ET-120 Core transducer module

EESM Coaxial Transducer

A driver taken apart and looked at

The EESM coaxial transducer is the common building block behind every BitDiamond product. It integrates magnetless Lorentz-force drive and active magnetic levitation into a single 120 mm coaxial module: the voice coil floats inside an actively controlled closed-loop magnetic field, and the diaphragm uses a CVD diamond / CNT airbag-foam composite sandwich structure that pushes the first breakup mode beyond 35 kHz. The diamond outer skin reaches a sound speed of 17,320 m/s and a Young’s modulus of 1050 GPa, providing absolute stiffness, while the ultra-light airbag-foam core has a density only one fifth that of a conventional paper cone. Together they resolve the diaphragm’s physical contradiction — rigidity and internal damping cannot both be had — at the level of materials.

Book a listening session How it works

Principle and structure deconstruction of the industrial 5-inch EESM test unit

Specifications

Diaphragm material: CVD diamond / CNT airbag-foam composite
Diamond outer-skin sound speed: 17,320 m/s
Core layer density: 1/5 of a conventional paper cone
First breakup mode: > 35 kHz
Total harmonic distortion: < 0.005%
Per-driver stroke: X_max ≤ 1 mm
Effective radiating diameter: 125.0 mm
Acoustic span: 2 kHz – 100 kHz

Design notes

Magnetless Lorentz-force drive

With the permanent-magnet gap removed, drive force is strictly proportional to input current, eliminating magnetic saturation and non-linear harmonics.

Active magnetic levitation

A microsecond-latency feedback loop compensates voice-coil position in real time, so temperature drift and manufacturing tolerances no longer turn into audible distortion.

Composite metamaterial diaphragm

The high stiffness of diamond and the high internal damping of the airbag foam are laminated into one structure, pushing the first breakup mode beyond 35 kHz.

Single-stroke micro-displacement

Long stroke is broken into the spatial energy summation of multiple drivers, buying enough sound pressure at THD < 0.005%.

Engineering diagrams

Acoustic diaphragm physics diagram: the natural opposition between rigidity and internal damping, and the CVD diamond composite metamaterial answer — Diaphragm physics: a composite sandwich structure of a CVD diamond outer skin over an ultra-light airbag-foam core

Implementation guide for acoustic metamaterials and COMSOL multiphysics simulation — Simulation validation: coupled acoustic, structural and optical fields, and the micro-displacement array strategy

Structural design diagram for the high-impedance CLD composite acoustic material — CLD constrained damping layer: composite absorption and structural decoupling design

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