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High cabin noise (even with ANR headset)

Camillo

Well Known Member
Hallo.

I haven't flown too much since completing my -4. So, I am still fixing some issue.

Now, I feel that even with an active noise reduction headset (Zulu) the noise in the cabin is really high when RPMs are over 2.000. Even worst when side vents a-la-RV10 are opened. I have a 4 exhaust system.

Noise is way more than that on my previous -9A. The latter had the complete Classic Aero Design padding and pockets (side pockets, rubber floor). The -4 has nothing. Could the upholstery make the difference?

How can I improve the soundproofing? I read that a padding on the FF, cabin side, will not improve the SP...

Thanks.
Camillo
 
Camillo, this is all from my experience (lots of I's in this write-up!)

On my -7, the noise level was very high (to my ears at least, my first extended exposure to the propeller aircraft). The sound seemed to be coming from the floors, ie. I could move my feet around to different spots and change the sound level by damping an area with pressure from my foot. There was still engine/prop noise, but the sound from the floor was much less.

The solution was to build a sandwich of insulating materials that covered the floor area from my heals up to the firewall. I used 1/8" heavy rubber type material on the base, on top of that 1/2" of heavy wool felt (horse blanket!) topped with a thin layer of non skid material. All was bonded together with contact cement and is not attached to the floor itself. The sound level difference is amazing, and it added about 8 lb to the aircraft, a worthwhile tradeoff for me.

There is also a similar but lower level of sound from the sidewalls, and a pad there might be helpful but in my mind not worth the weight.

This approach basically changed the weight (and maybe the stiffness) of the vibrating floor panel, changing the frequency where it was most likely to resonate. Damping and also absorbing sound.

So maybe the first effort would be to identify if you have a similar problem, experimenting while in flight. Just for reference, I fly the Catto three blade as well but behind an IO-360, 4 into 2 Vetterman crossover exhaust.

Good luck and keep moving forward. Cheers!
 
Sound proofing considerations

Something to think about. If do you use any material that can catch fire or smoke and the engine compartment catches fire the smoke would incapacitation you before you hit the ground. Of course to insulate the firewall from heat on cockpit side you want to use fiberfaux and stainless steel foil on the engine compartment side. Dan Horton has a good description on how to do it. You also may want to do that on the belly of the plane from the exhaust exit back 3-4 ft. There was an RV10 that caught fire and lucky the pilot was flying barefoot and felt the heat from the floor and realized the engine was on fire and landed the plane. Part of the floor board was burned away by the time he landed.

After insulating the firewall on the engine you can most likely use wool on the cockpit side of the firewall for some soundproofing
 
Hear what you're sayin'. The fire risk was part of my decision... also keeping the pads removable does give the option of pulling them off the floor if necessary! Just balancing absolute risk against likely risk during the life of the plane.

... and now about flying barefoot !!! :eek:
 
By far, the most cost-effective approach is to wear foam ear plugs as well as your headphones. Turn up the radio/intercom volume as needed.
 
RV-4 Cabin Noise

I have a high powered RV-4 (over 210 hp) with a 4 into 1 exhaust and absolutely no interior or sound proofing other than leather seats. When I upgraded my 320 w/ 4 into 2 exhaust to the high powered IO-360 with the header the noise went up substantially. The floorboard idea deserves consideration but in my case with a 1000 lb airframe I didn’t want to add the weight yet.
I’ve tried several brands of ANR headsets including the Bose and the new David Clark’s and AKG’s and to my amazement these headsets seemed to amplify the high frequency noise ! I’m talking painful as in making my ears bleed... tongue in cheek but was uncomfortable enough to terminate the flight. It seemed as if the ANR system was being overwhelmed by the high noise environment. Since I switched power plants I’ve been using my old Sennheiser ANR’s which out perform the newer ANR’s by a large margin. When I spoke to DC about this they explained because of the large amount of high frequency noise I needed headsets with better passive noise protection than the DC’s offered (same explanation from Bose). DC gladly accepted my return and even apologized that their headsets didn't work out for me. Excellent Customer service. The ANR does well with the low frequency range but my noise appears to be in the high frequency range. ( somewhat subjective) and I need a balance of both passive and active to be comfortable.
My Sennheiser’s seem to be the best balance that I’ve been able to come up with so far and recently was able to purchase a new old stock set to keep me flying. I’ve not tried the Zulu’s.
I’d appreciate others thoughts but it seems to me the modern light weight ANR’s are not the answer in our high noise environment.
 
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I purchased 2 sets of Lightspeed QFR XC headsets around 2007. They worked great. and they were cheap!

