The realistic range of a Public Address (PA) System / Acoustic Hailing Device (AHD)

True values explained

A Human Not A Robot


At STG Media Systems, our speciality is to provide very high power, long range, mobile, portable and fixed PA systems. Systems that are loud, clear, and intelligible; systems which accurately amplify and reproduce the human voice with all its various tones and nuances.  It has been shown that humans react much better, and follow the instructions, when public announcements sound like a calm human voice rather than the "robot" voices produced by most loudhailers. This is essential for emergency situations!



What is the range of a loudspeaker - Really?


Specifying the effective range of a loudspeaker can be very complicated and confusing. For example, some manufacturers may quote their product’s range as being 1200m. But this could be the distance at which the very last remnants, of a high pitch alarm signal, can be heard on a warm, still summer day with absolutely no background noise. The distance at which the human voice can just be heard, assuming no background noise, could then be quoted as 800m. However, the slightest whisper of background noise would completely drown out the voice. It is necessary to have approximately 10dBs, over and above the background noise, to be heard clearly. To be utilised in situations with a high level of background noise (e.g. evacuations, crowd control etc), then the system will have to produce around 85dB, at the location of the listener, to be heard effectively. The distance at which the voice could be clearly heard above an average level of background noise could then be 600m – and then assuming average environmental conditions (temperature, pressure, moisture etc) could then reduce this to 400m. 


We therefore quote the range of our products as “usable range” @85 dBs – meaning that the system will still be producing a Sound Pressure Level (SPL) of 85 dBs at the target. Which is the range at which the human voice can be clearly heard assuming average background noise and ideal environmental conditions. The “practical range” includes the effects of average environmental conditions (Air attenuation of 1KHz, air temp of 20 degrees C and a windspeed of 2m/s).

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