I am not as well educated in electrical as most of you

[barrybynum]

I was hoping maybe you could answer.
Can the current (alternating current) coming from speaker output of a powerful audio amplifier power a small motor, and would the speed change as audio changes volume?

 

[rjenkinsgb]

Not in general, and for an AC motor the speed is more likely to be controlled by the audio frequency, with power (torque) related to volume.

You could possibly feed audio via a capacitor to a full-wave bridge rectifier and use the output from that to run a small DC motor, with the speed being controlled by the motor.

It could cause audio distortion if you were trying to listen to audio at the same time, and it may also overload the amp, or damage the motor if the volume (and voltage) gets too high.

I did once run an aircraft gyroscope (400Hz 3 phase) from the output of an audio amp, using a 400Hz tone in to the amp & turning up the volume until the speed stabilised.
(A capacitor from one of the outputs to the third phase wire gave the phase shift to set the direction).

 

[Diver300]

Power tools that run on AC are often series-wound motors. That is a type of motor called "universal" because it can run on DC or AC. If you have one that is small enough and an amplifier that is larger enough, the speed would be controlled by the amplitude of the signal from the amplifier.

If you also connect a speaker at the same time there will be loads of noise from the motor.

It is probably only the bass frequencies that would have an effect. Normal audio doesn't have a lot of power in the high frequencies, and the inductance of the motor windings will mean that the current will be less for the same voltage at high frequencies.

Please tell us what you are trying to do. If you have a particular application in mind, it might be better to process the audio signal and feed that into a motor controller.

 

[tepalia02]

I don't think it will be an efficient method to drive the motor and control its speed this way.

 

[crutschow]

I was hoping maybe you could answer.
Can the current (alternating current) coming from speaker output of a powerful audio amplifier power a small motor, and would the speed change as audio changes volume?

What will this motor do?

 

[canadaelk]

Yes, it is possible. There have been commercial sub-subwoofers using a DC motor as driver. E

google: servo drive subwoofer

 

[rjenkinsgb]

Re. motors - A conventional speaker voice coil and magnet is also technically a "motor" - a form of linear motor.

Normal servo feedback subs typically use an extra winding or accelerometer on the cone to sense position and modulate the drive, so it can be made to conform to the required position, with an otherwise normal voice-coil actuator.

 

[bob4bvm]

Huge rabbit hole IMO, far better to do some signal conditioning on the audio signal and use that to drive a std controller for the type of motor you have.

 

[ZipZapOuch]

I helped our local high school "industrial automation and robotics" teacher build up a prop for the theater department recently. He had a box of synchronous motors and wanted to use them to shake some sheets of Mylar backdrop at different speeds. We used a tone generator app on an iPad fed into few donated audio amplifiers to control the speed of the "shaking" with the synchronous motors.

 

[crutschow]

There have been commercial sub-subwoofers using a DC motor as driver. E

google: servo drive subwoofer

Of course a speaker cone driver can be considered a linear motor, but its driven by an AC signal, not DC.
There can be servo position feedback from the cone driver (I have such a subwoofer) but it still fundamentally the same as a non-servo driver.

 

[eTech]

Sounds interesting (no pun intended).
Seems like a FtoV converter could be used as a front end to a motor controller/driver.