Music Production
Calculate comb-filter notch frequencies from mic spacing.
What this calculator does
Microphone placement and phase cancellation is a critical consideration in audio recording and live sound. When multiple microphones capture the same source, or when direct and reflected sound interact, phase relationships between the signals dramatically affect frequency response. Phase cancellation occurs when two signals that are nearly identical but shifted in time combine destructively, causing certain frequencies to cancel out completely while others are reinforced. The distance between microphones, distance from sound source, and sound propagation speed determine these phase relationships. This calculator helps producers understand at what frequencies phase cancellation occurs based on microphone placement, enabling informed decisions about mic positioning to achieve desired tonal characteristics. Understanding phase relationships is essential for drum miking, stereo recording, close-miked versus room miking combinations, and live sound system design.
How it works
The calculator uses the relationship between wavelength, frequency, and the physical distance between microphones or between a mic and reflective surfaces. When two signals arrive with a time delay of half a wavelength (180-degree phase shift), they cancel at that frequency. The calculator determines what frequencies will experience maximum cancellation based on the mic separation distance and speed of sound (typically 343 m/s at room temperature). For a given distance, it calculates which frequencies are most affected. You can adjust mic placement to either cancel unwanted frequencies (like room rumble) or preserve desired frequencies by moving mics to positions where cancellation is minimized.
Formula
Frequency with maximum cancellation = Speed of sound / (2 × Distance). For example, with 1 meter separation: 343 m/s / 2m = 171.5 Hz maximum cancellation. Wavelength = Speed of sound / Frequency. When two signals are separated by distance D, they are 180° out of phase (maximum cancellation) when D = Wavelength / 2. Additional cancellation occurs at odd multiples: 3/2, 5/2, etc.
Tips for using this calculator
- Use the 3-to-1 rule in multimic recording: maintain at least 3x the distance between mics as the distance from source to nearest mic to minimize phase issues
- Identical microphones closer in time (distance) = more potential phase issues; dissimilar mics or mics with intentional spacing can be used strategically
- Room reflections and direct sound always interact; understanding the calculated cancellation frequencies helps you anticipate tonal coloration and adjust mic placement accordingly
- Phase alignment is especially critical when miking drums or close-miking multiple instruments—use this calculator to position mics to preserve frequencies you want
- In live sound, use this calculator to understand how main speaker and monitor speaker proximity affects frequency response; adjust mic placement or delay-align speakers accordingly
Frequently asked questions
Why do drum kits sound different depending on mic placement?
Drum microphones often experience phase cancellation with room reflections, kick drum bleed from other mics, or interaction with overhead mics. A kick drum mic placed closer to the drum head captures more direct sound with less room interaction. Moving a mic just a few inches changes the phase relationship with reflections, shifting which frequencies are canceled or reinforced. This explains why moving a kick mic 6 inches away can dramatically change the tone—you're changing the phase cancellation pattern.
How does the 3-to-1 rule work with this phase issue?
The 3-to-1 rule states that if a mic is 1 meter from a source, place other mics at least 3 meters away to minimize phase interaction. This spacing means that sound arriving at both mics is delayed by more than the typical cancellation distances, spreading potential cancellations across a wider frequency range instead of creating a noticeable dip. Large spacing means each frequency doesn't experience severe cancellation—instead effects are distributed across the spectrum, sounding more natural.
Can I use this calculator for stereo recording?
Yes, absolutely. When recording stereo with two mics, the separation distance affects which frequencies experience phase cancellation between left and right channels. For natural-sounding stereo, you typically want minimal cancellation—aim for spacing where calculated cancellation frequencies are outside your mix priority range. For certain techniques like mid-side stereo or intentional stereo width effects, understanding phase cancellation helps you achieve the desired effect.
What if I don't want phase cancellation to happen?
Position mics so calculated cancellation frequencies fall outside the important frequency range for your source, or position them far enough apart that cancellation spreads across many frequencies with no single dramatic dip. Alternatively, use phase correction tools: time-align mics using your DAW's delay compensation, or use phase-invert switches on tracks if one is significantly out of phase. Combining microphone placement knowledge with post-production phase alignment gives you the most control.
