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«Our organization designs and installs public address systems, and we sometimes encounter the problem of poor speech intelligibility at facilities. This is most often encountered in airport halls and train stations, where there are large rooms with high ceilings and increased noise levels. We increase the number of loudspeakers in the broadcast area, but this does not always help. Tell me, which loudspeakers are best suited to ensure good speech intelligibility? — Alexander MOLCHANOV, Moscow»
Svetlana Anisimova, Head of the Notification Systems Department at Bosch Security Systems, answers a reader's question.
Many modern public buildings use hard, sound-reflecting materials for covering floors, walls and ceilings. In large areas, such as transport facilities, due to their size and the lack of sound-absorbing materials, the reverberation time will be quite long and the ratio between reflected reverberant sound and direct sound will be high. This has a negative effect on speech intelligibility. Increasing the number of loudspeakers in this case does not save the situation, and often even worsens it.
For high-quality sound reinforcement of rooms with unfavorable acoustic conditions, special acoustic systems of the «line array» type with a controlled directional pattern can be used. In such active devices, the frequency response and signal delay are adjusted using a built-in digital processor with subsequent multi-channel amplification.
Using a computer-based configuration program, the array is tuned to the acoustic conditions and its output sound energy can be optimally directed toward the audience to achieve the best possible ratio between direct and reflected sound and the best intelligibility. The intuitive program interface provides a graphical representation of the array's directivity, making system setup quick and easy. From an aesthetic point of view, variable-beam line arrays are more attractive because they do not require mechanical pointing of the loudspeaker toward the audience; the loudspeakers in the array are virtually directed using electronic tuning.
For emergency notification systems, active line arrays are suitable, as they have real-time monitoring functions for the operating status of the loudspeakers and amplifiers in the array.
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