Quarter Wave Resonator to Kill Exhaust Drone

[niles]

I installed my header-back exhaust about a week ago, it sounds and performs amazing! Except for an insanely annoying drone in the 1500 to 2500 RPM range. It annoys my ears and pretty much ruins any music I want to listen to. I am automatic BTW. So I was reading around the interwebs about solutions and there really only seems to be two:

A) Install an resonator (inline) after the cat like in a stock system
B) Add a quarter-wave resonator (perpendicular) to the exhaust pipe

I am leaning towards B because I love the way my exhaust sounds, except for the drone. A 1/4 wave resonator is designed to cancel out certain resonant frequencies in the pipe, and can be tuned to any frequency you want. I found a lot of hot rod and truck forums discussing this, as I am sure that the drone on a big block would be even more insane. I want to design mine with a trombone style tube so I can tune it to perfectly cancel out my drone. I am thinking I will have room for it in the back next to my muffler.

If I went with A: I think a standard resonator (probably Vibrant brand) it will kill a lot of the tone, which I want to keep. Plus, a standard resonator costs around $60 and I think that's stupid. It's basically an expansion chamber and to me it's not worth the money. I could always build one, but I do not think it will fit my need.

My current setup:
Pacesetter Header
2.25" pipe all the way
Vibrant high-flow cat
Borla straight-through muffler

Here are links to the best threads I found:
I did it. Eliminated the 2000 rpm exhaust drone - Hot Rod Forum : Hotrodders Bulletin Board (http://www.hotrodders.com/forum/i-did-eliminated-2000-rpm-exhaust-drone-154608.html)
How to build an exhaust resonator tube to eliminate drone - PerformanceTrucks.net Forums (http://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/how-build-exhaust-resonator-tube-eliminate-drone-489463/)

Anybody here ever have experience with this idea? It's news to me and I am glad I found the option before I threw away money on something I didn't need.

http://i1286.photobucket.com/albums/a607/NilesHenke/Honda/IMG_20131122_171548_zpsn1jb3yf0.jpg

[RAZR]

Where is your exhaust tip in relation to the back bumper? If it too short it couldbe resonating the exhaust sound back into the cabin

[niles]

Where is your exhaust tip in relation to the back bumper? If it too short it could be resonating the exhaust sound back into the cabin

Right now it is just a piece of pipe clamped on to the muffler and it sticks out about a half inch from the bumper.

I am considering redoing the angle at which the pipe goes into the muffler to try to relax it a little. The piping in the rear wheel area is a little tricky. I am thinking the angle at which the exhaust is entering the muffler could be part of the problem too.

I have also discovered that the sheet metal in the trunk, right above the muffler, rings like a drum :thumbdn: When I do whatever I end up doing I will take off the heat shield and try to reinforce that section of paneling. I like the sound to stay on the outside of the cabin lol

[niles]

Here is a video of the drone. It might not seem like much but when on a road trip going up long hills it is very annoying. Also the engine was cold, its louder when warm.


http://youtu.be/zG2SBI12rEY

[2oodoor]

I would be upset if I had your system (awesome) and had a drone @ cruise rpm. Are you using factory style hangar set up at the muffler? Isolation of the exhaust parts from tbe suspension and body is key usually. Then you can still have frequency vibrations from differences in density of assembled parts by the exhaust turbulance. Kinda like a reed effect.
i thought the original Borla systems came with tip resonators, some dual out tips.

[niles]

Borla does still offer mufflers with tips, I bought a generic one because I was unsure if the tips on their mufflers would extend beyond my body kit, also because I found the model I bought on eBay for $60. I was actually planning on installing a dual tip once my system is solidified.

Ya know 2oodoor, my brother noted how worn out the rubber hanger gromits looked, but none were cracked or broken so I reused them. Do you think old rubber could be a problem? I'm not very exhaust experienced.

Also the pipe does rub on the heat shield in one spot, which will be addressed when I install the 1/4 wave resonator. It doesn't sound metallic like I would imagine a rubbing noise though, just a very dominant tone that overpowers all other sounds. I am going to get the extra pipe this week and I hope to do the install soon.

