Schroeder Frequency
Definition
Schroeder Frequency
The Schroeder frequency marks the transition between the modal region (where individual room resonances dominate) and the statistical region (where modes overlap sufficiently to create a diffuse sound field). Named after Manfred Schroeder, this frequency depends on reverberation time and room volume. SonaVyx calculates the Schroeder frequency from measured RT60 and room dimensions.
fs = 2000 × √(T60 / V), where T60 = reverberation time (s), V = room volume (m³)
How It Is Measured
The Schroeder frequency is calculated from the measured reverberation time and room volume. SonaVyx computes it automatically when RT60 measurement and room dimensions are available. Below the Schroeder frequency, the spacing between individual room modes is wide enough that they are individually audible. Above it, there are at least three modes per modal bandwidth, creating a statistically smooth response.
Practical Example
A living room (5 × 4 × 2.5 m, V = 50 m³) has measured RT60 of 0.6 seconds. The Schroeder frequency is 2000 × √(0.6/50) = 219 Hz. Below 219 Hz, individual room modes create position-dependent peaks and nulls that cannot be reliably corrected with EQ. Above 219 Hz, the sound field is diffuse enough for EQ and acoustic treatment to produce predictable, position-independent improvements.
Significance for Room Acoustics
The Schroeder frequency divides room acoustic behavior into two regimes requiring different analysis and treatment approaches. Below the Schroeder frequency, the response at any position depends on the specific modal pattern — moving the microphone a few centimeters can produce dramatically different measurements. SonaVyx uses the Schroeder frequency to guide users on where frequency response data is reliable for EQ decisions and where position-dependent modal effects dominate.
Room Size and Schroeder Frequency
Larger rooms have lower Schroeder frequencies because more modes fit within each frequency band. A large concert hall (V = 20,000 m³, T60 = 2.0s) has a Schroeder frequency of approximately 20 Hz — below the audible range, meaning the entire audible spectrum behaves statistically. A small control room (V = 40 m³, T60 = 0.3s) has a Schroeder frequency of approximately 173 Hz, meaning bass frequencies below that point are highly position-dependent.
Implications for Measurement
Below the Schroeder frequency, a single measurement position does not represent the room accurately. ISO 3382-1 addresses this by requiring multiple source and receiver positions and averaging results. SonaVyx highlights the Schroeder frequency on transfer function plots to indicate where measurement data becomes position-dependent and cautions against applying narrow EQ corrections to modal frequencies.
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Calculate Schroeder frequency — free room analysis