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Ohm Switch/ Dual Voice Coil Questions...

Discussion in 'Amps and Cabs [BG]' started by bigblondeafro87, Oct 17, 2009.

  1. Hey all, I have to do a project for my sophmore engineering clinic at Rowan and I chose to do it on making a speaker cabinet designed for a working musician who may face a large variety of sizes of gigs, while still accomadating to limited stage room.

    My plan is to design a 2x12 speaker cabinet with a switch from 4-8 ohms and fit easily in the back seat of most cars. The technology of the switch is what I will be doing the majority of my research on, and so far all I have found on the subject is the Epifani DIST system, the failure of the Accuswitch, and I heard rumour of a a similar device in a Mesa cab....

    I've read that the dual voice coil has an effected high frequency range because of the extra weight on the speaker, so I'm also looking at any other solutions. Couldn't a large resistor be hooked up so that when the switch is turned to 4 ohm, the resistor will run in series with the speakers?

    My question to you is if you have any knowledge on this subject or links to any helpful articles, put em up!
  2. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    sure, you can use a resistor, but the resistor will just be converting its power to heat which, IMO, is not a good way to go about it.
  3. A transformer works. Just not worrying about it works to.
  4. 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)
    With a resistor, you will lose more than you gain.

    A 4-ohm resistor in series with a 4-ohm speaker, to give you 8 ohms, will result in a major hump in the bass response because the driver's Qes will be doubled. You'll also lose 3 dB of efficiency.

    Bypassing an 8-ohm speaker with an 8-ohm resistor to give you a 4-ohm load will usually reduce the power delivered to the speaker to less than if you'd left it at 8 ohms. Bypassing with a resistor will never increase the power delivered to the speaker, and in this case will just make life harder for your amp.

    An autoformer or transformer is a better solution... but the ones I've see that can handle a lot of power are pretty expensive.

    If you have a dual voice coil speaker and you only run one voice coil, the Qes will be halved and the efficiency reduced by 3 dB (relative to using both coils), just like running a resistor in series. This applies whether you normally run the dual coils in series or in parallel. So that's not a practical solution either.

    It MIGHT be practical to make a dual coil speaker with one 4-ohm coil and one 8-ohm coil, and just switch back and forth between them. I suspect it would take some juggling and optimizing and compromising to minimize the tonal change going from one to the other.

    As I recall, Alex Claber of Barefaced Bass thought of this before I did.

    related link: http://www.talkbass.com/forum/showthread.php?t=532441&highlight=dual+voice+coil
  5. That's what I thought, and a resistor that large should be pretty heavy as well... This is probably not the proposed solution I'll use.

    Just not worrying about it? Did you read my post? This is for a paper, I saw a problem and and making a proposal for a solution. Some people need the volume of their amp at 4 ohms into one cab, but still need the option of running two cabs at 4 ohms and can't affor to buy three cabs.

    I'm going to do more research on the topics of dual coils and transformers, especially after reading through that thread :confused:

    I just thought of another possible idea, wouldn't it be possible to create a speaker cabinet that makes it very easy to change out a speaker? That way you wouldn't have to worry abput efficiency or sound quality losses from the dual voice coils, although it may be rather unmarketable...
  6. It's a problem that doesn't need a solution IMO. All you need is for bass amplifier manufacturers to stop using 4Ω as their minimum impedance. The technology for driving 2Ω and less is quite mature. You can get "car" amps that are quite happy to drive 1Ω loads so why not a bass amp. I can't think of one professional modern stereo power amp that CAN"T drive 2Ω per channel. The lightweights aren't there yet but they will be within the next little while.

    All my cabinets are 4Ω and my poweramps stable to 2Ω. For me there is no problem.

  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Not really. The difference between 4 and 8 ohms at low levels is only 3dB, which is audible, but not huge. At full output from the amp it's more like 2dB, as amps can't actually put out twice as much power into 4 ohms as they can into 8.
    There is no problem. The notion that one needs to have as low an impedance load as the amp will run at to 'get all the watts out of my amp' just isn't true.
  8. hm... OK not using this as the basis of my project anymore! Therefore, I declare epifani's DIST technology to be BS

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