Noise Reduction
 

When you crank up an RX3 it's not very noisy. Even rev it up to, say, 5K and it's not all that loud. On the highway I have discovered that the noise level gets pretty loud under certain conditions. Specifically, when the throttle is open about 90% or more at highway speed. If the throttle is partially closed while on a slight downhill slope or even just maintaining 60 mph the noise level drops quite a bit. I'm thinking that the culprit is not exhaust noise but rather intake noise. Anyone else giving this some thought? Any ideas on how to mitigate the noise if it is intake related. I thought about coating the inside of the air box with some kind of rubber. I'm open to any suggestions because I am already wearing ear plugs and the noise is starting to concern me due to my known hearing loss.

Peter Y.

Sucking decibels.
 

Your conclusion of noise generation is correct.
I've played around with exhaust silencing also and concluded the same as you.

Lining the inside of the plenum isn't likely to do much to mitigate the intake pulse noise, it's more a need of sonic wave diversion or baffles inside the plenum.

It may be a result of plenum size/shape making it louder than it needs to be. I wonder if the RC3 uses the same box and does it make the same sounds. That would require the evaluation on someone who has access to both models. cough cough Gatling cough

I also wonder if the body & windshield bits amplify the noise. Anyway, since the air filter chamber isn't something that easily pops out, I haven't bothered to pursue the issue. Now if someone decides to replace the stock system with a pod filter on the end of 4 feet of radiator hose, perhaps they can report back.:tup:

I did the pod (minus 4' radiator hose) and it didn't make much difference regarding noise. I also discovered that it didn't make much, if any difference regarding power. I went back to the stock filter box, like rtking.
I did however, cure the intake noise problem by installing a slightly louder muffler! ;-)

I have this same complaint as Peter; in fact, I find that the noise level at WOT is starting to annoy me. I wonder if the airbox walls are flexing, and maybe even getting into a harmonic pattern? I am thinking of pop-riveting some stiffeners on the outside or inside of the box. Another idea - I think I have some adhesive backed sound-deadening material. Worth a try!

Red hawk, let us know what helps. When I did the Iron Butt on my RX3 the droning was quite noticeable. I do believe it is air box resonance, rj

Yes, especially odd since the box inlets are under the seat.
Maybe we need Cooper & Wolowitz to team up and look for a solution.

You saw what Wolowitz did with the Mars Rover....I'd look to Raj

Ear plugs and/or build a larger chambered/baffled air box with a flat small engine style airfilter

How about noise cancelling headphones? Personally, for long rides, I use ear plugs. It'll help save your hearing from the wind noise as well. Oh, and I get them for free too.

:yay:

Thanks for all the great ideas. You'll note that I already wear ear plugs. Noise canceling headphones might be OK if I were flying an airplane but I suspect they won't fit very well under my full face helmet. For now I'm stuck with the best plugs I can buy, with a 31DB reduction. Doing some mods to the airbox might be my winter project. I'm wary of doing much in that area because the engineers tend to have a reason for the airbox size and design, something to do with resonance and engine performance.

Peter Y.

You could try a down facing snorkel on the airbox. That may redirect the sound down and away from you, but it may suck up water if you ride through deep water.

Any luck with this? I'm finding the intake roar under high-load (uphill, fully loaded, my fatass on the bike) is really loud, even with really good earplugs.

Charles.

The RX4 has the same symptom under heavy load when im using my full helmet.. I've found though that with my half helmet mated with ear buds there is no drone and is much more comfortable overall, not ideal I know, but works for longer rides

This might help:

http://www.chinariders.net/showthread.php?t=28511

It really doesn't. I can't tell what he's actually done there.

Charles.

Also trying to figure out the solution.
To me it looks like an "inner" airbox inside the regular one. So basically an extra chamber made of a rubber car mat

Interested to see what comes of this solution and if it becomes a workable DIY for others as it appears the RX4 also has the loud intake symptom most prevalent during high load situations, ie, accelerating up a highway grade

for those interested I will explain what I did and how it works the walls in the filter box are lined with new rubber because it is the safest material, it does not crumble and does not dust the rubber absorbs sound bouncing back from it so you should lining the walls as much as possible on the outside the box is covered with sound absorbing sponge but the biggest effect is the modification of the outlet

1) a rubber chamber to reflect sound going from chamber 2.
2) A rubber chamber that absorbs the sound going directly from the throttles.

1) original outlet plugged with rubber.
2) New outlet.
3) A wall made of rubber.

I can see from the pics that the RX3 airbox differs from the RX4 but the premise should be the same.. if rubber and foam helped quiet it down that should also be the case on the RX4 if it is indeed the airbox that is the noise maker under load (especially annoying when i wear a full helmet, hence have been using my half-helmet mostly)

ok any question you want to i record the sound of engine or something?

As a percentage, by how much would you say you were able to quiet it down by with your mods?

If someone is not sure whether the sound is coming from the air can, unscrew the seat, start the motorcycle, plug the air intake with a sponge or a towel and accelerate a few times, this should dispel any doubts and unfortunately the motorcycle muffler is not very quiet, so I ordered a new one.

ambient sound with engine off is 30db in neutral gear engine 0n the app shows 77 db at max throttle 89 db when driving below 6000rpm you can't hear the engine above 6000rpm you can hear the bass (instead of the metallic sound that makes your teeth hurt) generally the rubber walls dampen and modifying the exhaust by making a maze for the air noticeably reduces the sound you can check by unbolting the seat and plugging the intake

I have a sticker (that i removed) on the RX4 that says 80db at 6k

I use the application from the phone and you cannot trust it too much, especially since it believes 30db with the engine off unscrew the seat, start the motorcycle, stick the intake sponge or cloth and see the difference and let us know how you can

you can also measure the sound with the phone your engine idling and open throttle and see what the difference for me is 12db

I decided to do the test again I locked myself in the garage I used the same app as in this videohttps://www.youtube.com/watch?v=7ONhvaDBds0 I took pictures with the engine off at idle 4000RPM and at 6000 RPM here is the result.