Exhaust Drone!
#41
Team Owner
Pro Mechanic
I think what the Corvette needs the most is more BENDS in the system, to reduce that hummmm noise that is made by the even firing of 8 cylinders. Just a theory though...
Last edited by Tom400CFI; 12-26-2017 at 07:18 PM.
#42
Melting Slicks
I have headman headers on my 85 383 engine, only standard mufflers keep the drone away. Is a nice and quiet ride with the standard mufflers no drone at all.
Last edited by gerardvg; 12-26-2017 at 07:41 PM.
#43
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Here's my H pipe. Connects the two collector reducers at the front of the pipes leading to my Y pipe at the back of the transmission. The crossover is removable by undoing the band clamp at the RH collector side, and then rotating/ pulling the crossover off if needed.
Made a significant reduction in drone, and according to Vizard the crossover here is usually worth about 3-5 horsepower improvement. A worthwhile endeavor, IMO, at only a pound and a half weight penalty.
Made a significant reduction in drone, and according to Vizard the crossover here is usually worth about 3-5 horsepower improvement. A worthwhile endeavor, IMO, at only a pound and a half weight penalty.
#44
Race Director
I'll throw some additional perspective into this thread. Through my 18-yr ownership, I've had SIX exhaust combos.
Stock L98
Stock, main cat, Targa Mufflers
Stock, bullet cats, main cat, Targa Mufflers
Headers, bullet cats , Y-pipe, Spin-Tech Muffler, side pipes (2.5")
Headers, bullet cats, Y-pipe, main cat, side pipes (2.5")
Headers, bullet cats, Y-pipe, side pipes (2.5")
Three of these six combinations were annoying. Three had marked "drone" at cruising rpms....the 2nd, 4th and 5th combo. And, it's not necessarily what you'd expect when you consider more is less...meaning more components to dampen = less drone. Consider the final config is way better than the two iterations prior to it.
Intuition MIGHT suggest that removing components should increase drone. Yet, when I eventually removed a "belly" attenuator (in my 383 setup), the sound improved dramatically. Granted, my setup is somewhat different due to the total system length but Matt has a point when talking about the total "system resonance". When you change mufflers or add an "H" or "Y" pipe, you're changing the overall tuning/resonance of the system.
My newest theory piggybacks on Vizzard's tuning theory. He points out the addition a "terminator" box can make a longer system "look" like a shorter one when tuning for power. For reasons beyond the scope of this thread, lengths in header/exhaust piping can affect the "tuning" of exhaust for power. The wave theory involved in this seems likely to (at least partially) correspond to sound tuning.
My point borrows from my knowledge of bass cabinet tuning. It's not just the length but also diameter that affects frequency of "tuning" for a PORTED bass cabinet. (An internal tube focuses maximum loudness/resonance at a certain frequency. Music near that frequency get's amplified. Ironically, dampening material must be used to prevent unpleasant "drone" in bass cabinets.) When building an exhaust system, the diameter and length HAVE to play a part in the overall drone/tone. If you've ever heard 2.5" vs 3" exhaust, you'll know what I mean.
I think bullet cats (at least partially) disrupt resonance waves in the exhaust. There body size is so small additional resonance of their chamber size doesn't add sound back in. In other words, bullet cats are better than main cats. I would add that larger bodied mufflers increase the POSSIBILITY of drone from their chamber size.
Whether it related to the dynamics of wave theory (ala terminator box) or tuning (more similar to bass box...or musical instruments), the introduction of a muffler may actually HURT. Most performance mufflers don't contain packing or significant baffling. The combination of the change in diameter PLUS the lack of real attenuating can create a "tuning" point that may add to drone versus subtracting it. I disagree with the poster who claims the diameter won't affect the result. L98's and LT1's have essentially the same engine but different diameters of exhaust. And they OFTEN don't have the same results when adding specific mufflers.
"H" pipes are different than "Y" pipes in the method they use to vent gases to the opposite "bank". I think "H" pipes add more "system volume" to the opposite side. By that, I mean air volume...or space. A large increase/decrease in length/diameter IS going to shift that optimal tuning frequency where "drone" happens....where the system is loudest. Like speaker cabinets, packing/batting will eliminate the echoing/bouncing of sound to create something more pure. But packing also reduces the extra volume of the resonance tuning.
