subwoofer design problem

[f4ier]

I haven't read anything about such circuitry as used in Velodyne subwoofers... have to admit that I think it's a current limiter basically because I think that is its primary function -- throttling back the current once the driver unit is at or past its mechanical/electrical limit (which is, I think, Xmag). I think that once the sub is asked to operate beyond its limits, no amount of signal correction can successfully reshape the output as per the input signal... I think that current in this case will have to be brought back to practical levels. Within the driver's operating range or specifications, however, things are just a little bit nonlinear, so I think this is where all the extra algorithms in those chips come into play to make the sub sound better.

Of course, I could be WAY off in my assumptions, sorry

IMO, with high quality drivers such as the ones mentioned in this thred, I myself would not use such circuitry. The money would be better spent on an active sub. crossover with *variable* signal phase (useful), higher order filter(s), parametric equalizer, higher quality opamps/power supply, better power amp and so on...

Isaac

[Edited by f4ier on 11-13-2001 at 12:52 AM]

[pkgum]

f4ier

I have read in some magazines and projects that subwoofers using those things produce one of the best bass available.

Im just interested at this way of reducing distortion.

Someone mention a thread or web page that describes in detail how this is done?

[ThomasW]

Designing and implimenting a proper servo feedback mechanism isn't a trivial undertaking. There have been numerous Speaker Builder/AudioXpress articles about this. I'm sure back issues are available.

It's interesting that people like Tom Nousaine consider 10% distortion not audible in subs; and use that figure as the testing limit when comparing sub output.

[GRollins]

This is one of those points I like to toss in when people get wrung in the withers about whether their amp has .001% distortion or .0001%--when the speakers are running into upper single digits and lower double digits, it seems rather an exercise in applied foolishness to worry about such small amounts in the amp...
The accelerometers I'm familiar with aren't sampling, they're analog. If they're used with a class D amplifier, the feedback signal will have to be sliced and diced just like the input signal, but with all other classes of amplification, they'll just be added in like any other feedback signal.
No, they're not current limiters, any more than any negative feedback loop is designed to function as a current limiter. If an amp is driven into clipping, the feedback loop will try (futilely) to correct the problem. Likewise, if someone exceeds the mechanical limits of their driver, the feedback loop will try to correct the problem. The results will test how well the cone was glued to the basket at the factory. You can add a cutout to keep from overdriving the driver if you're worried about it.

Grey

[BAM]

You know, just to see what it's like. I want to see a cone and voice coil go shooting off into the distance like it happens at car subwoofer competitions.

[GRollins]

I've seen it happen. There was this fellow in an electronics course I took years ago who thought it'd be funny to hook the AC line to the speaker outputs. Yeah. Big laughs. A sound like a gunshot when I turned the circuit on and the cone went thataway! Ripped the surround and spider clean out of the basket. The only problem was that just moments before turnon I and another fellow had had our hands all over the output hookups, and the only reason we'd let go was that we had to reach way over sideways to plug the thing in. Otherwise, we'd have gotten a good jolt of AC--after all, the output is usually a safe thing to touch. Unless, of course, you've got some moron with a warped sense of humor.
Not to mention the fact that he ruined a perfectly good speaker.
And no, in case you're wondering, the powers-that-be didn't do a damned thing to him. If it'd been left up to me, I'd have shot him at sunrise.

Grey

[kelticwizard]

GRollins:

Please keep us posted about your optical approach to speaker motion control. I have been thinking of a similar idea for some time, but never sat down and tried to implement it.

Is there any good reason a servo system cannot be used on ported or passive radiator systems? Most of the systems that use it are sealed. I admit that there is a complication-you have to design a circuit that compensates for the fact that as the ported system approaches Fb, the cone motion is suppressed, although the sound output is not. But I would think such a compensating circuit would not be so very complex. Anyone have any thoughts or experiences on this ?

[Edited by kelticwizard on 11-16-2001 at 08:22 AM]

[walker]

Kelticwizard, the idea of closed loop servo control is to get the best control of the waveform produced. Deep bass notes are a problem because of the intrinsic resonances, masses and inertia/momentum of the driver.
If a ported sub was used it would be very hard to control the port's output.
Thats my take on it.
Regards WALKER

[GRollins]

kelticwizard,
I'll be posting here about the optical feedback circuit, just like I did with water cooling and the SOZ w/current sources. My bottleneck is hours in the day. I'm trying to get some writing done (sold two more stories...yeah!), but am woefully far behind on absolutely everything. Incidentally, in case anyone was wondering, that's why the SOZ/current source thread hasn't moved any faster. I got new & improved current source boards etched and populated, but they kinda got conscripted into the front end of my tube amps. I'll need to make up another pair for the SOZ experiment, but haven't had time.
How a feedback circuit would work in a ported cabinet, I don't know. I tend to think that you'd need a pressure sensor (microphone) in the port, then mix the two different modes of feedback. However, I'm not sure whether that would work well due to the phase differences between the driver and the port. Dunno. Let me get the dingus put together and you're more than welcome to try it out on a ported cabinet.

Grey

[pkgum]

what is the best ultra excursion driver u guys have seen?