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[in progress] identifying and canceling drone

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Clint Beastwood

Clint Beastwood

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Thread Starter #21
Just curious...What monetary wise have you got into this setup? [scratch]
It was kinda expensive because I keep taking it back for fine tuning which incurs additional charges for welding and materials, I’ll work up a sheet. If I could do it again I wouldn’t use 2 vibrant resonators, I think just the ultra quiet would give a nice “raw” sound. That’d save 100 bucks. I think my system could be replicated for 400-500 bucks without the fine tuning of the drone stuff, cheaper if using less expensive non vibrant parts. The 1/4 wave resonator required some drive time so there’s really no way to front load that cost accurately.

If at some point I sell this system or remove it to make another one (after I buy a welder) I might do one of vibrants 5” round front resonators, no rear, then probably 2 quarter wave resonators or a real helmholtz chamber to tame the drone that’s left over.
 


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Clint Beastwood

Clint Beastwood

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Thread Starter #23
Do you have any picture you could share? 😉
Just a few, was grabbing pics of the welds and tip- I’ll snap more including the 1/4 wave hidden above the rear resonator, as soon as I can get it up on some ramps.

I asked for as close to a stock tip as he could get, I wanted either stock tip or a raw steel turndown. Overall goal was to look stock:





Clean welds and the one original hanger - ordered a 3 pack from whoosh should have ordered 4 lol.
 


dmb

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#24
old school, gas weld exhausts with coat hangers, arc weld bulldozers, ships, tanks ect. now Mig, and Tig, my neighbor used to Tig weld top fuel motors back together in the 70's he was a busy guy with O.C.I.R. I should have used ear plug's, but nobody used them back then. Bad mistake for not being a pussy. very nice exhaust top notch.
 


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#25
Interesting. Can you talk a little more about the quarter-wave resonator? Is it something your purchased or built? I'm looking at replacing my resonator/muffler but don't want something super drone-y.
 


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Clint Beastwood

Clint Beastwood

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Thread Starter #26
Interesting. Can you talk a little more about the quarter-wave resonator? Is it something your purchased or built? I'm looking at replacing my resonator/muffler but don't want something super drone-y.
What would you like to know about it? Basically, you identify the frequency you're droning the worst at, then build a chamber to actively cancel it out . Say your frequency is ~107hz like mine - that's a wave length of 11.34 feet, so hitting it with a half length wave will cancel a big chunk of the resonance. A 1/4 wave resonator gives you a half length wave (its 1/4 the length of the wave, so the sound goes down then comes back, totaling half the overall wave length) which cancels out your specific targeted drone range.

I picked all the parts and provided materials and measurements myself, but had a shop throw it all together (I can't weld worth a damn and definitely couldn't do stainless). On the first go round I knew I'd get some drone, so I made sure there was an adequate area to fit the resonator above the rear muffler space (I have no muffler, just a resonator in the stock muffler location) and spent a week test-driving. I recorded video and sounds, as well as made notes of where the drone was most painful. I charted the drone range, and aimed for right in the middle. The measurement of 106.67hz correlated with my sound recordings as viewed in a spectrum analyzer (double confirmed!) and I used that number to determine my resonator length. I would *really* like to hear what 2.25" exhaust or 2.5" exhaust with just a vibrant canister style resonator up front would sound like after taming the roar with a quarter wave. A 2.25" straight pipe with a different-length split exit (say pipes side by side, but they split like 2ft from exit with one pipe being 25% longer than the other) might give a really interesting sound. I may try it, as I had mine built with a removable rear section so I could play later when I had more time. I'd probably go from my existing 3" to a pair of 2.25's at the end using the differential lengths I mentioned.

You may see mentions of a helmholtz resonator - that's functionally different from a quarter wave, though people all over the internet seem to use the phrases interchangeably. A quarter-wave resonator uses length, and a helmholtz uses volume (wherein the aperture, neck, and chamber volumes all matter). A helmholtz covers a much broader range of sound, a quarter-wave is often easier to fit, covers a narrower range, but attenuates more sound in that range.
 


