Boom Mic Distance Calculator

How it is calculated

Both distances are measured from the sound source (the actor's mouth) in inches. d1 is the reference distance and d2 is the boom mic distance you are considering. By the inverse-square law, the level at d2 compared with d1 changes by ΔdB = 20 × log₁₀(d1 ÷ d2), rounded to one decimal. A positive number means louder (the mic is closer than the reference), a negative number quieter. The distance ratio shown is d2 ÷ d1. Every doubling of distance costs about 6 dB. The recommendation looks only at d2: between 12 and 36 inches (1 to 3 ft) it says that range is ideal, outside it suggests moving the boom into 12–36 inches. Both distances must be above zero, otherwise no result is shown.

Common mistakes

• Typing the distances in feet or centimetres. The fields are inches, so 3 ft must be entered as 36; otherwise the 12 to 36 inch check judges the wrong number.
• Swapping the two distances. The sign flips: 48 to 24 inches gives 6.0 dB, but 24 to 48 gives -6.0 dB.
• Measuring from the boom pole or the camera instead of from the mouth. The inverse-square law uses the distance between mic and source.
• Expecting the dB change to model room reverberation. The law assumes a free field; in a reflective room the level falls by less than 6 dB per doubling and the balance of direct sound to reverb gets worse.
• Treating the dB figure as the whole story. It ignores the microphone's pickup pattern, so a mic pointed away from the mouth loses level on top of the distance loss.