Thought of the day..

Which is dangerous, but hell, thats what this forum is for..

Anyway, thinking about the dual voice coil drivers and that the second VC may be left undriven, but connected to resister for electo-braking. Then thought occures that really you want that resister to be variable based on speed and ultimate voltage. When really fast delta on the voltage, you want *no* braking. But when delta has gone to near zero, and voltage has begun to peak, you want maximum braking.

Now, I understand the servo units use feedback to alter the signal. I am not interested in that approach as I dislike injecting anything into the signal as it would require a great deal of active electronics to accomplish this change. However, I can see a fairly simple device used to change the resistance following the voltage.

Am I nuts? Thoughts on implementing this? This train of thought is for use in a large set of IB's where Qts is lower than optimum for IB use, but with braking, they work. But why give up the lower Q until I have to?
 
A sound thought.
Voltage dependant semi-shortcircuit/excoursion limiting. Just got an idea to use a zener-diode in series with a resistor. A zener sets the attack-voltage, and since it's not entirely linear, makes the attack soft. The resistor decides the dampingfactor/breakforce, and limit the current through the zener!
Why not?

Not encoded ;o))
 
Glad I am not totally nuts...

Pixie - in the two voice coil subwoofers, you can drive the two of them in several ways. Series for 8ohm and Parallel for 2ohm. Or you can drive just one for 4ohm. Leaving a coil open. If you add resistance to this coil, it effectively adds a brake to the whole unit - moving through the magnetic field generates some electical current, burned off by the resister. This process adds Qes and thus increases overall Qts.

(Ignoring phase here - it just complicates the example)

During the peak movements, you want no added resistance. You want it to make the cone go out with the least effort. However, when it has reached its voltage peak, the cone is still tending to go forward, held in check by the speaker spider and surround (and the damping of the amp). If at that moment, you added the resistor to the extra voice coil, it would add to the breaking, thus helping stop the cone where it should be...and yes, giving you increased control on the diaphram.

Keep them thoughts coming... I may build this.
 
If a passive approach to utilizing the second voice coil is what you're wanting, you're wasting a good opportunity:
1) Set up one voice coil as per the typical woofer system.
2) Run the second coil from a separate *lowpass* crossover such that its -3dB point corresponds to the rolloff point of the woofer system as a whole, say, 28 Hz, thus providing extra drive for the woofer just at the point where it needs it. Presto! Instant deeper bass. There have been sporadic commercial efforts in this direction, some of which have been quite impressive. Active versions of this same concept can be truly terrifying.
I don't think you'll find that using the second coil as a brake will prove fruitful. Adjustable damping systems have never worked properly. Even if it's not adjustable, you'll have a hard time integrating it into the overall Q of the cabinet/driver system, ending up either under- or over-damped. (I.e. Q not critically damped.)
That said, it should be a cheap, easy experiment...have fun.

Grey
 
GRollins
As I see it, it's not about extra level at the low end, but meerely a matter of control in the extreme situations in order to avoid damaging the voicecoil.
Sawzall, correct me if I'm wrong.
But GRollins, You're suggestion is absolutely correct, if it's extra 'oumph' in the low end thats the target, and You can ignore the phase cancelations occuring.
 
Just ttying to keep it linear..

Not really caring about the extra hump. Nuff drivers and enough amp cures any of those issues - I eqed the car this weekend. 122dB at 20hz is oppressive and I have no need for any more. What I would like to do it tighten up the bottom. And thats just using two 10" in sealed boxes. (cabin gain is your freind).

And as I design for my house, this is more important. So looking for ways to do so. Big amp with lots of damping helps. Not driving to far past the ends of the voice coil so that when it does come time to bring them back the amp has something to work with and is not waiting on the spider to do it. The active stuff scares me as to just how much does it color the sound? Simple always seems better.
 
Has anyone built a subwoofer with multiple electromagnets?

Like an electromanetic accelerator.

This could be used to create a very long piston action. I would think this would increase the volume of air the speaker would push.

This would provide absolute control of braking, etc. Of course, this would mean the speaker would have to be controlled by a microcontroller.

That's my thought for the day...

Of course, I've been thinking about this for several months. I just don't have the cash or resources to try this idea.

Patent Pending...

pixie
 
Well with enough money

I could dream up a dozen different ways to do it. The servo motor concept is a good one, and have loved it since I heard the first one at a pro sound demo back in the early 80's. But it has had limited money invested in the ideal motor, using lighter weight parts like carbon fiber, super cooled, etc. Ideally, you could use an incredible stiff piston that had little mass, but absolutly controlled by a really strong, but fast as needed motor. All of this is possible, and I think the future since we are running out of material improvements.

