As a mechanical engineer, gear-head and fellow tinkerer, I appreciate a video explaining the science rather than the typical exhaust comparison. Well done 👏!
I followed your directions exactly as you specified. I used an audio analyzer and determined the peak hertz was 117. I measured my exhaust gas temp after a ride home from work (20 miles) and measured 230 F. Your spreadsheet suggested a 32 inch pipe. I have a 3 inch exhaust pipe so I had the shop use 2 1/2 inch pipe. It worked perfectly. No more drone..it was ,100% effective.
lol..... I love how all the videos from 2020 are forever gonna have covid easter eggs.... I had to do a double take on the masks hanging from the rear view mirror for a second "wait... what??"
Just wanted to add my experience. I was a certified Vibration analyst for NASA. One of the issues discovered about vibration or "Drone" was that it is all about "Frequency Resonance". Where did the Frequency/Drone occur? Without any testing or frequency readings on your vehicle, "Just add Mass". Example - find some lead sheeting or heavier sheet metal and wrap it around the muffler and secure. By adding enough "Mass" to the muffler it will change the frequency of the vibration inside the muffler, thus moving the frequency to another level. It might take some playing with the amount of mass but it worked on many of the vibration frequencies" affecting critical NASA equipment. Just food for thought.
I put “titanium” header wrap on my exhaust pipes where I pinpointed the drone vibration were coming from. There was a slight reduction in the cabin. I didn’t take any readings before hand with an analyzer tho.
I'm a mechanical engineer and a car lover as well, and man this was a really awesome explanation. Very easily relatable to principles studied and also very enlightening. Keep putting out these videos 👊🏿
Here some answers to common questions I’ve seen. 1. I confirmed with some mechanical engineers that this modification should not affect air flow or back pressure at all. 2. While diameter of the pipe is not critical, I assume a larger diameter will create a greater cancellation effect. I used 1.5" OD vibrant tubing. 3. If you have a frequency range, make your calculation for the highest amplitude frequency measured in the app. 4. If your car has dual exhaust, (i.e. you calculate 36" for your V8 truck), you need to put 36" pipes on both sides of the exhaust.
What if you have dual exhaust that is connected in an H-pipe, like in a V8 Mustang? Is the dual J-pipe method needed there, and if so, would you place them before or after the crossover pipe?
@@ColinAverill the J pipe will only impact waves on the pipe it is installed on. If before or after X. It will only cancel 50% of the total sound waves
@@ethanmelbinger3421 I have this. I put the 1/4 wave resonator at the merged portion, and only have one installed. Makes a huge difference. I used 2.5" diameter piping.
Hi Alex your info was spot on as I had a really annoying drone from a internet bought muffler delete on a RAM truck. Sick sound tho. At 130hz and about 1800 revs at 100kph the engine would switch to eco mode (shuts down 4 cylinders) and literally vibrated the crap out of the vehicle. It was really easy to work out the frequency that was causing the issue as when the drone was at its worst 130Hz reached max amplitude and stayed constant rather than fluctuating. I used the calculations on your spreadsheet to work out 87cm was what I needed. Worked unbelievable.
This is a great explanation, good job! I actually just did one of these for my Golf R, only I had room to do a straight pipe down the length of the car. So I cut the pipe and used a slightly smaller end pipe with a band clamp so I could experiment with different lengths. What I found is that these rough calculations can get you in the ball park, but after a bunch a trial and error I found certain lengths are far more effective over a broader range of frequencies, and it was not very close to what I had calculated. My car was droning a lot from 2800 to almost 4000 RPM (50-130 Hz) , there wasn't one particular frequency that really stood out. So with experimentation I found a length that worked best and gave the sound I preferred. I used the same spectrum analyzer app, it works okay but I did notice that in some cases my hearing perception did not always match what the app was showing me. So I used it, but ultimately went with what sounded best to my ear. In my application 41" to 42" seemed to work best.
Making a sliding-end w/ band clamp is probably the best way to do this, but I did not want to spend that much time/labor adjusting. Also since my RPM range was only about 250, so I could much easily pin-point the frequency.
