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Accugroove ohm switch

Discussion in 'Amps and Cabs [BG]' started by Chef, Jul 27, 2005.

  1. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    Anyone know how the Accugroove ohm switch works?
    Why don't more cab makers offer this?
    I would find it real handy...
  2. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    It's patent pending and thus very secret!

    I've noticed it's only in their dual woofer cabs though, but I can't fathom a way of it working without changing the crossover function (and thus sound); i.e. sharing the bass between the woofers would get you 4 ohms, whilst splitting the upper and lower bass would get you 8 ohms. But that seems far too compromised and everyone says they sound the same regardless of impedance.

    So maybe it's dual voice coils. But that doesn't seem cunning enough to patent!


  3. If it's actually patent pending it doesn't need to be secret any more. The only way it could be legally copied is if it was disclosed before the patent application was made. Of course, Accugroove doesn't stand to gain anything by divulging its design, so why would they? :D

    There are several ways to skin this cat...
  4. All that needs to happen is someone taking theirs apart and examining it. If it's quite so secret, it would either not be in pubic yet, or already have patent coverage (either an approved or pending patent). I'm quite curious too, so I may just check it out myself. The dual voice coil seems like the most reasonable solution to me as well, but who knows?
  5. KJung

    KJung Supporting Member

    Could it be that they wire the cab to 4 ohms and then put some sort of electronics in to increase the resistance to 8ohms when switched? I'd be interested in hearing how they do it. The Groove Shoppe advertises a little box that 'adjusts' the impedence of multiple cabinets... so it seems it can be done without multiple coils, etc. Great option though.
  6. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    Got a link to that little item?
    Can it go "both ways?" In other words make an 8 ohm cab 4, and a 4 ohm cab 8? That'd be nifty...

  7. The speakermate basically uses series/parallel wiring schemes to accomplish this.

    Mark Wright has said that they're not using dual coils. Series/parallel is out too. They've either designed an impedance matching network using passive components or a transformer. At any rate it is a cool option.
  8. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    Is there a "weight penalty" to be paid with this feature?
  9. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    Fremont, Ohio
    Editor-in-Chief, Bass Gear Magazine
    However it works, I do not notice a tonal difference with my Tri 210L or El Whappo (my earlier model Jr. does not have the switch, nor do any of the single woofer models).
  10. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    Fremont, Ohio
    Editor-in-Chief, Bass Gear Magazine
    Nothing even remotely noticable.
  11. KJung

    KJung Supporting Member

    I'm surely not an electronics guy! I do really like this feature. I guess it really doesn't matter how it works (TBers in an earlier thread where this is discussed mentioned that the 8ohm/4ohm setting doesn't change the tone....e.g., mask the clarity when switched a certain way, etc.). However, if anyone figures it out... start a thread please!
  12. K Dubbs

    K Dubbs Just graduated from OSU, Go Bucks!

    Mar 16, 2002
    Toledo, Ohio
    Just so everybody knows I have no affiliation with, nor do I or have I ever owned or even laid eyes on an Accugroove cabinet in person or schematic, so nobody sue me.

    I think I have figured out how they accomplish their accuswitch. With the exception of using woofers that are dual voice coil and switching one on and off (which would seriously alter the performance and sound of the cabinet), there is only way that Accugroove could do it. (as far as my knowledge goes)

    Their method must involve a dual crossover setup that is only possible with speaker setups which contain two or more woofers. The whappo and their other 3/4 way cabinets have either two woofers or a subwoofer and a mid-bass woofer. Without a crossover, two woofers hooked up to an amplifier are going to attempt to produce the full input frequency spectrum from the amplifier. So if you have two 8 ohm woofers, regardless of their design parameters, if you don't use a crossover, they'll both attempt to produce sound accross the full sound spectrum. If the woofers are similar enough in their impedence curves, when connected in parallel, they'll have a total minimum impedence near 4 ohms (no woofer is its nominal impedence accross the whole frequency spectrum)

    On the other hand, if you cross over two 8 ohm woofers in the region where their minimum impedences would overlap (in parallel it would mean a minimum 4 ohms) you can preserve the total minimum impedence of 8 ohms.