I hope to see the day that analog comes back. I am the technical radio and sat business. I know the opportunites that digital is going to bring (and already brought) - lots of new stations with "near" CD quality (near is subject to debate that I will leave alone till another time). But if you have set in a real studio listening to a small string group, recorded on a Studer 950 with $15,000 tube mics (with prewar Nazi tubes, even), then played back in the same studio through about $25,000 of monitors, it still sucks compared to the same thing recorded on really good analog gear. You don't need golden ears to hear the difference. But I can't send that analog up my 4.5m dish to the bird, and then down to the local station near you.

Digital is what we are stuck with. Hopefully, some really bright kids will figure out new materials for high density, high quality analog. who knows? I suspect we are the last generation that will know how good it could sound. The magic that got me sucked into this addiction will be gone.

RANT MODE off
 
Well...speaking as a guy who just this afternoon bought The Trio--Live From Chicago, Verve V6-8420 at my friendly vinyl emporium, I can safely say that I believe in analog. Granted, digital has made great strides from the early 'Pure perfect sound, forever' days, but analog is *far* from dead. Them what sez that analog can't cut it...you know what I say?
GREAT!
Leaves more for me...get outta my record shop, you're driving the prices up.
I have heard SACD and believe that it has promise, but have yet to hear it under controlled conditions. I have not yet heard DVD-A, and have no opinion on its sound quality.
Um...I feel I must express reservations about anyone overdriving a driver so far that it's reaching its mechanical excursion (spider/surround/magnet structure) limits. By the time you reach that point, the driver has been seriously non-linear for a *long* time, and a circuit for the express purpose of limiting the excursion isn't the answer. Either more drivers, larger drivers, or turning down the volume are the answers, not a 'failsafe' circuit to keep the driver from hitting the stops.
122dB at any frequency isn't happenin' by my standards, as it's quantity over quality, not to mention being bad for your hearing. (I look forward to having my revenge on these idiots with their boom-boom car stereos in another fifteen years when they are either fighting encroaching deafness or tinnitus. I, myself, noticed a touch of tinnitus, and started taking all those warnings seriously.)

Grey
 
I hear ya...

No, analog is still hanging in, but few youngsters will be exposed to it the way we were. I had a *very* understanding salesman at a highend store spend many hours with me, auditioning lots of stuff, stuff he knew I could not afford for years, to develop the, well, love of it. To show me that with the right stuff, it was three diminsional. That with the right shopping, you could get OK, if not great, stuff - but ignore all that hype. That the JBL hump was really junk, no matter the sales hype. Yes, it was ok to buy this Grado cart even if it was so much cheaper. Trust your ears. I ended up spending alot of money with him. But he had no way of knowing that. He just did it as part of his service.

With rare exception, that won't happen today. Hell, find a highend store that would let a kid in to listen to everything in the store. Hell, find a highend store period.

And you are right. They are trashing their ears. I eqed the car, but with earplugs. I worked prosound for several years, but allways wore the plugs. Now at 40 I am thankful.

And to your other point. My concern is not overdriving the driver. But even in a non-overdriven driver, they are subject to overshoot - the mass is moving and something has to stop it. There is mechanical effects of the spider and such. There is the damping from the amp. You can provide lots of damping by design (large Q cab), but that has a negative effect too. So to me, I may foolishly look for additional help to keep the driver from that overshoot, even at reasonable levels. And even at reasonable levels, the subwoofer does have to make big movements to get pressure at the lowest of octaves.
 
I used to enjoy spending time with the younger critters back when I was still in the business, as they were somewhat less likely to have absorbed a bunch of hooey from all the ads and stuff. That, and they enjoyed the *music*--unlike so many people who get so wrapped in themselves and in the equipment that they lose sight of the music. Once you get someone who gives a damn about music, the rest will flow naturally, as they will use their ears rather than fall prey to some b.s. techno-hype with lotsa numbers and low distortion. Once you've exposed the lies (and to be fair, there are some people who just don't know any better) they never look back. They always follow the music.
One of my favorite customers was a violinist in the local symphony. She was soooo weary of numbers that didn't mean good sound. I sat her down and let her listen to some decent gear--didn't say a word--and let her ears take a rest. After that...she was hooked. Why? She loved music, and wasn't about to let some stupid numbers tell her that her ears were wrong. Good for her!
As for drivers and low end (home only--I gave up on auto sound years ago), I went from 4xKEF B139 per channel (1/2" excursion--each driver roughly equivalent to a 10") to six 12" (Dayton 'Titanic,' 1" excursion) per channel. I don't play all that loudly, but insist on accuracy, as thirty years as a bassist (plus a love of organs and other low frequency instruments) have taught me that most speakers that claim low frequency accuracy are, to put it politely, not quite realistic in their claims. At any rate, even at what I consider pretty substantial volumes, and with Chinese drum recordings or seriously deep organ pedals, I'm only using about 1/4" transit. My old rig went deep, but got rubbery because the drivers went out of their linear range. This time around, I've managed a lot more accuracy, although I still have much more to do. I won't waste more space here, as I've detailed that project elsewhere.

Grey