Why?

[Electroenthusiast]

Why do we hear an annoying loud sound when a switched on speaker and mic is brought together/ brought nearer? ( This happens now and then during some functions,.)

And my other question is Why do we see propogating lines when a Televison screen is captured in an Handycam? (A wave like things, that distorts the video quality)

 

[Grossel]

Why do we hear an annoying loud sound when a switched on speaker and mic is brought together/ brought nearer? ( This happens now and then during some functions,.)

The phenomen is called Audio feedback.

And my other question is Why do we see propogating lines when a Televison screen is captured in an Handycam? (A wave like things, that distorts the video quality)

Because the cameras record framerate is slightly different from the tv's refreshing rate.

 

[ke5frf]

Why not? LOL

It is the result of positive feedback, the amplifed signal of the microphone coming out of the speaker is "fed back" into the microphone, which is further amplified, goes out to through speaker, fed back into the microphone etc etc into a progressive loop until the amplifier is driven to saturation. Thus the squeal.

In proper operation an amplifier will use negative feedback to keep the amplification stable. This is where the concepts of proportional band and gain come from and apply to any amplifier. You can see a similar phenomenon occuring in an industrial control loop when a valve or actuator responds to an error in the process.

 

[Electroenthusiast]

thanks for the answers