This topic is currently doing the rounds of the US sites.
Bose is the name which keeps coming up.
My view is that it is almost certainly bogus in the case of the Bose X or Bose A20. I would find it hard to believe they would let this out because their business would be badly hit if this was proven true.
The only mechanism I can imagine for this would be a high frequency oscillation. It would have to be inaudible, and because some pilots are only about 15 years old, it would have to be above 20kHz, otherwise it would be readily detected.
There are also fairly obvious routes whereby Bose ANR headset owners might have more tinnitus:
However, there are some facts which cannot be avoided:
So I am going to do some tests, with this wide bandwidth mike and a spectrum analyser, and will report in due course.
Is that real tinnitus (chronic) or just ringing ears for some hours after the flight just like after a loud rock concert?
I got my tinnitus before I had my first ANR headset. My first 1,000 flying hours or so I wore no headset at all, the aircraft of the flying school where I went had no intercoms or even sockets. I always thought this was a contributing factor but if there is truth in this ANR-causing-tinnitus thing it might have made no difference… Which is something that is hard to believe because without ANR or with a non-ANR headset you have to turn up the volume to an incredible level in order to understand your communications. Just turn the radio on again after shutting down the engine and listen.
I think chronic tinnitus is suggested.
I am 99% sure it is bogus, but one cannot be 100% sure, obviously… It is not the sort of thing which will be production tested. And it is known that QA is (obviously) not 100% – witness the duff mikes which Bose shipped in large quantities in the early 2000s (replaced under a long warranty extension in the USA but not here – I eventually managed to sell them on US Ebay).
Like WN, I have tinnitus from the days before being an Bose X, later A20 owner, that is, according to Peter, before I was rich ;)
In this period of 11 years, no worsening. But of course this is just one data point.
As I understand, tinnitus is a neuro-brain kind of thing where the brains natural ability to filter out noise is somehow distorted so you “hear” background “noise” instead, even when there are no real noise. A condition normally caused by stress or minor neck injury. An ANR headset does very much the same thing as the brain is supposed to do naturally. Therefore the brains natural ability is weakened or distorted by continuous use of ANR headset. Sounds kind of logical, but then again not so much, but who knows?
I have a Lightspeed headset and have no tinnitus.
So, what is the best headset again?
Z for Zulu is naturally more advanced than the X, and certainly the A. By 25 development cycles to be exact.
Mind you one still does get a bit numb after spending 4 hours a day behind a 300hp reciprocating…
Today with the help of my son I did a proper test with a wideband (to 80KHz) mike and a spectrum analyser, of Bose A20 (2 specimens) and Bose X.
The mike used was a Knowles SPU0410LR5H-QB.
No high frequency components were evident.
This video shows a test with an A20, then the X, then another A20
The noise floor varies but no particular care was taken to get the amplitude consistent; the mike was simply pushed into the earcup of the headset while it was being worn. The x axis is a linear frequency axis, with the bandwidth shown as below
What I was looking for were strange spectral lines in the kHz+ region, and there is absolutely nothing of the sort.
The mike was bench tested to 80KHz beforehand.
It is quite possible that the ANR circuitry contributes significantly to the noise floor, but that is some 30dB below the peak audio and thus not important while flying. It would however be relevant if the headset was used in a quiet environment. Bose do sell some products for e.g. airliner passenger cabin use, and I did return one of them a few years ago (a €300 headset) because it audibly hissed and whistled.
While you are at it, Peter, maybe you could do an overall comparison based on measurements between the Bose A20 and the Lightspeed Z. Of course Archie would love to loan you his Z so that you can prove him right 
Having said that, it seems that ‘noise’ is very subjective. Some frequencies/amplitudes are pleasant or neutral to some and irritating to others. A bit like different kinds of music..
Plus, people with tinnitus often have a hearing loss in certain frequencies but also often suffer from ‘hyperacusis’, where certain sounds are actually amplified in the brain. I have this and it can be annoying at times. A flight attendant slapping the overhead bag compartment closed sounds like a pistol shot.. Ahh, good, yet another reason to fly myself.
That test was purely for spurious high frequency (inaudible) emissions. It was nothing to do with ANR effectiveness. Testing that would need to be done extremely carefully, and would be IMHO almost impossible because the location of the mike would be critical.
where certain sounds are actually amplified in the brain
Ask any married man
