For simpler functions in small venue where only a couple of speakers are required the full range speaker used may need to extend its frequency response down 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 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-215B is designed to handle the low end of the frequency response down to around 40HZ.
The enclosure of LA-215B is of front horn loaded and rear vented design (See Figure 19). 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 and 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.
The enclosure is heavily braced internally and a black powder-coated perforated steel mesh grille protects the drivers from damage. The finishing is in black semi-matt texture paint. A rear connector plate fitted with two Neutrik Speaker NL4MP connectors for amplifiers and for loop-in and loop-out to additional enclosures (See Figure 27).
Two L15/100/06Z drivers are used in LA-215B, L15/100/06Z is developed by iBO specifically for horn loading
- Frame is die cast alloy
- The cone is a special formula of pulp and glass fiber. The depth of the cone is rather shallower with reinforcement ribs for better reproduction of low-frequency (See Figure 16)
- 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. (See Figure 17)
- The magnet is made from y30 high flux strontium ferrite weights 8.54kg
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-215B 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 (2in6out) digital speaker processor.
Applications and Technical Specifications
LA-215B 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)