Are you following me?
When you add a muffler/converter -- and the body is large enough -- you may change the harmonic frequency of the entire system. It may be good/bad in terms of performance....when you consider what Vizzard is saying. It also may be good/bad in terms of sound FREQUENCY of the system.
The first thing I'd recommend to anyone unhappy with their system is to REMOVE any performance muffler and observe the result. Clamp in a "test pipe" if you want to keep things cheap...and avoid a trip to the exhaust shop. Next, if you're considering the choice of a "Y" or "H" pipe, consider the "H" pipe is likely to make a bigger difference in terms of performance AND sound. When I considered the standard belly "Y" pipe of an L98 couldn't be THAT much different than a "Y" pipe on a dual setup, that's gotta be wrong. Longer runs of "resistance" create more OVERALL resistance. Plus, they do the OPPOSITE of a terminator box....they definitely can't create a pressure drop. Pressure seems likely to get HIGHER. I wonder if that actually aggravates drone?
Anyway, I would suggest smaller-bodied mufflers and/or "H" pipes when considering your options for changing sound. Corsa mufflers are internally smaller. If you listen to glass packs, their sound isn't totally different that Corsas either. Listen enough and you'll hear how larger-bodied mufflers "add" sound -- like a tuba.
The second setup (above) was loud because it sent the highest pressure impulses into the large body of a main converter. That was largely mitigated by (re)installing front bullets. When I finally removed belly components in my 383, the sound improved because I removed the resonance "chamber" in the middle. Side exhaust is so long...and has enough bends, that midrange volume is killed. Low frequency is still present because of the extreme length of the system.
Maybe some of this might spark an idea in your minds? For me, I need to consider that I killed some of my topend performance BECAUSE I don't have anything like a "terminator" box anymore. I have "longtubes" on the back-end...just like the "front-end". While I'm thinking about alternatives to address that, maybe you guys should consider the same -- when considering how you might change your exhaust.
Don't just consider sound, consider performance. "Vizzard exhaust tuning" is worth googling. One of the biggest things I was shocked by is that 100cu/ft of air weighs 38 tons. Really? I remember something like that in college but still hesitate to believe THAT much weight! Knowing how much air weighs, that there are fore/aft exhaust waves, and that the system presents resistance, makes it fairly hard to consider anything you do will end up more than an accident!
THAT ought to help, right!
Stock L98
Stock, main cat, Targa Mufflers
Stock, bullet cats, main cat, Targa Mufflers
Headers, bullet cats , Y-pipe, Spin-Tech Muffler, side pipes (2.5")
Headers, bullet cats, Y-pipe, main cat, side pipes (2.5")
Headers, bullet cats, Y-pipe, side pipes (2.5")
Three of these six combinations were annoying. Three had marked "drone" at cruising rpms....the 2nd, 4th and 5th combo. And, it's not necessarily what you'd expect when you consider more is less...meaning more components to dampen = less drone. Consider the final config is way better than the two iterations prior to it.
Intuition MIGHT suggest that removing components should increase drone. Yet, when I eventually removed a "belly" attenuator (in my 383 setup), the sound improved dramatically. Granted, my setup is somewhat different due to the total system length but Matt has a point when talking about the total "system resonance". When you change mufflers or add an "H" or "Y" pipe, you're changing the overall tuning/resonance of the system.
My newest theory piggybacks on Vizzard's tuning theory. He points out the addition a "terminator" box can make a longer system "look" like a shorter one when tuning for power. For reasons beyond the scope of this thread, lengths in header/exhaust piping can affect the "tuning" of exhaust for power. The wave theory involved in this seems likely to (at least partially) correspond to sound tuning.
My point borrows from my knowledge of bass cabinet tuning. It's not just the length but also diameter that affects frequency of "tuning" for a PORTED bass cabinet. (An internal tube focuses maximum loudness/resonance at a certain frequency. Music near that frequency get's amplified. Ironically, dampening material must be used to prevent unpleasant "drone" in bass cabinets.) When building an exhaust system, the diameter and length HAVE to play a part in the overall drone/tone. If you've ever heard 2.5" vs 3" exhaust, you'll know what I mean.
