Overview

The TEAC HP-F100 FillTune is a bone conduction headphone system released in Japan in April 2007, priced at 499 USD in the US market. The system comprises two units: a bone conduction headphone using a giant magnetostrictive transducer and a dedicated portable amplifier powered by 3 × AAA batteries with approximately 10 hours of runtime. Rather than transmitting sound through air to the eardrum, the HP-F100 vibrates the temples and skull to deliver audio directly to the cochlea, leaving the ear canals fully unobstructed. The product was co-developed with Frey Inc., with TEAC handling manufacturing, after-sales support, and marketing under the “FillTune” sub-brand [4]. The headphone unit also incorporates a built-in electret condenser stereo microphone for headset use. The HP-F100 is discontinued and no longer listed on TEAC’s official website; no new-unit retail availability exists.

Scientific Validity

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The HP-F100 is a bone conduction headphone; the Harman target curve for air-conduction headphones does not apply. The applicable measurement standard for bone conduction frequency response is IEC 60318-6 using an artificial mastoid fixture. A 2009 doctoral dissertation from Georgia Institute of Technology measured the HP-F100 transducer with a B&K artificial mastoid and found the frequency response to be “relatively flat extending to approximately 18kHz” within the bone conduction measurement context, noting superior high-frequency extension compared to competing bone conduction transducers of the era [2].

However, bone conduction physics imposes a fundamental limitation that dominates the overall assessment: bone-to-cochlea transmission produces near-complete attenuation of bass frequencies below approximately 600Hz. This constitutes a severe frequency response deficit that renders bass reproduction essentially absent in practice. TEAC’s manufacturer specification of 25Hz–25kHz (+0/−3dB) for the LINE input [1] describes the electrical frequency response of the amplifier unit, not the audible output delivered at the cochlea. No THD, S/N ratio, IMD, or crosstalk data is available from any source for this product. The confirmed, physics-based low-frequency deficit yields a low measured performance rating.

Technology Level

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The HP-F100’s core technology — the giant magnetostrictive bone conduction transducer — was developed by Frey Inc., not TEAC. TEAC’s role was limited to manufacturing, marketing, and after-sales support [4]. This places the product outside TEAC’s established core competency in tape and disc equipment, and no TEAC-held patents on magnetostrictive audio transducers have been identified.

Evaluated from a 2026 standpoint, giant magnetostrictive bone conduction technology is fully outdated and superseded. The consumer bone conduction industry migrated entirely to electromagnetic and piezoelectric transducer approaches; no consumer audio manufacturer has adopted or sought to license giant magnetostrictive bone conduction technology since the HP-F100’s discontinuation, and the material remains confined to military and industrial applications. The HP-F100 system is entirely analog with no DSP processing, no software component, and no digital integration of any kind. The product was discontinued within a few years of launch without a successor model, conferring no lasting competitive advantage. The accumulation of negative factors across every dimension of the evaluation framework results in the minimum score.

Cost-Performance

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This evaluation is based solely on functionality and measured performance values, without considering driver types or configurations.

The HP-F100 is discontinued; the original US launch price of 499 USD is used as the price basis. The comparison target is the Shokz OpenMove at 79.95 USD (representative regular price from the manufacturer’s official website) [3], which provides equivalent user-facing functions: bone conduction audio playback, open-ear design with fully unobstructed ear canals for ambient sound awareness, a built-in microphone for headset use, and portable battery-powered operation.

No standardized third-party consumer audio measurements are published for bone conduction headphones as a category — standard measurement infrastructure does not cover this transducer type — so quantitative THD, S/N ratio, and crosstalk data are unavailable for both the HP-F100 and the Shokz OpenMove. For frequency response, the HP-F100 transducer measured “relatively flat to approximately 18kHz” via B&K artificial mastoid [2]; bass attenuation below approximately 600Hz is a category-level physics constant that applies equally to all bone conduction headphones and is not a product-specific differentiator between the two devices. This comparison is therefore provisional, established on the basis of functional and product category equivalence.

CP = 79.95 USD / 499 USD = 0.160

Rounded to the first decimal place, the Cost-Performance score is 0.2.

Reliability & Support

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The HP-F100 carried a 1-year warranty at launch, below the current 2-year industry standard. As a product discontinued approximately 19 years ago, all manufacturer support has ended; no parts supply, repair documentation, or service infrastructure remains accessible. The design incorporates several elements inherently prone to degradation over time: the battery compartment (3 × AAA) presents a known corrosion risk in aged battery-powered devices, the foldable mechanical headband joint is susceptible to wear, and the specialized magnetostrictive transducers have no replacement part availability.

Rationality of Design Philosophy

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The HP-F100 targets bone conduction listening for conductive hearing loss and concurrent environmental awareness; that use-case alignment has a clear, evidence-based physiological rationale.

Judged against the consumer-audio context around its 2007 launch, the basic development strategy is coherent: bone conduction hardware for general listeners was still uncommon, and combining a specialized transducer developer’s magnetostrictive element with TEAC-scale manufacturing, distribution, and support was a reasonable way to bring a niche transducer into consumer channels. Later mass-market bone conduction products largely adopted electromagnetic or piezoelectric paths; that subsequent industry direction reflects later cost and integration trade-offs, not proof that the original co-development approach was inherently irrational at the time.

The main debit to rationality is positioning copy, not transducer physics: emphasizing “HiFi” and wide electrical input bandwidth can read as promising conventional full-range listening through bone conduction, even though low-frequency bone-borne transmission to the cochlea is strongly limited relative to typical air-conduction listening—a mismatch between stated breadth of audible experience and established bone-conduction constraints.

Advice

The HP-F100 is a discontinued product unavailable through standard retail channels. Any acquisition would require the used secondary market, where units from an approximately 19-year-old design carry significant reliability uncertainty with no remaining manufacturer support.

For users seeking bone conduction headphones to address conductive hearing loss or to maintain ambient environmental awareness during audio playback, current products such as the Shokz OpenMove (79.95 USD) deliver equivalent bone conduction functionality with the addition of Bluetooth wireless connectivity, integrated amplification, IP55 water resistance, and active manufacturer support — at a fraction of the HP-F100’s original price.

All bone conduction headphones, regardless of manufacturer or price, are subject to inherent bass attenuation below approximately 600Hz due to bone conduction physics. Users expecting conventional full-range audio reproduction should consider air-conduction headphones instead.

References

[1] ManualsLib — TEAC Filltune HP-F100 Specifications — https://www.manualslib.com/manual/326971/Teac-Filltune-Hp-F100.html?page=2 — Accessed 2026-04-30 (Official TEAC product page no longer accessible; ManualsLib spec sheet is best available substitute)

[2] Stanley, R.M. (2009) — “Measurement and Validation of Bone-Conduction Adjustment Functions in Virtual 3D Audio Displays,” PhD Dissertation, Georgia Institute of Technology — https://smartech.gatech.edu/bitstream/handle/1853/29754/stanley_raymond_m_200908_phd.pdf — Accessed 2026-04-30 — Measured with B&K artificial mastoid fixture

[3] Shokz — OpenMove Product Page — https://shokz.com/products/openmove — Accessed 2026-04-30 — Current price 79.95 USD

[4] AV Watch — TEAC HP-F100 Product Announcement (Japanese) — https://av.watch.impress.co.jp/docs/20070413/teac.htm — Accessed 2026-04-30

(2026.5.6)