Hearing Aid Prescriptions

The initial part of a hearing-aid fitting is typically performed using a prescriptive approach. Calculations, most often based on hearing threshold levels, are used to derive hearing aid settings that are appropriate for a large number of hearing aid users with the same audiogram. This initial setting may later be fine-tuned to account for individual loudness growth, practical limitations, or individual preferences. A number of studies addressing hearing aid prescriptions have been performed at ORCA Europe, both for verifying existing prescriptions and for examining prescription variants with selected groups of hearing aid users.

Discrepancy between Real Ear Measured and NOAH module predicted gain

Aim

The aim of this project was to investigate and analyze the differences between gain targets provided by a number of hearing aid manufacturers, and actual individual gain measured with Real Ear Measurement (REM) in a number of ears.

Main Outcomes

The individually measured gain was compared to the manufacturers “target gain” in the fitting software. We concluded that, for the estimated real ear targets from the manufacturer, the accuracy was high for ears with acoustical properties similar to those of an ear simulator and when a "typical" REUG was measured. We also saw that some devices were more appropriate for specific ears than others. To know which device to use and how much gain really is provided, it is essential to verify the hearing aid gain in the ear when fitting hearing aids.

Publications and Presentations

TeMA Hörsel (National conference for Audiologists, Engineers and ENT specialists), Linköping (Sweden), 2012.

High-frequency hearing 

Aim

The primary aim of the study was to explore high frequency hearing thresholds (from 8-20 kHz) for 10 normal hearing participants and 34 participants with mild to moderate hearing losses. Knowledge about the high-frequency thresholds was intended to be used for fitting hearing aids with extended bandwidth and to evaluate the potential benefits of these hearing aids.

Main Outcomes

The collected data showed, aligned with the literature, that hearing thresholds in the high-frequency range are deteriorating already at a young age, compared to the thresholds in the frequency area up to 8 kHz. There were larger between-subject variations for the high-frequency range than for the standard frequencies, especially for the normal hearing group. Audiograms measured at the standard frequencies were relatively similar, but showed large variations for the high frequencies. Hence, it was difficult to predict the high-frequency thresholds based on the traditional audiogram. Furthermore, the testing equipment showed some limitations regarding limited dynamics and increase in noise floor at the highest tested frequencies. This needs to be considered when measuring high-frequency hearing.

Publications and Presentations 

Larsson, J. H., S., Bergsten, A-I., Bergman, N., Smeds, K. (2010). "Högfrekvenshörsel- data och några mättekniska funderingar." AudioNytt 37(4): 2.

Audionomdagarna (National Swedish conference for Audiologists), Västerås (Sweden), 2010.
 
Hearing aid amplification at low input levels

Aim

An important hearing aid parameter for determining gain for soft sounds is the compression threshold (CT). Previous research using fast-acting single-channel hearing aids indicates that most hearing-aid users prefer a moderate-level CT rather than a low-level CT. The aim of the current study was to investigate if the subjectively preferred CT was influenced by either compression speed and/or the participants’ previous hearing aid experience.

Main Outcomes

The results showed that the inexperienced hearing aid users were less likely to prefer low CT compared to the experienced hearing aid users. The overall CT preference was not influenced by compression speed. In specific listening situations, the participants most often had no preference for either a moderate or low CT. If they had a preference in specific listening situations, they most often preferred the moderate CT, except for situations with quiet speech when combined with slow-acting compression. Overall, the results were not strongly in favor of the use of either a low or moderate CT. The findings also provided preliminary evidence that CT preference is related to the hearing aid gain acclimatization effect.

Publications and Presentations

Connor Sørensen H. 2010. Hearing aid amplification at soft input levels Centre for Applied Hearing Research (CAHR). Copenhagen: Technical University of Denmark, p. 145.

HEAL (International Conference on Adult Hearing Screening), Cernobbio (Como Lake, Italy), 2010. 

STAF (National Swedish conference for engineers and technicians), Eskilstuna (Sweden), 2010.

TeMA Hörsel (National conference for Audiologists, Engineers and ENT specialists), Jönköping (Sweden), 2009.

Gain for conductive losses – How do different hearing aid manufacturers compensate for conductive losses in their prescribed gain?

Aim

In this study, the aim was to investigate how the manufacturers’ implemented NAL-NL1 gain compared to NAL-NL1’s own compensation for conductive losses. This was done by box measurements of high-end hearing aids from ten different hearing aid companies. The aim was also to investigate the gain compensation for conductive losses for these hearing aids.

Main Outcomes

The study revealed that different hearing aid companies provide very different gain for the same audiogram configuration, even when the prescription is called “NAL-NL1”. Despite the use of NAL-NL1 as prescription method, the variation between the device providing the most gain and the device providing the least gain was about 20 dB for all measured input levels. Hearing aid manufactures also provide a more linear gain setting for the sensorineural hearing losses than expected. The study also showed that the strategies for compensating for conductive hearing losses are not very clear. One observation, though, is that in those cases where a choice between an own prescription method and the NAL-NAL method is offered, the NAL-NL1 compensation is always larger compared to the company-specific compensation. The “conductive compensation curves” for the NAL-NL1 showed to be very dissimilar to the “conductive compensation” advocated for the NAL-RP. The Maximum Power Output measurements (OSPL 90) showed that there is generally a difference of about 10 dB between OSPL 90 for sensorineural and conductive prescriptions. This is about 20 dB less than what is prescribed by the NAL-NL1 formula.

Publications and Presentations

TeMA Hörsel (National conference for Audiologists, Engineers and ENT specialists), Jönköping (Sweden), 2009.

Gain and acclimatization – Measured long-term average gain for 12 modern hearing aids

Aim

The aims were to document differences in prescribed gain for a selection of hearing aids implementing the NAL-NL1 prescription and to document how acclimatization steps were used to adjust the prescribed gain.

Main Outcomes

By measuring coupler gain, the study provided two main conclusions. The first was that the measured gain for hearing aids programmed with the same generic prescription, NAL-NL1, differed with over 20 dB for certain input levels. This means that some implementations of the NAL-NL1 are unacceptable, and it is impossible for an audiologist to know what a “NAL-NL1 fitting” represents. The second finding was that hearing aid manufacturers have chosen to implement gain acclimatization stages in very different ways. Some manufacturers do not employ gain acclimatization at all, whereas others reduce the gain for a first-time hearing aid wearer by up to 10 dB. Most manufacturers who have implemented acclimatization stages reduce the gain in a uniform way across input level, but three manufacturers reduce the gain more for low-level sounds than for high-level sounds.

Publications and Presentations

TeMA Hörsel (National conference for Audiologists, Engineers and ENT specialists), Jönköping (Sweden), 2009.

ORCA EUROPE

Maria Bangata 4
SE-118 63 STOCKHOLM
SWEDEN

Tel: +46 8 455 67 60

E-mail: orca@orca-eu.info

LOCATION

We are located at Maria Bangata at Södermalm in Stockholm, a central location with good communications and yet calm and lush surroundings.

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