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Author Topic: Chasing loudspeaker-level Crosstalk  (Read 6309 times)

Lee Buckalew

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #10 on: February 11, 2015, 10:19:38 pm »

Yes, driving analog from a PC interface direct into one side only yields same result.

There are 2 x 4 channel amps per side.

I can unplug the load and plug a monitor wedge straight into the rear of the amps. There is nothing audible above the amp noise floor with no input present . There is low level audible signal on the R side loudspeaker lines with L side driven-  even when not loaded onto an amplifier.

Hayden, you say that you tested the output with a monitor connected locally, directly to the amp.  You then said "There is low level audible signal on the R side loudspeaker lines with L side driven-  even when not loaded onto an amplifier."
What do you mean by this?
We need to understand the full signal path when you are testing.

If you test this with 2 locally powered speakers does the one that is undriven exhibit the same crosstalk as the installed speaker?
If so then it's not the cabling.
If it does not then you need to find the fault in the wiring.  It could be inductive, it could be a ground problem as JR alluded to.  You need to isolate the problem one step at a time.

It may also help, as requested by another poster, to know what the amp make and model are.

Lee
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Hayden J. Nebus

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #11 on: February 11, 2015, 11:04:23 pm »

Hayden, you say that you tested the output with a monitor connected locally, directly to the amp.  You then said "There is low level audible signal on the R side loudspeaker lines with L side driven-  even when not loaded onto an amplifier."
What do you mean by this?
We need to understand the full signal path when you are testing.

If you test this with 2 locally powered speakers does the one that is undriven exhibit the same crosstalk as the installed speaker?
If so then it's not the cabling.
If it does not then you need to find the fault in the wiring.  It could be inductive, it could be a ground problem as JR alluded to.  You need to isolate the problem one step at a time.

It may also help, as requested by another poster, to know what the amp make and model are.

Lee

I had the local monitor paralleled to the installed loudspeaker. Unplugged the NL4 on the rear of the amp, put a NL4MM barrel on it, and connected the local wedge.

I've now observed the same behavior while loaded on both Powersoft M50 and d&b D80, even loaded one side on one brand and one on the other, to no effect.

Some sort of LC coupling seems more and more likely. I may try and get conduit all the way to the rack. Anyone know if flex might provide adequate shielding, or is rigid absolutely necessary?
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Lee Buckalew

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #12 on: February 11, 2015, 11:37:40 pm »

I had the local monitor paralleled to the installed loudspeaker. Unplugged the NL4 on the rear of the amp, put a NL4MM barrel on it, and connected the local wedge.

I've now observed the same behavior while loaded on both Powersoft M50 and d&b D80, even loaded one side on one brand and one on the other, to no effect.

Some sort of LC coupling seems more and more likely. I may try and get conduit all the way to the rack. Anyone know if flex might provide adequate shielding, or is rigid absolutely necessary?

This is not a shielding issue unless something is getting into the speaker cable and being rectified in the amp. 
It is most likely a lack of the speaker wires being twisted pairs or a common ground between the two channels of the amp (in the speaker wire run).  This could be a short (maybe high impedance) between wires from getting skinned slightly during a wire pull.  Could be a connection someplace that's frayed in the speaker cable.

Lee
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Hayden J. Nebus

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #13 on: February 12, 2015, 09:16:43 am »

This is not a shielding issue unless something is getting into the speaker cable and being rectified in the amp. 
It is most likely a lack of the speaker wires being twisted pairs or a common ground between the two channels of the amp (in the speaker wire run).  This could be a short (maybe high impedance) between wires from getting skinned slightly during a wire pull.  Could be a connection someplace that's frayed in the speaker cable.

Lee

I understand the utility of twisting the pairs, but short of that (i.e. pulling new copper)- if this is happening across those first 30 ft of parallel bundle without a direct conduction path, it seems counter-intuitive that discrete conduits all the way to the rack wouldn't provide some sort of magnetic brake. I was really hoping to grasp at a few straws before having new copper pulled!   

