Conference napalm::guitar

    
    	Impedance ADDS in series, so you're looking at 24 ohms.
    
    	You can add as many monitors as you want, as long as they're
    	wired in series.  But the output of each monitor will drop as
    	more monitors are added.  The total output would be close to
    	the same, though.
    
    	To add monitors in parallel, make sure the mixer can handle
    	the load.  2 8-ohm monitors in parallel is equal to a 4-ohm
    	load, and 3 in parallel drops to about 1.33 ohms.
    

    Me thinks .0 MEANT parallel, so Shawns note is quit correct.
    Not bad, Shawn.
    
    jc

    
    	I think I botched up the answer for the 3 8-ohm loads in parallel.
    
    	What's the answer, if it's not 1.33?
    
    	Isn't it
    
    	a*b*c
    	-----
    	a+b+c
    
    	?
    

    Yup, it's botched.
    2 8ohm loads is 4 ohms
    4 8ohm loads = 2 ohms
    
    so 3 8ohm loads is somewhere between 2 and 4.
    
    The exact number is not so important as: Can the amp run without
    shutting down at 2 ohms?
    I forgot the mathematical equation for the values....  and it really
    comes in handy when you have a 16ohm and 2 8's and one 4.... etc.
    
    If the amp is mono and has two jacks, it is a convenience thing when
    you want one cable going left and the other going right....
    If the amp is stereo, there's a good chance that each output is capable
    of running a 4 ohm load - or even 2 ohms.    
    
    Generally, the THD and available power before clipping are "cheesy"
    on most amps at 2 ohms.   Better to bite the bullet and get another amp
    rather than run at 2...  (if your kids won't go hungry as a result)
    
    Mike
    

    
    	I think I've got it now:
    
    	a*b*c		512
    	------------ = 	--- = 2.59 ohms
    	ab + ac + bc	198
    

    So, running a four ohm load on each jack ( 2x8ohm monitors each side)
    doesn't come out to an overall 2 ohm load on the jacks combined. Im
    probably still missing something. Why have two jacks 1 inch apart.
    If you can only load the amp so far, and the monitors are connected
    in series, convienience isn't an issue. When and or why would you
    connect monitors differently.
    
                                                         Thanks again

    
    	If there are multiple output jacks on the mixer, each should
    	be able to handle its rated output, be it 4 or 8 ohms.
    
    	It should make no difference to jack "A" if there is some-
    	thing connected to jack "B", and vice versa.
    
    	If both jacks are rated to handle a 4-ohm load, you could
    	hook up a pair of 8-ohm monitors in parallel to each jack
    	and have no problems.  The output would not drop to 2 ohms
    	because jacks "A" and "B" are not connected to each other.
    

    
    
    	Usually MONO outputs are ganged in parallel. 
    
     	IF you try to drive a 24 ohm load with an 8 ohm amp, it will only
     	be able to provide "optimally" 1/3 the power.  Your best bet is
     	to plug (2) 8 ohm spkrs (wired in series =16 ohms) to EACH jack
     	of the amp.  Your total impedance will then be 8 ohms which should
     	make the amp quite happy.
    
    
    	CMD

    
    
    			Oh yeah, the answer is YES!

    Is it a stereo amp?
    it would have each output jack labeled differently  (such as A - B) or
    (1 - 2)
    
    A mono amp generally just has two jacks wired in parallel.  It _is_ 
    convenience if you aren't hooking one monitor into the other....
    
    For instance: You're probably doing this:
    
    [amp]----------[mon1]-------[mon2]
    
    Two jacks would help if you did this:
    
    [mon1]---------[amp]--------[mon2]      (instead of):
    
     /----------------------------\
    [mon1]---------[amp]        [mon2]
    
    (physical placement of amp and monitor speakers make it convenient.  2
    shorter cabels would work in the first and second idea, 
    but not the third... etc)
    
    re: .6   2x8ohm monitors in each jack *would* equal a 2 ohm load on
    the jacks combined.   And they are in parallel, not series.   Almost
    all audio gear (especially Peavey and 'like' components) are parallel 
    wired.
    The reason to use both jacks would be:  If you wanted your monitors 30
    feet apart, and you only had 15ft cables, put the amp in the middle and
    run in two directions.
    
    Does that help???
    
    Then again, if your amp as 2 volume controls on the front, and 2
    separate inputs, it's probably a stereo amp, and could handle 4
    monitors instead of 2 and still run at a 4 ohm load.
    
    Mike  (clear as mud, I'm sure..)
    
    
    

    
    Mike is right. A mono PA amp may provide multiple connection
    jacks, but that is ONLY for convenience and has nothing to
    do with the loading.

    Now, let me take a momentary technical journey here. It is
    correct to say for resistance, ASSUMING THAT ALL LOADS ARE
    EQUAL, that if the loads are wired in series the total
    load is "resistance * n", where n is the number of loads. If
    the loads are wired in parallel, the total load is "resistance
    / n".

