Audiometric earphone discomfort level and hearing aid saturation sound pressure level for a 90 decibel input signal (SSPL90) as measured in the human ear canal

The acoustical problems involved in matching the saturation sound pressure level for a 90 dB input signal (SSPL90) of a hearing aid to individual discomfort level were investigated. The real ear SPL (RE/SSPL90) produced by a supra-aural earphone used when measuring uncomfortable loudness (UCL), and RE/SSPL90 produced by three different hearing aids at 90 dB SPL input, were measured for nine subjects, using a miniature microphone technique, and compared to the corresponding coupler levels used when matching hearing aid maximum output to UCL. It was found that a hearing aid often gives about 5 dB, and sometimes 10 dB, higher RE/SPLs than the earphone, if the hearing aid output levels, as measured in a 2-cc coupler (IEC126), are equal to the earphone output levels as measured in a 6-cc coupler (NBS9A). It is recommended that a safety margin of at least 5 dB be used in the preliminary fitting when matching hearing aid SSPL90 to the patient's UCL, converted to dB SPL.     

Fitting hearing aids using clinical measures of loudness discomfort levels: an evidence-based review of effectiveness

Clinical measurement of the loudness discomfort level (LDL) historically has been part of the hearing aid fitting procedure, and this clinical practice remains popular today. LDL measurements also are recommended in contemporary hearing aid fitting protocols. Yet, surveys show that many hearing aid users are dissatisfied with the loudness of their hearing aids. In this evidence-based review article, we evaluate the effectiveness of clinical LDL measurements. Specifically, we asked the question "Are the clinical measurements of LDL for adult patients predictive of aided acceptance and satisfaction of loudness for high inputs in the real world?" Nearly 200 articles were reviewed; three met the criteria set forth in this review. The evidence supported using unaided LDLs for selecting the maximum real-ear output of hearing aids. No study using aided LDLs or aided loudness verification met the criteria. The level of the evidence for the three articles using unaided LDLs was low; no higher than Level 4. The limited number of studies, the level of evidence, and the statistical power of the studies prevents us from making a strong recommendation concerning the clinical use of LDL measures. Additional research in this area, especially research employing randomized controlled trials would be a useful addition to this body of literature.     

Probe tube microphone measures of loudness discomfort levels in children

Loudness discomfort levels (LDLs) have been advocated as a means for selecting the SSPL90 setting of an individual's hearing aid. Kawell, Kopun, and Stelmachowicz (Ear Hear 1988; 9: 133-136) recently developed a procedure to measure LDLs in children. Several procedural cautions, involving the hearing aid stimulus delivery and sound field calibration, have been noted with this method. As a means of overcoming these problems, a new method utilizing insert earphone derived stimuli delivered to a child's ear-mold with probe tube microphone monitoring of real-ear sound pressure level was explored. Twenty children, aged 7 to 14 years, served as subjects. The advantage of the present method lies in the procedural conveniences and the ability to compare real-ear audiometric measures and hearing aid performance.     

Control of hearing-aid saturated sound pressure level by frequency-shaped output compression limiting

To fit a hearing aid successfully, it is important to set the Saturated Sound Pressure Level (SSPL) or Maximum Power Output (MPO) appropriately. The SSPL should be low enough to prevent sounds from being amplified to uncomfortable loudness, and yet high enough to maximize speech intelligibility and signal quality. To help attain an optimum SSPL setting, a novel output compression limiting scheme, with shapable MPO (ShaMPO), has been devised. In ShaMPO, the SSPL is shaped across frequencies in accordance with the individual user's loudness discomfort levels (LDLs). The contributions of different frequency regions to loudness are controlled by summing the amplified signal power relative to the LDLs across frequencies, and using this signal to control a wideband compressor. This scheme and a conventional output compression limiting (AGCo) scheme have been implemented in a digital hearing aid. Ten subjects, with moderately-severe to profound sensorineural hearing losses, participated in a study comparing speech intelligibility and listening comfort for the two schemes. Results showed that there were no significant differences in the speech perception scores between AGCo and ShaMPO, even when the speech was presented at 80 dBA, at which level both schemes were in compression much of the time. However, an examination of how subjects selected the SSPL for the two schemes revealed that, in many instances, AGCo would permit some sounds with compact spectra to be amplified above LDL, whereas ShaMPO would not. Thus the ShaMPO scheme can improve listening comfort for some intense sounds without a loss of speech intelligibility. In contrast, half the subjects found speech at 80 dBA to be uncomfortably loud when listening through their own aids.     