    So what I think Accugroove is doing with their accuswitch is switching between two sets of crossovers which make their el whappo cabinet (and other multi-woofer cabs) switch between being a 3 way and a 4 way cabinet (with the mid and high frequency parts of the crossovers the same). Notice that the Accugroove web page no longer has a divided 3-way and 4-way section after their production of the accuswitch cabs.

    I would tend to bet that if you removed the grille from the cab
    and watched the speaker movement at high sound pressures, you'd notice a difference between how the subwoofer and mid-bass woofer move between being set in 4 ohm and 8 ohm operation.

    Again, to protect myself from hatemail and being sued, this is only speculation based on my own personal knowledge regarding electronics and sound amplification technology, and in no way is a testemonial or analysis of actual Accugroove intellectual property. Also, I wouldn't recommend anybody else attempt to produce such an intricately designed crossover network themselves, as the components Accugroove uses must be of the highest quality and expense. (plus it's going to be patent protected!) Anything less than careful design, high quality parts, and proper knowledge of true electrical and sound engineering will likely render a homemade builder with a really heavy paperweight!

    This is a brilliant idea, and I'm glad Accugroove is getting the idea protected by a patent (given i'm right about any of this, of course). Keep on rockin' guys! You've got the innovation and quality components and construction to be in great business. Anybody who owns an Accugroove cabinet should feel happy their their high dollar purchase is worth every penny in design,components, and construction.

    Oh wow...after i wrote this I saw the post by AlexClaber. What a bunch of wasted time writing! Good one on beating me to it AlexClaber.
  13. KJung

    KJung Supporting Member

    K Dubbs.... very cool... I didn't quite get what X was talking about. Anyway, if that is what they are doing, it's very, very clever. It seems like it would change the sound a little bit, but Accugroovers don't seem to notice.

    It will be interesting to see if you two guys are right. If they are doing it a different way.... maybe you two can start a line of your own cabs with your 'proprietary ohm switching' feature :D
  14. K Dubbs

    K Dubbs Just graduated from OSU, Go Bucks!

    Mar 16, 2002
    Toledo, Ohio

    Actually KJung, I'm in the process of starting a company to begin production of a vasty different cabinet product from Accugroove's, and one I think will really turn a bunch of you guys "to 11." But more on that in a few months...
  15. KJung

    KJung Supporting Member

    Keep us informed... good luck with it.
  16. Mario Lewis

    Mario Lewis

    Jul 6, 2001
    Clinton, MD
    I'm not a lawyer (but I did sleep at a Holiday Inn last night...)

    To have a patent pending doesn't mean that it can't be copied. If someone else wants to use it, they just have to compensate the patent holder. The price of that use may be(and usually is) prohibitive to the party requesting to use the patent. As such, the patent holder gets exclusive use of it while the patent is in effect.

    For instance, let's say (hypothetically) that Eden wanted to use the Accuswitch. They'd have to get Accugroove's permission to do so and pay Accugroove on some kind of per cab basis, maybe a percentage of the sales and an out right overall technology use fee. Accugroove can charge what they want - Say $30K for outright usage and $450 per cab sold and a 40% share of Eden stock (again, just hypothetical).

    Eden would then take a look at the proposed deal and decide that it wouldn't be in their best interest (business wise) to enter into that kind of a deal in order to use the technology. As such, Accugroove would continue to be the only cabinet with that feature.

    Any lawyers in the forum??
  17. Jack


    Sep 6, 2003
    Newcastle, UK
    Tag, Im so curious.

    Why doesnt someone just open one up?
  18. jsbarber


    Jun 7, 2005
    San Diego
    Thank you KDubbs for a very lucid analysis of something that many of us have pondered. I am not quite 100% clear on this so let me ask a couple of questions, if I may?

    You explained very clearly how the combination of the two woofers would lead to either an 8 ohm or 4 ohm minimum impedance, depending on whether they were wired in parallel or there was a crossover (between them). Got it. But what about the mid-range and tweeters? Is the operative concept minimum impedance, and is it typically the woofers that determine this, or is there another aspect of the analysis to get to the minimum impedance of the entire cabinet?


