powering a Subwoofer for mechanical motion - not sound

[BurnedFingers]

I want to use a Sub woofer to move a platform occasionally. The signal will be generated by software. The idea is to re-create motion recorded with something like an accelerometer. Since Sub Woofers can respond fast and move many inches they are a cheap effective way of reproducing movement. Linear actuators start at about $500 and cannot move as fast.

So, I need a really bad, high power amplifier. Something that can apply a lot of power to the voice coil where sound quality is not an issue. In fact accuracy is not that imprtant either it turns out. The most important factor is cost. Its got to be cheap.

I am guessing something off the shelf would be better than designing and building our own (unless its really simple).

The next step is to convert digital signals to an analog signal to move the voice coil.

Any suggestions would be appreciated

[Nrik]

Get a Class D module, and add a powersupply.
Google these : Tripath, Hypex, ICEpower, LC Audio

...isn't there also a forum-sponsor that sells Class D modules?

[mt490]

If you're not actually worried about anything to do with sound, then any micro-controller PWM module connected up to a suitably large H-bridge motor controller will do what you seem to be wanting to do.

[djk]

"BurnedFingers"

Is this Joe re-using your older name?

Think about this:

p-channel fets

±100V on the main rails should do 1KW/4R.

I have another idea for a 200V bridge amplifier if you need 2KW/8R.

[imix500]

Maybe a surplus shaker table setup?
Or a motor from an old servodrive sub?

[prairiemystic]

How much mass to move, how fast, do you need DC positioning?

I've used voice-coil actuators from surplus hard disk drives, the washing machine sized ones from mainframes. Extremely fast and strong, most of the expense is in the servo electronics which could position things (with feedback potentiometer). Google "voice coil actuator" to get more info.

[leswatts]

I have built a number of voice coil actuators from large eminence 18" woofer motors. I remove the cone/spider/basket and make pushrod assemblies from carbon fiber arrow (archery) shaft blanks.

These use optical encoder feedback, and are very low cost with high accelerations.

As stated, an H-bridge servo amp is ideal for driving these. In the lab I used a pair of Crown DC-300 amps as well.

Les
L M Watts Technology

[jackinnj]

Part's express has a "shaker" -- Aura Pro Bass Shaker | Parts-Express.com -- $39

I think servo positioner from a big old hard drive -- but you're not going to find it in the local scrap heap.

[BurnedFingers]

Some great responses. I have been reading for days.
I am really liking the voice coil actuator route
YouTube - 45 Voice Coil Positioning Stage
YouTube - 35 Voice Coil Positioning Stage Vacuum Compatible
YouTube - 26 H2W Voice Coil Positioning Stage VCS10-023-BS-12

I think these would be ideal, but I am not clear how they are controlling them.

The H-Bridge controller might not have enough subtlety for my needs so I am thinking of a SPDIF into one of those nifty amps like the Tripath/Hypex.

>How much mass to move
well the sprung weight is <50lbs, but I suspect I only need about 10lbs (peak) force or less. Its not an e-ticket ride!
>how fast
Another unknown. It needs to duplicate "bumps" as felt through suspension (which dampens the shock of the bump) so it does not need microsecond speed
>do you need DC positioning?
If this means the ability to move the actuator to different positions like these videos, then yes definatly.

This is where I get confused about how the control is handled. If I generate a digital audio signal and feed it to an amp, where does the feedback occur?

[mt490]

Typical loudspeaker voice coil systems only achieve proportional force control. Displacement control is open loop, derived from the spider's spring constant.

You have a couple of options:
1) If additional power consumption and some degree of displacement error is acceptable, then you can raise the spring constant k to reduce the loaded displacement error of the open loop displacement control.
2) Add a servo control loop, to attain closed loop proportional displacement control.

From the loadings quoted, likely only (2) is the acceptable solution.