Wave guides for very low frequencies Hz-kHz

As you all know wave-guides have a cut off frequency (which depends
mainly on dimensions of the guide) where in lower frequencies cannot
propagate in the wave-guide. Usually wave-guides operate in the GHz
range.

Do any of you know if same principle applies for lower frequencies, in
the Hz =96kHz range?????

Theoretically it should, but I built one where the dimensions are many
order of magnitude smaller than wave length but it seems that the
principle does not apply. EM waves (freq: Hz-kHz) were propagating
threw my guide.