[Tdurr]

okay, so I didn't read the link u posted, but from my experience with these motors(and 4bangeres if you will) any time you have a free flowing exhaust you will have a drone at some rpm. yes it blows, yes you want to get rid of it, esp going uphill; but a resonator is the best bet. get the longest one you can fit on the straight part of the cars exhaust and it will cut the drone. I personally have never dealt with the drone from an auto but I can picture where it can make things uncomfortable for the ear/body. When I had my 4door I put in a 10yr old resonator from a junk car we had. Pipe size was the same it made a world of difference. it made the exhaust note less raspy overall and took the db levels down a good bit at cruise and WOT.

if you want performance you HAVE to give up the luxury of having a exhaust you cant hear in the car. put a super long resonator in place of your cat and/or get rid of your muffler and replace it with one of a different brand. I know for a fact that vibrant has a very good note but no "drone" that most na cars have from 2-3grand.

[2oodoor]

okay, so I didn't read the link u posted, but from my experience with these motors(and 4bangeres if you will) any time you have a free flowing exhaust you will have a drone at some rpm. yes it blows, yes you want to get rid of it, esp going uphill; but a resonator is the best bet. get the longest one you can fit on the straight part of the cars exhaust and it will cut the drone. I personally have never dealt with the drone from an auto but I can picture where it can make things uncomfortable for the ear/body. When I had my 4door I put in a 10yr old resonator from a junk car we had. Pipe size was the same it made a world of difference. it made the exhaust note less raspy overall and took the db levels down a good bit at cruise and WOT.

if you want performance you HAVE to give up the luxury of having a exhaust you cant hear in the car. put a super long resonator in place of your cat and/or get rid of your muffler and replace it with one of a different brand. I know for a fact that vibrant has a very good note but no "drone" that most na cars have from 2-3grand.
The links are excellant reading but I read after posting and it breaks out science to describe what I said.
This subject interests me because my car didn't drone before now it does. Gotta fix it, Borla mufflers for 60 bucks wow thats good.
I like the those new dodge darts sound 4 cyl with ss catback oem dual output muffler parallel w/ bumper and outlets about 2.5 ft apart. No drone ever, just a guff guff crazy banshee sound...rice or not I like it. Disadvantage: extra weight, redesign lower bumper cover, possible departure angle dragging.

[niles]

Thanks for the advice Tdurr and 2oodoor, I know it is possible to get a silent exhaust and retian the high flow. (or maybe I'm irrational)

Oh, and the Borla muffler was being sold by a company that is in the town next to me (I wish I knew where so I could just go to their warehouse, but I'm sure they'd hate that) so I received it NEXT DAY! It blew my mind. US PARTS OUTLET (http://stores.ebay.com/uspartsoutlet/) Highly Reccommended!

I like the science behind the quarter wave resonator and the small amount of techical schooling I have agrees with the concept. I believe an in-line resonator is essentially doing the same thing, except killing the drone with turbulance rather than an 180* out of phase pulse. The math will say that a chamber approximately 36" will eliminate the lower freq drone (longer for lower tones) whether it is in-line or perpendicular.

The thing is, a decent resonator will cost me at least 3X as much as a mandrel piece of pipe and will have less attenuation to boot. Here is where everyone will think I am crazy - I believe it is possible to have high flow and zero bass note. I want to see how close to that I can get. It's the foundation of science after all :rockon:

Once I saw pictures of really high performance exhausts using this method, it really made the idea real for me, for example Corsa uses this method inside of their mufflers.
http://cdn.speednik.com/files/2011/09/IMG_6820.jpg

And here is an external design:
http://i801.photobucket.com/albums/yy294/BigRed585Lbs/DSC01818.jpg

[cygnus x-1]

Neat idea! Here's something even wilder. How about making the resonator pipe with a telescoping tube for tuning, but then connect that sliding tube to a linear actuator so it can change length on the fly as the engine RPM changes. Too much?

C|

[Tdurr]

Lol that would be the most creative and interesting thing id ever seen.

[niles]

I was thinking of making a trombone style tuner. But I could add electronics to the mix. I read about how some people rigged a switch to open/close the resonator on the fly. BMW has one that closes automatically after 3k RPM since it is not needed at higher RPM.

But I'm not sure if I am ready to work that hard :) most of my projects are limited to what I can achieve in one day, damn daily driver...