@@ac38 Understandable, given the space you had that design does not lend itself to easily making adjustments. I would add that the actual quietest length was actually around 38" however I found at that length it also killed a lot of the baritone at higher RPM. These Helmholts resonators don't just hit one frequency, they also affect 2nd, 3rd,.. harmonics. Also actual exhaust temperature, pressure, humidity, are hard to measure accurately and have a significant effect on sound wave velocity. I experimented with a lot of different lengths, and what I found is that it works to some extent at almost any length. However when you get into a very narrow range the effectiveness increases dramatically. To the point where it was to effective and changes of less than an inch were very noticeable.
@@ericmichel3857 I agree with everything you said. Harmonics are an important note that I kind of just brushed over. Didn't want to introduce too many Engineering concepts and confuse people even more 😁
Hi Eric, can you detail your exhaust setup from down to tip, I’ve got a tfsi hybrid k04 with 3” down, magnaflow resonator, magnaflow straight through muffler out to twin 2.5 tips and it has drone at 2k but it’s pretty loud everywhere... sounds good at wot through... trying to figure out how to shut it up without loosing power.
Eric, thank you for this! I also have a MK7 Golf R. My current setup is stock down pipe (2.5” piping) -> vibrant 17950 resonator (3” piping) -> Nameless catback (3” piping with two beautiful 5” mufflers and quad exhaust tips). It is literally ALMOST perfect i.e. deep tone, rumbles, growls, no loud cold start, quiet around town but sophisticatedly aggressive with wide open throttle. This is all EXCEPT for between that infamous MK7 drone range of 2800-4000 RPMs like you mentioned. The addition of the vibrant 17950 resonator helped a lot with drone in every RPM range except for the above. I appreciate you taking the time to experiment. Seems like 38” on our cars is TOO effective and 40 or 41” is that sweet spot. I’m going to attempt to have this done to see if I can achieve the same success as you and truly have a perfect OEM+ setup. 👍🏾
Great presentation. Thank you! Question: if the J pipe length calculation is 30 inches on a dual exhaust system, do you add two 30in J-pipes or two 15in J-pipes?
How does this calculator work with a 13b rotary engine with 6 pulses per revolution? Im trying to eliminate drone at 2500-3000rpms @100hz peak frequency Thanks
A true Helmholtz Resonator is a chamber rather than a pipe, but the calculation and analysis are more complicated. A J-Pipe is a simplified version that still works great!
Well done, sir. This has large applications in recording studios as well for similar reasons, to remove unwanted frequencies. Your explanation is much better described than many, if not all , of the other videos on the subject. The fundamentals of this are the same as used in pipe construction for pipe organs. But when you really want to get down to building an HR this video really shines for it's simplicity and details of measurements. Kudos.
No spectrum analyzer comparison on final test drive, compared to first test drive?? With ear buds in, sounds almost identical in that rpm range. In my opinion. But the analyzer comparison would show the changes. Great video. Very cool!
Hello Alex, congrats of your detailed explanation of all maths behind the drone and J-pipe. I got one doubt about the J-pipe diameter. Does it need to be the same of the exhaust or could it be narrower?
I have seen in many videos that works with smaller ones, but i think the best way is with the same diameter to fight with the same sound pressure the wave...
Super useful video, I knew the concept but the actual science was magic to me, now I understand it and will use this to solve a very bad droning issue with an exhaust I built for a customer of mine. Thanks for making this easy to understand!
So, before watching your video, I have called around to 4 separate local performance shops, and when i asked about this J pipe and if they had any experience with it, I got the same answer from them all. If your setup has Drone, then essentially you gotta deal with it. (not confidence inspiring at all) For the hell of it i looked up Moorespeed performance per your recommendation, and to my surprise your actually a fellow Ohioan. o7 So needless to say, I plan on driving 2 hours to this shop and getting something similar done to my car. I'm curious of how exactly this works though. Did you just present your measurements to the shop and they fabbed it with vibrant piping they had on hand? or did you bring the piping with you and they bent/welded it in? Also, I heard the closer to the engine you install the J pipe the better, as far as cabin noise goes. what made you decide on the placement near the axle?. Thanks for posting this vid, you very well might be the one key element to me not hating my new car.( @im at 100hz-105hz) around 2900 RPM, which makes freeway cruising absolutely unbearable. Will the shop be able to provide me with any guidance on this concept? Or is it up to me to pick proper length and placement? sorry for long comment. I'll shutup now! Great Video!
