PH-115 is a 2-way, 2element full range speaker. The enclosure is very small but with high output, up to 124.5dB SPL (130.5dB 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 use as a stage monitor. (See Figure 130)

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 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 131)


Figure 131

The HF section is a horn loaded design, a 80o (H) X 50 o (V) constant directivity horn is specifically designed for PH-115. The geometry of the horn is so designed that the dispersion angle would not be narrowed as the operating frequency raise.


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 132)

Figure 132

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 133)

Figure 133

The components

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

  • 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 134)

Figure 134

HF unit is a H2/44/01Z compression driver. The driver is coupled to a H8050 constant directivity horn which is made from die-cast ABS

  • The diameter of the diaphragm is 2-inch which is a very light and thin titanium. The voice coil is edge wound with feat aluminum wire on a Kapton former. The efficiency is very high and the high frequency response is very good
  • The throat diameter of H2/44/01Z is 1-inch whose cross section area is about equal to the total cross section areas of the circumferential patterned slits of the phase plug but less than 1/3 of the diaphragm. When the diaphragm vibrates, there is a high pressure zone built up between the diaphragm and the phase plug. The radiation impedance is high as well as the efficiency. (See Figure 135)

  • 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 136)

Figure 136

The Crossover Network

The goal of PH 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 PH-115. Crossover frequency is 3 KHZ. 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

PH-115 can be used in conjunction with any of the PH-110, PH-112 and PH-118B 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)


60 Hz ~ 22 KHz (± 4 dB )/40 Hz ~ 22.5 KHz(-10 dB)


98 dB(220kHz~22 kHz)


8 Ohm


450W (AES)


3 KHz


1×15〞woofer (3″voice coil)


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



80゜(H) ×50゜(V)


124.5 dB SPL, 130.5 dB SPL peak



720×472×385 (mm)


27 (kg)


2 Neutrik NL4MP connectors


Flying tracks (rear top)


Chick here for product PH-115