# Is it taboo to run only one coil on a DVC sub?



## freemind (Sep 11, 2008)

I have heard it both ways.

What do you think?

Have you ever done it?


----------



## King Nothing (Oct 10, 2005)

I dont know that its "taboo" but it changes the parameters of the sub.


----------



## 98kugt (Jul 27, 2007)

I've always heard that its a little dangerous to the sub (more likely to blow or have mechanical problems)


----------



## diamondjoequimby (Jun 30, 2009)

not taboo...just wrong


----------



## frankmehta (Jan 20, 2009)

Yea, nowadays a lot of subs come with slightly cheaper and (hence) slightly less hardy components that used to make up subwoofers of yore.
I dont know if it changes the parameters of the sub but surely puts a lot of load on the poor coil that is being being run at that time..


----------



## Chaos (Oct 27, 2005)

frankmehta said:


> Yea, nowadays a lot of subs come with slightly cheaper and (hence) slightly less hardy components that used to make up subwoofers of yore.
> I dont know if it changes the parameters of the sub but surely puts a lot of load on the poor coil that is being being run at that time..


If anything, autosound subwoofers are much, much more robust than they used to be. Just look at some of the freakishly huge motors and high excursion suspensions that we have on subs these days. 
For the most part, efficiency has been supplanted by heavy-duty power hungry monsters with extremely high displacement capabilities which are built like tanks. Not at all like their relatively delicate predecessors. 


Running one coil of a DVC sub does change the T/S and power handling, but as with anything, if you know what you are doing, there is nothing inherently "wrong" about it.


----------



## Hippo (Feb 12, 2009)

Doing this is not a taboo at all, it just raises speaker's Qts. Sometimes it's usefull. And there's almost nothing about "a lot of load to poor coi"l. It would still dissipate the same amount of heat, as when you use 2 coils.
Sorry for my poor english.


----------



## Oliver (Jun 25, 2007)

As long as you don't mind losing output [ 3 dB ], and using a larger box to make it sound good


----------



## Patrick Bateman (Sep 11, 2006)

It changes the thiele small parameters. In some situations, this could be a good thing. For instance, in an IB install.


----------



## jstutzman (Aug 11, 2009)

I talked to a REP at JL audio about this years ago when a coil of my W3Vd2 opened up. He said what others said above about the Qts. He also said that it limited the power to half of rated power due to the Total coil windings being cut in half. I have been using the sub this way for years. It is in a medium sealed box. This sub is in a daily driver and dont get beat on so no big deal to me.


----------



## chad (Jun 30, 2005)

I don't understand the power handling thing.. I mean unless it's 2 separate coils like in a differential drive thing thent he other unhooked coil will actually act as a heatsink and allow it to have more thermal handling than it did if the driver only had one coil from the get-go. you are just moving dead weight with the unhooked coil and that will change the Q as stated above.


----------



## jstutzman (Aug 11, 2009)

Keep in mind that i dont know much about the construction of subs. He explained it to me like this. (Keeping it simple for me as i know you know more about this stuff than me)

If you have a single voicecoil sub, then you x windings in the voice coil. As current is pushed thru the coil, it produces an electormagnetic field, being this is surrounded by magnet, it repels or attracts depending on which way the current is flowing. This moves the cone. 

If you have a two voice coil sub, then each coil has x/2 windings. therefore both coils have half the current flowing thru them at the same power to produce the same field as the example above. 

If one coil is removed, then you only have half the current flowing thru the coil(total), maybe better is the same current flowing thru each coil but 1/2 is removed, at the same voltage. To get to the sub to move as it was in example one, now current has to be doubled. Therefore limiting the overall power handling of the sub to .5 its power with two coils. He said it was similar to a transformer and said it is similar to how windings of a transformer worked. The other coil would probably be some sort of heatsinc so it probably dont exactly drop by a factor of 2. 

I could have also misunderstood him but i thought we were clear when i was done with the conversation. It made sence to me, but then again i dont have great experience with the internal construction of the sub. If this is way off base, please let me know.


----------



## capnxtreme (Feb 5, 2008)

http://www.diymobileaudio.com/forum...3-sounds-crazy-dvcs-individually-powered.html

http://www.diymobileaudio.com/forum/diy-mobile-audio/17550-dvc-sub-question.html

http://www.diymobileaudio.com/forum/diy-mobile-audio/62448-dual-voice-coil-sub-construction-s.html

http://www.diymobileaudio.com/forum/diy-mobile-audio/54834-4-ch-amp-dvc-sub.html

http://www.diymobileaudio.com/forum/diy-mobile-audio/3855-what-happens-if-u-use-1coil-dvc-sub.html


----------



## Brian Steele (Jun 1, 2007)

King Nothing said:


> I dont know that its "taboo" but it changes the parameters of the sub.


