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Old 08-29-2012, 05:19 AM   #1
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Hemholtz Resonator (1/4 wave resonator)

Anyone heard of this? The idea is to find what RPM your car drones. Then after some simple multiplication and division, you can find the length of tube required to add to your exhaust to kill drone at that RPM.

It's been around for a long time being used in intake tract silencers. There is a 13pg thread on a mustang forum where people have done this and came out with amazing results. This goes deeper than the mustang crowd too. Since researching, I have found it on Beemr forums,Audi forums and other "sensitive hearing" oriented car enthusiaites.

Quote from post in Mustang forum from the guy who started it:

"My magnaflow had the usual 2000 rpm drone, so I tried something a little different (I think) to get rid of it. The drone is now not just better, it is completely gone - the exhaust is downright quiet cruising at 2000 rpm. I read an article on the internet about "tailpipe resonance", and decided that this has to be the problem with aftermarket catbacks. They probably all have the same 6ft tailpipe mine has, which if the exhaust is at about 500 degrees, will resonate at 134 Hertz, which is the engine firing rate at 2000RPM. So I added a 134 Hz, 1/4 wave resonator to both tailpipes. Its just a section of pipe "T"ed into the tailpipes right in front of the gas tank. They are about 26" long each, which maybe a little shorter than ideal, but that's what fits in the available space. 26" must be long enough, because it sure as heck works. One end of each pipe is welded shut, and the other is T'ed into the tailpipes. If anyone is interested, I can try and post a picture."

Corsa of course promotes a RSC Technology in their mufflers which goes beyond this since they are able to tune the drone withing the confines of a muffler.

You would simply "T" off your exhaust with a centerline length of tube that you calculated and cap the end....done. My drone comes in at 1700 and stops around 2000, so I calculated based on 1750rpm giving me 29" of pipe needed.

How I plan to redo mine...mimic the Corsa single 3" but with a pipe "t'd" off. (not to scale)



On a Mustang:





On a GTO(was posted in mustang forum)


Cut away from a New Camaro muffler that suffers from drone:



Ohh, look...on a G8 lol:




Other exhaust companies have been doing this as well it seems:





I had a plan to do this to my Mach 1 when I had it, but then I threw in Dynomax VT mufflers and they worked well enough I was done with the "anti drone" quest.

My L/T's, catless mids and dual 3" SW catback with no mufflers drone BAAAAD, so it would be sweet if I could make a catless/muffler-less system not drone. LOL


Thought? Opinions? Ideas? I would link the Mustang forum thread so people can read for themselves, but I don't know how mods like that.


Sorry this isn't another "what exhaust is the best to put on my (enter year GTO here)??" lol Hopefully this will get a little technical.
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Old 08-29-2012, 05:48 AM   #2
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Lookout!

Hope you have your fireproof shorts on!
There's an old thread on here about these somewhere, sorry don't have time to grab the link right now. Haven't read it in some time, but yes it works great.
And now Im sure here come the SEARCH flames.....
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Old 08-29-2012, 05:55 AM   #3
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He would be flamed for digging up an old thread. Damned if you do, damned if you don't. That's how we roll around here.

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Old 08-29-2012, 06:16 AM   #4
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the g8 folks call them j pipes. you can actually get those
as a complete unit for some axle backs.
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Old 08-29-2012, 06:22 AM   #5
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I'm appreciative. Good info for those of us who didn't know of the existence of such things and searching on "drone" gives 10 pages of information not about this.
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Old 08-29-2012, 07:09 AM   #6
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What does it do to the tone of the exhaust?

Flame me all you want, but my car sounds perfect and I don't want it to change. I have no drone at all except for 1400-1500rpms. Then it is silent.
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Old 08-29-2012, 07:35 AM   #7
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Its not supposed to do anything to the tone. It works of pressure waves coming back 180 degrees out of phase at your drone rpm. It wont hurt flow either since the air in the tube is not technically flowing in and out from what I understand. The air in the tube vibrates at a frequency that cancels the exhaust drone frequency.

