Bose A20 Headset Silly Question
 

Possibly a very silly question here from a newbie, but would appreciate an answer from any current owner of a Bose A20 headset as I’ve found conflicting answers online…

I’ve just purchased a second hand pair and when they are turned on in a quiet environment (plugged in or not) there is a very noticeable hissing/static noise, about the volume of a running tap. This becomes less noticeable with louder background noise, in a GA aircraft with the engine running it can barely be heard at all - is this normal for an ANR headset? I just want to check as they were advertised to be in perfect working order.

I’ve tried cleaning them out and changing batteries.

TIA :)

I have a pair of Bose A20 but they have never had the batteries fitted. When powered by the LEMO connector I do not hear any hissing with avionics master on and engine at idle. Normally my headset volume is close to maximum and audio level is controlled at the audio sources.

If you don't receive any other answers I may try installing batteries in one A20 and run a check with the headset not connected to the aircraft.

Appreciate it EXDAC. Just want to make sure I haven’t bought a faulty set while I still have the chance to return them. I’ve never owned any Aviation headset with ANR before so I’m only going off my experience with standard noise cancelling headphones (e.g. AirPods Pro) with which I’ve never heard any static.

https://www.boseapac.com/en_in/suppo...0/article.html

Seems to say Bose does not expect you should hear hissing/static noise and headset requires servicing. It may be worth checking the auto on switch position. Confirm you do not have the headset paired to anything with Bluetooth.

Possibly related discussion here - https://www.pprune.org/medical-healt...-tinnitus.html

I just tried turning the noise cancelling on on a pair of mine while they were not connected and while I was in a quiet room environment. I can definitely hear a static noise, but I wouldn’t say it’s as loud as running tap water. Strangely enough, I never heard it while in the plane - on the ground with the engines shut down or while flying. Sometimes I can hear noise, but it’s coming from another pilot’s microphone, because once I turn the interphone off, it’s gone. I’m using full volume on my headphones and control the volume through the audio control panel.

My Bose A20 are in the airplane but I did check my DC 13.4 that I had converted to ANR. I can hear a slight hiss in my left ear but not with my right ear. I have had degraded high frequency response in my right ear for many years.

I used those converted DC 13.4 in my PA-28 and was never aware of the hiss when flying. Much quieter than a running tap and really only aware it is/was there today at ANR switch on and switch off.

What kind of AA batteries did you use? One (surprising) thing I noted a few years ago when I tried Energizer Lithium batteries in the A20 is that they didn't work well. There was a weird hiss that's never been there with any alkaline battery. While both nominally 1.5V, the Lithiums have a higher initial voltage - unsure if there's any other characteric that might have contributed. I just shrugged and went back to alkalines.

These are a GA twin plug pair so they don’t have an Auto-on switch.
The switches are positioned as follows:
BT/AUX : BT
INTERCOM : MON
AUTO OFF : ON
Connecting/disconnecting from
Bluetooth doesn’t change much, unless I play something loud enough through the Bluetooth to drown it out.

I’ve tried a pair of rechargeable AAs, as well as Energizer Max alkaline batteries, I can’t perceive any difference in static noise between the two.

I’ve got the number for Bose aviation support now, so I’ll give them a call tomorrow to see if they can shed any light.

It's about 5 years since I looked at the switches in my A20 control modules but I can see no need for an Auto On switch with LEMO power. Mine simply turn on when avionics bus powers the LEMO jack. The on-line Owner's Guide shows the Auto Off switch so that may be what the article I linked earlier was referencing.

Does the hiss change if auto off is disabled?

I suspect your best bet would be to compare with other Bose A20. Perhaps a local flying club?

I flew today and, at a quiet remote airstrip, I tested with LEMO power and internal battery power. In both cases there was an audible hiss but it was at low level and would not have been detectable with engine at idle.

There is an Auto On switch in the LEMO configured control module. I changed no switch positions for my test.



https://cimg6.ibsrv.net/gimg/pprune....4cefc3beb1.png

The topic of noise-cancelling headphones was discussed in Pax&SLF a while back from a pax point of view, https://www.pprune.org/passengers-sl...nes-again.html but some professional pilots also contributed comments about comfort when flying long-haul. The A20 wasn't specifically mentioned but the QC25 and QC35 were. Neither are particularly expensive. I went for the B&Ws but I'm just a pax and audio quality is my main concern; the Bose's are preferred by pilots from a comfort point of view.

Any power source has what is called a source impedance, and the 'wrong' impedance can adversely affect some circuits.

As has been suggested, try different makes of batteries. Even though headphones use very little power, batteries designed for high current applications - e.g. big photographic flashes or things with motors in - will have a lower source impedance and might help. If not, try some designed for low power applications such as clocks or television remote controls.

I have Bose QC 25's and they only use a single AAA battery for noise cancelling, and it lasts a long time. The QC 25 ANR does not introduce any significant noise when switched on. Significant hiss or static, sounds like a fault to me - although my highest frequency hearing is probably not as good these days, (thank you Motörhead, Black Sabbath and Van Halen concerts for doing that !).

I only ever used the A20 once or twice, but I have loads of hours using ANC headsets (Softcomm and D&C ones). Mine do have a constant bit of white noise at a relatively high frequency when switched on, but it should not be more than a running tap. It depends a bit on the quality of the headset and of the state of your hearing whether it is noticeable or not. At a guess, the A20 should not produce a hiss that loud.

Consumer style ANC/ANR headphones are better at this, but aviation headsets may use a more aggressive noise cancelling approach and this may (could) lead to this effect being more noticeable.

Many thanks all for the informed replies.

After speaking with Bose support and trying on a friends headset, hearing a very similar level of static, I’ve decided not to return mine.

It seems I am simply a little more susceptible to high frequency sounds than average - probably unsurprising given I’m in my early twenties and a newbie who has not yet been exposed to lots of constant loud noise. This was further confirmed by having my parents (late 50s) try on the headset, only for one to find the static to be barely perceptible and the other not able to hear it at all!

The headset seems to be doing its job perfectly well when being used in its intended setting - close proximity to an aircraft engine, rather than a quiet room. So I’m happy!

Excellent, I am jealous :)

And in your life, always use hearing protection - e.g. for DIY etc. You often see people use eye protection, and sometime gloves, but almost never hearing protection. But it's just as important.

I even use ear defenders when doing the vacuuming ! Too late to recover the high HF I've lost, but I don't want to lose any more !

What you hear is the echo of the big bang:rolleyes:. But do not expect to get a Nobel price for this discovery. Arno Penzias and Robert Woodrow Wilson have already got one for it!
But seriously: ANR uses highly amplified back-coupling of an external microphone which is prone to any kind of unwanted acoustic and electronic feedback. It's a wonder it works actually so well over a large range of frequencies, that's why they are not really cheap. I used the Bose (and other ANR devices) for quite a while during my flying in a noisy oldtimer and was always pleased for its quite ride and excellent voice transmission from both headset and noise cancelling microphone.

Nothing wrong with a bit of hiss.
I have tinnitus, so I hear hissing in or out of the aircraft, with or without cans on.
Bose are great........I have them in the car, albeit in the doors.
Maybe cleared to cross is right ....Big Bang Residue

With the old Telex headsets, one went deaf in the left ear as an FO, and then deaf in the right as a skipper…

Hiss can be very intrusive.

'Big Bang residue' is residual electromagnetic radiation detected by a suitable 'radio' receiver. So if the headset is receiving radio or BlueTooth, then yes, but if no receiver is involved; the hiss heard is the noise caused by the random nature of electrons flowing through audio circuit components.
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