
Post by boomzilla on Jul 20, 2020 13:46:07 GMT 5
Assuming, for the moment, that I end up with stacked Emotiva T2 speakers and different amplifiers for each pair, I'd have split the XLR signal from the preamplifier once per channel (pre out to a splitter & one XLR to each of the amp channels).
But I might want to also split the preamplifier's volumecontrolled signal AGAIN to include stereo subwoofers. In that case, I get the pre out to a first splitter & one XLR to one of the power amps, but the other XLR hits a SECOND splitter with one output to the second power amp and one output to the subs.
That means that (assuming all destinations are 22,000 ohms) that the preout will see only 7,333 Ohms. But if the "pro" amplifier uses 10,000 Ohms at its input, then the preamp might see as low as 5,238 Ohms.
Is this safe for the preamplifier?


DYohn
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Post by DYohn on Jul 20, 2020 15:05:40 GMT 5
Most modern preamps have a low output impedance so splitting to multiple amps is normally fine.



Post by garbulky on Jul 20, 2020 15:30:34 GMT 5



Post by boomzilla on Jul 20, 2020 19:20:56 GMT 5
Thanks y'all  Exactly what I wanted to know. May I throw in a second question? The T2 speakers are "nominally" 4Ohm loads. If I parallel them, I'd get a "nominal" 2ohm load. My Emotiva PA1 power amps are good down to 2.7Ohms. Provided I'm running at less than one watt output, will the PA1s handle the Parallel load of the T2 speakers without going into oscillation and frying themselves? Impedance curve from Stereophile magazine shown below: The low point seems to be at about 100Hz. (a frequency with a LOT of musical content). At that frequency, the woofer's impedance drops to 3Ohms. So a pair in parallel would offer about a 1.5Ohm load. But to that would have to be added the series impedance of the speaker wires. Assuming a 10foot pair of 16AWG stranded copper, and recognizing that the signal must traverse both conductors of the pair, the wire should add a minimum of 0.08Ohms. If I were to use 18AWG, I'd get 0.128Ohms. So with a total resistance of 1.58 to 1.63Ohms, I'm still nowhere near the PA1's "minimum" of 2.7Ohms. So, if I understand this correctly, the answer is "don't use the PA1 amplifiers with paralleled T2 speakers." As KeithL points out, though, since the speakers have identical crossovers, there would be no significant harm in running the speakers in series. That would give a minimum impedance of about 6Ohms at 100 Hz. This should be an easy drive for ANY current amplifier. And if I DO want to try the speakers in parallel, I still have the Ashly "pro" amplifier, the FTX2001 Series III, that IS rated for 2Ohm loads (675 WPC).


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Post by DYohn on Jul 20, 2020 19:46:04 GMT 5
I would not run two of those speakers in parallel unless the amplifier is stable to 1ohm. Run each off its own amplifier channel.



Post by boomzilla on Jul 20, 2020 19:50:00 GMT 5
Thanks, David  You're probably right. If I go below the amp's rated minimum, I'm relying on the amp protection circuits to avoid buying BOTH new speakers and new amps. Not a good situation...



Post by garbulky on Jul 20, 2020 20:12:15 GMT 5
A balanced amp sees a 2 ohm load as a 1 ohm load. This is why the PA1 is rated to 2.7 ohms. A 2 ohm nominal can dip down below 2 ohms. Which means the amp would be seeing loads below 1 ohm. I would not want to see what happens when it does.


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Post by Deleted on Jul 20, 2020 20:58:27 GMT 5
A balanced amp sees a 2 ohm load as a 1 ohm load. This is why the PA1 is rated to 2.7 ohms. A 2 ohm nominal can dip down below 2 ohms. Which means the amp would be seeing loads below 1 ohm. I would not want to see what happens when it does. So wire them in series. 8 ohms and that'll be 4 ohm load as seen by the amp.



Post by 405x5 on Jul 22, 2020 15:37:57 GMT 5
Assuming, for the moment, that I end up with stacked Emotiva T2 speakers and different amplifiers for each pair, I'd have split the XLR signal from the preamplifier once per channel (pre out to a splitter & one XLR to each of the amp channels). But I might want to also split the preamplifier's volumecontrolled signal AGAIN to include stereo subwoofers. In that case, I get the pre out to a first splitter & one XLR to one of the power amps, but the other XLR hits a SECOND splitter with one output to the second power amp and one output to the subs. That’s easy....Just ask an Italian!



