Performance of negative impedance amplifier

　　
　　When MFB is on in the case of closed box, you just feel decrease of bass sound or
effect as if it was replaced with the lower Q unit .

　　So I display the methods of detecting the effect of MFB so many ways .

　　Just using the negative impedance amplifier, MFB works on the speaker? Such
a foolish thing ! Who thought so should not miss this article .

　Tested with this 1. 1L closed box.



　　In case of the closed box , fo and Qo increase each other.　




　　 It became foc=190Hz.

　　It is possible to determinate approximately Q from this .



　　　　When driving with the negative impedance amplifier, as for Q like above calculated.
(Here I get Rp from height of the curve of impedance.)

method 1

I inspect low frequency character with 4 burst waves.

method 2

With voltage and current analysis, I observe at that control voltage occurs.

method 3
　
　　Sound is recorded with the microphone, that wave form is inspected. When inspecting the sound pressure, it is better to use the cosine wave .

200Hz four burst waves　






　　In this method the change of transient is well recognized, and Q is presumed .
(When it is closed box or naked unit which has not principal sounding body other than
cone)

　　How it was ?

　　As is mentioned with the front section, inspecting the speaker terminal voltage,
the voltage dipping with fs is seen .And making use of detection resistor, you'll see
the phenomenon the electric current has the valley about fs .(c.f. section 7 of "Introduction
to electromagnetic damping").

　　Because the distortion is little in this case , it cannot be observed well, but where
the distortion is large we would see that it will be corrected.

Conclusion

　　　In negative output impedance amplifier, the decrease of Q, improvement of transient
quality and decrease of distortion near fs which are characteristic with the verocity MFB
is really observed.

　　　In addition if behavior of voltage is observed, you can understand the fact that
it is MFB.

　　 It is possible to show this is almost equivalent with Verocity MFB theoretically
but this time it was observed in simple methods.