QU-218B

QU-218Bis a subwoofer with two 18-inch units fitted.

 

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 soundwave radiated from the speaker front with proper phase adjustment after passing through the vent. The vent itself functions as an additional radiator in 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 band width. 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 157)

Figure 157

The enclosure is so designed that the frontal dimension is not much larger than the two 18-inch unit and the vented ports are placed on four connors of each unit. (See Figure 158)

Figure158

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 use medium density fibre (MDF) board to reduce cost. But MDF has a fatal 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 159)

Figure 159

Components

Two L18/100/11Z drivers are used in W-218B 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 Figures 160 and 161).

Figure160 and Figure161

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 QU-218B has no built-in passive crossover network nor low pass filter. It is recommended that the QU-218B should be used in conjunction with external speaker processor with delay and equalization functions such as iBO D-24 (2in 4out) or D-48 (4in 8out) digital speaker processor.

 

Applications and Technical Specifications

QU-218B can be used in conjunction with any of the QU-112 and QU-115 as the main speaker of small to medium sound reinforcement system for assembly hall, multi-function hall or other audio visual activities or as auxiliary speaker for a large sound reinforcement system.

Technical Specifications and diagrams (See below)

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