Measuring Drone Hz Vs Calculating Hz. In Your Example They Matched Pretty Close. Is This True If The Exhasut Already Has Glass Packs / Mufflers Or Do Those Skew The Drone Hz Calculations Vs Drone Hz Measured? I'd Imagine Glass Packs Only Muffle But Some Mufflers With Baffles Could Maybe Change The Drone Hz????
343 ÷ ( highest hz ) ÷ 4 = # then change the # to inches . That's your length , also the closer to the front the less drone the back of the j pipe will have.
Hi, I have a question please I have drone on my 4 cylinder between 2500rpm (80hz) and 3500rpm (120hz) The peak is at 3000rpm: 100hz No drone when engin is cold, The drone is loudest when the motor is really hot I measure with a laser thermometer inside my Supersprint muffler 250-350 degrees Celsius I measure a temperature outside the tube after the catalyst a temperature of 120 degrees (but inside it must be about 300 to 400 degrees C??) MA QUESTION : Which temperature to use for the calculation of the resonator ? (knowing that it will be installed just after the catalyst so a hot part) Thank you for your help
Great video. I have a question that I'm pretty sure I know the answer too, but I want confirmation. If you have a true dual exhaust setup, you would need the J pipe on each side correct? I have a Porsche Boxster and the exhaust sides don't meet until the muffler.
thanks so much for your effort of explaining this. I have a question however, does it not matter where in your exhaust you put the pipe? like wether you put it right before your muffler or after the headers? maybe that would change how long the pipe needs to be, so you can run a shorter one for weight and space reasons?
Looking at your excel table, I see the length is being calculated by (Speed of Sound/Frequency)*(1/4)*(39.3701). Where is the 39.3701 coming from? Maybe I missed it somewhere in the explanation.
Hey guys, just looking for some help. I followed the video instructions and downloaded the app, but at peak drone, the app said the frequency was in the high 300s, low 400s. Obviously this is very high as everyone is finding readings in the low 100s. I tried to use the theoretical calculator, however, because I have a V6, I interpolated and it was in the 120s roughly. This is causing a major discrepancy in the pipe length. I was hoping if anyone can help with some advice. Could the reading on the app be wrong? (Most likely)
Awesome video, glad others are interested in the acoustics of exhaust. Great explanation for a traveling wave (like 1 dimensional in a way). Here’s some thoughts I had, maybe someone could shed some light on them Many exhaust companies don’t add a long pipe, but a chamber. This is my initial guess on variation in diameter and it’s effects- If you look at the exhaust like pulses of a certain volume, you can probably create a relationship between diameter and length. The relationship would be linear in terms of volume, but to the second power in terms of pipe radius. I would also guess that a flat end really nails down one frequency, I wonder if a domed end would give a smoother curve to the frequencies you cancel out.
The chamber they use is a Helmholtz resonator. It’s essential the same concept but the frequency is produced through the same mechanic as blowing air over the top of a bottle to make noise.
