We are studying guided waves on the surface of a one-dimensional acoustic metamaterial, also known as Spoof plasmons. The metamaterial is composed of a periodical array of rectangular cross section pillars, built in a sound-soft material, specifically, air structures on a polydimethylsiloxane medium. Our study is focused on the surface guided wave produced by the interaction of an incident wave on our metamaterial, when the periodicity of its structure is several orders of magnitude lower than the size of the wavelength of the incident wave. The problem is being studied experimentally and theoretically, using homogenization methods (Marigo. J. J, 2018, RSPA) to simulate the effect of the incident wave over the array and comparing the results with the experimental measurements. We have theoretically demonstrated the possibility of tuning the frequency of the spoof plasmons by changing the acoustic impedance contrast between the inclusions and the medium [ABSTRACT FROM AUTHOR]