REV.
SURFACE ® J47
MAR2005
VEHICLE Issued 1975-05
RECOMMENDED Revised 2005-03
PRACTICE
Superseding J47 JUL1998
Maximum Sound Level Potential for Motorcycles
1. Scope
This SAE Recommended Practice establishes the test procedure, environment, and instrumentation for
determining the maximum sound level potential for motorcycles under wide open throttle acceleration and
closed throttle deceleration.
1.1 Rationale
Changes were made to References, Sections 4.1, 4.2, 5.1, 6.2, 6.2.1, 7.6, and 8.7. Section 9 was added.
2. References
2.1 Applicable Publications
The following publications form a part of this specification to the extent specified herein. Unless otherwise
indicated, the latest issue of SAE publications shall apply.
2.1.1 SAE PUBLICATIONS
Available from the Society of Automotive Engineers, Inc., 400 Commonwealth Drive,Warrendale, PA
15096-0001.
SAE J184—Qualifying a Sound Data Acquisition System
SAE J213—Definitions, Motorcycles
SAE J331—Sound Levels for Motorcycles
SAE J1349—Engine Power Test Code—Spark Ignition and Diesel
2.1.2 ANSI PUBLICATION
Available from the American National Standards Institute, 25 West 43rd Street, New York, NY 10036-
8002.
ANSI S1.4—Sound Level Meters, Specifications for
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Copyright © 2005 SAE International
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SAE J47 Revised MAR2005
3. Definitions
3.1 Rated Engine Speed
The speed in revolutions per minute at which the engine delivers maximum net brake power output as
defined in SAE J1349, as determined by the manufacturer.
3.2 Manual Clutch
A clutch which must be disengaged by the operator to prevent engine stalling when the vehicle’s forward
motion is stopped.
3.3 Longitudinal Plane of Symmetry
As defined in SAE J213.
4. Instrumentation
The following instrumentation shall be used where applicable.
4.1 A sound level meter which meets the Type 1 or Type S1A requirements of ANSI S1.4. At intervals
of not more than 2 years, the sound level meter shall be calibrated for compliance with the Type 1
or Type S1A requirements of ANSI S1.4. As an alternative to making direct measurements using a
sound level meter, a sound data acquisition system may be used, provided that the system meets
the requirements of SAE J184.
4.2 An acoustic calibrator with accuracy of ±0.5 dB. (See 8.6.4.) At intervals of not more than 2 years,
the acoustic calibrator shall be calibrated to its original specifications.
4.3 An engine speed tachometer, or other means of determining engine speed, with steady-state
accuracy of ±3% at 60% and 100% of rated engine speed.
4.4 A speedometer with steady-state accuracy of ±3% at a vehicle speed of 100 km/h, or the vehicle
maximum speed, whichever is less.
4.5 An anemometer with steady-state accuracy of ±10% at a wind speed of 5.0 m/s.
4.6 An acceptable wind screen may be used with the microphone. To be acceptable, the screen shall
not affect the microphone response more than ±1 dB for frequencies of 4000 to 10 000 Hz, taking
into account the orientation of the microphone.
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SAE J47 Revised MAR2005
5. Test Site
5.1 The test site (Figure 1) shall be a substantially level open space accommodating a straight vehicle
path and the following points:
5.1.1 ON THE VEHICLE PATH
A—Microphone target point
B—End point—a point 7.5 m beyond the microphone target point
C—Acceleration point—a point at least 7.5 m before to the microphone target point established by the
method described in 6.2 and 6.3.
D—A point 15 m before the microphone target point
E—A point 15 m beyond the microphone target point
5.1.2 OFF THE VEHICLE PATH
F—Microphone point—a point 15 m from the centerline of the vehicle path on the perpendicular line
which passes through the microphone target point.
5.2 The measurement area within the test site shall be a triangular area defined by the microphone
point (F) and the points D and E. The surface of the ground within at least this area shall be
portland cement or bituminous asphalt concrete, dry and free from snow, soil, or other extraneous
material.
5.3 The test site shall be free of large sound-reflecting surfaces (other than the ground) such as parked
vehicles, signboards, buildings, or hillsides, located within 30 m of the measurement area.
5.4 The vehicle path shall be relatively smooth portland cement or bituminous asphalt concrete, dry
and free of extraneous material such as gravel, snow, or ice and of sufficient length for
acceleration, deceleration, and stopping of the vehicle.
5.5 The microphone of the sound measurement system shall be located above the microphone point.
The microphone shall be positioned 1.2 m ± 0.02 m above the ground plane. The microphone's
reference axis shall be perpendicular to the vehicle path. (See 8.6.1.)
