Space plays or stops the last tone while no button or field has focus.
Play each tone above, then answer. The centre tone should sit midway between the speakers, or in the middle of your head on headphones.
Both sides play the same 440 Hz tone. In phase, a correctly wired pair sounds centred and fuller. With the right side inverted, the same tone sounds wider, thinner and harder to place. Play both versions, then say which one sounded centred and fuller.
The tone rises from 20 Hz to 20 kHz in 30 s, with equal time per octave. Press "I hear it now" when it appears and "it stopped" when it disappears.
The result combines what this speaker can play and what you can hear, so compare devices with the same ears and at the same volume. Reaction time moves each mark slightly; run the sweep twice to confirm.