Meeting Review, April 11, 2006
Constant-Directivity Horn Development, TEF Measurements, And The Nearfield Paper” by
veteran loudspeaker design and test engineer and Academy Award winner Don Keele. About 35
attendees were treated to an audio history lesson, including several highlights of Mr. Keele’s
own 34-year career.
The presentation started with the first generation of constant-directivity horns, beginning with
the Electro-Voice HR models (also known as the “white horns”) and the TL Bass Boxes. The
HR line was a new direction in horn design, making its public debut in 1974. In 1975 Mr. Keele
presented on the technology at the 51st Convention of the AES. The TL line was also developed
around the same time, and was initially only sold as plans except for one model.
In 1976, Altec Lansing started producing its Manta Ray line of Horns, about which Cliff
Henricksen and Mark Ureda presented at the 58th Convention of the AES in 1977. Having some
advantages and disadvantages over previous designs, one practical advantage was ease of
manufacture due to the lack of curved surfaces. The JBL Bi-Radial line was the last of the first
generation of CD horns, with production starting in the late 1970’s. Mr. Keele reviewed two
patents he received during this period.
The next part of the presentation covered the early history of Time-Energy-Frequency (TEF)
measurements, and its implementation with the test products developed by the Tecron Division
of Crown, International. This prompted a spirited, sentimental group discussion about the TEF
System 10 of the early 1980’s.
Mr. Keele concluded with a brief recounting of the history behind his 1974 AES Journal paper
titled Low Frequency Loudspeaker Assessment by Nearfield Sound Pressure Measurement,
being sure to give credit to Ray Newman, who inspired the work but declined to co-author the
The lesson was a valuable reminder of how audio technology was advanced back when
computational power was rare, so the analysis was fundamental out of necessity. This resulted in
practical, elegant designs that remain the roots of many of today’s products.