Wiring Cabs, Speaker OHMS all in one thread

Discussion in 'The Squawk Box' started by JakeM, Feb 19, 2011.

  1. emptyisvarah

    emptyisvarah Senior Member

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    yes sirs, I was talking abt a 2:1 ratio head to cab. but I meant tube amps and not SS.. is that safe? I run my PV c20 (16 ohms) thru an 8 ohm 2x12 100 watts. so far everythings fine.. on a side note, I run my BF showman (8ohms) thru the same cab which is a tight fit right? but a friendly told me that BF showman can run 4,8,16 ohm cabs as he has been doing that. any truth to this sirs?
     
  2. JakeM

    JakeM Senior Member

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    I have no idea without seeing either the head or cab but It's not wise to mismatch ohms with a tube amp. SS is ok as you will only notice a reduction in Volume but DO NOT MISMATCH TUBE AMPS AND CABS. I cannot make it any clearer. Although there may not be any problems YET there is always a slim chance that down the line there could be one.

    4=4, 8=8, 16=16

    Jake
     
  3. Syn

    Syn Senior Member

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  4. Syn

    Syn Senior Member

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    Hey guys,
    This might seem like a dumb question, but I'm treading on the side of caution. If I have a combo with a 12" 8ohm speaker and a 2x12" 8ohm cab. Does the amp need to be switched to 4ohm to use all three speakers? Is it literally the same as running two 8ohm cabs or am I missing something?
    This is the first time in 11 years I'm not using a standard head/cab setup and if I've got the combo to carry I might aswell use the extra speaker right?
    Thanks in advance.
     
  5. JakeM

    JakeM Senior Member

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    If the amplifiers speaker jacks are wired in series then yes, switching the amp to 4ohms will allow you to run all three speakers.

    Jake
     
  6. Syn

    Syn Senior Member

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    Thanks jake! Just wanted to double check.
     
  7. guitarcase

    guitarcase Senior Member

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    I have a 1 x12 cab. I am going to add a second 1x12. Both will have 16 ohm speaker. How do I wire in a second jack to first 1x12 so I can daisy chain? (this makes it 8ohm?) Anyone got a diagram? Thanks
     
  8. aneas fool

    aneas fool Senior Member

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    Use a "Y" jack cable at Amp which will combine the two 16 ohms into 8 ohms
     
  9. Dwin

    Dwin Senior Member

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    How can I wire 4 8ohm speakers in a 412 to be 8, or 4 ohms total load? I'm having alex B build me a cab, and I already have 2 of the 4 speakers. I'm going to buy two more Vet 30's, and have 4x 8ohm speakers, how can I have him wire the cab to result in 8, or 4 ohms?
     
  10. aneas fool

    aneas fool Senior Member

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    Series two pairs of 8 which will become two 16 each then parallel the two 16 which will then be 8 ohms
     
  11. Dwin

    Dwin Senior Member

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    So, right now I have 2x 8Ω speakers. You're saying I should buy 2x 16Ω speakers?
    Then my cab would have 16 and 8 ohm speakers mixed? And I should have it wired as if it were 2 212's on top of each other, have have the two 16 ohm speakers wired to 8 ohm, and the two 8 ohm speakers wired to 16 ohms?
    I'm just absolutely lost. Should I order 16Ω? or 8Ω? I already have two 8Ω. And I need to know how to wired this thing up! I hate math.
     
  12. aneas fool

    aneas fool Senior Member

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    you need 4 speakers all 8 ohms and they should be the same efficiency ..wire 2 speakers on the right parallel + to + and - to - this will become 4 0hms....now do the same to 2 speakers on the left side which will be 4 0hms....now you have two sets of 4 ohms speakers ...now wire the two sets in series which will make the cab 8 ohms..series is wire - on left set to jack input then wire the + on the left to - on the right and the right + to input jack
     
  13. Resolve

    Resolve Guest

    On my Marshall DSL50 I have one dedicated 16ohm output and the other two are laberlled as "4 & 8 ohm parallel jacks" with a 4ohm/8ohm switch..

