Making a muffler

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ptuomov
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Re: Making a muffler

Post by ptuomov » Sun Jun 11, 2017 2:38 pm

http://ansol.us/Products/Coustyx/Valida ... iption.pdf

That's a very short paper that in my opinion illustrates well the impact of filling an expansion chamber with packing material. Perforated tube thru a can, and either empty or filled with packing. Packing does nothing to low frequenicies but is very effective at high frequencies. The solution to muffling mid and high frequency seems to be pretty clear: install the biggest can that fits and then fill it with packing. The low frequencies are going to need a resonator of some sort.
[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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Re: Making a muffler

Post by xr4x4ti » Mon Jun 12, 2017 10:10 am

Do a quick google search "resonant j pipe exhaust drone"

https://www.google.com/search?q=resonan ... 82&bih=741

Image

https://ls1tech.com/forums/cadillac-cts ... tubes.html


I had my doubts that such a thing could work, but I put it on my Turbo 327 Ford with a single 4in exhaust and I have to say it totally worked. If your goal is to get rid of a drone or make it quieter at cruising RPM, give it a try. They are easy to fit into odd places because they can be almost any shape. The length needs to be tuned to the cruising RPM, of course this results in it actually being LOUDER at other higher RPM, but usually you are "in the gas" at that point anyway and it only adds to the fun :D

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Re: Making a muffler

Post by ptuomov » Mon Jun 12, 2017 10:48 am

xr4x4ti wrote:Do a quick google search "resonant j pipe exhaust drone"

https://www.google.com/search?q=resonan ... 82&bih=741

Image

https://ls1tech.com/forums/cadillac-cts ... tubes.html


I had my doubts that such a thing could work, but I put it on my Turbo 327 Ford with a single 4in exhaust and I have to say it totally worked. If your goal is to get rid of a drone or make it quieter at cruising RPM, give it a try. They are easy to fit into odd places because they can be almost any shape. The length needs to be tuned to the cruising RPM, of course this results in it actually being LOUDER at other higher RPM, but usually you are "in the gas" at that point anyway and it only adds to the fun :D
Problem with those external quarter-wave resonator pipes in general is that they have to have a cross-sectional area that is close to the main pipe's cross-sectional pipe. Once you do that, they take so much space that either they don't fit or you might as well add more real mufflers there. So for them to work well in practice for space constrained situations, I think you need to be clever. For example, in the exhaust being fabricated currently for my car, we increased the diameter of the wastegate dump pipes that merge to the main pipes solely for the reason that they'd become more effective quarter-wave resonators. Also, in a dual exhaust with generous crossovers both upstream and downstream of the dual pipes, you can set up a butterfly valve to block one of the two dual pipes at low exhaust mass flow rates and both dead end branches now turn into a quarter-wave resonator pipe each.

Car factories use the quarter-wave resonator idea a lot, but never with an external pipe (that I've seen). Instead, they have a long, relatively small diameter resonator can in the exhaust. The main pipe is inside the resonator can shell. Then they drill some holes to the end of the main pipe section that is inside the long resonator can. Now, the resonator can works like a quarter-wave resonator, it's just that the resonator pipe is around the main pipe. A lot easier to fit in most situations, given that the outer resonator shell also does double duty as a heat shield.
[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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Re: Making a muffler

Post by ptuomov » Mon Jun 12, 2017 6:48 pm

By the way, if one decides to fix an existing drone with a quarter-wave resonator, here's an informative paper: http://data.mecheng.adelaide.edu.au/avc ... h_geom.pdf The practically relevant finding here is that "a bellmouth" style joint of the dead-end pipe to the main pipe suppresses noise a lot better than sharp joint.
[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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Re: Making a muffler

Post by ptuomov » Tue Jun 13, 2017 2:19 pm

In case someone is interested, I found this Borla muffler blueprint from the web:
IMG_0116.JPG
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[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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Re: Making a muffler

Post by n2xlr8n » Wed Jun 14, 2017 10:53 am

Great find.

I wonder how much bending the perforated tube affects the attenuation of the specific frequency? Without doing the math, it appears that high freq would not be affected, but lower freq would, possibly? The drawing indicates they are targeting 250 Hz and above, no?
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Re: Making a muffler

Post by ptuomov » Wed Jun 14, 2017 9:15 pm

n2xlr8n wrote:Great find. I wonder how much bending the perforated tube affects the attenuation of the specific frequency? Without doing the math, it appears that high freq would not be affected, but lower freq would, possibly? The drawing indicates they are targeting 250 Hz and above, no?
I don't know. Anyone?

Here's something interesting that I came across recently. Some muffler construction choices that may have an impact on the overall noise levels:
MufflerConstruction.jpg
http://ijiset.com/vol2/v2s7/IJISET_V2_I6_64.pdf
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Re: Making a muffler

Post by MadBill » Wed Jun 14, 2017 9:28 pm

Wow, glass wool sure is the silver bullet! =D>
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Re: Making a muffler

Post by ijames » Wed Jun 14, 2017 11:12 pm

Notice they didn't say where the magic location was for the weld seam. That plus the embossing almost add up to the glass wool. Oh, they didn't specify the embossing, either. Wonder if simple rings from end to end would be best, you could do that with a bead roller just making parallel lines after you roll and weld the oval. If you wanted lines along the muffler axis you could do some after you roll the oval but before you weld the seam, depending on where the seam is. Hmm, if you could put the lines at 45 deg to the axis of the oval, that would stiffen the shell in both directions but I can't see how to do that with a simple bead roller #-o .

