Från bullertråden i Racingforumet. Verkar vara bestämt hur man skall mäta ljudnivån inför tävling:
3.1.2 Ljuddämpning, alla klasser.
Ljudnivå enligt lokal miljöföreskrift eller Svemo, UEM eller FIM’s regler.
Officiell ljudmätning skall ske genom (av FIM föreskriven) ”2 meter max” metod enligt följande:
Vid varje tävling skall ljudmätare kalibreras i närvaro av minst två förar/teamrepresentanter. Kalibrering skall ske i intervallet 93,5-113,5 dB(A).
Varmkörd motorcykel skall vid mätning vara uppställd på en icke reflekterande yta (gräs/grus) i en miljö där bakgrundsbuller ej överskrider 95 dB(A. Ljudmätning sker med ljudmätare
fast placerad 2 meter bakom bakhjulets (MCS sidvagnshjulets) kontaktpunkt mot marken och i 45° vinkel mot motorcykelns längdriktning samt 1,35m över marknivå. Ljudmätare skall vara ställd på mätmetod ”A” och samplingstid ”fast” med presentationsmetod ”Max”. Vindskydd skall vara monterat på ljudmätarens mikrofon. Om omgivningstemperaturen är +10°C eller lägre skall 1 dB(A) dras bort från mätvärde. Mätresultat anges alltid i heltal genom att mätvärdet avrundas nedåt (mätvärde 108,9 dB(A) = mätresultat 108 dB(A)). Mätning skall ske på a) den sida avgasröret mynnar ut på. b) vid avgasrör på bägge sidor skall mätning ske på den sida insugsluftintag befinner sig. c) vid avgasrör på bägge sidor och centralt insugsluftintag skall mätning ske på bägge sidor (mätresultatet är då medelvärdet av dessa två mätvärden). Vid betydande vind skall sträckan MC till ljudmätare vara i motvind, så att mekaniska ljud från motor/transmission ej adderas till mätvärde. Motorvarvtalet skall hastigt bringas till maximalt under en tid av minimum 1 sekund och maximalt 2 sekunder. Om avgasdetonationer uppträder under mätproceduren skall mätningen göras om.
Maximalt tillåtet mätresultat ”2 meter max” för deltagande i tävling är 108 dB(A), vid efterkontroll är +2 dB(A) tillåtet.
Baserat på FIM
THE OPERATING PROCEDURE
The ‘2 metre max’ method will consist in quantifying not only the sound
level produced by the silencer of the exhaust, but the maximum global
sound level achieves by the motorcycle when the engine rpm’s are raised
to the maximum engine speed, limited by
➯ natural regulation for 2T, or
➯ rev limiter for 4T.
For 4T engines used in Speedway, Long track and Ice speedway, without
rev limiter, it would be advisable to limit the full open the throttle for 1 or 2s
maximum.
36
General(e) Section
THE PREPARATION OF THE SOUND METER
• Calibrated the sound meter at 93,5 dB or 113.5 dB to take into
account the incidence of the wind foam ball
• Position the wind foam ball on the microphone
• Activate the ‘A’ weighing
• FAST time weighting must be activated
• Select range Hi 80~130 dB
• Activate the function MAX MIN – set on MAX
THE SET UP OF THE SOUND METER AND THE MOTORCYCLE
The sound levels will be measured with the sound meter/microphone fixed
on a tripod, in the horizontal position, at the rear of the motorcycle.
The sound meter will be positioned at a distance of 2 metre behind the
motorcycle, with an angle of 45° away from the centerline, on the exhaust
side and at a height of 1.35m above the ground. The 2m distance is
measured from the point where the centre of rear tyre touches the ground.
It is preferred to make the tests on soft ground, not reverberating, i.e. grass
or fine gravel.
The ambient sound level muss remain lower than 95 - 100 dB/A.
THE POSITIONING OF THE MOTORCYCLE
The reference points:
• For a motorcycle: the contact point of the rear wheel on the
ground.
• For a Quad vehicle: the vertical line to the ground from the centre
point of the rear axle.
• For a Side-car: the contact point of the side wheel on the ground.
• For motorcycles fitted with 2 exhaust outputs, the measurement
will be made on the side of the air intake. If a central positioned
air intake is used, both sides will be tested.
• For Quad vehicles with exhaust outlet moved by the median axis,
the measurement will be made offset side.
To make repetitive measurements, all motorcycles can be positioned into a
small frame fixed on the ground.
37
General(e) Section
THE NEW 2 METRE MAX METHOD
THE OPERATION – PROTECT YOUR HEARING – USE EAR PROTECTION
• The measurement is made with motorcycle on its wheels, in
neutral, hot engine.
• The technical steward takes place besides the motorcycles,
opposite to the microphone, or in front of the handlebars near
the front wheel, not to screen or stand between the bike and the
microphone.
• If a 2nd steward is permanently attending the sound level checks,
it is strongly advised for him to use earplugs (headset or ear
protectors) .
• The throttle is turned as fast as possible (instantly) until the
appearance of the first signs of engine speed regulation (by the
rpm limiter), then released quickly to avoid possible back fire.
• If the engine tends to suffocate, accelerate slightly before
opening full open throttle.
• If detonations appear, the measurement must be started again.
A solution to avoid post combustion in the silencer could be a progressive
relaxation of the throttle.
THE MEASUREMENT – RECORDING OF THE SOUND LEVEL
• For motorcycles without rev limiter, the opening of gases will
have to be lower than 2 seconds.
• A mnemonic to count: ‘one thousand and one, one thousand and
two’, or ‘1y, 2y’.
• When the measurement is considered acceptable, write down the
result, then reset (push on the sideline) the MAX MIN setting until
the disappearance of the previously displayed value.
• Push again on the sideline MAX MIN to arm the sound level
meter.
• The sound level meter is then ready for the following
measurement.
38
General(e) Section
The perfectible point of this method is the possible cheating by
"temporary" decreasing the maxi engine speed reached by:
• the clogging in engine 2T
• a switch on the programmable CDI/ECU for 2T and 4T
engine
A noticeably lower engine speed is detected easily by hearing. If doubt,
control of the value of the rpm limiter with a tachometer.
Sound levels will be controlled to limits as stated in Art. 79.11.
For the initial sound control and technical inspection, a rider (or his mechanic)
shall present only one spare silencer per machine.
Other spare silencers may be presented after all participants have presented
their motorcycles, or on the following days of the event.