Balance between bass, mids, and treble as well as clarity are the ideal sound goals of many audiophiles, but this is easier said than done with multi-driver hybrid IEMs. This is because the multiple drivers naturally produce frequencies that overlap and interfere with each other. Thus, crossovers that divide the frequencies to be produced between the drivers are needed in order to achieve clear, coherent sound.
Thus, the RC circuit design is used to manage the crossover in the higher frequencies, with the treble driver with the higher resonant frequency being used as the high-pass filter. For managing crossover of the lower frequencies, the traditional low-pass filtering LC circuit requires components that take up too much space in the naturally small in-ear monitors. However, this did not stop FiiO from finding a solution to ensure bass frequencies produced by the drivers were of high quality. The development team worked with the understanding of the basic principle of sound waves. As these waves travel after being produced by the drivers, they will be attenuated when hitting other surfaces – the higher the frequency of the sound wave, the shorter the wavelength, and thus the faster the attenuation. The FiiO development team worked with this basic principle and developed the patented S.Turbo acoustic design*.
*Patent No: ZL2018211416279
To hit our mid and treble sound goals for the FH15, we filter the higher frequencies produced by the bass driver in a low- pass filter, the S.Turbo acoustic design. This design reduces frequency response overlap between the bass and mid drivers for more coherency between the different drivers and a more balanced frequency response, for a cleaner and more natural sound.