[niles]

Odered the pipe today. Can't wait to install it, but we just got snowed on so it might take a while - weather permitting.

I found the perfect cavity in front of the gas tank right before the muffler. I measured the resonant frequency to peak at around 100Hz - annoying is an understatement. I have to crank my tunes to hear any bass from my subwoofer.

To cancel 100Hz, I calculated that the resonator needs to be about 36" long. Good thing the pipe is a U-bend! I am also going to try to angle it so that condensation doesn't collect in the pipe and cause problems.

[niles]

Mini update - I have all the supplies and should be able to install this coming weekend. Can't wait to compare the before and after videos.

[niles]

VICTORY! The installation and function is a complete success. Here is the after video:


http://youtu.be/6w4o5oS1dTM

[niles]

I bought the J-bend and added 4" of pipe, the total length on the outside of the bend is exactly 36" total. Capped the end with a giant washer from the hardware store. I opted for a non-adjustable design just because I didn't want to take it all back apart for final welding once I had it tuned correctly. But it ended up working perfectly anyway.

About the before and after video: the effect is actually less noticeable in the after video. But when riding in the car the exhaust tone no longer completely dominates all other sounds. I can once again enjoy my music at a low volume without interruption, aaaand most importantly my wife and I can once again talk to each other without shouting!

Additional Notes: With this design the resonator is nearly at the physical limitations of the cavity. There is this piece of the frame that hangs down in the middle of the chassis right in front of the gas tank. If the resonator was any longer it would hit that piece.

Just to clarify: this mod only notches a small bandwidth of frequency. The exhaust still is full volume. I eliminated the loudest bass tone only. I still have some very low frequency drone <70Hz. This does not change the actual sound of the exhaust. I still have rasp, and it is still loud due to the high flow, high performance nature of the design. :thumbup::thumbup::thumbup::thumbup:

Now for the pics::::

Finished product
http://i1286.photobucket.com/albums/a607/NilesHenke/Honda/DSC_0021_zpsc34qn3qm.jpg

Rear LCA clearance
http://i1286.photobucket.com/albums/a607/NilesHenke/Honda/DSC_0022_zpsk6oxjaz5.jpg

Wheel Clearance
http://i1286.photobucket.com/albums/a607/NilesHenke/Honda/DSC_0031_zpsydotsyfb.jpg

Ground/Vehicle profile
http://i1286.photobucket.com/albums/a607/NilesHenke/Honda/DSC_0028_zpsvmkyq1i4.jpg

[Tdurr]

glad it worked out for ya man! that thing looks crazy.

[2oodoor]

Wow, congrats on the objective accomplished !

[gp02a0083]

I got an exhaust drone as well once I had my 2.25 stainless steel system made. I have a magnaflow Cat, Jones resonator and a Flowmaster 50 series muffler and its still kinda loud. I believe that the closer the resonator is to the cat the less the drone will be

[niles]

I wanted to put it closer to the cat, but these cars are like skateboards... no clearence anywhere until the rear. I might still add a typical cherrybomb resonator after the cat if I want to go back to stealth exhaust volume

[Hazwan]

Thats some crazy piece of engineering haha.

Exhaust sounds great tho!

[niles]

Mini update: I am going to be adding some type of resonator after the cat. Still deciding on what to throw in there though. Open to ideas.

Right now I am really interested in Powersticks from classicchambered.com. It's like a glasspack and a muffler had a baby. I've had them on big-blocks before and they sound amazing.

Anyways, I am doing this because I don't like the rasp. Here is a video of my custom rasp:


https://www.youtube.com/watch?v=Qi3dtQ8wySM

[gp02a0083]

I wanted to put it closer to the cat, but these cars are like skateboards... no clearence anywhere until the rear. I might still add a typical cherrybomb resonator after the cat if I want to go back to stealth exhaust volume

Niles , there is plenty of room under the whole car, plenty to even tuck a 2.5" system nice up until the rear section

[niles]

Niles , there is plenty of room under the whole car, plenty to even tuck a 2.5" system nice up until the rear section

I was referring to the quarter-wave resonator in post # 16, nowhere under the car is there room for a pipe sticking out from the exhaust like that.

But yes, I have plenty of room for traditional resonators after the cat.