Duration, compression, and the aided loudness discomfort level

OBJECTIVE: The purpose of this investigation is to determine how the unaided and aided loudness discomfort level (LDL) varies with the duration of the input signal and whether the electroacoustic characteristics of compression circuits affect this relationship in a manner that may alter the listener's dynamic range for short duration sounds. DESIGN: Ten hearing-impaired and 20 normal-hearing listeners participated. LDLs were determined for noise bursts of durations ranging in six steps from 32 to 1024 msec, using a two-alternative, forced-choice adaptive tracking procedure in which input level varied until LDL was achieved. LDLs were also obtained for continuous discourse, using a clinical procedure. Subjects were also given the opportunity to self adjust maximum output SPL to their LDL using either output limiting or volume controls in response to fixed 90 dB SPL noise bursts. Testing was conducted unaided and with hearing aids representing two analog (output compression limiting, wide dynamic range compression) and four digital compression circuits. Primary circuit contrasts included compression threshold, compression ratio, attack time and the presence or absence of unity gain at high levels. RESULTS: For the unaided condition, both normal-hearing and hearing-impaired subjects showed increasing LDLs with decreasing signal duration. Under aided conditions, circuits with compression thresholds of 45 to 50 dB SPL and compression ratios of 2:1 produced LDL functions that were similar in slope to the impaired listener's unaided functions. Slopes were steeper when the attack time was slow (128 msec) than when it was fast (2 msec). Circuits with compression ratios of 8:1 produced flat LDL duration functions (i.e., a loss of duration-dependent effects). Similar duration-dependent LDL effects were also observed when subjects adjusted their own hearing aid output characteristics in response to 90 dB noise bursts. CONCLUSION: For the unaided condition, results suggest that normal-hearing and hearing-impaired listeners can tolerate short duration sounds at higher levels than long duration sounds, a finding that has implications for hearing aid design. Circuits that preserve the relationship between duration and LDL should allow brief phonemes to be presented at higher levels without discomfort than circuits that do not, possibly resulting in greater audibility or speech recognition. Current results suggest that circuits with low compression thresholds, low compression ratios, and slow attack times might accomplish this objective better than circuits with high compression thresholds, high compression ratios and fast attack times.     

Evaluation of relationship between hearing threshold and loudness discomfort level in sensorineural hearing loss.

The relationship between hearing level and loudness discomfort level (LDL) for narrow-band noise was evaluated in two groups of patients with sensorineural hearing loss. Group I had thresholds ranging from 25-60 dB SPL and Group II's thresholds ranged from 65-100 dB SPL. LDLs were determined for narrow bands of noise centered at 500, 1000, 2000, and 4000 Hz. The LDLs for Group II were greater than those for Group I and the differences were statistically significant. It is speculated that one reason for others not finding differences as a function of hearing level may be the absence of severe to profound hearing loss in the test populations.     

Various uncomfortable loudness thresholds, their correlation and use in general practice]

In the present study we examined the relationship of the loudness discomfort level LDL of different signals. We carried out measurements in 97 patients, all of whom suffered from a sensorineural hearing loss. The results showed almost no difference between the LDL of pure tones and narrow band noise. The LDL of broad band noise showed a good correlation to the LDL of 250 Hz. Only the LDL of monosyllables ranged at a higher SPL. For an up-to-date hearing aid fitting, all forms of LDL should be taken into consideration. This is especially necessary when using digital hearing aids.     

