When choosing a new headset, for most of us we have to rely upon the marketing information in order to decide as it is difficult to try before you buy. Well I have both Bose A20 and Sennheiser S1 headsets and thought I would pass on my personal experience for anyone trying to choose.
I bought the Bose A20 set a year ago to replace my ageing DC 20-10s and was extremely pleased with the light weight, comfort and noise attenuation. However, I am getting on and have started to suffer from a slight hearing loss, particularly at the high frequency end of the audio range. After the initial euphoria over the Bose noise attenuation I started to realise that I could not hear all transmissions as clearly as I could on my old DCs. When Sennheiser announced the S1’s with digital sound processing and a treble boost facility I took the plunge and bought a pair. On the down side this headset is larger, although very comfortable, and I have found that the noise cancelling mic does not seem to cancel the cockpit noise as well as the Bose, despite adjusting the mic gain. This means that the intercom squelch control has to be set very accurately. Also, despite the marketing hype and performance figures, the Bose headset sounds quieter than the Sennheiser and it is necessary to press the button on the outside of the Sennheisers whenever engine noise changes if maximum noise reduction is to be achieved.  However, with the treble gain set to the mid boost position, to my ears, there is absolutely no contest when it comes to clarity of transmissions – the Sennheiser wins hands down. I relegated the Bose headset to the P2 position but more recently designed and installed a variable treble gain circuit to sit between the intercom and the earphones: the result is that, again to my ears, the intelligibility is now as good as the Sennheiser’s.