I didnt bother searching since people still complain about drone and not once have I seen this mentioned in a thread since I joined.

Just found this thread about them. It was Vteckiller2000 who's GTO is in the pics above.
http://www.ls1gto.com/forums/showthr...sonator&page=2

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Old 08-29-2012, 08:08 AM   #8
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It affects the tone only at the tuned frequency and then as said works to cancel that note. A good muffler in the right spot does it a lot easier.
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Old 08-29-2012, 08:37 AM   #9
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Quote:
Originally Posted by svede1212...View Post
It affects the tone only at the tuned frequency and then as said works to cancel that note. A good muffler in the right spot does it a lot easier.

Mind expanding on this? What determins a "good muffler" and in the "right spot"? We only have 2 options for muffler placement...04 location and 05/06 location.

Maybe instead of redoing my exhaust to a sinlt 3" I will simply "snail-route" my resonator pipes where the mufflers would sit for an 04. I would rather "test" the theory that way than spend the money for a whole diff exhaust routing.

Just a bunch of 90" bends and T it off my pipes. I'll have to measure the size of the cavity I have n my car and model up some 2.5" and 3" pipes to see what the longest pipe I can make.

Using Excel for all it's glory, I came up with the following: My drone in bold.

RPM / Tube length (in)

1500/ 33.75
1550/ 32.66129032
1600/ 31.640625
1650/ 30.68181818
1700/ 29.77941176
1750/ 28.92857143
1800/ 28.125
1850/ 27.36486486
1900/ 26.64473684
1950/ 25.96153846
2000/ 25.3125
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Old 08-29-2012, 11:26 AM   #10
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Quote:
Originally Posted by smitty2919...View Post

I didnt bother searching since people still complain about drone and not once have I seen this mentioned in a thread since I joined.

you haven't even been here 9 months though, lol. The forum is near 10 years old.
I appreciate what you're trying to do, but it's old news
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Old 08-29-2012, 11:27 AM   #11
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Old 08-29-2012, 11:36 AM   #12
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Quote:
Originally Posted by HunterKiller89...View Post
you haven't even been here 9 months though, lol. The forum is near 10 years old.
I appreciate what you're trying to do, but it's old news

Not saying it's anything "new" but if it works so well, I haven't come across a TON of threads about it even with the forum being 10 years old.

But like some have said, they have never heard of this. I didn't want to convey it as I was the one bringing this new great idea to LS1GTO forum.
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Old 08-29-2012, 03:14 PM   #13
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Quote:
Originally Posted by smitty2919...View Post
Mind expanding on this? What determins a "good muffler" and in the "right spot"? We only have 2 options for muffler placement...04 location and 05/06 location.

Maybe instead of redoing my exhaust to a sinlt 3" I will simply "snail-route" my resonator pipes where the mufflers would sit for an 04. I would rather "test" the theory that way than spend the money for a whole diff exhaust routing.

Just a bunch of 90" bends and T it off my pipes. I'll have to measure the size of the cavity I have n my car and model up some 2.5" and 3" pipes to see what the longest pipe I can make.

Using Excel for all it's glory, I came up with the following: My drone in bold.

RPM / Tube length (in)

1500/ 33.75
1550/ 32.66129032
1600/ 31.640625
1650/ 30.68181818
1700/ 29.77941176
1750/ 28.92857143
1800/ 28.125
1850/ 27.36486486
1900/ 26.64473684
1950/ 25.96153846
2000/ 25.3125

It's an interesting idea (and much older than this forum). They are often used on the other end on intakes to cancel sound coming out the intake. Quite a few people have conquered drone conventionally tho. I know my exhaust does not drone. I have had it with other ones I had on my car so I know you can manipulate it with configuration.
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Old 08-29-2012, 03:35 PM   #14
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Quote:
Originally Posted by svede1212...View Post
It's an interesting idea (and much older than this forum). They are often used on the other end on intakes to cancel sound coming out the intake. Quite a few people have conquered drone conventionally tho. I know my exhaust does not drone. I have had it with other ones I had on my car so I know you can manipulate it with configuration.

this
OEMs use them on the intake side a LOT, and almost never on the exhaust side, because the exhaust has a muffler (and OEM mufflers baffle enough that you dont hear resonant frequencies), and if there is still droning, OEMs will usually just put in a resonator as well before going this route. I think that's what was meant earlier in proper muffler selection post above
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Old 08-29-2012, 04:23 PM   #15
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Making a single 3" setup like Corsa and adding a resonator tube T'd off would be no more work than having a whole catback made with mufflers.