Just short the other coil. The Qts will not shift much, if any.


----------



## jstutzman (Aug 11, 2009)

Brian Steele said:


> Just short the other coil. The Qts will not shift much, if any.


brian, can you comment on my above post about power?


----------



## chad (Jun 30, 2005)

Brian Steele said:


> Just short the other coil. The Qts will not shift much, if any.


OH **** MAN that will cause heat from braking the coil from "back EMF." It may RUIN the power handling


----------



## Brian Steele (Jun 1, 2007)

chad said:


> OH **** MAN that will cause heat from braking the coil from "back EMF." It may RUIN the power handling


LOL....


----------



## Brian Steele (Jun 1, 2007)

jstutzman said:


> brian, can you comment on my above post about power?


If you're talking about the thermal power handling, then that's quite dependent on how fast the magnet structure can wick heat away from the coil (s) before they burn up, so I think it's a bit more complex than just taking the rated power handling and dividing by two.


----------



## jstutzman (Aug 11, 2009)

Brian Steele said:


> If you're talking about the thermal power handling, then that's quite dependent on how fast the magnet structure can wick heat away from the coil (s) before they burn up, so I think it's a bit more complex than just taking the rated power handling and dividing by two.


yea, i agree. if you have 1/2 the total VC missing, then the ratio of heatsink to VC just went up so one coil should be able to handle a little more current than originally. Seems like the mass of the VC compared to magnet would be almost irrelevant. Also the second VC could suck up some of that heat also. 

Too bad someone dont have some subs they want to blow up so we could test this.


----------



## MarkZ (Dec 5, 2005)

jstutzman said:


> Keep in mind that i dont know much about the construction of subs. He explained it to me like this. (Keeping it simple for me as i know you know more about this stuff than me)
> 
> If you have a single voicecoil sub, then you x windings in the voice coil. As current is pushed thru the coil, it produces an electormagnetic field, being this is surrounded by magnet, it repels or attracts depending on which way the current is flowing. This moves the cone.
> 
> If you have a two voice coil sub, then each coil has x/2 windings. therefore both coils have half the current flowing thru them at the same power to produce the same field as the example above.


Correct so far... 



> If one coil is removed, then you only have half the current flowing thru the coil(total), maybe better is the same current flowing thru each coil but 1/2 is removed, at the same voltage. To get to the sub to move as it was in example one, now current has to be doubled. Therefore limiting the overall power handling of the sub to .5 its power with two coils.


And there's the error. Chad already mentioned why. Yes, the one coil is now taking all the current, but there's more metal to dissipate it. It's not like we're literally removing the second coil from the sub.

[By the way, it's not inherently a BAD thing to use a smaller coil. After all, manufacturers decide at SOME point to stop adding mass. There's a reason they don't use 9 lb coils. Yes, a 9lb coil would handle a lot of current, but it would add too much mass to be useful.]

So...anyone know what the difference is between an unused (shorted) coil and a shorting ring? Shorting rings are supposed to be good, right? 



> He said it was similar to a transformer and said it is similar to how windings of a transformer worked. The other coil would probably be some sort of heatsinc so it probably dont exactly drop by a factor of 2.
> 
> I could have also misunderstood him but i thought we were clear when i was done with the conversation. It made sence to me, but then again i dont have great experience with the internal construction of the sub. If this is way off base, please let me know.


One thing to keep in mind is that for years JL Audio had posted on their tutorials section that running a single coil of a DVC sub was WRONG and would result in DESTROYING the speaker. They've apparently softened their stance a bit since then...


----------



## VP Electricity (Apr 11, 2009)

Remember that JL Audio has to cater to the lowest common denominator in order to continue growing... so they don't get theoretical, they just try to keep Skip and Biff out of trouble. 

But yeah, they used to be way militant on that.


----------



## MarkZ (Dec 5, 2005)

VP Electricity said:


> Remember that JL Audio has to cater to the lowest common denominator in order to continue growing... so they don't get theoretical, they just try to keep Skip and Biff out of trouble.
> 
> But yeah, they used to be way militant on that.


Yeah, that's exactly why I wouldn't ask their advice on much of anything.


----------



## chad (Jun 30, 2005)

jstutzman said:


> Too bad someone dont have some subs they want to blow up so we could test this.


I have one to donate


----------



## Chaos (Oct 27, 2005)

I can't remember where I heard this, but my understanding about the power handling was that using only 1 coil reduced total Bl, which in turn would take less power to drive the sub beyond its mechanical limits. The thermal power handling wouldn't be effected that much, since the same mass is still present to dissipate heat.

I am also under the impression that shorting the unused coil reduced the overall inductance, as opposed to leaving it open.

