T E S T I N G FM SYSTEMS with the FONIX 6500-CX Hearing Aid Analyzer (Requires software version 4.20 or above) FRYE FRYE ELECTRONICS, INC. P.O. Box 23391 Tigard, OR 97281-3391 (503) 620-2722 (800) 547-8209 Fax: (503) 639-0128 www.frye.com e-mail: sales@frye.com
Contents Introduction........................................................................ 1 General Fitting Protocol.......................................................... 2 Curve Labeling System.......................................................... 2 Arrangement of This Workbook................................................... 3 Section 1: Coupler Measurements with FM Systems 1.1 Coupler Setup in the sound chamber................................................ 4 1.1.1 How to Attach the 2-cc Coupler.............................................. 4 1.1.2 Hearing Aid Setup......................................................... 6 1.1.3 FM System................................................................ 7 1.1.4 Environmental Microphone Setup............................................ 9 1.2 Omni-directional: FM-only........................................................ 11 1.2.1 Test aid alone with typical input EHA65.................................... 11 1.2.2 Test FM microphone with typical input EFM80.............................. 12 1.2.3 Test aid alone with high-level input EHA90................................. 13 1.2.4 Test FM system with high-level input EFM90................................ 14 1.3 Omni-directional: FM+ENV....................................................... 16 1.3.1 Single frequency output of omni-directional hearing aid in the sound chamber...... 16 1.3.2 Single frequency output of omni-directional FM mic at 65 db SPL................. 17 1.3.3 Verify increase in signal level................................................ 17 1.3.4 Test aid alone with typical input EHA65.................................... 17 1.3.5 Test FM+ENV microphones with typical input to FM microphone EFE80......... 18 1.3.6 Test environmental microphone response with typical input EEF65.............. 20 1.3.7 Test aid alone with high-level input EHA90................................. 21 1.3.8 Test with FM system using a high-level input EFE90.......................... 21 1.3.9 Test environmental mic response with high-level input EEF90.................. 23 1.4 Coupler Setup in the Sound Field.................................................. 24 1.4.1 Hearing Aid Setup........................................................ 24 1.4.2 FM System Setup......................................................... 26 1.4.3 Environmental microphones on body-worn receivers........................... 28 1.5 Directional: Testing FM-only....................................................... 30 1.5.1 Test aid alone with typical input EHA65.................................... 30 1.5.2 Test FM microphone with typical input EFM80.............................. 31 1.5.3 Test aid alone with high-level input EHA90................................. 32 1.5.4 Test FM system with high-level input EFM90................................ 33 1.6 Directional: Testing FM+ENV...................................................... 34 1.6.1 Single frequency output of hearing aid....................................... 34 1.6.2 Single frequency output of FM mic at 65 db SPL................................ 35 1.6.3 Verify increase in signal level................................................ 35 1.6.4 Test aid with typical input EHA65......................................... 36
1.6.5 Test FM+ENV microphones with typical input to FM microphone EFE80......... 37 1.6.6 Test environmental mic response with typical input EEF65.................... 38 1.6.7 Test aid with high-level input EHA90...................................... 39 1.6.8 Test with FM system using a high-level input EFE90.......................... 40 1.6.9 Test environmental mic response with high-level input EEF90.................. 41 Section 2: Real-Ear Evalutation with FM Systems 2.1 Setup......................................................................... 42 2.1.1 Hearing Aids............................................................. 42 2.1.2 FM System............................................................... 43 2.1.3 Setup for Testing Environmental Microphones................................. 44 Environmental microphones on body-worn receivers........................... 45 Environmental microphone on a hearing aid................................... 45 2.2 Testing FM-Only................................................................ 46 2.2.1 Test aid with typical input RHA65......................................... 46 2.2.2 Test FM system with typical input RFM80.................................. 47 2.2.3 Test aid with high-level input RHA90....................................... 48 2.2.4 Test FM system with high-level input RFM90................................. 49 2.3 Testing FM+ENV................................................................ 50 2.3.1 Single frequency output of hearing aid....................................... 50 2.3.2 Single frequency response of FM mic at 65 db SPL.............................. 51 2.3.3 Verify increase in signal level................................................ 51 2.3.4 Test aid with typical input RHA65.......................................... 52 2.3.5 Test FM system with typical input RFM80................................... 53 2.3.6 Test environmental mic with typical input REF65............................. 54 2.3.7 Test aid with high-level input RHA90....................................... 55 2.3.8 Test FM system with high-level input RFE90................................. 56 2.3.9 Test environmental mic with high-level input REF90........................... 57 Glossary:.......................................................................... 58
