M-112

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 with four-face profile, it is a five-face profile. (See Figure 167)

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 168)

Figure 168

HF Section is horn loaded. A horn specifically designed for M-112 with a directivity of 80o (H) X 60 o (V). It is a constant directivity horn and is rotatable. No matter it is placed up right or laid flat, always maintain an 80o (H) X 60 o (V) pattern. (See Figure 169)

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 170)

Figure 170

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 171)

Figure 171

The Components

LF unit is a L12/75/09Z 12-inch cone type driver.

  • The frame is die-cast alloy
  • The cone 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 6.15kgs
  • The diameter of the voice coil is 3-inch edge wound with flat aluminum wire on a Kapton former.

(See Figure 173)

Figure 173

HF unit is a H1/34/05Z compression driver

  • The diameter of the diaphragm is 1.25-inch and made is of ultra thin titanium plus the edge wound flat aluminum wire is also very light. The whole mess of the diaphragm/voice coil assembly is very small, efficiency is very high. The high frequency can be extended to 22KHZ
  • The diameter of the throat is only 1.0-inch, the cross section is much smaller than that of the area of the diaphragm. There is a high pressure zone built up between the diaphragm as the phase plug whose total cross sections of the slits are about equal to the cross section of the throat
  • 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, and there are therefore phase difference occurred.
  • 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 176)

Figure 176

  • The horn that coupled to the H1/34/05Z driver is made of fiberglass reinforced plastic.

(See Figure 174 and 175)

Figure 174Figure 175

 

Crossover Network

M-112 most often used individually as stage monitor. The difference of sensitivity between LF unit and HF unit is not great. A passive crossover network is built-in. Crossover frequency is 2.4KHZ. All iBO passive crossover networks use precision metal film capacitors and air core inductors where possible. All components are carefully checked before assembling. Any sub-standard or exceeding tolerance would be rejected and return to the suppliers.

 

Applications and Technical Specifications

M-112 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)

FREQUENCY RESPONSE

63 Hz ~ 20 KHz (±4 dB )/ 50 Hz ~ 22 KHz(-10 dB)

SENSITIVITY (1W/1m)

99dB(63 Hz~20 kHz)

NOMINAL IMPEDANCE

8 Ohm

POWER RATING

350 W (AES)

CROSSOVER FREQUENCY

2.4 KHz

LF COMPONENTS

1×12〞woofer (3″voice coil)

HF COMPONENTS

1×0.75〞exit compression driver(1.25″voice coil)

 

NOMINAL COVERAGE

80゜(H) ×60゜(V)

CALCULATED OUTPUT (MAX)

124 dB SPL, 130 dB SPL peak

DIMENSIONS (H×W×D)

635×370×357 (mm)

WEIGHTS

23 (kg)

CONNECTORS

2 Neutrik NL4MP connectors

 

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