By: Amit Gosalia, Au.D., FAAA
Board Certified Doctor of Audiology
Audiology Clinic, Inc.
505 NE 87th Ave., #150
Vancouver, WA 98664
(360) 892-9367
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www.audiologyclinic.com
“Dr. Gosalia, I just bought a pair of $8500 hearing aids from XYZ in Portland. I was told that I would hear normally in all environments, including restaurants and ball-games. I am less than pleased because I still can’t hear or understand in noise. Did I waste my money?”
This was a case I dealt with a few months ago. This patient went to a business to purchase hearing aids, and this franchise/chain location set some lofty expectations for the patient. As hearing instrument technology improves, so do patient expectations. Terms such as noise reduction, noise management & directional hearing (along with many other proprietary terms) give the perception that the end-user will not hear background noise, and only hear the person in front of them. Unfortunately and fortunately, this is not true. Below I’ve touched the surface of noise, noise reduction and directivity.
Let’s start with noise. Noise is any disrupting event (in this case, sound) that impedes one’s ability to sense (in this case, hear) a signal (in this case, speech). For the purpose of this post, we’ll concentrate on hearing speech within a noisy environment. A general term and formula that is used in hearing healthcare is Speech-to-Noise Ratio (SNR) which tells us how loud speech is in relation to noise. For example, average speech is 45-55 decibels (dB) hearing speech in a basketball stadium where the crowd is cheering over 90 dB is difficult because the speech is 35-45 dB lower than the noise. This is considered a very low SNR; now compare this to speaking at a normal volume in a quiet library, the SNR will be high making speech much easier to understand. When someone has a hearing loss things change. Without amplification important parts of speech are not heard well, making understanding the person next to you difficult, if not impossible. The natural ability of any person to hear through noise decreases as hearing loss increases. This is a fact that has been well established in research on the human auditory system. Thus, a hearing aid can help make missing pieces of speech more easily heard but it cannot repair one’s ability to hear through noise and find valuable pieces of speech. For this reason, modern hearing aids focus on managing noise and amplifying clean speech.
Hearing instruments can come with or without venting. Vents are holes that are drilled through either the hearing instrument or the earmold for the purpose of letting air and sound travel in and out of the ear canal. The larger the vent, the closer you get to a more natural, open ear. Newer technology has allowed us to keep the ear open with small hearing instruments that rest behind the ear and even some custom molded devices (please see other postings for detailed descriptions of hearing technology). As cute as they may be, if your hearing is not within or near normal limits in the lower frequencies, an open ear device may not be for you.
One advantage of an open ear hearing aid is to allow low frequency sound to escape the ear canal, keeping the user’s voice more natural. When the user complains of hearing their own voice in their head or sounding as if they are speaking in a barrel, it’s usually a phenomenon called occlusion (or ampclusion). Keeping an ear canal open minimizes this effect but also introduces two detrimental issues. First, low frequency environmental sounds will bypass the hearing aid and travel into the ear naturally through the vent. These sounds that bypass the hearing aid are often heard naturally because most hearing losses are minimal in the low-frequencies and greater in the high-frequencies. This also means that the hearing aid is not able to process the sound before it’s heard, so technologies such as noise reduction do not affect low-frequency sounds in the open ear hearing aid.
Secondly, directional microphones will prove less beneficial in the open-ear fitting.2 What this means is that the more open the ear canal, the harder it becomes to hear what’s in front of you. So, theoretically, if our goal is to have the instruments focus more front-facing, the ear canal should not be very open. Note that normal low frequency hearing will be affected by closing the ear canal, and opening the canal with moderate to profound low frequency hearing will result in less hearing in those frequencies.1,2
So, what does this tell us about hearing in noise with amplification? You will hear background noise in noisy environments. You will most likely hear the kids screaming four tables away. You may still have difficulties hearing the person across the table from you. The good news is that with proper hearing aid selection and the correct technology that meets your lifestyle and budget, you’ll hear much better. Only a well trained hearing care professional can make these choices and help you to establish reasonable expectations for better hearing.
“Ms. XX, although the level of technology you purchased is consistent with an Active Lifestyle (in our clinic approx $7500 – $1000 less than the chain!!), you should know that hearing aids only supplement your hearing in those difficult environments. In fact, with normal hearing, I have difficulty hearing at basketball games and certain restaurants as well. Although we can not restore normal hearing, we can help you hear much better in more environments. You will still have some difficulty hearing and understanding in certain environments, but, with some realistic expectations, expert advice, and some auditory retraining, you will find greater success.”
1 What is the Effect of Venting on Directivity? Audiology Online 10/2009; Todd A. Ricketts, Ph.D., CCC-A, FAAA
2 Efficacy of an Open-Fitting Hearing Aid; Hearing Review February 2005; Francis Kuk, Phd, et al
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