Basic characteristics of sound
Frequency
It's the measurement of waves or vibration (in HZ). It is how high or how low the sound is. A bass drum, thunder. Heavy traffic noise. Truck passing by are examples of LOW frequency. A bird chirping, a whistle, a child's voice are examples of HIGH frequency.
High Frequency = Short Wavelength
Low Frequency = Long Wavelength
Wave Length
It is related to the frequency of the sound waves. The higher the frequency, the shorter the waves. The lower the frequency, the longer the waves.
Low frequency is much more powerful and requires much more effort so it's the best to recommend soundproofing acoustic panels or framed acoustic panels (they're double). While high frequency will be absorbed easily. Diffusion breaks those waves. It absorbs them and then breaks them apart.
Amplitude
The volume of sound in decibels. Humans and animals sense a wide range of sound amplitude, volume and loudness - from the very quiet to extremely loud.
Loudness is measured in decibels, which really measures the energy of the sound. The loudness of sound depends on the amplitude of the waive. The bigger the amplitude, the louder the sound.
Phase
Describes the relationship between 2 waves. Waves that are out of phase can cancel each other.
Imagine hill (peak) of waves and valley of waves. When both hill coincide with each other, waves become higher. When both valley coincide each other, the wave become lower. When hill and valley coincide, it cancel each other.