Hi AndrewT,
Interesting subject. No matter how many times I hear about it, I get this feeling that not everyone agrees.
If two closely spaced drivers are each fed with the same as one alone is, we have +3dB. That is, twice the electrical power, and twice the acoustic power response.
The thing is, SPLs are supposed to add like voltages. This would suggest a 6dB increase.
I have heard that acoustic power response only 'gels' in a large room at a decent listening distance, and the SPL version applies in the nearer field.
Am I missing something?
Interesting subject. No matter how many times I hear about it, I get this feeling that not everyone agrees.
If two closely spaced drivers are each fed with the same as one alone is, we have +3dB. That is, twice the electrical power, and twice the acoustic power response.
The thing is, SPLs are supposed to add like voltages. This would suggest a 6dB increase.
I have heard that acoustic power response only 'gels' in a large room at a decent listening distance, and the SPL version applies in the nearer field.
Am I missing something?
I just ran the numbers on that mid, at No=0.36% it's only about 87.5dB/W midband. It has a massive peak around 4Khz, that's why they claim 91dB average.
As regards parallel conected drivers on a solid state amp. The gain will be 6dB at anything below clipping at frequencies up to the point where the drivers are 1/4W apart. Until you reach the point of clipping, it matters none that the amp may only be able to do 1dB more power at 4 ohms vs 8 ohms.
MTM boxes have terrible power response at the crossover point. The JBL 4612 looks like a MTM, but is not. One driver is rolled off way below the crossover point to the HF driver, so it sounds much better than a typical MTM.
I would send those drivers back and start over.
As regards parallel conected drivers on a solid state amp. The gain will be 6dB at anything below clipping at frequencies up to the point where the drivers are 1/4W apart. Until you reach the point of clipping, it matters none that the amp may only be able to do 1dB more power at 4 ohms vs 8 ohms.
MTM boxes have terrible power response at the crossover point. The JBL 4612 looks like a MTM, but is not. One driver is rolled off way below the crossover point to the HF driver, so it sounds much better than a typical MTM.
I would send those drivers back and start over.
Hi Djk,
To get the full 6db you need +3db from the sensitivity increase (two drivers close together with respect to frequency) and +3 db from the doubled power input.
One will find that an amp that reduces voltage badly when asked to drive half load impedance will also reduce voltage at any power below clipping as well as at clipping, The db loss at reduced output will not be as bad as when at full output.
if the amp can only manage +1db into half the load impedance then the gain by paralleling the two bass drivers (<1/4w apart) will be +4db (+3db+1db), not 6db.
To get the full 6db you need +3db from the sensitivity increase (two drivers close together with respect to frequency) and +3 db from the doubled power input.
One will find that an amp that reduces voltage badly when asked to drive half load impedance will also reduce voltage at any power below clipping as well as at clipping, The db loss at reduced output will not be as bad as when at full output.
What someone didn't think about is amps have feedback, they act like a voltage source. At anything below clipping they will seem to play 6dB louder into two drivers.
A tube amp will behave exactly the same way, and for the same reason. The only problem with a tube amp is if you mis-match the impedance taps, while it will play louder at low volume, it will not play as loud at full volume as if the impedance was matched.
Because of this, two drivers on a tube amp with properly matched impedance will only play 3dB louder than one driver.
Practically speaking, virtually all solid state amps will increase 6dB if the program material is not completely squashed flat by compression.
A tube amp will behave exactly the same way, and for the same reason. The only problem with a tube amp is if you mis-match the impedance taps, while it will play louder at low volume, it will not play as loud at full volume as if the impedance was matched.
Because of this, two drivers on a tube amp with properly matched impedance will only play 3dB louder than one driver.
Practically speaking, virtually all solid state amps will increase 6dB if the program material is not completely squashed flat by compression.
Hi,
Topic wandering all over the place as far as I can tell.
The issue here is what is the current amplifier power into what
efficiency current loudspeakers. If the current loudspeakers are
not efficient then the 1.5kW requirement does not make sense.
Probably the current amplifier will be fine with high efficiency speakers.
/sreten.
Topic wandering all over the place as far as I can tell.
The issue here is what is the current amplifier power into what
efficiency current loudspeakers. If the current loudspeakers are
not efficient then the 1.5kW requirement does not make sense.
Probably the current amplifier will be fine with high efficiency speakers.
/sreten.lndm said:AFAIK, punkrokr1701 is planning to use two 12" woofers in parallel per side. Each has a sensitivity of 96dB/W/m. ie 99-102dB/W/m
If they could handle 1500W, and I don't think they can, we're looking at over 130dB at 1m.
AFAIK, these are for a home system
Hi,
Quick analysis of a ~ 96dB/W typical 12" with ~ 4mm of excursion
in a reflex cabinet indicates excursion limited handling is ~ 200W.
(Thats for 4mm one way, 4mm both way limits at 50W drive)
/sreten.Hi,
the bass drivers are described as 300W, presumably a thermal limit.
I think the Xmax is slightly bigger than 4mm, but not much.
The problem is that someone invented 1500W and passed it on to the thread starter and he has assumed that this becomes easy to achieve without understanding the problems he is introducing by starting at the wrong end with the wrong advice.
He is not playing to a 250 person assembly each wanting their ears to bleed.
We await a brief and from there we can help him develop a specification (within a tight budget).
the bass drivers are described as 300W, presumably a thermal limit.
I think the Xmax is slightly bigger than 4mm, but not much.
The problem is that someone invented 1500W and passed it on to the thread starter and he has assumed that this becomes easy to achieve without understanding the problems he is introducing by starting at the wrong end with the wrong advice.
He is not playing to a 250 person assembly each wanting their ears to bleed.
We await a brief and from there we can help him develop a specification (within a tight budget).
Ok guys, this is no longer about amps, so I'll close this thread. Please continue the discussion over in this thread. I've copied the last couple of posts over so you should be able to carry on as normal.
Thanks
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