how can an object be a specular reflector for some electromagnetic waves, yet be diffuse for others?

an object can produce both specular and diffuse reflection  depending on the degree of roughness of the reflecting surface, if the  wavelength of the incident radiation is   less than the size of the articles making up the object the object will produce a specular reflection but if the wavelength is longer than the size of the particles making up the object the reflected rays will be diffused. therefore same object can produce either diffused or specular reflection depending on the wavelength of the electromagnetic radiation.