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Dual Voice Coil bass cabinet speakers

Discussion in 'Amps and Cabs [BG]' started by brianmharrison, Apr 3, 2009.


  1. brianmharrison

    brianmharrison

    Oct 11, 2007
    Atlanta
    Just wondering...why doesn't anyone manufacturer dual voice coil speakers for cabinets? You see this all the time in car audio and it would give you alot more flexibility in wiring or changing the resistance of a cab.
     
  2. jarrod cunningham

    jarrod cunningham

    Apr 24, 2007
    sylacauga alabama
    spector basses
    i have wondered the same thing for years and years ....
     
  3. KJung

    KJung Supporting Member

    The new Epifani D.I.S.T. cabs do this.

    From what I understand, there are a number of reasons this is not common:

    1) Cost... the drivers are more expensive

    2) Demand... I would think the typical 'less gear head' type player doesn't agonize over mixing and matching cabs constantly, and more typically buys the cab or cabs he or she needs in the appropriate impedance given the cab combination and head he/she uses.

    3) 2ohm heads... SO many of these out now, that keeping cab combinations above 4ohms is less of an issue than it was even a few years ago.

    4) SPL.... I'm getting over my head here, but I believe that a dual voice coil driver set to the lower impedance is not identical to that same driver wired for 4ohm operation to begin with (or the lower impedance setting in multiple driver cabs). I could be wrong here, so just posting it as a possible issue for the EE's to either validate or eliminate.

    5) Most small cabs can be pushed to full output with a moderate powered SS head running at 8ohms. So, little advantage for this switching in a 112 or 115 in general.

    That being said, the DIST cabs are due to start shipping relatively soon.
     
  4. brianmharrison

    brianmharrison

    Oct 11, 2007
    Atlanta
    you could wire them in series or parallel so you could possibly raise or lower the resistance of cabinet depending on your changing needs for example
    if you started off and bought a 4x10 cab wired at 4 ohms with dvc drivers you could possibly rewire it to pull 8 ohms so you add another cabinet
    or you could rewire it to 2 ohms to pull more watts from you amp
    right?

    what is DIST?
     
  5. KJung

    KJung Supporting Member


    Your points above are what I tried to address in my previous post. For example, is it a better deal to buy a cabinet that you can switch from 4 to 8ohms so that you can run a single one at 4ohms, and two at 8ohms in parallel when using a 4ohm minimum head, or is it easier to just get a head that can run at 2ohms, which makes the whole thing moot?

    I'm not saying it can't be a cool idea in some cases, but rather given the issues I outlined in my previous post, the demand/interest would seem quite low, given that you would be paying a bit for it.

    If the effiency/SPL issue that I've heard about is in any way correct (and it may not be), then it really is a dud of an idea.

    DIST is a new cabinet line from Epifani that uses dual voice coil drivers in order to be able to switch the cabs from 4ohm to 8ohm impedance.
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Because it's unnecessary. The intent of dual coil woofers is to sum the left/right low frequency content from a stereo source, not impedance selection. 20 years ago when these drivers were designed it was a useful feature. Today it's redundant in both HT and autosound subs, where electronic crossovers are now ubiquitous. For that reason you can expect them to disappear from the scene as older model drivers are phased out.
     
  7. KJung

    KJung Supporting Member

    Hey Bill, I'm glad you showed up here.

    I actually can see a 'use' for this if you have a variety of cabinets and a moderate powered solid state amp that is safe only to 4ohms.

    However, does a dual voice coil driver (let's say 4ohm/8ohm) behave the same as the 4ohm and 8ohm version of that same driver design regarding SPL, efficiency, etc.?

    Put another way, will a cabinet with dual voice coil drivers (lets say a 212) 'set' to 4ohms sound and behave the same as the same cab with traditional single voice coil drivers wired for 4ohm cabinet impedance?
     
  8. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    I'm with Bill on this one. I really see no necessity for dual voice coil woofers. The problem is, as I see it, the poor design of almost all bass specific amplifiers. Very few of them can handle 2Ω loads.

