Running One VC on a DVC Sub

Not in this case as nothing discussed in the paper is theory.  But you can decide to believe what you want.

I owned some Type-R Subs and it said to make sure you hook up both coils. I personaly would be wized if an installer only hooked up one coil of my subwoofer. The last time I made the mistake of letting someone else hook up my system (Best Buy) they put my subwoofer crossover on high pass!

sparky3489 wrote: I still disagree. What a paper says and what has been performed and measured are two different things.

Sparky, did you even LOOK at the paper, and read the whole thing? That paper was written by Dan Wiggins, of Adire Audio. Not EXACTLY the kind of guy to go about spewing crap... If you are thinking that this paper is wrong, where are YOUR supporting documents, papers, webpages... whatever, supporting the validity of YOUR experiments, using SPEAKERS, not MOTORS. Yes, an electromechanical MOTOR will behave as you describe, and while in the most basic of terms, a loudspeaker is little more than a motor, they do not behave the same way. I've already done all of your research for you... Read on. For YOUR theory to hold water, you would need a motor with two distinctly and electrically separate motor windings on the SAME ARMATURE, they must be immersed in the SAME MAGNETIC FIELD... This is the same as a DVC woofer - two motor windings (coils), on the same armature (former), with the same magnetic field (gap), working on the same load (cone). Let's say, to analogize your example of two motors connected by the same shaft, that you put two SVC woofers face to face (with a spacer), and we'll use PP cones, to minimize any air leakage through the cone, we'll seal the edges and holes of both baskets (to prevent leaks). The air mass between the cones will be a bit springy, but so is the wire insulation in your example. Now that we have done this, run a signal into one of the woofers. You will have an output from the backside of the OTHER woofer, correct? Any arguments so far? Now, short the voicecoil of the UNDRIVEN woofer. What will happen? Output will drop, right? This is the SAME thing as the powered motor in your example, being slowed slightly by the electrically shorted motor. Will there be more heat generated in the driven voice coil? Yes, but as the paper by Dan states, and in the case of a woofer with an n0 (eta null) of .4%, or an 88dB sensitivity, somewhere less than .4% of the power input will be additional heat. (Because it is still making output, right?) One more hole in your theory: Electric motors are FAR, WAY, DRASTICALLY, PAINFULLY more efficient at converting electrical power to horsepower power than a loudspeaker "motor" is. They start around 75% efficiency, NOT (up to) 3% as in a loudspeaker's case... I am getting all of my math from this paper, and it's information will be pretty much the same anywhere you look (it was when I looked...) You are trying to place "motors" with two DRASTICALLY different work efficiencies into the same "efficiency basket". They MUST be kept on the same playing field! Again, read on. Let's use a motor with a nameplate rating of 1HP, (about 1000 watts input power) to keep it simple. 1000 watts input generates 750 watts (the 1HP rating) output, with 250 watts being generated as heat in the motor windings. 250 watts is ALL THE MOTOR WINDINGS ARE DESIGNED TO TAKE. If you overload that motor, or captivate the motor shaft, to keep it from turning, now there is MORE power being wasted in the windings, in the case of a locked shaft 4 TIMES or 400% of the motors safe thermal rating, (or ALL 1000 watts ) NOT 100.4% of a loudspeaker's "shorted" power dissipation, of (if we use a 1000 watt woofer, for even playing field) 1004 watts, dissipated from a coil rated 1000 watts... So: shorted motor, rated 250 watts, dissipating 1000 watts or shorted woofer, rated 1000 watts, dissipating 1004 watts Which will fail sooner? The 400% overpower situation, or the .4% overpower situation? I think you'll understand better now. During normal operation, ALL THE POWER BEING APPLIED IS ALREADY BEING TURNED INTO HEAT in a loudspeaker - (almost) 100%. In an electric motor, only 25% is being turned into heat - the remaining 75% is being converted to rotational energy to DO SOMETHING. I'll put it to you this way. Your ideas are wrong. Dan's paper is right. Read the whole thing, and try to learn something. Everybody here learns a little something new, everyday, and you could too, if you would open your mind to it. (AAS... uh, huh... Read, and contribute something helpful... THEN I'll believe you have an AAS with 25 years or whatever you claim...)It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

sparky3489 wrote: Hmmm. I have to admit I underestimated some facts and figures. I have a hard time getting my mind around odd circumstances such as this as I'm as stubborn as they come. I was always told to NOT run one coil by several respectable people for the very fact of inefficiency, less power handling and that it changes the T/S parameters of the sub. Is this true or false?

