DIY exhaust resonance cancellation

[AcampoDave]

Anyone ever made a 1/4 wave resonator? https://www.performancetrucks.net/fo...-drone-489463/

[b454rat]

All the exhausts I've had over the years, never had drone bad enough where I wanted to do something. Prolly the loudest truck was my old CCSB with a tired 5.7, headers, cats, H-pipe, dual Cherry Bomb extreme I think they where called, kinda like a Flowmaster type muffler, 2 1/2" up to the mufflers, then 3" out the back, then 5x24" tips going all the way straight out the back. It was LOUD, and super throaty. But even cruising at 70, you could have a conversation without yelling, and don't recall any drone. To me that is the sweet spot where the exhaust sounds the best lol....This was discussed on the Tundra forum too. I put duals on mine, and, no drone.

[sweetk30]

biggest think i find helps is get the exhaust all the way out from under the body . no turn downs or dead stops under the body .

my old plow truck i had it dump under the bed and it droaned so bad . all i did to fix it and make it 1,000x better was a tail pipe out to the bumper and wow was it better . that was a flowmaster 50 delta flow 3" in/out .

next is muffler past the rides seat or if truck past the cab .

[AcampoDave]

Let's se if they work then....Using the leftovers from my Summit DIY exhaust kit, I fashioned up a pair for my truck. It has duals with Super Turbo's, the intermediate and tailpipe diameters are 2.25" constructed from the Summit mandrel bent kit. The head pipes are 2" crush bent. I have no crossover and I already exit out the bumper but do experience the drone at around 2000 RPM. The resonator J bends will tap in before the mufflers, run parallel to the exhaust and point forward anchored with a hangar. I do have a bit of telescoping incorporated into the joint (at the pencil in pic) where I'll use a clamp. I smacked a couple of chainlink fencepost caps on the ends. I Dont know if being domed will have an effect, but they were a no-brainer to put on. I also downloaded a spectrum analyzer app for my tablet and after I get my driveshaft back in (different project), I'll hit the road and see what frequency I need to cancel. Then I'll get busy tayloring them to length and weld them in. Stay tuned I hope to report back in a couple of weeks or so.

[cadillac_al]

It looks like your mufflers are just behind the cab. I think moving them back toward the rear end will help with your drone.

[weq92f]

Originally Posted by AcampoDave

Let's se if they work then....

Based on the article quoted and the looks of what you have built, I'm going to predict no adjustment will be required...Those are going to cancel all your drone nicely!

-klb

[AcampoDave]

I appreciate the optimism on that Weq. Also thanks for the reply Al. The mufflers are the 16" case dynomax so on my shortbed, that about as far back as they go. The tailpipes turn up right after the exit and headup and over the axle. Then run parallel to the rear gas tank to a pair of turndowns just barely below the bumper. My desire was to build a quiet performance exhaust and for the most part I succeeded. Once the cruise RPM's surpass around 2300 the drone is gone. Conversely, rolling along below 2000 is pretty dang quiet too. The drone is not horrible but its right in the 55 to 65 MPH range and it gets old after an hour or so.
From what I understand sound flowing thru a tube has a specific range or frequency in which it will begin to vibrate causing drone. A guitar playing friend of mine compared it to a tuning fork, and to me that seems pretty accurate. Another example that comes to mind is rolling down the rear door windows of my Silverado, but not the front when at speed causing a whupping sound.
My driveshaft goes to the shop tomorrow to get balanced so after that I can get busy to see if I can slam the sound waves against themselves and bust up the drone. I read that modern cars use a similar device on their intake tracks and some also use a chamber on the intake and/or exhaust called a Hemholtz resonator designed to direct sound waves into themselves. Further reading revealed the 1/4 wave and the Hemholtz resonators to have been around for a long time and to have been successfully used in a variety of applications, automotive and otherwise.

[aknovaman]

Best description of the problem and easy solutions are found here:
https://ls1tech.com/forums/conversio...ps-solved.html

A bit of way down my post (reply #14) is a zipped spreadsheet. You can download and enter your parameters to determine side branch resonator length.


Mustang, and GM truck guys use Branch resonators and they work remarkably well.

