Sound Sources

Type 4720  Speech Intelligibility Measurement Software – Echo Speech Source

Type 4720 Speech Intelligibility Measurement Software – Echo Speech Source

In combination with DIRAC6, the Echo Speech Source quickly and easily performs speech intelligibility measurements in accordance with IEC 60268-16. Impulse response and background noise are measured in one pass using intermittent MLS (Maximum Length Sequence) stimulus followed by an equally long period of silence.


  • Speech intelligibility measurements with DIRAC
  • Measurements including background noise

With a calibrated speech source there is no need for external equalizers or speech level adjustment. The signal can be set at an elevated level, making STI (speech transmission index) measurements possible even if the background noise is significant. DIRAC 6 recognizes the output level and corrects calculations appropriately.

Echo Speech Source can be used to set the volume of PA systems using a male speech signal with a standard level of 60 dB(A) at 1 meter. For STI measurements, it contains pink MLS signals. The MLS is far less intrusive than an e-sweep signal.


  • Wireless sound source for DIRAC 6
  • Calibrated speech levels and spectra
  • Mouth directivity
  • Five built-in stimulus signals
  • Intermittent stimulus accounting for background noise
  • External input and output
  • Compact and lightweight (10x10x17 cm, 1 kg)
  • Mounts on standard tripods
  • Battery powered
  • External power supply included