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Sound travels about one foot every millisecond. So if your subwoofer sits closer to you than your speakers, its bass reaches your ears first, and around the crossover the sub and speakers can partly cancel each other out. The result is a thin, hollow spot in the bass that no amount of turning up fixes. This calculator works out the delay and the phase setting that line them back up, gives you the delays for every speaker in a home theater, and does time alignment for a car.
- Sub timing and phase: enter the distances to your speakers and sub, your crossover, and how you can adjust the sub. You get the setting to use.
- Speaker delays: enter the distance to each speaker for the delay in milliseconds, for systems that ask for it.
- Car time alignment: measure from each speaker to the driver’s head and get the delays for your head unit or DSP.
Measure from each speaker to your ears at the main seat. If the sub and speakers are at different distances, their bass arrives at different times and can partly cancel at the crossover.
- Sit in your main seat and play an 80 Hz tone from our test tones page at a moderate volume.
- Try the suggested setting, then one step either side (or flip the phase switch).
- Keep whichever is loudest at the seat. A sound level meter or phone app makes the difference easy to see.
Enter the distance from each speaker to your main seat. Leave speakers you don’t have blank. Most receivers ask for these distances and work out the delays for you; if yours, a soundbar or a DSP asks for milliseconds instead, use the delay column.
Measure from each speaker to the centre of the driver’s head, at ear height. Time alignment delays the closer speakers so sound from every speaker arrives at the same moment, which moves the stereo image to the middle of the dash.
Quick reference
How much a difference in distance matters at an 80 Hz crossover. At 90° or more, the sub and speakers start working against each other.
| Distance difference | Time difference | Phase gap at 80 Hz |
|---|---|---|
| 1 ft (0.3 m) | 0.9 ms | 26° |
| 2 ft (0.6 m) | 1.8 ms | 51° |
| 3 ft (0.9 m) | 2.7 ms | 77° |
| 5 ft (1.5 m) | 4.4 ms | 128° |
| 7 ft (2.1 m) | 6.2 ms | 179° |
| 10 ft (3.0 m) | 8.9 ms | 104° |
Distance setting, phase dial or phase switch?
- AV receiver: use the distance (or delay) setting. Enter the measured distances and the receiver delays the closer speakers, which aligns the sub at every frequency. Leave the sub’s own phase dial at 0°.
- Phase dial: if there’s no receiver doing the timing, as with a stereo amp, the sub’s 0–180° dial delays the sub at the crossover frequency. It only aligns one frequency exactly, which is why it’s set for your crossover.
- Phase switch: a 0/180° switch is a coarse version of the dial. It’s still worth trying both positions, because the wrong one can cost several decibels at the crossover.
Our guide to subwoofer phase and polarity explains the difference between phase and polarity in more depth.
Why room correction sets the sub “too far away”
Run Audyssey, YPAO or Dirac and you’ll often find the sub’s distance set several feet longer than your tape measure says. That isn’t a mistake. The sub’s amplifier, low-pass filter and any DSP inside it delay the sound slightly, and room correction measures that delay along with the real distance. Keep its number. The calculator’s figures are the starting point for systems that can’t measure, and our article on the subwoofer distance setting covers this in more detail.
Time alignment in a car
In a car you sit much closer to the left speakers than the right (or the other way in a right-hand-drive car), so the stereo image collapses towards the nearest door. Time alignment delays the closer speakers so everything arrives together, pulling the image back to the centre of the dash. Measure from each speaker to the centre of your head with a laser measure or tape, enter the numbers, and copy the delays into your head unit or a DSP such as the Dayton Audio DSP-408. Some head units ask for distances rather than milliseconds; in that case enter the measured distances directly.
Frequently asked questions
How do I measure the distance to my sub?
Measure from the front of the sub’s driver (or the port, for a ported sub facing the room) to where your head is at the main seat. For a down-firing sub, measure from the middle of the cabinet’s base.
Should the sub distance match what I measured?
Start there. If room correction sets a larger number, keep it: it includes the sub’s internal delay. You can then fine-tune in one-foot steps while playing a tone at the crossover frequency and keep whichever setting is loudest at your seat.
My sub is in a corner far from the speakers. Can the settings fix that?
Timing, yes: the delay or phase setting lines the sub and speakers up at your seat. But it can’t fix room modes, the peaks and dips that depend on where the sub sits. Our placement calculator helps with that.
Does the phase switch matter if I have a receiver?
Usually not, because the receiver’s distance setting handles timing. It can still help in some rooms, so it’s worth a quick test with a crossover tone.
What delay should I set for the sub in my car?
Set the speakers by measurement first, then adjust the sub by ear. A trunk sub’s sound takes a longer route to you than a tape measure shows, so the right number is usually found by listening for bass that seems to come from the front.