a curiosity, theoretical kinda' thing.

[tonequester]

tonequester here.

If a non-powered loudspeakers(conventional) cone were to be mechanically moved back and forth, would it not generate voltage/current ? If it were to be moved the same degree in the same exact manner as a powered/signal fed "perfect" clone, would the voltage/current be the same ? I invite anybody who gives a c___ to
elucidate on this phenomenom. I am serious about this, and have not found out much Googling it. I'm sure that there are physics and math involved which are beyond me, but any thoughts would be appreciated. I already know a few things relative to this query, such as a speaker can be a microphone. However, not much more, and I'd like to know more. Sorry if this seems inappropriate for the forum, but I felt it was my best bet.

[J M Fahey]

1) yes, it does generate voltage.
And if it's connected to a load, some current will flow through it.
2) said voltage and current are much smaller than the ones needed to move it the same distance at the same velocity .
Why?: because a speaker is *very* inefficient .
Believe it or not, only 1 or 2% efficient and that's the best ones.
Compare it to transformers and electrical motors (over 90%), gas engines (in the order of 30%), lightbulbs (around 20%).

[soundguruman]

You should spend $10 on this textbook:
Amazon.com: S. L. Herman's 3rd(third) edition (Delmar's Standard Textbook of Electricity, 3E [Hardcover])(2003): n/a: Books
It explains just about all theory, from the most simple and soforth...

[Jazz P Bass]

My take on it is the 'voice coil / magnet' assembly is a motor & a generator at the same time.
Feed it a varying voltage: motor
Push on it: generator
Michael Faraday gets credit for the concept.
Michael Faraday - Wikipedia, the free encyclopedia

[Mark Hammer]

And that is precisely why, for decades, there have been schematics for household intercom systems that use the speaker as either speaker or mic.

http://www.instructables.com/id/SPKR...rom-a-speaker/

http://prorecordingworkshop.lefora.c...s-microphones/

[Enzo]

Any speaker can act as a microphone. Yes, it has been at the core of intercoms forever, I had one close to 60 years ago. ANd I recall in grade school there was a speaker on the wall of each classroom, wired to the PA system in the main office. They could page the classroom, and the teacher could just talk back at the speaker for the office to hear. (Or they could secretly eavesdrop)

But even in todays modern world, there are guys who mount a large woofer in front of their kick drums and use the resulting signal for various purposes. Recording, PA system, trigger signals, etc. (Ah. Mark's link covers that)

The hell with google, get out your meter and a speaker. Find out. Takes just seconds. And it will stick in your head better than google.

Sit a speaker down with your meter connected to the voice coil terminals. Set it for volts. Now push in and out on the cone. Get voltage peaks?

Leave the meter connected but set for ohms. If it is an 8 ohm speaker, the resistance will probably be about 6 ohms or so. Doesn;t really matter. YOu get some resistance reading. Now push on the cone, I bet your resistance reading goes nuts. It can sometimes be difficult to get a stable voice coil resistance measurement reading because you are moving the speaker or there is sound energy in the air. The voltages the movement causes will confuse your ohm meter.

Not only can you use a speaker as a microphone, if you send a signal into a dynamic microphone it will try to act like a tiny speaker. DOn;t do it with any mic you care about, but you can make sound come out a mic.

As Juan explained, inefficiency will result in the voltages generated being not at all the same as those needed for the same motion.

[madkatb]

I once bought an old combo tube amp at a flea market after testing it with a set of headphones. No microphone around so I plugged in the headphones and between tapping them and talking into them it confirmed that the amp worked.

[tonequester]

tonequester here.


