# Chapter 33 - -Development of the Prism Sound System 1984-1986- After we completed the Arena System project, we sat down as a group with Jim Brawley to discuss the design goals for our new sound system. We realized that our current systems were not very directional, especially for the low frequencies, and as a result the systems radiated audio frequencies in all directions especially up into the roof and off the walls of the arenas and stadiums. As the sound waves were reflected off of these surfaces, they reached the audience as indirect, and delayed, sound as compared to the direct sound from the speaker cabinets. As we increased the power levels of the sound systems, we were increasing the sound level of the indirect sound and in many arenas with really bad acoustics, the indirect sound was as loud or louder than the direct sound from the speaker cabinets which caused the sound to be muddy and unintelligible to the audience. We decided that our primary design goal for the new sound system would be to control the directivity of the speaker system so that the sound would be directed to the audience and not to the roof and walls of the venue so the audience would hear clean direct sound from the speaker cabinets with minimal indirect sound from reflections off of the roof and walls. We asked Jim Brawley to explain what would be required to control the directivity of the speakers, especially the low frequencies, and he said we needed to have the low frequency speakers configured in a long vertical column to direct the audio energy forward towards the audience. If we had several long columns of low frequency speakers, we could bend them in a horizontal arc to control the directivity in the horizontal plane. The challenge was how to bend a long column of bass speakers in the vertical plane to cover the audience evenly with sound from close to the stage all the way to the back and top seats of the arena. Jim also said that we needed to design a speaker array where there were no gaps between any of the cabinets, because we wanted all of the speakers to operate together as one big speaker to minimize the interference caused by multiple sound sources spaced apart in a sound system. I thought about what Jim was saying and I picked up a coke can sitting on the conference table and I said “why don’t we design a speaker array that looks like this?” Jim said the challenge with the coke can array idea would be how to bend the directivity of the array vertically without actually curving the speaker cabinets in the vertical plane. We didn’t know how to bend the cabinets in both the horizontal and vertical planes simultaneously. After studying the problem, Jim Brawley at a later meeting, explained that he had discussed the problem with George Augspurger, an audio and acoustical engineer that Jim had worked with at JBL. Augspurger and Jim had already been studying loudspeaker array geometries that could control the directivity of the column of bass and mid bass speakers. Augspurger wrote a software program that ran on an Apple II that allowed the acoustical designer to vary the directivity of the column by the curving or spacing distance between the speakers. The Augspurger program would allow us to “bend” the column of bass and mid bass speakers vertically without actually physically bending the column. Using Augspurger’s program, Jim designed a speaker array specifically for indoor arenas that consisted of eight columns of four trapezoidal shaped cabinets stacked together in a 20 ft high vertical column. The columns were attached to a curved hanging grid designed by David Evangelista, the structural engineer who designed the trusses for the 1979 Bee Gees tour, that was made of 8” diameter aluminum tubing that was bent using a special machine into a custom curve developed by Brawley to provide even horizontal coverage in an arena. Two 2-ton CM motors were required to lift the array. The trapezoidal cabinets nested together vertically and were connected together vertically with ½” X 18” stainless steel pins connected to aluminum rigging frames built into the inside of each cabinet. The eight columns of cabinets were suspended from the hanging grid with no horizontal gaps between the columns of cabinets to form a solid curved array of cabinets. Multi-conductor speaker cables, with 41 \#16 conductors and Pyle National connectors, connected all of the speaker cabinets in a vertical column using jumper cables between cabinets so that every individual bass transducer and each pair of mid bass and high frequency transducers in the cabinets had their own pair of wires connected down to the amplifier racks. This allowed the cabinets to be hung from the hanging grid or stacked on the stage in any quantity or any order with the wiring in the Pyle National cables would always connecting each transducer to its correct amplifier channel. Robin Magruder came up with the Prism name for the new sound system – symbolizing its unique polygonal form and innovative beam steering technology. We trademarked the Prism Sound System name. We later reached a significant settlement with a major multi-national manufacturer for infringing our Prism trademark - an unexpected benefit of this intellectual property. __The Digital Crossover