I was on another forum and they were discussing hearing protection.
A chap from California put up a interesting post regarding foam plugs, electronic plugs and earmuffs. Also about doubling up on plugs and muffs.
This is a copy and paste from the forum.
Normmatzen Posts: 17 Joined: Mon Dec 20, 2010 4:35 pm
Location: California [h=3]
Re: hearing protection[/h]
#4 Postby
Normmatzen » Fri Mar 03, 2017 12:45 pm
Did I hear some one call my name??
I have commented on this subject so much on 6mmBR that I'm sure folks are tired of seeing my name!
I am first an Electronic Engineer and designed analog Bipolar Integrated circuits for 40 years. My last job prior to retiring was for a company that did research and product development for the ear. The company was founded by and owned by a fellow named DR. Mead Killion. This guy is the smartest person I know. He started the company in the mid "80's and his goal was to build a hearing aid based on a patented device his phD was based on, I got into this arena as I and two other engineers were hired as consultants to integrate Mead's bread board. Which we did, the device became the most used hearing aid amplifier world wide till the digital world exploded. Ironically, the old device is still the simplest, most competent aid for mild to moderate hearing!
Well, I was enticed to go to work for them in the early 90's and as I was immersed in audiology, I marched down to San Jose State University and took the graduate program
in audiology.
That's where my knowledge of ear protection came from. We made, and they still do, Hi-Fi earplugs as well as musicians earplugs that both sound really good, especially the musicians plugs as they were designed for some of my bosses friends in the Chicago Symphony.
Fast forward to today, I will outline the world of shooters hearing protection.
First, when your gun fires 3 ft from your ear, it makes a noise that measures about 160-170 dB SPL. SPL stands for "Sound Pressure Level" and it is the standard for expressing sound loudness. The value is a logarithmic based number and the actual sound increases a factor of two for a 6 dB change, a factor of 10 for 20 dB and a factor of 100 for 40 dB change. Now, the 160 - 170 dB number is 100 plus 60 and 100 dB is 100,000 times the reference and adding 60 makes it go up 1000 times more. By the way, 0 dB is about the hearing threshold for normal young folks.
An interesting reference point is 120 dB SPL which is usually considered the threshold of pain and our guns are 40 to 50 dB above that which is 100 to 200 times louder!
This magnitude of noise means you are NOT doing yourself any favors by buying "convenient" or "easy to use with a gun" protection unless it can honestly produce close to 40 dB noise reduction. I know, subtracting 40 from 160 to 170 still le4aves you with a level inflicting pain.
Turns out, you could fill your ear canal with epoxy and you still will hear somewhat over 40 dB of reduction as no matter what you did in your ear canal, your mastoid bone passes sound through your skull with some what over 40 dB attenuation.
With that all in mind, the safest hearing protection still is the old yellow foamies. But with a caveat! They MUST be inserted correctly, only then will you get the 38 dB reduction they are capable of. Of course, these sound terrible as all you hear is bass thanks to your mastoid bone as well as occlusion effect makes your own voice sound very loud and strange.
Probably ear muffs are the most popular hearing protection you will see at the range.
Every one seems to be wearing them. Unless you are at my range you will notice I do not use them! The muffs with the built in compressor amplifier is convenient but unfortunately, any muff you see on the range will only have about 26 dB of noise reduction. Yes, there are much better ear muffs, but you hardly ever see them because first, they are very expensive and second they are very BIG.
I used to use a solid silicon plug till my old employer brought out a product called the Blast Protector. It is basically the hearing aid amplifier we developed late in 1988 modified a bit and placed in a universal aid that accepts many ear tips so the user can select the one that fits best. Same caveat as yellow foamies, they MUST be inserted correctly. Only then will they have near 40 dB of reduction for loud sounds. So, let's see how this works
The amplifier is a compressor amplifier as well as a hi-fidelity amplifier. The gain for soft sounds is way higher than for louder sounds. So, when no one is shooting, you can clearly hear your neighbor talking to you. Then when folks start shooting but you haven't yet, the gain is reduced about 15 dB or by a factor of 5. The many folks shooting does not sound as intrusive now. Then, you and your neighbors start shooting and what now happens, the amplifier is clamped at a fixed output of 117 dB SPL This is in the vicinity of a yellow foamie! So, once the noise is really loud, the device has turned itself into an expensive yellow foamie.
