Acoustical Society of America
Test facilities

Test facilities

Reverberation time testing, sound transmission and PA and venue site studies: measured on site, simulated in our software, and reported.

A man holding a measurement meter in a room with colourful benches, a dodecahedron loudspeaker on a tripod beside him; the title reads “How to measure Reverberation Time RT60”.
How to measure reverberation time (RT60). Image: ar.inspiredpencil

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RT (reverberation time) testing: software-based

Reverberation time (RT60) is how long sound takes to decay by 60 dB after a source stops. It decides whether speech is clear or muddy in a hall, classroom or studio. We measure it on site with a calibrated measurement microphone (omnidirectional, with a stand and preamp), an audio interface and a dodecahedron or omni loudspeaker. Our acoustic software then processes the recordings.

At site we play swept-sine or MLS signals, or burst a balloon or starter pistol in the room. The software calculates impulse responses and gives RT60, EDT, T20/T30, C50 (speech clarity), C80 (music clarity), D50 and STI per octave band from 125 Hz to 4 kHz. We repeat the readings at several microphone and source positions and average them.

The same software lets us simulate the room before any treatment is installed. We model absorbers, diffusers, ceilings and wall panels, compare predicted and measured values and fix the treatment to the target RT for the room’s use. After the work is complete we measure again and issue a report, so the client sees before and after results.

Plan of a small test room about 2.3 by 2.3 metres: four microphone positions around a central table, the loudspeaker in one corner, and the PC and signal analyser outside the wall by the door.
Microphone and source positions for an RT measurement. Image: academia

STC: sound transmission and flanking

A Rion handheld sound level meter reading 53.0 dB, held up in a factory hall with green steel frames and ducting.
A sound level meter in use. Image: ikki-group
A handheld digital sound level meter reading 50.2 dB, held in front of industrial plant with two workers in hard hats behind.
A handheld sound level meter. Image: nordicmetrology

Sound requirement: PA and venue site study

Wiring diagram of a professional auditorium sound system: wireless microphones, mixer, feedback suppressor and processor feeding amplifiers for line-array, stage monitor and auxiliary loudspeakers.
Professional sound system solution for an auditorium. Image: fity
Loudspeaker simulation software: a 3D view of seating coloured by sound level, line-array settings, a coverage cut-view and a frequency-response chart.
Speaker coverage mapping and simulation. Image: audioXpress

Define the use

  • Speech only: conference rooms, classrooms, courts. Clarity matters most; a target STI of at least 0.60 is usual.
  • Speech and music: auditoriums, banquet halls, worship halls. These need wider bandwidth and more headroom.
  • Live performance: stages and clubs. These need high SPL, monitors and a mixing position.
  • Video conferencing: needs echo control, ceiling or table microphones and a DSP.

Survey the room

  • Length, width and height, seating plan, balcony or stage, and the audience area.
  • Surfaces: glass, concrete and hard floors reflect sound, while carpet, curtains and acoustic panels absorb it.
  • Background noise from air-conditioning, outside traffic and nearby rooms. The system must exceed it by 10 to 15 dB.
  • RT60. A long RT, over about 1.2 s for speech, hurts clarity however good the speakers are.

Set the performance targets

  • Level: about 75 to 80 dB SPL for speech and 90 to 100 dB for music at the listener.
  • Coverage: a variation of no more than ±3 dB across all seats.
  • Clarity: STI, C50 and speech-intelligibility targets.
  • Feedback margin: enough gain before feedback for the microphones in use.

Design from the results

Speaker type and countRoom shape, throw distance and RT: line array, column, ceiling or distributed
Amplifier powerSPL target plus 6 to 10 dB headroom
MicrophonesWired, wireless, gooseneck, lectern or ceiling, depending on use
Mixer and DSPNumber of inputs, feedback control, delays for rear zones and presets
Cabling and racks70/100 V line or low impedance, rack position and power
Acoustic treatmentNeeded if RT or echo is too high for the system to work

Verify

After installation we tune the system with measurement microphones, check coverage and STI at the seats, and give a commissioning report.

Tell us the room

Send dimensions and intended use. You get back an indicative acoustic treatment, a systems outline and a budget range.

Start an enquiry+91 94170 08304