and Drive System for the Prism 1986\-__ The other critical component in the system was the crossover drive system. Jim Brawley wanted an electronic crossover designed that exactly matched the crossover input to the sum of the outputs of the four crossover frequency passbands with no loss or phase shift. In addition, Jim wanted the ability to time align all of the components in each cabinet based on each transducer’s distance from a reference plane which was the position of the mid-range driver furthest from the plane of the front baffle of the cabinets. Building a crossover like this was not possible using traditional analog Butterworth or Thiele-Linkwitz-Riley derived high-slope crossovers which exhibit phase distortion. Clay Powers had attended an AES convention in 1983 and heard a presentation by two Canadian researchers, Stanley P. Lipshitz and John Vanderkooy, from the University of Waterloo in Ontario, Canada. The title of their paper was “A Family of Linear-Phase Crossover Networks of High Slope Derived by Time Delay” and the abstract stated in part “A recent suggestion is generalized, and it is shown how, by introducing a suitable time delay into the signal path, a family of complementary constant-voltage crossovers can be synthesized with high slopes in both low-pass and high-pass outputs”. Clay had studied this paper thoroughly and was fascinated by the possibility of making a perfect crossover. He discussed the concept with Lee Hardesty, a brilliant electronics engineer working for Showco - Lee suggested using the new Motorola 56000 DSP processor to create a digital crossover based on the Lipshitz/Vanderkooy paper. Clay Powers and Lee Hardesty invented, designed and built a digital crossover using the Motorola 56000 DSP or Digital Signal Processor chip. Their crossover not only divided the frequencies into four bands that summed perfectly to the input signal without loss or phase shift but also provided time alignment delay for each type of transducer to the reference plane. It was a remarkable achievement and was a big contributor to the sound of the Prism array and to the Prism’s huge success in the market. The Prism crossover also included a separate fifth crossover passband from 30 to 60 Hz for the subwoofers that allowed an adjustable delay between the subwoofers and Prism array to time align the system for various subwoofer physical configurations. The Prism crossover fed multiple drive line master panels each with four VU meters, four illuminated mute switches, four volume controls, a mono switch and individual limiters for the four bands to drive separate Prism arrays or full range fill cabinets. {{< StoryImage id="showco-clair-global-showco-showco-archival-photos-03" title="Showco Prism Crossover 1986 designed and built by Clay Powers and Lee hardesty. The front panel featured a stereo input level meter and stereo “signal present” status indicators for low, low mid, mid and high frequency band outputs. Photo Clair Global" caption="Showco Prism Crossover 1986 designed and built by Clay Powers and Lee hardesty. The front panel featured a stereo input level meter and stereo “signal present” status indicators for low, low mid, mid and high frequency band outputs. Photo Clair Global" credit="Photo Recovered Showco Archive" size="large" >}} {{< StoryImage id="showco-clair-global-showco-showco-archival-photos-05" title="Rear view of Showco Prism crossover 1986 featuring two XLR female connectors for left and right inputs and two sets of four XLR male connectors for low, low mid, mid and high output connections to the drive units. Photo Clair Global" caption="Rear view of Showco Prism crossover 1986 featuring two XLR female connectors for left and right inputs and two sets of four XLR male connectors for low, low mid, mid and high output connections to the drive units. Photo Clair Global" credit="Photo Recovered Showco Archive" size="large" >}} Showco Prism crossover drive unit. The connector labeled “Remote” is for a remote fader box that was positioned on top of the mixing console to control the overall level of the Prism sound system. The four orange switches were: “Active” to turn the drive on and off; “Mono” to run the system in mono; “Master” and “Slave” were used to have one of the drive units control the levels of other drive units (for front fill, rear fill, etc.). The knob labeled “Master Level” was the control for the overall level of the entire sound system. The operator could use either the level control on the front panel or the remote fader. Each frequency band had a stereo output meter, a volume trim pot and stereo lighted mute switches. White was for the sub woofers, green for bass , blue for mid bass, yellow for mid range and red for high frequencies. Rear view of Showco Prism crossover drive unit. The top row of 10 female XLR connectors were input connectors for each band of frequencies for the left channel and the right channel from the crossover unit. The second row of 10 male XLR connectors were used to daisy chain the signals from the crossover to other drive units. The bottom two rows of XLR connectors were for the actual drive signals that were connected to the power amplifier racks and each frequency band (other than bass and sub bass which used the same type