Fiio FH15 In-Ear Monitor Earphones

In 2018, FiiO implemented cutting-edge technologies such as the TRISHELL chassis, the S.Turbo acoustic design, and a 10mm polymer composite driver in the FH5, which gave listeners a rich yet detailed listening experience.

After the launch of the FH5, it was widely praised by users for its excellent deep bass and high resolving ability in an affordable package. On the market for more than 50 months, the FH5 is a testament to Fiio's dedication to great sound. The FH5 was also acknowledged by the industry – winning awards at the summer and winter 2019 VGP as well as in the 2020 VGP. In 2021, FiiO launched the FH5s/FH5s Pro, with replaceable filters that allowed for more sound customization by the user. This time around, Fiio wanted to go back to the basics and take on the daunting challenge of bringing the sound quality of the FH series to new heights.

The FiiO development team chose to use carbon-based materials for the dynamic driver diaphragm, which allows for excellent transient performance. Carbon’s light weight, strong rigidity and high internal resistance means that the dynamic driver can quickly start and stop movements when responding to changes in the input signal. The high internal damping of the thousands of stacked and woven cross-fiber filaments of the carbon-based diaphragm means that the edge and the middle of the diaphragm can move together in the same direction quickly - minimizing breakup of the driver that results when different parts of the driver do not move in synchronization. This results in less distortion and ultimately clearer sound. 

For mid frequencies, the FH15 employs the custom Knowles ED BA drivers. These drivers work in conjunction with specially placed tuning holes in the shell of the FH15 which allows for lusher vocals and a more musical sound. Treble is handled by 2 Knowles RAD BA drivers, which are capable of high treble resolution and capture every last detail in the music, for a truly airy sound. These drivers ensure that you get a listening experience as if you were there with the performing artists.

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.