[RogerH]

This was an editorial in the TACCOC magazine "Bespoke" in 2011 which finds that the noise testing procedure at Pukekohe is flawed :


Another row seems to be brewing over noise control. This one is centred around Pukekohe, where, according to the rumour, a recently-arrived resident has been making complaints to the Council about excessive noise levels. The Council’s response has been to demand the stationing of an individual with a noise meter just past the kink in the back straight. This presence is now compulsory at every race meeting, and the hirers of the circuit are required to pay for the privilege. We encountered this imposition for the first time at our recent Pukekohe event, and I was curious to see just how this new requirement would work out in practice.

It took me a while to spot him, but eventually I could see him, sitting in a small utility truck, on the grass behind the fences on the infield. I hope he wasn’t parked on the horse racing track itself, as the equine racing fraternity are very protective of their valuable animals, and get extremely upset if the track surface is damaged in any way. A stationary vehicle parked there at right angles to the track all day might leave significantly dangerous craters in the soft greensward.

The Motorsport NZ rules are very clear on the noise level issue. In Schedule A, regulation 3.8.2 reads: “No vehicle may exceed 95 db(A). The measurement shall be taken 30 metres at a right angle from the track at a point where the vehicle is at maximum power. No compensation for differing climatic conditions shall be applied.”

The decibel, or dBA, reading is a sound pressure level made on the A-scale of a sound level meter. This unit of measure approximates the response of the human ear. The Motorsport NZ ruling is all very well and good, and is almost identical to the CAMS requirement in Australia, but no guidance is given as to the operation of the meter itself. And the requirements are very specific.

Sound level meters measure sound pressure level and are commonly used in noise pollution studies for the quantification of almost any noise, but especially for industrial, environmental and aircraft noise. However, the reading given by a sound level meter does not correlate well to human-perceived loudness; for this a loudness meter is needed. The current International standard for sound level meter performance is IEC 61672:2003 and this mandates the inclusion of an A-frequency-weighting filter and also describes other frequency weightings of C and Z (zero) frequency weightings. The older B and D frequency-weightings are now obsolete and are no longer described in the standard.

The NORDTEST method states procedures for measuring road traffic noise inside and outside buildings and in open terrain, under specified traffic and environmental conditions. The accuracy is that of an ISO engineering method (Grade 2). The method aims at obtaining noise levels as they occur during slightly downward atmospheric refraction. Measurements carried out in accordance with this Nordtest method yield as the main result the total A-weighted energy equivalent sound pressure level. The method also enables measurement of the maximum A-weighted sound pressure level and sound pressure levels in octave bands. The method specifies how to measure the noise level at a given position in a well defined way, and how, by measuring road traffic noise simultaneously in several microphone positions, the noise levels in these positions can be determined in an efficient way. The operational parameters required to run the meter to obtain accurate readings run to twenty pages, and looks like things like temperature, wind, shields on measuring equipment, etc. Care must be taken that noise due to wind acting on the microphone does not influence the result of measurement. A microphone wind shield must always be used. You can check it out on http://www.nordicinnovation.net/nord...er/acou039.pdf

The method is useful – within its constraints due to measurement uncertainty etc. – to test compliance with noise limits, for example when residents complain about their exposure to traffic noise.

Among NORDTEST’s many findings are the following:

6.2 Calibration
Prior to and after each measurement the measurement system shall be checked at one or more frequencies using an acoustical calibrator according to IEC 60942.

And:
7.1.2 “Free-field”
The distance from the microphone to any sound reflecting surface apart from the terrain shall be at least twice the distance from the microphone to the dominating part of the sound source.

And:
7.1.3 “+6 dB”
The microphone shall be located directly on a plane and hard facade (of concrete, tile, glass, wood or similar material). The measurement yields a noise level equal to the level of the incoming sound plus 6 dB. The facade must be plane within ±0.05 m within a distance of 1 m from the microphone, and the distance from the microphone to the surface edges shall be larger than 1 m.

Note Annex E - road type at higher speeds can have up to a 9 dB correction factor so this could mean that a reading of 104dB could actually have a car-generated level of 95 dB.

Does all of this mean that failure to follow the proscribed operational procedures to the letter puts the accuracy of all of the readings taken at risk? Probably. Worse than that, it leaves the operator, and Motorsport NZ, dangerously exposed should an aggrieved competitor, put off the track because of an over-95 dBA reading, decide to contest the ruling in court.

