BWA-4's backward electromotive force decrease data

BWA-4's backward electromotive force decrease data
Measurement of backward electromotive force going into high frequency. Measured by playing 50Hz, 100Hz and 200Hz tone burst signal.

Data A is bi-wire adapter BWA-4
Data B is attached jumper board
Data C is expensive jumper wire

As for the attached jumper board and expensive jumper wire, quantity of backward electromotive force does not change.But BWA-4's backward electromotive force

decreases dramatically.