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

rom

: heari

ngdir

ect

.com

• 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.