Everything is energy. Even as you are reading this your brain is using electrical impulses to decode and interpret the squiggles on this page (known as words) into information. The information came from my thoughts and is transmitting in this medium called language.
It is intuitive that sound is energy. You have probably felt the energy from the speakers at a rock concert. Even on the smallest level, the pluck of a guitar string generates physical vibrations which are transmitted as sound waves and ultimately absorbed and interpreted by the body as physical energy or emotion. In fact, we are walking energy decoders. Our eyes interpret the energy of light and our ears and skin interpret the energy of sound. The world is made of energy and so are we. There are also many other energy patterns such as radio waves, brain waves, electromagnetic waves, wifi etc...that we are not as acutely aware of.
Human hearing covers a range of roughly 20hz to 20,000hz. Hertz (hz) is the measure of frequency. (They are called hertz because the name was coined by Heinrich Hertz.) Of course, just because we can't hear in the other ranges doesn't mean sounds and frequencies don't exist there. Some dogs can hear as high as 60,000hz and dolphins can hear as high as 150,000hz!
The energy of sound also manifests as form. The science that studies this phenomenon is called Cymatics (see videos below). For more search Cymatics on YouTube.
The study of Cymatics shows that the higher frequencies also produce more complex geometric patterns, while lower frequencies produce simpler patterns.
The videos below give a brief look at how sound manifests into form.
For sound downloads click here.