# Help on Impedance Essay

Discussion in 'Homework Help' started by veenife, May 20, 2014.

1. ### veenife Thread Starter Member

Jan 16, 2014
42
0
Hi,

I`m writing an essay about how impedance affects the frequency response of dynamic microphones... My teacher read it and said that it ins`t good enough, he wants me to give more EXAMPLES OF CIRCUITS and explain better how the whole thing REALLY affect the frequency response of a dynamic microphone step by step in details of how the whole process of loss of frequency occurs... I have not much knowledge of electronics and I can`t find any book or article that gives me this information in details...

I need help to figure something out, some ideas of what to do and how to make my essay better... specially on how to get to the point of how impedance affects the frequency response of a dynamic microphone and make more sense from content to title.

I`m linking a website where a pdf file of my essay is,the essay isn`t so long... I appreciate your help and I thank you in advance!

https://onedrive.live.com/redir?resid=74574A17DF3DA466!309

....if the link doesnt work when you click, thats because "allaboutcircuits" is blocking the link... plz copy it and paste on your browser...

Any sort of help is very welcome!

Last edited by a moderator: May 20, 2014
2. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,995
1,117
Hmm it seems that you don't know how to copy a link.

https://onedrive.live.com/redir?resid=74574A17DF3DA466!309

3. ### AnalogKid Distinguished Member

Aug 1, 2013
4,711
1,303
Why does load impedance affect the frequency response of a dynamic microphone? Because Faraday's Law has a minus sign in it. That's the complete answer; everything else is just arithmetic.

Maxwell's Field Equations
Ampere's Law
Lorentz Force

A microphone is a generator, just like the ones in a power plant. Both have a coil of wire moving past a magnet, a classic example of Faraday's Law. But when electrons flow in a wire it creates a magnetic field around the wire according to Ampere's Law.

Faraday's Law has a minus sign in it, while Ampere's Law does not. This means that the field produced by the current opposes the field that produced the current. That opposing force is called the Lorentz Force.

Due to the Lorentz Force, the wire gets harder to move as the current increases, the current increases when the external load is increased, and the load is increased by decreasing the external load impedance. Because the wire is harder to move, so is the diaphragm attached to it. Because all of these fields and forces are proportional to frequency, the diaphragm responds less and less to higher frequencies as the external load impedance is reduced. When a microphone data sheet states a preferred load, that is the impedance that dampens the diaphragm movement a small amount so it doesn't overshoot and distort with loud transients, but not so much that normal audio sounds muffled.

The amazing thing about this is that Maxwell figured out all of it during the US Civil War. True, he was in Scotland at the time, but still - that was 15 years before the telephone, 50 years before the vacuum tube, and 86 years before the transistor. Smart Guy.

ak

Last edited: May 20, 2014
veenife likes this.
4. ### veenife Thread Starter Member

Jan 16, 2014
42
0
i just didnt get one point...

by "...the current increases when the external load is increased, and the load is increased by decreasing the external load impedance..."

you mean that, current increases when the mic pre amp power is increased, and the mic pre amp power is increased by decreasing the output impedance of the mic preamp???

5. ### AnalogKid Distinguished Member

Aug 1, 2013
4,711
1,303
Nope. In your original post you asked about how impedance affects frequency response. The impedance you mention is the input impedance of the preamp. that input impedance is the only thing the midrophone sees. The microphone is an electrical generator, and the current it generates flows through the preamp input impedance. The preamp input impedance is the electrical load on the generator, the microphone. So, like any other generator, Ohms law says that if the generator output voltage is constant, then the low the impedance of the load, the greater the current through it. In electronics, increasing a load means decreasing its impedance.

ak