London Audio Fair

Wireless World, December 1971 585 London Audio Fair Review of a show attended by more than 70,000 In reporting on last year’s Audio Fair material and how much is required for we diagnosed an increasing interest in piano reproduction. The final lecture (and awareness of) the standards of good demonstration was on horn loudspeakers, fidelity amongst visitors to the exhibition. for which ‘Toneburst’ brought a pair of A recent publication, Audio in Transition*, wooden horns based on the concrete predicts that the present boom will soon design published in Wireless World in pass away leaving a steady growth rate of May 1970. Besides the clarity and 20% per annum for the better quality frequency range of the system the solid products. (Does this really mean that the stereo image attracted comment - the horrid systems associated with some speakers were, of necessity, twenty six ‘household names’ will vanish? One feet apart. can only hope so!) It is regrettable therefore that so many of the British manufacturers of well Noise reduction in cassette machines engineered audio equipment opted out of To the list of current noise reduction the Olympia show — although it must techniques for cassette machines that we be noted that a fewheld satellite exhibitions have mentioned recently - Dolby B, and in hotels off Kensington High Street — and systems used by JVC, National, Sanyo, it is a disappointment whatever the reason Philips - we must add the Trio/Kenwood for non-attendance One thing is for certain ‘denoiser’ (KF-6011). This is another — it is possible to put on a first rate demon- playback-only system that attenuates stration if the room is big enough. This high-frequency low-level signals depending was proved by Bang & Olufsen who made New–style bass reflex enclosure from on the signal level. the most of the stand construction Ferrograph. Just before the exhibition, Philips gave facilities offered, and created a highly a demonstration of their dynamic noise civilized sound proof apartment conducive limiter. They also demonstrated their DIN- to relaxed listening. Of course there is a standard cassette machine, N251O, which sound level limit for any size of room made will be marketed at the end of 1972. Philips of flexible panels, and our conclusion is plan to market chromium dioxide tapes that proper assessment of equipment is then, and their cassettes willhave two extra possible under Audio Fair conditions only holes so that when a cassette using the new if the sound level is tailored to room size. tape is inserted, it automatically changes (Some loudspeaker demonstrations actually the bias and alters the equalization took place in square rooms!) time constants from 120 and 3,180 to 70 Once again Wireless World sponsored and 3,180µs. a lecture demonstration on each day. Returning to noise limiters, Philips Tristram Cary fascinated many visitors admit theirs is not going to make cassette with an audio visual demonstration of reproduction into ‘hi-fi’ reproduction. basic waveshapes, and showed how Given this qualification, it will be a voltage controlled oscillators are used in welcome innovation for most cassette modern synthesizers. Ralph West had users, even though material containing assembled an enormous array of historical low-level passages at high frequencies equipment all of which he miraculously got will be attenuated, the amount depending to work, spicing his discussion of the on level – see Fig.2. (When the h.f. or com- landmarks in audio with some very amusing plete signal is zero there is full noise asides. Arthur Bailey’s discourse on reduction of 10dB at 6kHz and 20dB at loudspeakers included a demonstration 10kHz.) The argument in all this is of the new Ferrograph enclosure and that musical instruments .when played the effect of cross-over component value softly do not have a high harmonic tolerance on colouration. John Linsley content, and that they mostly have Hood used AR3a speakers, a high-quality fundamentals below 4.5kHz the 70W per channel class B amplifier and a frequency at which the noise circuit flashing-light meter to show how little signal Fig. 1. Typical curves showing effect of starts to take effect. (A point that power is required for average symphonic playback-only dynamic noise reducing Philips make is that the Dolby B system circuit. As input signal falls in level, circuit is not fully mono/stereo compatible – a * Finnresearch Ltd, 30 Baker Street, London progressively attenuates tones above about stereo cassette processed using the W.l. Price £18. 