    However, when we are talking about speakers, we are not
    talking about resistance; we are talking about impedance,
    which is resistance to AC current. Impedance is not a scalar
    quantity, it is a vector. In other words, although you
    perform the same math operations to calculate the load,
    you must do it with COMPLEX numbers (vectors) not SIMPLE
    numbers (scalars). On the other hand, we can make reasonable
    approximations based on the nominal load impedance given
    for each speaker (which many people mistake for resistance
    and are often quite confused when they take the Ohm-meter
    to the speaker terminals and find something like 6 Ohms
    on an 8 Ohm speaker.) When can we not make such reasonable
    assumptions? When we involve passive cross-overs, which
    might be found in certain monitor cabinets. Don't assume
    you can easily calculate the system load impedance...

    Now, one thing that is clear to me is that .0 is confused
    about what wiring in parallel and series amounts to...
    just because the cabinets are daisy-chained IN NO WAY
    means that they are in series. In fact, in most cabinets
    with an "in" and "out" facility, the net result is that
    to daisy-chain the cabinets actually puts them in a
    parallel circuit!! That means that the total system load
    is always less than the impedance of the individual
    cabinets. I saw the number 24 being bandied around in
    an earlier note, and I believe this number to be in error
    (although I admit I have not following all that closely...)

    My point is, one should definitely NOT assume the way the
    cabinets are wired based solely on the appearance of
    a daisy chain, but if one is determined to guess, guessing
    that they are wired in series is more likely than not a
    bad guess...

    Now what WAS the unladen air speed of an African Swallow...

    -b
        

    I disagree with .7
    It's not a mixer, but an amp.   True, most outputs on mixers are
    individual outs - but not necessarily true on amps.
    Plus, a mixer generally deals with line level signals in the 10-20
    thousand ohm range.
    
    I think it's somewhat confusing.   Someone needs to see this
    equipment....
    Mike
    

    re: .11
    Vectors vs Scalars?  You musta had some training!!!!
    
    Quite true of the dynamics of impedance.  Even Peavey, as "simple" a 
    company as they may seem, has built a subwoofer with an 8 ohm speaker
    that presents a 4 ohm load based on the "compression" of air inside 
    the cabinet, and resultant pressure on the cone....
    
    But let's keep this simple... for humans.   We don't do the 'new math'
    very well.
    
    Mike    (y'know, if two swallows flew side by side, and grasped the
    husk of the coconut with their tiny claws....)
    ;-)
    

    Ok, I can help here.  The amp is mine and Jim is my bandmate.  He
    correctlyy came here to solve a problem that we've been having and I
    wish I'd thought to post here sooner.   So here's the deal:
    
    	I have a basic Peavey monitor amp - model number unknown at
    	the moment - which (if memory serves) can drive 130 W into 8 ohms.
    	It is a mono amp although it has two speaker jacks in the back.
    
    	We also have a total of 4 monitor speakers available, one
        SoundTech, one Yamaha, and two home-grown "near-field" (read
    	small, stand-mounted) units.  Currently we have the SOundTech
    	and the Yamaha daisy-chained off one of the speaker jacks
    	from the PV amp.  But we have 4 singers and we need to find
    	a way to bring the other two speakers into play without smoking
    	the amp.
    
    	It has been my (possibly mistaken) belief that the two speakers
    	daisy chained together, are actually in parallel and therefore
    	presenting a 4 ohm load to the amp.  Since the legend on the back	
    	of the amp only mentions 4 ohms, I'm not certain that it can
    	handle a 2-ohm load.  So I've been reluctant to add the other
    	two monitors to the other speaker jack.
    
    	On the other hand, if the daisy-chained monitors are, in fact,
    	series wired, and the output jacks of the amp are parallel,
    	then I can actually go like this:
    
    	spkr--(series)--spkr--[AMP JACK1 | AMP JACK2]--spkr--(series)--spkr
	
    	with (2) 16 ohm loads in parallel, presenting 8 ohms to the amp.
    
    	I'll bring my ohmmeter to the next rehearsal (tomorrow) and
    	see if I can verify what kind of wiring the speaker daisy chain is.
    
    	Thanks for the help so far guys!!
    
    	Rick
    

    
    	Brian, parallel wiring isn't as easy as R/N.
    
    	3 8-ohm loads in parallel is not 24/3, but
    
    	512
    	--- or 2.59 ohms
    	198
    

    re: .5
    
    Well-- you're getting closer.
    
    Your formula is right--  it's just that 64 + 64 + 64 = 192.
    
    Resistors in series add as the reciprocal of the sum of the 
    reciprocals of resistance values.  So, for 3 8-Ohm loads:
    
    	    1		1
    	---------     -----     8
    	1   1   1  =    3     = - = 2 2/3 = 2.66666667
        - + - + -       -       3 
    	8   8   8	8
    
     (which is the same as 512/192).
    
    
    re: -.1
    
    Note that an ohm meter measures resistance, not impedance --
    an 8 Ohm speaker will almost certainly NOT register 8 ohms of 
    resistance.  