Binaural loudness summation in the hearing impaired

Binaural loudness summation was measured using three different paradigms with 10 normally hearing and 20 bilaterally symmetrical high-frequency sensorineural hearing loss subjects. An adaptive paradigm and a loudness matching procedure measured summation at the lower and upper level of comfortable loudness and the loudness discomfort level (LDL). Monaural and binaural LDLs also were obtained with a clinical procedure designed to select maximum output of hearing aids. Stimuli for all three tasks consisted of 500- and 4000-Hz pure tones and a speech spectrum noise. Binaural summation increased with presentation level using the loudness matching procedure, with values in the 6-10 dB range. Summation decreased with level using the adaptive paradigm, and no summation was present with the clinical LDL task. The hearing-impaired subjects demonstrated binaural summation that was not significantly different from the normally hearing subjects. The results suggest that a bilaterally symmetrical sensorineural hearing loss does not affect binaural loudness summation. The monaural and binaural dynamic range widths were similar, and the LDL results suggest that binaural loudness summation may not be an important factor in selecting maximum output of hearing aids.     

Loudness discomfort levels in children

Loudness discomfort levels (LDLs) traditionally have been used to set the saturation sound pressure level (SSPL) or maximum output of a hearing aid. Many procedures have been used to obtain LDLs for adults; however, no systematic study has been conducted to determine if LDLs could be obtained reliably for children. In the present study, LDLs were measured on 20 hearing-impaired children aged 7 to 14 years using a modification of a procedure described by Hawkins, Walden, Montgomery, and Prosek (Ear Hear 1987; 8: 162-169). Test-retest reliability measures were obtained for 8 of the 20 children, and this modified procedure was found to provide reasonably reliable results. Data from the group of 20 children also were compared with similar data obtained from 20 hearing-impaired adults. These results revealed no systematic differences in LDLs between the two groups, suggesting no a priori reason to limit the maximum output of a hearing aid for a child in this age range below the levels that are appropriate for adults. Poor correlation between LDLs and hearing levels for both age groups indicate a need for determining LDLs on an individual basis whenever possible.     

Effects of speech materials on the loudness discomfort level

Clinicians have used speech stimuli when measuring the loudness discomfort level (LDL) to determine the upper intensity limit for test stimulus presentation, and to select the saturation sound pressure level for an individual's hearing aid. Because little research has investigated the effects of speech stimuli on the LDL, this study was undertaken to compare LDLs using six commercially available speech materials on 120 normally hearing listeners. Our comparisons showed no significant differences between the mean scores for any of the speech stimuli. These findings suggest that any differences in the mean LDLs among studies probably are not attributable to the speech stimuli. The intrasession reliability of LDL measurement was also assessed using a modified method of limits procedure with 2-dB increments and instructions stressing initial discomfort. It was concluded that examiners probably could attain a high degree of reliability by simply averaging the results of two ascending trials, because 95% of these test/retest differences did not exceed 6 dB. Our findings were integrated with previous studies in terms of: (1) test stimuli; (2) listener experience; (3) instructional set; and (4) psychophysical method. This discussion points to many unanswered questions and concludes that the LDL should be interpreted very cautiously. Moreover, it is suggested that the stimuli selected for LDL measurement should reflect the examiner's purpose.     

Short-term and long-term hearing aid benefit and user satisfaction: a comparison between two fitting protocols

Currently published hearing aid fitting protocols recommend speech-in-noise testing and loudness measures, but it remains unclear how these measures affect hearing aid benefit and user satisfaction. This study compared two protocols in their effects on benefit and satisfaction. Protocol A included an electroacoustic analysis, real-ear measures, and hearing aid adjustments based on users' comments. Protocol B included all of Protocol A and a speech-in-noise test, loudness discomfort levels, and aided loudness. Thirty-two participants completed the Abbreviated Profile of Hearing Aid Benefit (APHAB) and the Satisfaction with Amplification in Daily Life (SADL) at 45 days and three months post-initial fitting. Fewer hearing aid adjustments were made to the hearing aids for participants fitted with Protocol B than participants fitted with Protocol A, but final gains were similar for both groups. Although similar APHAB scores were obtained for both protocols, SADL scores decreased between 45 days and three months for Protocol A.     

