Sounding-Off is an opportunity for occasional informal comments and opinions (rants) on issues vaguely connected with noise and vibration. These are personal opinions and should not be construed etc ... Please feel free to reply.

Noise Kills - New WHO Data Quantifies the Risks November 2007
Noise is stressful and can damage your health - particularly if you show up at 3am to an all-night party asking them to turn the noise down... New evidence collected by the World Health Organisation indicates that c 3% of deaths from heart disease is attributable to long term exposure to environmental noise - mainly nighttime noise exposure, with 2% of the population suffering from severe sleep disturbance, 15% from serious annoyance and with additional significant effects on the learning abilities of children. As noise complaints in the UK have increased by a factor of 5 over 20 years, this indicates that the problem of LOUD NOISE is rapidly getting worse.

Now for the figures: the threshold for cardiovascular problems is c50dB(A), with sleep disturbance at 42dB(A) and annoyance at 35dB(A) (all at night). 55dB(A) day or night has a negative effect on the learning ability of children (a 25% drop in long-term memory recall of children has been directly linked to the noise from a nearby airport). However: as these figures are all in dB(A) and a significant proportion of sleep disturbance cases involve low frequency noise that does not contribute significantly to the dB(A) value (think of bass beat, fan tones, transformers, combustion noise, distant diesel boom..), they must under-estimate of the scale of the problem.

We were designed a few million years ago to have ears that stay awake at night and with a brain and body that react to sounds. This ability has obvious evolutionary advantages - a rapid change from a potential puma buffet into a fully leapt-up and running away type creature at the merest hint of claws on stone was a good thing for a small ape. Nowadays, however, noise can cause the associated stress hormones to circulate constantly which can cause long-term physiological damage leading to heart failure, strokes, high blood pressure and immunity issues. And that’s not counting the apoplexy brought on by the neighbours doing .... just about anything that you do, but obviously without the same consideration for others. Apart from the dog, which should be put-down...

Plugging Entertainment Noise
Have you noticed that the PPE manufacturers are rushing out new devices - “now with added less protection” - for lower levels of noise exposure and for the entertainment industry? I can personally recommend these plugs for rock concerts - the music sounds better, but you do have to forgo the traditional post-gig head-buzz and “temporary” deafness. Talking of which, the new regs apply to entertainment from April 2008. If our experience is anything to go by, much of the industry still has its hands over its ears and is trying its best to ignore the whole thing...

Satisfying Super-Sensitive Complainants with Psychological Silencing
If you play white noise to a group of people and tell them that the song “White Christmas” is hidden in the sound, about 30% of them will be convinced that they can hear it. The human mind is always looking for patterns - even when they aren’t there. This propensity explains a significant proportionof complaints where noise levels are actually very low (they can be close to, or below, the threshold of hearing at low frequencies) or the complainant has mild tinnitus. The imagined pattern may betriggered by low level noise that isn’t itself the real cause of the subjective “nuisance”. Based on this understanding, we have developed an innovative solution based on “psychological silencing”. Thisinvolves broadcasting a carefully designed noise signature (matched both to the existing background and to the disturbing sound) from a bespoke sound system installed at the “culprit” site. This destroys any character in the sound and, coupled with an explanation and demonstration to the complainant as to how the “pattern” has been removed, they no longer hear it. Et - voila! No more complaints.

