Measuring high noise levels at a clay pigeon shooting range

MEASURING HIGH NOISE LEVELS

The Campbell Associates team attended a clay pigeon shooting range as part of an experiment to capture accurate high noise levels and sound pressure levels. Measurements were taken from various shotguns at a distance of 0.5m from the trigger, using a sound level meter designed for high sound pressure level measurement.

This type of noise measurement is sometimes required to assess the hearing protection used by individuals participating in gun-related leisure activities, where exposure to impulse noise can be significant.

The sound level meter used during the experiment was tested in three configurations to assess its suitability for high SPL measurement:

1. The standard meter with a 140dB full-scale measurement range
2. The standard meter in high-level mode, increasing the full-scale range to 150dB
3. The standard meter fitted with a quarter-inch high-level microphone capsule, extending the measurement range to 160dB

The Results:

1. In the standard measurement mode, the system frequently overloaded when the microphone was positioned closer than 1 metre from the gun being fired, highlighting the challenges of measuring extreme noise levels at shooting ranges.

Figure 1.

1. How does a high range option work – How do you get an extra 10dB from a standard ½” microphone?

When the extended measurement range is activated, the standard 200V microphone has its polarisation voltage reduced from 200V to approximately 70V. This reduces microphone sensitivity by 10dB, allowing the instrument to measure peak sound pressure levels up to 150dB.

This change in polarisation voltage causes a small variation in the microphone’s frequency response. However, this is automatically compensated for when the high-range measurement mode is selected. Corrections are specific to each microphone type and should not be mixed when performing precision acoustic measurements.

With this option activated, most high noise level measurements were achievable using the sound level meter.

Figure 2

However, at a distance of 0.5 metres from the gun, particularly when using heavier shot, the sound level meter still experienced overloads, with measured levels exceeding 150dBc peak.

1. Using a quarter inch microphone

With the use of an adaptor, a ¼” microphone can be fitted onto a standard ½” preamplifier, enabling measurements to be taken using a standard sound level meter.

Using this configuration, it was possible to measure peak noise levels without overload, with the highest recorded level reaching 157.9dBc peak.

Figure 3.

Why quarter inch microphones?

Quarter-inch microphones are inherently lower in sensitivity than ½” microphones. Their smaller diaphragm surface area makes them less flexible, meaning the same sound pressure produces a lower output voltage from the microphone capsule.

This reduced voltage output is highly desirable for very high sound pressure level measurements, as excessive signal voltages are the primary cause of overloads during extreme noise measurement.

How to measure beyond 160dB?

1/8” Microphone: Enables measurements up to 175dB, or up to 178dB when used with a 120V preamplifier supply.

Preamplifier Voltage: For extreme sound pressure level measurement, it is essential not only to use a low-sensitivity microphone but also a high-voltage preamplifier capable of handling large signal voltages without clipping.