Developed through collaboration with Jerry Harvey Audio, the Astell&Kern Billie Jean are universal in-ear monitor headphones that are the first in the Siren Series to feature dual drivers in a universal-fit IEM from Astell&Kern and Jerry Harvey Audio. The Billie Jean ensures a well-balanced and wide sound stage, remarkable dynamic range, and Jerry Harvey's patented Freqphase technology.
Featuring two (low+mid and high) custom-made, balanced-armature drivers per side, the Billie Jean offers a frequency response of 20 Hz to 17 kHz. The patented Freqphase technology aligns each driver's output to be within 1/100 of a millisecond of each other; this ensures the correct time alignment and phase of the two drivers and results in highly accurate music reproduction. The special acoustic chamber sound bore design has been carefully crafted to bring up the frequency response while smoothing out the high-frequency audio signature.
A silver tinsel cable is made from copper, plated with silver, and wrapped with Kevlar for high strength and flexibility. Once inserted, the Billie Jean offers noise isolation of -26 dB, which helps keep the ambient sounds of your surroundings to a minimum. The Astell&Kern Billie Jean includes a single unbalanced 3.5mm cable, three sets of silicone ear tips, and a carry case.
Most multiple-driver IEMs suffer from phase and timing issues. Low, mid, and high drivers all have different impulse times. The higher the frequency, the faster the impulse time of the BA driver. The lower it is, the slower the response speed. This causes improper arrival times and phase shifts. The Billie Jean applies Jerry Harvey Audio's patented Freqphase technology, which uses precisely cut tube lengths for each driver to minimize the phase shift of each frequency. This allows for the high and mid-low drivers to be aligned to 1/100 ms for the most ideal phase curve. It ensures the correct time alignment and phase of all drivers resulting in outstandingly accurate music reproduction.
The balanced-armature drivers used in the Billie Jean are a customized BA only available from Jerry Harvey Audio and designed to bring more power with less weight. The Billie Jean offers an efficient, yet powerful, sound. Jerry Harvey Audio's Freqphase, Timephase, and Waveguide technologies allow this two-way, two balanced-armature IEM to deliver the full range of audio performance. The special Acoustic Chamber Sound Bore design has been carefully crafted to bring a wide soundstage with a wide dynamic range, without adding any interference.
The Billie Jean is over 30% smaller compared to the Michelle Limited. Its design has been optimized after a series of studies of different shapes of ear canals from both men and women of different ages. It fits and sits comfortably in your ears without bulkiness. With solid noise isolation, the universal-fit Billie Jean can be used for Pro Audio applications such as sound monitoring.
The cable used in the Billie Jean is not common copper; instead, it's a copper cable plated with silver. The cable is manufactured by first compressing the silver-plated copper wire, then flattening and rolling it into a steady interval, eventually wrapping it around Kevlar. This newly developed cable has significant tensile strength and delivers the full dynamic range of music. There is a 3.5mm unbalanced cable provided. Conventional straight cables do not handle frequent bending well; consequently, they often short out. The intertwined cable disperses the stress and offers better resilience. It's also easier to wear around the outer ears, as the cable shape can be easily adjusted for a comfortable fit.