Comments to date on DRAFT AES56-xxxx, AES standard on acoustics - Sound source modeling - Loudspeaker polar radiation measurements,
published 2008-09-11 for comment.
4.1.1 The terms "small devices" and "large devices" are ambiguous and undefined. Recommend replacing the last sentence with "The minimum measurement distance shall be at least 3 times the maximum linear dimension of the source, including the enclosure."
In addition, I could find no reference within the text of this document with respect to the Conditions of the Measurement, i.e., Free Field, half space, 4p, quasi anechoic (gated/simulated free field), etc. I recommend a sentence to this effect be added to 4.1, preferably before 4.1.1,
Christopher J. Struck
1. A complete discussion of measurement methods of real-world boxes would be a substantial tutorial document, however this standard on angular measurements is not the intended place for that discussion. Specifically, the consideration of measurement distance is not intended to be part of this standard. However, we understand that it is important that naive users should not interpret the provision in 4.1.1 (that normalizes reporting at 1 m) as sanctioning measurements at 1 m. This was the intent in the existing text but we agree it could be interpreted ambiguously. Accordingly, we propose that the text in 4.1.1, "The measurement distance ... annex A.1", should be replaced by the following Note as an editorial matter.
"NOTE Consideration of actual measurement distances for individual loudspeakers is not covered in this standard, however practical measurements will seek to reduce phase errors in complex data by ensuring that the measurement distance is large compared to the dimensions of the loudspeaker. Typically, the measurement distance would be a minimum value of 4 m or, more typically, 8 m. See also annex A.1."
2. Many issues of practical measurement are not considered in this standard on measurement angles, although they would, of course, be relevant for a complete measurement protocol. The consideration of conditions of measurement is currently outside the scope of this standard.
Please let me know as soon as possible if this response is not acceptable to you. You may also ask us to consider your comments again for the next revision of the document. You may also appeal this decision to the Standards Secretariat.
What you have proposed is excellent and covers the issue quite elegantly.