    A lot of players basically grab whatever speakers they can afford with little thought about how they are going to drive them. Yes, I've been there, we all have! Still others want to get the very last watt that their amplifier can give not knowing that the difference between say 300W and 375W is almost undetectable. Add to that players going from tube to SS or vice versa and you are back to having speakers that are incompatible with the newly purchased amp.

    Before I bought my speakers back in, IIRC, '97, I had decided to run them from a stereo power amp one on each channel. This being the case I went with the 4Ω versions. So I had a choice, I bought a power amp capable of 2Ω operation. I can run these cabinets either singly or both on one channel leaving the other channel available for some other use in an emergency.

    Ohms are not a difficult concept and matching your load to your amp is similarly uncomplicated!

    Paul
     
  9. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Pretty much a solution that isn't that needed for a problem that isn't there, and causes more problems than it can solve.

    The big bottleneck in most rigs is not wattage, it's excursion limitations.
     
  10. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    It's not obvoius to me how a dual coil driver could go from 4 ohms to 8 ohms by changing the coils from series to parallel. If anybody else sees how that would work, I'd be interested.

    After thinking about it a bit, here is how I would make a switchable system: One coil is a 4-ohm coil and the other an 8-ohm coil, and we just use one at a time. The unpowered coil would be added mass, but that could be compensated for in other parts of the driver (suspension and motor), at some increase in cost.

    edit: In a similar thread, I now see that Alex Claber came to the same conclusion long before I did, back on 2-26-09.
     
  11. seamonkey

    seamonkey

    Aug 6, 2004
    JBL makes Differential Drive speakers with dual voice coils for pro sound
    http://www.jblpro.com/catalog/support/getfile.aspx?docid=1253&doctype=3
    You can't buy just the speakers though.

    It's really not a big deal to build a self contained powered speaker to get it's max wattage at whatever ohms the internal speaker is. Just design with a higher voltage if the driver is 8 ohms. Maybe amp manufacturers will get smarter about reading the speakers impedance and adjusting voltages. Of course this would get expensive, and bass amps are the only place left where this seems to be a big concern.
     
  12. KJung

    KJung Supporting Member

    The whole point IS the mix and match of cabs and heads in the bass amplifier category. I agree, it would make even less sense in the PA or guitar category. It does seem to be 'bass backline specific', but again seems like a day late and a dollar short to me in these days of 2ohm amp operation and heads with dual power amps built in like Eden, SWR, Genz, TecAmp, etc., etc.
     
  13. brianmharrison

    brianmharrison

    Oct 11, 2007
    Atlanta
    I was really referring to multi driver cabinets like say a 4x10 where both coils are used all of the time and are the same resistance and switching the wiring from series to parallel or vise versa. But really a single driver would apply too. For example, in my car I have a dvc memphis 12. I could have gotten a single coil 4 ohm version but I chose to go with the dvc 4 ohm version for 10 bucks more which allows me to run my audio system in different ways such as
    2 channels, one into each coil for 4 ohm total operation
    bridged series which would be 8 ohms
    bridged parallel which is 2 ohms
    so instead of running 250 watts at 4 ohms, I'm running 500 watts at 2 ohms.

    As for wattage, if you had the option of dvc speakers, it would make a difference in your db output, if your amp doubles in wattage with lower resistance like the above example.

    All these options are with one speaker, imagine if you had multiple drivers, then your options for wiring for different loads would increase significally.
    It just seems to me if you are going to drop a grand or two or more on a boutique cab, should you have this option so you can always get the best performance out of the cab in the most situations?
    Just my two cents worth...maybe I'll build a 4x10 one day using dvc drivers and show you what I mean? It would definitely be way more versatile than anything on the market
     
  14. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    bharrison, to the best of my knowledge there are no off-the-shelf dual-coil woofers suitable for bass guitar use. Not too long ago I had such a woofer custom-made for me (with identical voice coils) by a specialty driver manufacturer (nope, not Eminence), but in the end decided not to have it put into production. My specific application wasn't bass guitar, but the woofer would have theoretically been suitable. Based on my experiences with that woofer, I'm not inclined to go that route again - but that doesn't mean it can't be done and done well.
     