It’s not the noise limits themselves that are the problem. In 1992, mainstream motor racing, including classic and historic cars, had noise limits imposed. Here, our MotorSport Association got in first, just as the general public were starting to make noises (sorry) about the sport. MANZ chose a level of 95 dBA, to be measured at a 30 metre distance, while the car is on the track. Individual cars were banned from racing if they didn’t comply. There was no allowance made for different climatic conditions. We didn't know if we could comply, but rather than ignoring it we started work on making it happen even before the deadline.

In the Summer 1993 issue of this very magazine, I commented:

“MANZ have for once, taken the initiative. They have imposed these controls to obviate the need for outsiders to impose other, more stringent noise controls upon us. Public pressure groups could easily have decided that 75 decibels should be the maximum. Or 65. By getting its own house in order; by voluntarily getting all its members to conform to an acceptable standard; by being seen publicly to be doing something about a perceived problem, New Zealand motorsport can be hailed as a public spirited organisation, taking due consideration of the Resource Management Act. We, the members of the Motorsport Association should be praising MANZ’s actions in this. Ultimately, it’s our sport they are protecting. The benefits we will continue to reap long after the pain is over..”

As time went on, we had periodic grumbles and localised problems, especially at Pukekohe. There were difficulties with the rules’ interpretation due to the woolly way in which they appeared in the Motorsport Manual. Circuits all round the country cope in their own ways, but there was always seemingly a greater problem at Pukekohe. The Pukekohe circuit promoters have to cope with an aggressive lobby group; locals who were apparently unaware that there was a motor racing circuit in the neighbourhood when they moved there (sound familiar?)… The 95dBA figure is a level set by Motorsport New Zealand, and is in line with accepted international motorsport guidelines. It does not work quite as well in practice, as it is enormously affected by weather conditions, but the drivers quickly learnt to compensate. They take evading action; they go past the noise meter in groups, they temporarily reduce revs, or redirect their tail-pipe away from the meter, thus guiding the same amount of noise in another direction. The car is not quieter; the meter just thinks it is… Again, from “Bespoke” in the Winter 1998 issue:

“At Pukekohe, the position chosen to set up the meter clearly does not comply with the operating instructions for these sensitive units. These instructions specify that the measurements are to be taken from an open, level space, with no nearby buildings or structures to reflect the noise being measured. At Pukekohe, the meter is set up in a natural land contour that acts as a sound-shell. It is pointed at a small gap in the solid steel Armco safety fencing, and is right beside the Scrutineering building. A significant change in the readings can be effected just by opening or closing the shed doors!
“There are certain local bylaws with which we must comply. Forget motor racing; the Franklin District Council’s District Scheme and the Resource Planning Act provide a fixed maximum limit for all property owners of 45dBA (I’m told) measured at the boundary of the property. This, surely, is what really counts here; not some arbitrary reading taken by a meter near the track. At the Levels circuit, in Timaru, the promoters have created a wall of huge hay-bales along one boundary where they had a noise problem - a very simple and effective cure. Measuring the Pukekohe perimeter noise levels would seems a logical first step. Solve that problem (if indeed it exists at all) and the locals no longer have grounds to object.
“This is not to say that the cars can then do what they like, but there must be a discretionary leeway in the interpretation of any regulations. In the glory days of the Wellington Street Races, there was no way in the world that any noise restrictions could have been met - an exemption was available and granted. The Grand Prix in Melbourne is painfully loud when the Formula 1 cars are on the circuit - earmuffs are essential. At Pukekohe earlier this year, every single car in the main race at the Formula Libre meeting failed the noise test. The organisers would have had to cancel the event had reason not prevailed. Imagine the chaos that would have caused, and the large amounts of money from sponsors and spectators that was at stake. Yet, technically, the event was illegal. We can; we must do better than this.”

The current position for the noise meter just past the kink in the back straight does at least get the thing away from the surrounding buildings we had in the old Paddock area. However, it still does not meet the requirements outlined in 7.1.3 above, of being mounted more than 1 metre above a plane and hard façade of concrete, tile, glass, wood or similar material, which itself has been laid to an accuracy of ±0.05 m.