Every object or space has a resonant frequency (resonance). When you pluck a string it vibrates at its resonant frequencies. When you sing or beatbox in a shower you will notice that certain notes sound louder. Resonant frequencies are created where the wavelength of the sound is equal or a multiple of the dimension of the object or space. For example, if a shower cubicle is 2m wide then there will be standing waves (resonance) at whatever frequencies have a wavelength of 2m, 1m, 0.5m, 0.25m, etc. Beatboxers create sounds at the resonant frequencies of club spaces to emphasise bass and sub bass sounds.