My end goal would be to run a L/T, catless and straight pipe exhaust with no drone.
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Old 08-29-2012, 07:52 PM   #16
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Quote:
Originally Posted by svede1212...View Post
It's an interesting idea (and much older than this forum). They are often used on the other end on intakes to cancel sound coming out the intake. Quite a few people have conquered drone conventionally tho. I know my exhaust does not drone. I have had it with other ones I had on my car so I know you can manipulate it with configuration.

Thank you, SS.

Exhaust drone (and popping/rasp) has been the primary reason I still have, reluctantly, stock exhaust on my GTO.

With your comments on 'intake side' applications, I cant help but wonder if this explains LT1 Camaro 'donkey dongs'. I plugged mine long ago to no noticeable effect.

http://www.mifbody.com/vbulletin/sho...nkey-dong-tube
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Old 08-29-2012, 08:49 PM   #17
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Or you could run a set of mufflers in the 04 location and a crossover pipe and stop trying to solve a problem that shouldn't exist
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Old 08-30-2012, 04:07 AM   #18
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Anyone have proof their aftermarket system doesn't drone? Much like the video I made when I had my Mach 1


That decibel drop may not seem like a lot, but it is linear. So that drop was very noticeable in the car. So much I went to a catless midpipe after that and was still happy with those mufflers.

A lot of people SAY there is no drone in their exhaust...then again a lot of people SAY they picked up a some good HP with a K@N intake. I'm lean more towards hard numbers. I'm gonna try to get a reading of my car now and see what it gets up to. then do the same after.
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Old 08-30-2012, 05:21 AM   #19
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Quote:
Originally Posted by 04QSMGoat...View Post
Or you could run a set of mufflers in the 04 location and a crossover pipe and stop trying to solve a problem that shouldn't exist

More expensive and heavier. Again I'm not doing it for the weight though since it's a DD.

I'm trying to be productive with this idea of killing drone for people on this board, not just me. Someone on the G8 board tried this and everyone loved it. I'm also not playing it off like i invented this, but if it works so well why is this not common umung the GTO crowd? I like to tinker and play around, so since my CB now is a bit of a hack job by the PO, I will modify it to see what I can do.

If you want to go spend the money on 2 mufflers have at it. Only issue I have with my setup now is the drone. If I wanted it quiet, I would put my stock catback on.

God forbid I make a thread other than "is this muffler right for me?" or "what exhaust sounds best?" lol

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Old 08-30-2012, 02:31 PM   #20
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It was kind of hard to recreate your "test" as you gave no parameters as to how far away from the exhaust at idle, if the windows were up or down, etc. I had to take my car out to a photo shoot this afternoon with street and freeway driving. I could not video my dB meter and drive my car at the same time safely but I made note of dBs. At idle from 10 feet away, 5 feet off the ground my car is 80 dB. At 1,500 with widows up meter at ear level while driving it was 82-83 dB. At 2,000 same it was 83 dB. At 3,000 same it was 85 dB. WOT it was 91 dB. When cruising the major change in dB was more related to vehicle speed and road noise than exhaust as I pushed in the clutch and coasted to see if there was a change, it dropped about 3 dB. My car is heads/cam/LTs/!cats/X pipe and 2 Borla Pro XS in the '04 location on 2.5" pipes. Just my word for it but no drone and excellent power.

