Motional FeedBack loudspeaker system (MFB) Introduction A motional feedback system is a combination of a power amplifier and a loudspeaker in which (a part of) the feedback is obtained from the movement of the cone of an electro dynamic loudspeaker. In the picture at the left the difference is shown.
What is an example of shunt feedback?
An example of shunt – shunt feedback. Amplifier and feedback network have same input and output port voltages Input current to the amplifier is the sum (the “mixture”) of input and feedback path currents. The feedback network samples the output voltage and contributes a. current to correct the input.
How much feedback does a negative feedback MFB have?
This shows that the negative feedback of this MFB works from less than 20 Hz up to about 500 Hz. The feedback is 17 dB at 65 Hz, which is the resonance frequency of the speaker in the small enclosure (with damping material). Here the distortion is largest which will be reduced nearly 10 x. Two speakers?
What is feedback in a system?
In all feedback (every time the word: ‘feedback’ isused, I mean: ‘negative feedback’. In Dutch: ‘tegenkoppeling’) systems one has to deal with stability problems. The larger the bandwidth of a system the more feedback could be applied (e.g. with a unity gain stable op amp the gain could be reduced to 1). We all know
Why didn’t the Motional Feedback system catch on?
The Motional Feedback System unfortunately never really caught on in a big way. The Philips technology was expensive at the time, meaning price-wise it competed with high quality conventional loudspeaker and amplifier separates that actually sounded better.
How much does THD drop without Motional Feedback?
A company called Servo Speaker continued this idea showing in their measurements that THD would drop below one fourth (12dB) of the THD of the same speaker driver without motional feedback. This would typically equate to a drop of around 50% (6dB) at 20 Hz.
How do subwoofers vibrate?
The ceramic sensing device on the cone ‘vibrates’ and as it does so an electrical signal is generated. This is then fed back and compared with the signal that made the woofer vibrate in the first place. If there is any difference then corrective action takes place in the amplifier.