    An ohm meter applies a DC voltage through the circuit being
    tested and measures the resulting current.  Impedance is the
    measure of AC resistance, not DC resistance.  
    
    I personally would not apply a DC voltage to my speakers.
    
    If you have four 8-ohm speakers, wiring them in series-parallel
    will give you a single 8-ohm load:
    
                   +      -     +      -
           +-------speaker1-----speaker2-----+
    	   |				     |
     + ----+				     +---+
    Amp    |				     |   |
     - -+  +-------speaker3-----speaker4-----+   |
        |          +	  -	+      -         |
        +----------------------------------------+
    
    
    Since your speakers, if they have an output jack, probably actually
    wire things in parallel, you'll probably need to make your own
    cable. 
    
    
    Jim

    
    	Interestingly, IMO, the Bose 901's use a series/parallel combo
    	for 9 4" drivers:
    
    	     |
    	sp - sp - sp
    	|    |    |
    	sp - sp - sp
    	|    |    |
    	sp - sp - sp
    	     |    
    
    	I believe this is what it looks like, anyways.
    

    The Peavey 130 watt amp has barely enough power to push 2 monitors.
    If you made custom cables and wired them in series, they'd be nearly
    useless.
    
    Next, trying to keep your custom wiring job intact in a working band
    environment is impossible.   Someone will inevitably replace your weird 
    looking cables with standard and smoke something.
    
    Your idea of:
    [mon1]----series---[mon2]---[amp] 
    is neat, but would take modifications..... (yuck)
    
    Suggestion #1.
    Buy another amp.  Even used.   You need power.   If you went through
    the effort to custom wire these things, you'd have only 32.5 watts of
    power in each monitor.   
    
    35 watts of power is useless.   I may be jaded, but if you can hear
    them fine with 35 watts, you must not even need them.
    
    Suggestion #2.
    See #1  :)
    
    You'll thank me for it later!
    Mike
            Who, after putting the 'big amp' on monitors once, will never
    go back to wimpy, compressed monitor sound.
    

    
    Shawn,

    I'll try and not make you look too bad... but given my training
    as an EE, I think I'm entitled to have a bit of fun now at
    your expense. :-)

    First, as someone already stated, the correct formula for calculating
    the resistance/impedance of parallel loads is to take the reciprocal
    of the sum of the reciprocals of the loads. However, there are
    shortcuts one can use, one of which can be applied in the case where
    all the loads are equal. This is the R/n equation I gave earlier.

    Now, for three 8 Ohm speakers wired in parallel, my equation yields
    a result of: R/n = 8/3 = 2.67

    Now, let's do it the "real way". Let's sum the reciprocals. The
    reciprocal of 8 is .125. Summing that for three loads yields
    .375, the reciprocal of which is: 2.67.

    And Shawn, as they say in the 'box: NNTTM.

    -b

    Jim and Rick;
    4 singers and 2 monitors?
    Tell them to share!   :)
    

    
    Seems like you could get a pretty small, low power amp to drive the
    little monitors and use the Peavey to drive the floor monitors.
    
    Justine

    
    	RE: Brian
    
    	Wow, never even noticed that.  You are quite right.
    
    	And when were you ever concerned about making me look bad?
    
    	8^)
    

    
    
    Unless you're doing acoustic music, a 130W Monitor amp is never
    going to be worth the trouble of carrying it around. You could use
    it for your car stereo, but it's worse than useless for a monitor
    amp. I'm not just saying this to be a smart-ass. You'll never
    get enough sound thru the monitors for the singers to be able 
    to hear themselves. The result will be that they end up having
    to scream to be heard over the onstage mix and damaging their
    voices (this comes from long years of experience trying to sing
    with garbage monitor systems!!) If you're mixing for a rock'n'roll 
    band, you'll need, at the very least, a 400W amp (if there's a 
    Marshall onstage, at least 800W ;^)
    
    So, save your voices, and get more power!!! You can always pick up
    a used Peavey 400W power amp for cheap bucks, it'll be worth it.
    
    Just my 2 cents,
    
    Bill_K

    Thanks for all the advice.  I would respectfully disagree with .-1 in
    that the 130 W amp had more than enough power to drive my own floor
    wedge (the SoundTech) when I was in a loud rock band (and we did have
    a Marshall onstage :-)).  However, the spirit of your reply is noted
    and I agree with it.  Until I got a good sized monitor and drove it
    with its own, dedicated amp, I was working way too hard in competition
    with stage volume.
    
    Our band has independently arrived at the same conclusion as many of
    you all did - buy another monitor amp.  We're picking up a 400W amp
    (Crown, I believe) which will drive the two big wedges.  The Peavey
    130 will drive the two near-field monitors (am I using that term
    correctly?  Small (6") cones, stand-mounted?).  This is country music
    and the stage volume is nothing like what it was in my rock band, so
    the levels we can get from this layout should do just fine.  
    
    The only other improvement we might make is to standardize the monitors
    such that they are all the same make/model.  This will simplify setting
    levels and setup/teardown.
    
    	Thanks again,
    
    	Rick