Hemholtz resonator - design and implementation ideas

[alia176]

Hi all,

I'd like to design a Hemholtz resonator for my 2.5" mandrel bent exhaust system and would like some feedback from anyone here who has done this. I want to kill the drone at a specific frequency and don't want to throw mufflers at it, which simply creates more backpressure as they muffle. Look at the gigantic OEM mufflers vs aftermarket mufflers and you'll see what I mean.

I tried four different mufflers with my exhaust system while watching the boost gauge and ended up with the muffler that had the least amount of back pressure and the lowest drone. However, you can't have a "high flow" muffler and not expect to hear drone at certain freqs.

I'm watching the drone freqs using a freq analyzer app for my phone, which isn't going to be too accurate but I don't have any other means of measuring. I don't dB readings, only need the actual annoying frequency readings. The link below shows the app I am using.

If you had a shop do this work, did you find out the calcs or equations they used to figure out the resonator chamber design? Maybe this is a tried and true design based on our engines, CFM, displacement, etc? Having a turbo does increase the air flow somewhat, obviously.

Here's a quick read on what this thing is and does: link

YouTube link for the equation

Here's the excel spreadsheet from the link above

Thanks for your feedback.

 

[FirstToy]

So that's what it's called. I see these on intakes as well. Isn't the BOSE sound wave a type of this?
Sounds difficult, like creating a wind insturment and needs a lot of tuning... how far away from the muffler etc...
i would love to get one too!

 

[alia176]

So that's what it's called. I see these on intakes as well. Isn't the BOSE sound wave a type of this?
Sounds difficult, like creating a wind insturment and needs a lot of tuning... how far away from the muffler etc...
i would love to get one too!

Quite a few vehicles have them on the intake as well, and the 4.7 engine has a weird shaped unit. It's not really difficult, since you're just welding up pipes but it is an exact science, so to speak. There's a fella with a LX450 who has done this and I'll let him detail out his system. @doc_random I think we can learn a lot from his experience.

 

[doc_random]

This is what I had fabricated and I am very happy with the lack of drone on the highway. The Helmholtz resonator is the J-pipe in the diagram. The idea is to have the sound pulse go into the closed end J-pipe and reflect back into the exhaust path to cancel the next pulse. Noise cancelation. I had the J-pipe connection in line with the exhaust flow. The calculations showed 24-27" was the right range for my vehicle at 70-80mph (LX450, 4.88 gears, 35" tires, about 2800rpm at highway speed). The shop set it to 25.5" with adjustable clamps in 2016 and I never changed it. It also has two resonators. Spare tie obviously relocated.

LX450 2800 RPM * 3pulses/rev / 60 sec/min = 140 Hz resonant frequency. YMMV.
It's not the exhaust temperature, it's the gas temperature in the closed tube that goes into the sound reflection calculation.

 

[doc_random]

 

[doc_random]

More tuners call it a "J-pipe" than a Helmholtz resonator.

YouTube video on calculations and results. Two sites say the pipe should not be in line with the flow, but perpendicular to it, but they don't say "why".


Calculator:

Drone Calculator

Web Site Builder Description

super-null.com

Drone pipe length in inches for my 4.5L 6 at 2800 RPM: 25.30"

 

[White Stripe]

I personally really don't know where you would typically put that under a cruiser unless you remove the spare. I do plan on removing my spare to a bumper, but then a auxiliary tank will be swapped in. On my v8 I have a 5.7 oem tundra muffler. It's tight but pretty quiet.

 

[alia176]

I personally really don't know where you would typically put that under a cruiser unless you remove the spare. I do plan on removing my spare to a bumper, but then a auxiliary tank will be swapped in. On my v8 I have a 5.7 oem tundra muffler. It's tight but pretty quiet.

Remember that the Hemholtz resonator does not have to be at a specific place in your exhaust system, as long as it is perpendicular to the air flow. This gives us some sort of flexibility, especially if you get rid of the 25+ year old exhaust pipes, mufflers and cats.

 

[doc_random]

Further reading shows I built a quarter wave J-pipe. The pulse goes down the tube and back and impacts the next pulse in the exhaust 180' out of phase (noise cancelling).
There is also a Helmholtz resonator that is a shorter pipe to a larger can. I don't understand the math on this yet, but here is a picture. It is from the site @alia176 linked to above.
Many sites say you can put these anywhere in the system.

 

[alia176]

Further reading shows I built a quarter wave J-pipe. The pulse goes down the tube and back and impacts the next pulse in the exhaust 180' out of phase (noise cancelling).
There is also a Helmholtz resonator that is a shorter pipe to a larger can. I don't understand the math on this yet, but here is a picture. It is from the site @alia176 linked to above.
Many sites say you can put these anywhere in the system.
View attachment 2922604

Yup, I was thinking of going the coffee can route but I like the J pipe concept better. Thanks again for chiming in and educating us ,as most of us, if not all, want to solve the problem by throwing mufflers at it. Here come the questions!

