ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: 3-Wire Biamp?  (Read 2922 times)

Jim McKeveny

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1104
3-Wire Biamp?
« on: January 13, 2015, 07:38:19 am »

Over the years I have occasioned upon soundco's who use 3-wire speaker cable, tying negative terminals together in an NL4. It always seems not...quite...right. I get the impression that it ratchets up the BLOOEY! potential.

On the plus side - we purchase 25% less copper, wrap and cart around less weight.

What are possible downsides?

« Last Edit: January 13, 2015, 07:44:47 am by Jim McKeveny »
Logged

David Morison

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 676
  • Aberdeen, Scotland
Re: 3-Wire Biamp?
« Reply #1 on: January 13, 2015, 08:19:07 am »

Over the years I have occasioned upon soundco's who use 3-wire speaker cable, tying negative terminals together in an NL4. It always seems not...quite...right. I get the impression that it ratchets up the BLOOEY! potential.

On the plus side - we purchase 25% less copper, wrap and cart around less weight.

What are possible downsides?

If either amp is internally bridged, then that would be out the window, also if one amp develops a fault that puts voltage on the neg terminal that could damage the other amp, not just the attached speakers.
Just a couple off the top of my head,
David.
Logged

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3328
  • Isle of Wight - England
Re: 3-Wire Biamp?
« Reply #2 on: January 13, 2015, 08:39:22 am »

If the common wire is of a high enough resistance, the LF will modulate the HF and the HF will modulate the LF.

I think it would need to have quite a high resistance before you could hear the effect though.


Steve.
Logged

Jim McKeveny

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1104
Re: 3-Wire Biamp?
« Reply #3 on: January 13, 2015, 09:14:00 am »

If the common wire is of a high enough resistance, the LF will modulate the HF and the HF will modulate the LF.

I think it would need to have quite a high resistance before you could hear the effect though.


Steve.

I am going to suppose that there is a huge difference in potential  if we are talking about a single modern stereo DSP amp sharing a ground, vs. legacy systems w/external crossovers, etc.

I saw this app most often on (gasp) Carvers.

But where/how back EMF is terminated does not make a difference? Or is Neg terminal a simply ground, and is a ground a ground?
« Last Edit: January 13, 2015, 09:19:30 am by Jim McKeveny »
Logged

TJ (Tom) Cornish

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 4284
  • St. Paul, MN
Re: 3-Wire Biamp?
« Reply #4 on: January 13, 2015, 09:23:08 am »

I am going to suppose that there is a huge difference in potential  if we are talking about a single modern stereo amp sharing a ground, vs. legacy systems w/external crossovers, etc.

I saw this app most often on (gasp) Carvers.
If you're using a single amp where L drives the HF and R drives the LF AND if the amp's negative terminals are bonded between channels (assuming that's OK for that particular amp which isn't universally true) AND if there isn't a cable failure, it's probably not a big deal.

If you're using two amps, now you're bonding the negative terminals of different amps together, which could create issues depending on the design.  Some amps like the larger Behringers and Peavey IPRs (I believe) put two smaller bridged amps in a chassis for the higher power models.  The negative terminals of these definitely can't be connected together.

If the common wire breaks loose anywhere, you have a situation very much like a multi-phase electrical system that loses the neutral wire - you are now putting the sum of the amp channels' output into the sum of the impedance of the LF and HF drivers, which could cause unintended visual effects.

Seems to be a poor compromise to me, as well as difficult to wire - putting jumpers inside NL connectors is difficult.
Logged

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3328
  • Isle of Wight - England
Re: 3-Wire Biamp?
« Reply #5 on: January 13, 2015, 10:35:29 am »

I was thinking about  the LF signal creating a voltage drop across the shared ground.

Lets use some values which are a bit unrealistic for now, just to see the principle.

If the LF amp is 1000 watts and has a 4 ohm load but the shared ground conductor is 1 ohm, then a fifth of the output voltage from the amp appears at the speaker end of this ground connection. Probably around ten volts.

So as far as the HF amp is concerned, what should be a zero volt return path is now going positive and negative with the LF signal and this will have an effect on the HF signal current through the HF speaker.

And the HF is affecting the LF in the same way.


Steve.
Logged

Riley Casey

  • Hero Member
  • *****
  • Online Online
  • Posts: 1541
Re: 3-Wire Biamp?
« Reply #6 on: January 13, 2015, 10:56:24 am »

This was a common practice in the 70s and 80s when three wire twist locks where common and four pin EP connectors hard to find in the US.  Worked fine with 200 watt low and 100 watt high frequency amps for relatively low output things like stage monitors- as long as the wire pockets in the twist lock remained tight.  Not an appropriate practice for modern hi powered amps and no real need since four pole connectors are the standard of this industry.

ProSoundWeb Community

Re: 3-Wire Biamp?
« Reply #6 on: January 13, 2015, 10:56:24 am »


Pages: [1]   Go Up
 



Page created in 0.063 seconds with 22 queries.