QU-115

QU-115 is a 2-way, 2-element full range speaker.

The enclosure

QU-115 is a 2-way, 2-element full range speaker. The enclosure is very small but with large output, up to 125dB SPL (131dB peak). At top view, the enclosure is not a normal four faced square or rectangular or trapezoidal, it is five faced enclosure. This design is suitable for a variety of placements. It may be placed up right or laid flat on the stage to used as a stage monitor. (See Figure 149)

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 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 150)

Figure 150

HF is horn loaded

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 151)

Figure 151

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 using 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.

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 Speakon NL4MP connectors for amplifiers and for loop-in and loop-out to additional enclosures. (See Figure 152)

Figure 152

The Components

LF unit is a L15/63/05CZ 15-inch cone type driver.

  • The frame is stamped iron
  • The cone is light and very rigid. The whole vibrating system including the surround and the spider is soft with very good low frequency response
  • The magnet is made from y30 high flux strontium ferrite weights 4.2kgs
  • The diameter of the voice coil is 2.5-inch edge wound with flat copper wire on a Kapton former (See Figure 153)

Figure 153

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
  • 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.
  • The horn that coupled to the H1/34/05Z driver is made of fiberglass reinforced plastic. (See Figure 154 and 155)

Figure 154 and 155

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.

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 156)

Figure 156

The Crossover Network

The goal of Q Series speakers are to design a series speaker of very good tonal quality for small to medium scale activities not necessarily with very high output SPL. Only small number of speaker needed for each activity. If external speaker processor is used instead of built-in passive crossover network, a greater number of power amplifiers would be needed. The operating cost would be high. Besides, the price of a high quality digital speaker processor is higher than a power amplifier. The advantage of cost effectiveness of small to medium size sound reinforcement system is lost. Therefore it is decided that a passive cross network would be built-in the Q-115. Crossover frequency is 3.2KHZ. High quality metal film capacitors and air core inductors are used where possible. All elements are carefully checked before assembling, those sub-standard or exceeding tolerance would be rejected and return to the suppliers.

 

Applications and Technical Specifications

QU-115 can be used in conjunction with any of the QU-112, QU-181B and QU-218B as the main speaker of small to medium sound reinforcement system for assembly hall, multi-function hall or other audio visual activities or used as stage monitor or as auxiliary speaker for a large sound reinforcement system.

 

Technical Specifications and diagrams (See below)

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