Since we are acoustics engineers and have a website, we often get calls from flakes. A ‘flake’ is someone who has developed some previously unknown affliction to some noise. They phone me up and then, full of apologies, explain that they hear a buzzing or drone in their ears and they are not sure what it is actually but they know it is not tinnitus because . . . well, they just know.
What they want is for me to dispatch an engineer with a sound-level meter to do measurements and find the source of the noise. Naturally, they avow, they have very little money, so could we perhaps just quickly come out at no charge? I curb my suggestion that, perhaps, they should consider what benefit we will get out of the interaction and, not wanting to waste the time of my engineers, I go myself.
It is always the same. Wherever they can hear, I cannot hear at all. So, I switch on my Type 1 Sanas-calibrated sound-level meter with 1/3-octave spectral analysis and I show them that there are no frequencies that are audible. “Not to you, perhaps,” they say. Then they produce a few screen shots of a smartphone screen which are of a sound-level meter app and tell me, see, this reads it. We have a discussion about the accuracy difference between R100 000 calibrated sound-level meters and an Internet app and I can see they are disappointed. With me. Because I am a nonbeliever.
But I persist. I show them that the 50 Hz unweighted value we measure at their premises is about 55 dB, which is 29 dB weighted and is a very faint noise indeed. Yes, they say, it is very faint. So I try the final test – I ask them to put on a pair of noise-cancelling headphones. If they say they cannot hear the buzzing or droning, then it may be that they can, in fact, hear a 29 dB 50 Hz noise. If they still hear it, then it is a doctor they need, not an engineer.
However, last Wednesday, in the UK Newspaper, The Guardian, there was a story about a mysterious ‘hum’ that millions of people in urban areas around the world claim to hear. Every person who hears it has a different explanation – industrial machinery, high-speed traffic, propellers, aliens – and all strongly resist the idea that the noise is psychosomatic or in any way inside their heads. It has been reported by persons from all around the world: Canada, Mexico, the UK, the US, and so on. I get about two reports a year from locals in Cape Town.
When I investigate, the person looks at my ageing figure and suggests that, since I am getting old, um, perhaps . . . my hearing is shot?
I tell them that my ears are tested yearly and I have supernormal hearing, so . . . nope.
Let us imagine that the hum is coming from the Koeberg power station. To be 55 dB at 50 Hz at Rondebosch, 35 km away, it would have to be astonishingly loud, which is comforting, since it means we really will not hear any of the reactors blowing up but will have to wait until we glow in the dark to know it happened.
I do agree that there are low- frequency noises in some towns and cities. Notably in Napier, in the Overberg, there is a compressor which starts at 07:00 and stops at 18:00. When I pointed this out to some of the residents, they could not hear it.
I am convinced that the hum exists but I do not think it is from a specific source but, rather, from a number of sources and always at low frequency, since high-frequency noises are absorbed by the atmosphere. If readers have any ‘hum’ experience, do let me know.