The Steranko Traveller is a new, fully custom made two drivers per ear IEM. Each side consists of a 10mm dynamic driver with a diaphragm made of a sensitive Bio composite material and an inhouse planar driver developed for this IEM. The casing is metal made from a specially developed alloy consisting of Silver, Nickel and Copper finished with a special coating for longevity. It will be limited to 80.
The vision for making this IEM is to create the smallest IEM made for someone who travels and, on-the-road, but wants the convenience of a beautifully crafted and high-quality sound in a small form factor which is not only comfortable but also durable to take knocks. We believe that something durable should also be made of the highest quality materials.
"We believe that something durable should also be made of the highest quality materials, crafting a high-quality sound in a small, comfortable form factor."
SOUNDCHECK 20 FULL TEST ANALYSIS
This is an earphone acoustic performance test conducted using the industry gold standard Listen SoundCheck 20 software, covering 3 groups of core data that comprehensively address the three key indicators of frequency response, consistency, and distortion. The following is a professional analysis combined with the positioning of the "Steranko Traveller".
I. Curve Characteristics and Listening Experience
Frequency Response
Low Frequency (20Hz~200Hz)
The curve gradually decreases from around 125dB, with no excessive prominence in the 20~100Hz range, indicating excellent low-frequency extension and deep bass. The listening experience features solid and full low frequencies with sufficient atmosphere and strong spatial sensation, suitable for reproducing pop music, electronic music, and film/TV sound effects.
Mid Frequency (200Hz~5kHz)
The overall full-band response is flat, with only a very slight dip around 6-8kHz. Vocals are naturally transparent with high fidelity; not overly sibilant, nor muffled or muddy. Compatible with the vast majority of scenarios including vocals, instruments, and ACG content.
High Frequency (5kHz~20kHz)
Natural roll-off after 10kHz, a small peak around 15kHz, and attenuation of approximately 30dB at 20kHz — typical high-frequency characteristics of a high-quality earphone. The listening experience features smooth, non-fatiguing highs with adequate resolution and natural detail reproduction, suitable for everyday pop music, easy listening, and classical music.
Left/Right Tracking
The full-band curve is almost hugging the 0dB line, with only minor fluctuations of <2dB above 10kHz, indicating highly consistent sensitivity and frequency response between left and right channels. Stereo imaging is precise, the sound field is balanced, and there will be no issues of uneven left/right volume or image shifting — a hallmark of high-end earphone quality.
Distortion (Total Harmonic Distortion, THD)
Low Frequency (20Hz~200Hz)
THD is stable below 1%, with excellent low-frequency distortion control. The listening experience features clean low frequencies without breakup or muddiness, with solid dynamic performance.
Mid Frequency (200Hz~5kHz)
A resonance peak of approximately 3.2% appears at 1kHz, which is an inherent characteristic of dynamic driver units and is a normal phenomenon. THD in the remaining frequency bands is <2%, with pure vocal reproduction, no obvious distortion, and a natural and pleasant listening experience.
High Frequency (5kHz~10kHz)
THD rapidly falls below 1%, with good high-frequency resolution. The sound is clear and non-fatiguing, with clear detail reproduction.
| Indicator | Performance Rating | Summary |
|---|---|---|
| Frequency Response Curve | Excellent | Balanced three-frequency response: solid low frequencies, transparent mids, smooth highs, suitable for all scenarios |
| Left/Right Channel Consistency | Excellent | Precise stereo imaging, balanced sound field, excellent quality control |
| Total Harmonic Distortion | Pass (Mainstream High-End Level) | Pure sound, clean low frequencies, natural vocal reproduction |
SoundCheck 20 is the gold standard testing software in the global audio industry, with authoritative and reliable data, and is a mandatory testing item before earphones leave the factory. The THD peak at 1kHz is an inherent characteristic of dynamic driver units, not a quality issue — this resonance peak is universally present in high-end dynamic earphones, differing only in peak level. For the frequency response of the "Steranko Traveller", fine-tuning via EQ is possible: slightly boost high frequencies above 10kHz to enhance resolution; or slightly boost low frequencies around 80Hz to enhance atmosphere and suit personal listening preferences.
