Sound islands (3D)
About this app
An exhibition hall in 3D with three listening stations: omni speakers, directional speakers, sound domes and ultrasonic beams set, through directivity and reverberation time, where one station clearly leads and where stations overlap. The floor map shows sound islands, signal-to-noise ratio, level and speech intelligibility (STI); wavefronts and reverberation travel visibly through the hall. “All louder” leaves the map unchanged, directivity and damping create islands; at the visitor’s spot the mix is audible in space.
Why louder does not create listening islands
When several sound stations share a hall, every spot hears a mix of direct sound from its own station, direct sound from the neighbours and the reverberation of all of them. Intelligibility depends on the signal-to-noise ratio: if your own station is about 10 dB above everything else, it is clearly intelligible. Turn all stations up by the same amount and every component grows equally, so the ratio stays the same. Islands only come from directivity, which concentrates direct sound on the listening spot, and from damping, which shrinks the shared reverberant field.
What the app shows
A hall of 30 × 18 × 5 m with three listening stations along the long walls. Each station gets a speaker type (omnidirectional, directional horn, sound dome or ultrasonic beam), content, a level and an aim. The floor map shows which station dominates, the signal-to-noise ratio, the level or speech intelligibility as STI. Wavefronts travel through the room in slow motion, and a shimmer shows the reverberation. The critical distance is drawn around the chosen station; readouts at the visitor give level, signal-to-noise ratio and STI.
What you can try
Compare the scenarios: with omnidirectional speakers the signal-to-noise ratio at the visitor in the normal hall at 1 kHz is only about +1 dB, with sound domes about +12 dB. The “All louder (+10 dB)” scenario shows that the islands barely change. Switch between reverberant, normal and damped hall and between 250 Hz, 1 kHz and 4 kHz: directivity helps mainly at high frequencies. After clicking “Listen” you can hear the mix spatially at the movable visitor position.
Frequently asked questions
- How do you stop sound stations in an exhibition from bleeding into each other?
- What matters is directivity and room damping. Directional loudspeakers, overhead sound domes or ultrasonic beam speakers concentrate the direct sound on the listening spot, and absorbent surfaces shrink the reverberant field that otherwise carries every station through the whole hall. Turning all stations up by the same amount raises every component equally, so the ratio between them stays the same; more volume only helps against a constant background noise.
- What is the critical distance (reverberation radius) and how is it calculated?
- The critical distance is the distance from a source at which direct sound and reverberant sound are equally loud. Approximately r_H ≈ 0.057 · √(Q · V / T), with room volume V in m³, reverberation time T in s and the source directivity factor Q (Q = 1 for an omnidirectional source). Within this radius direct sound dominates and directivity pays off; beyond it the reverberant field takes over.
- What signal-to-noise ratio does speech need, and what is STI?
- As a rule of thumb, a speech source is clearly intelligible when it exceeds background noise and competing sources by about 10 dB; below about 3 dB the sources blur together. The Speech Transmission Index (STI) rates on a scale from 0 to 1 how well the level fluctuations of speech survive reverberation and noise on their way to the listener. Common categories: below 0.30 bad, 0.30–0.45 poor, 0.45–0.60 fair, 0.60–0.75 good, above 0.75 excellent.
- What can I try in the listening islands app?
- In a 3D exhibition hall you set the speaker type, level, aim and content for three listening stations and choose a reverberant, normal or damped hall, the background noise and the frequency band. The floor map shows which station dominates, the signal-to-noise ratio, the level or the STI, while wavefronts and reverberation travel visibly through the room. At the movable visitor position you can hear the mix spatially.
Subject: Architecture & scenography
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