comfort and loudness measures
TRANSCRIPT
BEYOND THE AUDIOGRAM: COMFORT AND LOUDNESS MEASURES
Ozarks Technical Community College
First, Let’s Review some psychoacoustic concepts …
Psychoacoustics and HL
Recall that acoustics are physical properties of a sound that are measureable (intensity, frequency, wavelength)
Having a hearing loss does not change the acoustics of sound or the sound wave itself
Hearing loss changes our psychoacoustic perceptions of sound
Dynamic Range (DR)
DR=the range of intensities from the softest sounds we can hear to the loudest sounds we can hear
Image f
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• In normal-hearing individuals, the DR of our ears is 140 dB SPL (from 0-140 dB)
• When we are referring to hearing loss and the fitting of HAs, the dynamic range refers to the range of intensities from the threshold of hearing (red circles) to the loudness discomfort level (“L”)• On the audiogram at
right, the DR at 500 Hz is 80 dB HL and at 4000 Hz is 55 dB HL
The DR of Human Speech
The DR for the voiced phonemes of the English language is about 30 dB wide, which is depicted by the speech banana, at right.
Placing this speech dynamic range within the confines of the patient’s residual dynamic range is a challenge in fitting hearing aids. Image from: firstyears.org
What happens when there is OHC loss in the cochlea?
The response of the basilar membrane becomes more linear Loud sounds are not compressed as they
once were As a result, loudness recruitment occurs
Loudness Recruitment Recruitment is an abnormal loudness
perception in individuals with hearing loss Oftentimes, patient’s with hearing loss report
that sounds that were once a comfortable volume are now uncomfortably loud
Patient’s with SNHL have an elevated threshold (sound has to be louder for them to hear it); however, the loudness discomfort level does not change significantly (it is the same as it was when they had normal hearing) As a result, the rate of loudness growth to their
ears is much more rapid This results in loudness recruitment
WDRC
The purpose of wide-dynamic range compression (WDRC) in modern hearing aids is to keep the dynamic range (DR) of speech within the patient’s DR in an attempt to recreate the non-linearity of a normal cochlea
Remember, DR=the range of intensities from the softest sounds we can hear to the loudest sounds we can hear The softest sound audible is determined by the
patient’s air-conduction threshold at each frequency But, how do we know what the loudest sound level
that a patient can tolerate is? By measuring the patient’s loudness discomfort
levels (LDLs)
To this point, we’ve discussed the standard audiogram: Puretone Audiometry
Air and bone conduction Speech Audiometry
SRT and WRS The following slides will discuss MCL,
UCL, and LDLs.
Most Comfortable Level (MCL) The dB level of speech that the patient
feels is most comfortable. Measured with a cold-running speech stimulus (i.e. the
Pledge of Allegiance, nursery rhyme, etc) May be performed monaurally (one ear at a time) and
binaurally (both ears at same time) Recall the advantages of binaural hearing?
The binaural MCL will be about 5 dB less than the individual MCLs for fairly symmetric losses
Start at ~20 dB above the patient’s SRT and gradually increase the intensity until the patient reports that the speech is “comfortable”
Many clinicians perform word recognition testing at the patient’s MCL
Uncomfortable Loudness (UCL)
The dB level of speech that the patient feels is uncomfortable. Measured with a cold-running speech stimulus (i.e.
the Pledge of Allegiance, nursery rhyme, etc) Begin speaking at MCL and ascend until the patient
reports that speech is uncomfortable Because MCL and UCL measure
loudness across a broad frequency spectrum, they are difficult to use when programming multi-channel hearing aids
Loudness Discomfort Level (LDL)
The loudness discomfort level (LDL) is the level at which the patient reports sound to be uncomfortably loud at specific frequencies Stimuli: pulsed tones or narrow
bands of noise at .5, 1, 2, 3, and 4kHz
Why are LDLs important?
