I guess that since you are an audio engineer, you are more worried about "cumulative damage" over time. 120db is more than enough to cause permanent damage over time but your main concern should be the sound of the aircraft itself.
I have been able to hear my ProTrack with ear-plugs in while it is inside of my Bonehead helmet. I will usually wear ear-plugs if I am doing some hard-core JM'ing and have to spend a lot of time in or have to ride the plane down.
While in free-fall, I don't think it would be too much of a problem as the wind-noise itself will act as more of a pink-noise mask.
While my Pro-Track is ungodly loud on the ground, in the air it is "just right" and is not startling at all, more of a light "intrusion" with or without ear-plugs.
As sympathetic as I am to your concern I think that the audible being tooloud is a small concern that could be remidied with a small bit of fabric or tape. I think that you should remember that you primary reason for wearing an audible is to HEAR IT. Just a thought.
I tested my Skytronic Pro and my ProTrack with a sound level meter and found them both to be acceptable given the actual time of exposure. I wrote the numbers down someplace, and I'll post them if I can find them. I have my hearing checked every couple of years (had some loss at an early age due to gunshots and operating heavy equipment without protection) and so far there has been no additional loss. I was also worried about the time spent on the airplane without any protection but, again, so far, so good.
Airplane noise will definitely damage your hearing. Wear earplugs during the airplane ride. I have worn earplugs for my last 2000 skydives and have little difficulty equalizing. If you are worried about equalizing or hearing your beeper, then hang you earplugs on a string and tuck them inside you helmet just before you turn onto jumprun. I don't always hear my beeper, but I write that off to fear induced deafness. Besides, my beeper is set to go off at line stretch, so I am pretty busy when it beeps.
Some marketeers even advertise that earplugs help airline passengers equalize!
I used to sell high end audio... (yes i'm suffering from hearing loss.) Assuming that you are a male and concerned, that probably means you've hit the big three-o. Hearing loss is a gender specific problem (or a plus if you're married). At about age thirty, ALL males will begin to lose a fair amount of hearing (specifically higher frequencies). It is very important that you take any steps to preserve your hearing... (WEAR EARPLUGS ON AIRCRAFT!) The beeps of your ditter need to be at 120+dB to overcome the ambient noise of freefall. If it was "quieter-more comfortable" you would not hear it. At about age 35 I gave my new ditter (120dB+) to a newer jumper because i quit hearing it. Don't worry about the loud audible altimeter; start worrying if you quit hearing it. The short, loud sound is nothing compared to the continuous noise of the aircraft or freefall.
What? Is someone talking to me? Is that music playing?
Chris (soon to join Billy Vance and John Woo for the record attempts attempts...You guys rock!)
I just read an article in Modern Drug Discovery relating to your interest in hearing loss. It appears people exposed to high levels of noise who take anti-oxidents have significantly less hearing loss. So jump on the vitamin C,E, selenium, alpha lipoic acid and BHT!!!
Skydiving is not a static excercise with discrete predictability...
Yeah, I agree, when you test it on the ground it seems pretty loud, but in the air, its amazing how quiet that beep gets.
Slightly off topic question here...for those of you who jump two ditters...how does that work out for you. Are they generally going off at the same time? Or is there a noticable lapse between the two ever? (this is assuming that they're both set at the same altitudes.)