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Throughout the history of sound reinforcement, the exclusive instruments for focusing and projecting sound over distance have been horns. Dozens of different horn types and combinations have been developed over the years, and considerable improvements have been realized since the designs of the 1940's and 1950's. Contemporatry devices such as the Meyer MSL-10 are able to maintain a narrow beamwidth over considerable distances. However, at a certain point, all horn-based devices run into a barrier imposed by the laws of physics.
Parabolic devices have a well-known ability to maintain a narrow beamwidth over far greater distances than horns of any type. However, use of parabolic devices in general audio applications-in particular as reinforcement transducers-has been limited by a serous drawback: in all parabolic reflectors, beamwidth narrows as frequency increases. Over the past four years, a team of engineers at Meyer Sound Laboratories has been working to develop a parabolic-based device that could maintain a consistent beamwidth of less than 10 degrees across a useful audio bandwidth of five octaves for distances of 400 feet or more. This device, the Sound Beam SB-1, has completed its initial beta production run, and ten SB-1 units were incorporated in a rock concert reinforcement system that toured through very large domed stadiums in Japan in early 1997.
Background: Why Dishes Throw Further
Parabolic reflectors are inherently superior to horns because they are not subject to the inverse square law, which states that sound drops off 6dB with each doubling of distance. The inverse square law, however, applies to spherical waves generated from a point source. Sound waves emanating from a parabolic reflector behave more like plane waves, which drop off at only 3dB with each doubling of distance. Although sound from some stacked horn configurations effectively simulates plane wave characteristics over short distances before collapsing into spherical waves, sound from the Sound Beam is able to maintain plane wave behavior for distances of 400 feet and more.
However, despite their inherent long-throw superiority, parabolic devices have found limited applications in audio. True, they have proven useful in some microphone applications for boosting high frequency response when picking up distant sound sources. But as far as projecting audio signals, the only use of parabolic reflectors before the Sound Beam has been largely limited to test and measurement applications.
The Precursor: ARTS
In 1993, Meyer Sound introduced the Audio Ranging Transceiver System (ARTS). Designed as an extension of the Meyer SIM system, ARTS sent out a highly focused 2kHz tone burst, listened for it to come back, and then used a SIM-2201 to analyze the results. ARTS was useful for detecting the presence and altitude of inversion layers, and it was used at Disneyland to help determine how sounds from an attraction were carrying into nearby residential neighborhoods. Although ARTS maintained an 8 degree beamwidth and generated 130dB SPL at 100 feet, it had a frequency response of only a single octave (1.5 - 3 kHz).
Despite the daunting obstacles, the wide-ranging benefits implied by ARTS were tantalizing. An engineering team began exploring ways of significantly extending bandwidth while still restricting beamwidth to under ten degrees. The Sound Beam development team consisted of John Meyer, Bob McCarthy, Peter Soper, Paul Kohut, Frank Kavka and Jeff Weiner. Initial design work was largely theoretical because there was no immediate market demand for the product, and also because early testing of prototypes was inconclusive.
Accelerated Development: A Request from Japan
In early 1995, Meyer Sound completed construction of a new, state-of-the-art anechoic chamber at its Berkeley facility. This allowed the engineering team to conduct accurate, painstaking tests of the prototype Sound Beam designs, and further refine the theoretical models. Then, the following year, accelerated design was prompted by a request from Meyer's Japanese distributor, Acoustic Technical Laboratory (ATL). One of their customers, ARTE, was designing a concert sound system to be used for rock concerts in four very large domed stadiums. Distances from the stage to furthest seats would be upwards of 400 feet, and high quality sound was desired all the way to the back. Hanging of delay speakers would be difficult in all cases because of post-Kobe-earthquake safety restrictions, and virtually impossible in one case because the Tokyo dome has a soft pillow roof. Attempting to throw all sound from the front speaker towers (on extremely sturdy scaffolds) was discouraged by the prominent mixer for the tour, Akira Shamura, who did not want bleed from long throw devices at his FOH mix position. Representatives of ATL and ARTE therefore specified a beamwidth of less than ten degrees.
At that time, John Meyer had been using the new anechoic chamber to investigate new horn configurations, and he knew no horn was capable of such a tightly defined pattern. A parabolic-based device was the only possible solution.
