Inline 6 and V-12 engines are “naturally balanced,” which is a math exercise that takes a couple of whiteboards full of trig to prove.
They truly are smoother. They also sound better. IMHO, a V-12 is the best sounding engine design, with an I-6 as next best.
Modern I-4, V-6 and V-8 engines have become almost as vibration-free with computer design of better balancing including the use of balancing shafts, etc., but they sound “lumpy” to my ear.
That lumpy sound is what makes a V8 sound so good.
“They also sound better. IMHO, a V-12 is the best sounding engine design, with an I-6 as next best.”
My Vanden V12 was a purring machine I had custom pipes put on it so it was also throaty. The I6 is just half a V12 stood upright this is literally true if the connecting rod design of that engine is fork and blade. You have two I6 connected at an angle by the forks and blades. German WWII fighter engines sound amazing inverted V12s at high rpm hearing one run in at an airshow is a real experience.
“but they sound “lumpy” to my ear.”
Not all V-8s.
Cross plane cranks. Mustang GT 5.0
That is because the firing order has sequential pulses on a side.
Flat plane cranks alternate sides with each firing. Mustang GT-350 5.2.