Post by boomzilla on Jul 22, 2020 15:45:24 GMT 5
I think there's some confusion about loads (or else I'm confused). An 8Ohm load is 8Ohms. It doesn't matter what amp drives it  the load is not amplifierdependent.
Bridged amplifiers see "half the load per channel." If I took a stereo amplifier and bridged it into a single channel, the 8Ohm load would "look like" 4Ohms to the single bridged channel.
But if I were using a FullyBalanced amplifier in stereo mode, the 8Ohm load would still be 8Ohms to each channel. But since each individual stereo channel is actually two branches of amplification (a positive and a negative), each "branch" of the stereo channel would have a load that "looked like" only 4Ohms. So for a fullybalanced amplifier to tolerate a "real" 4Ohm load, each branch of a channel should be capable of driving 2Ohms.
Is this correct?



Post by AudioHTIT on Jul 22, 2020 20:25:32 GMT 5
I think regardless of what type of amp it is you read the specs and stay within them ... if it says it’s stable into 4 ohms or 2 ohms, it doesn’t matter what it’s topology is, no?



Post by leonski on Jul 28, 2020 2:26:04 GMT 5
Thanks y'all  Exactly what I wanted to know. May I throw in a second question? The T2 speakers are "nominally" 4Ohm loads. If I parallel them, I'd get a "nominal" 2ohm load. My Emotiva PA1 power amps are good down to 2.7Ohms. Provided I'm running at less than one watt output, will the PA1s handle the Parallel load of the T2 speakers without going into oscillation and frying themselves? Impedance curve from Stereophile magazine shown below: The low point seems to be at about 100Hz. (a frequency with a LOT of musical content). At that frequency, the woofer's impedance drops to 3Ohms. So a pair in parallel would offer about a 1.5Ohm load. But to that would have to be added the series impedance of the speaker wires. Assuming a 10foot pair of 16AWG stranded copper, and recognizing that the signal must traverse both conductors of the pair, the wire should add a minimum of 0.08Ohms. If I were to use 18AWG, I'd get 0.128Ohms. So with a total resistance of 1.58 to 1.63Ohms, I'm still nowhere near the PA1's "minimum" of 2.7Ohms. So, if I understand this correctly, the answer is "don't use the PA1 amplifiers with paralleled T2 speakers." As KeithL points out, though, since the speakers have identical crossovers, there would be no significant harm in running the speakers in series. That would give a minimum impedance of about 6Ohms at 100 Hz. This should be an easy drive for ANY current amplifier. And if I DO want to try the speakers in parallel, I still have the Ashly "pro" amplifier, the FTX2001 Series III, that IS rated for 2Ohm loads (675 WPC). It's not necessarily the impedance that'll get ya, but rather the combination of an impedance LOW at the same time as a high phase angle. Look a little lower than the 100hz low point to see where impedance line crosses the Phase line. That's the REAL kicker here. Call it 4 ohms at nearly 60 degrees. THAT'S gonna be a problem and worse if parallelled. Your amp.....any amp will deliver far LESS power under those conditions than rating. I think you use the COSINE of the phase angle which in this case is 0.5 so that's the multiplier. The final question? IS the amp capable under those conditions? Will the impedance / phase (reactance, as it were) react poorly with the output Zobel of the amp? 'D' amps have generally speaker impedance sensitive with high frequency output dropping with impedance. Stereophile calls the min impedance 2.85 ohms and the phase angle about 53 degrees at the slightly lower frequency where impedance is 4 ohms.........Not the easiest load.



Post by boomzilla on Jul 28, 2020 4:05:19 GMT 5
It's not necessarily the impedance that'll get ya, but rather the combination of an impedance LOW at the same time as a high phase angle. Look a little lower than the 100hz low point to see where impedance line crosses the Phase line. That's the REAL kicker here. Call it 4 ohms at nearly 60 degrees. THAT'S gonna be a problem and worse if parallelled. Your amp.....any amp will deliver far LESS power under those conditions than rating. I think you use the COSINE of the phase angle which in this case is 0.5 so that's the multiplier. The final question? IS the amp capable under those conditions? Will the impedance / phase (reactance, as it were) react poorly with the output Zobel of the amp? 'D' amps have generally speaker impedance sensitive with high frequency output dropping with impedance. Stereophile calls the min impedance 2.85 ohms and the phase angle about 53 degrees at the slightly lower frequency where impedance is 4 ohms.........Not the easiest load. Thanks, leonski  I had not payed attention to the phase, and I should have. At the moment, I have lots of amplifier channels to work with, so there's no reason to even think of running the speakers in parallel. But I might consider trying them out in series... What happens to phase angle when speakers are daisychained in series? Running in series would also allow me to bridge the Ashly FTX2001 amplifiers, achieving somewhere between 1,000 and 1,350 watts per side. Would this improve dynamics? Inquiring minds want to know...

