Common sense can help you obey new Michuki rules on noise
The Sunday Nation
Nairobi,
17 January 2010
Gilbert Maina Ndungu is till having trouble understanding the noise control regulations. In particular, he would like to know the relationship between the power output of a sound amplifier and the decibels produced. He is concerned because his church has a public address system that is rated 800watts.
He explains: “In the church sanctuary the amplifier volume operates between 40 to 50 per cent, but for outdoor meetings it operates between 45 to 65 per cent. My queries are as follows:
“How many decibels are we producing when preaching in the sanctuary and outside? What is conversion rate for every watt produced from the speakers, i.e. watts to decibels? What volume is allowable or compliant to Michuki rules within the stated distance of a radius of 30 metres?”
Let’s start with the last question because it is easier: the environmental noise regulations state that sound shall not be loud enough to interfere with normal conversation 30m away. Now, you don’t need technical knowhow to establish that the sound from your equipment is interfering with normal conversations!
If you are in doubt, just walk about 40 steps (approximately 30m) from the speakers and try to hold a conversation. If you find that you need to raise you voice a little more than usual, then the equipment is too loud.
The first and second questions are a bit more technical. Unfortunately, there is no one answer. The number of decibels produced by one watt of power going into a loud speaker depends on the design of the speaker. Some are very efficient and others not so.
Efficient speakers produce more than 90dB per watt (measured from one
metre away) and inefficient ones will give less than 85dB/W. The actual
figure is given in the user’s manual – but not all manufacturers provide
this
Now you might think that setting the volume control knob at 50%, you will be getting 400W from your 800W system, but that is not so! The scale is not linear meaning that a fraction on the controls is not equal to a similar fraction of the power; thus, half on the scale is equal to half the power and so on.
Perhaps you have noticed that sometimes pushing the knob to a higher level does not give discernible difference in the sound produced. For this reason, if you want to establish the power being pumped into your speakers at various levels on the control, you will have to measure the voltage and current in the cables.
Despite all this technical jargon, common sense should be a good guide. When operating the public address system inside the church, set the volume to a level so that it is just audible from the gate of the compound. If you have an outdoor session, make sure the sound is just barely noticeable at the perimeter of the field.
After all, when you raise the volume too high, the sound bounces off the walls of nearby buildings causing loud echoes that interfere with the main output from the speakers. The net result is unintelligible noise that is annoying to everybody… including your congregation!
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