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Ph E audio art seems to THshare of so-called majorhave a n impressive 'break-throughs', with developments in loudspeakers in the vanguard. This is predictable, as there are s o many ways of creating and radiating sound that designers have plenty of scope for their efforts. 1975 saw the release by some four manufacturers throughout the world of 'Linear Phase' dynamic loudspeaker systems, one of which was British. From our recent correspondence files, unquestionably, 'phase linearity' in loudspeakers is interesting, and confusing, many hi-fi devotees. One of the most recent treatments of 'this subject appeared in Wireless World1, in which H. D. Harwood (BBC Research Department) discussed the effects of phase-frequency response in relation to perceived sound quality and stereo image formation. Mr. Harwood's scepticism about the audible effects of non-uniform phase-frequency response is, perhaps, best summarised by a direct quotation from the article: 'Until, therefore, someone can demonstrate that phase effects of this nature affect the sound quality of loudspeakers on programme, and not just o n highly artificial signals, the appropriate treatment appears t o be to pull down the blind and pretend that phase, in this sense, does not exist'. This is also his reaction to stereo image formation effects. This topic has been debated in the audio literature many times before (and latelyWireless World, March 1976: 'Phase and Sound Quality' by James Moir, and Michael Gerzon's Ietter'Audibility of PhaseDistortion')ofcourse, including a reference to it in the early G . A. Briggs' texts2. Other useful material has appeared in B. B. Bauer's article on 'Audibility of Phase Distortion', Wireless World3, and several articles in the JOURNAL OF THE AUDIO ENGINEERING S O C I E T Y . ~1973 E. R . Madsen, In ~ ~ er al, presented a paper t o the 44th Convention of the AES at Rotterdam, on the 'Threshold of Phase Detection by Hearing'=. Another AES paper was published in 1974 & Loudspeakers Background to the debate by ~ o n a l d Aldous by Villy Hansen and E. R. Madsen,' dealing amplitude response. This latter shows the with aural phase detection, and last year Bang phase/frequency curve that should be obtained & Olufsen's Erik Baekgaard (assisted by S. H. if the loudspeaker were a completely minimum Pramanik) contributed an important paper on phase system, and comparison of the two the Beovox Uni-Phase loudspeaker systems to curves revealed that the ELS justifies the claim the 50th AES Convention, in L ~ n d o n . ~ 'minimum phase' to a far greater degree than In our advertisement, as well as editorial any moving-coil loudspeaker, including recent pages, we have carried descriptions of the designs claiming particular attention to this B & 0 Uni-Phase loudspeaker designs, aimed feature. at producing a linear phase response. T o obtain The ever-modest Peter Walker, commenting this so-called 'uniformed phase' in the Beovox on these findings, said 'at this point I might fa