I think bullet cats (at least partially) disrupt resonance waves in the exhaust. There body size is so small additional resonance of their chamber size doesn't add sound back in. In other words, bullet cats are better than main cats. I would add that larger bodied mufflers increase the POSSIBILITY of drone from their chamber size.
Whether it related to the dynamics of wave theory (ala terminator box) or tuning (more similar to bass box...or musical instruments), the introduction of a muffler may actually HURT. Most performance mufflers don't contain packing or significant baffling. The combination of the change in diameter PLUS the lack of real attenuating can create a "tuning" point that may add to drone versus subtracting it. I disagree with the poster who claims the diameter won't affect the result. L98's and LT1's have essentially the same engine but different diameters of exhaust. And they OFTEN don't have the same results when adding specific mufflers.
"H" pipes are different than "Y" pipes in the method they use to vent gases to the opposite "bank". I think "H" pipes add more "system volume" to the opposite side. By that, I mean air volume...or space. A large increase/decrease in length/diameter IS going to shift that optimal tuning frequency where "drone" happens....where the system is loudest. Like speaker cabinets, packing/batting will eliminate the echoing/bouncing of sound to create something more pure. But packing also reduces the extra volume of the resonance tuning.
Are you following me?
When you add a muffler/converter -- and the body is large enough -- you may change the harmonic frequency of the entire system. It may be good/bad in terms of performance....when you consider what Vizzard is saying. It also may be good/bad in terms of sound FREQUENCY of the system.
The first thing I'd recommend to anyone unhappy with their system is to REMOVE any performance muffler and observe the result. Clamp in a "test pipe" if you want to keep things cheap...and avoid a trip to the exhaust shop. Next, if you're considering the choice of a "Y" or "H" pipe, consider the "H" pipe is likely to make a bigger difference in terms of performance AND sound. When I considered the standard belly "Y" pipe of an L98 couldn't be THAT much different than a "Y" pipe on a dual setup, that's gotta be wrong. Longer runs of "resistance" create more OVERALL resistance. Plus, they do the OPPOSITE of a terminator box....they definitely can't create a pressure drop. Pressure seems likely to get HIGHER. I wonder if that actually aggravates drone?
Anyway, I would suggest smaller-bodied mufflers and/or "H" pipes when considering your options for changing sound. Corsa mufflers are internally smaller. If you listen to glass packs, their sound isn't totally different that Corsas either. Listen enough and you'll hear how larger-bodied mufflers "add" sound -- like a tuba.
The second setup (above) was loud because it sent the highest pressure impulses into the large body of a main converter. That was largely mitigated by (re)installing front bullets. When I finally removed belly components in my 383, the sound improved because I removed the resonance "chamber" in the middle. Side exhaust is so long...and has enough bends, that midrange volume is killed. Low frequency is still present because of the extreme length of the system.
Maybe some of this might spark an idea in your minds? For me, I need to consider that I killed some of my topend performance BECAUSE I don't have anything like a "terminator" box anymore. I have "longtubes" on the back-end...just like the "front-end". While I'm thinking about alternatives to address that, maybe you guys should consider the same -- when considering how you might change your exhaust.
Don't just consider sound, consider performance. "Vizzard exhaust tuning" is worth googling. One of the biggest things I was shocked by is that 100cu/ft of air weighs 38 tons. Really? I remember something like that in college but still hesitate to believe THAT much weight! Knowing how much air weighs, that there are fore/aft exhaust waves, and that the system presents resistance, makes it fairly hard to consider anything you do will end up more than an accident!
THAT ought to help, right!
#45
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Same solution. It isn't the headers that are causing the great majority of the problem. It's the 8&4 and the 5&7 sequential firing cylinders exhaust dumps that cause the increased instantaneous noise and mass flow. The H pipe, installed as far forward as possible, reduces the double exhaust mass dump/noise, and increases the frequency of the noise that the mufflers have to contend with. It's easier to muffle/filter a low amplitude-high frequency noise than the opposite (a high amplitude-low frequency noise).
IIRC Chevrolet put crossover H pipes on production vehicles (with the stock cast iron manifolds) way back when.
IIRC Chevrolet put crossover H pipes on production vehicles (with the stock cast iron manifolds) way back when.