5.6 The test site layout in Figure 1, for the purposes of clarity, illustrates an approach from left to right.
Sound level measurements are to be made on both sides of the vehicle; therefore, it will be
necessary to establish either a second microphone point on the opposite side of the vehicle path
with a corresponding measurement and clear area, or use approaches from both directions with
corresponding acceleration points and end points.
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SAE J47 Revised MAR2005
FIGURE 1—TEST SITE
6. Procedure
6.1 Overview
The intention of this test is to have the vehicle under test reach the end point under its maximum noise
conditions—at wide open throttle and at rated engine speed, or as close to rated engine speed as the
powertrain and conditions permit. Vehicles with a manual clutch approach the acceleration point at a
steady engine speed. All other vehicles begin accelerating from the acceleration point using a standing
start procedure. Each vehicle uses a different acceleration point in the test. The acceleration point for
each vehicle is established by, basically, running the test procedure in the reverse direction in order to
determine how to run the test in the normal direction.
6.2 To establish the acceleration point for vehicles with a manual clutch—the end point shall be
approached in first gear from the direction opposite to the direction of the test run at a constant
speed corresponding to 60% of rated engine speed. When the front of the vehicle reaches the end
point, with the clutch fully engaged the throttle shall be rapidly and fully opened to accelerate the
motorcycle past the microphone target point under wide open throttle. By trial, the lowest
transmission gear shall be selected that will result in the vehicle traveling the shortest distance from
the end point to the place where rated engine speed is reached, but which is not less than 7.5 m
past the microphone target point. The location of the front of the vehicle on the vehicle path when
rated engine speed is attained shall be the acceleration point for test runs to be made in the
opposite direction.
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SAE J47 Revised MAR2005
6.2.1 When the procedure described in 6.1 results in an unusual operating condition such as wheel
spin, the next higher gear shall be selected for the test, and the procedure rerun to establish the
new acceleration point. In any event, the procedure shall result in the vehicle being at the end
point when rated engine speed is attained without wheelspin or clutch slippage.
6.3 Vehicles without a manual clutch shall use a standing start acceleration, starting from the end point,
to establish the acceleration point. With the front of the vehicle at the end point and with the
transmission in the lowest selectable range, the throttle shall be rapidly and fully opened to
accelerate the motorcycle past the microphone target point under wide open throttle.
6.3.1 For vehicles that allow for operator selection of transmission gear ratio, the lowest transmission
gear shall be selected, by trial, that will result in the vehicle traveling the shortest distance from
the end point to the place where rated engine speed is reached, but which is not less than 7.5 m
past the microphone target point. The location of the front of the vehicle on the vehicle path when
rated engine speed is attained shall be the acceleration point for test runs to be made in the
opposite direction.
6.3.2 For vehicles that do not allow for operator selection of transmission gear ratio, the location of the
front of the vehicle on the vehicle path immediately before the place where the first transmission
upshift occurs which is not less than 7.5 m past the microphone target point, shall be the
acceleration point for the test runs to be made in the opposite direction.
6.3.2.1 For vehicles with continuously variable transmissions, the location of the front of the vehicle on
the vehicle path where the vehicle speed reaches its maximum or 100 km/h, whichever is
lower, shall be the acceleration point for test runs to be made in the opposite direction.
6.3.3 If the speed at the acceleration point established in 6.3.1 or 6.3.2 is over 100 km/h, then the
procedure to establish the acceleration point shall be rerun and the location of the front of the
vehicle on the vehicle path where the vehicle speed reaches 100 km/h, shall be the acceleration
point for test runs to be made in the opposite direction.
6.4 For the test under acceleration, the same basic procedure shall be used as was used in
establishing the acceleration point, except that test runs shall be made in the opposite direction.
The rider shall rapidly and fully open the throttle when the front of the vehicle reaches the
acceleration point to accelerate the motorcycle past the microphone target point under wide open
throttle. Full acceleration shall continue until the applicable ending conditions determined according
to 6.2 or 6.3 are achieved, which should be the end point, at which time the throttle shall be rapidly
and fully closed.
6.5 Sufficient preliminary runs shall be made before measurements begin to familiarize the rider with
the motorcycle under test and to establish the engine operating conditions. The engine temperature
shall be within the normal operating range prior to each run.
6.6 The longitudinal plane of symmetry of the test vehicle shall be on the vehicle path for all test runs.
6.7 Unless it is apparent that maximum noise occurs under acceleration, the following test shall be
performed to establish maximum sound levels under deceleration.
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SAE J47 Revised MAR2005
6.7.1 For the test under deceleration for vehicles tested under 6.2, the vehicle shall approach the end
point from the reverse direction at rated engine speed in the gear selected for the test under
acceleration. At the end point, the throttle shall be rapidly and fully closed and the vehicle shall be
allowed to decelerate to an engine speed of one half of rated engine speed.