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#27
What would you like to know about it? Basically, you identify the frequency you're droning the worst at, then build a chamber to actively cancel it out . Say your frequency is ~107hz like mine - that's a wave length of 11.34 feet, so hitting it with a half length wave will cancel a big chunk of the resonance. A 1/4 wave resonator gives you a half length wave (its 1/4 the length of the wave, so the sound goes down then comes back, totaling half the overall wave length) which cancels out your specific targeted drone range.

I picked all the parts and provided materials and measurements myself, but had a shop throw it all together (I can't weld worth a damn and definitely couldn't do stainless). On the first go round I knew I'd get some drone, so I made sure there was an adequate area to fit the resonator above the rear muffler space (I have no muffler, just a resonator in the stock muffler location) and spent a week test-driving. I recorded video and sounds, as well as made notes of where the drone was most painful. I charted the drone range, and aimed for right in the middle. The measurement of 106.67hz correlated with my sound recordings as viewed in a spectrum analyzer (double confirmed!) and I used that number to determine my resonator length. I would *really* like to hear what 2.25" exhaust or 2.5" exhaust with just a vibrant canister style resonator up front would sound like after taming the roar with a quarter wave. A 2.25" straight pipe with a different-length split exit (say pipes side by side, but they split like 2ft from exit with one pipe being 25% longer than the other) might give a really interesting sound. I may try it, as I had mine built with a removable rear section so I could play later when I had more time. I'd probably go from my existing 3" to a pair of 2.25's at the end using the differential lengths I mentioned.

You may see mentions of a helmholtz resonator - that's functionally different from a quarter wave, though people all over the internet seem to use the phrases interchangeably. A quarter-wave resonator uses length, and a helmholtz uses volume (wherein the aperture, neck, and chamber volumes all matter). A helmholtz covers a much broader range of sound, a quarter-wave is often easier to fit, covers a narrower range, but attenuates more sound in that range.
Interesting. So given the wave length, you just got a resonator that was 1/4 that long to cancel it out and put in the exhaust, essentially? How did you do the recording/spectral analysis?
 


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Clint Beastwood

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Thread Starter #28
Interesting. So given the wave length, you just got a resonator that was 1/4 that long to cancel it out and put in the exhaust, essentially? How did you do the recording/spectral analysis?
i used a zoom h4n sound recorder and adobe audition to view the waveforms. Recordings from inside the car reflected a 120hz drone but that was a secondary drone, done measured at the exhaust tip was 107hz
 


Dpro

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#29
What would you like to know about it? Basically, you identify the frequency you're droning the worst at, then build a chamber to actively cancel it out . Say your frequency is ~107hz like mine - that's a wave length of 11.34 feet, so hitting it with a half length wave will cancel a big chunk of the resonance. A 1/4 wave resonator gives you a half length wave (its 1/4 the length of the wave, so the sound goes down then comes back, totaling half the overall wave length) which cancels out your specific targeted drone range.

I picked all the parts and provided materials and measurements myself, but had a shop throw it all together (I can't weld worth a damn and definitely couldn't do stainless). On the first go round I knew I'd get some drone, so I made sure there was an adequate area to fit the resonator above the rear muffler space (I have no muffler, just a resonator in the stock muffler location) and spent a week test-driving. I recorded video and sounds, as well as made notes of where the drone was most painful. I charted the drone range, and aimed for right in the middle. The measurement of 106.67hz correlated with my sound recordings as viewed in a spectrum analyzer (double confirmed!) and I used that number to determine my resonator length. I would *really* like to hear what 2.25" exhaust or 2.5" exhaust with just a vibrant canister style resonator up front would sound like after taming the roar with a quarter wave. A 2.25" straight pipe with a different-length split exit (say pipes side by side, but they split like 2ft from exit with one pipe being 25% longer than the other) might give a really interesting sound. I may try it, as I had mine built with a removable rear section so I could play later when I had more time. I'd probably go from my existing 3" to a pair of 2.25's at the end using the differential lengths I mentioned.