Ok, i'm curious about your second resonator. Like you, I have the Vibrant tailpipe resonator but mine is 2.5" and yours is 3". Why do you have a second resonator?

Did you do the calcs then take the info to the muffler shop or did they know how to do this? I'm assuming you drew out the drawing below and handed it to the muffler shop monkeys is what I'm thinking.

Did you use a freq analyzer app to come up with the annoying freq or use some other resource? I've been using the feq analyzer app in the link above but having difficulties isolating the freq due to the wind noise that is entering the cab. At slow speed, I'm getting 80hz and at higher speeds, I *think* i'm getting 120hz but not really sure.

 

[93yotasr5]

The cat back exhaust on my tundra came with one of the resonators. It makes a huge difference.

6", 8", 10" or 12" 2010+ Tundra Exhaust - Performance Without Drone

This system is family friendly and good for people who tow frequently. The cabin ride is the most enjoyable with this set-up. The 10" muffler option is the

dirtydeedsindustries.com

 

[doc_random]

It could work on an 80 with the spare tire in place. The J-pipe could parallel the exhaust after coming over the last frame member. It does not have to be straight, in fact some are wound like a coil. The two clamps on this one allow adjusting the length plus/minus a couple inches to tune it to eliminate the drone.

Exhaust mocked picture below credit to Well i did a thing.. my 97 lx build. distributorless/turbo/h151f - https://forum.ih8mud.com/threads/well-i-did-a-thing-my-97-lx-build-distributorless-turbo-h151f.1213151/post-14198786 @audi2nr

 

[doc_random]

Yup, I was thinking of going the coffee can route but I like the J pipe concept better. Thanks again for chiming in and educating us ,as most of us, if not all, want to solve the problem by throwing mufflers at it. Here come the questions!

Ok, i'm curious about your second resonator. Like you, I have the Vibrant tailpipe resonator but mine is 2.5" and yours is 3". Why do you have a second resonator?

Did you do the calcs then take the info to the muffler shop or did they know how to do this? I'm assuming you drew out the drawing below and handed it to the muffler shop monkeys is what I'm thinking.

Did you use a freq analyzer app to come up with the annoying freq or use some other resource? I've been using the feq analyzer app in the link above but having difficulties isolating the freq due to the wind noise that is entering the cab. At slow speed, I'm getting 80hz and at higher speeds, I *think* i'm getting 120hz but not really sure.



View attachment 2922639

* Why do you have a second resonator?
The headers came with a resonator where the catalytic should be. I had them cut that resonator out and thought "I might as well use it", so that's how it ended up downstream in the system. Probably helps and can't hurt.
* Did you do the calcs then take the info to the muffler shop or did they know how to do this?
I printed out the sheet that is pictured here and took it in to Scottsdale Muffler with the major parts. They installed it. Great work, 6 years later zero issues.
* Did you use a freq analyzer app to come up with the annoying freq or use some other resource?
I calculated it from what I found on the internet in 2016. There is now a calculator that I'm happy to see give the same result. 2800 RPM = 140Hz for a 6 cylinder in a warm place. I picked the RPM that may not have been the most annoying, but is highway speed (with 35" tires, 4:88 gears). Tire size and gearing will change the cruising RPM a bit. It looks like there are more sophisticated phone apps for dB and frequency today than 2016, but I have not messed with them.
Caculator:

Drone Calculator

Web Site Builder Description

super-null.com

 

[alia176]

Thanks again dude, for your contributions to this thread. Lots of stuff to learn and digest here! Given that I now see you're SC'ed, we probably have the same CFM and most likely the same annoying freq at hwy speeds.

 

[doc_random]

IS300 SX:

Dodo´s 'IS300

Hello guys! I already wrote a tutorial for wiring up your ECU when going manual. Now I decided to share my project with you as I have realized how far I have still gone and I want to participate and share knowlege with you! When hail destroyed my old car in 2019, I was looking for a new one...

www.my.is

Check out this "adjustible" exhaust drone fix

Adjustable exhaust drone fix: I'm sure most of you have already heard of a Helmholtz resonator to fix the drone of many aftermarket exhausts. My wife's ears seemed to be directly tuned to hear the drone, so I hit all the message boards looking for the exact size, shape, and placement of the...

www.tundrasolutions.com

 

[lsustang05]

This is what I had fabricated and I am very happy with the lack of drone on the highway. The Helmholtz resonator is the J-pipe in the diagram. The idea is to have the sound pulse go into the closed end J-pipe and reflect back into the exhaust path to cancel the next pulse. Noise cancelation. I had the J-pipe connection in line with the exhaust flow. The calculations showed 24-27" was the right range for my vehicle at 70-80mph (LX450, 4.88 gears, 35" tires, about 2800rpm at highway speed). The shop set it to 25.5" with adjustable clamps in 2016 and I never changed it. It also has two resonators. Spare tie obviously relocated.