of connector) used a different type of XLR connector and followed the Showco standard format that had been adopted in the early years of the company. The Master/Slave connector was used to allow one of the drive units, (usually the MAIN unit), to be the master level controller for other drive units to control the overall level of the entire system with one level control. This scheme ensured that the levels of all other arrays (front fill, side fill, etc.) always precisely tracked the MAIN system level. __The Prototype Mockup and Parking Lot Test of Prism 1985\-__ {{< MultiGalleryComponent galleries="1986-prism-system-construction" >}} {{< MultiGalleryComponent galleries="1986-prism-system-parking-lot-pa-test" >}} {{< MultiGalleryComponent galleries="1986-prism-system-reunion-set-up" >}} When Jim Brawley and Clay Powers had completed the design of the Prism array and crossover, we built a prototype system of 10 columns of five cabinets per column. We did not build any provisions for rigging into the prototype cabinets. We strapped the columns of five cabinets together using long pieces of 2” wide X ¼” thick steel flat stock. We built a scaffolding structure in the parking lot to support two steel I-beams with cross members to support 10 chain motors, one for each column. Scaffolding supporting two steel I-beams with cross members to support chain motors for the prototype Prism array for the parking lot test 1985. Photo Recovered Showco Archive. Database Link2>Bornhorst Edits>Recovered Showco/VL Pix JPEG Photo Archive>Showco Photos>Showco Sound Gear>1986 Prism System>1986 Prism Parking Lot Test>19 Parking Lot Test.j {{< StoryImage id="showco-1986-prism-parking-lot-test-23-parking-lot-test" title="Maneuvering the 25 ft long Prism column of speakers out of the building in preparation for rigging in the scaffolding structure with the I-beams 1985" caption="Maneuvering the 25 ft long Prism column of speakers out of the building in preparation for rigging in the scaffolding structure with the I-beams 1985" credit="Photo Recovered Showco Archive" size="large" >}} {{< StoryImage id="showco-1986-prism-parking-lot-test-36-parking-lot-test" title="Hanging the first prototype Prism column for the parking lot test 1985" caption="Hanging the first prototype Prism column for the parking lot test 1985" credit="Photo Recovered Showco Archive" size="large" >}} {{< StoryImage id="showco-1986-prism-parking-lot-test-54-parking-lot-test" title="Rear view of the Prism prototype system with ten columns in the Showco parking lot test 1985. The trapezoidal shape of the cabinets allowed them to form the horizontally curved shape designed by Jim Brawley that consisted of two curves, a tight curve to cover the floor of the arena and a flatter curve to cover the sides and rear of the arena. This mockup used individual chain motors for each column. The final prism system used David Evangelista’s hanging grid to suspend all of the columns and accurately set the curve Brawley designed. The mockup did not have individual cabinets. Each column was one assembly with the mocked-up cabinets strapped together with long pieces of steel strap" caption="Rear view of the Prism prototype system with ten columns in the Showco parking lot test 1985. The trapezoidal shape of the cabinets allowed them to form the horizontally curved shape designed by Jim Brawley that consisted of two curves, a tight curve to cover the floor of the arena and a flatter curve to cover the sides and rear of the arena. This mockup used individual chain motors for each column. The final prism system used David Evangelista’s hanging grid to suspend all of the columns and accurately set the curve Brawley designed. The mockup did not have individual cabinets. Each column was one assembly with the mocked-up cabinets strapped together with long pieces of steel strap" credit="Photo Recovered Showco Archive" size="large" >}} {{< StoryImage id="showco-1986-prism-parking-lot-test-59-parking-lot-test" title="Front view of prototype Prism system rigged using an individual 1-ton chain motor for each column 1985. The prototype Prism array had 10 columns with five cabinets per column which was the outdoor stadium configuration. The production version of the full Prism indoor arena array used eight columns of four cabinets per side. The Prism cabinets that Jim Brawley designed, starting at the bottom of the column are two identical ported bass reflex cabinets #1 and #2 each with two JBL 2240 18” speakers (cabinet #1 was removed from the arena array), a cabinet #3 with one non-ported JBL 18” 2240 speaker, two JBL 8” 2118 mid bass speakers, a JBL bi-radial horn with a JBL 2445 driver mounted on a baffle that is angled downward with two JBL 2404 high frequency drivers with the slots removed and custom designed Community horns, a cabinet #4 with ten JBL 8” 2118 speakers and two JBL 2404 high frequency drivers and Community horns, and a cabinet #5 with two JBL bi-radial mid-range horns each with a JBL 2445 driver, one JBL 18” 2240 speaker in a ported reflex configuration and two JBL 2404 high frequency drivers and Community horns" caption="Front view of prototype Prism system rigged using an individual 1-ton chain motor for each column 1985. The prototype Prism array had 10 columns