Connect the mixer to the playback devices you will use to output the two audio signals, using the 1/4-inch connector cable, the audio output jack on the playback devices and two audio input jacks on the mixing board. If you are using mp3 or CD players, you will typically need to obtain an 1/8-inch to 1/4-inch plug adapter, which you will connect to one end of the 1/4-inch connector cable before plugging it into the audio input jack on the mixing board.
Plug your preferred speakers into the mixing board using the audio input jack on the speaker unit and the audio output jack on the mixing board. If your speakers require stereo cables, plug the red and white 1/4-inch plugs into the matching audio output plugs on the mixer. If your speakers utilize a line connection, simply plug the line cable into the previously mentioned input and output ports.
Cue the two tracks you will be using for phase detection, preparing one track for playback in each of the two playback devices.
Raise the two vertical volume sliders assigned to the two playback channels on the mixing board to identical, mid-range levels. This will ensure that both signals can be heard without allowing one source to overpower the other.
Press play on both playback devices at the same time. Each of the tracks should begin playing back through the speakers.
Slowly lower the volume on one of the tracks and listen for an increase or decrease in volume. If, when raising the volume of the softer track, the overall volume level decreases, the two audio sources' sound waves are traveling at different speeds, causing phase cancellation.
Listen carefully for "beats," or audible pulses, while both tracks are playing simultaneously. These rhythmic pulsations occur due to minute inconsistencies in speed between the two waveforms. Although not directly related to the orientation of two identical waves, comparing frequencies of two sound waves is easily accomplished with a mixing board as well. As the frequency, or speed, of a waveform is directly related to the pitch of a tone, these pulses are used by musicians and performers as an indication of tuning discrepancies between two sound sources.