Is making ear impressions for in ear monitors (IEMs) different than making ear impressions for hearing aids?
With custom IEMs, fit is king. As with hearing aids, fit and comfort are extremely important with IEMs. With IEMs, between performing, rehearsals, and MP3 listening, many of your patients will likely be using them for several hours each day. IEM users will generate far more perspiration than the typical hearing aid user, and a proper fit is also responsible for keeping sweat from making its way up the ear canal.
By contrast, a poor fitting IEM can lead to discomfort, a tendency to fall out of the ear, and poor sound quality as sound leaks around the poor seal. This, in turn, can have a domino effect of other negative consequences, such as the volume setting and mix being compromised to compensate for the poor sound quality, inadequate hearing protection due to the poor seal, and ultimately, rejection of the IEMs by the performer.
With custom IEMs, a good fit is a primarily the result of a good, deep ear impression.
Most of the major custom IEM manufacturers make the following recommendations for taking IEM impressions, some of which may differ from typical hearing aid impressions. First, use a 2" bite block to keep the patient's mouth open while the impression material sets. This is because jaw movement slightly alters the shape of the ear canal. With IEMs, you need to maintain a good seal when your jaw moves into a wide-open position while singing or speaking. Next, it is also beneficial to have the impressions taken as deeply as comfort allows, preferably to the second bend in the ear canal. This increases the hearing protection of the IEM by adding mass between the external stage volume and the eardrum. It also minimizes the occlusion effect by reducing the air volume between the IEM tip and the eardrum.
It's important to note that you should choose a manufacturer who will rework the fit should it not be perfect the first time, just as with custom hearing aids.
Keith Gordon is Director of Marketing and Sales at VitaSound Audio Inc. (www.vitasound.com). He is a veteran audio engineer who mixed monitors for over a decade before overseeing development of a DSP-based hardware/software IEM system in conjunction with Westone Laboratories. He can be contacted at email@example.com