be stated. But it doesn't have anything to do with the statement you quoted from me. I was trying to point out that the drivers on the list WILL NOT work in the same type of alignments at all so they are in fact apples and oranges. The Alpha will ONLY work well on OB while the other drivers listed work best in other alignments, so rating them based on displacment alone has limited usefulness.
And I also said before that you could EQ to get the right kind of response.
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Old 15th November 2011, 08:03 PM   #22
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Sure, as MJK has shown you can get good response down to a fairly low frequency from an Alpha 15 on OB. But don't expect to get much more than 100 db out of it. Add another one (effectively doubling the displacement and power) and you can get 6 more db.

Anyway, I understand what you are saying and (I think) we are (at least mostly) on the same side here. Sorry for the misunderstanding.
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Old 15th November 2011, 08:35 PM   #23
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Originally Posted by just a guy View Post
Actually the change in the impedance curve looks pretty dramatic when you compare 1 cab vs 8. I have no experience with the driver itself and certainly no experience with stacks of horn subs so I don't know how much difference the change in impedance makes in real world power handling.

Anyway, here's the original quote.
I do have extensive experience both with the Lab 12 driver and stacks of horn subs with as many as 80 drivers.

The quote says,
“In general it would be safe to say that 1000W per box shouldn't fry drivers, and when using 4 or more boxes coupled, 2000W per box should not be a problem, WITHIN THE BOX'S PASSBAND.”

The quote does seem to infer that coupling increases power handling, which is not the case.
A 2000 watt peak with 10 dB of dynamic range is only about 200 watts of average power, not enough to burn the Lab 12. Pink noise has 12 dB of dynamic range, and most forms of music have more dynamic range than pink noise.
That said, folks with a propensity to run stuff into heavy clip decrease dynamic range to the point where a 1000 watt amp may put out almost a continuous 1000 watts, which will burn a pair of 400 watt voice coils.

If an array does result in “dramatic difference in impedance”, say a doubling of average impedance, the higher impedance will only draw 1/2 the power given the same voltage.

The large, higher impedance array does not handle more power per driver, it simply consumes less power per driver from the given amplifier voltage, which is fixed by limiting, clipping or a combination of the two.

At any rate, most drivers easily handle the thermal load from peak power required to drive them to Xmax, so Xmax rather than power determines ultimate peak output.

But you knew that..
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Old 15th November 2011, 09:07 PM   #24
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Originally Posted by weltersys View Post
The quote does seem to infer that coupling increases power handling, which is not the case.
I like the acoustic side of things more than the electical so I'm a bit out of my league here but...

Coupling increases efficiency, the difference between 1 cab and 8 is dramatic. With more efficiency, more power is converted to sound, less to heat. If a driver doesn't heat up as much it should be able to handle more power.

Comparing 1 cab to 8, below 50hz the impedance on average doubles. To me that looks like it takes less current for a given amount of output, in other words more efficiency and less heat. Less heat allows for higher power handling.

Am I wrong here?
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Old 15th November 2011, 09:31 PM   #25
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I should have used this Danley quote intstead of the Seaton quote, it's much more to the point.

Quote:
In an efficient horn, the load impedance may be 2 times the driver resistance so the
current is cut in half for a given voltage and since it is current squared divided by
R, the heating is reduced to 1/4 the old value. With the LAB horns, like all other bass
horns, the measured power capacity, efficiency and response will change depending on the
number of units used. The predicted impedance for 6 units for example suggest that the
power capacity will be several times the normal rating for the drivers.
Again, this is not my area of expertise, I'm just quoting what I've seen. But it seems to make sense to me. (I realize the Labhorn itself is not a great example as it wasn't folded well (back chambers way too small).

Last edited by just a guy; 15th November 2011 at 09:34 PM.
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Old 15th November 2011, 10:56 PM   #26
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Quote:
Originally Posted by just a guy View Post
I should have used this Danley quote intstead of the Seaton quote, it's much more to the point.

Quote:
In an efficient horn, the load impedance may be 2 times the driver resistance so the current is cut in half for a given voltage and since it is current squared divided by R, the heating is reduced to 1/4 the old value. With the LAB horns, like all other bass horns, the measured power capacity, efficiency and response will change depending on the number of units used. The predicted impedance for 6 units for example suggest that the
power capacity will be several times the normal rating for the drivers.


