54,000 watts of audio power... 105 dB SPL at one mile... 200,000 satisfied rock fans...
February 20, 2012, by Wayne Yentis
Oh, what an interesting time it was! Concert sound reinforcement was in the early stages of moving to where we are today.
This article originally appeared in the June 1974 issue of Recording Engineer Producer (REP) magazine, and Live Sound also ran a text-only version many years ago. It is presented here in its full glory, without editing and much as it originally appeared, to provide a fuller understanding and appreciation of that time and place and the people behind it all.
It also shows that marvelous “new” concepts like digital delays really aren’t so new at all. And, see if at least some of the names mentioned sound familiar. They should.
Shortly after one o’clock in the morning on April 6, 1974 young people from throughout the West started snaking through the gates of the Ontario Motor Speedway in Ontario, California.
By two A.M. over 15,000 people were bedding down on the grassy infield and at sunrise the crowd was well over 150,000. At ten A.M. over 200,000 rock fans began shouting their approval as Rare Earth opened THE CALIFORNIA JAM, a twelve-hour rock concert produced by the American Broadcasting Company and Pacific Presentations.
In a motel a mile away seven other groups were standing by to be flown by helicopter into the backstage compound at the speedway. They had come from around the world.
Months of careful planning had preceded the Jam and the on-site construction and installation was started weeks in advance. Miles of chain link fence had been installed. Thousand of drinking fountains and portable toilets were in place. A 45-bed hospital had been constructed in the infield. A six hundred foot length of railroad track was laid across the front of the staging area.
Here’s what it looked like on the cover of REP, June 1974.
Dubbed “The Grand Funk Railroad,” the track supported three moveable stages constructed on railroad tracks. One stage was to be permanently set for the closing act, Emerson, Lake and Palmer. The other groups would alternate between the remaining two staged. While one act performed, equipment would be set up and checked out on the remaining stage for the following group. The plan was to cut the set-up time between acts to almost nothing.
The concert was to be recorded for commercial album release and videotaped by ABC-TV as material for future “In Concert” programs. To knit the entire project together the producers needed a sound reinforcement company with the know-how and equipment to saturate the broad expanse of infield, provide two-channel monitor to the stages and feed signal to the recording vans (Wally Heider Recording) and the television audio trucks.
They called in TYCOBRAHE SOUND COMPANY of Hermosa Beach, California. Tycobrahe had provided both equipment and technicians for most of the groups on previous tours and had developed a very sizeable inventory of high power sound reinforcement gear.
In the early stages the Jam producers were estimating an attendance of approximately 60,000, and the initial objective was to provide coverage only to a distance of 1,000 feet from the stage.
“The Grand Funk Railroad” – side view of the moveable stages.
One of the first factors considered was the placement of the staging area within the infield to take advantage of the prevailing winds. The stage was set on the western quadrant of the field so the prevailing westerly winds would carry the sound eastward across the audience area.
“We were lucky,” said Jim Gamble, Tycobrahe Vice President and Director of Engineering, “The wind blew just the way it was supposed to all day long. If it didn’t, there would be nothing we could have done to compensate… nothing.”
The amount of power required to cover the area to the 1,000 foot perimeter was swiftly determined. According to the company’s V.P. and Director of Marketing, Ralph Morris, “We rate our standard arena system as adequate for 10,000 people in an outdoor situation. That’s a 6,000 watt system. We use that formula and add in multiples thereof. Of course, it’s only a rule of thumb because the sound doesn’t just go out so far and then stop. But the formula works.”
Some days before the concert it became apparent that the attendance would almost certainly surpass the 200,000 mark and appropriately the capability of the reinforcement system was upgraded. An additional array of speakers was added on towers at the 1,000 foot mark. These speakers were faced outward and fed through an 859 millisecond delay.
All the basic hardware used by Tycobrahe was designed and built by them and carried their brand name. The company began manufacturing its own equipment when it recognized the need for a specialized sound refinforcing mixer. The specifications established by their engineering team called for a mixer that was simple and straightforward, highly ruggedized and portable.
The Tycobrahe Model MX24-4 input mixer has stereo main and monitor outputs, with separate panpots on each input. It was designed solely for sound reinforcement and can accommodate the “screaming microphone levels which would clip the inputs on most studio consoles.”
View from the mixing tower, looking toward the stage.
Each input has 3 band equalizers with 3 selectable frequencies in each band. There is no EQ on the outputs so that inexperienced, or overzealous mixers cannot get into too much trouble with a single EQ control.
Overall EQ is available for the monitor mix, but those controls are included in the monitor power amp circuitry. Dual band limiters are in the outputs of the mixer which limits about a half a dB from the clipping point of the power amps. They are similar to Altec dual band limiters, with a crossover frequency of 250 Hz. 250 was chosen because that frequency is just about the dividing point between vocals and bass.
Dual band limiting is necessary, according to chief engineer Jim Gamble, to prevent pumping the midrange and highs during those very heavy bass parts.
