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rewire 8 Ohm cabinet to 4 Ohm (clear explanation needed)

Discussion in 'Amps and Cabs [BG]' started by pablomigraine, Jun 24, 2005.


  1. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    Okay Have my new Monster 410 from Basson. It's rated at 8 Ohms but has 12lb magnets and it needs 750 watts rms to really breathe. In other words, when you turn up the Bass, the cones begin to sound "fuzzy". This is not farting or overdriven cones, it's a matter of the magnets not getting enough juice from the 480 watts @ 8 Ohms head to run the voice coils efficiently.

    As I understand it, as there have been some threads on this, the conversion is relatively simple. However, amongst the chiding and silly arguments over who knows how much and who has been doing whatever longer than the other etc....there hasn't really been a clear explanation on how to accomplish it, or at leats not one that i could find searching the forums.

    If anyone knows EXACTLY HOW TO DO IT please post, or if you know where to find a diagram that explains specifically how to rewire 4 8ohm speakers into a 4 ohm total load, please explain. Thanks.

    :help: :help: :help: :help: :help: :help: :help: :help:
     
  2. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    I don't buy the "magnets not getting enough juice" explanation. I've never heard of such a thing from a reputable source, nor have I ever seen it. My guess is that your amp is clipping. Or that your pushing your speakers into overexcursion when you pump up the bass. Perhaps you're trying to get bass at a frequency that the cab design doesn't want to give you. What amp are you using now, and how many watts do you have available?

    But as for the question, you can't just rewire four 8 ohm drivers to get a 4 ohm load.

    Series = 32 ohms
    Parallel = 2 ohms
    Series-parallel/parallel-series = 8 ohms

    There's probably a complex way of arriving at 4 ohms that involves wiring in extra components, but IIRC you would lose more than you gain.
     
  3. unrealrocks

    unrealrocks

    Jan 8, 2004
    I allways thought the only way to achieve 4ohm from an 8ohm cab is to put in a dummy load, which won't give you anymore power than you allready have as you will simply dissapate the extra power as heat (through the dummy load).
     
  4. 8mmOD

    8mmOD

    Mar 20, 2005
    USA
    I endorse & use Tech 21 pedals, Eminence loaded cabs, EMG pickups, Jim Dunlop picks & Ernie Ball Strings, BC Rich Basses.
    this is not possible.
     
  5. Unreal rocks is correct. You can change the impedance of a 4x10 by a factor of 4 2 different ways.

    Depending on the how its currently hooked up. If they're currently hooked up series-parallel Richard has it exactly right.

    That means you have 4, 8 ohm speakers.

    Randy
     
  6. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    I dont know enough about this stuff to say you're wrong, but what about all the cabinets loaded with 8 ohm Eminence drivers that are available as either 4 or 8 ohm cabs? what about switchable cabs (accugroove?) some of thos have 8 ohm cabinets
     
  7. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    going to check that the speakers are 8 ohm right now....
     
  8. 8mmOD

    8mmOD

    Mar 20, 2005
    USA
    I endorse & use Tech 21 pedals, Eminence loaded cabs, EMG pickups, Jim Dunlop picks & Ernie Ball Strings, BC Rich Basses.

    Basson directly told me the speakers were front loaded & sealed with silicone. Break the silicone seal... void the warranty... actually that may have been their guitar cabs, but I imagine bass cabs as well.
     
  9. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Those Eminence drivers are not all 8 ohm, they are 8 or 16 ohm and are chosen depending on the desired total cabinet impedance.

    The concept that you don't have enough power for the magnets makes no sense, as the reason for oversize magnets is to increase driver sensitivity, which should reduce the power requirement. However, it is also quite possible that in the quest for additional sensitivity the boys at Basson went too far. One consequence of larger magnets is reduced Qts, and a direct result of reduced Qts is loss of bass response. The bass can be regained through the use of EQ, but that requires power, and lots of it.

    Your only rewire option is to 2 ohms, which is only possible if your amp will handle the current load.
     
  10. Passinwind

    Passinwind I Know Nothing Supporting Member

    Which ones, specifically, are you referring to? There are also 4 ohm, 16 ohm, and 32 ohm Eminence drivers, and for a given configuration (say 4 X 10), one of those will inevitably come into play if there are two inpedances available in the same model cab.

    what about switchable cabs (accugroove?) some of those have 8 ohm cabinets

    That's a patented (or patent pending, at least) Accugroove feature, so you can pay Mark for a cab and enjoy it, or do without, as far as I know. :meh:
     
  11. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    slow down 8mmod..........I'm not a fool........just pulled off the lpad and peeked inside..........
     
