Noise is relative to the listener and their location.

We can enjoy the delicate sounds of water in a babbling brook, or be awed by the deafening roar of a waterfall. We can enjoy music quietly, or attend a rock concert where the sound levels can take us to pain thresholds similar to standing near a jet engine.

As members of the general community we all try to allow for the differences in lifestyle and different world views that we all have. A dynamic society is active and "doing things". As the city spreads into once quiet fringe areas, of course there will change and change is unwelcome to some. Similarly, urban areas are become increasingly crowded. But Life is for living and so we all do our best to accommodate each other while we get on with our own lives. Some individuals are selfish and so we have Rules created by agencies of government in an effort to curb selfish excesses.

These Rules must be clear as to whether they are to make living together easier, or are unreasonably restrictive.

(1) Social Issues

What you hear can be "pleasant" or "unpleasant" noise. This is a matter of opinion, based upon your own prejudices and preferences.

We need to be careful to not let prejudices cloud the issues here. If a person has a morbid fear of light aircraft due to some terrible experience in their past, the sound of a light aircraft may trigger a sense of fear. The ability to hear the light aircraft may have absolutely no relation to the emitted sound level from the light aircraft, but still it generates the sense of fear. This is a personal problem that the community may wish to consider in context. In a case like this, we would be very careful to quantify and qualify the actual problem before enacting sweeping reforms to regulation of light aircraft noise.

Similarly, if an individual has prejudices about motorcycles developed from a particular experience, from newspaper articles or folklore about criminals who ride motorcycles, then the mere sound could cause them to have a bad feeling and take actions based upon those prejudices, rather than upon any objective assessment of the actual noise level produced, or the depth of the problem.

Riders would readily admit that there are a few motorycles on the street with excessively loud exhausts. There are few indeed, yet these few selfish individuals create a public image problem for all the other motorcycle riders due to the endemic nature of prejudices.

(2) Technical issues

Normal conversations are carried out at about 40db
A quiet restaurant is about 50db
Normal 'burbs road noise is about 60db
City traffic noise is about 80db
Discotheque is about 110 db

The "Ride-By" test under ADR 39/00 allows a motorcycle to emit a sound level of up to 82dB(A)

This noise includes all of the "other sounds" made by the motorcycle, including engine clatter, air intake noise, driveline noise, etc.

The test microphone is placed 7.5 meters from the path of the motorcycle, while the bike is accelerated as rapidly as possible and then the throttle closed as rapidly as possible. The test attempts to provide a simulation of real world use on the road.

The "Static" test method is quite a different test. The microphone is placed almost in line with and 500mm away from the exhaust pipe outlet while the engine is revved to the "test RPM" and then the throttle closed as rapidly as possible.

The closeness of the test microphone dictates that the sound levels will be higher when tested by the static method.

These details are in ADR 39/00

Both RTA Regulations and EPA Regulations stipulate that when tested by the "Static" test method, the motorcycle shall not exceed 94dB(A).

A 3dB(A) rise in sound output level is effectively a doubling of the sound pressure at the microphone. This is almost meaningless, except to engineers.

The human ear "hears" logarithmically and it takes a 10B(A) increase in sound level output to be heard as "twice as loud".

Hence, a motorcycle with a sound output level of 104dB(A) is "twice as loud" as a motorcycle at the 94dB(A) level required by Regulations.

Human ears are rarely "calibrated" so to be able to tell the exact sound level arising from an exhaust. Some people have delicate and acute hearing and others have varying degrees of deafness.

When a motorcycle is presented for annual registration inspection at an RTA Authorised Inspection Station, a sound meter is only required if, as stated under Rule 351 of the Rules for Authorised Inspection Stations: "Where a motorcycle upon inspection is considered to be excessively noisy the Authorised Examiner must ask the owner to have the exhaust repaired or to provide the results of a static noise test."

It is easily understood that an Examiner will make errors in determining sound level output of a motorcycle when they do not have a sound testing facility available. These errors would generally be expected to lie in the range between 94 and 104 dB(A), with far fewer errors occurring as the upper end of this range is approached.

This is the historical practice for Registration Inspections in NSW and the "minor errors" have been occurring for all time.

Any effort to place an absolute limit of 94dB(A) is going to find a large number of "non-compliant" motorcycles. This does not mean that these motorcycles are "excessively noisy". Far from it.

It means that most are not "excessive", there is an absolute minimum of "excessively noisy" motorcycles with most bikes being within reasonable levels. It means that AIS Examiners who are professionals with experience in their trade and have a damn good idea of what is "excessive" and what is not have considered those bikes are not excessively noisy. It serves nobody to malign them for exercising their judgement to the best of their ability within the constraints of the tools available to them.

It does however, leave a large number of motorcycle riders exposed to the sudden introduction of noise testing using a calibrated machine.

To force compliance to the machine at the stroke of a pen means an immense expense in retrofitting a very large number of motorcycles with "sound meter compliant" exhaust systems, to replace the "human compliant" ones fitted and considered reasonable by professional safety examiners.

If the government wishes to remove the aftermarket exhausts from the road they can pay for it, as they did in the gun buy-back schemes, as the individual expense to riders is prohibitive.

Riders have discussed this issue at length and are in general agreement that a motorcycle emitting over 100dB(A) can be classed as "excessively noisy", and it is these motorcycles that generate noise complaints.

If the EPA was serious about reducing the number of noise complaints, they would only target those motorcycles over 100dB(A)