AR-218B

AR-218B is another subwoofer of the AR Series

 

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 physical and acoustic limitations. As part of a line array, the AR-218B is designed to handle to low end of the frequency response down to around 40HZ.

 

The Enclosure

The enclosure is of phase inverted (or vented) design. The advantage of this design is that sound wave radiated from the rear of the speaker be in phase with the sound wave radiated from the speaker front by proper phase adjustment after passing through the vent. The vent itself functions as an additional radiator is this case, and its radiation can add constructively to that of the speaker over certain frequencies. It requires less speaker excursion and therefore reduced amplitude distortion for a given acoustic output in the lowest portion of its usable bandwidth. This effect is most noticeable for frequencies in the neighborhood of the system lower cutoff frequency.

 

For the same lower cutoff frequency, the enclosure can be made smaller and due to this reason, the air within the enclosure acting as an air cushion at very strong transient signals. (See Figure 111)

Figure 111

• The vented ducts of the AR-218B is so designed it works like a regular vented enclosure under normal situation, the air within the enclosure act as air cushion when transient strong signal applied. (See Figure 112)

• For an enclosure housing two 18” units, it is only slightly larger than the two elements when viewed from the front. It is very compact

 

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 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 113)

Figure 113

The components

AR-218B housed two L18/100/11Z 18-inch cone type drivers.

Two L18/100/11Z drivers are used in AR-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 glass fiber. 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.

(See Figure 114 and 115)

Figure 114

Figure 115

 

The Crossover Network

Normally there is no built-in passive crossover network is 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 AR-218B has no built-in passive crossover network nor low pass filter. It is recommended that all AR 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

AR-218B can be used in conjunction with nay of the AR-215B, AR-115/64, AR-115/45 AR-112/64, AR-112/45 and AR-153 subwoofers 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)

FREQUENCY RESPONSE	40 Hz ~ 280 Hz (±3 dB )/ 25 Hz ~ 310 Hz(-10 dB)
SENSITIVITY (1W/1m)	103 dB(40 Hz~280 Hz)
NOMINAL IMPEDANCE	4 Ohm
POWER RATING	1200 W (AES)
LF COMPONENTS	2×18〞woofer (4″voice coil)
CALCULATED OUTPUT (MAX)	134 dB SPL, 140 dB SPL peak
DIMENSIONS (H×W×D)	1050×580×700 (mm)
WEIGHTS	80 (kg)
CONNECTORS	2 Neutrik NL4MP connectors

 

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