Speaker Cable Impedance

[johnwhit]

Can anyone tell me the Impedance of the old Talk 3 speaker cable?

TIA,

John

[DSJR]

It's very low and Kevin Edwards (Talk Electronics) designed it when he was half of Cable talk (he designed all their cables as sold). Should be fine and easy with any amp up to 10m or more a run since it's around 2.5mm cross section.

The slight inductance in the spacing of the 3 and 3.1 is of more interest I think.

Ask Kevin... I believe the current Talk 3 is a closer spaced version of the (better insulation) 4.1 that CT used to make and then placed in an outer jacket

[johnwhit]

Thanks David, I was looking at buying another pair of speakers and noticed the maximum cable impedance was quoted at 0.1Ω, I've never really taken much notice in the past, I'd just hook them up a try them but it got me thinking.

ATB,

John

[Reffc]

Thanks David, I was looking at buying another pair of speakers and noticed the maximum cable impedance was quoted at 0.1Ω, I've never really taken much notice in the past, I'd just hook them up a try them but it got me thinking.

ATB,

John

Hi John

What speakers are they?

TBH, the impedance of the speakers is usually much more significant than the cables in the circuit, not forgetting that impedance rises significantly with frequency (for most loudspeaker voice coils) to the point that the cable DC resistance becomes a non issue.

The cable impedance is actually made up of three elements though:

1. DC resistance (usually quoted in Ohms/Km);
2. Impedance due to inductance
3. Impedance due to capacitance.

Of these, the DC resistance is by far the greatest consideration since the loudspeaker voice coils' capacitance and inductance are far more significant than that of the speaker cable.

Capacitance though has another effect in that with some amplifiers, a very high capacitance cable (typically multi-cored braided varieties) can create instability in the amplifier's output stage as well as contribute to a rolling off in HF response (it adds to the x-over capacitance value). High inductance will not cause instability in the output stages but can over very long lengths cause some roll off.

Rule of thumb with most systems is to keep the cable impedance within 5% of the loudspeaker impedance, so for a 6 Ohm load at 1KHz, cable impedance should ideally fall below 0.3 Ohms.

Talk 3 has a DC resistance of around 3 Ohms/km or 0.003 Ohms/metre.

Taking the 5% rule, this means that for a 6Ohm nominal load, the cable can be up to 100m!!!

In reality, the inductance would start to roll off HF response slightly (perhaps by 1dB) at around 20m.

Given that Talk 3's resistance is 0.003 Ohms/m (3 Ohms per Km), you could safely use lengths of up to 20 or 30 metres with your speakers.

[johnwhit]

Hi Paul, thanks very much for the detailed reply. The longest run of cable is probably 7-8m so I should be well within spec.

Kind regards,

John