ISO 17201-1 pdf download – Acoustics -Noise from shootingranges – Part 1: Determination of muzzle blast by measurement.
7.1 General remarks
Apart from the muzzle blast the event signal may also include projectile sound. reflections from objects and from the ground. When planning a measurement. it should be taken into consideration how these unwanted contributions can be separated from the muzzle blast in the later data analysis Commonly used methods are the following.
a) Window techniques: This ted1nique is applicable for signals that arrive at the microphone separated in time, where the width and position of the window is adjusted in such a way that only the sound from the muzzle blast can be analysed. It Is typically used for reflecting objects and projectile sound, In a measurement layout with soiace and receiver heights that ensure a dear separation of the direct and the reflected wave from the ground, it may also be used to exclude the effect of ground reflections. In this case is 4gr= 0.
b) Ground Impedance models These models are used if the measured signal Is a superposition of the direct wave and the reflected wave from the ground They yield a prediction of the ground effect based on the reflection of a spherical wave at a complex impedance ground
Other methods may also be used. The methods used shall be described.
7.2 Gun
The barrel should preferably be horizontal and at least 1.5 m above the ground In some directions, the projectile sound wave and the muzzle blast can be separated by window techniques. For directions where this is not possible, the correction may be computed. Projectile sound is also generated by projectiles from shot guns and pistols as long as the speed of these projectiles is supersonic.
7.3 Measurement position
The measurement positions may be arranged in either a semicircle or a full circle. The angular increment of angle a should preferably be regular. The angular increment step should not exceed 45. One measurement position should be close to the line of fire. Care shall be taken not to choose measurement anØes too close to the border of the projectile sound region. The difference in the averaged broadband sound exposure level of the frequency range of interest between adjacent measuring points shall be smaller than 5 dB. In order to reduce meteorological effects, the distance between the source and measurement position should be chosen to be as short as posstle.
The microphone should normally be placed at a distance of at least 10 m up to 50 m to ensure that the peak pressures do not exceed 1 kpa. It should be tested (considering the pressure limit of 1 kPa) at which distance this prerequisite Is fulfilled. By increasing the measurement and source heights, the time delay between the direct and reflected signals can be increased.
7.4 Measurement equipment
Sound level meters and similar measurement instrumentation shall comply with the requirements for a type 1 instrument as specified in IEC 61672-12002.
Compliance with additional requirements for the measurement of impulsive noise is recommended Such requirements are specified in IEC 61672-1.
If a digital or analog recording instrument is used for (intermediate) storage, it shall have an adequate bandwidth and dynamic range.
The measurement equipment in particular the measurement microphones, shall be suitable for measurement of hh peak sound pressures.
12 Report
The report shall document the primary data recorded (at least octave-band Sound exposure and the peak sound pressure level of each shot) and reported, together with a description of the measurement and analysis conditions including measurement uncertainty (see Clause 11).
All measurement quantties shall be given in SI units.
The height of the microphone above the ground or relating to the sound source shall be stated.
The way in which the sound from supersonic projectiles and ground reflection have been eliminated, how the octave-band analysis has been performed, and which corrections were used shall be descnbed. At least one example of the lWne/pressure signal for one measurement position shall be shown The directivity pattems are given by listing the interpoLation coefficient of Equation (9) for each frequency ban&
All measurement equipment shall be specified, together with the date and result of the last traceable calibration. The guns and the ammunition shall be specified, as well as the meteorological conditions (wind speed, temperature, humidity, air pressure and cloud cover).
ISO 17201-1 pdf download – Acoustics -Noise from shootingranges – Part 1: Determination of muzzle blast by measurement
