Speaker Phase and Polarity
Speaker phase and polarity are different problems. Polarity is a sign: the whole signal inverted at every frequency, usually by wiring. Phase is timing relative to the period, so it changes with frequency, and comes from distance, filters and cab type. Fixing both is the cheapest extra bass you will find in boxes you already own.
Polarity: a wiring fault
A positive voltage on the positive terminal moves the cone forward. Swap the leads and it moves back. Two identical subs side by side, one inverted, cancel at low frequencies where their outputs overlap, and the loss is worst on the axis between them.
Usual causes: a crossed lead inside a cab, a mis-wired Speakon, or a bridged amp channel connected the wrong way. See Speakon wiring and impedance and wiring.
Checking it
- Battery test. Driver disconnected from any amp: briefly touch a 1.5 V or 9 V battery across the terminals, + to +. The cone should move out. Keep it brief.
- Polarity tester. A pulse source and receiver checks finished cabs you cannot open, from the amp or desk.
- By ear. Mono bass through two identical subs, flip one, keep the setting with more bass.
Some horn-loaded designs reverse a driver on purpose. Check the design notes before "correcting" it.
Phase: timing at each frequency
One cycle is 360°. Two equal sources at the same frequency sum to +6 dB in phase and cancel at 180°. Phase shift comes from:
- Distance. Sound travels about 343 m/s at 20 °C, so 2.9 ms per metre.
- Filters. Every crossover filter and box roll-off shifts phase; steeper slopes shift more.
- Cab type. A folded horn or scoop path adds acoustic delay against a direct-radiating top.
A polarity switch is 180° at every frequency. It can fix phase at one frequency and break it at another, so it is not a substitute for delay.
Wavelength makes it physical
| Frequency | Wavelength | Half wavelength (180°) |
|---|---|---|
| 40 Hz | 8.6 m | 4.3 m |
| 80 Hz | 4.3 m | 2.1 m |
| 100 Hz | 3.4 m | 1.7 m |
| 1 kHz | 34 cm | 17 cm |
At a 100 Hz crossover, 1.7 m of path difference between sub and top is 180°: full cancellation where the two are equal in level. Plugging in is not aligning.
Aligning subs and tops
The goal is matching phase through the crossover region.
- Placement. Keep acoustic centres close where you can.
- Delay. Delay whichever source arrives first. A measurement mic and software show phase and the summed response directly.
- Polarity. Try both at the listening position; keep the one with the stronger, flatter crossover.
- Matched filters. Linkwitz-Riley crossovers sum flat in level when the two sources are time-aligned.
Without measurement kit: play a tone at the crossover frequency, stand at the main listening position and adjust delay for the loudest result, then check with music. The XR204 4-way crossover has phase invert switches for lining up bands and cabinets.
Multiple subs
Deliberate phase is how sub arrays work: placement plus delay cancels bass behind a stack or steers it forward. The same physics gives power alley and dead spots between two widely spaced stacks. See sub arrays and cardioid.
Safety
Battery tests only with the driver disconnected from the amplifier. Tune at moderate levels and wear hearing protection when testing loud.
Sources: standard acoustics (speed of sound in air at 20 °C, wavelength = c / f, coherent summation); XR204 phase invert switches from the Wavemark XR204 spec sheet. Values rounded.
Questions
What is the difference between phase and polarity?
Polarity is an inversion of the whole signal at every frequency, usually from wiring. Phase is the timing relationship between two waves, which varies with frequency and comes from distance, filters and cabinet design.
What happens if one speaker is wired out of phase?
Strictly, it is in reverse polarity. Its cone moves opposite to the others, so low frequencies cancel where their outputs overlap and the bass goes thin, worst between the boxes.
How much delay do I need per metre between subs and tops?
About 2.9 ms per metre of path difference, since sound travels about 343 m/s at 20 °C. Horn-loaded subs add internal path length, so measure or adjust by ear at the crossover frequency.
Should I flip the polarity on my subs?
Try both settings at the listening position and keep the one that is fuller and smoother through the crossover. If neither is right, the subs and tops need delay alignment, not a polarity flip.