Conference napalm::guitar

    I'm not sure I can answer all your questions, but I've done some
    re-loading and re-wiring of my speaker cabs before, so I can provide
    some info.  I'll start with the simpler 2x12 configuration.  In
    a series circuit the impedance is additive, therefore 2 eight ohm
    speakers wired in series would yield a 16 ohm load. The formula
    for calculating the impedance in a parallel connection is:
    
    		1   1   1
    		- = - + -
    		X   Y   Z
    
    where X is the total impedance and Y and Z represent the impedance
    of the individual speakers.  That would give a total of 4 ohms for
    two eight ohm speakers wired in parallel.
    
    Most 4 x n cabs I've seen are wired in series/parallel combination,
    which yields a total impedance equal to the impedance of one speaker
    (provided all 4 speakers have the same impedance rating.)
    
    Four 8 ohm speakers wired in series would give a total impedance of 32
    ohms, and a parallel connection would give a total of 2 ohms.
    
    I hope this has been some help.
    
    /Steve

    My cabs have 2 16's in parallel for 8 total ohms;
    this is then in series with an 8 ohm yeilding 16 total, for a 3x12.
    

    .1 is exactly right. 
    
    It's true that speakers do not act like resistors, but all you are
    trying to calculate is *nominal* impedance. Resistors have the same
    resistance regardless what signal you put through them. Speakers
    impedance varies with frequency, however, for the purpose of matching
    speakers to amps, nominal impedance is all you need to know.
    
    	Wire it up series/parallel for an 8 ohm load and you should be
    all set.
    
    	Good luck. BTW, what are you strapping this beast to ?
    
    	Mark
    

    Thanks to you all, that REALLY helps.

    >It's true that speakers do not act like resistors, but all you are
    >trying to calculate is *nominal* impedance.

    THANK you!!!  That was the piece of the previous discussion I was
    missing.  That had me really confused.  Your explanation really
    clarifies it for me.

    So, just to make sure I'm clear on this...  From my original question,
    this would be the correct diagram for series/parallel (which using 8ohm
    speakers would be an 8ohm wiring)?

              |------|-(-)
         (+)--|-----||
           |  |     ||
       ----||-|- ---||---
       |  /--\ | | /--\ |
       | |    || ||    ||
       |  \--/ | | \--/ |
       |       | |      |
       |---||--| |--||--|
          /--\     /--\
         |    |   |    |
          \--/     \--/
    
    If I wire this in this way, can I use a common ground through all the
    speakers?  

    I've been thinking and what I'd eventually like to do is wire the
    cabinet in stereo, like GK does, where if you plug into only one input
    jack, you get all the speakers wired like a normal mono cabinet, but if
    you plug into both jacks you get a separate stereo wiring.  Given what
    you've told me so far, if I can use a common ground, I think I can do
    this by putting in a jack with a switch in it to disconnect the
    positive wire of one of the series 2x12 sets from the other.  Does this
    sound feasible, or am I way off base?

    >   	Good luck. BTW, what are you strapping this beast to ?

    For now, a Hiwatt 100wt, but sometime in the "near" (near being a
    relative term, if ya know what I mean) future, it'll probably be hooked
    up to a stereo rack setup.  I have most of the pieces for this now, I
    just need the power amp.  Unfortunately, the holiday season is about
    upon us and excess money is starting to get scarce.

    Tanks,
    Greg

I may be confused, but your diagram in .4 looks like a full
parallel wiring to me. I'll attempt a diagram of a series/parallel
set-up and see if I can cloud the issue even more!!! ;-)

	(+) -----------|----------------|
                      (+)              (+)
                      SP1              SP2
                      (-)              (-)
                       |                |
                      (+)              (+)
                      SP3              SP4
                      (-)              (-)
	(-) -----------|----------------|

Make sure and get it right, I hate smoked transformers!!

I'll let someone else cover the mono/stereo switchable wiring
as I am not certain how that would be accomplished.

Steve

    Your diagram in .4 is definately a full parallel circuit. Impedance
    would be:
    
    	1/x = 1/8 + 1/8 + 1/8 + 1/8 = 4/8
    
    	x = 8/4 = 2 ohms.  Very few power amps can handle a 2 ohm load.
    
