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The Coaxial Transducer

High Frequency Horn Driver
DriverLow distortion is very important in not only studio monitor speakers but in all loudspeakers, especially at high frequencies where listeners are more sensitive to sound details and character.  Although important, seldom do you see published distortion figures for loudspeaker systems.  Since our ears are sensitive to the 2nd and 3rd harmonic distortion products at higher frequencies, it is important to minimize these distortion products in the HF drivers. One way to accomplish this at low and high power levels is to use a very efficient HF driver. As explained before, horns are known for their high efficiency and pattern control benefits and when combined together with a compression driver and the proper EQ response, distortion levels are substantially reduced, especially when compared to direct radiator type HF drivers producing the same sound pressure levels.

Figure 6 illustrates the low distortion curve of the Q12 studio monitor when the speaker is driven at 10 watt and 100 watts with a sine-wave signal input. This signal approximates a music signal equivalent to almost double the power. Distortion levels that are 40 dB down represent a distortion level of 1%.  Generally 10% is audible.

 
Harmonic Distortion
Fundamental = Black, Red = 2nd, Green = 3rd
SPL 

The equator Q Series line uses titanium compression drivers together with constant directivity horns to achieve a believable "you're there" live sound quality.

Titanium is an excellent material for tweeter diaphragms because it has an incredible weight to strength to weight ratio compared to other metallic materials. Its strength to weight ratio is four times greater than aluminum. It does not fatigue easily and it can be made very thin which reduces its overall weight. This results in extended high frequency response, improved transient response and increased sensitivity.

Controlling the HF energy to the listener is important in a studio monitor. Directing the sound to the listener minimizes the high frequency unwanted reflections generated from indirect sound information. The indirect sound information that usually generates and builds off the side walls, ceiling and floors re-enters the path of the direct sound energy, making it difficult to hear clearly the main information emitted from the loudspeaker. A horn provides a means to control the HF energy path, keeping it away from the side walls, ceiling and floors, allowing the listener to hear the direct sound information from the loudspeaker clearly and as one.

All equator Q Series horns are designed as 90H x 40V constant directivity devices which provide a smooth frequency response and constant coverage pattern in both the horizontal and vertical coverage angles. A uniquely designed throat section provides extended horizontal high frequency response coverage compared to typical horns.

Generally speaking, sharp transitions or quick changes in path flow direction when working to guide high frequency energy can cause aberrations in the frequency response. Therefore the corners of the horizontal and vertical horn walls in the Q Series horns have been blended into a gradual transition to provide better summation between coverage angles and smooth out overall frequency response. The horn material is a molded formulated polyurethane based material that is acoustically damped and treated to eliminate unnatural resonant properties.
 
Coaxial Woofer
 
DriverReproducing the midrange frequencies when using large woofers is a problem that transducer design engineers are faced with. The engineer is tasked with providing good low-end which requires a flexible surround with good excursion capabilities. On the other hand, to achieve good high-end response, the surround needs to be firm and light-weight so it remains in phase with the cone material or anomalies in the woofers frequency response will occur. In order to achieve all these attributes, Equator engineers turned to a specially treated durable polyester half-roll surround material which exhibits good excursion properties, has a good weight-to-strength ratio and holds its shape to produce good high frequencies and remains under control at high sound pressure levels. To maximize driver linearity and power handling the design of the surround and spider geometry were set to provide an optimum excursion to Thiele-Small parameter relationship.

Cone material used for the coaxial driver consists of a blended fiberglass/pulp mixture to add dampening and additional strength as well as reduce cone break up. A straight-sided cone shape was selected to minimize any decoupling of acoustic energy with the surround or voice coil energy. Bass response is fast and tight; midrange response is clean, accurate and natural sounding.

When a driver is reproducing midrange energy such as in vocals or keyboard information, the woofers voice coil can get very hot. To help cool the voice coil and reduce power compression, Equator engineers designed a performance enhancing top plate for the woofer's magnet assembly. The result is better midrange performance and a cooler running voice coil. Additional improvements include higher BL parameters and better power handling, thereby allowing the speaker drivers to optimally perform in a compact, efficient enclosure package.

The coaxial driver basket is made of a CAD cast aluminum structure which provides support for the magnetically shielded motor and attached compression driver. Aluminum is a good heat conductor thus the basket also serves as a heat sink to the top plate of the magnet structure allowing the loudspeaker to dissipate heat fast and the speaker to run cooler at high power levels. Each coaxial driver is fully magnetically shielded so the loudspeakers can be used near recording consoles or CRT displays. Each ferrite motor structure is also equipped with a back EMF distortion reducing ring to further enhance driver performance and sound quality.
 
Amplifier Technology

Each Q Series studio monitor utilizes advanced digital amplifier technology. The result is state-of-the-art performance and at high efficiency.  Conventional Class D amplifiers have been known to be sensitive to imperfect power supplies, prone to distortion, timing errors and impedance load dependencies in the output filter which causes frequency response variations. Our technology solves these problems in various ways. Distortion is suppressed by feeding the PWM signal back into the Multivariable Enhanced Cascade Control (MECC) system. The MECC compares the PWM signal with the original input signal and compensates for any differences and suppresses any distortion introduced in the power stage. By modulating the PWM signal using its patented Controlled Oscillation Modulation (COM) technology, it eliminates the problems associated with imperfect power supplies.

To compensate for output filter load impedance and frequency response variations, the amplifier feeds the analog signal after the output filter back into the MECC. By utilizing COM and MECC technology, the amplifier can use a lower switching frequency, thus offering as high as 96% efficiency and lower distortion than conventional Class D amplifiers. The result is an amplifier that is efficient, clean, fast, accurate and not harsh sounding.

Each amplifier has thermal, under-voltage and short circuit protection. A metal back box shields the outside world from stray EMI. The Q8 and Q10 model have universal mains ranging from 85V to 265V while the Q12 and Q15 models require internal jumper change at our factory for operation with 115V or 230V power source.