Years later, I purchased the first Zulu offered..... One flight and back to the QFR's. Zulu went back into the box and shelved.

Don't count on electronics to solve all of your cockpit noise problems. Rely on passive noise protection first, then ANR. In the past, headset manufacturers would list passive and ANR in their specifications. They don't seam to do that any more. Look for, and ask about 23db passive minimum on any headset used in an RV.

Example..... https://www.mypilotstore.com/mypilotstore/sep/9639
 
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First make sure there is no mechanical contact anywhere which could transfer engine vibration to the airframe. For example, if one of the baffle walls is too tall and contacts the cowl, it can resonate another part of the airframe. Same for exhaust pipes and other parts.

The canopy assembly can vibrate due to prop blast.

Lining a single wall floor skin with rubber foam is a bad idea, period. We've seen multiple reports of melted floors right here on VAF. Assuming the owner does not wish to shield the exterior of the belly, a separate floorboard with an air space between it and the belly skin would be safer and probably just as effective.

Can't endorse wool or anything else on the cabin side of the firewall, even with a good insulation package on the engine side. The issue is small point hot spots, for example, AN3 bolts through the insulation and firewall.

I'll have very complete insulation kits available shortly, cored with better than fiberfrax 970.

FWIW, after a few different Lightspeed models over the years, I've switched to passive in-ear headsets and am unlikely to ever go back.
 
Floorboars

I too have noticed a significant difference in noise when resting my heels on the floorboards and lifting them of off them.

Don't know if it's prop blast, exhaust pulses or just some resonance.

I have 1/8" fiberfrax sandwiched between 6" wide SS shim stock from firewall to under pilot seat.

Finn
 
What I did

I built my -4 with the Vetterman 4 pipe, which historically created drumming in the floor of the -4, depending on pipe tip angling. I had no floor covering for first several flights, and had slight noise , but the floor also got pretty warm..I was wearing boat shoes and could feel it. At my day job, I used a lot of high temp silicone foam rubber sheeting (1/8" thick or so) for various airliner flame resistant applications, pretty much the same stuff the red valve cover gaskets are made from. Its high density, burn proof and easy to cut. I made pieces that fit the footwells and the battery tunnel. In the foot wells, I also made .025 titanium (SS would work also ) overlays. These pieces are bonded to the floor with a small bead of red silicon RTV. No more heat, less sound. The titanium makes a nice finish for your heels to slide on. As a last note, I fly with Halo in ear headsets, which provide really good noise elimination and comfort second to none.
 

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Thank-you.

Thank-you to everyone.
May 4 pipes are slightly tilted (almost horizontal). I may try to angle them down (cutting some part of the lower cowl).
Also, I understand the drummy 4 pipes issue.
So, as Bill said, the silicon RTV layer is for sound proof and the titanium for heat shield, right?
Coupled with Halo headset...
I will try.
Thanks.
Camillo
 
I encountered exactly the same issue and solution on my -7. Low frequency, high amplitude, uncomfortable sound and associated vibration. I thought it was coming from the prop at first but I found out, same as wcalvert, when I rested almost anything on the inboard bays of the floors, the noise and vibration dramatically reduced. Prop/and or exhaust pulses were in sync with the natural frequency of those floor panels. I used self-stick heat shield and thin aluminum strips on the floor, then carpet padding, then carpet. Took care of it completely and my -7 is much more pleasant.
 
I've switched to passive in-ear headsets and am unlikely to ever go back.
Same here. I used Bose A20s for awhile and the ANR just wasn't doing enough, so I started wearing earplugs under the headset but found that I didn't like the radio/intercom/music being muffled.

A few months back I bough a Card Machine Works CQ1 headset and have been very happy with it. Practically all the noise reduction benefit of in-ear foam plugs, with really good audio and light weight as well.

HTH

Dave
 
I initially thought maybe my noise cancelling wasn't up to the job but after adding stuff to the floor I concluded the problem was not my headset at all. It's just great now. But I may eventually check out the other headset types too.
 
I have built both a -4 and a -7. On my -4, I too found a Bose headset rather ineffective and finally settled on a DC ANR model. My theory is that in. -4, your ears are very close to the canopy and a good portion of the noise is higher frequency wind noise. The -7 is totally different and your ears and much further from the windshield and perhaps a subject to lower frequency noise. My A20s seem fine in the -7.
 
Me too

Had a similar experience with Zulu 3's and noise.

Tried the CQ-1s and liked them a lot better. My only problem is I apparently have one deformed ear canal and could not get the ear foam inserted correctly consistently. I tried all the different sizes and types and my left ear is just weird.