  12. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    8 ohm speakers (not proprietary incidentally). The website states a need for 750 watts minimum. This may just be salesmanship, but it's countereffective if so..(name two bass heads make 750+watts at 8 ohms) if people think thier head is insufficient, they'l but a different cab.........

    I've farted out speakers and clipped amps aplenty.........not the same sound I'm getting here...............as far as overexcursion...the cabinets look like 12" ers due to the inch of "M" roll surround.............

    either way, if i cant rewire it, I'm faced with the choice of scrapping my GK head for a pre / power setup and spending more dollars to get it, or returning the cabinet..........
     
  13. 8mmOD

    8mmOD

    Mar 20, 2005
    USA
    I endorse & use Tech 21 pedals, Eminence loaded cabs, EMG pickups, Jim Dunlop picks & Ernie Ball Strings, BC Rich Basses.
    That was just a friendly "heads up" about the warranty. The Basson 410 cabs can't be 4 ohms without replacing all of the speakers... thats one of the reasons why I don't own one.
     
  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I can't comment directly on the driver that Basson uses as I have no personal experience with it. But I suspect that if the specs on that driver were revealed that we'd see a Qts figure well below .2, which means very little bass response without a lot of EQ and thus a lot of power. That would explain the recommended minimum of 750 watts and why it won't work with your amp. That leaves you with two options: a bigger amp or a different speaker.
     
  15. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    stewart 2.1 bridge mono 1300 watts. the 1.6 does a little less. most qsc plx will do 750 + bridged into 8. eden wt-800 800 watts into 8 ohms bridged, swr sm-900 750 or so into 8 ohms bridged...............etc.......... ;)
     
  16. Avatar has 4 ohm drivers made for them. I bought a 4 ohm delta 12lf from them once.

    You CAN NOT wire an 8 ohm 4x10 cab to 4 ohms. I don't know how the accuswitch works but I do know that you CAN NOT wire an 8 ohm 4x10 to 4 ohms.
     
  17. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Personally I would get rid of the cab. It's too bad it doesn't work for your cab but that GK head is awesome.

    What if you keep the cab and your power amp or preamp bites the dust. How easy would it be for you to pick up a new components? Seems to me that it would be easier to borrow a head and I bet that what is readily available is under 750w.

    But then...CAN you borrow enought power to see if you can't live without this cab? Maybe that would be the best way to go for you since you already have it.

    :D

    Joe.
     
  18. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    Well thanx for all the suggestions guys...I've had a closer peek at the cabinet...the speakers definetly seem to be the type engineered for some large scale installation. a Tremendous amount of excursion on them, and the strangest cones I've ever seen. Looks like a normal paper cone infused with parrafin of something. Either way, even with the lack of power from the GK, it sounded AWESOME in the store, so I think I'll keep it, and I've narrowed myself downt to two options:

    Get a GK 2001rbp Preamp and run it with a Crest CPX 1500 Power amp (1000 watts B/M @ 8 Ohms)

    or

    Rewire the cabinet for Two Ohms and Slide a Mesa Boogie Big Block 750 (750 Watts @ 2 Ohms) into my road case...this way i can eliminate my sansamp.....

    is there any real harm in rewiring the cabinet for 2 ohms so long as it's being paired with a head specifically designed to run at 2 ohmns?
     
  19. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    no but label the cab in back as a two ohm cab. in big red warning letters. otherwise one day some poor shmuck is going to plug their 4 ohm minimum amp into it and fry it.

    or.........you could have an amp failure, need to borrow or rent another amp, and find out that you can only get one that is 4 ohm minimum/8 ohm minimum bridged and that night you dont have time to rewire the cab because it's last minute, etc........ ;)
     
  20. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Pablomigraine...are you saying that the cabinet is not loud enough with your 480 watt amp? If your amp is not clipping (causing the fuzzy sound) then maybe the drivers are exceeding their Xmax and causing the distortion. Adding more power is only going to make it worse.

    An amp does not put out its full power continuously...so anything less than a constant sign wave at the particular frequency that the Monster 410's impedance is exactly 8 ohms with an amp that delivers 750 watts at 8 ohms is going to cause the cabinet to draw some other amount of power.

    A cabinet's impedance varies widely with frequency, the rated 8 ohm impedance is an assumed nominal impedance, rated that way so that you choose an amplifier that can handle the load.

    The frequency and signal output from our instrument is anything but constant so the concept of us saying that were constantly giving our cabinets "W" number of watts is pretty optomistic.

    You might want to find out if your cabinet needs to be broken in first. Some cabinets, like Acmes for instance, require a significant break-in period, before the low end capabilities really present themselves. Asking too much of the woofers before they're properly broken in causes creases in the cones and necessary replacement. Something to consider.