Friday, May 15, 2009

So exactly how good are the best HAs? The facts and my experience.

I will find out more in a few days when my HAs are reprogrammed and will share my experience on that and how much better I hear. What I currently hear is shown below:

250Hz(75db HL) and 500Hz(90db HL): I hear low frequencies up to 500Hz very loud. I can still hear those from the other side of the house!

750Hz(105db HL): I still hear this tone very loud but notice it's half as loud as the 500Hz tone. I can hear this tone from the other room!

1000Hz(110db HL): Much softer than 750Hz, about half as loud and about a quarter as loud as 500Hz. I can still hear 1000Hz from the other end of my room!

1250Hz(115db HL): Less than half as loud as 1000Hz, this tone is quite hard to hear even if I put my ear to the speaker. I can't hear it from more than about 3 feet away.

1500Hz and 2000Hz+(115db-120db+ HL): Most of the time, 1500Hz is inaudible. On a good day, I hear it from a few inches away at threshold levels. 

I am personally surprised by that disparity, once I reach 110db HL, each few db above that quickly fades into nothing. But I hear sounds very loud and well at levels below 110db HL, even the 750Hz tone I can hear very well! I have a piano when when I play it, there is a small difference in loudness between the low(first set) and mid frequency keys(second set). It's when I get to the high frequency keys(third set) that I can tell a noticable volume decrease between each key. My parents do not experience this however for any keys. My dad only experiences this for the last few highest keys since he has a moderate high frequency loss. But for me, the last dozen keys are silent, and the keys before that are very faint.

Some possibilities and theories:

1. Perhaps the dynamics of the ear changes at 110db and up. Below 110db HL, there still is enough functioning hair cells that can be stimulated/amplified. Once you get to 110db and up, there is so few, if any hair cells. Ive read into cochlear dead regions where a very loud sound actually stimulates adjacant hair cells and this does give the person a perception of hearing. The sound may be noiselike, very distorted, off-frequency, felt as a woosh, or simply very faint.

2. I wonder if it's a limitation of HAs but after trying my old HAs from 1998 and comparing my new HAs from 2008 with neither giving me hearing above 1250Hz, but the new HAs making sounds at 1250Hz and below 2-4x louder, yet still not being able to give me anything usable at 1500Hz, I suspect it's my ears.

3. I am able to get a response on the audiometer at 1500Hz, 2000Hz and sometimes even 3000Hz in the 115db to 120db range. But I don't recall hearing any shrill tones or whistles. It's likley I heard a low frequency distortion that came from the audiometer and/or due to the cochlear dead region phenomenon. I also hear the same distortion comming from my speakers at 1500Hz, 2000Hz, 3000Hz, 4000Hz, etc. It sounds like "ehhhh" like humming or static.

4. I will find out more when I ask my audie about this and when he reprograms my HAs. He did say that at 120db, HAs cease to become useful. I can ask him what about at 110db, 115db and in between 110db and 120db.

5. I do know that the pain threshold as well as UCL(uncomfortable level) occurs at or around 120db. Thus even if you could attempt to amplify a 120db loss with an insane amount of gain/SPL, it won't be pratical as there's zero dynamic range, would not be comfortable and might even cause damage to adjacant functioning hair cells.


On another note, given the max SPL of my HAs(Phonak Naida V UP) as well as the UCL/pain threshold, the worst unaided audiogram(assuming no cochlear dead regions) someone can have and still hear anything is as follows:

frequency/db HL/SPL HL/HA max SPL dbA/dynamic range

125Hz: 95/120/123/3
250Hz: 105/121/126/5
500Hz: 115/127/130/3
750Hz: 115/125/135*/5
1000Hz: 115/124/140*/6
1500Hz: 115/125/135*/5
2000Hz: 115/127/130/3
3000Hz: 110/126/128/2
4000Hz: 100/116/119/3
6000Hz**: 85/106/110/4
8000Hz**: 60/86/90/4

Above 4000Hz can't be aided with my HAs, however you can give transposition/soundrecover a try. This shifts the high frequencies down as low as 1500Hz from what I heard.

* My HA is capable of above 130dbA SPL, however for many good and obvious reasons it's not recommended to exceed 130dbA SPL. I assume all SPL figures to be "A" weighed.

** A different HA meant for mild-moderate HOH people is capable of going up to 8000Hz. HAs for profound losses don't go much above 4000Hz for many good and obvious reasons.

I will have to find out what SPL my HAs have been set at. I can tell you right now that I am happy with the SPLs up to 1000Hz. I barely hear anything at 1500Hz and I am going to find out if it's my HA or if my cochlear dead regions start around 1500Hz. Ill also find out what's the min dynamic range required to get usable aided hearing. I do know it's more than 1db, probably at least 5db. If so, subtract about 5db from the worst unaided audiogram.

There are no 120db HL figures above since my audiologist said a 120db loss can't be touched/aided by any HA. For those with 120db HL, it may in reality be 116 or 117db since you didn't respond to a 115db tone so the next increment was 120db which you responded to. You may also have the SPL set to 132-136 dbA. Some people experience discomfort and risk damaging their residual hearing but they feel they have no choice. I do have a choice for the low frequencies and don't need insane amounts of SPL. I would rather not hear 1500Hz than hear that frequency with the SPL turned up to uncomfortable levels. HAs should never be uncomfortable and right now they aren't for me. My audie is going to try for more gains and even SPL and that will depend on comfort levels. Maybe I can get a couple db more, well see.

I would get a CI myself if my low frequency hearing got much worse to the point where HAs ceased to be useful. I have no high frequency hearing and little mid frequency hearing but a decent amount of low frequency hearing and that's where most of my benefits come from. 75% of sounds and 60% of speech takes place at 500Hz and below so I don't feel I am missing that much by not hearing any high frequencies. I still have some mid frequency hearing so I can hear more than 75% of sounds and 60% of speech. I have read some good articles on the usefullness of those with left corner audiograms who have mostly or only low frequency residual hearing. Ill post about that some other day and link to the article.

I am tired now, ill keep you guys updated with any new facts and experiences. Thanks for reading, feel free to comment and I shall respond.

1 comment:

  1. I only wear one hearing aid in my right ear.
    It is a Beltone and I don't know any other specifics about it, I'm at work and don't have all the info on it.

    I like my aid, it helps when dealing with people during the day.

    But, I have to admit, I look forward to taking it out at the end of the day.