    And on my 1936cab it has two inputs the right one labelled "8ohm input 150watts" althought both inputs are also labelled L+R respectively with "stereo 75watts 16ohms" under each..

    Does this mean I'm using the right hand side "mono 8ohm 150watt" input with ONE of the parallel outputs jacks from my head? (selected to 8ohms of course)

    and if I were to use two 16 watt cabs I'd use them with the 8ohm outputs, one in each?
     
  14. cmcoram

    cmcoram Senior Member

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    This is a great sticky! Lots of info. Here's my set-up and question:

    I run two combos. A Crate Palomino V32 loaded with an 8ohm Eminence Governor, and a Marshall DSL 201 loaded with a 16ohm Governor. Each combo has one out for speakers. Neither amp has a switch for changing the impedence.

    How can I run an extension cab, preferably 212s, with each combo?
     
  15. Bigneil

    Bigneil Senior Member

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    My head unit is set on 16 ohms, my cab is rated a 16 ohms, but I just checked the impedance of the cab on a multimeter and it is reading 13.4 ohms. is this a sign that all is not well with the cab? and is the mismatch enough to damage my head unit?


    I am gonna pop the back off and rewire it all with some new good quality speaker wire tonight, i'll check the individual impedance of each speaker in the process...maybe it will help?
     
  16. JakeM

    JakeM Senior Member

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    No mate you're grand! each speaker, when built, is built within certain tolerances of resistence so a 4ohm speaker could actually be 3.4ohms etc. so when you multiply that by 4 you will get a lower reading on the multimeter.

    Jake
     
  17. Bigneil

    Bigneil Senior Member

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    cool:slash:

    I replaced the old wiring with good stuff anyways....it had been badly redone at some point in the past...maybe my imagination maybe not but it appeared to make a difference to the sound.
     
  18. ANEAS

    ANEAS Senior Member

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    Speakers have a nominal rating impedance 4,8,16 Ohms but their voice coil have a lower amount usually 3.5,6,8 and 13.6 and when added together 2 or 4 speaker drivers will measure much lower but they refer to the nominal as the output where they are used
     
  19. JMFahey

    JMFahey Junior Member

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    The DC resistance you measure with your multimeter is usually around 20% less than the rated impedance.
    So 13.5 DCR is correct for 16 ohms nominal impedance.

    When measuring lower values (4 or 2 ohms), remember to first short the multimeter probes together, it won't show 0 ohms but a low value , around 0.6 to 0.8 (even over 1 ohm if too dirty) which is the internal multimeter resistance (wiring/contacts/switches/etc.) so you must substract this from what you measure.
    So if your "parasite" resistance is 0.8 ohms, and you measure 4 ohms from a cabinet, it really has 4-0.8=3.2 ohms DCR ... which would mean 4 nominal ohms.
     
  20. 2themax

    2themax Senior Member

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    I searched through the thread and basically became pretty well lost... so :hmm:

    I've got a Vox AC4TV head (4w Class A) with a 16ohm out going to a 16ohm Egnator 12" Rebel Cab (30w rated). On the 4w setting it sounds great, but on the lower .25w and 2w settings the tone is pretty dark which I think is due to the 12" speaker cab. If I were to build a 2x8" test cab, what ratings would the speakers need to be (ohms/watts - parallel or series)?

    Or would an Attenuator be a better solution? - I bought this little Vox to use in a small area. Hitting the sweet spot on this amp is either really loud at 4w, or undesireable at the lower wattages.

    Will appreciate any ideas on this... :cool:

    Weber 15 Watt Micro MASS Attenuator [att-web-micro-mass] - $85.00 : The Vintage Sound, Your source for vintage tube amplifier and guitar parts!

    One of these would probably be a little cheaper than building a new cab.
     

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