No, you are absolutely correct, the TS parameters WILL change, but only the mechanical parameters, Cms, specifically. It will go down, affecting the Qts of the driver, usually lowering it, allowing for use in a larger enclosure. Nice, so you can tune (potentially) lower, especially in the case of a vented enclosure. As far as efficiency, I don't think the No (eta null) changes, so the efficiency doesn't change JUST by not running one of the voice coils. Once the second coil is DAMPED, be it with a short or a resistance, yes, the efficiency will drop by a small amount (I think the number is actually 1.5dB with a shorted secondary). Also the efficiency will drop MORE, the LOWER the resistance placed on the second voice coil.

sparky3489 wrote: This also brings up other questions:

(It always will, won't it?)

sparky3489 wrote: Why even run one coil and short the other? Why not get the right sub for the job in the first place?

Well, running one coil and shorting the other is an extreme. Another nice part of having a second voice coil is you can tune the woofer for the enclosure, instead of the other way around... If your box ends up too large, you can install a potentiometer on the secondary coil, and tune the woofer to the enclosure. (once tuned, you can insert a fixed resistor of the appropriate value and leave it there permanently...) I even went so far as to build a "reverse crossover" - an RLC network with a low impedance peak, which allowed me to tune ONE CENTER FREQUENCY out of the response of a VERY peaky system. Worked like a champ. Effectively it was a "one band, passive, parametric EQ".

sparky3489 wrote: Does the power handling get split between the two coils of a DVC? I had always thought so.

When both coils are powered, yes. When only one coil is powered, the THERMAL MASS of the voicecoil and former hasn't changed, has it? The thermal mass of a 1000 watt voice coil, whether SVC or DVC, will only take 1000 watts, ever. Once you pass that 1000 watt range, you will be rapidly moving into a meltdown territory. This means only that now the current supplied to the woofer will be the major determining factor. Because the thermal mass is the same, that means it will take pretty much the same amount of power, right? Current limitations now apply, because a DVC woofer, rated 1000 watts, the manufacturer is expecting 500 watts per coil, so they only provide the voice coil with a gauge of wire rated for 500 watts at THAT impedance. (Actually for a respectable manufacturer, (i.e. NOT AudioBahn) it's a bit more than that, for safety margin... but BASICALLY that's correct) In our 500 watt case, (at 4 ohms) that would be approximately 11A. If properly cooled, and ONLY as an an example, an 11A rated wire SHOULD BE ABLE to take 14 to 15 amps or so for short periods of time, (i.e. dynamic power) providing somewhere in the vicinity of around 780 to 900 watts - this is our derating factor - about 10 to 22%, give or take. Now, because the woofer is not powered at that level all the time, music being the dynamic animal that it is, and the voice coil being cooled simply by moving (remember, dissipating around 499.6 watts already?), the actual de-rating is around 10-20%, as per Dan Wiggins (again, of Adire). Me? I de-rate 25-30%, but that's just me.

sparky3489 wrote: Stubborn, but willing to learn.

Me too... But that's what makes this such a SUPER forum. I learn new stuff ALL THE TIME, and we (they) are always willing to help. P.S. Sorry about the AAS jab... I have no idea of your CV, and I shouldn't have judged.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

sparky3489 wrote: Just for clarity... If the the power handling is halved if only one coil is used since each coil is 500 watts then that's what I could feed it or because of other dynamics at play it changes power handling? What would be the resulting power handling of using one coil of a 1000 watt 4 ohm DVC?

Power handling isn't halved.  I posted this on page 3, but here's a quote by Dan Wiggins explaining how much power handling is cut:

"Lastly, power handling isn't compromised by a factor of 2; it's usually decreased 10-25%. The reason is that rarely are you current-limited by the gauge of the wire, and voice coils are wound concentrically so you still have the entire thermal mass working for you. Just that now all the power is dissipated in a single voice coil (typically two of four layers) so you may end up with an inert, non-conducting thermal mass insulating one side of the voice coil. This does not halve power handling, but can reduce it somewhat."

Dave mentioned he likes to be a little more conservative with that number, which never hurts.  But the above should be fairly accurate.  I believe subs are usually current limited by the glues used to hold the coils together.  When I worked at Adire heading up the warranty department, we normally saw unwound coils when current limits were exceeded.  What a lovely smell those UPS deliveries were.

sparky3489 wrote: I'm in a debate with what seems to be common sense and what's actual.

You would be surprised at how much is counter-intuitive in this field.  A perfect example is the whole transient response and moving mass argument ("a 15 can't be as punchy as a 10").

Steven Kephart wrote: I believe subs are usually current limited by the glues used to hold the coils together.

Ok, now I've heard everything. How in the world can glue limit current flow? This would be saying the glue is acting as a resitance to the coil. Is the glue conductive? wth?

I was using the same wording Dan used above in the quote to prevent confusion.  What I meant was that the weak thermal (heat created by the current) link in a subwoofer is the glues used.  I didn't think I needed to spell it out.