#46
Team Owner
You don't need an H or X when you already have a single exhaust. The pulses should be able to perform a similar function where the "y" joins as in an X or H pipe; expand.
I think what the Corvette needs the most is more BENDS in the system, to reduce that hummmm noise that is made by the even firing of 8 cylinders. Just a theory though...
I think what the Corvette needs the most is more BENDS in the system, to reduce that hummmm noise that is made by the even firing of 8 cylinders. Just a theory though...
#47
Melting Slicks
Air 0.0765 lb/(cu ft)) according to ISA (International Standard Atmosphere).
times 100 is 7.65 lbs. Mr Vizard as usual is wrong again. It is a long reach to 38 tons
https://www.thoughtco.com/density-of-air-at-stp-607546
times 100 is 7.65 lbs. Mr Vizard as usual is wrong again. It is a long reach to 38 tons
https://www.thoughtco.com/density-of-air-at-stp-607546
#48
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You don't need an H or X when you already have a single exhaust. The pulses should be able to perform a similar function where the "y" joins as in an X or H pipe; expand.
I think what the Corvette needs the most is more BENDS in the system, to reduce that hummmm noise that is made by the even firing of 8 cylinders. Just a theory though...
I think what the Corvette needs the most is more BENDS in the system, to reduce that hummmm noise that is made by the even firing of 8 cylinders. Just a theory though...
More bends equal more restriction to flow. Increased restriction equals more backpressure.
A Chevy engine is even firing, but the exhaust pulses per side are not.
Expansion is not possible unless the pipe cross sectional area change (at the Y) is greater than the increased exhaust mass due to the combining of the two bank pipes.
A Y pipe puts the crossover position further back than an H pipe, resulting in lower efficiency.
#50
Team Owner
Pro Mechanic
I know. The even firing is what creates a tone or "pitch". The "hummm" sound that IS the droning noise. The syncopated pulses are not "drone". That sound is the major part of the luscious V8 sound that we all like.
I'm no "Acoustical exhaust engineer"...but I've done a fair bit of exhaust experimenting for sound. Look HERE, AND HERE.... HERE TOO
I believe that I've found an important factor to great sounding exhaust. Bends. My benchmark was set years ago with '80's 5.0's and my own 3rd Gen TA that had shorty headers, a mediocre "y pipe, 3" single into a 1 > muffler. Sounded just like this:
...it had lots of bends in it (compared to a Y-Body exhaust) and it had no drone. Mmmm-MM!
Last edited by Tom400CFI; 12-26-2017 at 11:09 PM.
#51
Race Director
Air 0.0765 lb/(cu ft)) according to ISA (International Standard Atmosphere).
times 100 is 7.65 lbs. Mr Vizard as usual is wrong again. It is a long reach to 38 tons
https://www.thoughtco.com/density-of-air-at-stp-607546
times 100 is 7.65 lbs. Mr Vizard as usual is wrong again. It is a long reach to 38 tons
https://www.thoughtco.com/density-of-air-at-stp-607546
It's kind of mind-boggling....to me.
#52
Race Director
That said, I understand your thinking...if you think sound waves diminish with directional changes. I'd have to look that up.
#53
Team Owner
Pro Mechanic
On the surface, I don't agree with that either. My sidepipes...with their 360-deg worth of bends contain as much/more bends than the clip above. The drone is less evident sans muffler...than with. It doesn't match your theory. Plus, tuned port (bass) systems often use ports with bends in them...for space. Nothing I've read indicates a change in tuning/efficiency.
With the Kart, it started off w/the factory Y and I stuffed a big magnaflow muff on then end of the Y that terminated just ahead of the diff. I did this for no other reason than to quiet it down b/c it was SO loud with just the ope Y pipe....too loud for driving around my neighborhood. Anyway, with the factory Y, with or without the muff, it sounded like a typical 'Vette with that "Hummm-y" sound 'Vettes make combined with some "V8 pulse" sound. But it sounded rather shitty. I didn't care b/c I knew I'd be changing it. I did change it and now it sounds radically different. The "hummm-y" drone of 8 cylinders is mitigated and replaced by that nice, "Mustang 5.0 burble". I wish I had done a "before vid" for comparison, but I didn't think to record it simply b/c it sounded lame; not worth recording.
