For live sound engineers, bands, churches, and school sound crews
Check speaker polarity and left/right routing with your iPhone
A speaker can play sound even when its positive and negative connections are reversed. That polarity mismatch can weaken low frequencies and make a centered vocal feel less focused. Check1.2 lets you check speaker routing and compare normal and reversed polarity by ear for free.
Connect your iPhone to the mixer and play the spoken Left, Right, and Center signals in order. Listen from the audience area. If Left comes from the right speaker, the left and right outputs or cables may be crossed. If Center sounds focused between the speakers, the channel placement is behaving as expected.
Compare normal and reversed polarity by ear
Check1.2 can play a reversed-polarity version of one side so you can compare it with Center. When the system is wired with matching polarity, the reversed version should sound less focused in the center and more spread between the speakers. If the reversed version sounds more centered, one speaker may have reversed polarity.
Listening results depend on the room, speaker placement, program material, and your listening position.
Measure speaker output and polarity with the Full version
Connect your iPhone to the mixer's two outputs or a stereo output and keep the PA level low.
Stand around the center between the left and right speakers, hold the iPhone around chest height, and start the measurement.
In about 6 seconds, the app checks whether sound reaches each side, whether left and right are assigned correctly, and whether speaker polarity appears to match.
If polarity does not match, the result screen lists places to check. A single iPhone mic cannot identify which individual speaker is reversed.
This is a practical check, not a calibrated measurement instrument. Speaker type, placement, processing, and the room can affect the result.
Free listening check; optional one-time Full version
Free: download at no cost and play Left, Right, Center, reversed polarity, and frequency sweep signals for listening checks. No account required.
Full version: microphone measurement is included in the one-time purchase. On the U.S. App Store it was $6.99 in October 2026, not a subscription. Prices may differ by region and can change; check the App Store.
7-day free trial: try Full version features for 7 days. If you do not buy when the trial ends, the app returns to the free version and you are not charged.
What does reversed polarity mean? One speaker's positive and negative signal connections are reversed relative to the other speaker. Sound still comes out, but the speakers may interact differently, especially in the low frequencies.
Can the iPhone tell me which speaker is reversed? The Full version can report a polarity mismatch, but one iPhone mic cannot tell which of the two speakers is reversed. Check the signal path and each speaker's settings.
Do I need an external measurement mic? No. The mic measurement uses the iPhone's built-in microphone. The free listening check does not require measurement.
Is this a substitute for a professional analyzer? No. Check1.2 is not a calibrated measurement instrument. Treat its result as a practical indication and confirm the system by listening and checking the signal path.
Is the Full version a subscription? No. It is a one-time in-app purchase. The 7-day trial does not automatically charge you when it ends.
Check speaker routing and polarity at your next soundcheck
Start with the free Left, Right, Center, and reversed-polarity listening checks. Install Check1.2 and try them with your PA system.