## 2 Materials and Methods  
The data of 6 patients who underwent comparative trials in our department between October 2021 and August 2022 were retrospectively examined. This study was approved by the Institutional Review Board of Keio University (Ethics Number 20200033). The diagnoses of the enrolled patients included external auditory canal obstruction (two cases), external auditory canal stenosis (one case), external middle ear malformation (one case), superior canal dehiscence syndrome (one case), and postoperative chronic otitis media (one case). Four of these cases were unilateral while the remaining two cases were bilateral. CC-HA optimally adjusted the gain according to the patient's hearing ability. This procedure was similar to those used for AC-HA [13]. ADHEAR was used in default mode (directivity of the microphone, howling suppression, and noise suppression) without any further fitting changes. Patients were able to adjust the volume of ADHEAR devices by turning the dial. The volume was adjusted individually to the most comfortable level for each patient. Baha was programmed using specific fitting software provided by the Cochlea Corporation according to each patient's direct bone conduction hearing thresholds obtained through the BC Direct function. CC-HA was affixed using double-sided adhesive tape to the skin of the tragus or auricular cartilage (Figure 1). ADHEAR was snugly attached to the skin of the mastoid with no hair (Figure 2). Sweat made the device easy to peel off, and therefore, the adhesion part of the seal was wiped off before its application. After confirming the hearing gain of CC-HA and ADHEAR by the sound field threshold test, the trial was performed for a month. During this time, sound localization tests, and evaluations of quality of life (QOL) using the Glasgow Benefit Inventory (GBI) were performed. Baha was worn using a sound arc for the trial (Figure 3). After confirming the hearing gain by a sound field threshold test, patients tried the device in the hospital for about an hour, then the same evaluation was performed. Figure 1: Example of ear with a cartilage conduction hearing aid (CC-HA). Profile views (left side) of a patient fitted with a CC-HA. Transducer and sound processor components of CC-HA are attached to the skin using double-sided adhesive tape. Figure 2: Example of an ear with an ADHEAR. Profile views (left side) of a patient fitted with an ADHEAR. Sound processor is attached to the skin with an adhesive adapter. Sound field audiometry was performed according to the Guidelines for Hearing Aid Fit Testing (2010), which are advocated by the Japan Audiological Society [14]. Patients were seated 1 m from the sound source speaker in a soundproof room, and the height of the speaker was the same height to the center of the patient's head. The speaker and the patient were kept at least 1 m away from the wall. A hearing aid was worn on the affected ear and the unaffected ear was masked with narrowband noise during sound field audiometry. The sound localization test was performed according to [PERSON]'s report [15]. Nine speakers were installed at equal intervals (22.5\({}^{\circ}\)) on a semicircle 1 m in front of the patient and from the left end, No. 1 (\(-\)90\({}^{\circ}\)) to No. 9 (90\({}^{\circ}\)). CCITT (Comite Consultatif International Telegraphique et Telephonique) noise was used as the sound source and it was presented twice at 60, 65, and 70 dB SPL, for a total of 54 times. The numbers answered by the patients, denoting the speakers from which they thought the sounds were presented, were recorded. Localization accuracy was evaluated using the root mean square (RMS) score. A lower score indicated a more accurate sense of direction. The sound localization test was performed only in cases of unilateral primary disease. GBI is a questionnaire that evaluates the extent to which the QOL of patients improves in association with intervention on a scale from \(-\)100 to 100 [16].