Unbelievably I am doing research on this very subject using four old helmets. While still in the preliminary stage these factors appear to dominate: (not in order of importance)

1. Uneven surfaces over the ear area outer surface.
2. Open areas at bottom of helmet.
3. Hard surfaces on outside of helmet.
4. Lack of sound absorbing materials over ears inside.
5. Uneven surfaces over other areas of helmet.
6. Poor windshield air control.
7. Poor visor seal and or uneveness.
8. Bike noise excessive, motor and or fairings.
9. Tire noise excessive.
10. Wind speed and direction. Essentially uncontrollable.

Solutions to this problem will have to address all of these problems. I am looking for funding sources to quantify these factors. At present I am going for rides and using my ears instead of using a wind tunnel and microphones!! If anyone knows of some entity that might fund this research please let me know. To do it right would be about $15,000! I have one helmet that is approximately half? as noisy? as when I started with only minimal weight gain and greater comfort. It is, however, very ugly since it has been modified so much.

I have found some neck warmers that sharply reduced the noise for unfaired bikes, but others that seemed similar, did not. The only apparent difference was the total weight and density of the neck warmer material - heavier seemed better, which makes sense from an acoustic standpoint.

Neck warmers do almost nothing to reduce noise on a faired bike. For them to be effective, they have to be in a non-turbulent flow.

The helmet-to-jacket "gasket" for unfaired use is something that should be explored further.

The overall quietest riding combination seems to be one or more neck warmers on an unfaired bike, with tape at the top of the visor to fill the gap.

In my limited opinion, I think the problem is with the lack of seal around the ear. After wearing an SPH4 flight helmet (and ear plugs) for years working around helicopters and jet engines, it is no less than amazing the amount of noise attenuation provided by that helmet (appropriately fitted) and ear plug combination.
Wearing such, the head could be place near a running jet engine that would produce severe ear pain when the earcup seal around the ear was broken and still be able to hear through the speakers. With the same combination, one could poke their head out the door at 100+ kts and still be able to converse with ease.

A Nolan N100 in combination with ear plugs and a Slik provide a quiet enough environment for me to hear a satellite radio through Chatterbox speakers. Not as quiet as I'd like, but sufficient. My complaint is the lack of weather proofing. Haven't found a helmet yet that wouldn't fog or would keep out a driving rain for more than a few minutes. You'd think by now these sort of complaints would be history.

Been dealing with a combination of helmet buffeting/noise, on my Vstrom. During the summer I use a "very" low windscreen that allows smooth airflow around my helmet with out buffeting, but I need to wear ear plugs at high speed because of the air flow noise. My wife riding on the back said I block much the air flow giving her a lower noise ride. We both wear full face helmets.

Installed a Rifle +5" over stock height windscreen for the winter and found one setting to reduce most buffeting and high level of noise. Still had some buffeting at high speed that caused helmet rattle/vibration and buffeting noise. While riding down the road, I grabbed the chin strap and pulled down at high speed. Reduced helmet buffeting rattle/vibration and buffeting noise enough to make a very pleasant ride. Switched helmets with my wife and resolved some problems. Both of our helmets are the same size but from different manufacturers. Her helmet fit me tighter without discomfort reducing the helmet buffeting rattle/vibration and much of the buffeting noise. My helmet is a looser fit which is more comfortable without any buffeting for her with less noise than the lower summer windscreen.

wow interesting. 300 ohms is a lot of ohms! normally we see 8 or 16. quick look on the internet suggest hi impedance used so bunch of headsets can be run in parallel (say the entire flight crew..)
is this the theory?
so how would you get around the large impedance missmatch? electronics needed i would wager?

i am very happy to read the above thread - i though i was alone in my total displeasure of the amount of noise i have to put up with. Cal-Sci +6" windscreen + full face (with many large scoops) + earplugs = still too loud! i mean STILL TOO LOUD ! i am not happy that you are also suffering but rather sounds like the assembled talent might be able to come up with a fix.

let us know skywagon how the NC headphones work out. hope to read about it here.

& thanks for the tricks - i will try to dampen the resonating bell that is my helmet ( via strap down force, and balaclava - the weather now allows for this) and try some taping.

This is a very interesting thread. Noise is something I'd like to reduce in all my helmets.

I currently have a one year old HJC AC-3 open face helmet and a 2 year old Scorpion EXO-700 full face helmet. I don't have any empirical data, but to me the open face AC-3 is much quieter than the full face Scorpion. That seems contrary to logic, but I have noticed it more than once. I almost always use ear plugs now, although often only on one side. The other side is pretty deaf already due to illnesses and infections when I was younger, and flying around in airplanes for 30 years in the Navy didn't help. <G>

Can anyone explain that?

I think an open-faced helmet will often be quieter than a full face helmet, since the open-faced helmet is sealed around the head and face, whereas the full face helmet is open at the bottom, which often acts as a scoop for the air flowing up the body.

I found the earlier comments about the helmets used by carrier flight deck crew members interesting. If a helmet can be designed that will insolate against the ear-splitting noise of a jet engine, catapult, etc., then surely one can be designed to insolate us against the noise of riding on a motorcycle.

If we ever do get a really quiet helmet, a nice feature to have would be a switch to allow us to hear the ambient noise, so we can flirt with the toll gate attendents, etc. This shouldn't be much of a problem since I want mine wired for sound anyway. Just something that would turn on a mike to the outside.

I have found that it is necessary to pull down very strongly to reduce the shell vibration - so much that it would be comfortable only for a few seconds.

The random roaring sound from fairing blow off with a full face helmet has frequency content to maybe only a couple of hundred Hz, and I suspect may be peaked at only about (80 Hz my guess).

This means the wave length of the sound is like 10 ft, which means that any effective absorbing media will have to be a moderate fraction of 10 ft thick to absorb the resulting pressure waves. My guess from that is that a foam thickness of only say 1 inch won't be very effective to reduce the sound pressure from shell vibration at those frequencies. If the frequencies were a l ot higher, it might be possible. The low frequencies of a shell first mode vibration in the bell mode is a lot of our problem.

The sound pressure from a jet engine has much higher frequency components in it, where passive sound absorption materials would be more effective. I'd sure like to see one though to figure out why.

I also suspect an open face helmet might be quieter because the vibration mode nodes (i. e. the place of maximum motion amplitude) would be less concentrated immediately adjacent to the wearer's ears, and there is more of an escape path for the resulting pressure wave.

To a non-techie, that sounds like the vibration I feel from hip-hop playing in an amped-up car a half-block away. While annoying in its own way, that wouldn't interfere with voice or music, which I assume are much higher frequencies. What I would like is to have insulation from the noises that prevent me from enjoying music or voice sounds.