LA-315

 

LA-315 is a 5-element, 3 way full size full range loudspeaker system.

 

The Enclosure

Theoretical continuous line source with essentially no space at all between individual devices (loudspeaker enclosures). In practice, we can only make the devices put together as close as possible.

 

Because the physical dimension of an array’s transducers effect the interaction between the sound waves they produce. It is most important when the wave length become comparable to or shorter than the space between elements. Since the wave length of a 16 KHZ is 21.3mm which is very small relative to the spacing of the elements that product them. It is therefore the enclosure must be made flat to reduce the distance between elements.

 

Besides, the enclosures that make up the line array be put together tightly to avoid gaps between them as these gaps are non-radiating. These non-radiating areas must be minimized (See Figure 14).

Acoustically, 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 26).

Figure 26

High-frequency compression driver is coupled to a device called Compression Transfer Ribbon (CTR) which is developed by iBO specifically for the Line Array Series. This device transfer the sound wave radiated from the compression driver to plane wave. The CTR is then coupled to a horn which form part of the enclosure. The specific opening of this horn and its geometry is designed to control the directivity of the high frequencies (See Figure 15)

Figure 15

Mid-frequency section uses two 8-inch driver also coupled to the horn that form part the enclosure (See Figure 15).

 

Low-frequency section uses one 15-inch driver which is also horn loaded.

 

All these elements are arranged in an asymmetric manner and are all horn loaded.

 

The reason for choosing horn loading design is that 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, so 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 , sodoes the efficiency of transformation. (See Figure 29)

Figure 29

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. (See Figure)

Figure

The enclosure is heavily braced internally and a black powder-coated perforated 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 .

 

Components

Low-frequency section of LA-315 uses one L15/100/06Z 15-inch LF unit.

 

L15/100/06Z is developed by iBO specifically for horn loading

  • Frame is die cast alloy
  • The cone is a special formula of pulp and fiberglass. The depth of the cone is rather shallower with reinforcement ribs for better reproduction of low-frequency (See Figure 16)

Figure 16

  • Surround and spider are stiffer to increase the mechanical stiffness
  • The cone is treated with inflammation resistant agent
  • The diameter of the voice coil is 4-inch edge wound with flat copper wire on a Kapton former. (See Figure 17)

LA-315

Figure 17

  • The magnet is made from y30 high flux strontium ferrite weights 8.54kgs. Two M8/50/05Z handle the mid-frequency section is coupled to a CTR plane wave generator and the CTR is then coupled to the horn which form a part of the enclosure (See Figure 15). Low/mid-frequency sections of LA-208 use two L8/50/08PS 8-inch drivers which is developed by iBO specifically for LA-208.
  • Frame is die cast alloy
  • The cone is a special formula of carbon fiber, glass fiber and wool
  • The cone is light and thin but very rigid
  • Magnet is of high flux y30 strontium ferrite weights 3145kgs
  • The diameter of the voice coil is 2-inch edge wound with flat aluminum wire. The coil former is of Kapton. (See Figure 9 and 10)

 

  • There are several equal acoustic distance passages in the CTR. The sound wave radiated from the compression driver transfer to plane wave after passing thru these passages (See Figure 17)

The H3/75/03Z is developed by iBO featuring:

  • The diaphragm is made of titanium and its surround is Mylar. The voice coil is edge wound with feat alumimium wire, (See Figure 11 and 12) the diameter is 3-inch (75mm)
  • The diameter of the throat is 1.4-inch (35mm)
  • The slits pattern of the phase plug is of circumferential type
  • y30 high flux strontium ferrite is employed and the magnetic structure weights 6.05kgs.

The H3/75/03Z also coupled to a CTR’s.

■The Crossover Network

The sensitivity of LA-315 high frequency component (112dB w/m) is much higher than the low frequency component (100dB w/m). The difference is more than 10dB. If a build-in passive crossover network is employed, the sensitivity of LA-315 can only be 100dB w/m. It does not make sense to sacrifice the 10dB of the high frequency component. Besides, any passive crossover network have an insertion loss. The actual sensitivity of LA-208 would be less than 100 dB w/m. We decided not to employ passive crossover network for LA-315 and recommend using external speaker processors that incorporate delay and equalization functions such as iBO D-26 (2 in, 6 out) digital speaker processors.

 

Applications and Technical Specifications

Maximum (not the peak) long term SPL of a single LA-315 is 137dB (HF), 132dB (MF) and 128 (LF). Several LA-315 put together to form a line array is sufficient to cope with almost any venue such as large outdoor concert, touring, arena and stadium, theaters and discos. LA-315 can be used together with any subwoofers (LA-215B and/or LA 218B) to form a four-way system.

 

Technical Specifications and diagrams (See below)

 

Rigging

 

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