Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Shoreline Sound Level Measurement Procedure for Recreational Motorboats: SAE J1970-2018
Scope and Rationale
SAE J1970-2018 establishes a standardized procedure for measuring the maximum A-weighted sound pressure level of recreational motorboats operating under non-stationary conditions, as measured from the shoreline or up to 6 meters into the water. The 2018 revision expanded the original scope to allow measurements at virtually any distance inland, addressing the issue of wave noise that often made measurements at the water’s edge impractical. This change provides a more realistic assessment of noise exposure for shoreline residents. 🛠️
Engineering Design Insight: The revised standard allows measurements at any distance inland, overcoming previous limitations. Additionally, setting the minimum microphone height at 0.91 m (3 ft) minimizes ground effect interference, ensuring more consistent results across different terrain types.
Key Measurement Requirements and Procedure
The procedure specifies detailed requirements for the measurement site, microphone positioning, boat operation, and ambient noise correction. Key parameters include:
- Microphone height: at least 0.91 m above the underlying surface (any surface is allowed).
- Distance from reflective surfaces: no closer than 3 m from large obstructions like buildings or tree trunks larger than 0.3 m.
- Sound level meter settings: A-weighting and slow response (AS-weighted).
- Ambient noise must be at least 6 dB lower than the measured boat sound level; corrections apply for marginal differences.
| Difference between Boat SPL and Ambient SPL (dB) | Correction Applied to Boat SPL (dB) |
|---|---|
| ≥ 10 | 0 |
| 6 to 9 | -1 |
Measurement site can be any location inland or up to 6 m into the water. The boat does not have to be at a specific distance from the shoreline. The observer must read the maximum sound level during a pass.
⚠️ Important Restriction: The microphone must be positioned no closer than 3 m from any large reflective surface to avoid erroneous readings. Always verify there are no buildings, walls, or large tree trunks within this zone before measuring.
Calibration and Personnel
Acoustic calibration must be performed before and after each test sequence using a sound calibrator meeting IEC 60942. Only one additional person besides the observer may be within 15 m of the microphone, and that person must stay directly behind the observer. A windscreen is required and must not affect the reading by more than ±0.5 dBA. Measurements are invalid if changes in ambient sound level affect the boat reading.
Pro Tip: When measuring from a boat, hold the sound level meter at arm’s length outside the boat to avoid structural vibrations. Ensure all other requirements (height, distance from reflectors) are still met.
Frequently Asked Questions
- 1. Can I measure with the sound level meter hand-held?
- Yes, the microphone may be hand-held or mounted on a tripod. When hand-held, ensure the microphone is at least 0.91 m above the surface and pointed toward the boat. If measuring from a boat, hold the meter at arm’s length outside the boat.
- 2. What if the ambient noise is less than 6 dB below the boat noise?
- The procedure requires ambient noise to be at least 6 dB lower. If the difference is 6–9 dB, subtract 1 dB from the measured boat level. If the difference is less than 6 dB, the measurement cannot be performed under those conditions; choose a quieter time or location.
- 3. How do reflective surfaces affect the measurement?
- Large reflective surfaces can cause sound waves to bounce back to the microphone, potentially increasing the reading. The standard requires a minimum distance of 3 m from such surfaces. Trees with trunks larger than 0.3 m are considered reflective; smaller shrubs and grass are not.
- 4. Why is calibration required before and after each test sequence?
- Calibration ensures the accuracy of the measurement system and verifies that no drift occurred during testing. If the post-test calibration deviates significantly, the entire test sequence is considered invalid.
For more details, refer to the full text of SAE J1970-2018.
