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Author:Admin     Click:584     Time:2018-01-03 09:37:00

AR-115/45 is a 2-way, 2-element full range speaker.

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 is 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 89)

Figure 89
High-frequency section is a horn loaded design, a 45 o (H) X 45 o (V) conical exponential horn is specially designed for AR-115/45.

As compared to direct radiator type speaker, the advantage of horn loading is:

The sound wave radiated from the diaphragm (cone) to free space, the wave front changes (expanding) rapidly. The radiating resistance is low, and so does the efficiency.

As the cross section of a horn changes (expanding) gradually, and as does the wave front of the sound wave radiated from the diaphragm (cone) that couple to the horn. The radiating resistance is high, the amplitude of the vibrating diaphragm is reduced and as does the efficiency of transformation. (See Figure 90)

Figure 90
The exponential horn was chosen due to its minimal changing rate of cross section. We expect the acoustic impedance of a horn be kept constant pure resistance for a widest possible frequency band. Exponential horn fulfilled this requirement. The materials of the horn is fiberglass reinforced plastic.

The enclosureis 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 Speaker NL4MP connectors for amplifiers and for loop-in and loop-out to additional enclosures. (See Figure 91)

Figure 91
The components
LF unit is a L15/75/12Z 15-inch cone type driver which features.
Light and rigid cone with high compliance surround and soft spider. The bandwidth is wide and better reproduction of extended low frequency
The materials of the cone are specially formulated pulp, fiberglass and wool
The magnet is made from y30 high flux strontium ferrite. The magnetic structure weight 6.15kgs
The diameter of voice coil is 3-inch (75mm) which is edge wound with flat aluminum wire on a Kapton former. (See Figure 92)

Figure 92
HF unit is a H3/75/03Z compression driver.
The H3/75/03Z is developed by iBO featuring:
The diaphragm is made of titanium and its surround is Mylar. The voice coil isedge wound with flat aluminum wire, the diameter is 3-inch (75mm)
The diameter of the throat is 1.4-inch (35mm)
The slits pattern of the phase plug is circumferential.
y30 high flux strontium ferrite is employed and the magnetic structure weights6.05kgs. (See Figure 93 and 94)

Figure 93 Figure94
Without the phase plug, the radiation from the center of the diaphragm or cone and the radiation from of the edge reach the throat at different time as the distances are different, as well as phase difference .
With the phase plug, the radiations from the center and from the edge are traveling at equal distance. When these radiations reach the throat, they are in phase. (See Figure 95)

Figure 95
The slits pattern of the phase plug is circum ferential (See Figure 96)

Figure 96
Crossover Network
The sensitivity of AR-115/45’s high frequency component (110 dB w/m) is much higher than the low frequency component (98dB w/m). The difference is more than 10 dB. If a build-in passive crossover network is employed, the sensitivity of AR-115/45 can only be 98 dB w/m. It does not make sense to sacrifice the 10 dB of the high frequency component. Besides, any passive crossover network have an insertion loss. The actual sensitivity of AR-115/45 would be less than 98 dB w/m. We decided not to employ passive crossover network for LA-208 and recommend using external speaker processors that incorporate delay and equalization functions such as iBO D026 (2 in, 6 out) digital speaker processors.

Applications and Technical Specifications
AR-115/45 may be used in conjunction with any of AR-112/45, AR-112/64, AR-115/64 or AR-153 plus AR-215B or AR-218B to make up a 3-way or 4-way array for fixed installation sound reinforcement system of any scale such as theaters, multi-function hall and large disco or used individually as stage side fill.

Technical Specifications and diagrams (See below)


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