Bose Aviation Headset X Generates More Noise Than It Suppresses (Figuratively Speaking)

Ever since BOSE introduced their first active noise reduction (ANR) aviation headset in 1989, there has been nothing but noise coming from BOSE and their major advertisers about the headset's superiority to all others on the market. If nothing else, BOSE has pulled off a marketing coup, and the blame for that rests squarely on the shoulders of their competition and the ill-informed pilots who buy BOSE products.

The purpose of this post is not to bash BOSE; the facts do that all by themselves. The important thing to know about any message is that if you repeat it often enough, no matter its validity, people will begin to believe you--especially when they begin to hear other whispers of agreement. BOSE has accomplished this task with very aggressive advertising. They are present at nearly every big aviation event in the country. They advertise heavily in most major aviation publications, and are offered on new aircraft equipment lists. BOSE represents what a pilot aspires to--just like a light jet does. Why? Because it's sexy, it's sleek and it's expensive! Like a Rolex, BOSE is what you want on your head because it means you're special. Who cares about your hearing, right?

The main function of a headset is to suppress noise to protect your hearing. The second function is to allow for clearer communications. There are many variations on that theme, but that is really what any headset is trying to accomplish for its wearer. So how well does BOSE do on noise suppression? That's difficult to determine really, because they don't publish any data on noise reduction ratings. (NRR) Even a simple set of foam earplugs has an NRR published on the box. The only information related to noise suppression is a reference to a 95 percent intelligibility score the headset received in a 115 decibel noise environment. (Reference) What does that mean? Intelligibility is a subjective measurement of a test subject's ability to understand words. It has nothing to do with noise suppression other than the suppression somehow helps add clarity to communications in loud environments. The only information I could find on cockpit intelligibility were two Army studies from 1990 where it was concluded that ANR improved intelligibility in military cockpit environments. (Reference) For noise suppression, BOSE fails to show how well the X protects your hearing. In fact, I couldn't find any information, third party or otherwise, regarding noise reduction for a BOSE headset.

You may ask yourself why I haven't contacted the company to ask this information. The simple answer is that a consumer should not have to contact the factory to find out how well a product does the job it's intended for. BOSE does a great job of touting its "Tri-Port" and "Adaptisense" technologies. They are also very good at placing juicy quotes from airline captains and magazines throughout their literature. What they fail to do is convince me their headset is better than any of the competition. Sorry BOSE, you don't get my vote. Please visit this page to see a few more opinions about BOSE headsets from Mooney owners.

A review in Aviation Consumer magazine named Bose as the champion of ANR headsets. Reading the article, I was disappointed to find they only tested headsets in the 300-3000 Hz frequency range—that of the human voice. The problem with the test is it completely missed one of the main generators of noise in a propeller-driven airplane: propeller and engine noise. Propellers and engines produce ear damaging sounds in the 50-120 Hz range. The human ear can detect sounds from about 20 Hz all the way up to 20,000 Hz. Because Aviation Consumer only tested ANR suppression in the lab-controlled 300-3000 Hz range, we still don’t have any objective data regarding in-cockpit suppression.

As for in-flight testing, Bose came out on top in a non-scientific, subjective test. On a 1-10 scale, Bose performed 1.5 points better than Telex, its nearest competitor. This test misses the boat entirely, because it contained none of the elements of a true blind study. Only four testers were used, and the headsets had nothing to disguise the brand. A test based upon the perception of the tester has to at least disguise the equipment being tested. To reach a true statistical conclusion, a minimum of 30 testers would need to be used.

For those of you who wear Bose headsets on a daily basis, you may think this is an exercise in futility, but let me ask one thing. Does Bose recommend you carry a spare set of earplugs in case of a headset power failure? The reason I ask is because if you are to experience a failure of the ANR on a Bose headset, your ears are pretty much out in the open. Those little Triports on the side of your ear cup provide little resistance to ambient noise once the speakers inside fail. Of course, a couple of hours exposed to 97db is going to slightly damage your hearing, but it isn’t going to make you go deaf.

