The equivalent magnetic noise spectral density level for long type magnetostrictive-piezoelectric laminated composites has been investigated by using a 1D equivalent circuit model, and exemplified for a longitudinal-transverse mode. The theoretical developments explain well our experimental results. The findings show that similar ultimate magnetic noise spectral noise density can be expected whether using either charge or voltage amplifier detection methods. The findings show that a volume effect and the dielectric loss factor of the piezoelectric layer are the dominant sources of the noise floor. Our findings show that the noise scales as 1/root f. The lowest equivalent noise floor value that has been observed is 10/root f pT/root Hz for f << 10 kHz, with a white noise level of 100 fT/root Hz above 10 kHz. (C) 2011 American Institute of Physics. [doi:10.1063/1.3594714]