Q-118B

Q-118B is a very compact subwoofer about half the size of Q-218B fitted with single 18-inch unit 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 162)

The enclosure is so designed that the frontal dimension is not much bigger than the two 18-inch unit and the vented ports are placed on four connors of each unit. (See Figure 163)

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 164)

Components

Q-218B is fitted with a single L18/75/01Z18-inch unit

  • The frame is die-cast alloy
  • The case is made from specially formulated pulp with fiberglass and wool
  • The cone is light in weight and very rigid. The surround and spider are quite stiff and the bandwidth is wide
  • The magnet is made from y30 high flux strontium ferrite. The magnetic structure weights 6.1kgs
  • The diameter of the voice coil is 3-inch edge wound with flat aluminum wire on a Kapton former. (See Figure 165)

Figure165

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 Q-118B has no built-in passive crossover network nor low pass filter. It is recommended that the speaker should be used in conjunction with external speaker processor with delay and equalization functions such as iBO D-24 (2in 4out) digital speaker processor.

 

Applications and Technical Specifications

Q-118B can be used in conjunction with any of the Q-112 and Q-115 as the main speaker of small to medium sound reinforcement system for assembly hall, multi-function hall or other audio visual activities or used or as auxiliary speaker for a large sound reinforcement system.

 

Technical Specifications and diagrams (See below)

 

FREQUENCY RESPONSE

40 Hz ~ 200 KHz (±3 dB )

SENSITIVITY (1W/1m)

98dB

NOMINAL IMPEDANCE

8 Ohm

POWER RATING

400 W (AES)

LF COMPONENTS

2×18〞woofer (3″voice coil)

CALCULATED OUTPUT (MAX)

124 dB SPL, 130 dB SPL peak

DIMENSIONS (H×W×D)

540×580×700 (mm)

WEIGHTS

40 (kg)

CONNECTORS

2 Neutrik NL4MP connectors

 

 

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