Microphone 3-to-1 Distance Calculator
When several microphones capture different sources in the same room and the signals are mixed, sound bleeding from one source into a neighbouring microphone can cause comb filtering, a hollow phasey artifact. The 3-to-1 rule prevents most of it: keep the distance between two microphones at least three times each microphone's distance from its source. This calculator takes the mic-to-source distance and returns the minimum mic-to-mic spacing, plus the inverse-square level difference the spacing produces. Use it to position vocal, drum, and instrument mics for clean multi-track recordings.
3-to-1 rule formula
Minimum spacing = ratio * source distance
Level difference = 20 * log10(ratio)
(Ratio of 3 gives about 9.54 dB)
The level difference is how much lower the bleed signal arrives compared to the wanted signal at the more distant microphone, following the inverse-square law.
Multi-mic setup notes
- A 3:1 ratio yields about 9.5 dB of separation, enough to keep comb filtering inaudible.
- Larger ratios increase separation; 4:1 gives about 12 dB.
- The rule applies to separate sources mixed together, not stereo pairs.
- Closer mic placement to the source allows tighter overall spacing.
- Comb filtering sounds hollow or phasey; the rule keeps its notches shallow.
Microphone 3-to-1: frequently asked questions
What is the microphone 3-to-1 rule?
The 3-to-1 rule is a recording guideline: when using multiple microphones on different sources, the distance between any two microphones should be at least three times the distance from each microphone to its source. This keeps the bleed of a neighbouring source into a microphone at least about 9 to 10 dB lower than the intended source, reducing audible phase cancellation (comb filtering) when the signals are mixed.
How do I calculate the minimum spacing?
Multiply the mic-to-source distance by three: minimum mic-to-mic distance = 3 * source distance. If a vocalist's mic is 0.2 m from the mouth, the next mic should be at least 0.6 m away. This calculator returns the minimum spacing and the level difference the rule yields.
Why three to one and not some other ratio?
A 3:1 distance ratio produces a level difference of about 20 * log10(3) which is roughly 9.5 dB between the wanted and bleed signal at the more distant mic, following the inverse-square law. About 9 to 10 dB is generally enough to keep comb filtering inaudible when the mics are combined. Larger ratios reduce it further.
What is comb filtering?
Comb filtering happens when the same sound arrives at two combined microphones at slightly different times, causing a series of peaks and notches across the frequency spectrum that sounds hollow or phasey. The 3-to-1 rule reduces the relative level of the delayed copy so the notches are shallow and far less audible.
Does the 3-to-1 rule apply to stereo pairs?
Not directly. The rule is for separate mics on separate sources that will be summed to mono or mixed. Coincident and spaced stereo pairs are designed around intentional time and level differences for imaging and follow their own spacing conventions, so the 3-to-1 rule does not govern them.
Official sources
- NIST: National Institute of Standards and Technology.
- NIOSH (CDC): Noise and Occupational Hearing Loss.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.