Y-axisseries Design Considerations ADAMSON SYSTEMS ENGINEERING TORONTO • CANADA T el: 905•683•2230 - Fax:905•683•5414 w w w. a d a m s o n p r o a u d i o . c o m AXIS Y18 AXIS . Y10 AXIS . . Geddes clearly described the geometries of the Cylindrical. . . All in the field of line array technology. Earl Geddes. Adamson has developed many useful line array geometries founded on our early use of waveguide technology. before the introduction of the line arrays of the 90’s. In 1987. waveguides.AXIS Introduction to Y-axis Adamson Y-axis Line Arrays offer the best possible solutions to the complex questions of line array geometry. Sound chambers. Since then. Adamson holds numerous patents. driver size and box angle are all critically optimized in the integration process of array design. In the past fourteen years. . Elliptical Cylindrical and the Oblate and Prolate Spheroidal waveguides. . It is simply not possible for every manufacturer to produce a top performing line array with only a few years devoted to its development. This is reinforced by the fact that many key technologies are defined by patents or patent applications that are in progress by Adamson and others. . has new patents allowed (but not yet published) and has new applications filed. Adamson has pioneered the use of waveguides based on the work of Dr. . Each of these components plays a significant role in the outcome. 5” horn throat). the wavelengths (2. There are four basic types of line array source geometry: . We at Adamson would like you to know that the Y-axis employs the very best of all possible line array geometries and drivers and we’d like to explain it clearly. Since not all types of transducer/structure geometries couple optimally.000Hz = 6.long flat radiator (ribbon tweeter) .1. This is a good thing. . But high drivers are equal to. But the ratio of wavelengths of wide-band audio from low to high is 1000:1 (20Hz 20. to equal to. the operating wavelengths (20. Simply put: drivers don’t exist that are small enough to couple at the highest frequencies with sufficient output for professional use. So the first thing we need to do is compare driver size to wavelength.closely spaced row of horns . Simple observation indicates that woofers are much smaller than the operating wavelengths (200Hz = 68”).continuous row of iso-phase energized slots (curved or flat exit sound chamber) All currently available line arrays employ a combination of at least two of these source geometries.AXIS Line Array Elements The properties of a multi-way line array are complex and often misrepresented. .68”). .8”). But which method is best?.000Hz).000Hz = . It is simple to see that there is a problem with the driver/wavelength size relationship. Wavelengths and Coupling Multiple sound sources in an array must be centered within a wavelength of the highest frequency for coupling to occur. Mid drivers range from smaller than. it is important to examine them carefully. This small fact is a large problem.closely spaced row of direct radiators . First consideration: size matters. All line arrays contain closely spaced rows of acoustic transducers and associated structures that comprise line array source geometry. The ratio of large to small loudspeaker diameters is approximately 10:1 (15” woofer . or larger than. (In another sense it is the very low directivity of the mid and low drivers that allows them to couple. SPL and crossover frequencies.. Low frequency direct radiators can be arrayed with little difficulty. Mid range devices may be chosen small enough (7”) to be arrayed in the required frequency range. but offers poor upper-mid frequency array performance since the output is curved and the box to box driver spacing is too large. but the magnetic structure of the driver is much larger and prevents the correct spacing. This type of horn throat dates from the 70’s and was found in the Manta-Ray and Constant Directivity Horns. the resulting slot is energized by a curved wavefront that expands spherically. contains too much overlap to couple properly in a line array and delivers correspondingly poor far field performance. Ribbon tweeters have limited output and thus. by definition. This problem is not as great an obstacle. The exit of a compression driver is likely small enough. Mid-range direct radiators can be made small enough. It was not considered a solution to vertical arrayability at the time and should not be considered a solution today. since typical wavelengths in this frequency band are many times greater than driver diameters.. But.) “Unworkable Solutions” for the High and Mid It seems like a simple matter to place a horn throat section in front of a compression driver with an exit in the shape of a vertical slot.AXIS The High Frequency Dilemma High frequency drivers are the most obvious problem. but there will be a real limit regarding distortion. Horn loading with a typical mid driver (10” . An array of these devices. limited use. They may be chosen a little larger (10”) with poorer upper-mid array response.12”) solves the power problem. but show serious limitation in SPL and distortion. . The array is shaped and positioned so listeners face multiple elements of the array at nearly equal distance. . Most line arrays are designed (and marketed) with two primary things in mind: .AXIS Horizontal Spacing: A Different Kind of Trouble The exact same rules concerning coupling in the vertical array apply to horizontal driver placement within the enclosure. Secondly. if you are listening on-axis. in fact. which far exceeds the vertical window. the time delay error is magnified as you move further from the center of the array. So. In other words. violation of horizontal spacing rules has a far more serious effect because the listener can move further off-axis in the horizontal plane. But when you are listening off-axis. in some respects. we have precise vertical control of the driver/array/audience position. However. within the enclosure. Why is it so much more difficult and how can it be more important? Firstly the horizontal dimension of the geometry needed (such as horn flares) for wide horizontal coverage is so