Again, this is not my area of expertise, I'm just quoting what I've seen. But it seems to make sense to me. (I realize the Labhorn itself is not a great example as it wasn't folded well (back chambers way too small).
Quote Tom, then dismiss the design he gave away that performed as well with an off the shelf driver as the BT7 he designed that Mark Seaton was still trying to sell ?
Tom Danley’s quote makes sense, but does not claim a doubling of load impedance from one to eight horns, it simply says an effecient horn may be double a driver’s DCR.
Most BR cabinets also have an average impedance greater than DCR too.

You may have caught Tom and Mark in a kind of semantic flub, as less power is delivered to a higher load impedance, while the “normal rating for the drivers” is in an infinite baffle, much closer to the DCR of the drivers than six LabSubs.

Doubling cone area adds 3 dB efficiency, going from one driver or one cab to 8 cabinets adds 9 dB of efficiency, assuming said cabinets are within 1/4 wavelength of each other.
This means only about 1/10th the power is needed to achieve the same SPL. from 8 vs 1, a huge difference. Of course, to get another 3 dB efficiency requires 16 cabinets, and they are unlikely to be crammed within 1/4 wavelength ...

For most, the reason to add drivers or cabinets is to increase SPL, so they add power as well as cabinets so the drivers can reach Xmax (or more).
Just as much heat per driver is wasted, but the overall SPL is much greater, the additional power handling of 8 vs 1 brings the net gain to 18 dB, with perhaps another 3 more dB due to directivity.
In the case of most FLH like the LabSub, with mouth area too small individually for good LF response, in addition to the 9 dB sensitivity gain from one to eight cabinets, frequency response goes a bit lower and flattens out. That said, most of the gain is from the multiples, not the mouth area, as can be seen when comparing any FLH response from singles to multiples.

Given the choice between adding 9 dB in efficiency, or 9 dB of power to reach the same SPL, one has to weigh whether 8 times the cabinetry can fit in the home, truck or venue.
The driver, wood, and real estate costs required for ultimate efficiency are not such a bargain, especially when amplifier power is now so cheap.

For most, the high excursion woofer in a sealed or ported (BR) box is the solution they can live with.
And if you want another 6 dB of efficiency over BR, but can’t afford the huge size required for FLH, and don’t mind a box 1/2 to 2 times a BR, tapped horns are the solution.

Tom Danley has returned to FLH designs for really large enclosures where the advantage of TH are not as great as the disadvantages.

Art Welter
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Old 15th November 2011, 11:12 PM   #27
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Quote:
Originally Posted by just a guy View Post
Sure, as MJK has shown you can get good response down to a fairly low frequency from an Alpha 15 on OB. But don't expect to get much more than 100 db out of it. Add another one (effectively doubling the displacement and power) and you can get 6 more db.

Anyway, I understand what you are saying and (I think) we are (at least mostly) on the same side here. Sorry for the misunderstanding.
Don't worry about it.

But, consider the Alpha 15 in a regular box instead of just in OB. Get the best possible alignment in a box simulator and then use EQ to get the rest of the way there. Then, it just becomes a matter of feeding the box enough power to hit the displacement-limited SPL (that is, if the drivers can handle it - which they probably can). I'll play around with some curves tonight.
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Old 15th November 2011, 11:21 PM   #28
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Originally Posted by 454Casull View Post
Don't worry about it.

But, consider the Alpha 15 in a regular box instead of just in OB. Get the best possible alignment in a box simulator and then use EQ to get the rest of the way there. Then, it just becomes a matter of feeding the box enough power to hit the displacement-limited SPL (that is, if the drivers can handle it - which they probably can). I'll play around with some curves tonight.
Unfortunately, EQ won't increase displacement limited output, all you can do is knock down the peaks where the driver makes lots of output.
In the case of the Alpha 15, you are stuck with only around 100 dB in the 40 Hz range in a BR at Xmax, and that whimpy motor won't push a TH.
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Old 15th November 2011, 11:45 PM   #29
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Originally Posted by weltersys View Post
Unfortunately, EQ won't increase displacement limited output
Sure, but that's the crux of the argument. Bass is limited by displacement only, all else equal.

As for not being able to push a TH, well, I've haven't looked at that. I recall being able to get decent results from a Beta-12A-2 sim, though.
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Old 16th November 2011, 04:09 PM   #30
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It's interesting you debate the Alpha15 so intense. To me it's overall unfortunate that this unit has got a status of 'The OB Woofer' just on gounds of bass output at medium SPLs without EQ. It certainly is not based on quality grounds. It produces bass in OB but how does it really sound compared to ..... ?

/Erling
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