In recent months I've been discussing various aspects of recordings with wide
dynamic range. I have pointed out the difficulties of coping with the 64-dB
dynamic range that appears to be the maximum on present analog recordings,
let alone the problems that will arise with the potential 90-dB range of true
digital recordings.
It is quite unfortunate that the proponents of the laser/optical and capacitance types of digital discs are still battling each other to establish their supremacy. The various systems are incompatible with each other, and agreement on standardization still seems to be a long way off. Industry pundits are prophesying that digital discs are at least 5 to 10 years away from commercial reality. Well, friends, this reporter believes that we will have some form of true digital disc (not necessarily a standardized version) within three years, and I wouldn't be at all surprised if it arrives on the scene considerably earlier.
The main problems we encounter with the reproduction of analog disc recordings with ultra-wide dynamic range are groove tracking (especially with high-energy low frequencies), adequate amplifier power to avoid clipping, and loudspeaker efficiency related to the full-frequency-spectrum power-handling capacity of the speakers. Now let us assume that some form of digital disc has been introduced.
Whether the disc employs the laser/optical or capacitance system, groove tracking will no longer be a problem since the traditional phono cartridge groove/stylus relationship of present analog discs will not exist. A step forward to say the least. But what about a typical playback system, as found in the homes of myriads of music lovers, and its ability to handle the dynamics of digital recordings? Usually there is a receiver with low to medium amplifier output coupled with a pair of low-efficiency loudspeakers. To put it bluntly, such a combination simply cannot reproduce the 90-dB dynamic range of digital recordings. In a typical situation, allowing for a fairly quiet room with an ambient noise level of about 45 dB and with the volume controls set so that pianissimo passages are barely audible, as soon as the first "blood and 'thunder" fortissimo passages occur in the digital recording, the system will blow its protective fuses or circuit breakers will trip. Adjustment of the volume controls so that the fortissimos will be heard without activating the protective devices is of no avail, since the pianissimo and probably even the mezzo-piano passages will not be audible at all! It should be noted that the elements in either analog or digital recordings that principally will cause the fuse blowing are the high-energy low frequencies of bass drums and tympani. I should also point out that I am not singling out "cheapie" low-power, low-efficiency systems for their inability to handle wide dynamic range, since many very expensive combinations of exotic amplifiers and speakers are similarly plagued by inadequate dynamic headroom. The hard fact of the matter is that very few amplifier/ speaker combinations presently available will be able to reproduce the full dynamic range of the digital disc without distress. It is obvious that whatever the sonic attractions of low-efficiency loudspeaker designs, except for a few special cases, manufacturers will have to develop new high-efficiency designs for the proper playback of digital recordings.
above: Production of loudspeakers at Cerwin-Vega's plant in Arleta, Calif.
The above dissertation on dynamic range is a preamble to my main thrust this issue. One of the special pleasures of writing this column for Audio is that from time to time the various manufacturers of audio equipment tender invitations to visit their plant and laboratories for a behind the-scenes (plug intended) look at their activities. Sometimes these visits are in company with other audio journalists; on some occasions I make solo visits, although I must admit I'm usually accompanied by my wife, Ruth. Incidentally, as a personal aside and a perspective on her visits, Ruth is that rarest of creatures: A woman who knows and loves music and audio. She has sold hi-fi equipment at retail, handles the take sheets on my recording sessions, sets up mikes, knows how to handle any audio equipment, and has a very critical and discerning ear, a fact well-known to many manufacturers. Best of all, she prefers records played back at the requisite SPL for full dynamic expression.
Cerwin-Vega's Founding Thus it was that we were invited to visit with a gentleman whose company has long been identified with high-efficiency speaker designs, Gene Czerwinski, the genial head of Cerwin-Vega. I've known Gene for about 15 years and have ribbed him in these pages through the years about his speaker demonstrations with their awesome sound pressure levels. But he is a very serious engineer with impressive credentials which help explain his preoccupation with high SPL and his design philosophy. Like many other engineers in the audio industry, he was involved with a number of disciplines in the aerospace industry.
With Bendix Corp. he worked on high-powered sonar transducers and related equipment, and at Douglas Aircraft electro-acoustic instrumentation for sound and vibration phenomena, including the design of wide-range speaker systems capable of 150 dB SPL! Gene founded Vega Labs in 1954 as a part-time adjunct to his aerospace work. In 1957 he introduced the first solid-state amplifier, with 125-watt output, a huge amount back then. In 1967, Gene's love of music and audio prevailed. He left the aerospace industry, changed the name of his company to Cerwin-Vega, and devoted his energies to its growth. With his commitment to high-efficiency speaker designs, he became a big OEM supplier to the musical instrument amplifier manufacturers. In the early '70s, Gene was supplying 50,000-watt amplifier systems and huge high-efficiency speaker clusters for rock concerts of more than a hundred thousand people. In 1972, he began to concentrate on the audio consumer market, with an extensive line of high-efficiency loudspeakers. These were bread-and-butter designs, but they found a ready market with rock music fans with their seemingly insatiable thirst for high playback levels. Gene didn't neglect his research into innovative ideas for high-quality loudspeakers, however, always the underlying design philosophy of high efficiency. He developed an 18-inch woofer rated at 1,000 watts, and one of his stunts at hi-fi shows was to plug this brute into an a.c. outlet, with obviously an almighty 60 Hz signal! One of his company's most interesting designs was the Magnastat.
