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Best Practices Checklist

Why Ear Mold Vent SIZE is Critical for Hearing Aid Performance

By: Dr Cliff Olson
January 18, 2019
Video Transcript

I often explain to my patients that every little decision that is made about how a hearing aid is fit and programmed will have a dramatic impact on their overall hearing performance. This is especially true when it comes to vent size.  Yes, the hearing aid technology is important, but you have to ensure that the right venting is selected.There are a variety of vent sizes when it comes to hearing aids, from completely open to completely closed and anything in-between.  Getting the vent size correct will have an impact on 4 factors.

1. Occlusion Effect - This is an effect you experience when you plug your ears and hear your own voice as boomy or loud.  This occurs because the bone conduction of your own voice can't escape your ear canal.  If your vent isn't large enough for your voice to escape your ear canal, then you will experience the Occlusion Effect.

2. Blending Low-Frequency Sound with High-Frequency Sound - Most people with hearing loss have better Low-Frequency Hearing  than High-Frequency hearing.  Venting not only allows for your voice to escape your ear canal, it also allows some natural sound into your ear canal.  If you have normal low-frequency hearing, you want this sound to come in through your vents.  Then, you want to blend this sound with amplified High-Frequency sounds.

3. Prevention of Feedback (aka. Whistling) - Feedback occurs when too much sound leaks out of your ear and recycles through the hearing aid microphones.  If your vent size is too LARGE you could be at higher risk of feedback.  In the cases of more severe High -Frequency hearing losses, you must reduce the vent size. 4. Amplification of Low-Frequencies - If you have a Low-Frequency hearing loss it is impossible to provide amplification of Low-Frequency Bass sounds if the vent size is too large.  These sounds must be trapped inside the ear canal to provide auditory benefit.  Vent sizes must be small enough to allow for amplification of these Low-Frequency sounds.  So how do you account for all of these factors to ensure you receive all the benefits of amplification while limiting the negatives?  If you use a generic rubber dome, you have the option of either open or closed.

If your hearing loss can't be addressed with this option, then using a custom ear mold with a custom vent size is likely your best option.  But how do you decide the exact right vent size?This is why the hearing aid manufacturer Phonak developed Acoustically Optimized Venting for their custom earmolds.  By combining your hearing loss data, along with the physical dimensions of your hear canal, they can create a customized vent.  The AOV vent from Phonak:1. Reduces Occlusion2. Preserves High-Frequency Amplification3. Allows for Low-Frequency Amplification

4. Creates a smooth frequency response to improve your hearing experience.They do this by calculating an Acoustic Mass Target Value based on a multidimensional equation that considers your audiometric thresholds, target gain requirements, the potential for occlusion, and the potential for feedback.  They use 3D instrument modeling software to design the vent, precisely modifying the shape, diameter, and overall length of the vent all while keeping the hearing aid as small as possible.  This customization results in a vent size and shape that maximizes the performance of your Phonak hearing aid.  

It also takes all the guesswork out of identifying the correct vent size to precisely meet your individual needs, which is why the Phonak Acoustically Optimized Vent is one of my favorite hearing aid features.  Hearing aids are the best treatment option for over 90% of hearing losses.  However, to maximize the performance of your hearing aids you need to pay attention to the details.  Because one small mistake can result in reduced performance with your hearing aids.  If you get the vent size right, you will be one step closer to maximizing the performance of whatever hearing aids you decide to use.

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