There are 14 pages of theory but it definitely works.

http://www.performancetrucks.net/for...ne-fix-424169/


For all you engineer types, begin reading at about page 41 of this document:

http://www.enoisecontrol.com/related...rrier_wall.pdf

[AcampoDave]

The one thing i still can't decipher is if the calculations for true dual or crossover systems are different. Unfortunately math makes my head swim, but wouldn't a crossed over system be truly a v/8 with all cylinders affecting both sides equally while a separated dual system would be like having two four cyl engines side by side? At first i was thinking it didn't matter because the Hz of the sound are what counts, but as i read the links most recently added by aknovaman I began to wonder because one of the variables in the equation is "pulses per second" my feeble grasp of math says separate duals will have exactly half the pulses per side. Perhaps being reduces by 50% still collides the sound waves but at half the rate?

[aknovaman]

You guys are overthinking all this. Just download my spreadsheet and enter the info. If you have drone at 2k rpm you need 26 inch long side resonators, one for each muffler. An inch variation wont prevent their efficiency.

[b454rat]

so whats inside the resonator?

[aknovaman]

Empty tube that's capped at the end. Think of how a coke bottle resonates then you blow across the open end of it. It acts just like a pipe organ. The guy who studied and calculated the math had a last name of Helmholtz. That's why they are named after him.

The exhaust sound 'pulse' enters the tube, bounces off the closed end and is 180 degrees out of phase and that cancels the noise pulse which quiets the exhaust.

[AcampoDave]

Originally Posted by aknovaman

You guys are overthinking all this. Just download my spreadsheet and enter the info. If you have drone at 2k rpm you need 26 inch long side resonators, one for each muffler. An inch variation wont prevent their efficiency.

Thanks for your insight, I read the link you authored at the other site and looked the spread sheet. It's great to have the calculations already made for me. The only other question that comes to mind is; would the mandrel 90* turn be counted in as part of the overall length, or just the straight section? I was thinking it is included as measured right thru the center of the radius. My plan is to lay a 26" string on center and make my cut accordingly since my drone is at 2k. Funny how 2k seems to be the magic number for most v/8 resonance regardless of the many possible variables on individual vehicles.

[AcampoDave]

So, I did it and it works pretty well. Not amazing, but better. No additional hangers were needed. I'm still gonna play around with the length adjustments but overall I'm pleased. Edit: I ended up putting the fencepost caps back on the fence and welding on a piece of exhaust pipe that i split open, smashed flat, and made into a circle. That let me remove the clamp at the end as seen in the pic. It looks better and I think it works better too having a flat surface to deflect the sound off of.

[AcampoDave]

All in all I'm calling this deal a failure. After driving a while now and tinkering with the length of the 1/4 waves, I have to say they don't work as well as I would have hoped. (Especially on those long drives) They helped a bit and most people would say my truck is kind of quiet, but my goal here is to build a decent flowing system that is as quiet as possible. Today I called Summit and ordered some "real" exhaust resonators called Vibrant Ultra Quiet. This week I'm going to install them in place of the 1/4 waves.So, I'll let you know

[Mike C]

Interesting experiment. I ran the DynoMax Hemi turbo mufflers on my Jimmy and bought a set for my short bed as well. The 20” case mufflers flow plenty for 400 whp and are quiet. Something else to consider in your pursuit of quiet without the drone.

I have not noticed the drone at all, but without a top and 35” tires there are plenty of other noises...

[AcampoDave]

Ok, so I figured I'd wrap this one up. First a quick reply to Mike; The cases on my Dynomax mufflers actually are 20 inchers but I mistakenly called them 16's in a previous post.
Today I intalled the Vibrant Ultra Quiet resonators in place of the 1/4 waves. They definitely work better and they are much more attractive too with their polished stainless cases. I did finally get the sound I was hoping for when I initially installed the exhaust. Most would probably now call it really quiet, but I'm going to go with pretty quiet . It's still got a rumble but it's pleasant enough to listen to. I can now hear important noises like cars coming up on my flanks when I'm on the freeway and I even caught my engine making a slight ping or two when I lugged it with the clutch from a dead stop with the a/c on. Long drives should definitely be easier on the ears.
Thanks for reading and for your comments. Dave

[greasemonkey]

This is good info, thanks for the follow up. I've been debating on trying the J pipe myself, but a resonator in line would be a lot easier and cleaner. I have a 5.3 with a Magnaflow knockoff and the drone is really bad 2000+ RPM. It seems to be a common complaint with the 4.8/5.3/6.0 crowd with Magnaflows.