II. Basic Principles of Earphone Acoustic System
The acoustic system of the Steranko Traveller earphone is a miniature closed acoustic system. Its working principle is as follows: electrical signals drive the diaphragm to vibrate and generate sound waves, which are transmitted to the human ear canal through the front cavity and sound outlet. Meanwhile, the rear cavity adjusts the low-frequency response through acoustic tuning structures (vent holes, damping meshes) to achieve balanced full-frequency output. The acoustic performance of the earphone is mainly determined by three core indicators: frequency response characteristics, total harmonic distortion (THD), and sound field uniformity. Among them, frequency response is the core metric for sound quality, directly affecting the clarity, atmosphere, and fidelity of sound.
Governing Equations for Acoustic Simulation
Where:
- p = sound pressure (Pa)
- ρ₀ = air density, taken as 1.21 kg/m³ at room temperature
- c₀ = speed of sound in air, taken as 343 m/s at room temperature
- ω = angular frequency, where ω = 2πf and f is the sound wave frequency
Sound wave propagation inside the earphone follows the Helmholtz wave equation, expressed in the frequency domain as:
For miniature acoustic systems such as earphones, the effects of viscosity and thermal losses on mid-to-high frequency response must be considered. The thermoviscous acoustic equations are used to correct the governing equations:
jωρ₀CₕT = ∇·(k∇T) + α₀T₀jωp p = ρ₀RT
Where:
- v = particle velocity
- σ = stress tensor
- Cₕ = specific heat capacity at constant pressure
- T = temperature variation
- k = thermal conductivity
- α₀ = thermal expansion coefficient
- T₀ = ambient temperature
- R = gas constant
Core Acoustic Evaluation Indicators
- Frequency Response Characteristics: The curve of sound pressure level versus frequency, which is the core indicator of sound quality. The ideal frequency response curve for in-ear earphones should fit a target curve (e.g., the Harman curve) to ensure balanced sound across the full frequency range without obvious peaks or dips.
- Total Harmonic Distortion (THD): The ratio of the total RMS value of harmonic components to the RMS value of the fundamental wave in the output signal, reflecting the degree of nonlinear distortion of the earphone. For in-ear earphones, THD should be controlled within 1% at 1 kHz; lower distortion results in purer sound quality.
- Sound Field Uniformity: The difference in sound pressure level at different positions within the human ear canal. Higher uniformity leads to more accurate sound localization and a more natural sound field.
Simulation Principle of the Finite Element Method
The finite element method (FEM) discretizes the acoustic space of the earphone into a finite number of small elements. Using the variational principle, the Helmholtz equation is transformed into a system of linear equations. Combined with diaphragm boundary conditions, human ear coupling boundaries, and material properties, the sound pressure values at each element node are solved, and performance indicators such as frequency response and distortion of the entire acoustic system are obtained.
III. Construction of the Acoustic Simulation Model
Research Object and Geometric Modeling
This paper takes an in-ear earphone as the research object, and completes geometric modeling based on 3D scanning data. The model includes core structures such as the front cavity, sound outlet, rear cavity, tuning vent, diaphragm, and earphone shell. A simplified human ear canal model (compliant with IEC 60318-4) is also established to simulate the actual wearing coupling state.
Material and Boundary Condition Settings
- Acoustic Medium: Air is selected as the sound propagation medium, with an ambient temperature of 20°C, air density ρ = 1.21 kg/m³, speed of sound c = 343 m/s, dynamic viscosity μ = 1.81×10⁻⁵ Pa·s, and thermoviscous losses considered.
- Structural Boundaries: Solid structures such as the earphone shell, front cavity, and rear cavity are set as hard acoustic boundaries (zero normal derivative of sound pressure) to simulate total sound reflection. The diaphragm is set as a vibration boundary, with vibration velocity input as the sound source excitation.
- Human Ear Coupling Boundary: A non-reflecting boundary is set at the end of the ear canal to simulate sound propagation into the inner ear and avoid reflection interference with simulation results.
- Tuning Structure Parameters: Damping material is applied to the rear cavity vent, with the damping coefficient calibrated based on measured data to simulate the acoustic resistance effect of the tuning mesh and adjust low-frequency response.