much greater than the size needed for 1 or 2 degrees of vertical coverage. the horizontal space between drivers is not an issue.Vertical driver spacing is minimized to reduce vertical lobing. This critical fact is ignored in the design of many current line arrays resulting in serious degradation of sound quality off-axis. more important. So. but it is actually. This makes it difficult to keep the drivers closely spaced horizontally. the horizontal listening window is up to 100 degrees. . in the horizontal plane it is not only much more difficult to comply with the spacing rules. are no fun to listen to. The off-axis frequency response.Off-axis. causing interference in the time domain. The horizontal lobing error generated by offset mids and highs is the same as the vertical lobing error seen in studio monitors. This “time smear” results in deep notches in frequency response and a remarkable reduction in transient response through the entire frequency band. You wouldn’t listen to a monitor 45 degrees below-axis. takes two common forms: . mis-aligned in time. . so why would you want to listen to a poorly spaced line array 45 degrees offaxis? What does this mean to line array performance? Unlike conventional arrays. . With improper horizontal driver placement. the impulse response and the polar response are all degraded. the line array system depends on the off-axis sound to cover the audience.AXIS Time smear and Cancellations Multiple sources. the off-axis audience is shortchanged.double rows of mid-range drivers (or slot sources) operating in the same frequency band spaced more than a few inches apart .rows of mid and high divers operating in different frequency bands separated by several inches .This time offset between two different sources affects frequencies in the crossover region. you are listening to two identical sources arriving at different times. The “time smear” that results as the listener moves off-axis. ribbon tweeter will not be considered due to limited SPL. as a result. then the wavefront we are looking for will be curved.) If we want a curved array. How do we form a long flat wavefront from the exit of a compression driver? The First “Sound Chamber ” In the early 70’s a JBL Engineer named Bart Locanthi designed a fascinating little tweeter. vertically. It is important to realize that in a correctly designed line array. The HF element in an array is likely equal in size to a wavelength at the lower end of its range and perhaps equal to 15 wavelengths at the upper end. The directional characteristic of this transducer is about 22 degrees vertical (as a result of diffraction) by about 120 degrees horizontal. The result of this innovation is a very flat isophase wavefront. But the next part is more interesting. the direct radiators operate as a coupled array. to the next driver in the array. So let’s look at how this little line array ought to behave and how we should integrate it into the bigger line array. Coupling. It became known as the JBL “slot tweeter” and is still available now. compared to operating wavelengths. from the diaphragm to the exit. possessing its own directivity characteristics. is complete. (As stated earlier. These drivers are small. The JBL device has some interesting features. then the wavefront from the HF element ought to be flat. is shaped so that the paths are equal in length. If the line array is to be straight and we want it to produce cylindrical waves. The paths that the sound wave would naturally travel. Since the HF element is so long. it in fact. since they are too large. First is the combination of an inner body and an outer shell that formed a passageway for the transmission of a sound wave to the rectangular exit. But the high frequency element is a very different matter. must be considered as a miniature line array in its own right. But the HF elements should operate as independent highly directional elements. due to the physical size of the average compression driver. to couple. relative to the frequency of operation and therefore very low in directivity. .AXIS The necessity of Sound Chambers Each driver element of the mid and low section of a typical three-way array can act fully coupled. Both wavefronts are allowed to change shape until they emerge from three parallel slots at the Co-Linear exit of the sound chamber.phenomenal headroom in the mids from Adamson’s Kevlar compression mid driver The result: seamless mid/high-frequency energy in the same linear waveguide.the system is completely symmetrical with an absence of lobing error .AXIS The Y-axis Drive module Sound chamber principles have been advanced by Adamson as by no other manufacturer. In a significant advancement. Adamson’s unique “sound chamber within a sound chamber” presents a radical new way to produce a curved. while separated by the walls of the high frequency sound chamber. at the entrance to the ninety-degree waveguide.the mids as well as the highs are capable of very long throw . Only the wave-shaping properties of Adamson’s new technology produces this result. Each module is powered by one Adamson 9” Kevlar mid driver and one JBL 2451 high frequency driver. iso-phase. Each Y18 enclosure contains two complete Drive Modules. This new technology resolves all the design conflicts inherent in line array design. . The high frequency slot is centered.. he benefits of an energized iso-phase slot source are introduced to the mid range. The Co-Linear Drive Module allows the mid and high frequency wavefronts to be propagated co-axially.) . co-linear sound source. (Numerous recent Patent Applications are the result of this ground breaking work. The heart of the Y-axis System is the proprietary Co-Linear Drive Module. with the mid balanced on both sides. AXIS Werchter 2001 Set Up Y10 Centre Fill Werchter 2001 Rigging the Main Stage 24 x Y18 Toronto rCanada www.adamsonproaudio.com 8 x 8 Y10 at Olympia Theatre (Paris) 8 x 8 Y10 at olympia Theater (Paris) . AXIS Werchter 2001 Y18 x 24 Stage Left . com . a d a m s o n p r o a u d i o . c o m [email protected]:905•683•5414 w w w.AXIS ADAMSON SYSTEMS ENGINEERING TORONTO • CANADA T el: 905•683•2230 .