    .5 has the right circuit diagram for series/parallel. Use this circuit
    for a mono system of 8 ohms impedance.
    
    Perhaps someone can figure out the GK trick, or you could find a friend
    with a cab, and peek inside to see the trick they use. I would imagine
    they use something like a nomalled jack, as found on a patchbay.
    
    

    Ah, I get it now!  (Your diagram is much easier to read too...)  
    Thanks Steve!
    
    I know someone that has a GK stereo cab, I'll see if they'll let me
    take it apart to check the wiring.  ;-)
    
    Greg

    
    A common feature in some cabs (particularly Ampeg) is to use 16 ohm
    speakers, switchable between series/parallel for 16 ohm operation or
    full parallel for 4 ohm operation.  The purpose of this is that when
    using *two* cabs in parallel, put each one in series/parallel (16 ohmms
    each) to get 8 ohms total, still drivable by most amps (as opposed to
    two 4 ohm cabs in parallel, total of 2 ohms, not drivable by most
    amps).  
    
    For stereo wiring, have two jacks to the cab, one a regular 2 conductor
    jack, the other a "switched" jack.  Use the regular jack for mono, both
    jacks for stereo.  I can't draw the wiring easily on this terminal, but
    basically the two jacks are shorted (giving a parallel connection) if
    only the regular jack is used, but plugging into the second jack breaks
    the connection (similar to how headphone jacks turn your speakers off
    on stereos).
    
    Using a series/parallel wiring with 8 ohm speakers, you would get an 8
    ohm mono load or two 16 ohm loads for stereo.  Using 16 ohm speakers in
    full parallel, you would get 4 ohms for mono, two 8 ohm loads for
    stereo.

    Yo EE dudes.........
    
    OK, so I have a 4x12 loaded with 16 ohm speakers wired to 4 ohms. What
    would I do (Keeping in mind I don't know squat about creating loads and
    shorting and stuff....basicly I need a picture or step by step
    directions) to make this 4x12 an 8 ohm stereo 4 ohm mono cab. If
    someone has the time I'd appreciate the explaination, diagram or even
    call me and say "now connect from + on #1 to +..bla bla bal"
    
    Thanks EE dudes. (Mom was righht I should have stayed in Electrical
    engineering)
    
    Brian
    DTN :293-5146 (For those who'd rather call and describe it over the phone)

    
    
      It's easy......
       
                4 ohm mono is the equivalent of all 4 speakers in
    parallel..
                    -> + --> + --> + -- +
                       [     [     [    [      equals 4 ohms 16/4=4
                    -> - --> - --> - -- -   
    
    
    
    Stereo 8 ohms   Left -> + --> +
                            [     [       8 ohms  16/2=8
                         -> - --> -    
                    
                   Right -> + --> +
                            [     [       8 ohms 16/2=8
                         -> - --> - 
    
    
    
                    Hope this helps...
    
                   R.B.

    How do you get them to switch from mono to stereo  though that's the
    concept that I really can't get ahold of.
     
    brian
    
    Oh ya..... thanks for the speedy reply. 

    
       Still very easy....
    
           A switch will be wired in between the 2nd and 3rd speaker
      which will either connect all speakers or segregate the last 2..
                                 
                                  ______ + Left stereo in
                                 |
     + Right ---> + ----> +  --- \----> + ------> +
       S/mono     [       [     SW1     [         [
     - ground --> - ----> -  ---  ----> - ------> -
                                 /
                                 |_______ - Left stereo ground
    
    
       Sw1 would switch 3rd/4th speaker to either the 1st/2nd speaker or
               to the Left input. The double pole/double throw switch wiper
               is wired to the 3rd/4th speaker + and - respectively..
    
                               R.B.

    You can buy switching jacks, like the kind they put in stereos that
    shut off your speakers when you plug in headphones.  These are called
    "closed circuit" jacks.  
    
    For mono, you plug into a non-switching jack and get all four speakers
    connected, plugging into the second (switching) jack connects each jack
    to two speakers apiece.  I won't bother to try to draw this out on a
    VT100...
    
    						Brian

    no switch required!!!!
    just plug both sides into the amp and they will be parallel
    anyway!
    -Bill
    

    Re: .12
    
    I'd avoid a switch and use the jacks as recommended in .13, because the
    day the switch gets bumped into the mono position and you short both
    channels of your stereo amp together will be a sad day indeed.
    
