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History of PA (Part 3)

the volume closes


Ben Duncan concludes his historic survey of PA and explains why we're not all deaf.

Between 1976 and 1979, coincident with the rise of the new wave and independent record labels, package spin-offs from the realms of big PA became widely available to musicians-at-large. One and two kilowatt mini-rigs emerged, replete with 12 channel "consoles", 500 watt rack-mounting power amplifiers (did you know that the fashionable 19in rack concept originally came from 1930s telephone companies?), and a pair of micro-stacks: one (bass) bin, a midrange "flare" – in fact a radial horn compression driver – and a couple of top-end horns per side. All painted black, of course.

Most responsible in the UK for bringing modular or package PA to a large audience were H/H, RSD/Studiomaster, MM/PA:CE, John Penn's SSE, and Soundcraft. There was also lots of plagiarism: Dave Martin copy bass-bins, for example, could be purchased in the furthermost reaches of Scotland at a fraction of the official price. Plagiarism is the lateral force by which fat bank balances and the odd Porsche displace the development of the art: if everyone copies Dave Martin's vision (for example), how on earth do we progress? And that, not to put too fine a point on it, was what stymied the leading-edge of PA development in the mid- to late-1970s, at least in the big league of hire companies.

The pain in the output stage



Back in 1967, Crown and WEM both went online with their respective 100 watt power amplifiers. Even up to the mid-1970s, putting much more than 150 watts into an eight ohm speaker was pushing power transistor technology to its limits, but PA people demanded more powerful amplifiers with cheerful aplomb.

In truth, what they were actually seeking was a near impossible amalgam of extreme qualities: the black box had to have the near infinite power sourcing capabilities of an industrial vibrator amplifier, the delicate sound quality of an audiophile (domestic) hi-fi amplifier, the mechanical ruggedness and ease of repair of US Army backpack electronics, and, to top it all, this mythical beast had to withstand any combination of electrical abuse that malicious/careless roadies could dream up – like hooking up to 415V three-phase mains, connecting the outputs to the inputs, or driving 980 watts of bass-end up a short-circuited speaker plug, for the duration of a concert.

In the early 1970s, these contradictory qualities simply didn't hang around behind a 19in panel. The Crown DC300 was really an industrial amplifier, and companies like Kelsey-Morris took to using hi-fi amplifiers with professional specs like the (50 watt) Quad 303, a 1969 design, which had already proven itself in recording studios.

Tiring of umpteen 50 watt amps, Kelsey-Morris discovered the Phase Linear, a truly OTT (domestic?) audiophile amplifier, rated at 700 watts per side, and aimed at the My Hi-Fi's Got More Balls Than Yours scene in the US. It was also built of impressive, chunky, aluminium members, and was almost roadworthy. The ultra-hefty transformers kept ripping the chassis apart as PA trucks negotiated the more bumpy sections of the North Circular (the ultimate vibration testbed), but with a few minor mechanical modifications the PA business had scored with its first credible amplification.

Meanwhile, the outrageous demands that rock 'n' roll touring placed on hitherto delicate electronics began to penetrate designer's heads, although the not-infrequent explosions, fires, and burnouts led manufacturers like H/H, for example, to look upon their clients "as a bunch of thugs who smashed up the equipment" (in Bill Kelsey's words). It wasn't until the second half of the 1970s that the first generation of serious, roadworthy PA amplifiers arrived. All in black boxes, of course.

Mike Turner's B302 and B502 were amongst the first. They had the emphasis on refined sound quality and became popular for driving top-end. Ditto the Uni-Sync, a fave amp in the US. Meanwhile, perhaps less refined, but making up on the balls, came macho amps from BGW, Crown (AKA "Amcron"), RSD, and H/H lending 400 watts or more per side to the nether frequencies. But the close knit hire companies weren't particularly prominent in these developments, with the notable exception of Malcolm Hill's DX series (HEAT generator to you) and the Fan-Amp, designed by Turbosound's Tim Isaacs, and used by SSE, amongst others.

As for the mass market, perhaps most memorable were MM's AP360 and RSD's 800b/c. These power amplifiers both embodied circuits "cribbed" from other companies listed, but not without some development effort: the RSD amps were really a much improved successor to the Phase Linear, while the AP360... well, the AP360 was simply based on someone else's amplifier. It couldn't get out of its depth, made plenty of noise on bass end, and cheerfully went on working without getting stroppy – to the extent that it came closest to meeting the optimistic allegations of "indestructibility" abounding in the glossy ads of the time.