Have found no common ground. If there's a high-z short, it's tricking my fluke 87 DMM, which displays into the Mohm range before displaying open. 
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John Roberts {JR}

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #14 on: February 12, 2015, 09:19:18 am »

This is not a shielding issue unless something is getting into the speaker cable and being rectified in the amp. 
It is most likely a lack of the speaker wires being twisted pairs or a common ground between the two channels of the amp (in the speaker wire run).  This could be a short (maybe high impedance) between wires from getting skinned slightly during a wire pull.  Could be a connection someplace that's frayed in the speaker cable.

Lee

+1... check the speaker ground return wiring... BUT I already suggested that.

If the two speaker grounds are shorted together somewhere that could cause it.

JR
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Jason Lavoie

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #15 on: February 12, 2015, 10:18:28 am »

Some sort of LC coupling seems more and more likely. I may try and get conduit all the way to the rack. Anyone know if flex might provide adequate shielding, or is rigid absolutely necessary?

If conduit for the last 30' is going to solve the problem then simply separating the bundle and putting a few inches between the pairs should show a noticeable (measurable) difference as a test.

Quote
I've now observed the same behavior while loaded on both Powersoft M50 and d&b D80, even loaded one side on one brand and one on the other, to no effect.
Does the crosstalk go both ways? or is it only from speaker line A to speaker line B?

Jason
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Hayden J. Nebus

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #16 on: February 12, 2015, 11:53:48 am »

+1... check the speaker ground return wiring... BUT I already suggested that.

If the two speaker grounds are shorted together somewhere that could cause it.

JR

With amplification disconnected from load, checked for cross-continuity across all pairs. all open according to my fluke 87 which ranges to 50Mohm.

I have found a pair of negatives between sides reading ~120kohm with amplification connected and powered down. This jumps down to 160ohms with amps powered up! 
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John Roberts {JR}

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #17 on: February 12, 2015, 12:06:41 pm »

With amplification disconnected from load, checked for cross-continuity across all pairs. all open according to my fluke 87 which ranges to 50Mohm.

I have found a pair of negatives between sides reading ~120kohm with amplification connected and powered down. This jumps down to 160ohms with amps powered up!

VOM Ohms readings with voltage present will not be accurate. The VOM imputes ohms by sending a reference current and reading the voltage rise, so if other currents and/or voltages are present you will read random results. Amps should not be dumping DC into output but that is a different issue.

What do you measure between amplifier grounds? While common speaker ground at the amps should cause minimal crosstalk, if at all.

OK all pairs are open with both ends disconnected (?), do any of the speakers have continuity to external metal parts and perhaps ground to ground path via speaker mounts? 

JR
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Hayden J. Nebus

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #18 on: February 12, 2015, 02:37:25 pm »

VOM Ohms readings with voltage present will not be accurate. The VOM imputes ohms by sending a reference current and reading the voltage rise, so if other currents and/or voltages are present you will read random results. Amps should not be dumping DC into output but that is a different issue.

What do you measure between amplifier grounds? While common speaker ground at the amps should cause minimal crosstalk, if at all.

OK all pairs are open with both ends disconnected (?), do any of the speakers have continuity to external metal parts and perhaps ground to ground path via speaker mounts? 

JR

 Measuring ~120k ohm between output grounds, loaded. Measuring ~60kohm from chassis to output ground, unloaded. Bonding conductors, chassis, and input pin 1's are all @ dead short to each other. 

Conductors are all open relative to flyware/conduit/tray.
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John Roberts {JR}

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Re: Chasing loudspeaker-level Crosstalkt
« Reply #19 on: February 12, 2015, 06:55:56 pm »

Measuring ~120k ohm between output grounds, loaded. Measuring ~60kohm from chassis to output ground, unloaded. Bonding conductors, chassis, and input pin 1's are all @ dead short to each other. 

Conductors are all open relative to flyware/conduit/tray.

tens of kOhm is effectively open circuit for speaker impedance loads.

If the signals are clean at the amp, and crosstalk occurs at the speaker end, it must be something. I ASSUme speaker grounds are similarly tens of K impedance separated?

JR
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Re: Chasing loudspeaker-level Crosstalkt
« Reply #19 on: February 12, 2015, 06:55:56 pm »


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