Thomas J. Norton, February 1996
Thomas J. Norton wrote about the Sennheiser HDC 451 NoiseGuard headphones In February 1996 (Vol.19 No.2):
On my recent trip to the UK (see "Industry Update" in this issue), I brought along the same set of Sennheiser noise-cancelling headphones reported on by Wes Phillips in the November 1995 issue (Vol.18 No.11. p.193).
Since I didn't want to carry along a portable CD player and a large enough collection of CDs to make the effort worthwhile, I used the Sennheiser 'phones either for straight noise canceling or in place of the airline's headset to listen to the in-flight entertainment.
As a pure noise-cancelling device on an airplane, I found the Sennheisers to be useful, but not a substitute for a good set of earplugs. There was a noticeable reduction of noise in the midrange, but I didn't find it in any way dramatic. After arriving at my destination, however, I found that the HDC 451s did provide a much more noticeable reduction in noise during highway car travel. I was a passenger; don't do this while driving!
Using the Sennheisers as conventional headphones with the noise reduction engaged, in the plane, proved to be a washout for me. The perceived frequency balance of the source went from okay (but hardly hi-fi) with the noise reduction off, to unpleasantly peaky in the voice region with the noise reduction switched on. I couldn't stand to listen to it for more than a few seconds. Needless to say, it was not possible to assess the absolute quality of the source herethe airline's in-flight music and movie but I found it much more listenable with the noise reduction switched off. Actually, I got the most listenable quality, overall, when wearing a set of earplugs under the Sennheisers. Muffled, but at least listenable.
Incidentally, the best earplugs I have ever found are 3M's model 1100 squeezable plugs. Unlike most such plugs, which start to unsqueeze before you have a chance to fit them into your ear canal, the 1100s stay compressed long enough to get a decent fit. And they're really effective. But if you do take to wearing earplugs on an airliner, watch for pressure changes. When climbing orespeciallydescending, leave the plugs out. With them in, it's hard to sense pressure changes and take the necessary steps to clear your ears. Don't wear earplugs if there's any chance you'll fall asleep just prior to or during descent. The most pronounced pressure changes occur during the last few thousand feet on descent. (Typically, an aircraft's cabin is kept at a pressure equivalent to an altitude of about 8000').Thomas J. Norton