I presume adding the resonator to the system as close to the engine as possible would be ideal. This would attenuate the resonance (drone) after the shortest distance reducing the amount of your exhaust system that will be vibrating in time with the resonant throbbing of the exhaust gas. Or do the out of phase pressure pulses travel up the pipe far enough anyway? Do they make it back to the valves? I expect in most installations this irrelevant as you are likely to be limited by the cars under body configuration (space). You were doing so well until you said the calculation of frequency from RPM was less accurate than using the app. Yes different engines have different tones but YOU identify the RPMs where drone occurs by ear, and the cars Taco. It is a subjective observation not a measurement. So it's you (and the cars Taco) not the Math or physics that is the source of error. If you identify the RPMs correctly then the frequency CANNOT be wrong. Regardless of Honda or Subaru, a drone at 2250 RPM is due to a resonant frequency of 70.8Hz. I found the Apps gave inconsistent and different results. If your App shows multiple peaks how does average Joe know which peak Freq. is the one that is annoying him. One App I tried was completely wrong. Ultimately I think using both is the right solution. It is after all a range of frequencies you are looking to dull, and the ideal resonator length varies with driving conditions due to temp anyway. So a few Hz resulting in a few millimeters is irrelevant. Oh and measuring the temp in the tail pipe (not so much). It's the operating temp of the gas inside the (not yet existent) resonator that matters. This is impossible to measure and hard to work out as there are SO many variables. It is functionally substantially different to the tail pipe. The exhaust gas doesn't even "flow" through the resonator. It just vibrates around inside the J tube. Still one of the best vids on this topic.
So if you have a dual exhaust, meaning two headers coming in and joining in an X pipe, then running dual pipes out, do you need two 61 inch j pipes? one on each exhaust pipe?
THANK YOU!! I'm a mech. engineering student and I wanted to use proper math and science to eliminate the 2000 rpm drone on my Mustang. I feel so much more confident in designing a branch resonator now.
Amazing video. I just bought Honda sx8 VTEC. I am going to make a custom full system exhaust. Usually, these 1.5 vtecs sound like a fart can exhaust. I'll use a stock resonator and this j pipe method to eliminate that fart can sound. Thank you so much.
Thanks for building the math tables, Sir. I was trying to work all this out several years ago via internet research and it was a dead end of lore and third party anecdotes. There's still some nuance and elbow room here in design, but you can at least get a good start an zero in on length with these tables.
Does the qw resonator work the harmonics in lower frequencies? If i make a pipe thats for 120 hertz, will the resonator also cancel out the frequencies at 60 hertz?
Is it possible to sleeve a pipe concentrically within the exhaust pipe that is the required length for ¼ wave with a capped off end and achieve the same the result?
29:06 so the total length of that bent jpipe installed was 61 inches? I drive almost the same car (8th gen civic) almost same level of drone based on the video & same rpm level (about 2k when drone starts to irritate my ears)
There must be some shortcut or a straight formula to do all the math without going too much in details. Any comments ? I am looking forward to attach a J shape resonator with my straight pipe muffler to reduce its loudness
I'm glad someone did an actual video explaining this. My designs use larger rear chambers to shorten the length, but either way, this is the way to tune your exhaust drone. One more tip is that it's often cleaner in terms of the cancellation including harmonics to place the resonator closer to the engine.
just finished mine using this guidance and it works perfect !! just before the last muffler and completely eliminated a heavy drone measured at 110hz frequency, the question is , what happens if I make another 1/4 wave resonator to further clean up the tone. , upstream, lets say right after the cat to cancel out another frequency, around 175hz, would they shifted waves from the 1st one interfere with the other?
Question, what happens if i dont have enough space for the full length? I need around 33 inches (calculated) and my space is for around 12 inch. Will it do something?
Hey Alex I don't remember hearing youth say how much it cost to have that built and installed. Do you remember approximately what it was? Im doings this on my subaru before we leave to Virginia beach in 3 months
I have a 3.5" single exhaust and results turn to be 36" pipe length needef to J-Pipe. I can only fit a largest diameter of 2.5" for J-Pipe for 36" length. What would be the correction factor from using a smaller diameter pipe? I'm assuming the wave would travel faster in a smaller diameter pipe or am I thinking this the wrong way and velocity of exhausts gases would only travel faster and wave is unaltered?
This was well done mate. I'm 56 and been messing with cars my whole life. This is a great explanation with both science theory and practical stuff relayed in a down-to-earth fashion. Top marks!
