Free tool: hear the room
Why can't people understand the announcements, and will more loudspeakers fix it?
Pick a space, a loudspeaker type and how many loudspeakers, then listen. You hear the same announcement as a listener in that room would hear it, from a small office to a station-sized concourse, and what adding loudspeakers does and does not change. Everything runs in your browser. Free, no email, no callback, just the result.
The tool
Critical distance 9.6 m
That is about the length of a bus. Closer than this to a loudspeaker, its direct sound is louder than the room; further away, the room is louder.
- Where the listener stands
- Outside critical distance, 8.0 m from the nearest loudspeaker
- Direct-to-reverberant ratio (DRR)
- −5.2 dB
- Reverberation time at this occupancy
- 3.5 s
- Background noise (indicative)
- 55 dBA
Heard as echo: 5 of 8 loudspeakers arrive more than 50 ms after the first, the latest 182 ms after.
Rough guide for a single, evenly reverberant space. Large, very absorbent, long or connected spaces behave differently; that is what a measurement is for.
Listen
The same announcement, as heard by this listener in this room. Switch between the dry recording and the room while it plays.
Anyone with the link sees these inputs and this result. Your name is not included.
Have your calculation checked
Send us these inputs and we will return a checked, signed calculation sheet.
What the critical distance tells you
Every loudspeaker in a room is heard twice: once directly, and again as the room's reverberation, the sound that has bounced around the space. Close to a loudspeaker the direct sound is louder. Further away the reverberation takes over, and words start to smear into each other. The critical distance is where the two are equal. The tool shows it in metres, and shows whether the listener stands inside or outside it as a direct-to-reverberant ratio (DRR) in decibels: above 0 dB the loudspeaker is louder than the room, below 0 dB the room is louder.
Will more loudspeakers fix it?
Only loudspeakers that bring the listener inside the critical distance. Extra loudspeakers at the same distance add reverberant sound as well as direct sound, so the balance at the listener does not improve, and the ones further away arrive late. Any loudspeaker arriving more than 50 ms after the first is flagged, because it is heard as an echo. A loudspeaker closer to the listener does improve the ratio, and only until the next limit: echo from its neighbours, cost, or ceiling height. Tick "Add one loudspeaker closer to the listener" to hear both outcomes.
How the figures are worked out
The tool treats the space as one evenly reverberant room (Sabine's method). From the volume and reverberation time it works out the room's total absorption, then the critical distance for the chosen loudspeaker type: about 0.057 × √(Q × V ÷ T) metres, where Q is the loudspeaker's directivity, V the volume in cubic metres and T the reverberation time in seconds. People absorb sound, so occupancy adds an indicative 0.45 m² of absorption per person and the reverberation time is worked out again; background noise rises with occupancy too. The loudspeaker types and their directivity are indicative.
The listen panel builds the room's response in your browser: one arrival from each loudspeaker at its own distance and delay, then a decaying reverberant tail at the level the figures give. The announcement is a synthetic voice recorded dry. The tool does not calculate an intelligibility score. Anyone who needs a figure for a real space needs it measured: consultancy, acoustic modelling and specification.