You can now buy similar electronic hearing aid style protection but most are digital and I don't recomment them. And, not just because my old employer makes the analog one, but because very few digital aids have good fidelity! The nasty secret not discussed in the hearing aid business! That's because good fidelity requires higher speed processors and bigger analog to digital converters and these cost POWER and hearing aid batteries cannot last for the accepted minimum 1 week before they must be replaced.
Another problem with digital aids that is not usually discussed is the reduction of "situational awareness!" Digital amplifiers with low speed, small converters have fairly large delays between what the microphone hears and what the wearer sees. With this delay, your brain has a harder time figuring out where that suspicious sound is coming from! This is why my old employers devices have been clinically tested to insure good situational awareness and are approved for military and police use because of that. It's all about hi fidelity and NO delay so environmental sounds can be properly processed by your brain.
So, now you know what to do. And, I'm not going to tell you who I worked for as my old boss would consider that "Unfair" advertising! Just, don't get muffs!
By the way, if you want to find out anything about this subject, google NAL. I believe that stands for National Audiology Laboratories. My old boss knows the director, and respects him and his group. They are world respected in audiology. Not sure but I think they are in Sidney.
Norm
Top Longranger Posts: 185 Joined: Sat Mar 02, 2013 9:49 pm
Location: Queensland [h=3]
Re: hearing protection[/h]
#5 Postby
Longranger » Sat Mar 04, 2017 3:17 pm
Norm, I never tire of reading your posts on hearing protection. I discovered electronic hearing protection rather late and it is most likely what you actually designed.
Is there any real benefit using say Etymotic GSP-15's with high end electronic earmuffs? I have some hearing loss from years of working in heavy industries and would at least like to mitigate further damage.
As it is, tinnitus seems to be getting worse as I get older so hearing protection is paramount for me. I do wear earmuffs over the earplugs sometimes. I wonder whether there is much benefit doing this if sound conduction through the mastoid bone is significant when firing larger center fires.
I'd appreciate your thoughts on this.
Top Normmatzen Posts: 17 Joined: Mon Dec 20, 2010 4:35 pm
Location: California [h=3]
Re: hearing protection[/h]
#6 Postby
Normmatzen » Sat Mar 04, 2017 4:49 pm
Longranger,
GSP-15's plus electronic ear muffs, Not really a benefit as the properly inserted GSP-15 offers close to 40 db of attenuation. That plus the 26dB or so from the muffs totals 55 dB or so, but your pesky mastoid bone screws up the works by paralleling the 55 dB from muff and GSP with 40 or so for a total of still around 40 dB attenuation.
All you need is the properly inserted GSP and you are there at approx 38 dB.
A workable alternative is to use your electronic muff over a pair of ER-20/ETY-PLUGS. These plugs have surprisingly good fidelity and a fixed 20 dB attenuation for a total of 20 + 26 for 46 reduced by the mastoid to 40. And, they are only about $10 US (I don't know what they are in Australia).
Actually, the electronic muff is a nice package and the amplifier works very similarly to the GSP plugs in that the soft sound gain is at a higher level and the gain drops as loudness increases. I don't know if the muffs have any limiting once dangerous levels are reached or not. The muff + ETY-PLUGS is way cheaper than the GSP plugs, but I'll still use my GSP-15 by itself. for the size and comfort. Many times I leave the range and after driving a few miles I realize I still have the GSP plugs still in.
What is a good idea that maybe you already have done is to experiment with the different tips as well as with the gain switch in both positions. The primary result of the switch is that it adds 15 dB of gain but it does screw up the nice gain vs loudness of the unit at the low gain position. I would only advise some one with a moderate hearing loss to use the extra gain. The choice of tips can be important also as every ones ear canals are different so trying a few different ones can improve the comfort and effectiveness. As an example, I knew the cylindrical foam plug had the best attenuation and long term comfort, but they get all grotty from ear wax and are almost un-cleanable! So, I switched to the large, grey three level rimed tips. They are pretty comfortable as well as staying clean then being cleanable with plain soap and water. Careful of the little plug in the tip of the plug where the tip fits onto. The colored material is not what it seams, it is in reality an acoustic resistor and is used to tune the capacitance and inductance and "Q" of the resultant acoustic circuit to smooth out the frequency response. Get it wet and the attached plug is out of commission till you get a spare and remove the old one and replace it. I think spares come with the GSP-15 along with a tool to remove-replace them.I don't know what they are called, maybe filters? But they aren't, they are resistors. But the guy on the street understands filter more than resistor.
Norm
