Technology-limited and patient-derived versus audibility-derived fittings in bone-anchored hearing aid users: a validation study.

OBJECTIVES: Current approaches to fit bone-anchored hearing aid (Baha) rely heavily on patient feedback of "loudness" and "sound quality." Audiologists are limited to this approach for two reasons: (1) the technology in current models of Baha does not allow for much fine-tuning of frequency response or maximum output on an individual basis and (2) there has not been a valid approach to verify the frequency response or maximum output on an individual basis. The objectives of this study are to (1) describe an alternative approach to fit Baha, an "audibility-derived (AD)" fitting, and (2) test whether outcomes improve with this new fitting compared with the current "patient-derived (PD)" fitting. DESIGN: This study used a repeated measures design where each subject experienced both the AD and PD fittings in random order. Subjects were tested on a variety of outcome measures including output levels of aided speech, hearing in noise test (quiet and in noise), consonant recognition in noise, aided loudness, and subjective percentage of words understood. RESULTS: Electromechanical testing revealed significantly higher aided output with the AD fitting, especially in the high frequencies. Subjects performed significantly better in all outcome measures with the AD fitting approach except when testing aided loudness and subjective perception for which the differences were nonsignificant. When the input levels to the Baha were soft, advantages for the AD fitting were emerging on these tests, but they did not reach significance. CONCLUSIONS: This study presents a more objective, fitting approach for Baha that leads to better outcomes in the laboratory. The next steps will be to test these fittings in the real world and to make the approach generally available to clinicians fitting Bahas.

A comparison of three approaches to verifying aided Baha output.

OBJECTIVE: The objective of the present study was to compare three methods of estimating the audibility of aided speech using the Baha. SUBJECTS: 23 Adult Baha users with primarily bilateral conductive hearing loss were recruited from the Bone Conduction Amplification Program at the Institute for Reconstructive Sciences in Medicine in Edmonton, Alberta, Canada. METHODS: A test Baha was set to each subject's preferred listening level. The same Baha was used to assess the audibility of the long-term average speech spectrum (LTASS) for each of the following three approaches: 1) Aided soundfield thresholds, 2) Real Ear SPL, and 3) Real Head Acceleration Level. RESULTS: Significant differences were discovered between the three approaches. Aided soundfield thresholds consistently over-estimated the sensation level of aided speech. The Real Ear SPL approach provided reasonable estimates in the mid-frequencies. However, low- and high-frequency estimates for the Real Ear approach have significant limitations. CONCLUSIONS: The Real Head Acceleration Level appears to be the most accurate method of determining aided audibility with the Baha.

The balanced electromagnetic separation transducer a new bone conduction transducer.

Conventional bone conduction transducers, which are relatively large, suffer from poor performance at low frequencies. A new type of electro-dynamic transducer, the balanced electromagnetic separation transducer (BEST), was developed to improve the performance of the conventional transducers. By using a balanced suspension principle, the quadratic distortion forces, as well as the static forces between the vibrating parts, are principally counterbalanced. Both the distortion and the size of the transducer can therefore be considerably reduced. Moreover, the static and dynamic magnetic fluxes are separated, except in the air gap regions, giving a more efficient transducer. For example, in comparison with a conventional B71 transducer, a prototype of the BEST has: Lower total harmonic distortion (THD), by 20-25 dB, and improved sensitivity by 10-20 dB for 100 to 1000 Hz and by 2-10 dB for 1 to 10 kHz. From a clinical point of view, the BEST offers a chance to measure bone thresholds, at 250 and 500 Hz, which are reliable at hearing levels not possible before. For example, at 250 Hz the BEST has 23 dB higher sensitivity than the B71; the THD is improved from 61% (B71) to 3.3% (BEST) at 40 dB HL (ISO 389-3, 1994).

Sound stimulation via bone conduction for tinnitus relief: a pilot study.

For some patients suffering from tinnitus, an external sound stimulator can offer some mitigation. Based on our positive experience with the bone-anchored hearing aid (BAHA), it seems possible to transmit a masking or habituating sound via bone conduction. A potential advantage of bone-conducted sound is that it is transmitted to the cochlea without affecting the normal hearing via the external and middle ear. The present pilot study, on patients who use a conventional BAHA and who experience mild-to-moderate tinnitus, shows that bone-conducted sound has the potential to relieve tinnitus in the same way as air-conducted sound. It was also found that these patients, having a significant conduction hearing loss, required conventional sound amplification via a BAHA simultaneously with the stimulus provided by the bone-anchored sound stimulator (BASS). Further studies on patients with more severe tinnitus must be conducted in order to justify the use of a BASS for tinnitus relief.