Mesh Generation and Solver Settings
Free tetrahedral meshing is adopted, with mesh refinement applied to fine structures such as the sound outlet and vent. The maximum mesh element size is guaranteed to be less than 1/6 of the sound wavelength (for a maximum simulation frequency of 20 kHz, corresponding wavelength 17.15 mm, mesh size ≤ 2.8 mm). The final mesh contains 82,000 elements, balancing computational accuracy and efficiency. A frequency-domain solver is used, with a simulation frequency range of 20 Hz–20 kHz (the human audible range) and a step size of 1/12 octave. The PARDISO direct solver is employed with a convergence criterion of 1×10⁻⁶ to ensure stable simulation results.
IV. Simulation Results and Analysis
Verification of Frequency Response Characteristics
The simulated frequency response curve of the earphone is obtained and compared with SoundCheck measurement data. The results show that:
- The overall trend of the simulated and measured frequency response curves is consistent, with deviations within ±2 dB in the low-frequency (20 Hz–200 Hz), mid-frequency (200 Hz–5 kHz), and high-frequency (5 kHz–20 kHz) ranges, verifying the accuracy of the simulation model.
- Low-frequency band (20 Hz–200 Hz): sound pressure level gradually increases as frequency decreases, with a resonance peak near 50 Hz. Mid-frequency band (200 Hz–5 kHz): relatively flat response. High-frequency band (5 kHz–20 kHz): a peak appears near 10 kHz, followed by gradual attenuation.
- Effects of structural parameters: increasing the sound outlet diameter raises the mid-to-high frequency (2 kHz–10 kHz) sound pressure level by 3–5 dB. Increasing the rear cavity volume shifts the low-frequency resonance peak to lower frequencies.
Simulation Analysis of Total Harmonic Distortion (THD)
The simulated THD curve shows that:
- Full-band THD is controlled within 5%, with THD at 1 kHz being 0.8%, meeting the industry standard (≤1%). THD in the low-frequency band (<200 Hz) is relatively high, reaching a maximum of 3.2%. THD in the mid-to-high frequency bands is below 1%.
- Effects of structural parameters: increasing the damping of the rear cavity vent reduces low-frequency THD by 1.5%–2%. Increasing the Young's modulus of the diaphragm reduces full-band THD.
Simulation Analysis of Sound Field Uniformity
Sound pressure level distribution results show that the sound pressure level is highest at the ear canal entrance and gradually decreases with increasing depth. The full-band sound pressure level difference is controlled within 3 dB. Offset of the sound outlet position causes significant variations in sound pressure distribution, with a maximum deviation of 5 dB. Therefore, the central symmetric design of the sound outlet is critical.
V. Optimal Design of Earphone Acoustic Structure
Sound Outlet Optimization
The original sound outlet diameter is adjusted from 1.2 mm to 1.5 mm to improve mid-to-high frequency response and high-frequency extension, making the frequency response curve better fit the Harman target curve.
Rear Cavity Tuning Optimization
The rear cavity volume is increased by 15%, and the vent damping coefficient is adjusted to shift the low-frequency resonance peak from 50 Hz to 40 Hz, enhancing low-frequency atmosphere while reducing low-frequency THD to below 2%.
Diaphragm Optimization
A diaphragm material with a higher Young's modulus is used to improve diaphragm rigidity, reducing mid-to-high frequency nonlinear distortion and lowering THD at 1 kHz to below 0.5%.
Post-optimization results: full-band deviation controlled within ±1.5 dB; THD at 1 kHz reduced to 0.45%; low-frequency THD to 1.8%; sound field uniformity improved to within 2 dB.
VI. Conclusion
- The finite element method can accurately predict the acoustic performance of in-ear earphones, with simulation-measurement deviations within ±2 dB, providing an efficient digital tool for earphone R&D.
- Sound outlet size, rear cavity volume, and tuning structures are core parameters affecting earphone frequency response and distortion.
- This simulation method enables rapid iterative optimization, shortening the R&D cycle and reducing costs.
In future work, coupled simulations of active noise cancellation and the effects of wearing sealing on acoustic performance will be further carried out to realize integrated simulation and optimization of overall earphone performance.