If this is a gross oversimplification, or just plain wrong, somebody say so.


----------



## zoomer (Aug 2, 2009)

Complicated subject
First, here is a link to some explanations 
Thiele-Small Parameters and DVC Drivers
basically Qes is twice that of the normal Qes, and the Qts would change accordingly and would be calculated automatically by the sub design program. Re and Le would be double as well. 

I created the T/S parameters in Win ISD Pro Beta for my Infinity reference 1042W as double VC and with one VC open.. See the results. From the open VC plot, it would sound rather boomy cause of the high Q. You would need a bigger box I think! At 1.5cuft (double the DVC setup) the plot does look better but then the Cone excursion doubles too.. limiting effective power handling. (sorry I didnt show the plots for this.)

As for power handling, Electrically would be about the same since it is really a matter of power dissipation. However, keep in mind that with DVC it is 2 ohms and most amps will deliver twice the power VS the 4 ohms in the open VC setup. Therefore with a given amp, the open VC setup will play half as loud. 

I hope my logic is correct. I would be happy to get feedback on this.

Zoomer


----------



## dejo (Jan 3, 2006)

would it not lower the inductance also?


----------



## zoomer (Aug 2, 2009)

dejo said:


> would it not lower the inductance also?


see my post and link
I depends... compared to what?
using a single VC would have half the resistance and inductance of a series connection DVC
using a single VC would have twice the resistance and inductance of a parallel connection DVC.

Most TS parameters of DVC subs are given with them in parallel. At least what I have seen. 

Zoomer


----------



## B_Rich (Mar 29, 2009)

Uhh a friend of mine had a 12" Type R in his car and he only hooked up one voice coil (it was his first time hooking up a system).

The sub lasted about 4 hours.....


----------



## zoomer (Aug 2, 2009)

B_Rich said:


> Uhh a friend of mine had a 12" Type R in his car and he only hooked up one voice coil (it was his first time hooking up a system).
> 
> The sub lasted about 4 hours.....


This tells us more about how little your friend knew about car audio than anything else... Type Rs are almost bulletproof under normal use. There could have been many reasons why he blew it up.


----------



## MarkZ (Dec 5, 2005)

Remember also that the ratio of inductance to resistance is more important than the absolute inductance value. The ratio is the same whether you use one coil or two coils. When you double the resistance by running two coils in series, you double the inductance (so the ratio remains the same). Run them in parallel, you halve the resistance and you halve the inductance. So, all the configurations give you the same inductance/resistance ratio.

However, it seems to me that shorting the unused coil would reduce the effective inductance of the circuit without changing the resistance. So your inductance/resistance ratio would be BETTER in that configuration.


----------



## zoomer (Aug 2, 2009)

MarkZ said:


> Remember also that the ratio of inductance to resistance is more important than the absolute inductance value. The ratio is the same whether you use one coil or two coils. When you double the resistance by running two coils in series, you double the inductance (so the ratio remains the same). Run them in parallel, you halve the resistance and you halve the inductance. So, all the configurations give you the same inductance/resistance ratio.
> 
> However, it seems to me that shorting the unused coil would reduce the effective inductance of the circuit without changing the resistance. So your inductance/resistance ratio would be BETTER in that configuration.


shorting one of VCs has the same effect on resistance and inductance as leaving one open.. Its just out of the circuit... see my previous post. 
It does improve damping as it is now a closed coil moving in the magnetic field. Similar to connecting it to an amp with zero output inpedance. It increases the damping factor.


----------



## MarkZ (Dec 5, 2005)

zoomer said:


> shorting one of VCs has the same effect on resistance and inductance as leaving one open.. Its just out of the circuit... see my previous post.
> It does improve damping as it is now a closed coil moving in the magnetic field. Similar to connecting it to an amp with zero output inpedance. It increases the damping factor.


How sure are you about that? 

The reason I ask is because my understanding is that the shorted coil acts as a brake, which is analagous to reducing inductance. In effect, you're changing the B part of the inductance equation. I may be overlooking something.


----------



## Oliver (Jun 25, 2007)

I think he justs wants to connect one coil, so he can get the most power he can out of the amp 

He is not looking for the secret to JBL gti subs


----------



## zoomer (Aug 2, 2009)

MarkZ said:


> How sure are you about that?
> 
> The reason I ask is because my understanding is that the shorted coil acts as a brake, which is analagous to reducing inductance. In effect, you're changing the B part of the inductance equation. I may be overlooking something.


The amp sees only the unductance of one voice coil.. 
the other voice coil being shorted is like being connected to an amp with zero output impedance.


