tags: #publish links: [[Acoustics]], [[Acoustic room treatment]], created: 2021-10-29 Fri --- # Room modes See also [[Speaker boundary interference response]], which involves the interference of direct and reflected sound, rather than resonance. ## Room modes Rooms vibrate as a resonant cavity, driven by the speakers. The resonant frequencies (modes) depend fairly predictably on the dimensions, especially for a rectangular box room. The resonance: - Increases (rings) certain frequencies at specific locations - Decreases (nulls) them at other locations - Muddies adjacent frequencies through partial resonance or nulling - Lengthens decay times, which messes with stereo imaging and clarity. (This also happens if the room is generally reflective and low on absorption and dispersion, but strong room modes also contribute.) No problem: - Frequencies below the deepest mode - Frequencies not close to any mode - Frequencies where modes are very dense In these cases the position of sound sources and listener should not be so important. Problematic: - Frequencies close to one mode, or to just a few modes away from other modes. Speaker placement can help a little, but mostly you have to absorb the problematic frequencies: either by tailoring it to absorb those narrow bands, or by generally absorbing a bit of everything. Schröder Frequency is the point below which room modes dominate because they are sufficiently sparse or clustered. https://amcoustics.com/articles/roommodes Room modes calculator: https://amcoustics.com/tools/amroc?l=350&w=300&h=240&r60=0.6 Microphone-based analyser: https://amcoustics.com/tools/amalyzer