Two words:

 

Flat Glass...

 

It's a legacy of the somewhat common tooling and construction of all of Boeing's smaller 'Section 41's'. It is even worse on the 727s. I had the privilege as a youngster (read: at least a decade ago ;|) riding jump in one of those. We only got up to .82 but it was well beyond normal speaking volume. I didn't have a headset and remember trying to read/hear...with difficulty...the F/Es instructions during the decent to get the approach plates and such prepped up for everyone. When I commented on the noise to the crew back on the ground, the crusty ol' F/E commented on how bad it was when they used to fly them balls to the wall up to .89. The crew were all wearing DC's.

 

I've only been up front in a 37 once...and it was an -200. I don't remember it being particularly loud...although I chalk that up to the fact that is was only a 45 minute trip and I only remember us getting up to FL270 or something around there. We probably only peaked out at .74 or something. Mind you that's what everything cruises at now so who knows how loud it really is.

 

By comparison the Crash-8 is quiet enough that one doesn't even operate them with headsets. Just use the palm mike and cockpit speakers. Been on lots of trips like that. Granted it wasn't the busiest airspace either though.

One night when I was a 727 engineer we were going Mach .89 and that was so loud I couldn't hear what the Captain and FO were saying. Of course it has the same cockpit shape as the 737 and it flies faster so it was louder even at normal cruise speeds. But the 737 is pretty loud though. I use a Clairty Aloft Pro Aviation Headset. Makes it nice and quiet.

Here is a link to a study that was done in 2001 for hearing loss in relation to pilots. It took readings on flight decks using standalone sensors and a test dummy observer (Kemar). The article is somewhat lengthy and boring so search for "table 2" if you want to get to the results. Granted, this is for a 737-400 but I think it is still interesting to see what they found. The results show the db readings for ambient sound on the flight deck and db levels with the headset sound. The 734 and Airbus 320-111 were pretty similar at least. Not sure what later variants have shaken out to be.

 

http://aeromedical.org/Articles/NIHL.html

In the report, Figure 5 is interesting because it shows that not all noise cancelling headsets reduced the background noise. Presumably they've improved since 2001.

 

For those who wear the earpiece on only one ear, I suppose you still have to crank up the volume to compensate for the noise in the other ear.

 

Also, in Figure 3, the sound level with the traditional headset, when there was no communicating, was about 4dB(A) higher than without it which is surprising considering that an increase of 5dB(A) is a doubling of the sound level.

Interesting thread indeed.

 

I assume Boeing fixed the " issue " on newer 787, correct ?