Measurements: RIC, RITE, and Thin Tube BTE (RIA) Hearing Aids
RIC (receiver-in-the-canal, or what some call RITE: receiver in the ear) hearing aids are major products in a dispenser’s hearing aid sales. This article will use the term RIC because it is thought to be a more accurate description when properly fitted, and some of the advantages identified as being associated with a RITE hearing aid are achieved primarily in a RIC configuration. In essence, a RITE hearing aid could have the speaker fit in the concha, and as a result, would not be able to provide the same acoustic benefits as would a RIC, where the hearing aid is positioned more deeply in the ear canal, and not in the concha.
RIA (receiver-in-the-aid) hearing aids contain all electronics in the hearing aid processor itself, and do not separate the speaker from the hearing aid. An RIA hearing aid could be either a conventional BTE or a thin tube BTE. RIC, RITE, and Thin Tube RIA category hearing aids are generally readily fit with patient acceptance and satisfaction high. However, a few hints/suggestions may assist in some problem solving or provide assistance in how to fit and test them more easily. For this discussion, the RIC and RITE hearing aids are considered to be closed coupled to the ear, rather than having vents.
When RITE may be WRONG and RIC may be Right – Speaker insertion depth
Manufacturers of all three of these hearing aid types generally offer a selection of speaker links to be able to appropriately fit different top-of-auricle-to-ear-canal lengths. Along with these dimensions, the speaker link insertion depth into the ear canal is directly related to its overall length as well. For example, a long speaker link inserts further into the ear canal than does a short speaker length (Figure 1).
The following discussion relates to the speaker insertion depths with RIC and RITE closed coupler hearing aids, and not to RIAs. Is this length, and subsequent insertion depth, critical to a successful fitting? The answer is that the depth that the speaker is inserted into the ear canal has a direct effect on the overall response of the instrument.
A casual observation of RIC and RITE hearing aids worn by individuals seen in daily life often reveals that many seem to be barely “sticking” into the ear canal. This provides ample armchair evidence that these individuals may not be obtaining as much satisfaction from the hearing aids as they should. Figure 2 shows REAR (Real-Ear Aided Responses) of different depths of insertions into the ear canal. In these measurements, the green-colored curve resulted from the proper fit and insertion. However, as can be seen, significant high-frequency amplification, as much as 8 dB or so, can be lost when the instrument is not fit as deeply into the ear canal. The shallower, and hence looser fit, is then also more prone to acoustic feedback because a good seal is less likely, even though feedback cancellation may have been activated in the hearing aid. With most RIC instruments, the proper depth of insertion occurs when the speaker and tip appear to slide around the turn in the ear canal. This position also provides for the best security of the device.
RITE hearing aids, where the speaker is positioned in the concha or just into the opening of the ear canal, are more likely to mimic the results of shallower ear canal insertion in Figure 2.
RIC and RITE Coupler Attachments
The standard method for electroacoustical measurements of RIC and RITE hearing instruments, especially those that are fitted occluded, is to use an HA-1 2cc coupler. Methods normally used are to seal the tip, either with the tip attached or with the tip unattached, using Funtak (Figure 3), to the coupler to prevent acoustic feedback and to hold the speaker in proper position for the sound bore to be directed into the coupler opening.
Modified HA-1 2cc SB Coupler
This method seems to work well, but when making measurements on multiple instruments, or even measuring over time, a visualization check would show that the sound bore may no longer be positioned properly with the entrance opening of the coupler. In other cases, the speaker tip may be extended downward into the coupler, thus reducing the distance from the speaker sound bore to the measurement microphone, or may have been displaced due to movement. A newly modified HA-1 2cc coupler seems to help resolve this problem, and at the same time, speeds up measurement. The modification is illustrated in Figure 4.
The SB coupler comes with 9mm diameter tips that can slip easily onto essentially any speaker used with RIC or RITE hearing instruments (Figure 5), regardless of the diameter or design of the speaker. The author has been using this coupler for hundreds of RIC and RITE measurements over the past two years. Until now, it has not been commercially available. However, the coupler is now available from Frye Electronics Inc. of Tigard, OR, developer and supplier.
Response Comparisons – Putty Seal vs SB Seal
A comparison of measurement results from the SB coupler versus the HA-1 2cc coupler with Funtack shows that they are comparable (Figure 6).