Test & Measurement

Sound source enables scale model measurements

1st July 2014
Siobhan O'Gorman

A battery-powered speech sound source, designated the Echo Speech Source Type 4720, has been launched by Bruel & Kjaer. The device enables users to measure acoustics within any room or space, make comparisons between one room and another, validate sound systems and perform scale model measurements.


Used in combination with the DIRAC 6 room acoustics software, the speech sound source enables users to perform speech intelligibility measurements, which meet standards IEC 60268-16 and ISO 3382-3.

The Echo Speech Source Type 4720 works as a standalone tool with five in-built calibrated signals, which are used by the DIRAC room acoustics software to calculate a range of speech intelligibility parameters, such as STI, STIPA and RASTI based on the impulse response of the room being measured.

Users can measure the speech intelligibility of a sound reinforcement system using an excitation signal, played directly from DIRAC, through the sound device output or from an external device such as a CD or MP3 player.

The speech sound source copes well with high levels of background noise, as the echo speech source uses an intermittent stimulus. The intermittent stimulus consists of a Maximum Length Sequence (MLS) sequence followed by an equally long period of silence. The full stimulus (MLS and silence) is measured in one go. DIRAC then extracts the impulse response and the background noise into two separate channels of a .wav file.

The Echo Speech Source Type 4720 is suitable for field and laboratory acoustics engineers interested in measuring room acoustics - and also for researchers and educational institutions.

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