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J2 amp driving these HF/MF ESLs?
J2 amp driving these HF/MF ESLs?
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Old 27th December 2014, 08:58 PM   #1
oltos is offline oltos  United States
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Default J2 amp driving these HF/MF ESLs?

Could this two-way speaker plan be worth the risk?

A pair of GPA Altec 416-8B 8 ohm midwoofers in 3 cu. ft. (interior) sealed boxes, which cut off their response off below 70Hz. A pair of 12Ē Rythmik sealed servo subs take over below that. The 416ís response is apparently good up to 1kHz, as shown here http://www.greatplainsaudio.com/down...ec%20Sheet.pdf and measured in boxes here Beyond the Ariel

For the HF and MF range, I expect to soon have access to a pair of ~ 8Ē x 6Ē electrostatic panels. They are claimed to have a flat response from 950Hz to 20kHz and ~ 92db sensitivity. So if I can strike a good balance when crossing over -keeping the Altec 416ís response closer to ~ 700Hz-I can minimize the 416ís IM distortion at its upper end, as I did with its lower end response.

However, will my J2 amp be up to handling this capacitive ESL load? It does
25 wpc/ 8 ohms but only 13 (15?) wpc/ 4 ohms. Thus, comparing the attached impedance vs. frequency vs. sensitivity curves, would any of them-where the averaged impedance is 14.25 @ 1kHz-ruin the J2ís performance? If yes, how so?

Would the violet curve be the best choice since its 14 ohms @ 1kHz but having at least 4 ohms @ 9kHz? Or would the J2 amp handle the yellow curve better, though with a probable sacrifice in sensitivity?

Regarding the J2ís distortion vs. power with this apparently difficult load, as the curves show here on p. 6 in the J2 manual FIRST WATT J2 , there is a 3.33 fold difference in distortion for 10 watts at 1kHz between 8 and 4 ohm loads. Would this be an audible difference through high performance HF/MF range ESLs?

Might it not be if the chosen ESL impedance curve had, say, at least 92db sensitivity? That way less power would be needed from the J2 amp, thereby minimizing its distortion.

But, of course, it also depends on how loud one usually listens to music, and at what distance. I am sure that my ears wonít tolerate more than 83db average SPL; possibly only 80db, when sitting 3 meters away.

Letís assume the curve is selected where the ESLís sensitivity is 92db SPL at
1 meter-even if its impedance is well above and well below 8 ohms, between 1kHz & 15kHz, respectively.

If loudness is halved when distanced is doubled-dropping by 6db-then amplifier power must be quadrupled to recover the same loudness? If yes, then at 4 meters away 16 wpc is needed. But at 3 meters only 8 wpc is needed to handle the 92db peaks-and which my ears would probably only want to take briefly, even from sweet sounding single-ended amps.

And this still leaves 5 or 7 wpc left over from the J2ís max. output @ 4 ohms to avoid clipping. Also, I may be quite wrong, but except for violin or piccolo solos, thereís little, if any content beyond 92db in most orchestral recordings from 20kHz to 40kHz range. Thus, power requirements in that range should be relatively light.

Unfortunately, I suppose thereís no getting around the fact that most of these impedance curves get very bad after 10kHz.

So what kind of sonic damage would 15 to 10 ohms from 1kHz to 6kHz inflict on the J2 amp? If very little, then would the yellow curve be better than the violet, with 4 ohms @ 15kHz; and ~ 3 ohms @ 17kHz?

There is one bright spot in that I would be bi-amping the Altec 416s and the ESLs at line level, using the B4 crossover http://www.firstwatt.com /pdf/prod_b4_man.pdf Thus, unlike passive speaker level crossovers, no amplifier power losses will occur. And speaking of power, even with stereo sources, we all do gain ~ 3db in apparent loudness for every identical speaker system channel we add beyond the first one.

But what might these capacitive HF/MF range ESLs actually sound like driven
by the J2 amp, when playing well mastered CDs-let alone 24 bit >88kHz downloads?
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Old 27th December 2014, 11:53 PM   #2
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