  15. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Two 4 ohm coils. You'd use either one 4 ohm coil for 4 ohms, two in parallel for 2 ohms, two in series for 8. Way more bother than it's worth though.

    Different topology, you wouldn't want to run those with only one coil.
    No. The only reason why players want impedance switching options is for the proverbial 'So I can get all the watts out of my amp'. They assume that their amps need to run at the lowest possible load to drive their cabs to full output. Probably some 99% of the time that's just not the case. If this was a real world concern it would have been addressed decades ago. But it's not, as increasing amplifier power has consistently stayed ahead of the ability of speakers to make full use of it.
     
  16. gerryjazzman

    gerryjazzman

    Dec 31, 2006
    New Jersey
    There is something a bit off here to me. If you have a speaker with say, two 4 ohm voice coils, they each would have the same number of turns "N". Now if that speaker is used as the originally intended purpose of summing two separate amplifier outputs (i.e. subwoofer application), then each amp would see a nominal 4 ohm load. If you connect the two voice coils in series you now have essentially a 2N-turn voice coil. Since the impedance is proportional to the square of the number of turns it seems like the impedance would be 16 ohms not 8 ohms. Remember this is not like connecting two separate speakers in series, the voice coils are in the same magnetic field and act as one continuous voice coil. It's the same as in a transformer winding or even just a simple inductor (inductance is proportional to the number of turns squared and impedance is directly proportional to inductance at a given frequency, so the impedance is proportional to the number of turns squared). It seems like you'd have to have two dissimilar voice coils, for instance a 4 ohm and a 2.828 ohm (4 / sqrt(2)) and use the 4 ohm alone for 4 ohms and the 4 + 2.828 ohm in series for 8 ohms.
     
  17. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Actually, it is. Details of why would bore most readers to tears. Just trust me.
     
  18. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Very intersting post, and it made me think really hard because you have an extremely compelling argument. Good for you!!! In fact I had to have a second cup of coffee before I could come up with a reasonable practical, easy to understand answer as to why it's a linear rather than exponential function. Note that this is not my area of specialty, I encourage others more practiced in the art of electromagnetics to correct me where necessary. It's been a whole lot of years since I thought of this stuff.

    When the two coils are wound on a common form or bobbin in a common field, the winding length increases so you will have the number of turns double (squared term) and the length doubles (linear term) and the squared more or less cancels out. Now this is not entirely accurate but it's part of the reason. When the coils are layered, it's similar because the diameters are different so the linear term is still present (but not identical). The DCR will double because at DC the wire length is the only factor. The other part of the equation is the fact that the wire coil is immersed in a static external magentic field and when the wire coil moves, a back emf is generated which increases impedance as well. Two seperate inductors do not share these somewhat unique properties. Two isolated windings and magnetic fields would tend to behave more as seperate inductances except that the effects of back emf will still be present.

    It's not a 1:1 ratio for a speaker because there are several variables present as well as constants, all of which tend to cancel out to a relatively linear equation.

    A transformer is different in that you have a common magnetic circuit (core) but the magnetic field is self-generated by the current in the wires, so the impedance that the primary sees is not a fixed impedance but a reflected impedance, based almost entirely on the loading of the secondary coil and the coupling of energy through the magnetic field. This impedance does behave as a squared function. (the squared is a function of the number of turns).

    I do not recall which is the dominating factor, I suspect that the numbers will be different with layered versus end to end coils but not sure how much.

    Hope this helps and doesn't cloud the waters too much.
     
  19. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    An easier way to visualize a dual coil woofer is as a single coil that's tapped in the center, just like a center tapped power transformer, which also may be configured series or parallel for different voltages. It's not exactly the same but close enough.
     
  20. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    The pure transformer example doesn't work for two reasons. The first reason is that the impedance of a transformer follows the square law regarding number of turns versus impedance (regardless of center-tapping), and the typical transformer is wound in layers.

    This is why I had to really think about the question, there's a couple of different mechanisms going on within a speaker.
     

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