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Old 08-30-2012, 02:41 PM   #21
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Both idle clips were about 5 ft away at a 45* angle from tips about 3 ft off the ground. Both highway clips were windows up, no radio etc and cruise set at 70mph and filmed the same stretch of highway and used the same decibel reader both set to A-scale. So that video was prob as accurate as you could get just "winging" it.

I mostly made the video because I haven't found any videos like that anywhere and especially about the Dynomax VT mufflers. I READ that they didn't drone and saw videos of in-cabin noise but there were WAY too many variables in those videos. Not to mention they didn't even do a "before" video. So I put some actual numbers to what people "said".

So it was great to compare them to Magnaflow's full size muffler, which with mustang guys is the more tame/least drone muffler. That video proved the VT's were even better at less drone and had similar exterior sound. Power...? Well I didn't dyno either setup and I didn't care about 1-2 hp (a wild guess) between the mufflers.

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Old 08-30-2012, 02:45 PM   #22
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Helmholtz resonators are not only nothing new, they have been utilized in everything from automotive exhaust systems, intake silencers, loudspeakers, drums and organs for centuries. They were used empirically long before Herman von Helmholtz published his famous equations 100 years ago. The "resonator" that has been on OEM exhaust systems since the sixties is indeed a helmholtz resonator. So is a soda bottle that you blow across the top of to produce a specific tone.
Sooooo.....the idea of a "J pipe" or 1/4 wave tuned tube is about as revolutionary as a can opener. The resonators manufacturers build into factory exhausts do not have to have that rather inefficient form factor or be "tunable" simply because the variables of pipe lengths, node and antinode points, and cavity resonances are all known. The idea of a tunable resonator is certainly applicable to an exhaust system that was not designed as a system, but rather contains a variable hodgpodge of pipes, mufflers, and bends is certainly worthwhile, but the idea of presenting it as some kind of technological breakthrough is ignorant in the extreme.
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Old 08-30-2012, 02:49 PM   #23
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Quote:
Originally Posted by mistermike...View Post
Helmholtz resonators are not only nothing new, they have been utilized in everything from automotive exhaust systems, intake silencers, loudspeakers, drums and organs for centuries. They were used empirically long before Herman von Helmholtz published his famous equations 100 years ago. The "resonator" that has been on OEM exhaust systems since the sixties is indeed a helmholtz resonator. So is a soda bottle that you blow across the top of to produce a specific tone.
Sooooo.....the idea of a "J pipe" or 1/4 wave tuned tube is about as revolutionary as a can opener. The resonators manufacturers build into factory exhausts do not have to have that rather inefficient form factor or be "tunable" simply because the variables of pipe lengths, node and antinode points, and cavity resonances are all known. The idea of a tunable resonator is certainly applicable to an exhaust system that was not designed as a system, but rather contains a variable hodgpodge of pipes, mufflers, and bends is certainly worthwhile, but the idea of presenting it as some kind of technological breakthrough is ignorant in the extreme.

I never said it was a breakthrough, in fact I stated the obvious that people have been doing this and it's nothing new. I was simply bring more evidence and fact to THIS forum. There is decently long threads about this on G8 forum and a Mustang forum. I figured I would open some people's eyes to this idea because I know not everyone has seen or even known about this.
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Old 08-30-2012, 03:01 PM   #24
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Mufflers can add or subtract to drone but it's the entire system that determines drone too. A muffler that doesn't drone on a Mustang in a location may drone in a GTO. I think my test was very applicable because it's on a LS engine. The genesis of exhaust sound is generated when the exhaust gases leave the combustion chamber and make the first turn at supersonic speed in the exhaust runner. Because of that a LS sounds different than a Hemi than a 5.0. Head work also changes that. What heads, how long of LT, how long of collector, X or H their location, location of muffler and pipe size all "tune the sound too. It took me 5 tries but after reading exhaust theory and calculating lengths for different collectors and locations I came up with what I have. The dyno showed my configuration picking up 20-30 RWHP below 2,500 RPM too. So much for 1 or 2 HP.
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Old 08-30-2012, 03:59 PM   #25
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I didn't post that video to compare a mustang drone and a GTO drone. I was just sharing what I had done before and agreeing on how a muffler can help with drone.