[AcampoDave]

Originally Posted by greasemonkey

This is good info, thanks for the follow up. I've been debating on trying the J pipe myself, but a resonator in line would be a lot easier and cleaner. I have a 5.3 with a Magnaflow knockoff and the drone is really bad 2000+ RPM. It seems to be a common complaint with the 4.8/5.3/6.0 crowd with Magnaflows.

Yep, from 2000k to 2200k. It's still not entirely gone but its clearly better and I can live with it now, For me, that rpm range is around 50 to 55 mph. Once i hit a freeway speed the rpm's become high enough to completely clear the "drone zone". The way I see it, even tho' it still drones a bit, what i have finally achieved is preferable to a restrictive stock style set-up. (283's need every advantage they can get EDIT: Next i think I might look into doing some Dynaliner. It's dang spendy but I do think gains could be made on the back cab wall where the gas tank used to be. I've done the acustical dampner stuff back there and also inside the doors and floor covering about 40% with stirps and squares. Then I did the jute pad under a mass backed carpet kit with more jute and carpet on the back wall. Another trick I did was make a removeable block off out of heavy cardboard painted black to block the cab corners where my bottle jack and stuff live. I stuck fiberglass duct wrap insulation on the backside with spray adhesive. Here's a pic...

[Mike C]

Check out the Noico mat on Amazon. 36 sq ft like $65. Bought some to do the upper cowl and firewall in the kid's Jimmy project but haven't installed it yet. Bought on recommendation from a buddy putting it in a 71 GMC.

[notsolo]

I also tried building my own exhaust with a magnaflow kit 2.5" stainless with crossover. drone was horrible, ended up removing the dual exhaust and going back to a Y pipe. Added a 2nd muffler as a resonator. Sounds good, but more important for me it's quite. I can play the radio etc at low volume and hear it no problem. No drone.

[AcampoDave]

I figured I'd give this one another update since I've done some more stuff in the name of peace and quiet.
First, thanks goes out to MikeC for the recommendation of the Noico. I went ahead and did the floor, and back wall with the Noico Red version and it's a great product. I also found that my mainfolds really didn't seal too well to the block. Not so bad as to say "Hey dude there's a leak here!" but bad enough to be noticeably quieter after having them resurfaced at the machine shop. I also added a crossover pipe, which does soften the tone, as well as second resonator to each pipe right at the end. This one also made by Vibrant. It's a sweet little stainless bottle style job that really helps.

[The Rocknrod]

I don't have an exhaust yet so I've been watching this. So a cross-over pipe and resonators are they key?

[AcampoDave]

Originally Posted by The Rocknrod

I don't have an exhaust yet so I've been watching this. So a cross-over pipe and resonators are they key?

Yes, but I've learned more than that too. See the thing is as you get it quieter you hear more noises that you never noticed before. As the exhaust note diminished I noticed lots of noise from the motor. That led me to switch from an air filter housing that was open 360 degrees to one only open in the front. (kind of my homemade version of the old Caddy unit.) That helped by dulling the sucking noise of the carb. I also learned that even a small hole in the firewall like a deteriorating grommet was a conduit for noise. Dropping a light under the hood and looking cabside in the dark suprised me at how many litlle gaps around hoses and grommets needed to be addressed. Also as I mentioned above, the manifold to block seal. I never hear a rythmic click or anything from there, but turns out it was an overall dull roar....and the stink of exhaust when working on the motor while it ran. After machining the manifolds I was able to lose the gaskets and when I fired it up I was surprised that what i thought was normal motor noise from the carb, fan and belts was actually the dull roar of leaking exhaust! Then I said....."Hey, I think my alternator is getting loud"

[mattfranklin]

Cool slide deck, novaman. I'll have to read more later. I remember touring the Donaldson company (filters and mufflers) as a student. To me the most trippy parts were being in the anechoic room and walking past an anechoic wall.

Originally Posted by aknovaman

Best description of the problem and easy solutions are found here:
https://ls1tech.com/forums/conversio...ps-solved.html

A bit of way down my post (reply #14) is a zipped spreadsheet. You can download and enter your parameters to determine side branch resonator length.


Mustang, and GM truck guys use Branch resonators and they work remarkably well.

There are 14 pages of theory but it definitely works.

http://www.performancetrucks.net/for...ne-fix-424169/


For all you engineer types, begin reading at about page 41 of this document:

http://www.enoisecontrol.com/related...rrier_wall.pdf