DSL prescriptive targets for bone conduction devices: adaptation and comparison to clinical fittings

Figures & data

Figure 1. The TU-1000 skull simulator (left), shown alongside the commercially available SKS10 skull simulator (right) developed for use within a commercial hearing aid analyser in clinical practice.

Table 1. Computational stages in the DSL v5.0 air conduction prescription, and adaptations within the DSL-BCD prescription.

Stage	Sub-stage	Air conduction prescription	Percutaneous BCD prescription
Assessment	Lower limit	Detection thresholds in dB HL.	Detection threshold measured through the abutment in dB dial level (non-standard).
	Transformation	Transform HL to 2cc SPL.	Transform dial level to dB FL on a skull simulator.
		Transform to ear canal SPL	Transform to on-head FL.
	Interpolation	Interpolate to provide data at one-third octave centre frequencies.	Same.
	Upper limit	Predict or measure upper limits of comfort in ear canal SPL.	Same, but further compressed and limited to the device-specific maximum output.
	Mapping	Apply a target generation procedure that maps inputs to outputs.	The DSL-BCD prescription initially used the same shaping (v1.0) but a modified shape was developed in this paper. Modified targets use a low-frequency cut (v1.1).
	Listener customisation	Customize for the listener type and listening situation.	Same.
	Device customisation	Customize for the device’s channel structure. Convert to linear gain if required.	Same.
	Verification customisation	Convert for use with other test signal and/or measurement types. Account for venting.	Venting is not a factor in BCD, so venting corrections have been omitted.

Figure 2. Device-specific maximum output curves for six bone-anchored hearing instruments of varying makes, models and fitting ranges. All curves were measured with a 90 dB pure tone sweep, with output force levels (dB) measured on a TU-1000 skull simulator.

Figure 3. Panel a: A BCD fitting for an average patient, for DSL-BCD 1.0 and 1.1 targets. Panel b: The same display, for patient whose fitted device provided an unwanted resonant peak at 1000 Hz.

Figure 4. Aided Speech Intelligibility Index (SII) values for 39 patients who use bone conduction devices worn on an abutment. SII values are displayed as a function of the Four Frequency Pure Tone Average hearing threshold levels expressed as dB FL at the user’s abutment. A non-linear fitted trendline is also displayed (–).