You may see mentions of a helmholtz resonator - that's functionally different from a quarter wave, though people all over the internet seem to use the phrases interchangeably. A quarter-wave resonator uses length, and a helmholtz uses volume (wherein the aperture, neck, and chamber volumes all matter). A helmholtz covers a much broader range of sound, a quarter-wave is often easier to fit, covers a narrower range, but attenuates more sound in that range.
Its fascinating watching you go through and do this process as there are a few off the shelf solutions for not much more than your winding up spending. None the less cool though. You piqued my interest with the dual pipe comment as one of two of my favorite S13 exhausts was the Greddy DD designed in Japan for the SR20DET powered 180sx. I put several of the on S13’s here and loved the the split twin pipe back design. It would be cool to build a split twin pipe exhaust for our cars. Not really that hard either has you can dual inlet outlet reasonatora and mufflers.
I bet the car would sound pretty cool. You could run dual 1.5 inch pipes or even 1.25 for the people afraid of putting a 3 inch diameter equivelent area surface exhaust on our cars stock for fear of affecting the back pressure to much due to the small Turbo.
 


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Clint Beastwood

Clint Beastwood

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Thread Starter #30
Its fascinating watching you go through and do this process as there are a few off the shelf solutions for not much more than your winding up spending. None the less cool though. You piqued my interest with the dual pipe comment as one of two of my favorite S13 exhausts was the Greddy DD designed in Japan for the SR20DET powered 180sx. I put several of the on S13’s here and loved the the split twin pipe back design. It would be cool to build a split twin pipe exhaust for our cars. Not really that hard either has you can dual inlet outlet reasonatora and mufflers.
I bet the car would sound pretty cool. You could run dual 1.5 inch pipes or even 1.25 for the people afraid of putting a 3 inch diameter equivelent area surface exhaust on our cars stock for fear of affecting the back pressure to much due to the small Turbo.
Yeah I totally could’ve bought something off the shelf, but I like blazing my own trail! The money wasn’t really an issue and I figure you gotta pay to play so I went for it :p

I was watching some 500abarth videos (that’s what I had before and really want that sound) and I noticed that Abarth with aftermarket exhaust didn’t have the same ragged wail. The commonality between the louder-but-less-fierce Abarth aftermarket exhausts was both equal length rear sections and larger diameter. Stock Abarth is really small diameter and he rear section is dissimilar lengths, and when you sit behind the car you can hear a left/right/left/right with the exhaust pulses. I think with no muffler and dissimilar length dual pipes out the back in a small diameter might get me the ferocious ripping sound I really want. I’ll get around to it eventually :)
 


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#33
I've still got a decent amount of drone under load from 3-4k. I've done vibrant ultra quiet and like you had drone at 107hz. So I ended up with 34 inches that my exhaust guy put right before the resonator. It's all 2.25 to the back where I have a magnaflow muffler and honestly I've resulted in a car that is quiet now but still retains the drone. While not as bad I think I would run the car off the road if I was going up an extended grade at interstate speeds
 


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Clint Beastwood

Clint Beastwood

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Thread Starter #34
I've still got a decent amount of drone under load from 3-4k. I've done vibrant ultra quiet and like you had drone at 107hz. So I ended up with 34 inches that my exhaust guy put right before the resonator. It's all 2.25 to the back where I have a magnaflow muffler and honestly I've resulted in a car that is quiet now but still retains the drone. While not as bad I think I would run the car off the road if I was going up an extended grade at interstate speeds
have you checked to make sure the exhaust isn’t hitting the frame of the car anywhere and that your tip exits at least as far out as stock? If you record a video accelerating from 2500-5000 ish I can run a spectrum analyzer and see what’s up
 


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#35
Here's my exhaust, 3.5"-3" Catless DP and full 3" catback. The front "resonator" is a Jones Turbine that has an airfoil in it, the rear is an Original Aeroturbine with about 6" of packing material in it along with another airfoil. My tips sit about 1/4"-1/2" beyond the bumper and the only "drone" I have is around 1700-1900rpms. While cruising, the car is very quiet with a mild hum from 45-60, 60-90 it's almost silent while cruising. When I put some throttle input in it get pretty deep and loud but it goes away as soon as I go back to cruising. I do also have a layer of Fatmat lining the hatch.

I had never considered the tip location having anything to do with effecting drone, but it makes sense.
 


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TyphoonFiST

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#37
Would dynamat in spare tire area help dampen .... got MBRP 3” T409 installed literally an hour ago and drone is like hearing straight pipe.

Curious on sound dampening
The sound damper called a Thermal R&D Exhaust will alleviate your straight pipe concerns and sound very righteous. [drummer]
 




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