[niles]

An interesting observation about the quarter-wave resonator; depending on the weather conditions, exhaust system temp, and exhaust gas temp the resonator has different frequency response and dB reduction. Careful calculation must go into incorporating on into an exhaust system.

I ordered a powerstick from classic chambered.com today so in a week or two I will have an update with a vid. There is no packing in a powerstick, just louvers and crimped chambers. So I am able to maintain a 100% straight-through exhaust!

http://www.classicchambered.com/pic/2B.jpg

http://www.classicchambered.com/pic/3B.jpg

[Tdurr]

that looks pretty freaking cool. im interested to see how it works out.

[gp02a0083]

Niles , it doesn't surprise me that the tone changes with environmental conditions. a good place to understand this is Ideal gas laws and environmental effects on such systems. I have a resonator just like the louvered one you showed. However in my case I think the muffler is the cause for the drone, it did sound nice prior to welding the 60 series flow-master on

[niles]

that looks pretty freaking cool. im interested to see how it works out.

I will definately post a video so everyone can see how the system evolves by changing the components. That was the most difficult part for me. Everyone says, "I have this setup," or "add this part," but rarely does anyone explain how it affected their system.


Niles , it doesn't surprise me that the tone changes with environmental conditions. a good place to understand this is Ideal gas laws and environmental effects on such systems. I have a resonator just like the louvered one you showed. However in my case I think the muffler is the cause for the drone, it did sound nice prior to welding the 60 series flow-master on

I could have done more research on the physics of the system, but I guess I wasn't motivated enough. After getting a rough idea of how long the 1/4 Wave resoantor had to be and the dimensions of the space I had to work with, I just went with it. Plus I don't have materials for prototyping.

The turbulence I will intorduce into the pipe with the Powerstick should be enough to break up the buzz and probably smooth out the bass note a little.

[lostforawhile]

Niles , there is plenty of room under the whole car, plenty to even tuck a 2.5" system nice up until the rear sectionnot really it took me a long time to get my 2 inch system tucked up under the car, I have the full length S&S header, so that made it even worse, I have a build thread up on that entire system

[gp02a0083]

not really it took me a long time to get my 2 inch system tucked up under the car, I have the full length S&S header, so that made it even worse, I have a build thread up on that entire system

I didn't have a problem when i mocked up both my DC headers and the stock down pipe. If you used the stock mounting locations it would have been fine..... don't believe me then here's some proof of my 2.25" SS system , I have more than enough clearance around to get my hands in there with heavy welding gloves on so more than 1/2" easily. Even with the stock support locations it fits as if it was factory and I have all my heat shields :)
6185

[lostforawhile]

I didn't have a problem when i mocked up both my DC headers and the stock down pipe. If you used the stock mounting locations it would have been fine..... don't believe me then here's some proof of my 2.25" SS system , I have more than enough clearance around to get my hands in there with heavy welding gloves on so more than 1/2" easily. Even with the stock support locations it fits as if it was factory and I have all my heat shields :)
6185
this isnt a stock down pipe, it's a full tube header,so four tubes coming under the car, and it ends up at some odd angle so I had to make a piece that bends and goes up to line it up. plus I have that side exhaust

[lostforawhile]

http://i62.tinypic.com/kcny9v.jpg

[JohnBoy]

hear is one the I had on a pickup that worked great.
MBRP Resonators - Free Shipping on All Orders @ JEGS (http://www.jegs.com/p/MBRP/MBRP-Resonators/2834612/10002/-1)

[niles]

hear is one the I had on a pickup that worked great.
MBRP Resonators - Free Shipping on All Orders @ JEGS (http://www.jegs.com/p/MBRP/MBRP-Resonators/2834612/10002/-1)

What was the internal construction like on the MBRP? Was it hollow or was there something inside?

[lostforawhile]

I would like to build one like that to add to my system, but I dont think I have space for it. The point in my exhaust was to build everything, even the muffler, only things not built are the header and the vintage dynomax tips,even those have work in them modifying things

[niles]

You have done great work Lost. I used your exhaust build thread to help me decide what I wanted to do to my car. I am a garage mechanic with limited tools (I even had to borrow a welder lol), I wish I had your facilities.