#54
Le Mans Master
Having the extra bends in my mind would introduce high and low pressure pockets around them which would increase turbulence and in effect induce mixing. With that extra mixing you are interrupting the some what smooth flow of the exhaust gas that is present and introducing more of a pulsing exhaust. Hence the burbley sound vs smooth. Also depending on where the bends are you can also introduce a resonant tuning effect in theory. All a muffler is is a series of directional changes and expansions/contractions. Reading through most of this has been said already though so sorry to repeat information.
In school we modeled different types of bends for pressure drops and short of using a straight 90 elbow, nice sweeping 90s that are mandrel bent don't offer that much resistance to flow on pressure driven systems. On something like a furnace that's a different story but I would guess an exhaust system is a pressure driven system or can be approximated by one. (This is just my experience so you all don't think I'm pulling this out of air lol.)
In school we modeled different types of bends for pressure drops and short of using a straight 90 elbow, nice sweeping 90s that are mandrel bent don't offer that much resistance to flow on pressure driven systems. On something like a furnace that's a different story but I would guess an exhaust system is a pressure driven system or can be approximated by one. (This is just my experience so you all don't think I'm pulling this out of air lol.)
#55
Melting Slicks
with a turbocharger:
If I am on a budget build I throw a cheap resonator, muffler into the mix then test it.
If there is drone or problems with the sound, I would add a test J-pipe, or change the length of the system a little bit if possible. Or even add an extra muffler. The reason all of this works in the end is because no matter how restrictive the system is, you can always add a cut-out for max turbine differential.
I don't feel like I am so much tuning out the sound this way, so much as moving it to an RPM range where I don't notice it as much.
---
High performance N/A requires testing. Even if we calculate the sound pulse in feet/second and compare with RPM just so it is leaving the exhaust valve at the correct moment- it will still need be "dialed in" on a dyno of some kind, because small unaccounted for variables in the system can dramatically move the relationship of exhaust acoustics as rpm is changing, even in different gears. Remember each gear is a variable with respect to rate of change of engine RPM, so each gear will have a set of "moving" differentials depending on the acceleration of the engine. Which brings the issue of part throttle acceleration, where total flow is cut down by a percentage that will have an overall effect on exhaust gas velocity, favoring smaller diameter pipes, etc...
If I am on a budget build I throw a cheap resonator, muffler into the mix then test it.
If there is drone or problems with the sound, I would add a test J-pipe, or change the length of the system a little bit if possible. Or even add an extra muffler. The reason all of this works in the end is because no matter how restrictive the system is, you can always add a cut-out for max turbine differential.
I don't feel like I am so much tuning out the sound this way, so much as moving it to an RPM range where I don't notice it as much.
---
High performance N/A requires testing. Even if we calculate the sound pulse in feet/second and compare with RPM just so it is leaving the exhaust valve at the correct moment- it will still need be "dialed in" on a dyno of some kind, because small unaccounted for variables in the system can dramatically move the relationship of exhaust acoustics as rpm is changing, even in different gears. Remember each gear is a variable with respect to rate of change of engine RPM, so each gear will have a set of "moving" differentials depending on the acceleration of the engine. Which brings the issue of part throttle acceleration, where total flow is cut down by a percentage that will have an overall effect on exhaust gas velocity, favoring smaller diameter pipes, etc...
#56
Burning Brakes
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2021 C4 of the Year - Modified Finalist
Here's my H pipe. Connects the two collector reducers at the front of the pipes leading to my Y pipe at the back of the transmission. The crossover is removable by undoing the band clamp at the RH collector side, and then rotating/ pulling the crossover off if needed.
Made a significant reduction in drone, and according to Vizard the crossover here is usually worth about 3-5 horsepower improvement. A worthwhile endeavor, IMO, at only a pound and a half weight penalty.
Made a significant reduction in drone, and according to Vizard the crossover here is usually worth about 3-5 horsepower improvement. A worthwhile endeavor, IMO, at only a pound and a half weight penalty.
Last edited by eutu1984; 12-27-2017 at 05:48 PM.
#57
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I've got a turbo on my '84, so my exhaust system there is configured very differently than the '69.