Test-Retest Stability and Effects of Psychophysical Methods on the Speech Loudness Discomfort Level

It is generally agreed that the saturation sound pressure level of a hearing aid should not exceed the patient's loudness discomfort level (LDL) for speech. This study investigated (1) the stability of the test and retest LDLs when obtained on different days using McCandless's and Berger's instructional sets and (2) the effects of a psychophysical method (adjustment versus limits) on the speech LDL using McCandless's instructions. Good reliability was observed since one-half of the listeners had test-retest differences of 2 dB or less and nearly all subjects obtained LDLs within 8 dB. The mean LDLs for the respective methods of adjustment and limits were 86.8 and 92.9 dB SPL, and statistically significant. Additionally, a significant interaction between the two methods was observed. The LDL measurement is also discussed in relation to other tests used to evaluate hearing aid performance.

II est généralement admis que le niveau de saturation en SPL d'un appareil de correction auditive ne doit pas dépasser le niveau du seuil d'inconfort du malade pour la parole (SIP). L'importance de ce SIP nous a done amené a en étudier les conditions d'établissement. Considérant d'abord sur 25 sujets normaux la stabilité des valeurs SIP au cours de plusieurs jours en utilisant les instructions données au sujet soit d'après McCandless, soit d'après Berger, nous n'avons trouvé que de faibles variations (différence test-retest de 2 dB ou moins) pour la moitié des sujets, écart de 8 dB si Ton considere l'ensemble des sujets. Considérant ensuite sur 20 sujets normaux les effets de la méthode psycho-physique employée (méthode des limites ou methode d'adjustement), nous avons pu montrer que les effets sont significatifs: la moyenne des niveaux de SIP se situe à 86,8 dB SPL par la méthode d'adjustement et à 92,3 dB SPL par la méthode des limites. De plus nous avons pu observer une certaine interaction entre les deux méthodes lorsqu'elles sont utilisées successivement. Nous discutons en terminant la valeur comparée du SIP et de celle d'autres tests.     

Assessment of FM systems with an ear canal probe tube microphone system

A technique is described to measure the real-ear performance of an FM system using an ear canal probe tube microphone device. The method involves placement of the FM microphone next to the monitoring (compression) microphone of the probe tube assembly to produce a constant sound pressure level input to the FM system. With the probe tube in the ear canal, a hearing aid alone is measured with a 60 dB SPL input and the FM system attached to the hearing aid (personal FM system) is assessed with an 80 dB SPL input to account for the higher input levels that occur due to the 6 inch distance between the speaker's mouth and the FM microphone. This technique permits a rapid comparison of the real-ear response of the hearing aid and the FM system.     

The objective estimation of loudness discomfort level using auditory brainstem evoked responses

The loudness discomfort level (LDL) is of importance in the fitting of hearing aids, but very young children are unable to provide a subjective judgement of LDL. Therefore the relationship between Jewett wave V latency and subjective loudness was investigated to ascertain if objective estimation of LDL is possible. ABR recordings were taken from 8 normally hearing subjects at the stimulus intensity corresponding to their LDL and at stimulus levels from 10 to 30 dB below this. The wave V latency/intensity function did not correlate well with the LDL. However, the slope of this function did correlate to a high degree and a predictive model of LDL was derived. Identical measurements were then taken from a sample of 12 cochlear-impaired subjects with a range of audiometric profiles. Their subjective LDLs could be predicted from the wave V latency function to an accuracy of +/- 5 dB, using the model derived from the normally-hearing subjects. This model appeared to be equally valid for all the degrees and profiles of hearing loss included in the sample and showed a closer relationship to LDL than did absolute wave V latency or estimates derived from the acoustic reflex.