Conference napalm::commusic_v1

    EIA probably has a standard to do it right in detail.  I heard it
    was measured a 1kHz.
    Measure it with a meter and if it's 6 ohms or more you know it must
    be an 8 ohm speaker.
    Tom

    
    Speaker impedance is a complex reactance function which has a bell
    shaped curve. It is generally rated in nominal impedance. I think
    Tom is right about it being measured at 1khz.
    
    Most speakers are 8 ohm, but this is not a hard and fast rule.
    The impedance should be stamped on the back of the speaker.
    
    Piezo's have no coil, therefore they have no theoretical impedance,
    and for this same reason they draw no measurable current. If you
    tried to force any real power through a piezo, it would turn to
    smoke. Because the piezo has no impedance, it can be ignored when
    calculating the impedance of the entire cab, however, it should
    always be wired in parallel, not series. 
    
    If your cabinet has four 8 ohm drivers, and you want to end up with
    an eight ohm load, wire them into serial pairs, and then connect
    the 2 pairs together in parallel.
    
    
    	8ohms + 8ohms = 16ohms-
                               |== 2 16 ohm loads in parallel = 8ohms
    	8ohms + 8ohms = 16ohms-
                          
    
    Hope this answers your questions.
    
    Mark Jacques
                
    

<<    < Note 1709.2 by ANT::JACQUES >
<                                 -< 2c worth >-
<    Piezo's have no coil, therefore they have no theoretical impedance,
Gee gosh capacitors have no coil, resistors have no coil, they have
    impedance.  I can't find a model for a pizeoelectric Xtal in my
    radio engineer's handbook, but rest assured a complex impedance
    model, perhaps partly active, could be developed.  I imagine they
    are capacitive with some series resistance.   Because
    dc can flow through the xtal, but the energy is spent by the electric
    field causing stresses.
    <    and for this same reason they draw no measurable current. If you
Sure they do. Go measure it AC.
    <    tried to force any real power through a piezo, it would turn to
<    smoke. Because the piezo has no impedance, it can be ignored when
    <    calculating the impedance of the entire cab, however, it should
<    always be wired in parallel, not series. 
>    Mark Jacques
                
    Tom

    FYI pizeo tweeters do have an impedance, it is generally greater
    than 1 k ohm and is therefore usually not required in impedance
    calculations for a speaker cabinet. The regular reostat volume controls
    ( the ones inside the speaker cab for high end) will not work properly
    with these either. Instead use a 1k- 20k potentiometer in series
    with the driver, using the middle and one of the outside terminals.
    Another advantage of these devices is the they do not require a
    crossover because of their impedance curve ( higher at low freq
    that hi)

    < Note 1709.4 by OTOA01::ELLACOTT "Freddie's Revenge" >
>The regular reostat volume controls will not work properly
>with these either. Instead use a 1k- 20k potentiometer in series
>with the driver, 
    
    is this type of pot commonly known as an 'L-Pad' ??
    
    karl

    A pot is not an L-pad and using a post in series with a speaker
    may possibly destroy the power section of an amplifier, especially
    if it's a transformer coupled output stage (read that as big $$ for
    an output transformer, trust me I know this first hand).
    
    Most 8 ohm speakers I have measured with a multimeter read close to 6
    ohms. That's DC resistance and not 8 ohms impedance which is a reactive
    value (ie: this contains a DC resistance value as well as the inductive
    and capacitive reactance of the speaker coils). Maybe this helps.
    
    dbii 

    
    Wirewound pots for audio use are L pads or T pads, depending on
    how they're wound. The L pad is a simple dividing network, just
    like most simple pots. I forget what the T pad looks like.
    
    Even though the piezo has high impedance, I would think you'd still
    need a fairly high power pot (or pad) in that application. Whether
    the normal 5W pot is hefty enough, I don't know, I've never tried
    it. I only use piezos as a last resort, and even then only for the
    8K--> range. They sound nasty below 8K.
    
    CdH
    

    Sorry I've been away for a while, but lets get this right!!!!!!
    
    A piezo is NOT a current device it is a Voltage device, it will
    not pass direct current at all (unless you fry it...xsive voltage)
    but it will respond to ac voltage. The approx voltage at 200 watts
    on an 8 ohm load is 42Vrms, and the calculated current through a
    2k load (approx of a piezo) would be .021 amps with power dissapation
    of .882 watts. but this is still loud. To cause the the voltage
    (&power) accoss the device to drop by one half for instance, a resistance
    of 2k would have to be added in series with the device, and that
    2k would then only be dissapating about 1/4 watt of power.
    
    	The correct value and rate of pot to use would be 2k-5k ohms
    with a power rating of 1-5 watts and should be wired thus:
                  ____________                   
                  V 2        |
    +______/\/\/\/\/\/\/\    |_________+ piezo -___________-
          1            3nc
             <-----cw
    

 
	Here is the drawing again.

    	The correct value and rate of pot to use would be 2k-5k ohms
    with a power rating of 1-5 watts and should be wired thus:
                  ____________                   
                  V 2        |
    +______/\/\/\/\/\/\/\    |_________+ piezo -___________-
          1            3nc
             <-----cw