Introduction This workbook contains procedures for testing FM systems with the 6500-CX hearing aid analyzer using coupler and real-ear measurement methods. An FM system consists of two main parts: a transmitter and a receiver. The transmitter microphone can come in many different sizes and shapes, and it can be omni-directional or directional. The body-worn FM receiver can be coupled to a button earphone or interfaced with the personal hearing aid via a direct audio input boot, silhouette coil, or via a neck loop. The ear-level FM receivers are housed within the BTE aid or attached to the base of the BTE via a boot connection. No matter the combination, all FM systems can be tested. These test procedures should be performed on an FM system at least once a year. For children under the age of 5, these procedures should be performed every six months. As with most hearing aids, both the gain and the maximum output (SSPL) of an FM system should be adjusted to meet the listener s auditory requirements. There are several issues to consider when comparing the hearing aid and FM performance. With FM systems, the pickup microphone is normally worn at the chest, 6-8 inches (15-20 cm) under the mouth of the talker, whereas with hearing aids, the pickup microphone is worn by the listener, typically at a minimum of 3 ft. (1 m) from the talker. This difference affects both the level and the frequency content of typical input signals. With FM systems, typical speech input levels range from 75 to 85 db SPL, as compared with 60 to 70 db SPL for hearing aids. With the chest-worn location of the pickup microphone, the high frequencies are relatively lower in level (about 5 db at 5 khz) and the low frequencies are relatively higher in level (about 5 db at 500 Hz) as compared with directly in front of the talker s mouth. The increased vocal effort by teachers in a classroom situation may create further changes to the speech spectrum at the input to an FM system, as compared with the speech spectrum at the input of a hearing aid (Cornelisse et al., 1991). FM systems often have an automatic gain control (AGC) or other nonlinear characteristic that could interact with that of the hearing aid being used to deliver the FM signal if such a hearing aid is being used in this fashion. The frequency response of an FM system is often not as adjustable as that of a hearing aid, limiting the range of electroacoustic modifications available. The procedures recommended in this chapter are based on the ASHA guidelines for fitting and monitoring FM systems (1999), available at: www.asha.org/audiology/fm_guidelines.htm. Introduction 1
General Fitting Protocol For the purposes of this workbook, we will assume that the hearing aid being tested has been fitted appropriately for the client s loss. We will adjust the FM system to the output of the hearing aid. Goals: For students with mild to moderately-severe losses (<80 db HL), the goal is to match the output of the hearing aid and the FM system when typical input signals are used. With typical inputs, the FM output will be the same intensity as the hearing aid output. For students with severe to profound losses (>80 db HL), the goal is to match the gain of the hearing aid and the FM system when typical input signals are used. With typical input signals, the FM output will be about 10 db more intense than the hearing aid output. Testing Order: Start with 2-cc coupler tests and adjustments if possible. Follow up with real-ear verification. If time doesn t permit both test conditions, omit the 2-cc coupler tests. For both 2-cc coupler and real-ear tests: 1. Test the user s hearing aid with typical input signal levels. 2. Test the FM system with typical input signal levels, and make any necessary adjustments. 3. Test the user s hearing aid with high input signal levels. 4. Test the FM system with high input signal levels, and make any necessary adjustments. Curve Labeling System In order to efficiently record and refer to the various measurements, we have adopted a curve labeling system created by Dr. Linda Thibodeau. This system is consistent with the type of measurement made and the SPL of the test signal used. The first letter indicates whether it was a coupler or a real-ear measurement. All coupler measurement labels begin with an E for Electroacoustic. All real-ear measurement labels begin with an R for Real-Ear. The second and third letters indicate the type of test taken. HA means a hearing aid test FM means an FM-only test FE means an FM+ENV test with the signal delivered to the FM microphone EF means an FM+ENV test with the signal delivered to the environmental microphone 2 Testing FM Systems with FONIX FP40 Analyzers
The numbers at the end indicate the sound pressure level of the test signal used. Examples: EHA65 is the electroacoustic coupler measurement of the hearing aid with the signal input at 65 db SPL EFM80 is the electroacoustic coupler measurement of the FM microphone with the signal input at 80 db SPL RFE80 is the real-ear measurement of the FM+ENV with the signal delivered to the FM microphone at 80 db SPL See the Glossary for a list of all the labels and their definitions. Arrangement of This Workbook There are two main sections in this workbook. Section 1 describes sets of coupler measurements of FM systems. Section 2 describes corresponding sets of real-ear measurements of FM systems. Section 1 contains four different sets of testing procedures, but you only need to follow the testing procedure suitable for the FM system being tested. Section 2 contains two different sets of testing procedures. Likewise, you only need to follow the real-ear procedures suitable for the FM system. Ideally, you should perform one set of coupler measurements and one set of real-ear measurements on each FM system. It is assumed that you will perform the specified tests in sequential order. For instance, the instructions in Section 1.2.2, Testing the FM response with typical input, assume that you have done the steps in Section 1.2.1, Testing the hearing aid response with typical input. If it is more convenient for you to alter the testing order, just be aware that some of the key presses will change. Introduction 3
1: Coupler Measurements with FM Systems Coupler measurements of FM systems allow you to adjust the system without needing your client present. The goal is to set the FM system controls so that the user receives the FM signal at an appropriate level with reference to the acoustic signal the user receives from his personal hearing aid. There are four different sets of measurements described in this section. Use the set that is appropriate for the FM system setup. If the FM receiver and hearing aid are omni-directional and will fit inside the sound chamber, and: The FM receiver is primarily set to receive FM-only signals, follow the procedures described in Section 1.2, Omni-directional: Testing FM-only. The FM receiver is primarily set to receive FM with environmental signals (FM+ENV), follow the procedures described in Section 1.3, Omni-directional: Testing FM+ENV. If the FM receiver or hearing aid is directional or cannot fit inside the sound chamber, and The FM receiver is primarily set to receive FM-only signals, follow the procedures described in Section 1.5, Directional: Testing FM-only. The FM receiver is primarily set to receive FM with environmental signals (FM+ENV), follow the procedures described in Section 1.6, Directional: Testing FM+ENV. For all procedures, the hearing aid should be set to user settings. 1.1 Coupler Setup in the sound chamber This section describes how to attach a 2-cc coupler to the FM receiver, and how to set up an FM system for coupler measurements. 1.1.1 How to Attach the 2-cc Coupler A variety of output devices can be used with FM systems. These include button earphones, BTE cases with microphone/earphones, BTE aids with an internal FM receiver, an external FM receiver boot, or options for coupling to the personal BTE hearing aid via direct audio inputs, silhouette coils, or neck loops. This section contains a description of how to arrange the 2-cc coupler with each type of output device. 4 Testing FM Systems with FONIX 6500-CX Analyzers
FM Receiver FM Receiver FM Receiver Foam Pad Foam Pad Foam Pad to Analyzer to Analyzer to Analyzer Figure 1.1.1A Figure 1.1.1B Figure 1.1.1C Button earphone Internal FM receiver Silhouette coil External FM boot receiver Direct audio input Button earphone (Figure 1.1.1A) 1. Remove the ear-level adapter from the HA-2 coupler, if necessary. 2. Snap on the button earphone to the HA-2 coupler. 3. Place the coupler/hearing-aid assembly on a foam pad outside the text box, 2 ft. (60 cm) from the transmitter during testing. BTE case with microphone/earphone or BTE aid with internal FM receiver, external FM boot receiver, or direct audio input (Figure 1.1.1B) 1. Attach the ear-level adapter to the HA-2 coupler, if necessary. 2. Attach the BTE hearing aid to the HA-2 coupler. 3. Place the coupler/hearing-aid assembly on a foam pad outside the test box, 2 ft. (60 cm) from the transmitter during testing. BTE aid with silhouette coil (Figure 1.1.1C) 1. Attach the ear-level adapter to the HA-2 coupler, if necessary. 2. Attach the BTE hearing aid to the HA-2 coupler. 3. Place the coupler/hearing-aid assembly on a foam pad outside the text box, 2 ft. (60 cm) from the transmitter during testing. Choose a location free of stray magnetic fields (away from video monitors and other electrical devices). It may be necessary to turn the analyzer s video monitor off during testing. 4. Align the silhouette coil underneath the hearing aid, simulating the way it would be worn on the ear. Section 1: Coupler Tests of FM Systems 5
BTE aid with neck loop (Figure 1.1.1D) 1. Within the range of the coupler microphone cable, choose a location to seat the listener that is free of stray magnetic fields (away from video monitors and other electrical devices), while also maintaining the required separation (2 ft./60 cm) from the transmitter. It may be necessary to turn the analyzer s video monitor off during testing. 2. Place the neck loop around the listener s neck or around the neck of a person of similar size. 3. Attach the listener s hearing aid to the HA-2 coupler. 4. While holding the coupler in hand, place the hearing aid at the listener s ear, as typically worn. 5. Take care not to move or touch the coupler microphone while testing. FM Receiver to Analyzer Figure 1.1.1D Neck loop 6 Testing FM Systems with FONIX 6500-CX Analyzers
1.1.2 Hearing Aid Setup 1. Make sure the sound chamber is leveled. 2. Attach the hearing aid, set to user settings, to the HA-2 coupler in the usual way. Be sure the FM transmitter is off and the aid is set to receive the signal from the hearing aid microphone. See Figure 1.1.2. 3. Insert the coupler microphone into the coupler. 4. Place the assembly into the sound chamber. 5. Close and latch the sound chamber door. Figure 1.1.2 Hearing aid setup with FM boot 1.1.3 FM System 1. Make sure the sound chamber is leveled. 2. Set the FM receiver to receive FM-only. 3. Insert the coupler microphone into the HA-2 coupler and attach the output of the FM receiver as explained in Section 1.1.1, and place at least 2 ft. (60 cm) from all transmitter parts. See Figure 1.1.3A. 4. Place the FM transmitting microphone at the test position in the chamber. 5. Close the lid and latch the chamber. Section 1: Coupler Tests of FM Systems 7
Test Chamber FM Mic (or Environmental Mic) 6500 Main Electronics Module Foam Pad Receiver 2 ft. (60 cm) Transmitter Figure 1.1.3A FM setup Isolating the environmental microphone When the FM system is usually used in FM+ENV mode, the testing procedures call for the environmental microphone to be turned on as well at the FM microphone. In most quiet testing environments, this will call for the FM setup described above. However, if you are testing in a noisy environment, you may want to isolate the environmental microphone from the room noise. To check if you need to provide sound isolation for the environmental microphone when testing the FM microphone in FM+ENV mode, do this procedure: 1. Set the FM microphone up for testing as described above. 2. Set the FM receiver to receive FM only. 3. Observe the RMS OUT for this FM-only signal. 4. Set the FM receiver to receive FM+ENV. 5. Observe the RMS OUT for the FM+ENV setting. If the RMS OUT is more than 3 db higher for FM+ENV than for FM-only, then you will need to isolate the environmental microphone when testing the FM microphone in FM+ENV mode. If the RMS OUT for both signals is within 3 db, no additional setup is necessary. 6. To isolate the environmental microphone, it is preferable to use a spare sound chamber if one is available to you. Otherwise, take a shoebox, line it with packing foam, and place the environmental microphone inside, covering it with some more foam. See Figure 1.1.3B. This should isolate the room noise from the environmental microphone. 8 Testing FM Systems with FONIX 6500-CX Analyzers
Isolate environmental microphone Shoebox lined with foam FM mic Figure 1.1.3B Isolating the environmental microphone 1.1.4 Environmental Microphone Setup Environmental microphones on ear-level FM receivers 1. Make sure the sound chamber is leveled. 2. Attach the ear-level FM receiver to the HA-2 coupler and set it to receive input from the environmental microphone only. 3. Insert the coupler microphone into the HA-2 coupler. 4. Place the ear-level receiver and coupler at the test position in the sound chamber. 5. Close and latch the sound chamber lid. 6. You are now ready to test the FM system with the signal delivered to the environmental microphone. Section 1: Coupler Tests of FM Systems 9
Lapel environmental microphones on Body-worn FM Receivers 1. Make sure the sound chamber is leveled. 2. Attach the output transducer from the FM receiver to the HA-2 coupler outside the sound chamber as described in Section 1.1.1. 3. Insert the coupler microphone into the HA-2 coupler. 4. Place the lapel microphone from the FM receiver at the test position in the sound chamber. See Figure 1.1.4. 5. Close and latch the lid of the sound chamber. 6. You are now ready to test the FM system with the signal delivered to the environmental microphone. Figure 1.1.4 Testing lapel receivers 10 Testing FM Systems with FONIX 6500-CX Analyzers
1.2 Omni-directional: FM-only This section contains a description of the four different coupler measurements of FM systems when the client primarily uses the system in FM-only mode. These measurements are: EHA65: typical electroacoustic response of the aid EFM80: typical electroacoustic response of the FM transmitter/receiver EHA90: saturation electroacoustic response of the aid EFM90: saturation electroacoustic response of the FM transmitter/receiver 1.2.1 Test aid alone with typical input EHA65 1. Set up the hearing aid according to the hearing aid setup described in Section 1.1.2.2. Press [RESET] to enter Composite Weighted Gain Mode. 3. Press [WEIGHT] to enter Composite Weighted Power Mode. The display will be labeled as OUTPUT SPL. 4. Use [ ] to set RMS Source to 65 db SPL. 5. Once the curve is stable, press [FREEZE] to pause the measurement. If the 6500-CX has the Multi-Curve Option, press [START] (not [CONTINUE]!) to save the curve into the Multi-Curve stack. For units without Multi-Curve, press [CRT] to print the measurement. 6. This will be referred to as the Electroacoustic Hearing Aid Response or EHA65. See Figure 1.2.1. Figure 1.2.1 EHA65 hearing aid response at 65 db SPL Section 1: Coupler Tests of FM Systems 11
1.2.2 Test FM microphone with typical input EFM80 1. Set up the FM system according to the FM system setup in Section 1.1.3. 2. Use [ ] to adjust the signal level to 80 db SPL. 3. This curve will be referred to as the Electroacoustic FM Response or EFM80. (Since the current running curve is always stored as CRV 1 in the Multi-Curve buffer, there is no need to press [FREEZE] and [START] to save the curve as you did in Section 1.2.1.) 4. To view the EFM80 and EHA65 on the same screen requires the Multi-Curve Option: a. Press [MULTI]. b. Highlight MULTIPLE CURVES. c. Press [START]. d. If necessary, use [<, >] to display CRV 1 in the first slot. This curve is EFM80. e. Use [ ] to select the second slot. f. If necessary, use [<, >] to display CRV 2 in the second slot. This curve is EHA65. See Figure 1.2.2. If you don t have the Multi-Curve Option, press [CRT] to print out EFM80 and compare it to EHA65. Figure 1.2.2 Comparison of EHA65 (CRV2), the hearing aid response at 65 db SPL and EFM80 (CRV1), the FM response at 80 db SPL 12 Testing FM Systems with FONIX 6500-CX Analyzers
5. If you have a client with a mild to moderate hearing loss (less than 80 db HL), the output of the two curves should be within 5 db of each other. If you have a client with a severe to profound loss (greater than 80 db HL), the output of EFM80 should be 7-10 db higher than the output of EHA65. If you have to adjust the system to obtain a better result, first adjust the FM receiver volume control if possible. When using FM systems coupled to personal hearing aids adjust the settings on the hearing aid as a final step if necessary. If this must be done, the teacher, parents, and therapists must be made aware that when the FM system is used, the settings on the hearing aid must be changed for optimum performances. 1.2.3 Test aid alone with high-level input EHA90 1. Turn off the FM signal, and set up the hearing aid for testing as described in the hearing aid setup in Section 1.1.2. 2. Press [SINE/COMPOSITE] button to enter Pure Tone Mode. The analyzer will automatically set itself to a signal level of 90 db SPL. 3. Press [START] to begin the pure-tone sweep. The response will be stored in the Multi-Curve stack when the measurement is complete. For instruments without the Multi-Curve option, press [CRT] to print a hardcopy. Figure 1.2.3 EHA90 hearing aid response at 90 db SPL 4. This response will be referred to as the Electroacoustic Hearing Aid Saturation Response or EHA90. See Figure 1.2.3. Section 1: Coupler Tests of FM Systems 13
1.2.4 Test FM system with high-level input EFM90 1. Set up the FM system for testing according to the FM setup in Section 1.1.3. The FM receiver should be set to receive FM-only signals. 2. Press [START] to begin the pure-tone sweep. The response will be stored in the Multi-Curve stack when the measurement is complete. For instruments without the Multi-Curve option, press [CRT] to print a hardcopy. 3. This response will be referred to as the Electroacoustic FM Saturation Response or EFM90. Figure 1.2.4 Comparison of EHA90 (CRV2), the hearing aid response at 90 db SPL with EFM90 (CRV1), the FM response at 90 db 4. To view both curves on the same screen requires the Multi-Curve Option: a. Press [MULTI]. b. Highlight MULTIPLE CURVES. c. Press [START]. d. If necessary, use [<, >] to display CRV 1 in the first slot. This curve is EFM90. e. Use [ ] to select the second slot. f. If necessary, use [<, >] to display CRV 2 in the second slot. This curve is EHA90. 14 Testing FM Systems with FONIX 6500-CX Analyzers
g. You may want to press [ ] and [FREEZE] to turn off the display of CRV 3, since it is not relevant to this comparison. Similarly, press [ ] and [FREEZE] again to turn off the display of CRV 4. If you don t have the Multi-Curve Option, press [CRT] to print out EFE90 and compare it to EHA90. 5. If EFM90 is greater than 5 db above or 10 db below EHA90, adjust the maximum output control if possible on the FM receiver or on the hearing aid if necessary. If the hearing aid is adjusted, the teacher, parents, and therapists must be made aware that when the FM system is used, the settings on the hearing aid must be changed for optimum performances. For mild to moderate losses it may be acceptable if the EFM90 is 5-10 db below EHA90. See Figure 1.2.4. Section 1: Coupler Tests of FM Systems 15
1.3 Omni-directional: FM+ENV This section contains a description of the different coupler measurements of omni-directional FM systems when the client primarily uses the system with the environmental microphone added to the FM signal (FM+ENV mode). These measurements are: Response of aid with 65 db SPL signal at 1 khz Response of FM transmitter/receiver with 65 db SPL signal at 1 khz Verify increase of FM transmitter/receiver when signal level is increased to 80 db SPL. EHA65: typical electroacoustic response of the aid EFE80: typical electroacoustic response of the FM transmitter/receiver EEF65: typical electroacoustic response of environmental microphone EHA90: saturation electroacoustic response of the aid EFE90: saturation electroacoustic response of the FM transmitter/receiver EEF90: saturation electroacoustic response of environmental microphone 1.3.1 Single frequency output of omni-directional hearing aid in the sound chamber 1. Set up the hearing aid for testing as described in the hearing aid setup in Section 1.1.2. The FM transmitter should be off, and the hearing aid set to receive input from the hearing aid microphone. 2. Press [RESET]. 3. Press [SINE/COMPOSITE] to put the analyzer in PURE TONE MODE. 4. If necessary, use [<, >] to adjust the frequency of the single tone signal to 1000 Hz. Figure 1.3.1 Hearing aid output at 65 db SPL at 1000 Hz 16 Testing FM Systems with FONIX 6500-CX Analyzers
5. Use [ ] to adjust the level of the signal to 65 db SPL. 6. Make a note of the AID OUT on the screen. This is the HEARING AID OUTPUT. See Figure 1.3.1. 1.3.2 Single frequency output of omni-directional FM mic at 65 db SPL 1. Set up the FM microphone for testing as described in the FM setup in Section 1.1.3. The FM receiver should be set to receive FM+ENV. 2. If you followed the steps of Section 1.3.1, the analyzer should be in PURE TONE MODE with a 65 db SPL signal at 1000 Hz. 3. Look at the AID OUT on the screen. This is the FM OUTPUT. 4. Adjust the FM receiver volume so that the FM OUTPUT is matched to the HEAR- ING AID OUTPUT found in Section 1.3.1. This matches the gain of the FM system and the hearing aid. 1.3.3 Verify increase in signal level 1. Leave the FM system and analyzer set up as described in Section 1.3.2 with the aid or FM receiver attached to the 2-cc coupler and set to receive FM+ENV. 2. Press [ ] repeatedly to increase the signal level to 80 db SPL. 3. Look at the AID OUT on the screen. This is the new FM OUTPUT. 4. Compare the HEARING AID OUTPUT found in Section 1.3.1 to this new FM OUT- PUT, and adjust the FM receiver volume control according to the following: If the increase is: 10 db, no further adjustments are necessary. 15 db, reduce the FM receiver volume control so that the FM OUTPUT falls by 5 db. 5 db, increase the FM receiver volume control so that the FM OUTPUT increases by 7 or 8 db. 0 db, the FM transmitter must have a very low compression threshold, so increase the FM receiver volume control so that the FM OUTPUT increases by 5 db. 1.3.4 Test aid alone with typical input EHA65 1. Set up the hearing aid for testing as described in Section 1.1.2. The FM transmitter should be off, and the hearing aid set to receive input from the hearing aid microphone. 2. Press [RESET] to enter Composite Weighted Gain Mode. 3. Press [WEIGHT] to enter Composite Weighted Power Mode. 4. Use [ ] to set RMS Source to 65 db SPL. Section 1: Coupler Tests of FM Systems 17
Figure 1.3.4 EHA65 hearing aid response at 65 db SPL 5. Once the curve is stable, press [FREEZE] to pause the measurement. If the 6500-CX has the Multi-Curve Option, press [START] (not [CONTINUE]!) to save the curve into the Multi-Curve stack. For units without Multi-Curve, press [CRT] to print the measurement. 6. This will be referred to as the Electroacoustic Hearing Aid Response or EHA65. See Figure 1.3.4. 1.3.5 Test FM+ENV microphones with typical input to FM microphone EFE80 1. Set up the FM system according to Section 1.1.3. The FM receiver should be set to receive FM+ENV. 2. Use [ ] to adjust the signal level to 80 db SPL. 3. This curve will be referred to as the Electroacoustic FM Response or EFE80. 4. To view the EFE80 and EHA65 on the same screen requires the Multi-Curve Option: a. Press [MULTI]. b. Highlight MULTIPLE CURVES. c. Press [START]. d. If necessary, use [<, >] to display CRV 1 in the first slot. This curve is EFE80 or the Electroacoustic FM and Environmental Response with 80 db input to the FM microphone. e. Use [ ] to select the second slot. 18 Testing FM Systems with FONIX 6500-CX Analyzers
f. If necessary, use [<, >] to display CRV 2 in the second slot. This curve is EHA65. If you don t have the Multi-Curve Option, press [CRT] to print out EFE80 and compare it to EHA65. Figure 1.3.5 Comparison of EHA65 (CRV2), the hearing aid response at 65 db SPL and EFM80 (CRV1), the FM response at 80 db SPL 5. Compare EHA65 (CRV 2) to EFE80 (CRV 1) to confirm that the desired FM advantage is maintained over the 500 to 2000 Hz range. In general, that advantage should be 7-10 db. See Figure 1.3.5. 6. For units with Multi-Curve, you will want to save EFE80 for a comparison in the next section. To do this: a. Press [CONTINUE] twice to exit from Multi-Curve. b. Press [FREEZE] to save the current EFE80 measurement. c. Press [START] to save the curve to the Multi-Curve stack. EFE80 has just become CRV 2 and EHA65 has just become CRV 3. You will use them in the next section. Section 1: Coupler Tests of FM Systems 19
1.3.6 Test environmental microphone response with typical input EEF65 1. Set up the environmental microphone for testing as described in Section 1.1.4. Set the FM receiver to receive FM+ENV signals. 2. Use [ ] to set the source level to 65 db SPL and wait for the response to stabilize. 3. This measurement will be referred to as EEF65, or the Electroacoustic FM and Environmental Response with 65 db SPL input to the environmental microphone. 4. Compare EEF65 to EHA65 (from Section 1.3.4) and EFE80 (from Section 1.3.5). If you have Multi-Curve, do the following: a. Press [MULTI]. b. Highlight MULTIPLE CURVES. c. Press [START]. d. CRV 1 will be selected for the first Multi-Curve slot. This is the EEF65 response. CRV 2 should be selected for the second Multi-Curve slot. This is the EFE80 response. Use [ ] to select the third Multi-Curve slot. e. Use [<, >] to select CRV 3 for the third Multi-Curve slot. This is the EHA65 response. f. Compare EEF65 (CRV 1), EFE80 (CRV 2), and EHA65 (CRV 3). For a successful fit, the EHA65 and EEF65 should be similar, and the EFE80 should be 7-10 db higher. See Figure 1.3.6. Figure 1.3.6 Comparison of EHA65 (CRV1), EFM80 (CRV2), and EEF65, the environmental microphone response at 65 db SPL 20 Testing FM Systems with FONIX 6500-CX Analyzers
1.3.7 Test aid alone with high-level input EHA90 1. Turn off the FM signal, and set up the hearing aid for testing as described in Section 1.1.2. 2. Press [SINE/COMPOSITE] button to enter Pure Tone Mode. The analyzer will automatically set itself to a signal level of 90 db SPL. 3. Press [START] to begin the pure-tone sweep. The response will be stored in the Multi-Curve stack when the measurement is complete. For instruments without the Multi-Curve option, press [CRT] to print a hardcopy. 4. This response will be referred to as the Electroacoustic Hearing Aid Saturation Response or EHA90. See Figure 1.3.7. Figure 1.3.7 EHA90 the hearing aid response at 90 db SPL 1.3.8 Test with FM system using a high-level input EFE90 1. Set up the FM system for testing according to Section 1.1.3. The FM receiver should be set to receive FM+ENV. 2. Press [START] to begin the pure-tone sweep. The response will be stored in the Multi-Curve stack when the measurement is complete. For instruments without the Multi-Curve option, press [CRT] to print a hardcopy. 3. This response will be referred to as EFE90 or the Electroacoustic FM and Environmental Response with 90 db SPL input to the FM microphone. Section 1: Coupler Tests of FM Systems 21
Figure 1.3.8 Comparison of EHA90, the hearing aid response at 90 db SPL, and EFM 90, the FM response at 90 db SPL 4. To view both curves on the same screen requires the Multi-Curve Option: a. Press [MULTI]. b. Highlight MULTIPLE CURVES. c. Press [START]. d. If necessary, use [<, >] to display CRV 1 in the first slot. This curve is EFE90. e. Use [ ] to select the second slot. f. If necessary, use[<, >] to display CRV 2 in the second slot. This curve is EHA90. g. You may want to press [ ] and [FREEZE] to turn off the display of CRV 3, since it is not relevant to this comparison. Similarly, press [ ] and [FREEZE] again to turn off the display of CRV 4. If you don t have the Multi-Curve Option, press [CRT] to print out EFE90 and compare it to EHA90. 5. If EFE90 is greater than 5 db above EHA90, adjust the FM system to obtain a better match. As a last resort, adjust the settings on the hearing aid. If this must be done, the teacher, parents, and therapists must be made aware that when the FM system is used, the settings on the hearing aid must be changed for optimum performances. See Figure 1.3.8. 22 Testing FM Systems with FONIX 6500-CX Analyzers
1.3.9 Test environmental mic response with high-level input EEF90 1. Set up the environmental microphone for testing as described in Section 1.1.4. Set the FM receiver to FM+ENV. 2. Press [START/STOP] to run a pure-tone measurement at 90 db SPL. 3. This measurement will be referred to as EEF90 or the Electroacoustic FM and Environmental Response with 90 db SPL input to the environmental microphone. 4. To view both curves on the same screen requires the Multi-Curve Option: a. Press [MULTI]. b. Highlight MULTIPLE CURVES. c. Press [START]. d. EEF90 (CRV 1) should be displayed in the first slot, and EFE90 (CRV 2) should be displayed in the second slot. e. Press [ ] to select the third slot. f. If necessary, press [<, >] to select CRV 3 for the third slot. This is the EHA90 measurement. 5. Compare EEF90 (CRV 1) to EFE90 (CRV 2) and EHA90 (CRV 3). All three curves should match. See Figure 1.3.9. Figure 1.3.9 Comparison of EHA90, EFM90, and EFF90, the environmental microphone response at 90 db SPL Section 1: Coupler Tests of FM Systems 23
1.4 Coupler Setup in the Sound Field When testing a FM system with a large or directional microphone, the measurements are performed in the sound field. Therefore, the corresponding hearing aid tests will also have to be performed in the sound field. This requires a little creativity; you may have to adjust the following recommended procedure to fit the particular equipment that you are testing. 1.4.1 Hearing Aid Setup 1. Enter the Real Ear Mode by pressing [START/STOP] on the remote module. All further key presses described in this section will be performed on the remote module. 2. Affix the reference microphone with Fun-Tak to the platform at the top of the floor stand, 6 inches (15 cm) in front of the sound field speaker, with the microphone pointing toward the speaker. See Figure 1.4.1A. (If you don t have a floor stand, the back of a chair can suffice. But be sure the chair is facing to the side of the setup to avoid reflections from the back of the chair.) 6 inches Reference mic Probe mic (not used) Figure 1.4.1A Sound field leveling setup 3. Stand clear of the test area, holding the remote module. 4. Press [LEVEL] on the remote module. 5. Remove the reference microphone and the platform from the floor stand, leaving the floor stand in its position in front of the sound field speaker. 6. Attach the hearing aid to the HA-2 coupler. 24 Testing Testing FM Systems FM Systems with with FONIX FONIX 6500-CX FP40 Analyzers
7. Thread a probe tube through the black probe tube adapter with the tube first entering the ridged end of the adapter. The tube should extend 1-2 mm past the other end of the adapter. Use Fun-Tak to secure the probe tube to the adapter. See Figure 1.4.1B. Figure 1.4.1B Thread probe tube through probe mic adapter 8. Insert the adapter into the HA-2 coupler, and attach the probe tube to the probe microphone. See Figure 1.4.1C. Probe mic adapter Probe mic Figure 1.4.1C Attach coupler to probe mic Section 1: Coupler Tests of FM Systems 25
9. Securely attach the assembly to the floor stand using Fun-Tak. The body of the hearing aid should be vertical with the hearing aid microphone pointed towards the sound field speaker. See Figure 1.4.1D. Figure 1.4.1.D Setup for testing a hearing aid in the sound field using a coupler 10. You are now ready to test the hearing aid. 1.4.2 FM System Setup Since the tests of the FM transmitter/receiver in this chapter always follow the tests of the hearing aid, it is assumed in this setup that you have already entered Real Ear Mode and leveled the sound field speaker. If you are testing out of order, follow the instructions found in Section 1.4.1, Steps 1-4, to level the sound field before testing. 1. Place the FM transmitting microphone on the floor stand six inches (15 cm) from the sound field speaker. Keep all sound-entry ports clear of the platform. Place the transmitter and its cord behind the transmitting microphone. 2. Thread a probe tube through the black probe tube adapter with the tube first entering the ridged end of the adapter. The tube should extend 1-2 mm past the other end of the adapter. Use Fun-Tak to secure the probe tube to the adapter. See Figure 1.4.1B. 3. Insert the adapter into the HA-2 coupler, and attach the probe tube to the probe microphone. See Figure 1.4.1C. 4. Attach the FM receiver to the HA-2 coupler as described in Section 1.1.1. 26 Testing FM Systems with FONIX 6500-CX Analyzers
5. Place the assembly 2 ft (60 cm) from the transmitting microphone, out of the sound field of the speaker. See Figure 1.4.2. 6. Stand clear of the test area, holding the remote module. You are now ready to test the FM transmitter/receiver. FM mic Reference mic (not used) Probe mic FM transmitter FM receiver attached Figure 1.4.2 FM setup system Isolating the environmental microphone The testing procedures in this section call for the environmental microphone to be turned on as well at the FM microphone. In most quiet testing environments, this will call for the FM setup described in Section 1.4.1. However, if you are testing in a noisy environment, you may want to isolate the environmental microphone from the room noise. To check if you need to provide sound isolation for the environmental microphone when testing the FM microphone in FM+ENV mode, do this procedure: 1. Set the FM microphone up for testing as described in Section 1.1.3. 2. Set the FM receiver to receive FM only. 3. Press [START/STOP] on the remote module to start a composite measurement. When the measurement stabilizes, press [START/STOP] again. 4. Observe the RMS OUT for this FM-only signal. 5. Set the FM receiver to receive FM+ENV. 6. Repeat Step 3. Section 1: Coupler Tests of FM Systems 27
7. Observe the RMS OUT for the FM+ENV setting. If the RMS OUT is more than 3 db higher for FM+ENV than for FM-only, then you will need to isolate the environmental microphone when testing the FM microphone in FM+ENV mode. If the RMS OUT for both signals is within 3 db, no additional setup is necessary. 8. To isolate the environmental microphone, it is preferable to use a spare sound chamber if one is available to you. Otherwise, take a shoebox, line it with packing foam, and place the environmental microphone inside, covering it with some more foam. See Figure 1.1.3B. This should isolate the room noise from the environmental microphone. 1.4.3 Environmental microphones on body-worn receivers 1. Enter Real Ear Mode by pressing [START/STOP] on the remote module or [PROBE] on the 6500-CX main module. 2. Affix the FM receiver to the platform stand in the manner shown in Figure 1.4.3A. Reference Microphone Figure 1.4.3A Attaching reference microphone 3. Using Fun-Tak, affix the reference microphone to the receiving unit so the entrance to the reference microphone is very close to that of the environmental microphone. 4. Place the FM receiver six inches (15 cm) from, and facing, the loudspeaker (Refer to Figure 1.4.3B) and set it to receive input from the environmental microphone only. 5. Choose a place to stand during testing, preferably away from the loudspeaker and microphone, holding the remote module. Stand precisely in this place during both leveling and testing. 6. Press [LEVEL] on the remote module. This levels the test signal at the place where the FM receiver microphone will be during testing. 7. Leave the reference microphone in place during testing. 28 Testing FM Systems with FONIX 6500-CX Analyzers
8. Thread the probe tube through the probe tube adapter so that it extends 3 mm past the end. Use Fun-Tak to hold the probe tube in place. See Figure 1.4.1B. 9. Insert the adapter and probe tube (attached to the probe microphone) into the HA-2 coupler, and attach to the button earphone, direct audio input hearing aid, or aid coupled with neck loop or silhouette, as explained in Section 1.1. 10. You are now ready to test the FM system with the signal delivered to the environmental microphone. Figure 1.4.3B Leveling the sound field Figure 1.4.3C Testing with body-worn receiver Section 1: Coupler Tests of FM Systems 29
1.5 Directional: Testing FM-only This section contains a description of the four different coupler measurements of FM systems when the client primarily uses the system in FM-only mode. These measurements are: EHA65: typical electroacoustic response of the aid EFM80: typical electroacoustic response of the FM transmitter/receiver EHA90: saturation electroacoustic response of the aid EFM90: saturation electroacoustic response of the FM transmitter/receiver 1.5.1 Test aid alone with typical input EHA65 1. Follow the hearing aid setup instructions found in Section 1.4.1 to set up the hearing aid for testing the sound field, enter Real Ear Mode, and level the sound field speaker. The FM transmitter should not be on and the aid should be set to receive the hearing aid microphone. 2. Press [MENU] on the remote module. 3. Press [ ] to highlight CREATE TARGET. 4. Press [<, >] to select SPL TARGET. 5. Press [START/STOP] twice. This will open the SPL Test Screen. Figure 1.5.1 EHA65 the hearing aid response at 65 db SPL 6. Look in the bottom left corner of your screen. If it says AUTO, press [UNAIDED] on the remote module. This will put you in MANUAL Mode. 30 Testing FM Systems with FONIX 6500-CX Analyzers
7. Press [MENU] to enter the SPL Menu. 8. Select COMP for AIDED CURVE 1 and AIDED CURVE 2. 9. Press [MENU] to return to the SPL Test Screen. 10. If necessary, select CRV 1 with [ ]. 11. Use [<, >] to select a source level of 65 db SPL. 12. Press [START/STOP] to begin the measurement. 13. Press [START/STOP] once the measurement has stabilized. This curve is the Electroacoustic Hearing Aid Response or EHA65. See Figure 1.5.1. 1.5.2 Test FM microphone with typical input EFM80 1. Set up the FM system for testing according to FM setup described in Section 1.4.2. 2. Use [ ] to select CRV 2. 3 Use [<, >] to set the RMS source to 80 db SPL. 4. Press [START/STOP] to start the measurement. 5. Once the measurement stabilizes, press [START/STOP] again to stop the measurement. Figure 1.5.2 Comparison of EHA65 (CRV1), the hearing aid response at 65 db SPL and EFM80 (CRV2), the FM response at 80 db SPL Section 1: Coupler Tests of FM Systems 31
6. CRV 2 is now the Electroacoustic FM Response or EFM80. 7. If you have a client with a mild to moderate hearing loss (less than 80 db HL), the output of the two curves should be within 5 db of each other. If you have a client with a severe to profound loss (greater than 80 db HL), the output of EFM80 should be 7-10 db higher than the output of EHA65. If you have to adjust the system to obtain a better result, first adjust the FM receiver volume control if possible. When using FM systems coupled to personal hearing aids adjust the settings on the hearing aid as a final step if necessary. If this must be done, the teacher, parents, and therapists must be made aware that when the FM system is used, the settings on the hearing aid must be changed for optimum performances. See Figure 1.5.2.77 1.5.3 Test aid alone with high-level input EHA90 1. Set up the hearing aid for testing in the sound field by following the directions found in the hearing aid setup in Section 1.4.1. If you ve already leveled the sound field speaker, you can skip to step 6 in that section. 2. Press [MENU] to enter the SPL Menu. 3. Select PURE TONE for AIDED CURVE 1 and AIDED CURVE 2. 4. Press [MENU] to return to the SPL Test Screen. 5. Press [ ] to select CRV 1. Figure 1.5.3 EHA90 the hearing aid response at 90 db SPL 32 Testing FM Systems with FONIX 6500-CX Analyzers
6. Use [>] to select a source level of 90 db SPL. 7. Press [START/STOP] to begin the sweep. 8. This response will be referred to as the Electroacoustic Hearing Aid Saturation Response or EHA90. See Figure 1.5.3. 1.5.4 Test FM system with high-level input EFM90 1. Set up the FM system for testing according to the FM setup described in Section 1.4.2. 2. Use [ ] to select CRV 2. 3. Use [>] to select a source level of 90 db SPL. 4. Press [START/STOP] to make the measurement. 5. CRV 2 is now the Electroacoustic FM Saturation Response or EFM90. 6. Compare EHA90 (CRV 1) to EFM90 (CRV 2). If EFM90 is greater than 5 db above or 10 db below EHA90, adjust the maximum output control if possible on the FM receiver or on the hearing aid if necessary. If the hearing aid is adjusted, the teacher, parents, and therapists must be made aware that when the FM system is used, the settings on the hearing aid must be changed for optimum performances. For mild to moderate losses it may be acceptable if the EFM90 is 5-10 db below EHA90. See Figure 1.5.4. Figure 1.5.4 Comparison of EHA90 (CRV1), the hearing aid response at 90 db SPL with EFM90 (CRV2), the FM response at 90 db SPL Section 1: Coupler Tests of FM Systems 33
1.6 Directional: Testing FM+ENV This section contains a description of the different coupler measurements of FM systems when the client primarily uses the system with the environmental microphone added to the FM signal (FM+ENV mode). These measurements are: Response of aid with 65 db SPL signal at 1 khz Response of FM transmitter/receiver with 65 db SPL signal at 1 khz Verify increase of FM transmitter/receiver when signal level is increased to 80 db SPL. EHA65: typical electroacoustic response of the aid EFE80: typical electroacoustic response of the FM transmitter/receiver EEF65: typical electroacoustic response of environmental microphone EHA90: saturation electroacoustic response of the aid EFE90: saturation electroacoustic response of the FM transmitter/receiver EEF90: saturation electroacoustic response of environmental microphone 1.6.1 Single frequency output of hearing aid 1. Set up the aid for testing according to the hearing aid setup described in Section 1.4.1. The FM transmitter should be off and the hearing aid set to receive input from the hearing aid microphone. Make sure you level the sound field speaker. 2. Press [MENU]. 3. Use [ ] to highlight MODE. 4. Use [<, >] to select PURE TONE. 5. Press [MENU] to exit from the Quik-Probe II Menu. Figure 1.6.1 Hearing aid output at 65 db SPL at 1000 Hz 34 Testing FM Systems with FONIX 6500-CX Analyzers
6. Press [START/STOP] to begin a single frequency signal. 7. If necessary, use [<, >] to adjust the frequency to 1000 Hz. 8. Use [, ] to adjust the signal level to 65 db SPL. 9. Note the MIC OUT on the screen. This is the HEARING AID OUTPUT. See Figure 1.6.1. 10. Press [START/STOP] to turn off the signal. 1.6.2 Single frequency output of FM mic at 65 db SPL 1. Set up the FM system for testing according to Section 1.4.2. The FM receiver should be set to receive FM+ENV. 2. If you followed the procedure described in Section 1.6.1, you should be in Real Ear Mode, with the analyzer ready to deliver a pure-tone signal of 1000 Hz at 65 db SPL. 3. Press [START/STOP] to start the measurement. 4. Note the AID OUT on the screen. This is the FM OUTPUT. 5. Adjust the FM receiver volume so that the FM OUTPUT is matched to the HEAR- ING AID OUTPUT found in Section 1.6.1. This matches the gain of the FM system and the hearing aid. 6. Press [START/STOP] to turn off the signal. 1.6.3 Verify increase in signal level 1. Leave the FM system and the analyzer set up as described in Section 1.6.2. 2. Press [START/STOP] to start the single frequency measurement. 3. Press [ ] repeatedly to increase the signal level to 80 db SPL. 4. Note the AID OUT on the screen. This is the FM OUTPUT. 5. Compare the HEARING AID OUTPUT found in Section 1.6.1 to this new FM OUT- PUT, and adjust the FM receiver volume control according to the following: If the increase is: 10 db, no further adjustments are necessary. 15 db, reduce the FM receiver volume control so that the FM OUTPUT falls by 5 db. 5 db, increase the FM receiver volume control so that the FM OUTPUT increases by 7 or 8 db. 0 db, the FM transmitter must have a very low compression threshold, so increase the FM receiver volume control so that the FM OUTPUT increases by 5 db. Section 1: Coupler Tests of FM Systems 35