What is CSA Technology?
Concentric Summation Array technology takes advantage of physics. This patented waveguide technology seamlessly combines the output of low and high frequency devices into a coherent waveform. This means the sound from each loudspeaker element will arrive at the listener at the same time allowing everyone to experience the same even and clear sound. To better understand, the explanation below covers how and why this technology was developed.
If both MF and HF are radiated in common by a coaxial transducer, they can be loaded on a single horn. The size of the horn can be maximized, and the polar pattern can be symmetrical both horizontally and vertically over a wide operating band.
However, this solution poses many engineering challenges. Coaxial transducers have generally been designed for use in two-way, full-range, low Q systems. They typically include a standard cone transducer (8”, 10”, 12” or 15”), with some modifications to allow a standard compression driver to be mounted on the back of the cone’s motor structure and fire through its center. The usual modifications include hollowing out the cone’s pole piece and shaping it to provide an initial horn bell for the compression driver. This waveguide section terminates at the end of the cone’s former, where the cone itself becomes a continuation of the HF horn. In essence, the MF cone acts as a low Q conical waveguide for the HF. A second modification is the replacement of the solid dust cap typically found on cone transducers with a mesh dust cap. The mesh prevents airborne particles from entering the gaps between the two voice coils and magnets yet is acoustically transparent in the high frequency energy.
Limitations of the Conventional Coaxial Transducer
Some limitations of a coax transducer occur with modulation of the HF when the device is used full range and low frequency signals driving the cone to high excursions. Since the cone is also acting as the main section of the HF waveguide, the high frequencies are modulated. A possible solution is to use the device as a part of a three-way system with a separate LF section.
Another limitation is inherent low Q since the coaxial transducer cannot be loaded by a horn. There are two reasons for this, both related to the requirement for temporal coherence. The first is the need for a continually increasing flare rate.
Classic horn design theory states that the bell curvature angle should always increase along the path of the horn. Simply loading a coaxial transducer onto a horn would break this rule. Initially the HF horn expands at an increasing rate through the pole piece and along the cone, but then the rate of expansion decreases at the base of the horn. It is intuitively obvious that this design would cause significant reflections off the horn walls, resulting in multiple arrivals and attendant problems (side lobes and transient smearing).
The last problem is related to the physical dimensions of the cone relative to the wavelengths of upper midrange frequencies. The cone moves like a piston, but the path length from the inside of the cone to the horn flare is longer than that from the circumference. At frequencies near the upper crossover limit, this difference is an audible fraction of a wavelength. The resulting uneven frequency response and smeared transients are rarely appreciated by the audience.
The goal is a common horn for both MF and HF, without multiple arrivals and interference issues. To eliminate these, we must provide both constant expansion for the HF device, and a phase plug to load the MF device. The chosen design integrates an acoustically translucent high frequency horn bell into the radial phase plug for the mid frequency device. This horn bell allows mid frequency energy to pass through unobstructed, while acting as a semi-permeable barrier for the high frequency energy.
A standard phase plug solves the temporal problems discussed earlier by creating a longer path length for energy from the central part of the cone to synchronize its arrival with the energy from the cone’s circumference. The pistonic cone is thereby effectively changed into a ring radiator, causing the beamwidth to narrow at lower frequencies than it would without the phase plug. The Radial Phase Plug design properly corrects the temporal inconsistencies while maintaining the directional characteristics of a piston, allowing it to be used in lower Q systems.
Concentric Summation Array Technology
Because phase plug is in place of the traditional coaxial transducer’s dust cap, it can be used for the initial section of the HF horn bell. The forward-facing section of the phase plug then requires a compromise between the configurations that would be ideal for the cone and the compression driver separately. For the mid-range cone, the ideal configuration is a radial phase plug that is loaded onto the horn without any barrier. For the compression driver, the ideal configuration is that it be loaded directly onto a solid horn bell. These two configurations are not perfectly compatible: the Radial Phase Plug design requires slots in the horn bell through which midrange frequencies can pass, but slots in the horn wall will “interrupt” the high frequency wavefront, acting as a mechanical high pass filter. A solid horn bell would obstruct the midrange frequencies and act as a mechanical low pass filter. Therefore, an optimum compromise design should minimize open area for the high frequencies while maximizing open area for the mid frequencies.
This semi-permeable horn bell acts as a low pass filter to the mid frequency device and a high pass filter to the high frequency device. Therefore, the open area must be chosen appropriately to achieve raw responses from each device that can then be effectively electronically filtered for a smooth overall system response.
Furthermore, attention needs to be paid to the location of the open area in the horn. For the mid frequency, it needs to be evenly dispersed to achieve symmetric off-axis response. For the high frequency, the open area must be randomized, to avoid any large nulls at any frequency/wavelength (corresponding to specific locations along the path of the horn). The chosen implementation maintains an 80% solid horn wall for the high frequency, while providing randomized openings (one per phase plug slot) for the mid frequency.
EAW products are continually improved. All specifications are therefore subject to change without notice.
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