Thanks for the great video! I remember seeing somewhere that the lack of a solid surface at the opening of the heimholtz resonator would generate less friction for the air molecules near it, and would increase flow rate slightly - I am guessing that the reasoning behind this is similar to the fact that a golfball with a dimpled surface has less aerodynamic friction than a golfball with a smooth surface. Perhaps it is negligible, since there is only one opening for the heimholtz resonator in your case? What if there were multiple heimholtz resonators? Or better yet, what if the inside of the exhaust piping was dimpled? Would that affect flow rate then? Also, if the flow rate is increased un-uniformly (only at one side of the piping where it has the opening to the heimholtz resonator), then does it create turbulence within the flow past the heimholtz resonator opening? Or is it negligible again, since there's only 1 heimholtz resonator?
I appreciate the detailed questions, but unfortunately these are geared more to a Mechanical Engineer with experience in fluid dynamics - which I am neither.
Awesome explanation! I kinda knew that it cancelled the sound out. But I wanted to make sure! I understood everything you said and I love the before and after of driving in the car, cold starts and warm starts! You covered it all! Now I just have to J-Pipe my 2005 Volvo XC90s custom quad pipe exhaust. Sounds MINT and mean. I just hate how much freakin drone it has. Its easily as bad as yours in the civic or worse! Its horrible
Could you make that J pipe like a sliding assembly like a trombone so you could dial it in when you find that drone and then stopped it there is it could you make it adjustable
Vary well thought out plan. My exhaust temp is from 500 to 1200 degrees . A 60 plus inch J pipe Is just not possible. That being said your This is not applicable has you like. I put a set of chambers of different sizes and use different materials inside the muffler to keep DB down to 87 or below Without power loss. Rember your sound wave is expanding. I make use of this energy to direct flow To where I want but Keep a clean channel from the back to the opening. Also my engine is spinning over 10,000 RPM's creating a tornado effect pulling air out faster then it is going into the engine with valve overlap I do not want to lose the efficiency at the chamber on the combustion cycle. Rember your wave is going into the J pipe and coming back out Giving back pressure. Loss of power. So my question to you is how to stop the back pressure created. I know the answer but want you to learn More.
So, I’ve got a 13 civic si so same 9th gen with same motor. The current exhaust is 3 inch. The painful drone level is when it hits 140hz. Normally I’ve noticed that from letting it coast off throttle. 70hz cruising. Would running the same length piping eliminate that as well if I’m understanding correctly?
Bro your cars idling was shaking my entire room through my bass LMAOOOOO. Dope video dude you did it perfectly right I hope this gets a ton of view. Great explanation and good sound clips all backed up with science!
As you said, that resonator cutting down your frequency and frequency x2, x4 and so on, so you can make 61,5 inches leght but also half of it, am I right? BTW great explanation!
Hi Alex! Thanks for your work! Unfortunately my english understanding is not the best and I might missed it. The lenght of the pipe is important, not the volume of the pipe right? How important is the diameter of the pipe? Thanks a lot and keep doing such good stuff!
You used peak hz. Did you average the hz for your length, i.e. mine starts at 105hz until 125hz, so 115hz? Or would you use 125hz, in my case? Thanks, Billy!
Can someone help clear this up for me. The second diagram kinda makes sense (where you only show 1/4 the full j-pipe); So does this exhaust travel back towards the engine? Where does it go from there? Second question: in the first diagram with the full j-pipe, the length of the j-pipe is certainly much more than 1/4th the full wavelength? So is it the width of the opening if the j-pipe that matters? Whats the point of the full j-pipe if just a quarter wavelength of pipe welded perpendicular would essentially do the same thing? Is the full j-pipe length enough so that once the exhaust come back out it is still 180 deg shifted? Or is the wavelength of exhaust actually that long? Super good video but still a couple holes that didnt seem to get completely answered.
I’m watching this to fix my droning, but something you said just flipped a switch in my head. You solved my problem with my tweeter sound reflections. Thank you sir
Thank you for making this informative video, it's great. 2 questions: Is there a way to calculate a specific diameter for how wide the J-pipe should be? Also, how was the length of the j-pipe calculated (in the "1/4 wavelength [inches]" section on the spreadsheet)?