The truth about power amps using the ordinary (bi-polar) transistors available in the later 1970s was that you could have either decent top-end sound, or ruggedness, but not both at once, in one box. In fact, sometimes you didn't get either.

In 1979, H/H made a bid to change this, using a new species of power transistor, the MOS-FET. Although the H/H V series amps didn't satisfy everyone, they did give credence to the idea of using natty, hi-tech Japanese semi-conductor technology. Ideally, MOS-FETs should make it possible for us to have our cake (smooth, silky top-end, and correct bass-end qualities too) without trading off ruggedness and ease of maintenance. And although some very highly spec'd and beefy power amps using much improved bi-polar transistors have subsequently appeared (Malcolm Hill's DX700, Crown's PSA-2 and Yamaha's PC2002, for example), the trend towards things light, easy, elegant and ultracompact bodes best for MOS-FETs.

Speakers: Round Three



In 1977, Chas Brooke (ex of Midas) unleashed a sophisticated active crossover, the MCS100, which was phase correct (ie drove each frequency band in perfect synchronisation). With flashy hi-tech power amps and consoles now on-stream, questioning looks were inevitably cast at the speaker stacks. As the 1980s dawned, awareness of the foibles of PA speakers in the classic JBL and Martin mould grew. Aside from the raised expectations of musician and audience alike towards sound quality brought on, perhaps, by the mass hi-fi market, the giant leap in speaker technology made some years earlier suddenly stood out as an anachronism.

Standard speaker systems required wearisome twiddling with EQ knobs to achieve acceptable tonality. Failing this, they ripped people's ears. Worst of all, their hideous black bulk was suddenly an embarrassment. Arties brimming with cabinets were no longer all kudos in the days of loss-making tours and tightened belts. Put simply, the speakers of the day occupied most of the truck space, and, despite being impressively statuesque once set up, the cost involved in setting up a typical 10 to 40k rig became rather dubious value-for-money.

To a great extent, these recurring hassles with our old friend the loudspeaker stemmed from the fact that it's one of the least well understood, least perfected and most devious pieces of mechanics in the cosmos. Building 'Umber bridge is nowt mate, pah! (Great bores of today No. 1206 spits into his Ruddles.) That's easy stuff, when set beside the deceptively simple collection of cones, voice-coils and magnets which together are asked to echo the subtle and not-so-subtle nuances of every instrument and musician, with 100% fidelity, over a 120dB (one millionfold) range of sound levels, whilst spanning the 19,980 frequencies between lowest bass and highest treble, and whilst projecting the sound wave coherently into a well-defined angle of solid space. All this despite the attempts of architects and acousticians – damn them by gad – to make our task impossible in the near-derelicted concert halls of England (that's enough hysteria for now).

Worse still, the PA business was wholly on its own: the development of mikes, desks, crossovers and amplifiers could rely on inspiration or ideas reflected from other areas, such as studios, broadcasting and hi-fi. But who else shares an interest in developing speakers that are both hi-fi and megawatt? Hasn't the hi-fi business had enough trouble getting its own 50-watt speakers together, without letting them loose on to the big stuff?

To an extent, many of PA's problems stemmed from outright misuse of basically respectable equipment. JBL compression drivers, for example. And all too often the rather untidy stacking necessary for the best sound and most even coverage of people who've paid to listen was sacrificed for the sake of macho cosmetics. Tall, smooth, black and menacing to the ears. Indeed as Rikki Farr had said in 1974: "People judge sound with their eyes." Going against the trend, some of the smaller hire companies – Muscle Music, for example – developed highly attuned and tightly-packed speaker systems using standard but carefully chosen and matched speaker components. For instance, they'd take a JBL driver, check out the performance in situ (instead of on a laboratory test bench), then drive the unit carefully over the frequencies (often very different from JBL's own recommendations) where it worked best. They also threw out the rulebooks, and experimented with the stacking of the enclosures, until the wavefronts from each were were syncronised, ie phase correct. This alone made the PA more efficient, because with more harmony – or less "fighting" – between adjacent horns, less power was wasted. Looking at it in another way, many multi-kilowatt PAs prior to this were nowhere near as loud as you'd imagine, because so much of the power was cancelled out by unfortunate phase relationships.

Anyhow, with better synchronisation, fewer cabinets could do more work. The new realism of tightly-packed PA speakers in 1979/80 was evident in Paul Weller's quip as he walked around the stage before a gig, inspecting the set-up, "When's the PA going to arrive?"

Ultimately, what Muscle Music and a few others were attuned to led straight back to the Claire Brother's S3 concept. Instead of an untidy or difficult-to-fit-together assortment of bins, horns and lenses, it should all be like a lego set.

