A bit later than your proposed period, but I recall attending an eye-opening lecture about Ambisonics at the IEE, Savoy Place in mid-March 1977, given by Peter Felgett - can't remember whether Gerzon was involved on that occasion - and in later months had several phone conversations with both Felgett and Michael Gerzon about aspects of the Integrex decoder design, since I was soldering one together at the time. Michael did accept the limitations of the design, but also was patient in explaining the necessary compromises needed to make something practicable and affordable.
Michael was - quite rightly - dismissive of my suggested "enhancements". Later on, I heard him lecture at the AES London meeting (maybe 1979 or '80?) in which he introduced his "Diametric Decoder Theorem", which basically explained in nice simple terms the mathematical reasons why Ambisonic speaker arrays of the time - driven necessarily by analogue decoders - were constrained to only certain geometrical shapes in order to satisfy the Theorem.
Michael presented as a theoretical case the notion that an array of N diametric speaker pairs could economically be driven by only N+1 (mono) power amps. This is because if the signal "S" (say) feeds one member of a pair, then its diametrically opposite speaker should take the signal (W-S). Hence in theory, for example, four (mono) power amps can drive six speakers, as the Integrex decoder was designed to do, using "speaker-matrixing". The first speaker of each pair gets its raw amp feed to its plus terminal, with its minus terminal connected to amp minus - notionally earth - as usual. Its opposite number gets the amp feed to its minus terminal and gets the W signal fed to its plus terminal.
That's the theory. In practice, if you try this out (and I did) you may find exciting artefacts, such as discovering tremendous earth-loop instabilities caused by the fact that different amp chassis may float away from earth for various electrical reasons. And when you're dealing with raw power amps, low impedances, and high currents, a little hum instability can go a long way... Things can smoke.
However: as a corollary, I did realise that the Integrex decoder could still be made to drive a hexagon array using three stereo power amps. You wired the main rectangle as normal from the Lf, Rf, Lb, Rb outputs, and you wired the extra pair (which could be set as Cf, Cb, or as Cr, Cl) feeding one speaker with its signal S, and its opposite with W-S, since the Integrex decoder most helpfully provided a W output for this purpose.
I did once wire up a college party (I was CUTRS not OUTRS) this way with an Ambisonic Hexagon array. Only stereo records to play - this was pre-CD - but it seemed to make a spectacular and enveloping noise.
(Of course, after all the grimy effort of crawling round the furnishings to pull cables round the JCR, I may have been biased about the outcome.)
Gerald W Wilson
Post by Daniel Hulme
Dear list members..
I work for the music department at the University of Oxford.
We are hoping to develop a project focusing on Michael Gerzon’s time in Oxford as a student in the 60s and 70s, the OUTRS, early surround sound experiments in the city, the eventual development of Ambisonics, etc. We hope to interview people who knew Michael at the time and through his lifetime; and as such are keen to get in contact with anybody who can help.
This will go towards a mini video documentary on Michael’s life and contribution to the world, produced with stereo and binarual audio.
Please do get in contact if you feel you can help. Firstly, can anybody put us in touch with the convenor of the Gerzon estate? (Michael’s brother?)
Many thanks for all help and advice is advance..
Daniel Hulme | Electronic Music Studio Manager
Faculty of Music | University of Oxford | OX1 1DB
Tel: +44(0)1865 276140 | Web: www.music.ox.ac.uk<http://www.music.ox.ac.uk/>
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