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What size speaker cables should I use when I bi-amp my speakers the amp is a Arcam A65 and a Arcam power amp.
I was thinking of using Van Damme blue 1.5mm for the the high`s and 4mm for the low`s speakers are Kef Q15`s
Cheers Gerry
The advice I got elsewhere was that passive Bi-Amping was a waste of time.
Primalsea
09-07-2014, 03:54
I would say try it to see if you think it makes a difference but just use some regular mains flex. If you are sure it will worthwhile then dig your hand into your pocket and buy the expensive cable. 1.5mm cable is massively overrated for hifi amp duty. 4mm cable is in the realms of welding machines, you may not need to go so large.
Depends entirely on the distance to the speakers and the load they represent. If under 5m per side, 1.5mm HF and 2.5mm LF is usually plenty. No need for 4mm.
As to bi-amping...it's not a waste of time but bi-wiring is. It adds nothing to the mix that increasing cable gauge slightly wouldn't otherwise do. Genuine bi-amping using a dedicated stereo (or mono) power amps for the bass units can be worthwhile.
1.5mm cable is not massively over rated by the way. The "rating" is determined by minimum speaker impedance and loop resistance. If your speakers are a minimum load of 4 Ohms then the total cable loop resistance should be within (ie under) 5% of that figure. You pick your gauge based on that.given that 1.5mm2 copper cable has a DC resistance of around 20 to 25 Ohms/Km, then a 5m run gives a loop resistance of 0.25 Ohms PLUS reactive impedance which depends on geometry and dielectric used. If we rounded up to say 0.3 Ohms, that would be somewhere handy. As 5% of 4 Ohms equates to 0.2 Ohms, then it's clear that 1.5mm2 section may be inadequate as too much power will be lost as heat energy, so 2.5mm2 section would be needed. That's a good, reliable rule of thumb to use. Ignore interweb myths on the subject.
The 5% rule of thumb is more to do with limiting the degredation of speaker damping, than the waste of power through ohmic disipation. (5% corresponds to a loss of 0.21dB.)
From the speaker's point of view the (loop) impedance of the speaker cables appears in series with the output impedance of the amplifier. The output impedance is thus increased and so the damping factor (the ratio of the speaker impedance to the amp/cable impedance) is reduced.
If we assume a damping factor of 20 is acceptable, then the total amp/speaker impedance ought to be no more than 0.4 Ohm. If we assume the amp has an output impedance of 0.1 Ohm, then we are left with a cable loop impedance allowance of 0.3 Ohm. So your suggestion of 0.25 Ohm for 5m of 1.5mm2 CSA cable is fine. However if it were me, I would prefer to use a heavier gauge wire, such as 2.5mm2 CSA.
Some power amplifiers are not fitted with a Zobel network, so may become unstable if used with unsuitable speaker cables. In these cases, it is imperative to use a cable as recommended by the manufacturer (often the manufacturer's own).
]The 5% rule of thumb is more to do with limiting the degredation of speaker damping, than the waste of power through ohmic disipation. [/B](5% corresponds to a loss of 0.21dB.)
From the speaker's point of view the (loop) impedance of the speaker cables appears in series with the output impedance of the amplifier. The output impedance is thus increased and so the damping factor (the ratio of the speaker impedance to the amp/cable impedance) is reduced.
If we assume a damping factor of 20 is acceptable, then the total amp/speaker impedance ought to be no more than 0.4 Ohm. If we assume the amp has an output impedance of 0.1 Ohm, then we are left with a cable loop impedance allowance of 0.3 Ohm. So your suggestion of 0.25 Ohm for 5m of 1.5mm2 CSA cable is fine. However if it were me, I would prefer to use a heavier gauge wire, such as 2.5mm2 CSA.
Some power amplifiers are not fitted with a Zobel network, so may become unstable if used with unsuitable speaker cables. In these cases, it is imperative to use a cable as recommended by the manufacturer (often the manufacturer's own).
It's both really Barry. If looking at damping factor, the bass inductor loss should also be added into the mix (its often overlooked and oughtn't to be as a typical figure for this is 0.25Ohms DCR). Basically, any cable which is within 5% loop impedance should be fine. I often advise on slightly less (3 to 4%) to allow for inductor losses and reactive losses (reactive capacitance and reactive inductance losses) as these things figure on the actual damping factor depending on cable geometry. The geometry is important, as you say, where there is no allowance for circuits to maintain amp stability on the power output side, where some manufacturers specify cables with a specific inductance value (Naim etc).
The amplifier output impedance includes any reactive component; the figure quoted is the modulus.
Another aspect of the speaker cable impedance is their effect as seen from the point of view of the driving amplifier: the cable impedance forms a voltage divider with the speaker's impedance. Since the speaker impedance varies with frequency (sometimes violently), the effect of the speaker cable impedance is to affect the flatness (or otherwise) of the speaker's frequency response. Obviously the exact effect depends on the actual speaker's impedance response (the variation with frequency), but a cable with 0.1 Ohm impedance could exacerbate the frequency response flatness by ~ 0.25dB, whereas if 0.5 Ohm the variation is ~ 1dB and if 1 Ohm it can be 2dB.
The 5% rule of thumb is thus a minimum requirement. Some would go further and suggest the speaker cables ought to add no more than 0.1 Ohm + 3uH.
Mark Grant
09-07-2014, 20:28
What size speaker cables should I use when I bi-amp my speakers the amp is a Arcam A65 and a Arcam power amp.
I was thinking of using Van Damme blue 1.5mm for the the high`s and 4mm for the low`s speakers are Kef Q15`s
Cheers Gerry
That really depends on the length as we dont know if you need 2 metres or 20 metres.
Van Damme Black series Tour grade 4 x 2.5mm is a popular choice for bi-amping at lengths up to about 10 metres and is a little bit neater than running two separate lengths of cable and does not cost much.
They need to be four metre runs can you give me a price please Mark ?
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