For simpler functions in small venue where only a couple of speakers are required the full range speaker used may be need to extend its frequency response to 50HZ or even lower to cope with the functional requirement. Not in the case of speakers as part of an array. An array usually consists of many speakers, each individual speaker or a group of speakers serve for specific purpose. There is no need for any speaker or part of the array to cover the entire frequency range. The full range speaker need not extend down to very low frequency as it would be covered by subwoofers. Besides, the full range speakers in line array can not be made very large as there are physical and acoustic limitations. As part of a line array, the LA-218B is designed to handle to low end of the frequency response down to around 40HZ.
The enclosure of LA-218B is of front horn loaded and rear vented design (See Figure 22). Two LF units are mounted on the bass horn that is farthest inside the cabinet. The front radiation is “squeezed” out of the horn. The rear radiation passes thru the phase inverted passages that would be in phase with the front radiation augmenting the low frequency response.
This design combined the advantages of horn loading and bass reflex enclosures. The enclosure need not made very large. The enclosure is made of 18mm (11-ply) birch plywood. All joints are tenon and mortise of Chinese tradition plus screws and adhesive to ensure the rigidity and durability.
Many domestic and imported speaker enclosures using medium density fibre (MDF) board to reduce cost, but MDF has a total weakness. It soften when moisten and loss its rigidity. iBO
rather uses expensive birch plywood to build the enclosures to ensure its strength and rigidity no matter used indoor or outdoor, rain or fine. (See Figure)
The enclosure is heavily braced internally and a black powder-coated steel mesh grille protects the drivers from damage. The finishing is in black semi-matt textured environmental friendly paint. A rear connector plate fitted with two Neutrik Speakon NL4MP connectors for amplifiers and for loop-in and loop-out to additional enclosures (See Figure 22).
Two L18/100/11Z drivers are used in LA-218B, L18/100/11Z is developed by iBO specifically for horn loading
- Frame is die cast alloy
- The cone is a special formula of pulp and fiberglass. The depth of the cone is rather shallower with reinforcement ribs for better reproduction of low-frequency
- Surround and spider are stiffer to increase the mechanical stiffness
- The cone is treated with inflammation resistant agent
- The diameter of the voice coil is 4-inch edge wound with flat copper wire on a Kapton former.
- The magnet is made from y30 high flux strontium ferrite weights 10.75kgs
The Crossover Network
Normally there is no built-in passive crossover network in a subwoofer or perhaps only a built-in low pass filter but even a low pass filter could cause phase problem and there is insertion loss. For these reasons, the LA-218B has no built-in passive crossover network nor low pass filter. It is recommended that all LA series speakers should be used in conjunction with external speaker processor with delay and equalization functions such as iBO D-26(2in, 6out) digital speaker processor.
Applications and Technical Specifications
LA-218B can be used in conjunction with any of the LA-208 and LA-315 to form a four-way system for any large venue such as outdoor concerts, touring, arenas, stadiums, theaters and discos. It works well both indoor and outdoor.
Technical Specifications and diagrams (See below)
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