Sound Beam: A Brief Description
The basic Sound Beam specification calls for a 5-octave bandwidth (500Hz to 16kHz) with a constant beamwidth of under ten degrees to below 1kHz. The only way to meet this specification was to design a horn with a frequency-versus-dispersion characteristic that counterbalanced the effects of the parabolic reflector, and then aim a transducer fitted with such a horn into the dish. This seemingly simple principle, however, required considerable engineering finesse to accomplish in reality. Also, testing of prototypes revealed unacceptable lobing characteristics at the lower end of the desired spectrum. These problems were solved by placing a 12-inch, band-limited cone driver in the center of the dish and using electronic processing to adjust frequency-versus-phase relationships. In the beta production version, the Sound Beam SB-1 comprises a 48-inch fiberglass parabolic reflector and a bullet-shaped driver pod housing a 4-inch compression driver and patent-pending conical horn. The dish housing contains the aiming mechanism along with signal processing electronics and dual 620 watt power amplifiers.
Sound Beam Debuts in Osaka
The tight production schedule allowed little time for final testing before the first ten units were shipped to Japan in February of 1997. Indoor tests at short distances were satisfactory, but outdoor long-distance tests were inconclusive because of the Bay Area's blustery winter winds. With no sufficiently large indoor facility available for short-term rental, the units arrived in Osaka without conclusive final testing. Bob McCarthy of Meyer Sound was assigned to set up and commission the units at the Osaka Dome.
The venue was set up for concert seating of 40,000. (The two shows by the Japanese techo-rock band were both sold out.) Maximum throw distance for the SB-1 arrays would be about 450 feet.
The SB-1s were hoisted, five for each side, to the top level of a 50-foot scaffold. Because the SB-1 had never before been tested in a horizontal array, angles of 10, 8, 6 and 4 degrees were tried and analyzed with pink noise. A splay angle of 8 degrees was selected, and a sextant was used for vertical alignment.
Preliminary SIM calibration produced astonishing results. At 360 feet (328ms.), the system was producing SIM S/N of 10dB to 15dB. (SIM S/N is ratio of direct signal to all other sounds picked up by the microphone, mainly reverberant.) When music was played through the system, McCarthy described the effect as "a striking illusion of proximity" with absolutely no horn signature. During the sound check, slight adjustments were made to vertical angles and to output levels on the SB-1 arrays relative to the other system components.
The SB-1s performed flawlessly during the performance. "Everything on stage is audible in exact detail, even in the further seats," reports McCarthy. "The audience loves it."
Reviews of the Sound Beam-equipped system sometimes eclipsed those for the bands using it. Akio Kawada of ARTE's parent company, Sound Craft, wrote that several newspapers specifically singled out the sound system for praise, and a principal of ATL called the Sound Beam debut an "epoch-making event in loudspeaker development." Click here to see excerpts from those articles.
Click Here to Zoom-In on the Sound Beam at Tokyo Dome
3 Graphics Approx. 20k Each
Sound Beam: A Visual Analogy
A modern stadium concert would not be complete without live video projection. The giant screens visually rescale the event. And, fortunately for the video people, the scaling is a simple linear function. An increase in venue size can be compensated by a simple linear increase in screen size, keeping the audience perspective constant. There is no visual equivalent of sound reverberation, and no frequency coloration. The same is not true of audio. While the volume of the system can be scaled by adding more speakers as venue size increases, this does not result in the equivalent sonic perspective. Indoors, the principal reason is excessive reverberation: as more speakers are added, more sound spills onto the walls and ceiling, creating unwanted reflections. A secondary cause is the overlap among additional speakers, which can create holes in the frequency response.
The Sound Beam overcomes this in two ways. First, the 8 to 10 degree polar pattern keeps sound focused on the audience and away from the walls and roof. Second, each seating area can be covered by a single Sound Beam, thus creating large areas where interaction can be minimized. The overall effect is to reduce the perceived space between the artist and audience in very large venues.
Sound Beam: Meyer Sound at the Forefront of New Technology
The Sound Beam reflects a commitment on the part of Meyer sound to serve audio professionals, not by simply following where the market is going, but by staying one step ahead of the market. Sound Beam obviously represents a radical departure from "designs-as-usual" in sound reinforcement devices. The project was undertaken at considerable risk, but the Meyer team was convinced that the possible future benefits to the professional audio community justified investment of considerable time and resources with no guarantee of ultimate success.
Fortunately, all preliminary indications are positive. Final Sound Beam development work continues, particularly on issues such as interaction in stacked arrays.
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