Transfer Function Measurement per ISO 3382-2

TL;DR

Transfer function measurement complements ISO 3382-2 reverberation time analysis in ordinary rooms by revealing the frequency-dependent behavior of the room. In smaller rooms covered by ISO 3382-2, the modal density is lower than in performance spaces, making individual room modes more prominent in the transfer function. SonaVyx transfer function analyzer helps identify problematic modes that cause uneven reverberation across frequency bands. The coherence display validates measurement quality at each frequency, ensuring your RT60 results are reliable across the full bandwidth.

Transfer Function in Ordinary Rooms

Ordinary rooms per ISO 3382-2 are typically smaller than performance spaces, which means room modes are more spaced apart and more audible. The transfer function reveals these modes directly as peaks and dips in the magnitude response.

Low-Frequency Mode Analysis

In rooms with dimensions under 10 meters, the first axial modes start below 50 Hz and can extend up to the Schroeder frequency. Transfer function measurement shows:

Axial mode frequencies as sharp peaks (Q factor greater than 5)
Mode spacing indicating room proportions
Positions with severe modal cancellation (nulls deeper than 15 dB)
Whether the room proportions create degenerate modes (overlapping frequencies)

Supporting RT60 Measurement

Measure transfer function before the RT60 session to identify problematic frequencies
High coherence (above 0.9) confirms adequate signal-to-noise ratio for decay measurement
Transfer function peaks indicate frequencies where RT60 may be longer than average
Use the information to select source positions that excite the room uniformly

Absorption Assessment

The overall shape of the transfer function, particularly the high-frequency rolloff rate, gives a qualitative indication of room absorption. Rooms with heavy absorption show steeper HF rolloff in the transfer function.

Common Mistakes

Interpreting every transfer function feature as a room characteristic when some may be source or microphone artifacts
Using insufficient averaging, leading to unreliable low-frequency data
Not checking that the measurement system has flat response in the range of interest

SonaVyx Workflow

Start with the SonaVyx transfer function analyzer for room characterization. Then measure RT60 with the RT60 tool at positions informed by the transfer function data. Capture impulse responses with the IR tool. Monitor levels using the SPL meter. Calculate treatment needs with AcousPlan. Follow the room analysis workflow for step-by-step guidance.

Standing Waves Haunt the Control Room