Tuesday, July 12, 2011

Does Audio Cable Length Matter

The length of your cables does matter. Not because the signal gets delayed if it travels through a longer cable or because it might get phase-shifted compared to the same signal traveling through a much shorter cable. The effect of the wire and cable lengths in the recording studio are so insignificant to the delay of the signal that we can just ignore them. (it takes about 0.00089 seconds or almost 1ms (millisecond) for sound to travel 1 ft in air at sea level. In order to get your signal delayed by 1ms just by adding length to your cables, it would take you about 186 MILES of cable)
The length of the cable does matter though especially if we are talking about a guitar unbalanced cable. The impedance of the guitar is so high that the capacitance of the cable would definitely affect the high end of your signal. See Gene Dellasala's detailed article on RLC losses in a cable. Also Unbalanced connections are susceptible to magnetic and Radio Frequency interference so the longer the cable the better the chances are you'll end up with unwanted hum or radio or who knows what in your guitar signal.
If we are talking about balanced microphone cable the length matters for the same reasons as the guitar cable although balanced cables tend to reject magnetic interferences pretty well. The problem with the microphone signal is that the voltage of it is so low (in the micro Volt range - 1 micro Volt = 0.000001 Volts) that after amplifying it 40-50 dB or so it is very important that the cables pick up absolutely nothing on the way to the mic-pre input. Also I personally had the weird experience with the Sony "Solid Tube" Mic (more than once on 2 different mics) where I had a 3 ft "Mogami" mic cable coming out of the power supply straight in to my studio's mic panel on he wall, and I was picking up some radio station. First I lifted the ground on the power supply but it got worse. Then I changed the cable with a 15ft Mogami and the radio disappeared. Now I always use the longer cables on the "Solid Tube" until one day I had that same radio... I changed the cable back to the 3-footer and the radio was gone. Maybe just a coincident or some capacitance match or who knows what... My point is CABLE LENGTH MATTERS.
If we are talking about speaker cable, a lot of people have the miss-conception it's OK to run Speaker Cables as long as you want. It is both true and not. Speaker level has the highest voltage and the lowest impedance out of all signal levels used in a recording studio. In that sense it is safest to run the longest runs. On the other hand, because of it's super low impedance the resistance of the wire makes a big difference on the power at the other end. Depending on the speaker cable a 50 ft run, depending on the gage, may have a total of 2 to 4 Ohms of resistance. If your speaker's impedance is 4 ohms and your amplifier is rated to drive 100 watts over 4 ohms (assuming) the wire resistance is 0 ohms, you'll get your full 100 Watts. What happens when you put your speakers 50 ft away from the amp... the resistance of the cable gets added to the 4 ohms of impedance of the speaker for a total of 8 ohms. Now the same 100 Watt at 4 ohms amp has 8 ohms of load instead of 4 ohm giving us only 50 Watts. Power(Watts) = E squared divided by the Resistance (impedance) where E=Voltage which is constant in the above example. Note the use of resistance vs impedance and vice-versa. We use resistance when we are referring to DC circuits, and Impedance when talking about AC circuit - all audio signals are AC (Alternating Current)
 See also the following blogs on this topic:

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