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Re: Making a muffler

Post by ptuomov » Thu Jun 15, 2017 5:45 am

ijames wrote:Notice they didn't say where the magic location was for the weld seam. That plus the embossing almost add up to the glass wool. Oh, they didn't specify the embossing, either. Wonder if simple rings from end to end would be best, you could do that with a bead roller just making parallel lines after you roll and weld the oval. If you wanted lines along the muffler axis you could do some after you roll the oval but before you weld the seam, depending on where the seam is. Hmm, if you could put the lines at 45 deg to the axis of the oval, that would stiffen the shell in both directions but I can't see how to do that with a simple bead roller #-o .
They have a fair bit of detail in that pdf:
MufflerCaseTest.jpg
It's not clear how "additive" these methods are, though.
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Re: Making a muffler

Post by j-c-c » Thu Jun 15, 2017 12:32 pm

MadBill wrote:Wow, glass wool sure is the silver bullet! =D>
That surprised me also at first, but then there no support info to explain that, and it also completely contradicts the link a few replies before that does go into detail, ie 200HZ and below is effected little by packing. I'm doubtful, and suspect there is a lot more to that claim of 6db reduction. Also, hope everyone understands those decreases in db are not accumulative.

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Re: Making a muffler

Post by ptuomov » Thu Jun 15, 2017 2:22 pm

j-c-c wrote:
MadBill wrote:Wow, glass wool sure is the silver bullet! =D>
That surprised me also at first, but then there no support info to explain that, and it also completely contradicts the link a few replies before that does go into detail, ie 200HZ and below is effected little by packing. I'm doubtful, and suspect there is a lot more to that claim of 6db reduction. Also, hope everyone understands those decreases in db are not accumulative.
Note that this paper focuses only on the noise radiated from the vibrating muffler case. The muffler itself can be completely ineffective in reducing tailpipe noise but look great on not radiating much noise. As an extreme example, think of a 3" ID lead pipe with 1" thick wall. That contraption is a terrible tailpipe muffler but probably doesn't radiate much sound from the vibrating surface!

I think (but don't know) that packing the muffler tight with anything, including fiberglass or even sand would reduce the noise radiated from the case surfaces. I don't see any mystery there, if tightly packed anything is applying pressure on a resonating surface it resonates less. I think just pushing the muffler case from outside with a finger would reduce the noise radiated from the case surface, right?

The mechanism by which fiberglass or rock wool attenuates the sound waves in the gas inside the muffler case is by my understanding different. Here, it's not just that the fiberglass packing is pressing against something, because air moves relatively freely inside even tightly packed material. I say relatively freely because flow resistivity of the packing material is the main determinant of sound absorption by that material. A small fiberglass packed cavity is not going to be very effective with low frequencies.

I agree that these methods of reducing case vibration are probably best thought of as alternatives for fixing a problem instead of things that can be accumulated to a great benefit.
[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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Re: Making a muffler

Post by n2xlr8n » Thu Jun 15, 2017 3:16 pm

j-c-c wrote:
MadBill wrote:Wow, glass wool sure is the silver bullet! =D>
That surprised me also at first, but then there no support info to explain that, and it also completely contradicts the link a few replies before that does go into detail, ie 200HZ and below is effected little by packing. I'm doubtful, and suspect there is a lot more to that claim of 6db reduction. Also, hope everyone understands those decreases in db are not accumulative.
Inverse square law dictates that, by their claims it would be equivalent to standing double the distance away from the sound source. I also think that there is likely a reflection component at a certain frequency that glass wool is attenuating. Db are logarithmic.

An observation about the chart: db (A)? As in A weighted IEC standard scale? Great tool to use, but audio is likely the most misunderstood / misrepresented technology I've ever been in/around. Sound Pressure Level is not equal to loudness...and that's what we care about here, no? I need to read the entire pdf tonight before commenting further, honestly.

I agree that a 3" ID lead cylinder 1" thick would not benefit from glass wool :mrgreen:

ptuomov- you've spent a lot of time on this and shared every step of it with us- Say the word and I'll loan you my personal copy of the Sound Reference Bible. It is that.
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Re: Making a muffler

Post by j-c-c » Thu Jun 15, 2017 4:20 pm

ptuomov wrote:
Note that this paper focuses only on the noise radiated from the vibrating muffler case. The muffler itself can be completely ineffective in reducing tailpipe noise but look great on not radiating much noise. As an extreme example, think of a 3" ID lead pipe with 1" thick wall. That contraption is a terrible tailpipe muffler but probably doesn't radiate much sound from the vibrating surface!

I think (but don't know) that packing the muffler tight with anything, including fiberglass or even sand would reduce the noise radiated from the case surfaces. I don't see any mystery there, if tightly packed anything is applying pressure on a resonating surface it resonates less. I think just pushing the muffler case from outside with a finger would reduce the noise radiated from the case surface, right?
Yes, the radiation thru the case premise should have better addressed in my response above as the primary topic of the paper.

Also, one upside of lead well known, it has very high relative mass, but not overly rigid, we have used lead in the past for sound proofing concert generators, it is very effective for transmission reduction But also consider, if the muffler case was fabricated out of the most rigid material suitable, it would then reflect all acoustic energy back internally, and whatever is not reduced by the muffler design at hand, this energy would eventually find its way out the taiipipe, at a higher level then with a less rigid housing. I'm sure there is a sweet spot for every application

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Re: Making a muffler

Post by ptuomov » Sat Jun 24, 2017 1:27 pm

Exhaust video update by John:

https://www.youtube.com/watch?v=zq6VwW_p-zc
[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

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