Hm, so canon-wise, sound was shown to be possessed by shinobis of Otogakure. Sound itself is essentially soundwaves/vibrations, consisting of both low and high frequencies depending on the technique. Sound can travel through basically anything from the ground, water, even air. It uses them as a medium for traveling, and its strength is due to its immense speed, much more compared to other elements like Earth and Water. To empower, or to make it more efficient, one can use a sound accessories to amplify their abilities, as shown in the manga during the Chuunin exams.
Now, sound is split into three branches. The first is Destructive Sound waves, which uses low frequencies, but high energy waves to deal physical damage. They aren't tangible, therefore techniques from this group are fairly strong. They appear as ripples in the air, clearly visible to the naked eye as well as a distinct sound, I'm guessing. Offensive Sound techniques using Destructive Sound waves travel slightly faster than the speed of Wind, in RP context of course.
Hindering Sound waves use high frequencies, but low energy. They are focused on hindering a target's body. body parts, or bodily functions like bones, balance, normal heart rate, etc. They travel at virtually instant speed, and because of its overwhelming speed, they cannot be avoided through normal means.
And lastly, as well as my favorite, Genjutsu-inducing Sound waves. They are using high frequency, low-energy sound waves as mediums to induce an illusion. They, like the last, are virtually instant and so are the illusion's effects. They are generally stronger than normal illusions but they can be expelled through normal means.
Strengths and Weaknesses of Sound
So, because it is an intangible element, I believe other intangible/somewhat-intangible elements have no effects to it (Fire and Lightning). So, a clash between two opposing elements, lightning vs sound/fire vs sound, will have no effect to both attacks, as far as I know. Sound is strong to Earth and Water, because it is essentially vibrations. They , as long as the rank permits it, can crush through the earth/disperse water with the power behind its vibrations/high energy waves.
Sound is weak to gas-like elements, and wind. I suppose the logic between its relationship with Gas should be similar to Wind. Wind is able to 'muffle' or disrupts the frequencies of sound and distorts it. Water and Sound combination increases the damage of Water, by +20, I believe. So, it's kind of like giving the body of water extra properties of physical damage once infused with Sound.
Sound Waves are disturbances in the air, traveling to another location. It is produced by vibrating items, like a drum to a stick, or your fingers to a guitar, etc. The vibrations causes the air molecules around it to vibrate, which causes a disturbance in the atmosphere, taking the form of a longitudinal wave.