The amplifiers used at the Jam were also Tycobrahe products, their 2,000 Watt BFA 2000 bi-amplifiers. Like the mixers, the amplifiers were designed specifically for location sound reinforcement applications. The low frequency section of the amp delivers 1,500 Watts, and the high frequency channel delivers 500 Watts. The crossover frequency is at 800 Hz. The units are packaged in a rugged portable case, and are mounted in drawers for easy access
The electronics for both amps are mounted on a single, fan cooled, heat sink which can be unplugged and instantly replaced in case of failure. The raw power supply transformer, rectifier and filter capacitors are mounted separately in the drawer, although the voltage regulators are mounted on the heat sink assembly.
According to Gamble, “Each of the amplifiers has its own voltage regulator, although they are fed from a common raw supply. This is necessary because of the very heavy power demands, especially from the bass amplifiers. Often the demands are so heavy that the AC supply for the entire concert site fluctuates up and down with the music, dropping from 120 volts to as low as 90 volts. We feed the voltage regulators from a +/- 75 VDC raw supply and regulate down to +/- 55 volts. This allows for nearly a 30 percent reduction of input voltage before the amplifiers will fall out of regulation.”
The monitor amps are packaged similarly; the electronics are mounted on a replaceable fan cooled heat sink, installed in a separate drawer in the same cabinet with the bi-amp unit. A six band graphic equalizer is included for the monitor amps to counter feedback problems that arise on stage due to the proximity of the monitor speakers.
The Tycobrahe loudspeaker units are the result of several years of research. In explaining the reasons behind selecting the elements of the Tycobrahe system, Gamble says, “bass horns are the most efficient, but there is a tendency to produce peaks and nodes as you walk across in front the speakers, differences in levels of as much as 10 dB. The infinite baffle is of course, the flattest, but it is really inefficient. The bass reflex has the next flattest response, and is more efficient.
“If you stack a lot of them together in the right configuration to get good bass coupling, you get a very flat response without those peaks and nodes, as you move through the audience. That is why we use, mainly, the bass reflex enclosure. We have tried all sizes from 7 to 30 cubic feet and there was a point where more cabinet volume didn’t make any difference. That was around 10 cubic feet. Our enclosures are 10 1/2 cubic feet and have 2 JBL 2220A’s, a 2482 driver with midrange horn and 2075 tweeters in them.”
To support the speaker arrays and amplifiers two, fifty-four foot, six level towers were installed, one on each side of the stage. The first level was a utilitarian platform left empty. On the second level of each tower were two eight-foot bass horns driven by 18-inch woofers. Seven smaller rear loaded horns were mounted on the third level. The upper three sections of each tower supported fifty Tycobrahe bass reflex cabinets.
Detailed view of one (right) of the main speaker towers.
Care was taken construct the towers and mount the loudspeakers so the speaker elements were directly over each other in a vertical line to keep the system in phase.
Following a standard company procedure, speaker lines are run individually to each woofer in the bass reflex enclosures because, as Jim Gamble pointed out, “If you put the two woofers in parallel across one line, there’s a chance that they won’t react exactly the same and you get a reflected impedance back across the speaker lines. Also, two speakers in parallel present twice as much of a load in series with the speaker cables. Any resistance in the cables will then become twice as significant and more power will be dissipated in the cables. It’s a matter of maintaining as much efficiency in power transmission as possible.”
Gamble went on to talk to REP about the sound dispersion: “A lot of people told us our bass was going to roll off. They said we were just going to have a hell of a time getting bass way out there. I said that’s just not true. The air disperses high end, not low end. And I was right. We found we had to really crank up the high end to get the tweeters out over that broad an area. We had about 225 tweeters in the system but what was really predominant was the bass. It was solid and it sounded good.
“If you put enough speakers together you get a big, wide plane to project off of and that acts as a huge coupling board and that’s what we were depending on that coupling. With that much coupling you can really project it out there. A lot of people say if you don’t have a horn you can’t get the bass out there. Well, that’s not true. We even found that the horns we did use contributed very little to the bass level.”
“The system developed 54,000 watts RMS and we measured 105 dB SPL at a point one mile distant from the stage. At the mixing tower we measured 120-126 dB, and that was about 160 feet from the stage. We were originally told to put the mixing towers up 50 feet from the stage, but no way were we going to be that close.”
The amplifiers were installed on the towers with standby units in place and a compliment of spare components handy. Each bank of amplifiers was manned by a technician who monitored the meters and was ready to exchange any amps that failed. A complete lab and repair station in a Tycobrahe van was located in the backstage compound.
Two Tycobrahe mixers fed the main system. They were installed on a tower in the audience area 160 feet from the stage. The cabling between the mixing tower and the amplifiers was redundant. A spare line was available to each tower and the tower technicians had the ability to switch lines instantly in the event of a failure by using specially constructed switchboxes.
One main system mixer was assigned to each of the two stages for which Tycobrahe was responsible. (The Emerson, Lake and Palmer set-up on the third stage was mixed by their own personnel.)
