The directional microphone is one of the most important elements of a hearing aid today. One of the biggest issues faced by people who suffer from hearing loss is the ability to separate speech from noise.
People with normal hearing are able to naturally and instantly filter out background noise along with other non-important sounds in their environment. It is what allows them to sit in a crowded restaurant and hold a conversation with the people at their own table at a normal volume.
People with hearing loss, however, cannot as easily distinguish between important and unimportant sounds. They hear everything at the same volume and it makes it very difficult to focus on speech.
Directional microphones are one of the only hearing aid features that improve speech understanding in noisy environments.
Directional systems in hearing aids have two or more microphones separated by a specific distance that work together to pinpoint the origin of the sound that you hear. Because there is more than one microphone, the device can calculate the difference in the amount of time it takes for sound to reach each microphone and then pinpoint how far away the sound is based on that calculation. The more microphones that work together, the more accurate the distance will be.
While directional microphone technologies vary from device to device and from brand to brand, you will find that it is this directionality that helps you hold conversations in noisy environments without frustration. Most directional microphones focus on the sound in front of you because that is the direction in which most conversations occur.
The following is a description of the importance that directionality plays in hearing aids along with a comparison of different types of directional hearing aids and the technology that leads to better directionality.
Directionality: What Is It and Why Should You Care?
Directionality is the ability of a hearing aid to pinpoint the direction and origin of the sounds it picks up. Hearing aids can then filter out background noise so that speech and other important sounds are heard more easily based on the direction from which the sound is coming. Without directional microphones, you would simply hear every noise at the same time. A hearing aid uses two or more microphones that work together to calculate how far you are away from the noise you are hearing and from which direction that noise is coming. These microphones then focus your hearing on speech based both on the direction and frequency of it.
One of the most prominent consumer-based complaints about hearing aids is the amplification level of background noise. Directionality is important because it is the only proven hearing aid solution to that complaint and as such it can improve speech understanding in noisy environments. No matter what stage of life a person is in, there will be noisy environments where you want to be able to hold a conversation and understand what the people you are with are saying. Whether at a restaurant, in a hospital, attending a sporting event, enjoying a concert, and many other noisy situations, you want to be able to hear the voices of those around you. Directionality is key in this endeavor. In addition, it is through the use of directional microphones that you can pinpoint both the direction and origin of sound even when your ears and brain can no longer do that for you.
Directional Hearing Aids
As important as directionality is in hearing, it is also complex. It is so complex, in fact, that different brands of hearing aids use different directional systems to help them pinpoint sound. The following are some of the terms you should know when doing your research on directional microphones for hearing aids:
Null
The least sensitive portion of the microphone response or the area that turns toward the sound to make it less noticeable.
Electret microphones
The majority of hearing aids today use this type of microphone. These microphones use a diaphragm held close to a metal plate that holds an electric charge. Sound moves through the diaphragm which allows the hearing aid to detect, amplify, and process the sound. The sound is changed into an electrical equivalent that can then be sent electronically to a microphone in your ear.
MEMS microphones
Often referred to as silicone mics or microphone chips, MEMS microphones are made from silicon crystals and are resistant to moisture and temperature changes. MEMS stands for “micro-electromechanical systems” describing the processing technique used to manufacture it.
Drift
Drift occurs when the sensitivity of your directional microphones is not matched.
Here is a brief overview of the two main directional systems that are out there, either simple directional microphones or adaptive directional microphones:
Simple Adaptive Directional Array
Simple directional microphones need two sound ports most often at the front and back of the hearing aid. It can either be two separate microphones or one microphone with two sound ports. Because there is a separation between the two places where sound enters, background noise will enter both microphones at the same time so that when noise is received equally by both sound ports, your hearing aid filters that sound as background noise. The sound that is coming from one direction, on the other hand, is more likely either speech or some other important sound and that sound is amplified so that you hear it over the background noise. Many times this type of microphone is all you will ever need to hear better in noisy environments.
Fully Adaptive Directional Array
An adaptive directional microphone is able to follow speech sounds around your environment no matter where they are coming from. These hearing aids create a map of the type and location of the sounds you are hearing, and based on the information collected, they can pinpoint where different sounds originated. These microphones can focus on the main noise source while minimizing the sounds around the hearer.
Adaptive directional microphones more effectively highlight important sounds while suppressing background and ambient noise. The caveat is that sometimes these microphones may suppress the sounds that you want to hear while amplifying the sounds that you do not.
While most systems are either adaptive or simple, there are some other directional systems that use aspects of simple, adaptive, and omnidirectional microphones to create new systems. They include the following:
Asymmetric Directionality
Asymmetric directionality was developed because most directional systems reduce low-frequency sounds because most speech occurs at higher frequencies. In this system, the hearing aid in one ear will be omnidirectional while the hearing aid in the other will be directional so that you hear sounds equally at all frequencies while at the same time placing more emphasis on sounds happening right in front of you.
Pinna Directionality
This type of directionality mimics the directionality of your outer ear. In this type of hearing aid, low frequencies are processed omnidirectionally while high-frequency sounds are processed directionally.
In general, there is not one directional system that is better, it comes down to the preference of the hearer. With that said, you should talk to your audiologist to decide which directional system and which brand works best for you. While most brands use the same basic microphones, they vary in how the information collected by the microphones is used. Your audiologist will know which brands can be set most effectively for your ears and level of hearing loss.
What Are Omnidirectional Microphones?
An omnidirectional microphone is one that picks up sounds from all sides and directions without prejudice. Sounds that come from behind you are just as important as those that come from in front of you or from the side because they are all given equal amplification. Every hearing aid you will ever wear includes an omnidirectional microphone. Omnidirectional microphones are often paired with directional microphones for optimal hearing aid performance. When they are paired together, you can combine the strengths of both microphones depending on the environment you are in.
Omnidirectional microphones work well in quiet environments. When you are sitting at home, hiking in nature, or doing things where you want to be able to hear every sound in your environment equally. Because it picks up and amplifies all sounds equally, it does not work as well in loud places with a lot of background noise. In those settings, the background noise will be amplified just as much as speech and other important sounds and it will be hard for the wearer to hear anything well.
Directional Microphones
Directional microphones pick up sounds from an assigned direction, usually directly in front of the hearer. These microphones are effective in noisy environments because you can focus on the sounds directly in front of you and filter out the less important sounds coming from behind and from the side. When you are holding a conversation with someone else, they are most likely directly in front of you and more than likely there is no other sound originating closer to you than they are. Because of this, in a noisy environment, the proximity of the speaker and the direction that their voice is coming from combine together to make the directional microphones on your hearing aid focus on that speech allowing you to hear their voice over all of the other sounds in the room.
Considerations For Choosing Directional Microphone Technologies
Almost every hearing aid manufacturer has developed directional microphone technology, and the higher end hearing aids feature adaptive directional microphones when it comes to hearing speech in noise. While each manufacturer uses directional microphones, it is the way they use the data that directional microphones supply that sets them apart from each other. While they each get there in a different way, there is not much difference between the end results of the directional microphones from each manufacturer, so it is up to your audiologist to decide which technology would suit your situation the best.
When choosing the directional microphone technology that you need, your specific type of hearing loss and the capacity of your hearing should be taken into account as follows:
Symmetric Hearing Loss with Good Central Auditory Processing
Pinna directionality is a good choice for your basic program because it preserves localization cues.
Symmetric Hearing Loss with Poor Central Auditory Processing
Aggressive adaptive directionality should be used so that you can easily localize sounds and focus on the more important noises in your environment.
Unilateral Hearing Loss
If you suffer from unilateral hearing loss, the main goal is to restore binaural hearing. In this case either Pinna directional or omnidirectional is preferred and automatic adaptation or noise reduction should be done only with caution. You want to have the best balance between your two ears that is possible.
Asymmetric Hearing Loss
When your hearing loss is asymmetric, your better hearing ear should take the lead in the fitting.
Directionality is one of the most important considerations for hearing aid wearers because it can mean the difference in whether or not you can converse with friends and loved ones in noisy environments.
Think about the different places you go. Spending time with a group of people in someone else’s home, going out to dinner, having a conference call at work, attending a sporting event, etc. Everyone finds themselves in loud situations where they want to enjoy the company of others. If you cannot hear them speak or hold a conversation with them, then what is the point?
If your hearing aid does not help you hear in these noisy situations, it can lead to annoyance, isolation, and in the long-term missing out on being with the people you love. Directionality is what helps you hear someone’s voice in a crowded room and allows you to hold a conversation or pay attention in a meeting and as such is one of the most important features of today’s hearing aids.