Yeah, yeah, so what? Who cares? Well, the reason I started this post in the first place was to ask a question. Is Bose creating an illusion? The answer so far is yes. Bose has optimized its headset to sound best in the range of the human voice. They’ve gone so far as to cut holes in the headset to prevent distortion, and they’ve created the illusion that they are better by producing a perceived level of sound quality and suppression better than their rivals. When it comes to at-the-ear noise suppression, there are no figures for us—even after the Aviation Consumer test, unfortunately. So why does all this matter? Your hearing, of course.

Here is an excerpt from an article printed on www.hearinghazards.com that describes noise reduction ratings and their significance:

“Many people do not understand the labels on ear protection that indicate the noise reduction rating or NRR. Take, for example, a foam plug that has a published NRR of 27dB. Now, good old common sense tells you that if you've got a noise level of 107 dB, and earplugs with an NRR of 27 dB, when you put the plugs on, the noise level at your ear level should drop to 80 dB (107 dB-27 dB = 80 dB). That's just common sense right? Well, actually this is just another safety myth (see "Safety Myths: What Everybody Knows Is Simply Wrong," OH, October 1996).
Don't believe me? Check it out. If you consult OSHA's Figure II:5-1, Calculating Hearing Protector Attenuation of the OSHA Industrial Hygiene Technical Manual, you will find that the agency instructs its compliance industrial hygienists to first subtract 7 dB from the NRR to compensate for spectral uncertainty. This is because the acoustical spectrum of industrial noise is not a pure tone like that used during a hearing test. That means that our original 27 dB NRR now becomes: 20 (27 dB - 7 dB = 20 dB).
But we're not done yet. The technical manual then tells us to apply a safety factor. Now, in many scientific and engineering applications, safety factors of four to seven are pretty common, but OSHA requires a safety factor of only two. In other words, we divide 20 dB by our safety factor of 2 and wind up with 10 db. So we've now gone from a published NRR of 27 to an effective level of protection of only 10 dB.
All of this complexity creates a public misperception as to the meaning of NRR. What people fail to understand, and some experts fail to communicate, is that the testing protocol uses a test panel that in essence receives two hearing tests: one without ear protection and one with it. The NRR is then calculated based on the results of these two tests.” (http://www.occupationalhazards.com/News/Article/33400/Does_OSHAs_Noise_Standard_Really_Protect_Peoples_Hearing.aspx)

I’ve been asking why Bose doesn’t publish a noise reduction rating. Let’s be generous and say the Bose headset has an NRR of 30 decibels. That takes your 97dB cockpit and gives you a fly all day safe sound level of 67 decibels. Applying the procedure above, we’ll take out 7dB for spectral uncertainty, leaving us with 23 dB of NRR. But now we need a safety factor, so we’ll divide that by two, which leaves us with 11.5 dB of guaranteed reduction for your 1000 dollars. Your 97 dB cockpit is now good for 85.5 dB. So what will 85.5 dB do to your ears?

85.5 decibels is considered hazardous to your hearing over long durations. (http://www.audiorelief.co.uk/en/tinnitus_protection.html) For some, hearing damage will not occur, but for others, it will. For those of you who wear a Bose headset in your airplane, it is possible that you are still being exposed to damaging levels of sound. Consider wearing foam earplugs in addition to your headset.

The contender to the Bose headset was the Telex Stratus 50D. The 50D advertises 50dB of protection—especially in the lower range of prop and engine noise. Applying the same factors from above, the Stratus can reliably give 21.5dB of protection. That gives you 75.5dB inside the headset—a safe level.

As pilots, we always fly with proper safety margins. What I don’t understand is why so many pilots are willing to gamble with their hearing using something as unreliable as perception to determine the effectiveness of their headset

Disclosure: Reggie Paulk does not receive advertising dollars from any headset manufacturer... yet.