Ordered the new DC One-X and they are about the same as the Zulus. Still wish I could use the CQ-1s.....

It seems like those itty-bitty things couldn't possibly be as good or better than those giant ear muffs and modern tech electronics. I was pretty surprised that I felt the noise reduction was better and so much more comfortable.

Cheaper, lighter, simpler, no batteries, and they just work better. And no, I have no affiliation with the company.
 
A few months back I bough a Card Machine Works CQ1 headset and have been very happy with it. Practically all the noise reduction benefit of in-ear foam plugs, with really good audio and light weight as well.

Dave
Dave, I'm glad you are enjoying your CQ Headset!

Had a similar experience with Zulu 3's and noise.

Tried the CQ-1s and liked them a lot better. My only problem is I apparently have one deformed ear canal and could not get the ear foam inserted correctly consistently. I tried all the different sizes and types and my left ear is just weird.

Ordered the new DC One-X and they are about the same as the Zulus. Still wish I could use the CQ-1s.....

It seems like those itty-bitty things couldn't possibly be as good or better than those giant ear muffs and modern tech electronics. I was pretty surprised that I felt the noise reduction was better and so much more comfortable.

Cheaper, lighter, simpler, no batteries, and they just work better. And no, I have no affiliation with the company.

Gary, here is a brief from 3M that you might find useful, as well as a quick guide from the CDC.
Specifically, lift the top of your ear to straighten your ear canal some. Imagine insertion somewhat forward and up, as if toward your nose. You can also experiment with different jaw positions which can make a big difference. My left ear is much different than my right too. If you can find the magic sequence it becomes very quick and easy.
 
Lighthspeed

I have always been very satisfied with the lightspeed headsets, several thousand hours in Citabria and Cessna 195, but was wondering how they would hold up in my recently completed RV4, no interior other than seat cushion. O320 and wood Sensenich. I’ve had situations where the ANR can become distracting when it is overwhelmed.

Just to make sure didn’t have any headset distractions I just wore an old DC (no ANR) For the first flight, What I’ve used when flying a T6 because of the high noise environment and occasional difficulties with ANR’s. Worked Good

Time for the subsequent flights I started wearing my light speed Zulu and am pleased with the performance. It was a nearly new headset. I’ve not had great luck with Bose. I believe different facial structures will perform differently with different headsets. Also on the Zulus I know I had to replace the ear pads after 8 to 10 years on a set and they worked much better.

The Zulus work great for me. I did take them off twice during the flight just to listen to the engine and was surprised at how much air noise there is across the canopy, Then realized what a good job they were doing.
 
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Leather Mic covers

I found the Microphone was picking up the cabin noises and sending them right back thru the Zulu Headset. After spending a lot of efforts to quiet the cabin on my RV9A, I added Leather Mic covers with a small hole, Works Great !! all cockpit noise reduced to acceptable. :D
 
ANR Headsets in RV's

I responded to this thread in reply #6 and have been following it to hear others experiences. My experience with the Bose and DC ANR's was so bad that I couldn't understand why my old Sennheiser ANRs worked so well. This year at Oshkosh I had an occasion to talk to a DC engineer and he explained it very simply. Both the Bose and DC headsets have their ANR microphone ports on the exterior of the ear cup which may actually amplify the high noise environment in certain instances, while the Sennheiser's have the microphone mounted internally in the ear cup. This allows the Sennheiser's superior passive noise protection to be the first defense with the ANR portion batting cleanup. The Bose and DC ANRs have inferior passive performance but obviously work well in quieter aircraft.
This may explain why I've seen some Warbird Pilots still using the old DC headsets because of their superior passive performance In their very noisy birds.
 
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RV-4 and ANR noise........

Both the Bose and DC headsets have their ANR microphone ports on the exterior of the ear cup which may actually amplify the high noise environment in certain instances, while the Sennheiser's have the microphone mounted internally in the ear cup. This allows the Sennheiser's superior passive noise protection to be the first defense with the ANR portion batting cleanup. The Bose and DC ANRs have inferior passive performance but obviously work well in quieter aircraft.
This may explain why I've seen some Warbird Pilots still using the old DC headsets because of their superior passive performance In their very noisy birds.

I have Bose that I use in the noisy open-door Cub and they seem to work well most of the time. I should try some of the other types as well..

In SuzieQ I have an ANR helmet that has the ANR microphone in the helmet and noise has never been an issue....
 
At the end I adjusted the microphone sensitivity to 25 (on a 30 scale) on both headsets and now it is a good compromise. Only concern is that one has to speak quite loudly and steadily to activate the microphone.
 
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