XBL Speaker Technology

ADI Technology has developed a patented(1) technology for linearizing loudspeaker drivers: extreme BL Linearity, or XBL² ™ (US patent 7,039,213). This new technology greatly flattens the BL curve (motor strength) over the majority of the driver’s usable excursion, with typically no net increase in production cost. The flatter BL curve means lower distortion (see Dr. Wolfgang Klippel).

The graph to the right shows an FEA comparison of the BL-versus-excursion of several driver motor topologies. These are the traditional short-gap/long-coil (SGLC), new-style long-gap/long-coil (LGLC), traditional underhung (UH), and our new XBL² motor topology. Each motor was optimized for a “typical” sub woofer Xmax value of 15.4mm one way, linear.

graph

As shown in the graph, the XBL² motor offers much flatter BL. In fact, the XBL² motor has less than a 5% BL decrease over 24mm of total excursion, while the other topologies range from 12 to 18mm for the same BL decrease. When XBL² has decreased 10%, the other motors have decreased between 18 and 23%. XBL² motors offer significant advances in BL linearity, meaning shorter coils and top plates can be used when targeting a specific operating range. Typically an XBL² motor uses the shortest voice coil length of any topology for a 10% BL variance.

graph 2

Compared to the overhung designs, the shorter coil length means more mechanical clearance in the motor and higher tolerance of rocking, meaning dual spiders are not required for high excursions. Combine this with a flatter BL curve, lower inductance, and lower moving mass and the advantages of XBL² over overhung topologies - both performance and price - are readily apparent.

XBL² reduces distortion. Keeping the BL flat means more constant motor force at excursion, which means better tracking of large-signal inputs. The graph below shows the output waveform for each of the above motors, when trying to follow an ideal ±12.7mm excursion signal. As shown, XBL² best tracks the input signal when the target excursion is still well within the “usable” excursion limits of the driver (rated Xmax of 15.4mm). As is evident, the XBL²motor is much closer to the input signal.

graph 4

This advantage translates into directly measurable and audible reductions in distortion. For the example motors analyzed in this paper, the distortion figures are given for ±10.8mm excursion (70% of Xmax). The XBL² motor has less than 30% of the distortion present in the other motors. graph 3

XBL² motors are useful for all audio transducers. While this example has focused on woofers, the advantages are also applicable for midranges and tweeters. In fact, the low inductance and moving mass of this motor are extremely beneficial in wide band transducers. Typically, XBL² will halve the inductance of a comparable-excursion overhung motor, which can result in adding a full octave of extension on the high end. Add in the lower moving mass from the short coil, and the driver designer has a greater degree of flexibility in driver creation.

advantages

XBL² represents a major step forward in loudspeaker design. To show its production viability, Adire Audio has implemented this technology in several loudspeakers, including their Brahma series car audio subwoofers which has a DUMAX-verified Xmax of ±27.3mm with only a 1.1” long voice coil. Most of our products here in RAW Acoustics use this technology from ADI Technology

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