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Megaphones come dead last as a means of communication

23rd October 2015

By: Terry Mackenzie-hoy

  

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Most of you (I hope) know that the Americans and the British, together with the Canadians and others, invaded France by landing on the beaches in 1944.

Prior to the landings, the Americans had wondered about the problem of communicating with the troops on the beach. As a result, they commissioned some acoustics engineers to determine if this communication could be achieved by having a large amplifier-powered megaphone mounted on a barge offshore. In theory, instructions would be given to the landing troops in this fashion. In practice, the gunfire from machineguns, 88 mm PAK guns, grenades and 12-inch shells fired from offshore made this idea impracticable. As we say in acoustics, “Never forget the background noise”.

But one thing seems not to have changed – the almost mythical belief in the ability of a standard megaphone to communicate with the crowd. The megaphone does not have a cone that moves (unlike a loudspeaker) and it relies on a small element (usually piezoelectric) supplied from an amplifier to vibrate to recreate the human voice such that others will hear. What people do not realise is that, very frequently, megaphones have a maximum frequency range of 700 Hz and, as a consequence, the human voice sounds very flat indeed when amplified by a megaphone.

Secondly, people using megaphones very seldom get them pointed in one direction. They wave them from side to side, with the result that half the crowd hear a virtually unintelligible sound and the other a vaguely intelligible sound. As a method of communication, the megaphone comes dead last. Yet, when communication is most needed, the megaphone is used – when workers go on strike, their leader tries to address them using a megaphone. While the police try to contain the strike, they try to communicate with the strikers using a megaphone. Thus, the strikers are exhorted to do something but do not know what, while the police are trying to tell the strikers not to do something in case there are severe consequences but the strikers do not know what. The result is confusion and frequently bloody conflicts that could have been avoided if each side communicated with the other.

About a year ago, we were contacted by a group of South Africans who had the agency to sell LRADs. An LRAD is a long-range acoustic device which is made by the LRAD company and consists of a number of acoustic drivers arranged in a Bessel, or Quadratic Phase, array. (For those of you Natal graduates, who do not know what this means, it implies that a group of loudspeakers are connected such that some are in phase, some out of phase, some operating at half power in phase and some operating at half power out of phase.)

But putting aside the gibberish for a moment, what this means is: if you point the LRAD (which looks like a flattened satellite dish) in the direction you want to be heard and talk into the microphone, you can be heard clearly and intelligibly at distances of up to a few hundred metres and more. These things cost R100 000 or so, so they are not likely to be bought by your average shop steward. The ones that are available double as a ‘sound cannon’, which can disperse crowds by directing very high noises at them. This is not required for your average crowd communication. Smaller ones do not appear to be available.

I am sure that LRAD does have patents for its systems but the fact of the matter is that the idea of a phased array is not patentable. It would not be difficult to make a smaller version that could be economically handed out to police and other people to at least ensure that crowd conflicts based on miscommunication do not occur. I doubt that this will happen. The public does not realise how useless megaphones are and they continue to be sold and used, despite their complete ineffectiveness. Or maybe because of? Do the police and the strikers secretly long for a fight and just pretend to communicate? Surely not.

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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