Sound Testing

Most of the information on this page is taken from the "Stationary Sound Test Manual for Off-highway Motorcycles and All-terrain Vehicles" published by the Motorcycle Industry Council. If you would like a complete copy of the manual you can get it by sending an email to pamela@mic.org.

 Intorduction

The U.S. Environmental Protection Agency (EPA) set sound level limits for new motorcycles and new motorcycle exhaust systems manufactured after December 31, 1982. The stationary sound test procedure in the manual has been approved by the Society of Automotive Engineers (SAE J1287 JUL98) and is recommended for in-use noise control. It is relatively easy to conduct and quite effective in identifying excessively loud vehicles in the field. This procedure may be used to allow motorcycles and ATVs to enter an OHV park, as a prerequisite for entry into a competitive event, or to support enforcement actions for those vehicles subjectively observed as being too loud. This stationary sound test procedure (SAE J1287) requires the use of a specific engine speed in revolutions per minute (RPM) for each vehicle tested. The manual publishes the engine test RPM for most of the 1985-2000 model year ATVs, off-highway motorcycles and dual motorcycles. The test RPM for future new motorcycles and ATV models are be available on the MIC website at www.mic.org, or in the next revised edition of the manual.<

 Sound Basics

The 20-inch stationary sound test, SAE J1287 JUL98, in the manual primarily measures exhaust sound. The decibel (dB) is the unit used to express the sound pressure level. Decibels are measured on several scales. The "A" weighting scale, expressed as dB(A), approximates human hearing and is used for the stationary sound test procedure. A moving motorcycle or ATV has many sound sources, including exhaust, air intake, engine and transmission, muffler shell, tire-surface interface, and many other small sources. Deteriorated or modified exhaust systems may increase sound. Other vehicle sound sources (e.g., air intake, transmission components) are usually not subject to as much modification or wear.

 Sound Test Equipment

The following equipment and materials are needed to properly conduct a stationary sound test.

1. Sound level meter

2. Sound level meter calibrator

3. Sound level meter windscreen

4. Engine speed tachometer

5. Test RPM (1/2 maximum rated RPM). Test RPM tables are included the manual.

Sound Level Meter

The stationary sound test procedure requires Type 1, Type S1A, Type 2, or Type S2A meters, based on the American National Standards Institute (ANSI) Sl.4-1983 specifications. Type 1 meters should be used when the need for accuracy is great, such as certification of exhaust systems, or enforcement action which may result in some form of penalty. Type 2 meters could be appropriate for some enforcement work, such as a preliminary screening test, or for general data gathering. Type 3 meters may be appropriate for use at a racetrack or motorcycle park, when the primary purpose is for some noise reduction within the area, and not for the purpose of meeting specific noise limits.

Typical Sound Meters

Sound Level Meter Calibrator

Calibrate the sound level meter before conducting the stationary sound test. Use only calibrators approved by the sound level meter manufacturer.

1. Turn on the calibrator and the sound level meter.

2. Set range switch to correct range.

3. Make sure calibrator is mounted to sound level meter correctly.

4. Adjust sound level meter to give correct reading.

Sound Level Meter Windscreen

Install a windscreen (a foam ball which fits over the microphone) according to the sound level meter manufacturer's recommendations. Always use a windscreen under windy conditions. The stationary test procedure should not be conducted if the wind speed is 20 mph or higher.

Engine Speed Tachometer

The use of a tachometer is mandatory to determine the correct engine speed during a stationary sound level test. Vibrating reed tachometers, which sense the vehicles vibrations, are the most practical and most widely used tachometers for the stationary sound test. There are also a variety of inexpensive electronic tachometers that use the spark plug pulse for determining engine RPM.

Test RPM

The stationary sound test procedure (SAE J1287) requires the use of a specific engine speed in revolutions per minute (RPM) for each vehicle tested (typically one-half the maximum rated RPM). The manual publishes that engine test RPM data for the majority of 1985-2003.

 Recommended Sound Limits

The Motorcycle Industry Council, Inc. (MIC) and the Specialty Vehicle Institute of America (SVIA) recommend the following maximum sound limit, based on the stationary sound test procedure (SAE J1287):

The 96 dB(A) limit is recommended as the maximum in areas where no sound level laws exist. Many states and localities, however, have ordinances mandating other sound level limits. Always check for the existence of local ordinances prior to riding in a new area.

 Sound Test Procedure

This is a summary of the SAE J1287 JUL98 stationary sound test procedure. This procedure may be used to allow motorcycles and ATVs to enter an OHV park, as a prerequisite for entry into a competitive event, or to support enforcement actions for those vehicles subjectively observed as being too loud.

Preparation

For convenience, attach a 20-inch string to the front of the sound level meter for the stationary sound test. Do not use a stick or wire for this purpose as the sound level reading may be affected. Allow the sound level meter to come to the same temperature as the surroundings. Set sound level meter to the slow dynamic response and the A-weighting network.

Test Site

No one should be within 10 feet (3 meters) of the vehicle other than the rider, the sound meter operator, an assistant to hold the front of the vehicle (if needed) and one other person directly behind the sound meter operator (if needed). The test area should be a flat, open surface free of large sound-reflecting surfaces within 16 feet (5 meters), such as parked vehicles, buildings, signs, and hillsides. The surface should be free of loose soil, snow or grass higher than 6 inches (150 millimeters). The ambient sound level (including wind effects) at the site shall be at least 10 dB lower than the sound level of the vehicles tested. Always use a windscreen under windy conditions. The stationary test procedure should not be conducted if the wind speed is 20 mph (9m/s) or higher. If it is necessary to test in higher winds, position the vehicle so the wind direction is parallel to the normal direction of travel of the vehicle. Also, do not attempt sound level measurement when it is raining or snowing.

Measuring the Vehicle Sound

Make sure the engine is warmed up and the transmission is in neutral. Have the rider sit on the motorcycle with both feet on the ground, or on the footrests, so that the vehicle is vertical and stationary.

1. Hold the sound meter (see diagram below):

2. At a 45-degree angle to the exhaust centerline (the normal line of travel)

3. Parallel to the ground

4. 20 inches (0.5 meter) to the rear of the exhaust outlet

5. At the same height as the exhaust outlet

6. Determine the test RPM for the make, model, and year of vehicle

7. Set the vibrating reed tachometer to the test RPM, or attach an electric tachometer.

8. Have the rider or assistant hold the vibrating reed tachometer against any solid part of the vehicle, or have the rider or assistant read the meter of the electric tachometer.

9. Have the vehicle operator slowly increase the engine speed to the test RPM. Have the vehicle operator or assistant signal when the correct RPM is held.

10. Read the sound level meter when the correct RPM is held.