I understand the GTO is a whole new animal and the 1/4 wave resonator idea/theory levels the playing field between the two cars.

While some are willing to put into a lot of research and calculation (you Svede and MisterMike) and will see this as "childish" and "old". Others will find it as another way to combat drone in a very simple and easy way.

Personally, I'm not a fan of your exhaust. Yes it is smooth and "good sounding" it just isn't the tone that appeals to me. Yet I am very impressed with your result of 20-30 rwhp simply made by collector length, x pipe location, and muffler selection though.

The goal FOR me, would be a straight piped exhaust with no drone. Maybe a lofty goal since straight pipes and catless is the pinnacle of a "drony" exhaust. I like the sound of my exhaust now.

I have even thought to redo from the headers back since I hate the flange at the end of my PS mids. In which case, collector length could be addresses. Not so much crossover location since I plan on a single 3" setup.

I am all for being throw "technical" information or articles to read. Svede, I came across your thread on Gtoforum about your exhaust and was impressed. From there I saw the articles you posted and the videos. If I'm going to redo my catback, I would rather make changes that are worth it (sound and performance) if possible lol
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Old 08-30-2012, 04:09 PM   #26
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That's cool most exhausts I've heard sound like they belong on a pig nosed WS6 racer car than the more sophisticated GTO but different strokes for different folks. I understand that but it's no more work and maybe easier to calculate a proper exhaust than a Helmholtz. You have to have the diameter and length just right as well as location. I forgot the weight savings going simple too.
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Old 08-30-2012, 04:26 PM   #27
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Quote:
Originally Posted by smitty2919...View Post
I never said it was a breakthrough, in fact I stated the obvious that people have been doing this and it's nothing new. I was simply bring more evidence and fact to THIS forum. There is decently long threads about this on G8 forum and a Mustang forum. I figured I would open some people's eyes to this idea because I know not everyone has seen or even known about this.

My comments were partially in response to an earlier post about a criminally overpriced German exhaust system that claimed resonators and 1/4 wave tuning to be the second coming. The problem is that this kind of thing in the hands of the average "car guy" just generates mountains of misinformation. Experience has established beyond a reasonable doubt that 99% of discussion in the Exhaust Section of this, or any other car board I'm familiar with is mindless babbling by people who have no idea what they are talking about. I don't mean to explicitly include you among those. OEM's are about the only people on this planet with the technical capability of developing this kind of stuff with any degree of science. I have enough knowledge of physics and acoustics to know that those guys are far more well equipped than I to design an exhaust system that behaves itself. Even with vast quantities of knowledge about fluid mechanics and acoustics processed through proprietary software, car makers still wind up having to build lots of prototypes. The 04 GTO is a case in point. Pontiac and Holden engineers had all kinds of sophisticated modeling available in an effort to replicate the sound of a 68 (I believe) GTO, one of which they shipped to Australia for the exhaust team to use. Even with those specialized tools at their disposal, they built over 40 prototype systems before they got it where they wanted it.
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Old 08-30-2012, 04:47 PM   #28
04QSMGoat
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Quote:
Originally Posted by smitty2919...View Post
More expensive and heavier. Again I'm not doing it for the weight though since it's a DD.

I'm trying to be productive with this idea of killing drone for people on this board, not just me. Someone on the G8 board tried this and everyone loved it. I'm also not playing it off like i invented this, but if it works so well why is this not common umung the GTO crowd? I like to tinker and play around, so since my CB now is a bit of a hack job by the PO, I will modify it to see what I can do.

If you want to go spend the money on 2 mufflers have at it. Only issue I have with my setup now is the drone. If I wanted it quiet, I would put my stock catback on.

