What do we know about loudness tolerance and dynamic range with normal hearing, conductive hearing losses, and sensorineural hearing losses?
- Normal hearing has a large dynamic range
- SNHL has a smaller dynamic range
- CHL: when we get over the conductive component, we usually see a large dynamic range
What is loudness comfort?
The term we use to describe the upper levels of comfort/the point of discomfort in loudness are numerous
- LDL (Loudness Discomfort Level)
- UCL (Uncomfortable Loudness)
- ULL (Uncomfortable Loudness Level)
- TD (Threshold of Discomfort)
- ULC (Upper Level of Comfort)
- HCL (Highest Comfortable Level)
Top two are the most popular
Average UCLs and MCLs (picture)
Variability in UCL (picture)
What is the maximum power output?
MPO refers to the maximum output of the hearing aid when specific settings have been set/determined such as gain for various inputs and compression specific to the patient’s audiological needs, their prescriptive targets, and their comfort
Is MPO and OSPL90 the same thing?
- MPO is not necessarily the OSPL90 (the maximum potential output of the hearing aid)
- MPO can not be higher than the OSPL90, but the OSPL90 can be higher than the MPO
- OSPL90 has nothing to do with patient audiologic profile
- MPO has to do with your patient
What is the process for MPO?
- Like setting appropriate levels of gain for our patients based on soft, average, and loud targets, setting of the MPO is another highly important measurement as we do not want to have the hearing instruments amplify to a level of discomfort
- Like measuring gain for soft, average and loud inputs, MPO is also determined, measured and verified, with adjustments being made as needed
- Can be done in test box
- Can be done on-ear (if patients can tolerate it)
What are we measuring with MPO?
What are we measuring: the SPL the hearing instrument is delivering to the ear, and adjusting the maximum power output as needed
The procedure of MPO is similar to a REAR with speech stimuli except…
- The test signal is LOUD (85 to 90 dB SPL)
- Short pure tones rather than speech (evaluating where the frequency response falls)
What do we have to do once the MPO test is completed?
Once the test is completed, we need to evaluate if the MPO needs adjustment:
- Turning DOWN MPO is the patient cannot tolerate the test signal
- Turning UP MPO if there is insufficient headroom (and if the patient can tolerate MPO)
- Between gain and MPO
Set MPO in ____ and measuring on ____
Software, verification equipment
What is a common complaint with HA users and what does this lead too?
- “Aids are too loud” is often a common complaint with hearing aid users
- This complaint can lead to rejection of use
- 42% of hearing aid users are satisfied with the loudness settings of the hearing aid when measured and set appropriately
- When set appropriately, this a a component of fitting that leads to high satisfaction
What are the 2 consequences of setting the MPO too high?
- Discomfort (leading to hearing aid rejection)
- Over-amplification (leading to noise induced hearing loss (either a TTS or PTS))
Note: patients will reject amplification if the MPO is too loud, not due to gain being off
Do MPO problems go away?
“Maximum Power Output problems don’t go away.
Either you take care of them when you fit the hearing aids, or you take care of them with repeat visits— or return for credits”
Example pic of before and after adjustments
- Previous to adjustment, the MPO is measuring above the UCLs of the patient
- When you make an adjustment you always have to re-measure
What is happening in this MPO measurement?
- At some points in the MPO measurement, primarily at 250 and near 3000 Hz, the 99th percentile for this speech input is reaching the MPO
- Ideally, we would first attempt to raise the MPO to create headroom
- If this is tolerable, doing so will lead to better sound quality.
How does loud speech saturation work when using obnoxious stimuli?
Was looking if you could stimulate something obnoxious (marbles) and bring it down to a comfortable level
How do we create more headroom?
To create more headroom, we either increase the MPO (if tolerable) or decrease gain
What happens when we don’t set MPO correctly?
- If MPO is set too high… discomfort, or rejection if loudness is perceivably too loud
- If MPO is set too low… sound quality issues may arise
- Distortion, muffled quality to sound when loudness nears the MPO
- Unnatural perception of the differences between soft, average, and loud sounds
What should you tell the patient about MPO?
- Explaining the procedure to patient, focusing on why we are performing this procedure
- “You will hear a series of loud beeps. We are measuring how the hearing aids will respond to those sounds. We want to ensure that the hearing aid is not boosting those sounds above your loudness tolerance”
- “if something loud happens in your environment, we are making it so that it isn’t going to be uncomfortable for you”
What do you do when the measured MPO is not representing the MPO of the hearing aid
- Regardless of adjusting gain, the MPO measurement does not seem to be changing…
- What to look at:
- What is the REUR of the ear? REUR gives a lot of good information about what the ear itself is bringing to the table
- This is a point where counselling is very important
Where are UCL targets derived from?
- Average or patient specific measures
- There is general agreement amongst clinicians that the MPO should be set below the level of discomfort
- There are differences of opinion amongst clinician on how to do this
- Should MPO setting be based on a measured UCL for an individual patient? Should we get that info from within the sound booth?
- Should clinician relay on a prescriptive rationale (NAL-NL2/DSL) that uses an average UCL calculation?
What are the pros and cons of average vs patient specific measures?
- Many clinicians don’t measure patient specific UCL’s (it takes a lot of time)
- Can calculate a average UCL based on thresholds, age, etc.
- But if we measure patient specific UCL’s, it is much more targeted to the patient
To measure or not to measure UCL?
- Fewer post-fitting hearing instrument adjustments were needed, based on patient comments, when UCLs are measured pre-fitting
- Patients who were tested for UCLs reported greater satisfaction with the hearing instruments compared to patients who had no UCL testing
- Measured patient specific LDLs may not be required if verification (with predicted LDLs) and validation measures of loudness perception are completed