6.7.2 For the test under deceleration for vehicles tested under 6.3, a standing start procedure shall be
used. The starting point shall be a point on the vehicle path which is the same distance from the
end point as the acceleration point, except in the opposite direction. With the front of the vehicle
at this point, the throttle shall be rapidly and fully opened to accelerate the motorcycle to the end
point under wide open throttle. When the front of the vehicle reaches the end point, the throttle
shall be rapidly and fully closed and the vehicle shall be allowed to decelerate to a vehicle speed
which is one-half that achieved at the end point.
7. Measurements
7.1 The sound level meter shall be set for fast response and for the A-weighting network.
7.2 The ambient sound level (including wind effects) at the test site, due to sources other than the
vehicle being measured, shall be at least 10 dB lower than the peak sound level produced by the
vehicle under test.
7.3 Measurements shall be made only when the wind speed is below 5.0 m/s.
7.4 The following measurements shall be made for both the acceleration and, if conducted,
deceleration test modes:
7.4.1 Measurements shall be taken for both sides of the vehicle.
7.4.2 The meter shall be observed during each test as the vehicle is accelerating or decelerating. The
highest sound level observed for each side during each test run shall be recorded.
7.4.3 Sufficient test runs shall be made until at least four recorded measurements for each test mode
and each side of the vehicle are within a 2 dB range. The sound level for that side and test mode
shall be the arithmetic average of the first four measurements within a 2 dB range.
7.5 The sound level reported for the vehicle shall be the sound level of the side and test mode with the
highest average sound level.
7.6 Measurements shall be made on vehicles unladen except for the rider. The tires of the vehicle
shall be inflated to the pressure recommended by the manufacturer for the vehicle in its unladen
condition. Before the measurements are started, the vehicle shall be brought to its normal
operating conditions with respect to temperature and tuning.
8. General Comments
8.1 Technically competent personnel should select equipment, and the test should be conducted only
by trained and experienced persons familiar with the current techniques of sound measurement.
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SAE J47 Revised MAR2005
8.2 While making sound level measurements, not more than one person other than the rider and the
observer reading the meter shall be within 15 m of the vehicle or microphone. The additional
person shall be directly behind the meter observer on a line through the microphone and the
observer.
8.3 The test rider should be fully conversant with and qualified to ride the machine under test, and be
familiar with the test procedure.
8.4 It should be noted that error in the engine speed indicator as well as error due to operator response
time may result in sound level measurement error.
8.5 Tachometers having steady-state accuracy within 3% of actual engine speed at 60% and 100% of
the rated engine speed are commercially available and are included on some motorcycles as
original equipment. This class of tachometers is regarded as being sufficiently accurate for general
sound level measurements. In circumstances where very accurate sound level measurements are
necessary, accurate engine speed determination is essential, and consideration must be given to
the accuracy and response time of the engine speed measurement system. Special care must be
taken not to exceed rated engine speed. Exact engine speed measurement must be based on the
time interval for not less than one complete engine cycle; i.e., two crankshaft revolutions for a four-
stroke engine.
8.6 Proper use of all test instrumentation is essential in obtaining valid measurements. Operating
manuals or other literature furnished by the instrument manufacturer should be referred to for both
recommended operation of the instrument and precautions to be observed. Specific items to be
considered are:
8.6.1 The type of microphone, its directional response characteristics, and its orientation relative to the
ground plane and source of noise.
8.6.2 The effects of ambient weather conditions (i.e., temperature, humidity, and barometric pressure)
on the performance of all instruments.
8.6.3 Proper signal levels, terminating impedances, and cable lengths on multi-instrument
measurement systems.
8.6.4 Proper acoustical calibration procedures, including the influence of extension cables, etc., shall
be followed. Field calibration shall be made immediately before and after each test sequence.
Internal calibration is acceptable for field use, provided that external calibration is accomplished
immediately before or after field use.
8.7 This procedure, SAE J47, was developed primarily as a tool to determine the maximum sound level
potential for motorcycles, and in no way intends to represent the way in which a motorcycle is
driven on the public highways. This procedure may not be appropriate for motorcycles equipped
with tires intended for off-road use. The procedure SAE J331 was developed to yield noise from a
new motorcycle under operating conditions more similar to motorcycles accelerating rapidly up to
cruising speed on an expressway on-ramp.
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SAE J47 Revised MAR2005
9. Notes
9.1 Marginal Indicia
The change bar (l) located in the left margin is for the convenience of the user in locating areas where
technical revisions have been made to the previous issue of the report. An (R) symbol to the left of the
document title indicates a complete revision of the report.
PREPARED BY THE SAE MOTORCYCLE COMMITTEE
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