Velocity is the speed at which sound travels. Sound travels about 1130 ft per second at 68 degrees Fahrenheit (344 m/s at 20°C). The speed at which sound travels is dependent on temperature. For example, sound will travel faster at higher temperatures and slower at lower temperatures, knowing that the velocity of sound can come in handy when calculating a standing wave or working with live sound.
Wavelength is the length of the sound wave from one peak to the next. Consider the wavelength to be one compression and rarefaction of a sound wave. In determining the wavelength, the speed of sound and divide it by the frequency. This will identify the length between these two peaks.
As seen in the figures, the lower the frequency the longer the wavelength. This demonstrates the power and energy that low end creates as a result of a longer wavelength. High frequencies are much smaller in length resulting in a weaker form of energy that is highly directional.