God forbid I make a thread other than "is this muffler right for me?" or "what exhaust sounds best?" lol

I just don't see the point when you could do what works and has worked for several years. I would rather spend $150 or less putting in some bullets and an x or h pipe but thats just me. A shop made h pipe isnt very expensive and I believe my x pipe on my Trans am was around $30. The bullets may shave off a db or two and smooth out the tone some while still being loud. I currently have Sweet Thunders dumped and even those don't drone. At the end of the day its your car and you can do whatever you want to it but as someone who has been through way more setups than most I can say that this is still a solution to a problem that shouldnt exist
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Old 08-30-2012, 04:53 PM   #29
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MisterMike, I understand where you are coming from and agree that most of the topics in exhaust threads in any car forum ends up being useless babble. I'm TRYING to make this into a interesting and more technical thread about exhaust/acoustics. Will some of this fly over a lot of people's heads? Certainly. Will some even go over my head? Probably. But with a Mechanical Engineering Degree (not saying I know everything) I am by nature more interested about the inner workings of such things. I could have accepted this theory and idea, made my exhaust and never brought it up.

But with people like yourself whom I have realized worked at SW, and Svede whom made the wonderful intake we all know and love, I was half expecting some useful information.

I'm not making a e-pissing match, just saying what I was trying to get out of this. I understand Svede has his opinion on my exhaust sound, and I have one of his, but that's not the point and that's where it ends...at an opinion.

I am simply trying to do a FRACTION of what the Pontiac/Holden engineers have done with "average car guy" resources and capabilities. I look forward to anything you, and Svede have to offer on this subject and to enlighten me on things.

If your "enlightenment" is going to be non-productive or "don't bother"...well I can't help that and will try to tackle this little project.

Now a technical question 1:
You can make the pipe length depending on the drone RPM. So my 1750 rpm drone needs a 29" pipe. The mustang thread always has people putting 2 pipes on. I will be going to a single 3" pipe...would I need double the pipe length if using 1 pipe?

Question 2:
Everything has a natural frequency, and this is what "drone" is...the natural frequency of the whole exhaust system. Also the fact that frequencies are cyclical and occur in multiples. So drone at 1750 would occur again at 3500 and again at 5250. Would it be true that a 29" pipe tunes for 1750 would also cancel drone at 3500 and 5250? (I'm going to guess not since if you make the pipe for 3500, you would need a shorter pipe)
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Old 08-30-2012, 06:13 PM   #30
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Originally Posted by 04 LS1 GTO M6...View Post
I'm not saying I know everything about NVH, but I am a product engineer for a tier 1 exhaust supplier and we do all the development on site. How in the jeebus are you calculating 29"? Usually our Helmholtz resonators are on the order of a few inches, granted they're in the mufflers though.

I'll take this to our development group and see what they say but I have a feeling there is a whole lot of misinformation going on.

No offense

Now VERY basic compared to what you do on a daily basis, but:

1750 rev per minute * 4 pulses per rev / 60 seconds per minute = 116.6 pulses per second

The speed of sound in air depends upon the temperature. I assumed 1125 feet per second.

To find the wavelength of each sound pulse:

1125 feet per second (assuming 90* F from HERE) / 116.6 pulses per second = 9.64 feet

You want the quarter-wave tube to be 1/4 of the wavelength so:

9.64 feet / 4 = 2.41 feet = 29"

This method has been said to obviously tune out drone at a very narrow rpm band. And I saw tonight (after looking for it) that when my car is "cold" and I drive, the drone is around 1500 rpm. When it's "hot" it kicks on like a ON switch right at 1750 rpm. So that shows how the speed of sound is temperature dependent. But 90*F exhaust temps??? Seems like it would be hotter than that. For kicks I will throw a thermocouple on a digital thermometer in my tail pipe to see how hot it is at the back.

EDIT:
Just did it and within 2 minutes of idling, I was getting 100*F at the tail pipe. So the 90* F temp is either WAY off, or it is 90* F inside the resonator tube when installed.

To get the most accurate reading, I would like to throw a thermocouple in the exhaust path in the area I want to add this resonator pipe and find my speed of sound from that.

I'm ALL FOR making a resonator "a couple of inches long" assuming you are willing to lend some education on how. If the work you do is not secret lol

Last edited by smitty2919; 08-30-2012 at 06:37 PM.
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