Return of the iconoclast



Akin to certain musicians, Tony Andrews (whom we met in volume two) refused to compromise his principles: his speakers were never painted black, but variously pink, purple, and later, deep blue. One of the first Andrews PAs was under the nose of Charlie Watkins and Rikki Farr, just outside the Isle of Wight compound, for the Pink Fairies and Hawkwind. After developing and building compact bass horns for Kelsey-Morris, and some early experimentation (albeit unsuccessful) with full-range modules (high and low frequency speakers in the same box), Tony met Tim Isaacs, and together they set about building an improved midrange horn, using an ordinary paper-coned (guitar) speaker instead of the usual compression drivers. All this was based on the premise that loud music should not hurt people.

In their experimentation, which involved such esoterica as a "pyramid" bin, they came across facets of horn-loaded speaker design that no one else had sussed. The "strangulation" effect they sought involved placing a specially contoured "bung" down the middle of the horn. Eventually a new midrange speaker evolved, looking rather like a jet engine. Subsequently, their invention was dubbed the "turbo" by musician Tim Blake. The development work continued on the free-festivals circuit, where they operated with Simon Renshaw as Sonic Trucking. Then in 1976, Tony made acquaintance with Rikki Farr, and went out to LA with Tim Isaacs. There, they built the first Turbosound rig under the auspices of TFA-Electrosound. This was their first opportunity to test the concept with major acts. Subsequent to this, they set up on their own again, as Turbosound, gaining John Newsham (ex-Hillage) in the process.

But what makes this potted history different from others is that these characters were first and foremost intent on getting high-power, high-fidelity speakers together, rather than just hiring out "plant", or being caught up in the whistles and bells – for example, 104-channel desks (guess who?).

By 1980, the Turbosound PA had reached the limits of idiosyncrasy, and the views of musicians and other PA system owners were strongly polarised – because the sound was so radically different to what they'd been used to hearing. Ten years of organic development had led to a wholly deviant approach to big speaker arrays – involving plane wavefronts (the emergent sound wave was straight, rather than curved), phase coherence, and point-sourcing (the speakers were grouped in a semicircle). The setback was that while wonderful when erected properly, the Turbo PA wasn't the easiest of rigs to use successfully.

The turning point came early in 1982, when this esoteric technology was packaged into a compact, easy-to-use (and affordable) module – the TMS3. Looking akin to a giant studio monitor, behind the (blue) foam front lurked two 15in bass-bins, two midrange horns with "turbo" designs and 10in cone speakers, and a pair of judiciously-chosen radial horns each with a high-tech Nipponese compression driver – the TAD. Each TMS3 occupied less space than many bass-bins alone, handled 1500 watts, outpaced every other system on sensitivity (one watt of amplifier power gave 107 decibels), and had tightly defined disperson (so the sound didn't overlap its neighbour's). It also sounded clearer than most domestic hi-fi speakers, and didn't neglect to cover the extremes of the frequency range. Not surprisingly, the TMS3 quickly became the standard speaker component in the upper echelons of PA. "The process continues," warns Tony Andrews. "The TMS3, which has taken ten years, and has brought coherent sound to a million people for the first time, is just the beginning."

Plus ca change...



Today, 14 years after the wholesale infusion of 1940s American technology, the minimalism more attuned to the 1980s has suddenly dawned, and proliferation of loudspeaker components has begun to revert to the simplicity of full-range enclosures, having more than a surface similarity to WEM's column speakers of the 1960s. For though modules may be horn-loaded, somewhere in there a 10in cone-speaker still lurks, and more than one person is of the opinion that "Charlie got it (basically) right in the beginning". Along the way, the power used may have shot up and up (from 1kW to 100kW or more) but the power required for any given sound level has fallen overall. So today's systems are more likely to be run within their capabilities, in other words without ear-ripping distortion. Meanwhile, rigs have grown and then shrunk, and countless decibels of nauseous sound have slowly been refined by the efforts of a few, to a state where loud music – or at least the PA – needn't be a danger to our health.



Previous Article in this issue

Martin Guitars

Next article in this issue

Cutec MX 1210 Desk


One Two Testing - Copyright: IPC Magazines Ltd, Northern & Shell Ltd.

 

One Two Testing - Aug 1984

Topic:

Live


Series:

History of PA

Part 1 | Part 2 | Part 3 (Viewing)


Feature by Ben Duncan

Previous article in this issue:

> Martin Guitars

Next article in this issue:

> Cutec MX 1210 Desk


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