    							Brian

    Re: .14
    
    Geez, how fast can people type around here?
    
    That's right, but you need two speaker cords when running mono.  Using a
    closed circuit jack you only need one when running mono.
    
    						Brian				

    gh's new cab has 15ohm Celestions in it!
    
    Good luck gh!
    ;^)

    What on earth are you taking about???
    
    gh

    15 ohms dude!

    I'd bet no such beast is on earth.
    
    I've noticed when you measure impedance on a speaker, the voltage
    from the VOM battery will make the impedance vary.  A good source
    of speaker info told me that a 4 ohm speaker will measure anywhere
    from 2 to 7 ohms...  Same with others. 
    
    jc

    Thanks guys.........
    
    I'll go to Radar Shack tonoght and get the stuff I need. I appreciate
    the help. 
    
    Brian

    RE: Coop
    
    If dat was da case, how come Celestion went through the trouble to
    print "30wt -- 15ohms" on the back of each speaker?!?"    

I was in a band in college that had 2 monitors with 15 ohm speakers.
When the band broke up & we divvied equipment I got these (and other
things) but could never use them since I didn't have the right cross
overs or whatever the heck I needed to drive them. They barely made
a sound on an 8ohm output. I assumed then (and still do) that 15ohms
is real (real weird) speaker for fun (weird fun) configurations...

    
    
    
    
    
    
                  I know you all already know this, but
    
    
    
    
    
    
           Resistance does not equal impedance except at 0 Hz.
    

    
    It's my opinion that 15 ohms is close enough for rock and roll.
    Two in parallel make 7.5 ohms and you can't tell me that that 
    a big deal to an 8 ohm output. I'd use 'em.
    
    RE: .23
    
    Butch,
    
    A 15 ohm speaker connected to an 8 ohm output will make
    lots of sound unless there's something dreadfully wrong with it. 
    It's not a good match but it will make plenty of sound. So maybe
    that speaker is blown. Does the cone move? If so, does it make
    a rubbing sound when you push down gently and evenly on the cone?
    If it's hadly making any sound, the voice coil could be jammed.
    
    --rjb

    Strange...
    
    Are these Green Backs ??
    
    And I would say that 15 ohms is close enough to 16 to run off a
    marshall.  :)
    jc

    I seem to remember from my electronincs training (many years
    ago that:  (R=resistance, same for impedence)
    
    series: R1+R2=Rt
    
    paralell: 1/R1 + 1/R2 = 1/Rt (LOTS less than half of sum)
    
    chuck
             

    
      If all R's are equal you can devide by the R by the number of R's..
    
     Or use the 1/R1 + 1/R2...+ 1/Rx = 1/Rt (total)...method 
    
                                         R.B.
                  

    
    	In the UK, their nominal impedance of 15 ohms is equal
    	to the USA 16 ohms. There is no electrical difference.
    
    	Neal
    

     Sorry kids but impedance=resistancecoupled with reactance which
    means that your speaker which is a coil of wire surrounded by a 
    magnet is a inductor and will have a definite change in the 
    "resistance" you measure as you change the frequency of the
    signal passing through it.
     Anyway you would need 2 cords to run the cabinet in stereo
    ....why go through a whole Rube Goldberg setup to 
    avoid carrying an extra cord when running mono?????
    -Bill

    re: .30
     You are correct that impedence changes with frequency.
    for coils it is:       for capacitors it is:
     I=2(pi)FL                    1
                               _______
                               2(pi)FC
    I=impedence
    F=frequency in hertz
    L=inductance in henrys
    C=capacitance in farads
    
    These properties are put to great use in crossover networks
    (for example). Impedence in coil increases as frequency rises
    letting the woofer get only lows. Impedence rises in capacitor 
    as frequency drops letting tweeter get only highs.
      But a coil and capacitor do have static resistance (coils
    approach 0, capacitors approach infinity). In an 8 ohm speaker
    the voice coil would measure approx. 8 ohms with an ohmmeter.
      Amps are designed with a certain load (speaker) in mind.
    They work best (without damage or diminished sound) when amp/
    speaker (load) are correct.