with five cabinets per column which was the outdoor stadium configuration. The production version of the full Prism indoor arena array used eight columns of four cabinets per side. The Prism cabinets that Jim Brawley designed, starting at the bottom of the column are two identical ported bass reflex cabinets #1 and #2 each with two JBL 2240 18” speakers (cabinet #1 was removed from the arena array), a cabinet #3 with one non-ported JBL 18” 2240 speaker, two JBL 8” 2118 mid bass speakers, a JBL bi-radial horn with a JBL 2445 driver mounted on a baffle that is angled downward with two JBL 2404 high frequency drivers with the slots removed and custom designed Community horns, a cabinet #4 with ten JBL 8” 2118 speakers and two JBL 2404 high frequency drivers and Community horns, and a cabinet #5 with two JBL bi-radial mid-range horns each with a JBL 2445 driver, one JBL 18” 2240 speaker in a ported reflex configuration and two JBL 2404 high frequency drivers and Community horns" credit="Photo Recovered Showco Archive" size="large" >}} {{< StoryImage id="showco-1986-prism-reunion-setup-12-reunion-set-up" title="The hanging grid designed by David Evangelista for the Prism indoor arena array with eight columns of four cabinets. The first row of eight cabinets attached to the hanging rig with ½” X 18” stainless steel pins. The pins connecting the wheel dollies to the cabinets were removed and the cabinets were raised off the ground and the second row of eight cabinets were rolled into position and connected to the first row with the ½” X 18” stainless steel pins from the wheel dollies and the Pyle National speaker cable jumpers (the crews named the jumpers “Donkey Dicks”) were attached and then the next row was rolled into place and so on until all eight columns of four cabinets each were suspended under the hanging rig. A long Pyle National cable was connected to the lowest cabinet and went down to the amplifier racks. The speaker cable had 41 #16 conductors. Each transducer or dual pairs of transducers were assigned a specific pair of conductors so that no matter how the cabinets were arranged and/or stacked, each transducer would be connected to the correct amplifier channel. A Prism system array could be assembled and raised into position in 25 minutes after the 32 cabinets were staged on the floor" caption="The hanging grid designed by David Evangelista for the Prism indoor arena array with eight columns of four cabinets. The first row of eight cabinets attached to the hanging rig with ½” X 18” stainless steel pins. The pins connecting the wheel dollies to the cabinets were removed and the cabinets were raised off the ground and the second row of eight cabinets were rolled into position and connected to the first row with the ½” X 18” stainless steel pins from the wheel dollies and the Pyle National speaker cable jumpers (the crews named the jumpers “Donkey Dicks”) were attached and then the next row was rolled into place and so on until all eight columns of four cabinets each were suspended under the hanging rig. A long Pyle National cable was connected to the lowest cabinet and went down to the amplifier racks. The speaker cable had 41 #16 conductors. Each transducer or dual pairs of transducers were assigned a specific pair of conductors so that no matter how the cabinets were arranged and/or stacked, each transducer would be connected to the correct amplifier channel. A Prism system array could be assembled and raised into position in 25 minutes after the 32 cabinets were staged on the floor" credit="Photo Recovered Showco Archive" size="large" >}} {{< StoryImage id="showco-1986-prism-reunion-setup-15-reunion-set-up" title="Hanging grid for arena sized system with three of the four cabinets in place for each of the eight columns. The curve of the hanging rig set the horizontal coverage of the array which was designed by Jim Brawley to provide even coverage of the arena. The Prism system also included six to eight sub woofers on each side of the stage. Each sub woofer had two JBL 2245 18” speakers in a ported reflex cabinet. One arena hanging grid with 32 Prism cabinets was rigged with two CM 2-ton chain motors and weighed 8,000 pounds" caption="Hanging grid for arena sized system with three of the four cabinets in place for each of the eight columns. The curve of the hanging rig set the horizontal coverage of the array which was designed by Jim Brawley to provide even coverage of the arena. The Prism system also included six to eight sub woofers on each side of the stage. Each sub woofer had two JBL 2245 18” speakers in a ported reflex cabinet. One arena hanging grid with 32 Prism cabinets was rigged with two CM 2-ton chain motors and weighed 8,000 pounds" credit="Photo Recovered Showco Archive" size="large" >}} {{< StoryImage id="showco-1986-prism-reunion-setup-19-reunion-set-up" title="Amplifier racks for an indoor arena Prism system of eight columns per side. One rack with two Crown MacroTech 1200 amplifiers and three Crown PSA2 amplifiers powered one column. The Pyle National multiconductor speaker cables are plugged into a panel at the bottom of the racks. The two racks with four Crown PSA2 amps powered the subwoofers" caption="Amplifier racks for an indoor arena Prism system of eight