Conference napalm::guitar

    
    I believe its parallel also.
    
    16 and 16 in parallel is 8 ohms
    
    8 and 8 in series is 16 ohms
    
    

    	You are both right...
    

    Yep, but it's not Ohm's Law.
    
    Bob

    Who's law is it ? Kirkoff ?
    
    Mark Jacques
    

    I don't think the formulas for summing resistances have names, but
    Ohm's Law is E (or V) = IR.  E: voltage, I: current, R: resistance.
    I can't recall Kirchoff's stuff (we're talking 1967!).  
    
    Ohm's law is DC anyway.  Speakers are AC.  In AC, you get into
    frequency dependence and inductive reactance and I don't remember
    what that means but it impresses people when you say it, unless
    they know what it means.
    
    Bob

    Well for starters your 8 ohm speaker has a dc resistance of about
    6 ohms, the other 2 ohms are 'reactance' or essentialy ac ohms.
    
    For all practical purposes though you can use the basic ohms law
    and it's derivatives to figure your speaker impedances.
    
    db2

    Speaker impedance or resistance follows the following formula (parallel) :
    
    (Resistance1 * Resistance2)  /  (Resistance1 + Resistance2)
    
    So.. two 8  ohm speakers in parallel = (8 * 8) / (8 + 8) =  64/16 = 4 ohms
         two 16 ohm speakers in parallel = (16*16) / (16+16) = 256/32 = 8 ohms
                                                                     
    The beauty of this is that it works with different resistances
    like 4 and 8 ohm, or 8 and 16 etc.
    
    Speaker impedance in series is additive : Resistance1 + Resistance2
    
    so.... two 16 ohm in series  16+16 = 32
    
    Your amp will deliver more power into a lower ohm load, however,
    amps usually have a lower limit, if you go below it, you can blow
    your output section. Be careful. 
    
    Hope this isn't too confusing,
    
    Tony

	This works also:

				   1
			   -----------------
			    1    1        1
			   -- + -- + ... --
			   R1   R2       Rn

	Where R1 is the impedance of the first speaker, R2 the second and
	so on for as many speakers as you have in parallel.

	You can also use the formula in .-1 except that for more than 2
	values, you must solve for 2 values first, then use that result
	with the next value then... etc.

Larry

    Apart from the impedance, does it make any other difference if the
    speakers are connected in series or parallel?
    
    I've just built a 2 x 12 cab and I'm now looking for speakers to
    put in it. I seem to remember reading many, many years ago that
    connecting speakers in series was not a good idea, but from what
    I can tell Marshall seem to do it - one of their 4x12 cabinets which
    uses 16ohm Celestions is 4ohm (parallel) /16ohm (series/parallel) 
    switchable - plus a lot of Notes in this conference (espec 900,X)
    seem to suggest that series wiring of speakers is an OK thing to do.
    
    Ignoring impedance, does it make any difference whether the speakers
    are wired series or parallel?
    
    Nick
    
    
     

    The only problem with series wiring is that if a speaker should blow or
    one of the leads opens, you lose all the drivers.  In the case of a tube
    amp this can be disastrous.
    
    The main reason to use series is to *increase* the impedance (going
    parallel *decreases* impedance).
    
    If you use Celestions, for example, and buy 16 ohm speakers, you
    probably want to do parallel, since 32 ohms aint a happening load
    inmpedance!  On the other hand if you use 8 ohm drivers, you can hook
    it up either as 4 ohm or 16 ohm, whichever makes more sense for your
    head.  If it's solid state, 4 ohms is preferable, it it's tube and has
    an impedance selector, it's a wash.
    
                                                     Brina

    Thanks for the information.
    
    I'm using a Hi-Watt R100 Lead head which is 8 or 16ohm selectsble.
    I think I'll buy two 8ohm speakers and wire a switch into the
    back of the speaker cab to select either 4ohm (parallel) or 16 ohm 
    (series).
    
    Thanks again,
    
    	Nick
    

    Well, the other thing is that a lot of company's make combo
    (series/parallel) set up to avoid totally unloading the final drivers
    on the head in case one of the speakers goes fftttts.
    
    GONZO

    
    Is there any way to wire a cab with 4 16 ohm speakers to yield an 
    8 ohm overall resistance ? 
    
     Lv

    > Is there any way to wire a cab with 4 16 ohm speakers to yield an 
    > 8 ohm overall resistance ? 

    Impedance, not resistance. And the answer is no. You can wire
    them for either 4 ohms (all parallel) or 16 ohms (two parallel
    pairs in series), but not 8 ohms.

    -b

    
     Thanks, that's what I figured, but I wanted to make certain.
    
      Lv

    Well, you could wire it for 4 ohms. Then get another one...

    
    Actually, it's one of the Peavey Classic 4x10 speaker cabs.  It's 16 
    ohms in mono mode, and in stereo mode, 8 ohms into 2x10.  My amp has an
    8 ohm external speaker out which can be used with the 16 ohm cab, and
    it sounds great, but there is a bit of a power loss.  But I can also 
    run the cab in stereo, and feed my normal speaker output into one 
    channel, and the external speaker into the other.  Since my amp is a
    12" combo, it definitely sounds lots better through the 4x10's. 
    
     Lv