Two additional MX24-4 mixers were used to feed the on-stage monitor systems. One was installed on each stage behind the acts so the monitor mix was completely independent of the main system feed.
The delay in the system that fed the auxiliary speakers at the 1,000-foot distance was accomplished by using tape delay recorders augmented by an Eventide Clockwork digital delay unit. It was found, however, that the delay system and auxiliary speakers were not necessary. The primary on-stage amplifier-speaker array was sufficient to cover the entire area.
Although the delay arrangement was stipulated in the contractual arrangements if the attendance estimated approached the 200,000 mark, the Tycobrahe people were confident that the on-stage system was adequate and the company is philosophically opposed to delay.
The effectiveness of the reinforcement system was checked prior to the Jam by simply driving to all points in the infield while recorded music was fed through the system.
A three-man Tycobrahe crew was assigned to each of the two stages for set-up and miking. The microphone selection was very straightforward; Sony ECM22p’s were used for the drum overheads and Shure SM57’s were used on each instrument.
The SM57’s were chosen because, according to Jim Chase, Tycobrahe’s director of operations, “You have to use a real close-pattern cardioid dynamic microphone on any instrument that is going to be put through the monitor system. Other people use a lot of wide-pattern stuff, even good cardioid patterns, but no good enough. There’s only one mike that works for us and that’s a Shure SM57.”
Everything on stage was miked except the bass, which was also taken direct, so as to deliver through the system the distortion and other effects created in the guitar amplifiers. As Chase points out, “We don’t much get into studio techniques in terms of miking or direct instrument feeds. The groups are looking for a sound and they want to be in control of that sound. They don’t want us to color it or change it. We’d make it clean if we had our choice. If we were to take the instruments direct we wouldn’t get the musician’s tube amplifier mushing and his power supply saturating and the speakers moving to maximum excursion, and all the other things that create the particular noises that you can get out of a guitar amplifier. The talent wants that and they want us to simply reinforce it.”
At the Jam the signal from each mike on stage had to feed four separate and distinctly different entities: the main Tycobrahe sound system, the Tycobrahe monitor system, the Wally Heider 24-track recording vans and the ABC-TV videotape trucks.
Two vans were use by Wally Heider, one for each stage, and it was determined that the Heider mixers would feed the signal to the ABC-TV mix.
From the early planning stages the interfacing of the four systems was considered one of the primary potential trouble areas. As Ralph Morris stated it, “The equipment was all different and the concepts were all different. And, of course, each group of engineers had different points of view. We anticipated ground problems as with any interconnected system so we left plenty of time to work them out. Sure enough, when we plugged it all in, it hummed!”
In considering how to isolate the various signal feeds from each microphone any resistive method was quickly discarded because of the substantial gain loss that would occur. Instead, each microphone fed a separate four-winding transformer. The transformers were special-ordered from Sescom and mounted in boxes with ground-release switches.
The installation of equipment began on the Tuesday before the Jam with Wednesday and Thursday devoted to the set-up of speakers and electronic hardware and the check-out of each individual system. On Friday morning the main system, monitor system, recording and TV systems were interconnected for the first time. It was then a question of methodically going through the systems and eliminating the ground loops. Ralph Morris told the story of one potential area:
“At one point we found we were still picking up an additional ground on some channels which was then no an overall problem. So we started going through them and found one connector with the shell wired to ground. Some manufacturers make them that way and they have to be disconnected. At that time our chief engineer said, ‘Oh, my God, we’re going to have to go through 180 connectors and clip the grounds on all the shell connections!’ But most professional audio engineers will remove the case ground if they use that brand of connector so as it turned out that was the only connector in the system that was causing the problem.
“Our MX2404 mixers are wired with all internal grounds returned directly to the center tap of the power supply secondary. If a mike cable with the connector shell wired to the shield is plugged in, this creates an exaggerated ground loop and a lot of hum, even if the input is turned down. We did this on purpose so we could instantly recognize an improperly wired cable.”
Another interesting point was the special attention paid to the delivery of power to the site. Separate mains were run to accommodate the Tycobrahe equipment and isolate it from the power source feeding the on-stage equipment of the groups. Otherwise, as Jim Gamble pointed out, “We’d have had the whole band playing and sucking up the A.C., especially on the bass notes. The power gets eaten up by the low end instruments. Consequently the AC starts dropping on every low note. It can drop from 120 volts down to as low as 90 volts. Instead of more power when you need it most, we’d get less.”
All-in-all the problems involved with bringing 12 hours of an ultra high level of audio entertainment to a potentially volatile audience of over 200,000 supercharged rock fans seemed to be very few… Very few, indeed, as typified by the comparative brevity of what the producers and their sound contractor had to say about problems.
Perhaps a statement from one of the producers summed it all up: “We were delighted to do without any lurid post concert headlines.”
Our sincerest thanks to Mark Gander and the gang at JBL Professional for supplying these materials.