Public address (PA) and Voice alarm (VA) systems in building complexes (airports, railway stations, shopping centres and concert halls) are designed to inform members of the public about evacuation directions in case of emergency. However, if such announcements are misunderstood due to the poor quality of the system, this can lead to tragic consequences. Therefore, it is very important to design, install and correctly verify the speech intelligibility of such sound amplification systems. In addition, public announcement systems may have legal or contractual requirements for the level of speech intelligibility, for example in a medical, industrial or commercial environment.
The Speech Transmission Index (STI) is applied in the deterioration of the speech intelligibility induced by the transmission channel. The STI method involves the use of a test signal applied to the transmission channel, and an analysis of the received test signal.
The speech transmission quality of the channel is determined and expressed in values from 0 to 1 in the form of STI. Using the obtained STI value, it is possible to determine the potential speech intelligibility.
The applications of STI include evaluation of sound reinforcement and emergency systems, communication channels, speech intelligibility, communication in rooms and auditoria, etc.
STIPA (speech transmission index for public address systems) is a STI derivative approach that was developed for fast measurements of electro-acoustic and acoustic environments effects that affect the speech intelligibility in the room acoustics and/or public address systems.
STIPA calculations are realized by sound level meter in accordance with the IEC 60268-16:2011 standard. Special smartphone/tablet application “BA Assistant” simplifies the measurement process and generates a report which can be sent to the other device via e-mail, wireless connections or communication applications.
Sound Level Meter
Sound level meter meeting class 2 or class 1 specifications of IEC 61672-1, compliant to IEC-60268-16.
Talk box
Test signal source (Audio TalkBox) offerring calibrated acoustic sound source emulating the speech levels of a person speaking.
STIPA function
Speech can be described as noise that is intensity-modulated by low-frequency signals. The STIPA signal contains such intensity modulations at 14 different modulation frequencies, spread across 7 octave bands.
BA Assistant App
Building Acoustics Assistant App smartphone application guides the user through the sound insulation measurement as well as STIPA procedures in accordance with choosen standard.
For STIPA measurements, it is necessary to use a meter which meets the requirements of the standard for sound level meters in accordance with IEC 61672-1 with the STIPA functionality that meets the IEC-60268-16 standard. In organizing STIPA measurements and calculations, the meter is supported by a dedicated mobile application. The STIPA signal is usually reproduced by loudspeakers available in the public information system under study, in some cases dedicated loudspeakers are used.
