Jump to content


Never use shielded cable for outut wiring


  • Please log in to reply
3 replies to this topic

#1 Duck-Twacy

Duck-Twacy
  • Members
  • 4 posts

Posted 28 January 2006 - 07:18 AM

Hello,

Just received my K2. I plan to use it as the bass amplifier for my speakers (Lambda Acoustics SB12  rolleyes.gif  ).

I noticed in the manual a warning (in bold characters) is given not to use shielded cable for the speaker wire. The internal cable of my basspeakers is shielded (not connected to earth). Should I replace this?  

What can go wrong?

Cheers,
Ronald

#2 Duck-Twacy

Duck-Twacy
  • Members
  • 4 posts

Posted 30 January 2006 - 09:24 AM

Of course it should have said "output wiring" in the topic title

huh.gif

#3 DGlass

DGlass

    .

  • Members
  • PipPipPipPipPip
  • 2,541 posts

Posted 30 January 2006 - 10:29 AM

Will shielded cable produce audio at the other end? Yes
Is it the best wire to use for speaker to amplifier connection? No.

There are generally two types of shielded wire in use in the audio industry: “single conductor shielded” and “two conductor shielded”. Single conductor shielded is the type of cable that is generally referred to as Hi-impedance Instrument cable….. you know the stuff that guitar players use. Two conductor shielded is what some people refer to as Microphone cable. Instrument cables as well as mic cables were made to conduct low-level audio signals before they get amplified. They are not designed to handle the higher current from an amplifier’s outputs. Some of these instrument/mic cables can even be as small as 26 gauge.

Over longer distances these smaller conductors add resistance quickly, which causes more power loss in the wires. This power loss takes the form of heat as the wire tries to dissipate the current going through it. This also means as the wire gets longer its resistance becomes large enough to affect the total impedance load to the amplifier.

Damping Factor, especially for subs, can be affected. By lowering the Damping Factor this type of cable affects the control of the cones motion at lower frequencies. This in turn affects how “tight” a bass sound you will get.

Speaker wire gauge becomes much more critical when the distance from the speaker to the amplifier increases as well as when using a higher powered amp (like those used in pro audio). It is always a good idea to use this heaviest gauge wire you can, and keep the distance between the speaker and the amplifier as short as possible.

Shielded Instrument cables have a higher cable capacitance. This higher cable capacitance could cause the loss of high frequency response. Some poorly designed amplifiers may even oscillate if the wire capacitance is high enough.

Now with that said there are “rare” cases were in a high EMF environment that a 2 conductor shielded cable may be need, as a speaker cable. This however is quite rare and in these case the proper gauge of wire is still used for the two conductors and the separate shield is grounded at one end only. smile.gif

#4 Duck-Twacy

Duck-Twacy
  • Members
  • 4 posts

Posted 30 January 2006 - 10:44 AM

Well thats a long reply, thanks.

To make my self clear, I am using the K2 as a bass amplifier in a home speaker with an active xover (at 150 hz), not professionally in studio's
I was first planning to use another class D amplifier and was worried about the EMF signal emmitted from the speakercords (the switching frequency of that amp is about 500Khz and you could see that easlily on an osciliscope).  

To prevend this EMF from reaching the other equipment, I used for the internal speakercord of my diy bass speakers 10 awg speakercord (from Canare) and put aluminium foil around it (hence the shielding). Of course I was planning to use (short, thick) shielded speaker wire from the amp to the speakers as well.

I don't know how much of the switching signal can be found on the output with a Crown K2?

But the speaker cable is thick enough (6 mm^2) and high frequency roll off is no issue, because I'm crossing at 150 hz.

I understand the Crowns will not oscillate because of a little shielding??