diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Full Range (http://www.diyaudio.com/forums/full-range/)
-   -   Precise cone position control (http://www.diyaudio.com/forums/full-range/203231-precise-cone-position-control.html)

bittuthegr8 27th December 2011 04:43 PM

Precise cone position control
 
is it possible to accurately control the position of the speaker cone? i'm planning on using a speaker to position some lightweight (<0.5g) mirrors for a laser project. would it be possible if i varied current instead of voltage? i'm looking at frequencies around 4KHz.

T101 27th December 2011 07:28 PM

They are doing it all the time with CD player laser assembly lenses - moving iron surrounded by coils.
You'll have to have either spring or sufficient weight to counter the motor force for precise positioning. Maybe high compliance (soft suspension), low Qms (allot of losses-shock absorber like-opposite of spring effect) and low Qes (strong motor)
Have in mind distortion, it is something you can't compensate for unless you use MFB (motion feedback) with proper resolution and I'm not sure for 4 kHz.

Best Regards!

jcx 27th December 2011 07:47 PM

it always good to see the performance specs of pro gear to get an idea of what the limits of a diy hack might be

in this case search for galvanometer mirrors, a quick search give 2 kHz broadband and 12 kHz resonant for purpose designed galvo mirror hardware

weltersys 27th December 2011 07:54 PM

1 Attachment(s)
Quote:

Originally Posted by bittuthegr8 (Post 2835847)
is it possible to accurately control the position of the speaker cone? i'm planning on using a speaker to position some lightweight (<0.5g) mirrors for a laser project. would it be possible if i varied current instead of voltage? i'm looking at frequencies around 4KHz.

Speakers have an impedance which varies with frequency, but the impedance does not change with voltage when used in itís linear power range .
The amount of current that flows through the speaker is dependent on the voltage applied and the speakerís impedance.
The lower the impedance, the higher the current flow with a given drive voltage.
Increasing the impedance will decrease the current flow with a given drive voltage.

Since the speaker impedance is fixed, you canít vary current without varying voltage.

Assuming you are planning a simple device such as the one below from (Laser Science Projects - Intermediate Projects - www.LaserFX.com) , more voltage (or louder music) will make a larger size pattern, while the pattern is determined by combining frequencies.


Frequencies above 16 Hz or so will appear as a continuous line due to persistence of vision.
At low frequencies, the speaker has much more excursion per given voltage, so a bigger pattern can be made with less power using lower frequencies to drive the speaker.

Squeak 28th December 2011 12:15 AM

The read/write head in a HDD is controlled by a voicecoil, so very, very good precision is possible. But as already said, to have it you need some kind of feedback control.

gootee 28th December 2011 12:49 AM

First, what are the positioning requirements, for your system?

gootee 28th December 2011 01:29 AM

There are many threads here about using cone position or "motional" feedback (aka MFB).

Here is just one: http://www.diyaudio.com/forums/subwo...bwoofer-2.html

bittuthegr8 28th December 2011 08:57 AM

Quote:

Originally Posted by weltersys (Post 2836055)
Since the speaker impedance is fixed, you canít vary current without varying voltage.
Assuming you are planning a simple device such as the one below from (Laser Science Projects - Intermediate Projects - www.LaserFX.com) , more voltage (or louder music) will make a larger size pattern, while the pattern is determined by combining frequencies.

i meant varying the current but not keeping the voltage constant because the force on the coil is proportional to the current flowing through it.

Quote:

Originally Posted by gootee (Post 2836368)
There are many threads here about using cone position or "motional" feedback (aka MFB).


motional feedback seems like a good idea, the capacitance method seems to be the easiest to implement. Tech

also when the speakers are run there will probably be a hissing noise, would it be alright if i cut a few slits into the cone


All times are GMT. The time now is 08:14 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2