LX450 2800 RPM * 3pulses/rev / 60 sec/min = 140 Hz resonant frequency. YMMV.
It's not the exhaust temperature, it's the gas temperature in the closed tube that goes into the sound reflection calculation.
View attachment 2922439

It’s funny. I know there is math involved and plenty of different variables to the j-pipe design but, I did one for my truck and it uses a 26” pipe to get rid of the drone. 6.2L V8, 37’s, 4.10’s, and trying to reduce/eliminate drone at 2100-2300 RPMs.

Makes me believe if you had a semi adjustable one installed that ranged from 25-28” you’d be able to dial in just about any vehicle.

 

[alia176]

It’s funny. I know there is math involved and plenty of different variables to the j-pipe design but, I did one for my truck and it uses a 26” pipe to get rid of the drone. 6.2L V8, 37’s, 4.10’s, and trying to reduce/eliminate drone at 2100-2300 RPMs.

Makes me believe if you had a semi adjustable one installed that ranged from 25-28” you’d be able to dial in just about any vehicle.

I like this idea quite a bit, make an adj one. This pic shows a smaller OD tube going inside a larger ID tube with a clamp. This clamp needs to be for both OD's but it isn't so I'm guessing some amount of air is probably escaping but not enough to negate the overall sound reduction. I suppose wrapping the smaller pipe with alum foil just thick enough will take care of any air/sound escaping.

 

[doc_random]

Looks like they make clamps with two ODs. 2.5" ands 2.25" example. The two diameters act like a slide trombone. Slide to the right length and clamp it.

Amazon product

 

[Bambusiero]

Oh! this is fun- have been intrigued with this idea for years (but have not tried to impliment).
You're the only other one I've ever heard mention this Helmholz business.
Like other have said - My Subaru forester has one (or two?) in the intake tract - no doubt tuned to suppress the most common highway cruising RPM drone frequency.

Some thoughts to ponder - you may be way ahead of me on any of these :
1) You want complete phase inversion as the standing wave arrives back at the port.
2) efficient acoustic reflection at the far end - a flat cap - this is obviously a flow velocity anti-node (zero mass flow through the cap - but might be a pressure node (pressure amplitude maximum - reversing/reflecting).
3) Probably not necessary to have your helmholz tube full exhaust tube diameter - smaller diameter tubing might work just as well, since net mass flow is zero. The Subaru Forester intake tract helmholz is ~ 0.6 of the main tube diameter.
4) The Subaru Forester intake tract helmholz is actually split into 2 half diameter tubes (and the shorter one is even further reduced).
Photos and length measurements of that are attached FYI - I don't know off the top - what's the cruising RPM - I'll have to take a drive - and it's 4 cylinder, not 6, which changes the frequencies.
5) A full diameter port would cause more main exhaust flow turbulence - a slit port might be just as good for the acoustics, and disturb the exhaust flow less.
6) From musical wind instruments - a straight diameter tube will have the sharpest / narrowest / highest "Q" resonance peaks, while a tapered tube will broaden the resonance peaks - Clarinets (straight) are hard to "bend" notes, while saxaphones (tapered) are easy to bend notes.
7) Folding the tube to have a longer resonator length in a shorter package should work fine.
8) Exhaust gas temperature will change the speed of sound, and wavelengths, but I doubt pressure is much above ambient down-stream from the engine, where you might be doing this. - on the other hand - gas temperture on the helmholz would be less than the main exhaust stream, since it's a dead end, not getting new heat, and has cooling surface.
9) A slip-joint would give you tunability.
10) browsing a textbook on RF Microwave transmission-line filter design might give useful design clues - waves is waves is waves.

 

[doc_random]

1, 2, 7, 8, 9 = Yes.
3: My J-pipe is 2" vs 3" exhaust, so pretty close to the 0.6 ratio you describe.
4: There are secondary, tertiary etc. resonances that you could try to catch using other J-pipe lengths in addition to the main one. It's not a "note", it's a "chord" and a complicated one.
The calculator for number of cylinders, speed of sound for a given temperature, and RPMs you are trying to cancel gives you the main offending drone. The chart below shows there are many dB peaks in a system. But the 1st peak is 10dB lower than the main one, which is a lot. It is also 1/2 the main frequency and you may reduce this one with the single J-pipe, I'm not sure.

This is for a V8 Ferrari F40. "The lowest peak is the fundamental frequency (59.2 Hz), and harmonics are multiple integers of it (120, 180, 240, and so on)."

YMEC software - MEASUREMENT OF F40 EXHAUST NOTE - Ferrari F40 Measurement

INTRODUCTION TO SIMPLE SOUND MEASUREMENT shows how to use the DSSF3 which is the greatest of allsoftware programs for sound measurement and a lot of examples.

www.ymec.com

Wikipedia on the original topic of sound deadening, but also shows the spectrum of some automobile.

Soundproofing - Wikipedia

en.wikipedia.org