This had a thin-film diaphragm, approximately 6x9 inches, which was inserted into an intense magnetic field, and coupled to an exponential horn.
The Magnastat produced a very clean, high-level output from 300 Hz to beyond 20 kHz. Unfortunately, the device proved to be too costly to manufacture.
Earth-quaking Speakers
Some years later, Gene designed the special effects speaker for the film "Earthquake." This was what he called a "corner plug," a huge exponential horn that coupled into each corner of the theater. Driven by 1,800 watts of power and turned on by a signal cue from the optical sound track at the precise moment the "earthquake" started on the screen, each of these monsters put out huge 16and 20-Hz waves which shook your whole being with its powerful roar. Sure it was a gimmick, but very effective! Not long afterward, at the banquet of the Audio Engineering Society at the Los Angeles Hilton Hotel ballroom, the entertainment was an electronic synthesizer concert, using Moog and Arp systems.
The main speakers, one at each corner of the ballroom, were huge Altec theater systems. Augmenting these from 50 Hz down to 16 Hz was a Cerwin-Vega "earthquake" corner plug behind each Altec. When the Arp performer played MacArthur Park, you wouldn't believe the awesome sonorities this system generated. Most of the assembled audio engineers responded with a standing ovation, but quite a few of the old guard stalked out of the ballroom in high dudgeon as a protest against the sound levels.
On this recent visit to Cerwin-Vega in Arleta, Calif., Gene proudly showed me his new 40,000-sq. ft. plant, with ground being broken for a similar plant in the rear of the property. Over 400 people work for him now, and the factory is a beehive of activity. I simply couldn't believe the stacks upon stacks of thousands of speaker basket castings, in every size from three inches to imposing 24-inch units for woofers. The same vast quantities applied to speaker cones, voice-coils on formers, and pallet after pallet of magnets in all sizes. There are long assembly lines where high-power amplifiers are put together and a cabinet plant for all the enclosures they make. Gene tells me that their production of two and three-way bookshelf speakers, which are covered with vinyl, constitutes the largest output of this kind of speaker in the country.
The company maintains complete lab and research facilities, replete with spectrum analyzers and all manner of other goodies from HP, Tektronix, B&K, and others. Gene was one of the first people in the country to acquire a Sony PCM-1 digital recording unit, and he made a considerable number of jazz and rock recordings to demonstrate both his big disco systems and his high-efficiency consumer tower type speakers. The PCM unit is particularly useful to him for its 85 dB of dynamic range and the fact that he can use high playback levels and not be bothered by hiss.
Speakers for the Future I remarked that with the coming of digital discs Cerwin-Vega is in a particularly advantageous position in respect to their speakers being able to handle wide dynamic range. Gene replied, "You know we have always made speakers of high efficiency, and they were rugged, because of the sustained high levels for which they are intended. Sure it is true that in most rock music there is really very little dynamic range, perhaps on the order of 10 to 12 dB, but that doesn't mean our speakers can't be used for classical music with 90 dB of dynamic range." He pointed out that for the most part the company uses cast speaker baskets, and the cones are chosen for the combination of mass and acceleration, compliant surround, and restoring force of the spider, plus large high-efficiency magnets that will give the closest approach to true pistonic action. Add a special high-temperature voice-coil for reliability. Gene added, "In classical music, the low frequencies are the problem areas in the achievement of full dynamic range.
You've got to move large masses of air, and efficient pistonic motion is the way to do this. This also will probably require certain amounts of bass equalization, which uses up gobs of amplifier power. Hence, high-output amplifiers will be needed." I said to Gene that while many people admit the efficiency of his speaker systems, and that his motto "Loud is beautiful ... if it's clean," is apt, they also feel that some coloration is evident. He answered that they were entitled to their opinion and then pointed out they were not likely to find fault with his first speaker specifically designed to handle the recordings of the digital decade with the highest possible quality. This is his Metron SUFT-FET-2 (Spiral Uniform Force Thin Film Electromagnetic Transducer), a mid-/high-frequency unit using 72 spiral voice grids on thin film diaphragms suspended in an intense radial magnetic field. Response is from 200 Hz to 30 kHz. The SUFT-FET-2 is coupled with the new Metron subwoofer, which incorporates a 15-inch woofer for sub-bass, and an 8-inch mid-bass driver with what is termed a "boundary layer air bearing" replacing standard annulus suspension. Crossover points are at 80 and 200 Hz. This system is said to have an SPL of better than 115 dB! At $4,000 a pair including the subwoofers, this kind of quality comes high, but Gene claims he is working on other audiophile speaker designs which can handle digital recordings with very high quality at more modest prices.
An interesting and modest man, Gene Czerwinski rarely fails to present some intriguing ideas whenever I see him.
-----------
(Source: Audio magazine, Jun. 1980; Bert Whyte)
= = = =