4kHz, Dolby B processor, is not truly mono 586 Wireless World, December 1971 Fig. 2. Complete circuit of Philips dynamic noise reducer. Capacitors C1, C2 and C3 form part of the high–pass filter. Diodes D1 and D2 and capacitors C4 and C5 form a peak detector providing a control potential to attenuator diodes D3 and D4Ÿ compatible because the two channels cassettes included (one U.S.A. -company one another. For instance a CBS coded normally require different processing.) is already producing coded cassettes) disc played through a Sansui decoder An add-on unit is expected to be available where there is no equivalent to the produces a left front signal in the left in March or April 1972, costing £12-13. stylus monon. So if you find circular, back speaker! What is needed seems to be The existing cassette machine N2503 elliptical or helical modulations confusing, a universal decoder designed to reproduce will be produced with the noise limiter, forget it – it is merely a consequence of any coded information, which, provided to be called N2506 and costing £4 or £5 the phase relationships between the two the coding system was known e.g. Sansui extra. Philips are offering their channels. or CBS (or others for that matter, but at circuit – shown in Fig.3 and in simpli- As regards the confusion between the moment it looks to us as though one fied form in Fig.4 – on a royalty-fee ‘matrix’ and ‘phase–shift’ systems, or both of these or a new derivative will basis to manufacturers using the methods that combine more than two win), could be switched to the appropriate cassette system. signals into two channels without multi- decoding matrix. We have just heard plexing or increasing bandwidth are matrix that Electro–Voice have produced an systems. The CBS and Sansui methods use integrated circuit for decoding which Four–channel systems 90° phase shift circuits in addition to claims to be suitable for all The newest thing to the exhibition this year matrixing (more details next issue). existing matrices, but we do not have was the ‘surround sound’ and quadraphonic Currently there are many equipments, details yet. equipment. It was however clear that especially from Japanese makers, which Of those equipments intended to provide many people are confused by the current use matrices to reproduce in four–loud- four-speaker sound from conventional four-channel situation. And if there’s speaker format either coded or conventional two-channel sources (2–2–4 systems), confusion among visitors (nay, even dis- two-channel discs (latest on the scene first to be made in the U.K. is the Pye tributors of equipment) what about is Zenith in the USA). The trouble, of Stereo +2 adapter which puts difference the public at large? The confusion course, is the lack of a standard at present signals. in the rear-speakers. (The is not so much about discrete vs and not all systems are compatible with two rear signals are usually in antiphase matrixed methods, but between what are misleadingly being called ‘matrix’ and ‘phase-shift’ methods of decoding and synthesis, and also about exactly how this is done. In the CBS method* for instance it happens that the locus of the stylus in the ‘coded’ disc groove can assume a helical path under certain conditions – i.e. one rear channel signal only – and this seems to have thrown some people off balance! The puzzled newcomer to four– channel coding. systems is best advised to forget what’s happening in the-disc groove. The point is that the four channels of information can be matrixed into two – with or without phase shifting circuitry – and conveyed by any two-channel medium, * ‘Quadraphony and home video steal the Berlin show’ Wireless World October 1971 pp. 486·8. This article gives a detailed description Fig. 3. Simplified diagram of dynamic noise limiter. High–frequency signals from the filter in of the CBS/SQ matrix system and also discusses some other four-channel systems, including the the auxiliary signal path (top of diagram) partially cancel the h.f. content of the inverted main JVC subcarrier–system. signal path (bottom) by an amount depending on the h.f. signal level (control voltage). Wireless World, December 1971 587 in this kind of set up, which has been found loudspeaker’. The trouble is that above to be subjectively more satisfactory than 1kHz intensity is dominant in establishing in-phase signals. In-phase signals would stereo images and much of this intensity produce an undesirable well-definedcentre information is lost by the off–axis back image.) There were seven other makes position. The Dimension 8 demonstration of such ‘surround-sound’ equipment shown, revealed a deficiency of transient infor- some of which introduce cross talk between mation. This could no doubt be cured by the two front speakers and some of which abandoning the ‘super stereo speaker put L – ∂ R and R – ∂ L in the rear angle’. speakers, and known under various names The Ferrograph speaker designed by like Quadralizer (Pioneer range), Quadrixer Arthur Bailey and demonstrated in his (Kenwood KA-8044), Quadrizer (Sanyo W. W.

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