----------



## zoomer (Aug 2, 2009)

BTW
just by coincidence I was looking at the box design for a DLS Irridium 10i DVC. The DLS web side specifically says to use only one of the 2 Voice Coils for a sealed box design! 
DLS - Products 
click on the sealed box dialog lower left.. or download pdfs. 

So even sub manufacturers do not think it is taboo!


----------



## chad (Jun 30, 2005)

zoomer said:


> BTW
> just by coincidence I was looking at the box design for a DLS Irridium 10i DVC. The DLS web side specifically says to use only one of the 2 Voice Coils for a sealed box design!
> DLS - Products
> click on the sealed box dialog lower left.. or download pdfs.
> ...


Nice... WIN


----------



## MarkZ (Dec 5, 2005)

zoomer said:


> The amp sees only the unductance of one voice coil..
> the other voice coil being shorted is like being connected to an amp with zero output impedance.


But a current is passing through the shorted coil. This current influences the magnetic field in the gap. This influence can have an effect on the inductance. Motional EMF affects the impedance of a single coil subwoofer in much the same way. The impedance an amp "sees" of a voice coil sitting on the table all by itself is going to be much different from the impedance it sees of the same coil in a speaker in a box.


----------



## zoomer (Aug 2, 2009)

MarkZ said:


> But a current is passing through the shorted coil. This current influences the magnetic field in the gap. This influence can have an effect on the inductance. Motional EMF affects the impedance of a single coil subwoofer in much the same way. The impedance an amp "sees" of a voice coil sitting on the table all by itself is going to be much different from the impedance it sees of the same coil in a speaker in a box.


good to hear from you! 
I did do another web search and found tested TS paramerters under different conditions

woofertester.com
this contradicts what the first web sites has 
(Thiele-Small Parameters and DVC Drivers 
I will try to bring up the contradiction with the 2 authors. 

If you dissagree with this information bring it up with the creators of that data. 
As for in a box vs on the table.. well TS parameters are what we are talking about and they are measured using several methods.. the woofertester site can help you there. I have better things to do ...like installing my DLS speakers and amps into my car!!! 

Have a good weekend

EdZ


----------



## MarkZ (Dec 5, 2005)

zoomer said:


> good to hear from you!
> I did do another web search and found tested TS paramerters under different conditions
> 
> woofertester.com
> ...


At quick glance, the data seems to support what I was saying. From the first link...

Series Parallel Short1 Short2 Open1 Open2
Revc 3.2529 0.7976 1.5885 1.6111 1.6381 1.6149ohms
Le 1.9055 0.4719 0.0967 0.0873 0.4967 0.4691 mH

Shorting the unused coil reduces the inductance considerably compared to the open-coil condition. It also exhibits a lower inductance/resistance ratio than either the parallel or series arrangements (which both exhibit about the same inductance/resistance ratio). So this seems to confirm my original point, that running a single coil can actually be advantageous from an inductance/resistance ratio standpoint.

The only real surprising part to me is that the open coil condition showed an inductance of about half of what I would have expected. Maybe I'm overlooking something obvious.

Edit: For the sake of readability, I've computed the inductance/resistance ratio from the data...

Series = 0.59
Parallel = 0.59
Single DVC (shorted) = 0.06
Single DVC (open) = 0.30


----------



## Chaos (Oct 27, 2005)

MarkZ said:


> Shorting the unused coil reduces the inductance considerably compared to the open-coil condition. It also exhibits a lower inductance/resistance ratio than either the parallel or series arrangements (which both exhibit about the same inductance/resistance ratio). So this seems to confirm my original point, that running a single coil can actually be advantageous from an inductance/resistance ratio standpoint.
> 
> The only real surprising part to me is that the open coil condition showed an inductance of about half of what I would have expected. Maybe I'm overlooking something obvious.


That's what I've heard in the past, only I thought the 1/2 inductance condition was with the unused coil shorted. Apparently not.

Even if you are missing something, which doesn't seem to be the case, you still know more about it than I do.



Changing gears back to another sub-topic:

Practically speaking, does anybody know for sure if energizing only one coil decreases efficiency, or not?

If you were to lose 3db by running only one coil, shorted or not, the whole point of doing that in the first place in order to double power from the amp is moot. May as well just run it with the coils in series, and live with it.


----------



## Oliver (Jun 25, 2007)

Chaos said:


> Changing gears back to another sub-topic:
> 
> Practically speaking, does anybody know for sure if energizing only one coil decreases efficiency, or not?
> 
> If you were to lose 3db by running only one coil, shorted or not, the whole point of doing that in the first place in order to double power from the amp is moot. *May as well just run it with the coils in series, and live with it*.


I would 

Best Option = Amplifier that can run it [ sounds great ], {cost}


----------



## djknowledge (Feb 12, 2009)

i did it before but thats cuz i didnt know i blew one of the voice coils lol


----------

