MEASURING THRESHOLDS DIRECTLY IN dB SPL
(AURICAL)
The Aurical Audiometry module has the unique capability to directly measure
hearing thresholds in dB SPL as opposed to dB HL. This is useful as it avoids
the necessity of measuring an RECD to transform thresholds from HL to SPL
and is particularly useful when setting hearing aids *. However, if you have a
younger child who will not sit still long enough for you to perform probe
microphone measurements in-situ (in front of the loudspeaker) you will still
need to measure a RECD to enable hearing aid verification in the coupler. To
measure thresholds directly in dB SPL you will need the following transducer
headset:
Figure 1. Standard SPL probe headset.
This Madsen REM/SPL combination insert phone and probe microphone
headset is supplied as standard. One disadvantage of using the above probe
tip is that audiometry must be carried out using the supplied coloured eartips
rather than a custom earmould. As you are primarily performing audiometry
to accurately set up the hearing aid less errors will occur if you use the custom
earmould. The following has been proposed to allow you to use the custom
earmould for audiometry. If you would like to continue to use the coloured
eartips, as in the set-up above, please refer to Aurical Manual page 3-32 to
3.41.
*
You may want to continue to measure thresholds in dB HL for diagnostic purposes but note
possible errors due to small ear canal volumes and transducer calibration issues- see Kevin
Munro’s lecture on day 2 of the generic event.
To use a custom earmould for audiometry you need to remove the ‘probe tip’
and attach the RECD coupling to the end of the plastic tube. You can then
attach the custom earmould (Figure 2). For comfort and work flow efficiency
you can also replace the thicker silicon tube with your usual REM thin probe
tube. In doing this you have the same test set up required to measure a
RECD.
Figure 2. Transducer with thicker tubing and insert nipple to allow attachment
of earmould.
Before any measurements are obtained the silicone probe tube must be
calibrated. To avoid having to remove the probe tube before testing it is
advisable to calibrate the probe tube in the REM module first, save your
calibration and exit and then calibrate the probe tube in the Audiometry
module. Please follow the instructions below which assume you have already
called up a patient via Auditbase.
1. Open AURICAL REM module, you are going to calibrate your probe
tubes. If the DSL target set-up page defaults on your screen click
on CANCEL. Check to make sure you are in In-situ SPL*. Prepare
to calibrate the probe tube:
If you are in Coupler Test rather than ‘In-situ SPL’ click on MODE and un-tick
‘Coupler Test’.
*
 Use a new black tip probe tube, attach it to the probe mic
attachment then position the end of the probe tube so that it is
aligned with the reference microphone. Hold the probe tube and
reference microphone facing the loudspeaker at the same
distance you will be placing the individual (90cm as
recommended by the manufacturer). Calibrate left and right
ears if you are fitting bilateral hearing aids. SAVE by clicking on
the GREEN save and exit TICK (top right of screen).
2. Open AURICAL AUIDIOMETRY module. Click on HL/SPL tool bar
and click on dB SPL. You should be in a SPLogram format.
3. Click on the TEST MODE tool bar and select PROBE
CALIBRATION.
4. With the end of the probe tube still over the reference microphone
opening hold the transducer 15cm from the loudspeaker. Calibrate
both the left and right probes.
5. Click
on
TEST
MODE
tool
bar
again
and
select
SPL
CALIBRATION.
6. You are now going to place the probe tube in the ear canal with the
intention of placing the end of the tube 5-6mm from the ear drum.
Make sure you use otoscopy to help guide the probe tube into the
correct position.
The probe
tube black marker should be
placed at the intra-tragal notch.
Use
age
appropriate
guidelines when measuring the
length
of
the
probe
tube.
Check to make sure the end of
the tube is approx 5mm past
the end of the ear mould. Once the probe tube is in the correct
position carefully place the earmould in the ear, taking care not to
displace the probe tube. Use lubricant if you are working with a soft
earmould or young child. Attach the RECD coupling end of the
thick plastic tubing to the end of the earmould tubing (see picture).
Check that Output is SOUNDFIELD INTERNAL and click on start.
The software will quickly present a 70 dB signal across frequencies
to use as a reference when determining actual SPL for each
determined threshold. Exit when calibration is complete. You are
now ready to commence standard audiometric testing, but
thresholds will be recorded in dB SPL rather than dB HL.
7. Once you have completed testing you may want to visualise the
audiogram in HL. To do this click on HL/SPL on the tool bar and
click on HL. Toggle back to SPL when you are ready to exit the
program. Click on the GREEN TICK to save and exit.
8. Click on AURICAL REM to re-open your REM software. The probe
tubes should already be calibrated so you are ready to commence
verification. If you are going to verify the hearing aid ‘in-situ’
remove the RECD tubing and attach the hearing aid to the
earmould. Check that you are in ‘In-situ SPL’ mode. If you are
going to verify in the ‘coupler’ you need to measure a RECD.
9. Click on MODE , ensure COUPLER TEST is selected and then click
on RECD. Make sure ‘Do coupler step first’ isn’t ticked and
proceed with measuring Step 1 which is the real ear portion of the
RECD. The earmould, probe tube and RECD transducer should
already be in the correct position. Click on START. Carefully
remove the transducer from the test ear and attach the end of the
thick tubing to the coupler and press START (or if you have
measured the coupler response at the beginning of the day click on
‘re-use saved coupler measure’. This avoids you having to remove
the earmould). This is the second part of the RECD measurement
(coupler test) and what you will see on your screen is the resultant
RECD.
10. Click on EXIT and you should see the RECD on the little gain
screen on the right side of the screen and Coupler audiogram and
targets on the big dB SPL screen. If you have this the other way
round click on VIEW and select SPL/Gain.
11. If you are happy with the RECD click on the GREEN TICK to save
and exit. This is good practice as if the software crashes at least
you have saved the measurements that required child co-operation.
You are now ready to open up the hearing aid manufacturer
software. Some manufacturer software will automatically use the
measured RECD to help ‘Auto-fit’ the hearing aid to prescribed
targets (Phonak). Re-open the REM software and attach the
hearing aid to the coupler and verify the response in the coupler.
The child does not need to be present at this stage.