M-112 is a 2-way, 2-element full range speaker designed for use mainly as stage monitor. The shape of the enclosure is suitable to lay flat on the stage floor with very low profile not to obstruct the view of the audience.


Instead of regular enclosure with four-face profile, it is a five-face profile. (See Figure 177)

It may be laid flat on the stage floor with two axis to floor angle (60 o or 40 o)


The enclosure is of phase inverted (or vented) design. The advantage of this design is that soundwave 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 178)


HF Section is horn loaded. A horn with 60o (H) X 40 o (V) is specifically designed for M-115. The horn is a constant directivity horn and is rotatable. No matter it is placed up right or laid flat, always maintain a 80o (H) X 60 o (V) pattern. (See Figure 179)


As compared to direct radiator type speaker, the advantage of horn loading is that: the soundwave 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 so does the wave front of the soundwave radiated from the diaphragm (cone) that coupled to the horn. The radiating resistance is high, the amplitude of the vibrating diaphragm is reduced and the efficiency of transformation is high. (See Figure 180)

Figure 180

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 181)

Figure 181

LF unit is a L15/75/12Z 15-inch cone type driver.

  • Light and rigid cone with high compliance surround and soft spider. The bandwidth is wide good for 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 182 and 183)

L15/75/12ZFigure 182

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 throast is 1.4-inch (35mm)
  • y30 high flux strontium ferrite is employed and the magnetic structure weights6.05kgs.

(See Figures 184 and 185)

Figures 184 Figures 185

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 186)

Figure 186

The horn coupled to the H3/75/03Z is made of fiberglass reinforced plastic.


Crossover Network

M-115 seldom used individually, it always used in group of four or more as stage monitor along the edge of the stage. Besides, the sensitivity of HF unit (108, 5 dB W/M) is much higher than the LF unit (97.5 d W/M). The difference is more than 10 dB. The sensitivity can only be 97.5 d W/M if a passive crossover network is built-in. It is no sense in sacrificing the 10 dB sensitivity. Furthermore, any passive crossover network has an insertion loss. The actual sensitivity would be less than 97.5 d W/M. Therefore, M-115 does not fitted with a built-in passive crossover network. It is recommended to use external speaker processor with equalization and delay functions such as iBO D-24 (2 in 4 out) digital speaker processor.


Applications and Technical Specifications

M-115 mainly used as stage monitor but due to its flexibility in placement, it may be used, at the user’s discretion, as the main speaker of small sound reinforcement systems.


Technical Specifications and diagrams (See below)



50 Hz ~ 16 KHz (±34 dB )/ 38 Hz ~ 19 KHz(-10 dB)


HF: 108.5dB(1.5 KHz~20 kHz)

LF: 97.5 dB(50 Hz~1.5 kHz)


8 Ohm


HF:150 W / LF: 400 W (AES)


1.5 KHz


1×15〞woofer (3″voice coil)


1×2〞exit compression driver(3″voice coil)



40゜(H) ×60゜(V)


HF: 130 dB SPL, 136 dB SPL peak

LF: 123.5 dB SPL, 129.5 dB SPL peak


466×720×462 (mm)


35 (kg)


2 Neutrik NL4MP connectors



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