Enzo. I wish to thank you for reminding me about the value of "hands on" education. In my old age, I've become too reliant on "book smarts". I worked 20 years as a
multi-million dollar printing press operator. I was trained for several years before I was "turned loose", as a pressman with "my own" press. The guy that trained me had a simple way of being outstanding at his profession. He got out "the book" when all else failed. He didn't like to get the book out because it didn't solve the problem half of the time, but he seldom had need for it anyway. As an operator, I built upon our combined experience, often doing things that could raise eyebrows, but they worked and you knew that they would. Being on disability has
made me lazy. You made me realize that 54 isn't too old to experiment in order to learn. I somehow, years ago came into possession of a 12", 32 Ohm, Eminence speaker. The big dog
weighs over 5 lbs. The last time I moved, it was somehow punctured. I couldn't bring myself to toss it out, so I have been patching the thumb sized hole with laminations of heavy paper towel, and Tite-Bond glue. She should be dry tomorrow. I'm going to do just as you suggested and hook up my meter and see what happens when I test that cone out. By the way, I don't think that I have ever seen another 12", 32 Ohm speaker before. I looked up the model # and was surprised that there was any info on it at all(must be 30 years old). The only other thing I could find out was that it was rated at 100W. Is this type of speaker very commonly used ? (impedance rating) thanks again Enzo. tonequester.

[tonequester]

Believe it or not ? I do now !

1) yes, it does generate voltage.
And if it's connected to a load, some current will flow through it.
2) said voltage and current are much smaller than the ones needed to move it the same distance at the same velocity .
Why?: because a speaker is *very* inefficient .
Believe it or not, only 1 or 2% efficient and that's the best ones.
Compare it to transformers and electrical motors (over 90%), gas engines (in the order of 30%), lightbulbs (around 20%).

tonequester here.

Thanks for the reply JM. I had thought that it might work "in reverse". However, I had no idea just how inefficient loudspeakers are. I wonder if that applies pretty much the same for all types of speakers. I mean to say, they must surely all be very inefficient, but how about something like a piezo ? Anyway I appreciate the
simple, and easily understood reply. Thanks a bunch ! tonequester

[tonequester]

tonequester here.

soundguruman. Thanks for the info on the book. For $10.00 it seems quite a bargain. I'm on it. I once had quite a library on electronics, but when I went on disability I had to sell off many things. now I am trying to re-stock. I really appreciate anybody steering me to a good text. Have a "good 'un" ! tonequester

[Mark Hammer]

And, lest we forget, what do folks think a "dynamic mic" is? It's a voice coil and diaphragm, around a magnet. But wait a sec, isn't that a......yes, it is. The difference is that since it doesn't have to handle large amounts of current, the wire making the coil can be very thin, and, like any coil, the number of turns determines the output. So, we end up with voice coils that measure 150-600 ohms, instead of speaker voice coils that only measure 2-16.

[tonequester]

And, lest we forget, what do folks think a "dynamic mic" is? It's a voice coil and diaphragm, around a magnet. But wait a sec, isn't that a......yes, it is. The difference is that since it doesn't have to handle large amounts of current, the wire making the coil can be very thin, and, like any coil, the number of turns determines the output. So, we end up with voice coils that measure 150-600 ohms, instead of speaker voice coils that only measure 2-16.

tonequester here.


Mark, you make a fine point, and in a very consice way. The Creator of the Laws of Physics(and everything else) sure had a way of making the complex yet elegantly
simple. In pondering this, the old chiken and egg analogy comes to mind. Which came first ? The speaker, or the microphone ? Oh, well. There's always Google.


Quote ; "The more you find out nabout the world, the more opportunities there are to laugh at it." Bill Nye(the" Science Guy").

[Enzo]

32 ohm speakers are nopt common, but they are out there. The 8x10 AMpeg cabs used 32 ohm drivers. I have one on my shelf. A driver, not a whole 8x10 cab.

[tonequester]

curiosity satisfied !

32 ohm speakers are nopt common, but they are out there. The 8x10 AMpeg cabs used 32 ohm drivers. I have one on my shelf. A driver, not a whole 8x10 cab.

tonequester here.


Thanks for confirming my suspicion Enzo, I thought that they might be rather uncommon. I can't for the life of me remember how I came across the
thing. I do know that it was NOS until it got damaged. I don't know if my patch job will make it functional or not, but I just couldn't throw away the big boy. Apparantly Eminence still sells that model, and it has to be well over $100.00 new. The patch job looks good, and feels good. In the morning I'm going to test what we had discussed with my meter. If it holds up to that, I'm going to hook it up and see if it can handle some proper cone movement.
Thanks again for the info.


Quote : "Don't let your dreams be dreams." Jack Johnson.

[Chuck H]

I don't have this book. But the light in which it is suggested sure makes it seem interesting.