How many times can you split an XLR signal?

[Boomzilla]

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 volume-controlled 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 pre-out 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]

Most modern preamps have a low output impedance so splitting to multiple amps is normally fine.

[garbulky]

It should be a cinch for the audio gd. Its output impedance is 10 ohms (supposedly)
www.audio-gd.com/HE/HE-1/HE-1EN_Specs.htm

[Boomzilla]

Thanks y'all - Exactly what I wanted to know.

May I throw in a second question?

The T2 speakers are "nominally" 4-Ohm loads. If I parallel them, I'd get a "nominal" 2-ohm load. My Emotiva PA-1 power amps are good down to 2.7-Ohms. Provided I'm running at less than one watt output, will the PA-1s 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 3-Ohms. So a pair in parallel would offer about a 1.5-Ohm load. But to that would have to be added the series impedance of the speaker wires.

Assuming a 10-foot pair of 16-AWG stranded copper, and recognizing that the signal must traverse both conductors of the pair, the wire should add a minimum of 0.08-Ohms. If I were to use 18-AWG, I'd get 0.128-Ohms. So with a total resistance of 1.58 to 1.63-Ohms, I'm still nowhere near the PA-1's "minimum" of 2.7-Ohms.

So, if I understand this correctly, the answer is "don't use the PA-1 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 6-Ohms 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 FTX-2001 Series III, that IS rated for 2-Ohm loads (675 WPC).

[DYohn]

I would not run two of those speakers in parallel unless the amplifier is stable to 1-ohm. Run each off its own amplifier channel.

[Boomzilla]

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...

[garbulky]

A balanced amp sees a 2 ohm load as a 1 ohm load. This is why the PA-1 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.

[Deleted]

Jul 20, 2020 20:12:15 GMT -5 garbulky said:

A balanced amp sees a 2 ohm load as a 1 ohm load. This is why the PA-1 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. 

[405x5]

Jul 20, 2020 13:46:07 GMT -5 Boomzilla said:

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 volume-controlled 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!

[Boomzilla]

I think there's some confusion about loads (or else I'm confused). An 8-Ohm load is 8-Ohms. It doesn't matter what amp drives it - the load is not amplifier-dependent.

Bridged amplifiers see "half the load per channel." If I took a stereo amplifier and bridged it into a single channel, the 8-Ohm load would "look like" 4-Ohms to the single bridged channel.

But if I were using a Fully-Balanced amplifier in stereo mode, the 8-Ohm load would still be 8-Ohms 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 4-Ohms. So for a fully-balanced amplifier to tolerate a "real" 4-Ohm load, each branch of a channel should be capable of driving 2-Ohms.

Is this correct?

[AudioHTIT]

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?

[leonski]

Jul 20, 2020 19:20:56 GMT -5 Boomzilla said:

Thanks y'all - Exactly what I wanted to know.

May I throw in a second question?

The T2 speakers are "nominally" 4-Ohm loads. If I parallel them, I'd get a "nominal" 2-ohm load. My Emotiva PA-1 power amps are good down to 2.7-Ohms. Provided I'm running at less than one watt output, will the PA-1s 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 3-Ohms. So a pair in parallel would offer about a 1.5-Ohm load. But to that would have to be added the series impedance of the speaker wires.

Assuming a 10-foot pair of 16-AWG stranded copper, and recognizing that the signal must traverse both conductors of the pair, the wire should add a minimum of 0.08-Ohms. If I were to use 18-AWG, I'd get 0.128-Ohms. So with a total resistance of 1.58 to 1.63-Ohms, I'm still nowhere near the PA-1's "minimum" of 2.7-Ohms.

So, if I understand this correctly, the answer is "don't use the PA-1 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 6-Ohms 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 FTX-2001 Series III, that IS rated for 2-Ohm 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.  

[Boomzilla]

Jul 28, 2020 2:26:04 GMT -5 leonski said:

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 daisy-chained in series? Running in series would also allow me to bridge the Ashly FTX-2001 amplifiers, achieving somewhere between 1,000 and 1,350 watts per side. Would this improve dynamics? Inquiring minds want to know...