Technical Background

A fundamental characteristic of a speaker, is its frequency response. Ideally, the frequency response of a loudspeaker should be flat across the audio spectrum and in all directions of space.

The most common method of measuring the frequency response of a speaker is On Axis frequency responce in anechoic chamber, where we place the measuring microphone directly in front of the speaker.

However, for the full mapping of a speaker’s frequency behavior in space, the on Axis Response is not sufficient enough. We must measure and record in detail the frequency response curves in all directions around the speaker.

Sound Power is the sum of the total emitted acoustic energy of a speaker as measured globally (at 360 °, with measurements every 10 °) around the speaker horizontally and vertically. Hence it is much more representative on how the speaker will aurally stimulate the listening space creating reflections, compared to the anechoic on Axis frequency response measurement.

The On Axis response reveals the speaker’s behavior just in front of it and only in a short distance from it (nearfield), whilst in a room, moving away from a speaker increases the ratio of reflected to direct sound.

The Sound Power response becomes more important for the actual In-Room response.

The 70 microphone locations used to acquire the amplitude response data, according the “ANSI/CEA-2034 Standard: Standard Method of Measurement for In-Home Loudspeakers”.

(The illustration is based on Floyd E. Toole, Sound Reproduction, Focal Press, 2008. This is an excellent reference book for loudspeakers and rooms. WiSound recommends this book to anyone who would like to get an in-depth consideration of acoustics and psychoacoustics).

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