Despite a long-standing debate on the benefit of providing gain at higher frequencies, a growing body of evidence suggests that an extended bandwidth provides more natural sound quality and better speech understanding in complex environments.1-5
Not surprisingly, hearing aid manufacturers have begun to tout the extended bandwidth of their devices in response. But, while acoustic hearing aids (AHAs) claim bandwidth capabilities of up to 10 kHz, they usually roll off at ~5 kHz6 given the physical limitations of hearing aid receivers and real-world fitting practices. Moreover, air conduction devices cause distortion in the output signal, in the form of harmonic distortion, comb filtering, spectral ripples and intermodulation distortion. At high levels, the tympanic membrane creates distortions in the signal at the stapes as well due to anisotropic properties. This is a key contributor to the common patient complaint about hearing aids, which is that they don’t sound “natural.”
Earlens was designed to overcome these limitations in providing audible gain by directly driving the eardrum. Earlens is a contact hearing solution that is the first and only nonsurgical direct drive technology. The Earlens system is comprised of a rechargeable behind the ear Processor, custom Ear Tip, and custom Tympanic Lens. Sound is digitally processed in the Processor and output as an ultra-low-power radio signal by a tuned transmission coil in the Ear Tip. This radio signal carries high fidelity audio data and power to a Tympanic Lens, which is mounted with circuitry that decodes the signal and powers a motor that drives the umbo of the malleus on the surface of the tympanic membrane, transmitting vibratory energy to the cochlea via the ossicular chain.
By creating sound without an acoustic signal, Earlens overcomes the limitations associated with hearing aid receivers. Because Earlens employs a Lens to directly activate the eardrum, Earlens is able to represent sounds much more naturally, providing the listener with much more of the full spectrum of sound. The direct coupling to the ossicular chain overcomes the impedance mismatch that limits energy transfer from the air into the ear. This advantage enables Earlens to consistently produce audible bandwidth from 100 Hz to 10,000 Hz with maximum output that increases smoothly from 500 Hz to 10,000 Hz. Measurements of the acceleration of the stapes footplate using laser doppler vibrometry confirm that directly driving the ossicular chain generates a signal at the stapes footplate that is free of distortions to the input signal.
However, this research invites a second question: do hearing impaired patients prefer the gains prescribed up to 10,000 Hz? Arbogast et al. recently explored this question in a study published in Ear & Hearing. To learn more, read the full paper.
- Carlile S,SchonsteinD. Frequency bandwidth and multi-talker environments. Presented at the 120th Convention of the Audio Engineering Society. 2006; 118:353-363.
- Turner CW, Henry BA. Benefits of amplification for speech recognition in background noise.JAcoust Soc Am. 2002; 112:1675–1680.
- Hornsby BW, Ricketts TA. The effects of hearing loss on the contribution of high- and low-frequency speech information to speech understanding.JAcoust Soc Am. 2003; 113:1706–1717.
- Plyler PN, Fleck EL. The effects of high-frequency amplification on the objective and subjective performance of hearing instrument users with varying degrees of high-frequency hearing loss.J Speech Lang Hear Res.2006; 49:616–627.
- Levy, SC, Freed DJ, Nilsson M, Moore BC,PuriaS. Extended high-frequency bandwidth improves speech reception in the presence of spatially separated masking speech. Ear Hear. 2015; 36: e214–e224.
- McElveen J, Gantz B, Perkins R, Murray M, Syms CA, Chen DA, Arriaga M, Mehta R, Levy SC. Overcoming High-Frequency Limitations of Air Conduction Hearing Devices Using a LIGHT-DRIVEN Contact Hearing Aid. Poster presentation at TheTriologicalSociety, 120th Annual Meeting at COSM, April 28, 2017; San Diego, CA.