Very psyched to get my powerstick in the mail though, and glad I can support a small US company. TBH, I think the powerstick will do everything that my 1/4 wave resonator does. Most everyone who incorporated a 1/4 wave is putting them on high-performance and big block classics.

[lostforawhile]

if I have a lot of drone, I may have room for one of these, right where the stock muffler would have been, there is a 90, I could add a flange and cap it off for now. It's called a hemholtz resonator, there is a formula for tuning these, but you really need the frequency of the drone. There are a lot of good guitar tuning apps for smart phones that will show a particular frequency, or you can record it and play it back through one of them, then you use the formula to calculate the length of the pipe for the resonator

[lostforawhile]

you know that the little pipe sticking out of the factory intake pipe does the same thing right? but to eliminate intake drone instead of exhaust drone,

[lostforawhile]

Wow, congrats on the objective accomplished !2door you ought to add hemholtz resonator to the title, as thats the technical name for this, when I get mine running, I will have to measure the drone frequency so I can calculate the length, I can run one straight back from the bend where the exhaust exists the car on the side , to where the muffler used to be.

[gp02a0083]

this isnt a stock down pipe, it's a full tube header,so four tubes coming under the car, and it ends up at some odd angle so I had to make a piece that bends and goes up to line it up. plus I have that side exhaust

i said i tried it with my DC down pipe as well , didn't have problems at all and the "stock" down pipe is not so "stock" anymore on my setup :P . Even with the header you have , other clearance issues are noted, but would not affect the exhaust fitment if was properly designed and fabricated. you even said yourself that there "is plenty of room to work under the hatchbacks" the 2" should not have been difficult at all. measure the resonance range at speed under load, otherwise your wasting your time. I have other comments about the workmanship on it, but ill keep things civil.

Niles, good work with thinking ahead and even adding some corrosion prevention.

[lostforawhile]

i said i tried it with my DC down pipe as well , didn't have problems at all and the "stock" down pipe is not so "stock" anymore on my setup :P . Even with the header you have , other clearance issues are noted, but would not affect the exhaust fitment if was properly designed and fabricated. you even said yourself that there "is plenty of room to work under the hatchbacks" the 2" should not have been difficult at all. measure the resonance range at speed under load, otherwise your wasting your time. I have other comments about the workmanship on it, but ill keep things civil.

Niles, good work with thinking ahead and even adding some corrosion prevention.

I was planning on measuring the resonance under load, I know the formula for determining the proper length once i have that information

[JohnBoy]

What was the internal construction like on the MBRP? Was it hollow or was there something inside?

if I remember it was hollow no louvers just a bunch of holes nice and smooth

[lostforawhile]

if I remember it was hollow no louvers just a bunch of holes nice and smooth

similar to this one? http://i220.photobucket.com/albums/dd158/lostforawhile/IMG_1380.jpg

[niles]

That is like what I was shopping for lost & johnboy. But they were all more than I was willing to spend or glasspack. I should've tried to convince you to build me one too lol. Love the stainless packing you added!

I'm still waiting on my powerstick from classicchambered. They had to get in more inserts before they could build mine...

[lostforawhile]

this is what I used they sell this in rolls for packing mufflers too, you dont need to buy an entire kit, he created the size I used and put it on the website so I wouldnt have to order a bunch of extra Muffler Packing (http://steelwooldirect.com/muffler-packing/)

[niles]

I installed the powerstick (26" long) this week and I am very happy with the results. Put it directly after my cat. There is no packing inside of it so there is no worry of anything burning out over time. Its just a louvered core with chambers to break up the sound.

http://i1286.photobucket.com/albums/a607/NilesHenke/Honda/DSC_0150_zpsqhhh0fk3.jpg

http://i1286.photobucket.com/albums/a607/NilesHenke/Honda/DSC_0153_zpsh57hsmz8.jpg

Sent from beneath a 3Gee with a wrench in the other hand

[niles]

Here is a before and after video I made. Both are filmed on a cold engine because I am too impatient to wait for the car to warm up. It is way quiet inside the car, so I can get back to enjoying music and conversation. At 70mph and above the car is whisper quiet. I didn't exceed 40mph in the video.


http://youtu.be/KpIH_oxBcyY

Sent from beneath a 3Gee with a wrench in the other hand