Preparing for Real Ear Measurements; equipment, protocol selection and calibration

Jack Bennett, International Clinical Trainer at the Interacoustics Academy, describes all the steps you need to take in order to prepare for Real Ear Measurements. This includes how to prepare your equipment and environment, how to select your protocol and review the audiometric information, and how to calibrate the probe tubes.

If you prefer reading, find the transcript below.

Room and equipment setup

First of all, I need to make sure that my room is set up correctly. And as you can see, I've got my loudspeaker here. And that is placed in a position that's far away from any reflective surfaces, and my patient will be sitting in front of it in a moment. I've also got my REM headset ready to go as well.

The next thing I need to do is make sure that the room is a suitable environment. And actually with the Affinity Compact, I've got an Ambient Noise microphone, which will help me monitor and measure the ambient noise in the room to make sure it's at a suitable level. My Ambient Noise microphone is in a reasonable position in the room and it's measuring and it's responding to my voice as I speak. If I go quiet for just a moment, you can see that generally, the room is nice and quiet. And it's just in the low frequencies that there's maybe a little bit of noise.

But if I now review my audiogram saved in this session here, we can see that the audiogram is actually near normal in the low frequencies. And in terms of the hearing aid fitting today, we'll be using an open fitting RITE. And so in that context, the low frequencies are not a concern. And it wouldn't actually affect the reliability of the hearing aid fitting and the real ear measurement process.

Reviewing the audiogram

So now that I've got my audiogram, I can actually review and remind myself of some of the information because of course this was previously measured. So as you can see, it's a sensorineural hearing loss. It's bilateral, and it's nice and symmetrical as well. I've also recorded ULLs or uncomfortable loudness levels, and so those will be factored into my hearing aid fitting as well.

And of course, we're taking note of the transducers that we use to measure the audiogram because this is important when we come to converting the dB HL into dB SPL in the real ear fitting screen and for all of those measurements later on. So once I'm happy with all of that information, I can then move into the real ear measurement screen.

REM protocol selection

Okay, so now we've opened the REM screen, and we're ready to actually put in all the information needed to conduct our real ear measurements. I've selected a protocol here, and it actually will default to the last protocol used. The steps in the protocol are shown down here, and this is defined by your local practices, and can actually be customized if that's something that you'd like to do.

Prescription settings

The first thing it will ask you to do is select the prescription settings. And you can see here that we've got NAL NL2 selected, but there are many other default prescriptions that you can use. These are all developed by bodies using evidence-based practices around the world. The settings that we can select are defined by those groups. And as you can see here, these are the ones that are defined by NAL NL2.

Other settings

The first thing as we mentioned earlier is that we need to review which transducers were used and so we've got the headphones selected here. We also needed to take note of the configuration of hearing loss, and we decided it was a sensorineural hearing loss and as such, I've selected to not use the bone values. All of the other settings are really to do with the hearing aids themselves. And if you need any help deciding what those settings should be, you should refer to your hearing aid manufacturer.

Probe tube calibration

Once you're happy with all of these settings, press OK. And we're now ready to do a probe tube calibration to get our equipment set up. Okay, so now we're ready to do a probe tube calibration.

The first thing I need to do is actually put the probe tubes onto the REM headset. And what I'm doing here is making sure that the probes themselves are sitting securely over the front of the reference microphones. So I placed the probe over the smaller microphone, and then the end of the probe into the little clips. They'll just hold it in place in front of the reference microphone.

And the reason we do that is that the whole point of the probe calibration is to make sure or rather to measure the difference between the frequency response of the probe microphone versus the reference microphone. The system will then remove that difference for all of the other measurements.

Since I'm happy, they're both in secure, I can then move to the software and start the REM probe tube calibration process. And I'm actually going to do this monaurally. I'm going to do one after the other. You can choose to do a binaural measurement, which will sequentially run both measurements.

So first of all, I'll do the right ear. So press the tube calibration, select the correct probe for the process that I'm doing. So the regular probe is the one that I'm using today. And then when I'm ready, I'll just hold the REM headset in front of the speaker. It doesn't matter the orientation or even the distance that you hold the headset. The important thing is that throughout the measurement itself, you hold it stable with nothing obstructing throughout the measurement.

So once I'm ready, I press regular probe. And it should run the measurement for me. So always watch the screen for a frequency response that I expect, but we'll also check this later on within our REUG. But once I'm happy with that first one, that I can move on to the left ear and do exactly the same process. So again, just checking for any sharp peaks or anomalies throughout that process.

Checking the calibration with an REUG measurement

And if I'm happy with that, then I can do run an REUG, which should show a flat line, which demonstrates that the frequency response to the probe tube has been removed from any subsequent measurements. So with the REUG selected in the protocol. Now I can do this binaurally. At this stage we'll get an information box that will come up to let us know that it's using the right reference microphone as the reference for both measurements. And that's perfectly valid.

Just press Start to begin running the measurement. As you can see, we have a flat line in gain view. So that demonstrates that the reference microphone and the probe tube microphones demonstrate the same response which means that the probe tube frequency response has been removed from the measurement exactly as we want it to be.