Acoustic Shock - Shock!! October 2006
Doesn’t the term “Acoustic Shock” sound nasty? If you renamed it “unexpected somewhat louder headset noise than usual that is still at only a tiny fraction of the noise level that is deemed to cause hearing damage in industry”, it wouldn’t sound so bad. The problem is that there is now a bandwagon with plenty in the media about “acoustic shock” in call centres and you can find a lot of “information” on the web. I was even told by someone recently that an event was so bad for one operator that it “made her ears bleed” - apocryphal, but he believed it. Headsets have limiters; people have volume controls. We’ve measured many call centre operator exposures and the highest still had daily noise doses in the mid 70s - 1/10th the level at which PPE is mandatory in industry. If the noise limiter on a station is not working, you could get startling events - easily solved by fixing the technical problem. The real problem is actually not technical and acoustic, but one or more of the human problems of poor working conditions, low pay and boredom that cause stress. Unless someone can show that the hearing of call centre personnel is an order of magnitude more sensitive than in industry, hearing damage could only happen via a combination of faulty equipment and a long term commitment by the operators to working at a volume of 11 (Spinal Tap scale ...).

Energy Efficiency, Global Warming, Fans and Pneumatics
Fans are at their quietest when run at maximum efficiency. Fan noise is proportional to the 5th power of speed. Rather than considering silencers (yet another loss in the system), look at improving airflow efficiency and reducing fan speed (a 20% reduction in fan speed drops the noise by a factor of 3). If tonal noise is a problem, our Quiet Fan technology is a low cost source control option that has no effect on efficiency. Copper pipes as pneumatic nozzles are a disgrace. Fit proprietary entraining nozzles - at 10dB quieter and using 20% less compressed air for the same thrust, it’s a no-brainer.

Instrumentation Convergence
We’ve now switched over from DAT recording to solid state and disk recording for data collection and analysis - purely in the interests of efficiency. The fact that mine also carries my entire MP3 collection is just a happy coincidence ...

The gloves are off ... April 2005
As for “AV” gloves - and I quote publicity "... transmissibility is defined as the ratio of vibration transmitted from a handle to the palm of the hand in the frequency range 31.5Hz to 1250Hz. ... reduces vibrationary shock by up to 70% on some tests .... and provides the workforce with a unique help to prevent this painful and all too common occurrence of "White Finger"”. Now whilst the technical bits (the technical leaflets are, in fact, the 4th most concentrated source of bullshit in the known universe*) are actually strictly true, we are into the realms of the shampoo advert (just how many different types of soap containing imaginary ingredients do we need and just why should fruit be good for your hair?). First, devise a glove test that covers only high frequencies and ignores the lower ranges where, embarrassingly, the gloves have no effect. This is despite the fact that it is often precisely at these lower frequencies that most damage occurs. Or maybe AV means Aloe Vera - to keep your hands as soft as a publicist’s brain ... There is no generally effective PPE for HAV.

Having got that off my chest, I’m off to wash my hair in something special - it’s slightly on the dry side of normal with a hint of frizz, a slight lack of inner glow that would respond to Neutrabullfaecamine90, a need for 20% more appearance of sheen (80% of the time) and a craving for fresh pineapple extract...

* Note: the 3rd most concentrated source is shampoo ads; the 2nd, party political manifestos; and the number one spot - Hi-Fi Magazines.

Patronised by experts ...
My 19 year old son has a quality rock band (not that I’m biased (!) - see for yourself at www.silentdawn.tk). However, my part as an occasional roadie and recorder of their gigs brings me into contact with that breed apart known as “sound engineers”. You’ve never been truly patronised until you’ve used the wrong jargon to a sound engineer and he’s reviewed your instrumentation DAT recorder (withering scorn, rolling of eyes). And me with all these qualifications in acoustics and more years of practical experience than I care to remember - but feeling only 6 inches tall (he was good - probably a subscriber to “What Jargon Monthly” and “Practical Patroniser” ....).

... confused by terminology ...
On the subject of jargon, noise and vibration terminology can be difficult at the best of times. There must have been a few “sound engineers” on the Noise Directive committee who saw fit to change the jargon unnecessarily - just to keep everyone on their toes. For example, the new UEAV (Upper Exposure Action Value) in place of 2nd Action Level and LEX,8h instead of LEP,d. Fortunately, however, in the UK regulations the HSC has stuck with the existing LEP,d instead of the new LEX,8h . Hurray!