Research has shown that the range of what patients rate as “uncomfortably loud” to be 20 dB
With that much potential variability between patients, it is not wise to assume that a patient has average LDLs (which is what manufacturer software assumes AND all manufacturers use different data for what is considered average) This may result in improper amplification
and rejection of hearing aids
Loudness Scaling to Determine LDL When performing LDLs,
the patient is asked to rate the loudness of frequency-specific stimuli (i.e. pulsed tones)
It is best to provide loudness anchors such as the Cox loudness descriptors (at right) rather than just having the patient raise their hand when the sound is uncomfortable
Image from: http://www.harlmemphis.org//index.php?cID=138
PATIENT INSTRUCTIONS FOR LDL TESTING
Provide pt with loudness categories on previous slide and state the following: THE PURPOSE OF THIS TEST IS TO FIND YOUR JUDGMENTS
OF THE LOUDNESS OF DIFFERENT SOUNDS. YOU WILL HEAR SOUNDS THAT INCREASE AND DECREASE
IN VOLUME. YOU MUST MAKE A JUDGMENT ABOUT HOW LOUD THE SOUNDS ARE. PRETEND YOU ARE LISTENING TO THE RADIO AT THAT VOLUME. HOW LOUD WOULD IT BE?
AFTER EACH SOUND, TELL ME WHICH OF THESE CATEGORIES BEST DESCRIBES THE LOUDNESS.
KEEP IN MIND THAT AN UNCOMFORTABLY LOUD SOUND IS LOUDER THAN YOU WOULD EVER CHOOSE ON YOUR RADIO NO MATTER WHAT MOOD YOU ARE IN.
Instructions from: http://www.harlmemphis.org//index.php?cID=138
Clinician Instructions for Measuring LDLs
Begin slightly above threshold at 1kHz and use an ascending technique to present pulsed tones Ascend in 5 dB steps for patients with threshold at
or below 50dBHL Ascend in 2 dB steps for patients with thresholds
above 50dBHL Determine the patient’s LDL, which is the level
that they rate as #7, uncomfortably loud Repeat twice at each frequency and take the
average LDL for the three trials Common LDL frequencies are .5, 1, 2, 3, and 4 kHz If you are pressed for time, .5 and 3 kHz will
provide you with good, useable information
Converting dB HL to dB SPL (real-ear)
When measuring LDLs on the audiometer, the LDL will be in dBHL; however, hearing aid output is in dB SPL
You CANNOT make a direct comparison of the patient LDL in dB HL to the hearing aid MPO in dB SPL Remember, 0dBHL at 1000 Hz (headphones)=7dBSPL
in the open soundfield. This is referred to as the RETSPL, which stands for real-ear threshold in sound pressure level.
But, what is that dB level when there is a hearing aid in the ear, which decreases the physical volume/space of the ear canal and increases the SPL?
Converting dB HL to dB SPL (real-ear)
The conversion formula is as follows: LDL in real-ear SPL=LDL in HL + RETSPL
+ RECD
Refer to the Audiology Online presentation: “How Loud is Too Loud? Using Loudness Discomfort Level Measures for Hearing Aid Fitting and Verification, Part 2” http://www.audiologyonline.com/audiology-ceus/course/loud-too-using-loudness-discomfort-18825
RETSPL Values – Most Common
500 Hz 1000 Hz 2000 Hz 3000 Hz 4000 Hz
Headphones (TDH 39)
11.5 7.0 9.0 10.0 9.5
3A Inserts (HA-1)
6.0 0.0 2.5 2.5 0.0
RETSPL Values – All Transducers
Roeser, Valente, Hosford-Dunn. Audiology: Diagnosis (2nd ed), p. 206.
Real-Ear-to-Coupler Difference (RECD)
Ideally, you would measure the patient’s individual RECD . However, it is usually safe to use average RECD values.
Average RECD values are provided below from Dr. Mueller’s AO presentation:
Average REDD Values
RETSPL + RECD=REDD (real-ear-to-dial difference)
I’ll make it very simple for you. Take your LDL in dB HL and add the average REDD values (adult) below to arrive at your LDL in dB SPL in the real-ear!500 Hz 1000 Hz 2000 Hz 3000 Hz 4000 Hz
Headphones (TDH 39)
15.5 15.0 16.0 18.0 22.5
3A Inserts (HA-1)
10.0 8.0 9.5 10.5 13.0
Finally…
After you’ve confirmed the patient LDLs and transformed the LDL in HL to real-ear SPL, you may compare the patient’s LDLs to the real-ear saturation response (RESR-90) when you are performing real-ear testing.
If the RESR-90 exceeds the patient’s LDL at any frequency, you should reduce the maximum power output (MPO) of the hearing aid at the corresponding frequencies.