Stainless steel IEMs with Tesla Valve bass tuning

The FiiO FD15 is a single dynamic driver IEM built around a 0.54-inch (13.8mm) magnalium diaphragm with a diamond-like carbon surround. Successor to the FD5, it combines a larger vibrating area with FiiO’s patented Tesla Valve acoustic design for extended bass and a full vocal presentation. Stainless steel shells, two interchangeable tuning nozzles, and a detachable Furukawa cable with swappable plugs give you flexibility in sound, fit, and connection.

Two materials with distinct acoustic roles

The FD15 pairs a magnalium diaphragm—a blend of magnesium and aluminum—with a diamond-like carbon (DLC) surround. The rigid magnalium diaphragm helps limit distortion for clear treble, while the DLC surround combines stiffness and flexibility to control movement and reduce breakup.

More diaphragm area to move air

The 0.54-inch (13.8mm) dynamic driver provides approximately 40% more effective diaphragm area than the FD5. Its W-shaped surround also increases effective vibrating area by 30% compared with conventional diaphragms of the same size. These changes allow greater air movement, supporting a fuller presentation with more body through the midrange.

A larger voice coil and stronger magnetic field

FiiO increased the voice coil diameter from the FD5’s 0.24 inches (6.2mm) to 0.34 inches (8.6mm). The longer copper winding improves efficiency and power handling. An external magnet design increases magnet volume by approximately 69.5% and achieves magnetic flux density up to 1.5T, helping maintain control over the diaphragm during demanding musical passages.

Controlled airflow for deeper bass

FiiO’s patented F.T.B.S. Tesla Valve design uses precisely shaped channels inside the shell to manage airflow. Air moving outward encounters resistance that lowers the cavity’s resonance frequency, extending bass response. Inward airflow passes more freely to help balance internal pressure and support consistent driver movement.

An acoustic prism for consistent timing

A frontal acoustic prism sits ahead of the driver to manage the different paths sound waves take toward your ear. By addressing small timing differences, it improves phase consistency and high-frequency diffusion, supporting clear treble alongside the FD15’s vocal-focused tuning.

Two nozzles to adjust the balance

Two pairs of interchangeable sound nozzles let you tailor the FD15 to your listening preferences. The red nozzles emphasize bass and give vocals a lusher presentation. The black nozzles emphasize high frequencies, bringing treble detail forward.

A fit refined around the ear

FiiO raised the sound nozzle angle by 6.7° while maintaining its length to improve alignment with the ear canal. Curved MMCX connector housings help reduce pressure against the back of the ear, while a narrower frontal contact surface reduces friction and movement. Fourteen pairs of included ear tips provide several options for finding a comfortable seal.

Polished stainless steel shells

The closed-back shells use 316L stainless steel formed through powder metallurgy sintering. Hand-polishing and a PVD finish create a reflective surface that follows the curves of the housing. Choose Obsidian Black or Racing Silver.

A detachable cable with two plug options

The included cable combines Furukawa monocrystalline copper with Furukawa monocrystalline silver-plated copper. Four braided strands contain 480 wires in total. Expanded MMCX connectors provide a reinforced connection at each earpiece, while twist-lock interchangeable plugs let you connect to 0.14-inch (3.5mm) single-ended or 0.17-inch (4.4mm) balanced headphone outputs.

Product highlights

• Single 0.54-inch (13.8mm) dynamic driver
  
• Magnalium diaphragm with DLC surround
  
• W-shaped surround for increased effective vibrating area
  
• External magnet design with magnetic flux density up to 1.5T
  
• Patented F.T.B.S. Tesla Valve bass enhancement design
  
• Frontal acoustic prism for phase consistency
  
• Two pairs of interchangeable tuning nozzles
  
• 316L stainless steel shells
  
• Detachable Furukawa copper and silver-plated copper cable
  
• Interchangeable single-ended and balanced plugs
  
• Fourteen pairs of ear tips included
  
• Hi-Res Audio certified

Specs

• Earphone type: Single dynamic driver in-ear monitors
  
• Acoustic design: Closed-back
  
• Wearing style: In-ear with cable routed around the ear
  
• Driver diameter: 0.54 inches (13.8mm)
  
• Diaphragm: Aluminum-magnesium alloy with DLC surround
  
• Voice coil diameter: 0.34 inches (8.6mm)
  
• Magnetic flux density: Up to 1.5T
  
• Frequency response: 10Hz–40kHz
  
• Impedance: 32Ω at 1kHz
  
• Sensitivity: 112dB/mW at 1kHz
  
• Shell material: 316L stainless steel
  
• Cable: Four strands totaling 480 wires of Furukawa monocrystalline copper and Furukawa monocrystalline silver-plated copper
  
• Cable length: Approximately 3.9 feet (1.2m)
  
• Earphone connectors: Expanded MMCX
  
• Audio plugs: Twist-lock interchangeable 0.14-inch (3.5mm) and 0.17-inch (4.4mm) plugs
  
• Weight per earpiece: Approximately 0.42 ounces (12g), excluding cable
  
• Colors: Obsidian Black, Racing Silver

What’s included

• FiiO FD15 earphones
  
• Detachable earphone cable
  
• Balanced ear tips: Three pairs, S/M/L, with M pre-installed
  
• Vocal ear tips: Three pairs, S/M/L
  
• Bass ear tips: Three pairs, S/M/L
  
• Foam ear tips: Two pairs, M
  
• HS18 ear tips: Three pairs, S/M/L
  
• HB11 storage case
  
• MMCX quick-release tool
  
• Cleaning brush
  
• 0.14-inch (3.5mm) and 0.17-inch (4.4mm) interchangeable plugs
  
• Red and black interchangeable sound nozzles: Two pairs total
  
• Quick start guide