#58
Race Director
I'd bet big money that those Chrysler mufflers are the reason your system sounds great now. I may never buy an oval/box muffler again. I think bullet cats, glass packs, bullet mufflers, resonators, and/or cylindrical mufflers are the way to go. Now that I think about it, they probably serve as a mid-range/bass attenuator. Low frequencies travel in all directions while higher ones are more directional. Glass packs and Corsas have a LOW BIG sound but they also have a high, raspy bark. They both are missing the mid-bass drone. With the mid-bass present, the sound can be more dastardly -- but with drone. To me, the Corsa/glass-pack sound retains good-old USA...with a hint of smaller-cylinder (Euro?) finesse. Removing the mid-bass frequency does that IMO. And, that is what the mufflers you installed accomplish.
I submit that high frequency sounds remain by traveling straight through cylindrical shaped exhaust components. Plus, a portion of the low-frequencies travel straight through as well. As with bass cabinet (speakers) lined with fiberglass batting, omni-directional bass frequencies are absorbed by attenuating their tendency to bounce around inside the cabinet. (The batting actually slows low frequencies making the box seem bigger than it is. And...the more batting, the slower the waves).
In oval, rectangular, baffled, or box mufflers, little-to-no packing exists. The only thing managing sound is how pressure waves "bounce" around in the box. While I'm certain exhaust companies look to optimize HP performance, they also have to market with sound. Magnaflow and Corsa are examples where sound rates as high as power. Flowmaster is an example where sound is less important...or is marketed to owners who may LIKE boomy exhaust. In these large-bodied mufflers, bass can bounce and reverb into itself -- creating nastier mid-bass reverb. It's not a clean sound. It's not representative of what the motor is actually doing. To me, they are like a bass-ported speaker where boom is more important that image.
That's what I'm saying.
If you want to quiet an exhaust, my theory is to stay away from large body exhaust components. If you use them, they better be internally designed to dampen bass frequencies...like Corsas or stock mufflers. Expensive, factory mufflers use redirection, baffling, chambers, and batting to completely eliminate bass frequency. "Sport" mufflers try to control how bass bounces around in a box....And, I don't think they do a great job of it. They might not be able to -- simply because they don't allow ANY direct transmission of bass frequencies. Corsas don't have much/any bass at all (to me). They are like a stereo system with 6" woofers. They bark and are nasty but they don't RUMBLE.
That's why straight pipes and/or cylindrical components sound better. There's still a straight-line transmission of the lowest bass frequencies....and the highest ones. You get the rumble AND the definition of sound.
As for "H" pipes or "Y" pipes, merging the pulses SMOOTHS what you hear. The rhythm is doubled from each pipe making it more like a constant tone vs pulsing. In everything but an idle, tone is mostly what you hear. Also, H/Y pipes can increase the volume (mass) of the system. That changes pipes...and possibly drone. In some older cars, they even added weights to the pipes to dampen the pipes themselves. In the past, I considered trying this to see what happens. Fortunately, that box muffler rusted and I did what I (now) tell others. Try a system with the minimum of components before adding mufflers. If you want sound dampening, start with converters. They help your nose and perform similarly to cylindrical mufflers. They attenuate "boom". If still unhappy, add resonators and/or cylindrical mufflers until you are happy. The exception would be for the person who really likes the Corsa sound and has the money to spend on it. Personally, I think straight-through mufflers sound better.
#59
Team Owner
Pro Mechanic
I had that same style on my C6 too, when I had the GHL system on it. Poo and drone.
Now that Trans Am in the vid above...oval housing, straight through, perforated tube, glass packed...that thing sounds good. I had that same muff on my own TA and no drone. But look at the number of bends in the 3rd gen system! Yikes.
I can't prove anything here...but consider this:
In my C6 days, I tried all kinds of "cat back" exhausts on the thing and none of them really made any diff in the sound (or the drone). What I didn't change, was the configuration of the piping -it was always made up of mostly straight sections w/a few bends.
Now with the Kart, the diff in the Kart exhaust now and earlier is pretty minimal; stock Y to a 2.75" round, straight thru, perforated tube, glass pack style muff. Poo.
Now it's a bendy Y into two, 2.25", round, straight thru, perforated tube, glass pack style muffs, then more bends to the side pipe tips. Music.
What changed? I added bends and separated the sides.
#60
Zen Vet Master Level VII