Balancing An iPod Output
It’s tempting to want to use an iPod as a program source for driving powered loudspeakers for room testing.
A few caveats
It’s tempting to want to use an iPod as a program source for driving powered loudspeakers for room testing. But since the output level of 1Vrms (0 dBV) may be well below what’s usually required, here’s a little trick for creating an interconnect cable and getting the extra level you need.
1. Make a cable using this diagram.
2. Create a stereo file from mono, and invert polarity of channel 2.
The source file is most easily generated in a wave editor. It consists of two identical channels that are reversed in polarity. This provides an identical signal to pin 2 and pin 3 of the balanced output (one of which is inverted). Balanced inputs like this type of signal, because they accept the voltage difference between pins 2 and 3 as the signal, and reject the common mode voltage between pins 2 and 3. What we are doing is giving up stereo in favor of a balanced source and 2x the voltage (+6dB).
3. Connect iPod to powered loudspeaker.
The level control can be advanced until clip/limit is indicated.
- The balancing method described is not a general-case solution for balancing an iPod. What it does is allow a balanced output at +6dBV that may be useful for a few demo tracks (i.e. a sine sweep, polarity pulse, speech track, and maybe a music track or two).
- The result is mono, not stereo.
- It only works with a specially modified source file.
- Be sure to switch phantom power “off” before using this cable, since no DC isolation is provided.
- Since the two channels are reverse polarity, typical stereo program material will play back with center channel information (e.g. vocals) canceled.
- Have available a direct box with proper summing network for summing left and right outputs into a single input channel for listening to your favorite stereo music tracks (in mono).
Source: Pat Brown, Syn-Aud-Con
