Why are some farts noisy, and some silent? Does it have to do with the amount of gas, or the tightness of the sphincter, or both?
Last time this came up, people mostly came up with ways to make the fart stink, without addressing the sound. I don’t know if that was because of the way the other OP was written, or because medical science hasn’t studied the phenomenon of SDBs yet.
My theory is that is has to do with the medium through which the gas must travel - farts that travel through a soft loose medium are louder than farts that travel through a dense, drier medium. I know Aglarond has recently experienced SBDs, maybe he has some insight.
But I’m just talking out my ass, so to speak. 
The noise is related to the shape of your anatomy. Some of us are blessed with the ability to create a lot of noise. Some are not.
Intestinal gas is highly idiosyncratic. No two guts are alike.
Well, as a “toy closet bisexual” who has experienced a range of sphincter muscle tones, sphincter dilation, and volume of flatus, I can authoritatively attest that the muscle tone is the primary factor in determining how much noise is produced by the passage of intestinal vapors, and is the principal means to control its timbre.
Think of the times you’ve inflated a balloon, and then released it. Most of the round ones make the traditional humorous loose cheek flapping sound. This is because the tension in the walls of the balloon and the rate of airflow out of the neck of the balloon are enough to put a small amount of tension in the neck, and set up low frequency standing waves that shed acoustic energy. This is generally what happens during the “classic male” fart… we just relax the sphincter to minimize tension, and push with the diaphragm to maximize airflow. Loose flapping parts in the path of the expulsion provide the acoustic component, generally considered rewarding - if not mellifluous.
Now go chase down your balloon and reinflate it. Use both hands to pinch opposite sides of the mouth between thumb and forefinger, and pull. This is the infamous “squeaker,” where more tension at the mouth allows the passing air to set up short wavelength standing waves, much in the same way that the tone of a guitar string rises as you crank the key and tighten the string. (Your vocal cords work on the exact same principle.) Such is the fate of the typical female farter who tries to tense her sphincter and restrict the airflow. Most of the time, this strategy can result in a slow, inaudible leak that releives pressure. Unfortunately, this strategy sometimes fails, resulting in a sustained high-pitched note resembling a dolphin call. (But ladies, you may be relieved to learn that very high pitched noises are difficult for human ears to directionalize, and seldom are dolphins present.)
Now, finally, reinflate your balloon again. This time you will also need some addtional props: a spool of thread for a sewing machine, and an empty toilet paper roll. First, restrict the air and stretch the mouth of the balloon over the spool of thread. Let the air flow, and listen: Nothing. Small hole, but nothing. Do the same with the toilet paper tube. Still nothing.
Why? Both of these openings, despite having vastly different diameters, are rigid enough to resist “flapping in the breeze.” This situation occurs occasionally in the human rectum and unnervingly frequently in the canine rectum. The cause of this condition varies - it could be posture, individual anatomy, a short pathway between a trapped pocket of gas and the final exit, or inflammation of the ringpiece due to any number of irritants. (Or it could be due to the insertion of a spool or cardboard tube.)
In all three of these cases, the amount of gas passed is generally independant of the sound produced. Some methods tend to achieve higher flow rates than others, but others make up for low flow rates with extended durations.
I encourage the student to experiment with his or her own anus, and explore the spectrum of sounds and effects it can produce. Large quantities of unfiltered, bottle-fermented beer, such as Sierra Nevada Pale Ale, is a reliable source of flatus.
Okay, that’s WAYYYYYYY too perfect. Permission to use it as a sig line?
Cartooniverse
You have my blessing.
A friend of mine gave me a bottle of Beano as a birthday gift once. She told me that it was important that I make use of it. I’ve tried to study up on the topic.
Curiously enough, the hair around your butthole acts as a muffler. Shave it off, and all farts are audible. Don’t ask me why I know this.
Farts in a warm shower, whether noisy or silent, are paurticulary pungent. I know not why.
This is what I want to know:
Why is it that dog farts are always silent? No advance warning, no chance to flee the room, nothing. Just a sneak attack as they float up behind you and WHAM!
As for the human variety, the decible level of a fart is inversely proportional to the force of the methane expulsion behind it.
Like this: g x p[sup]2[/sup] = F
Take a common whistle. The more pressure you use when forcing air through it, the louder the sound. Toss in some CH[sub]4[/sub]H[sub]2[/sub]S…I think…and you’ll achieve the full effect.
Useless Trivia: A fart is the sharpest thing in the world. It will go right through your pants without even making a hole.
A word of advice:
Never trust a wet fart.
This question about dog farts brought to you by Dire Wolf.
Simply put, they’re silent because a dog has no buttocks.
Think of a fart as a bolt of lightning. It’s powerful, and you don’t want to be around when it strikes.
As the lightning passes through the air, it creates a superheated column of air that expands. Upon the collapse, the explosive noise.
As the fart passes through your buttocks, it creates a superstinky pocket of air that seperates your asscheeks. When the fart bubble escapes, the ass-spacing collapses, and your butt slams shut.
On occasion, when my dog is jumping up onto something, I will hear her squeak one out. I make the general assumption that this is a brass effect, but I am not putting my lips there to find out.