1. I am not aware of how to consider the pipe diameter. Bigger diameter, larger amplitude of 1/4 wave, so a larger pipe may have a greater effect. For reference, my exhaust is 2.75", and I used a 1.5" j-pipe. But most of the time you are limited by space.
2. Length of the J-Pipe is calculated by the equation wavelength = (speed sound) / (frequency). Then wavelength divided by 4. If you download the spreadsheet and click on the cells, you can view the equation used!
I have been looking to find an in-depth explanation on these equations so I can calculate these j-pipes for my vehicles. I appreciate this video. I do know the diameter of the tubing and the opening size at the entrance to the j-pipe has an effect of the range of frequencies that get cancelled out. I’m trying to cancel out a large temperature range of frequency because my EGT’s vary about 150* between running E85 and 93 octane.
Good info but I have a C7 Corvette. i deleted my mufflers, installed a X-pipe, and used Corvettes muffers butterfly valves. I can set it to touring which closes both valve's when I'm in the neiborhood and Sport and Track when I'm on the road and freeway. NO DRONE..lol.. but i do understand what your SAYING good information.
Cool video. I can't help but commenting on thinking it was hilarious when you honked at that person and drove around them. Good stuff though, very helpful.
hmm here’s my situation: it drones at two spots, 74hz and 93-100hz. What should I use for the calculations? 74hz corresponds to 1.5k rpm and 93-100hz is 2.4k rpm. Hope you see this :)
Very well done. I had to replace my JeepWJ muffler and pipes, and with that went a little more aggressive which has produced the drone effect. I will be utilizing this method to address,. You stated this solution addressed 2000 -3000 RPM? So the length of the pipe will address droning in that 1000 RPM range?
Great video Alex..thank you!.. just one question.. can you share the before and after screenshots of the Spectroid.. I’d like to see the difference it made to the measured data. Thanks.
Hey, I'm still little bit confused about creating this for a V6 with twin pipe exhaust. Do I need to calculate with 6 cylinders or 3? I will be of course putting 2 J pipes, one for each bank/pipe. When I do the calculation with 6 cylinders I get 250 Hz frequency. When I put 3 cyl in the formula I obviously get 125 Hz. With Spectroid I measured 125 Hz as the loudest noise, so 3 cyl in the formula should be correct? I'm confused because of the separate pipes from each bank.
@@ac38 yes but there's no difference between having the 6 pulses in one pipe and in 3 pulses in each of 2 pipes? Still the same lenght of resonator only in both pipes in case of twin pipe V6?
Nice. work mate. I 've come across a couple vids on this,, one decent one explaining the science but not anywhere near the explanation required for me to start cutting holes in a 5k system hahaha. You've explained this bang on. I'm a sound engineer and I knew it was phase cancel but I really needed to see this in action. Cheers mate. Nerds fuck rule. Let's face it. No guess work no bs, and certainly math, science, theory and plain application is required before submitting informative vids and you nailed it. You even mentioned the speed of sound and it's fluctuations based on temp. I did notice too your exhaust sounded like iit almost accentuated the remaining freq. Sounded slot clearer and more grounded. So thanks bra I'm gonna go ahead and do my 5.7L V8. (350) but I'm in Australia and my drone is driving me round the friggn twist. 1350rpm's about 90hz at 76°C. But will run it thru your calculation and can't wait to see the results. Respect
One important question we want tu add a resonnator J-type to our FSAE car. do you think diameter of the cross section tube (J-type resonator) matter i the way the sound decrease?
Dynomax Ultra Flo dual-out mufflers have noise cancelling tubes in them. Then if you want your exhaust to have an even deeper tone you replace the inline muffler/resonator with a Thrush glasspack. With the J-pipe, its still too high pitch for me. The longer the deeper, wield two if needed, then you'll have something that sounds Very intimidating. Already set one up on a '04 2.4L Accord with a 26" and two Dynomax Turbos. Its like a better tuned Subaru flat-4. Simple....
