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ISO 7240-24-2010 pdf free download

ISO 7240-24-2010 pdf free download.Fire detection and fire alarm systems Part 24:Sound-system loudspeakers
Systemes de detection d’incendie et d’alarme — Partie 24: Haut-parleurs pour systèmes d’alarme vocale.
The standard baffle shall be made with a plane front surface that is acoustically reflective. The baffle shall have the dimensions shown in Figure A.2. The standard baffle shall be of a material of thickness adequate to ensure negligible vibration, such as plywood of at least 19 mm thickness. The loudspeaker shall be mounted as specified by the manufacturer.
NOTE For an identical loudspeaker, a measurement with a standard baffle can result in slightly higher on-axis sound pressure levels between 100 Hz and 500 Hz compared to a half-space measurement (see A.1.3).
A.1.5 Ground-plane measurement
In a ground-plane measurement arrangement, the loudspeaker shall be mounted above the acoustically reflective boundary surface, typically the floor, and aimed such that the reference axis is pointed at the measurement microphone. The microphone shall be placed directly on the boundary surface such that its reflection sums coherently with the direct sound (see Figure A.3). Consequently, a ground-plane measurement shall be corrected by —6 dB in order to achieve results that are equivalent to a measurement under free-field conditions.
NOTE 1 Ground-plane measurements can be camed out indoors as well as outdoors in half-space free-field conditions.
The test sample shall be mounted above the reflective boundary surface such that the radiation characteristics are not affected except for a linear increase in level by 6 dB compared to a free-field measurement.
NOTE 2 For example, if a line-source-type loudspeaker is mounted vertically above the reflective floor, the effective acoustic length of the array is doubled, thus changing both frequency response and vertical opening angles. In this example, the effect can be minimized by mounting the loudspeaker horizontally so that the effective acoustic length is not doubled and spatial radiation characteristics are not changed as much,
A.1.6 Comparative measurements
For practical reasons, as an alternative to measurements in free-field and half-space free-field conditions, comparative measurements of frequency response before and after environmental tests can be made using a non-free-field environment.
The frequency-dependent difference obtained in this comparative measurement shall be added to the result obtained in the reproducibility measurement (see 5.2). This result shall be taken as being equivalent to the frequency response that would be obtained in free-field or half-space free-field conditions after environmental conditioning.
The mounting arrangement for the test sample and measuring microphone shall be the same before and after the environmental conditioning.ISO 7240-24-2010 pdf free download.

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