arXiv:2611.08759v1 Announce Type: new Abstract: Optical frequency combs bridge the microwave and terahertz regimes by down-converting terahertz optical energy into microwave signals. A photodetector converts the comb's equally spaced lines, generated through optical nonlinearities, into a low-frequency tone at their spacing. Here, we present the first mechanical version of this process, using mechanical frequency combs to downconvert energy over 4 orders of magnitude, from the MHz to kHz regime. Thin-film lithium niobate (LN) is used to design an acoustic resonator with a wide range of mode frequencies. We achieve phononic comb excitation from 250 MHz to 900 MHz and compare the electrical and laser Doppler vibrometer (LDV) measurements at 277 MHz. We then show the low-frequency spectrum of the devices, highlighting mechanical motion at the comb's spacing and demonstrating energy transfer from 277 MHz to 21 kHz.