columns per side. One rack with two Crown MacroTech 1200 amplifiers and three Crown PSA2 amplifiers powered one column. The Pyle National multiconductor speaker cables are plugged into a panel at the bottom of the racks. The two racks with four Crown PSA2 amps powered the subwoofers" credit="Photo Recovered Showco Archive" size="large" >}} {{< StoryImage id="showco-robin-magruder-016" title="Prism Stadium Array for Rolling Stones Voodoo Lounge Tour 1994" caption="Prism Stadium Array for Rolling Stones Voodoo Lounge Tour 1994." credit="Photo Robin Magruder Archive" size="large" >}} ## The Aardvark 1986 After we built the first production Prism system for the 1986 Genesis tour, we found that the two Prism arrays on either side of the stage and the subwoofers worked so well, and particularly controlled the directivity of particularly the bass so well, that the bass frequencies from each array were interfering with each other and either adding together to make the bass louder or cancelling each other and making the bass weaker at various points in the arena. The problem was particularly bad on the floor of the arena at the rear center where the bass added together and was very loud. During a meeting to discuss the problem between Clay Powers, Lee Hardesty and Jim Brawley, Jim said the problem was caused because we had two separate speaker stacks instead of one big stack in the middle of the arena, which was not practical. Out of the blue, like Maxson's two more motors comment at the Salih's lunch, Lee said "wouldn't it be great if we could make the two sides of the speaker system different?" The first reaction from the group was, well we can't do that, but Jim Brawley thought about Lee's statement and an idea occurred to him about how to make the two arrays different so they would not add or cancel each other. Jim's idea was to program a comb filter into the Prism digital crossover software for each array where the bass frequencies in the comb filter for each array were slightly different and thereby cause the bass frequencies from the arrays to not add or cancel. The differences would be small and hopefully not audible to the sound mixer or the audience. Lee programmed the comb filters that Jim designed into the Prism crossover, and the concept worked perfectly. The bass response from the two Prism arrays was even throughout the arena, and the buildup of bass at the rear center of the arena was eliminated. The group named the concept The Aardvark, and it was programmed into all of the Prism systems. ## Prism Stage Reference Monitor (SRM) By 1988? we needed to develop a new stage monitor speaker system. The goal was to create a superb-sounding, high-powered, efficient, low profile stage monitor "wedge" that would complement the high performance, appeal and sleek design of the innovative and highly successful Prism sound system. Again, the team of Clay Powers, Howard Page, Richard Bratcher and Jim Brawley put their minds to the challenge. The team chose the latest high-powered/high-fidelity JBL speaker components and Crown amp for the project. The woofer was a 12" 8 ohm high power JBL 2206H rated at 1,200 watts program power. The mid-high driver was a 2" exit 16 ohm high power JBL 2445H. The driver was coupled to a constant directivity JBLhorn aligned 60 degrees vertically x 40 degrees horizontally. The amp was Crown's new Macro-Tech MA-36x12, specially designed for bi-amp applications. One channel produced 1,120 watts at 8 ohms (1,565 watts at 4 ohms) for the woofer, the other channel 310 watts at 8 ohms (480 watts at 4 ohms) for the mid/high driver. The JBL and Crown components all had numerous advanced design and performance features for the day. In addition to the state-of-the-art JBL and Crown components, the Prism SRM system included numerous innovative features: a unique milled aluminum front baffle panel, precision-milled wood corners with recessed handles and specially designed internal bracing to create a very strong and rigid speaker enclosure structure for excellent acoustic performance, power handling and durability; an advanced constant voltage crossover/drive system with performance enhancing pre-equalization and phase control processing; a unique low-profile, elegant curvilinear form (augmented by a visually striking gentle front panel curvature suggested by Robin Magruder); symmetrical enclosure configuration with parallel connectors on two sides that eliminated the need for separate left and right configurations when used in pairs; and an extremely durable finish derived from truck bed liner coating. When the team showed Rusty Brutsché the Prism SRM system, he exclaimed, "That stage monitor has more power than my entire stadium PA for Led Zeppelin in 1971." The Prism Sound System, with its digital System Controller/Crossover and Aardvark, the Prism Stage Reference Monitor (and later the Showconsole- see Chapter 35 below), reestablished Showco at the very pinnacle of the global live sound industry. These revolutionary systems significantly advanced the state-of-the-art in large scale live sound. They enabled Showco to continue its long-standing successful relationships with many major touring artists and they attracted dozens of new major artists to Showco during the 1980's and 1990's.