Magnetodielectric (magnetocapacitance) and magnetopiezoelectric effects in neodymium ferroborate are systematically investigated. The existence of a previously observed magnetopiezoelectric effect in samarium ferroborate is confirmed. This effect consists in indirect renormalization of the piezoelectric modulus as a result of the combined action of the magnetoelectric and magnetoelastic mechanisms. The manifestation of a new type of phenomena—direct renormalization of the piezoelectric interaction in a magnetically ordered phase—is observed. The ratio of the contributions of the rare-earth and iron systems to the magnetoelectric interaction is estimated. It is shown that the latter plays a ballast role, impeding orientation fluctuations of the magnetic structure as a whole. The boundaries of existence of the helicoidal phase on the H-T plane are determined. The phenomenological interpretation of the studied effects is given.