  19. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    DFW, Texas
    As Alex said, it seems this method would have some impact on the low end sonics (sound different at 4ohm (3 way crossover -- both larger drivers covering the same range) than at 8ohm (4 way crossover -- less overlap of the two larger drivers)).
  20. K Dubbs

    K Dubbs Just graduated from OSU, Go Bucks!

    Mar 16, 2002
    Toledo, Ohio
    In response to Jsbarber, the middle and high frequency units are likely set up as a total 8 ohm for the mid and 8 ohm for the tweets. You'd also likely have a crossover circuit separating the input signal at the appropriate frequency between their suited operating ranges. This part of the overall crossover network would be the same for both ways of the accuswitch setting (8 or 4 ohms).

    From here there are a lot more guesses and speculations. within any speaker's operating range, the impedence that the amplifier sees from it usually looks somewhat like an upside down shark fin (depending on the tuning/size/dimensions of the surrounding cabinet and any additionally impedence-modifying circuits). This means that for a given speaker in a given cabinet, there is a minimum of one point where the amplifier sees the lowest numerical impedence, and this is where the speaker draws the most power from the amplifier. As you sweep the frequency up within the speaker's operating range, the general trend of speaker behavior is to gain in impedence, therefore drawing less power up there from the amplifier. This is generally how many manufacturers get away with simple high pass filters on horns/tweeters, because the woofer will usually have such a high impedence at this point that adding the tweeter to the mix won't significantly enough lower the overall impedence to dangerous levels for the amplifier (read: below the minimum specified overall impedence)

    Anyway, back to my speculations regarding the accuswitch, with the above information digested, it might make better sense to you when I explain that you can use an 8 ohm tweeter with a 4 ohm woofer. It should make sense because the lowest impedence (and thus highest power draw) will go to the woofer, and while the tweeter will see power, it'll see less of it. You shouldn't, however, use a 4 ohm tweeter with an 8 ohm woofer. This is a bad idea because if your amplifier is rated to go only as low as an 8 ohm load and you hook up this "4 ohm tweet and 8 ohm woof" speaker, the speaker will attempt to make the amplifier put out power at an unsafe level.

    Ok, so from here, lets say the accuswitch is set to 8 ohms (4 way) Each of the speaker components are operating in 8 ohm mode within the overall crossover, and the amplifier will see a few different impedence dips around this area (8 ohmsish).

    In 4 ohm mode (3 way), what likely happens is that just the sub and midbass woofers are run parallel so that the amplifier sees a just one (or possibly two depending on the t/s specs of these low woofers) impedence dip to around 4 ohms and in the mid and high frequency range, dips around 8ish ohms.

    So here's where we get to the point lo-freq was making. With the different minimum impedence sections of the overall cabinet crossover network, the sound should be pretty different due to the difference in power draws from the amplifier, plus the different characteristics of the low frequency section (due to the change in crossover frequencies). This is where attenuation comes into play, and a little bit of counting on psychoacoustic effects of low frequency sound. To be honest I'm not quite sure how you'd go about attenuating the various parts of the crossover networks in order to even out the sound difference between the 4 ohm and 8 ohm parts of the circuit, but it is possible to do so in order to maintain similar sound. Perhaps they throw an additional 8 ohm resistance to the mid and high sections in 8 ohm operation to execute an across the board impedence shift. I dunno, cause i'm speculating. This may also be why accugroove cabs sound so deep in bass, being that the mid and high sections might be attenuated to be less sensitive than the low frequency sections.

    As far as the psychoacoustic effects I was referring to earlier: A long time ago (to me at least since i'm only 23) scientists figured out that human hearing features less definition, distinction, and sensitivity to low frequency pitches than it does to higher ones. My claim here is just that if I'm right about any of the above posting, Accugroove is probably counting on the fact that most people can't tell a difference between a fundamental 40 hz frequency and its second harmonic (80 hz). So naturally if the big switcharoo is in the low frequency section, it'd be a heck of a lot harder to discern a difference between operating modes, especially since in both instances the woofers are still both producing the tones, but just in different proportions.

    Again, don't read any of this like a text book or tech analysis. I'm just an audio and science dork drawing conclusions about a product and circuit I've never seen, based on my knowledge of the limited possibilities of the conventional electronics technology out there.

    Who knows, maybe the Accugroove folks figured out some sorta real magic :bassist: