Do hearing aids really block out background noise?

Hearing aids by their very nature are sophisticated amplification devices.  As such they do not cancel out noise.  They simply do not reproduce or amplify the noise while they ARE amplifying the speech sounds that you really need to hear.  Depending on the style of hearing aid and the amount of occlusion (blocking the ear canal) the hearing aid may block a portion of the sound.  Especially with more severe hearing losses, the patient is more dependent on the sound coming through the hearing aid and the dispenser will usually choose a style or dome that blocks and seals the ear canal more.  In those cases the hearing aid will help block some of that noise while the processor in the hearing aid filters out the noise and does not reproduce it.  Less severe hearing losses or high-frequency loss only will usually use a more "open" style dome or hearing aid that allows natural sound right through.  That style will not block any of the surrounding noise but because they are only amplifying the signal you want to hear it may seem like the noise is less but just because the rest of the sound signal has been increased so you hear proportionately more of the signal you want and less of the sounds you don't want to hear.  For patients who really struggle with noise it is possible to go with a more closed style or tip than would normally be selected and then increase the amount and range of sound being processed through the hearing aid (which will help filter a certain amount of the noise) to help offset the extra occlusion and allow better hearing in more noisy areas.

This is a simple question with a complicated answer that spans acoustics and electronics. First, the acoustics: There are basically two types of fittings from an acoustic standpoint, open and occluded. An open fitting may have a lot of air access to the air canal, as in an IROS fitting, or conversely may have a little pressure vent that admits very little outside sound. An open fit with a large amount of air access will only reduce background noise in the higher frequencies being amplified by the hearing aid because the low frequency background noise will leak through the open air spaces. An occluded fit will be more effective at reducing a wider range of background noise frequencies. However, only certain types of hearing loss will achieve maximum benefit from an occluded fit. 

Second, the electronics. Most hearing aids use a combination of signal processing and directional microphone arrays to reduce background noise. Microphones deteriorate over time and in doing so lose a good portion of their directional characteristics. Manufacturers show polar plots of microphone response and claim large amounts of background noise reduction in their premium hearing aids, but the reality is that laboratory measurements are done in a clean environment with brand-new microphones. In the real world, environmental stresses on the microphones ( and on the entire hearing aid ) take their toll on performance over time. That being said, some manufacturers do subject their products to environmental testing, but every manufacturer I have talked to admits to some degradation of performance over time. 

Finally, you may have noticed that I used the word "reduce" insead of "block". NO hearing aid actually blocks background noise, except maybe if it is an occluded fitting with the hearing aid having a dead battery! . What the manufacturers mean by "blocking" is that at certain angles off the front axis of the microphone array, incoming signal is reduced as a function of the polar pattern of the microphone array. Then the hearing aid's signal processing uses algorithms to emphasize the speech while reducing the envelope of background noise. The better the CPU in the hearing aid, the better the results. The battle between hearing aid companies is primarily a battle between engineering departments, and the winning engineering department usually has the best mathematicians cranking out sophisticated algorithms. 
 

It depends on perspective.  Hearing aids do not truly block background noise, but can limit what the hearing aids amplify.  The primary complaint of hearing aid users about their performance is how they function in background noise.  What they are really complaining about is not hearing background noise, however, but not hearing what they want to hear (i.e. the speech of a partner) while in the presence of background noise.  Without special features to help in this situation, hearing aids tend to amplify everything around them.  So, the solution for this would be features which limit what the hearing aids amplify.

The key feature for this is the use of directional microphones, which limit sounds based on what direction they are coming from.  Typically the signal of interest is directly in front of the hearing aid user, whatever is within their field of vision (100 - 120 degrees).  When the directional system is activated, the hearing aids no longer amplify sounds to the side or to the rear, so the primary signal of interest is emphasized over the surrounding sound.  There are some hearing aids that use what is known as "beam-forming" technology to narrow the field of amplification down to only 40 degrees, excluding even some sounds that are in the field of vision, when background noise is extremely troublesome.  In most modern hearing aids this directional technology is automatically activated, but some users still prefer to have manual access to it so they can activate it themselves if they feel they are having trouble.

Another noise-reduction tool is "digital noise cancellation", where the hearing aids analyze incoming signals to determine if it is more like speech or more like background noise.  This is where having a higher degree of resolution (or "channels") in the instrument is more important.  The computer chip in the hearing aid analyzes each channel separately, and either reduces or increases the amplification depending on whether it determines the primary sound in that channel is noise or speech, respectively.  As a result, it can help with situations of ambient, steady-state noise like fans and road noise, to reduce their effects on the speech signal that is desired.  The quantity of channels is important in this case because if you have a 4-channel system, a steady-state noise could cause the loss of 1/4th of the bandwidth of speech, whereas a 20-channel would only cause the loss of only 1/20th of the bandwidth, preserving more of the speech signal.  

Keep in mind there are limits to the benefit of any noise reduction system.  In should be noted that digital noise cancellation alone can improve comfort, but has not been clinically proven to improve speech perception in background noise.  The reason for this is that often the speech of other people (i.e. in a restaurant, called "speech babble") is perceived as background noise, and since speech is more broadband in nature, digital noise cancellation is less effective against it.  Improvement of speech perception in the presence of speech babble has only been effective with the use of directional microphones.

But even directional microphones are limited in their effectiveness.  Since the assumption is that the signal of interest is in front of you, the hearing aids will still amplify everything in front of you, including the noise you don't want to hear; if you see it, you will hear it.  So my recommendation is to consider this when choosing your seat in the restaurant.  If you sit with your back to the wall and your conversational partner in front of you, you're facing the noise and may lose your partner's voice in that noise.  If, however, you ask them to sit with their back to the wall and you sit with your back to the noise, you will make the directional microphones more effective since only your partner's voice will be coming from that direction.

Finally, both directional microphones and digital noise cancellation are limited in their effectiveness based on how the hearing aids are physically fit to you.  If you have an "open" fitting, where you only have a small tube or receiver in your ear and the canal isn't very blocked, a lot of the noise can enter it the natural way.  This is the weakest link in a statement that hearing aids "block" background noise.  Unless the ear is fully blocked, noise can still be an issue, and the expectation should be that the hearing aids will only reduce the amplification of background noise, not completely block it.  These technologies reduce any negative effects that the hearing aids might create by amplifying, not eliminate the noise itself.  If the ear canal was blocked completely, then the aids will act as filters for the noise.  This is why the noise reduction is more noticeable with patients who have a more severe loss since their ear canals are more blocked, proportionate to the degree of hearing loss.  Patients with milder losses are typically open fit in order to avoid altering negatively the sound of the own voice, so notice less of an effect on background noise.  Then again, since their loss is milder, they need noise reduction less than someone with a more severe loss.

In summary, hearing aids can prove beneficial in background noise when they are equipped with proper noise reduction technology, and luckily most hearing aids--even entry-level ones--are equipped with such technology.  As others have mentioned, how sophisticated this technology is depends on the level of technology you purchase, and that should be proportionate with your communication demands and how socially active you are.  The more active you are, the more you will benefit from higher-level technology.

Simply stated, yes, research indicates that hearing aids can block out some background noise.  However, it depends on the level of technology, and where that background noise is (ie. behind you or in-front of you).  Noise behind you can be "blocked out" much better than noise in-front of you.  Also, if you have a Speech-In-Noise score, which tests your ability to understand speech in noise, that is very low (good), then you should receive significant benefit from good hearing aids alone.  If you have a Speech-In-Noise score that is very high (bad), then you would likely need to use a remote microphone or FM system to hear in background noise.  

Hearing aids do not "block out" background noise. This is because the noise is there in the environment and hearing aids are not "noise canceling" devices. That said, hearing aids do have the capability to create a separation between sound in your environment that you would want to hear (i.e. conversational speech) and background noise (i.e. crowds, restaurant noise, etc.). The better the hearing aid, the better this separation will be, which ultimately translates to easier listening/communication/speech understanding in the presence of background noise. Now, a lot of different factors will come into play such as an individual's hearing loss, their word recognition ability, and the speaker's characteristics (i.e. soft spoken, versus clear speaker), to name a few, so there is no saying that an individual using the best hearing aids won't still experience difficulty understanding speech in the presence of background noise, but the hearing aids should make it easier.

There are certain kinds of hearing aids that can mask background noises.Hearing aids simply amplify the sound coming at your ear. However modern devices can be tuned so that they enhance only certain frequencies and filter out extraneous sounds that are lower or higher in frequency. 

Great question. The simple answer is NO! There are different microphone settings and noise reduction features that can help reduce noise somewhat,  but eliminating background noise does not exist. There are also some brands that might sell an external microphone that can be very affective in loud environments. Hope this helps! Feel free to give me a call if you would like more clarification.  980-819-9966. Thanks.

The short answer is no, no hearing aids truly block out all background noise.  What hearing aids CAN do, however, is reduce background noise.  Some do this more effectively than others.  High end hearing aids tend to do the best job of this.  Hearing aids reduce background noise in two different ways, multiple microphones and sound processing.  Multiple microphones is shown to the best job of reducing background noise.  Just remember, hearing aids will never know, if more than 1 person is talking at the table in front of you, that you DO want to listen to Aunt Mildred, but NOT to Cousin Tom, if they are both speaking at the same time, close by.