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adding a tweeter to my old combo

Discussion in 'Amps and Cabs [BG]' started by jackson0321, Dec 12, 2002.


  1. jackson0321

    jackson0321

    Apr 4, 2001
    Houston, TX
    yeah i have a fender bxr 100 and i want to turn it into like a keyboard/pa amp, i want to buy a little behringer mixer and then add a tweeter. to add teh tweeter all i would have to do is buy a tweeter and a crossover and put it in right??? help me
    thanks
     
  2. Here is the cheap and easy way. Get this (pic attachment)
    from http://www.speakerhole.com/product.cfm?ProductID=498ese and add an L pad to turn them up and down. You don't even need a x-over because piezo's don't respond to frequecies below 2K. Piezo's don't work vary good for hi-fi sound but they will do in a pinch are cheap and will take a beating.
     
  3. Lord Valve

    Lord Valve

    Dec 13, 2002
    Denver, CO.
    Check the attachment.

    Lord Valve
    *******
     
  4. rok51

    rok51

    Sep 2, 2002
    Crawfordville, FL
    If you go with a piezo, I recommend the LeSon tweeter from Brazil. To me, it's a lot less harsh than the Motorola style shown in the link above. It's the same tweeter that SWR uses in their WM series and Henry series. They are available for about $7-12. LeSon does recommend use of a capacitor and resistor to ease the little feller's life. I have retrofitted these, with a switch to my 115 cabs and have been pleased with the results.

    Kim
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    The other good thing about Piezos is that they don't affect the overall impedance. In other words, if the existing speaker is 4 ohms, add the horn and the inpedance is still 4 ohms. Beautiful.

    But if you use tweeter speakers and a crossover, the speakers will increase the impedance. So if you add a 4 ohm tweeter to the existing 4 ohm speaker, the total impedance increases to 2 ohms. You'll blow the amp.

    I say you should go the piezo horn. I used one in my home-made 2x10 which goes down as low as 800hz and as high as 20,000hz. It was a motorolla and cost about $125AUS, but it works great.
     
  6. Lord Valve

    Lord Valve

    Dec 13, 2002
    Denver, CO.
    Nope. Impedance is frequency-dependent. The speaker will have a characteristic impedance at the frequencies at which it is operating, and the piezo will also exhibit this effect. The impedance will be lower over the range at which the two drivers overlap, but higher where they don't.

    Nope. A crossover is a device which sends the woofs to the woofer and the tweets to the tweeter.
    The woofer will exhibit its own characteristic impedance over the range of frequencies it receives from the crossover, and the tweeter will do the same. They are *not* in parallel, but are isolated from each other by the inductors and capacitors in the crossover. A 2-way system utilizing an 8-ohm woofer, a crossover, and an 8-ohm tweeter will have a nominal impedance of 8 ohms, not 4. Of course, the operative word here is "nominal." Impedance is more properly shown on a graph, with input frequency on the X-axis and impedance on the Y-axis.


    Lord Valve
    *******
     
  7. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    A bit technical for me Lordvalve. But it raises the question - when a manufacturer makes a speaker cabinet for sale to the public, and says that it has an impedance of 4 ohms, they're not technically telling the truth are they? According to your theory it's only 4 ohms at certain frequencies and at certain conditions????

    If that's the case you'de be flaunting with danger every time you run 4 ohms into a 4 ohm amp.
     
  8. Lord Valve

    Lord Valve

    Dec 13, 2002
    Denver, CO.
    I don't deal in theories, just facts. ;-) It's a *fact* that a transducer (a "transducer" is a device which changes one form of energy into another - in this case, electrical energy {your amp's output} into mechanical engery {sound} - meaning, in this discussion, low-frequency drivers {"speakers"} and high-frequency drivers {"tweeters"}) will present differing impedances to the power amplifier based on the frequency being reproduced. Note also that this impedance is complex, being made up of an electrical component (the opposition of the magnetic field produced by the voice-coil to the stationary magnetic field of the driver's magnet) as well as several mechanical components, which include the mechanical "spring" of the cone's suspension components (surround and spider) and the opposition offered to the cone by the atmosphere (air) both inside and outside the speaker enclosure. This is why I said impedance is more properly represented on a graph than as just a simple number. However, manufacturers need to give *some* kind of spec related to impedance, and that's what "nominal" impedance is - a number which, given most normally encountered operating parameters, the speaker will not go too far below. The fact that there may be times when the actual (operating) impedance may dip below the nominal (rated) impedance is of little consequence, since these conditions will be transitory, seldom lasting for periods longer than a second or two. Power amplifers can deal with such complex changing impedances quite handily, considering today's advanced designs. BTW, did I mention that a speaker's impedance will rise as the voice coil gets hotter? That's one of the reasons you have to turn your amp up towards the end of each set. That and ear fatigue. Ear fatigue, however, is fairly subjective, and occurs in different people for different reasons. For instance, my ear gets fatigued by only around 10 seconds of rap music, while it can withstand several hours of Bach. ;-)

    Lord Valve
    *******
     
  9. Bigwan

    Bigwan

    Feb 22, 2002
    Ballymena (hey)
    Lord Valve speaks the truth...

    Impedance ratings of cabinets usually refer to the nominal impedance of the cabinet. All you have to do is look at the frequency/impedance plot of ANY driver - this impedance is usually reached at the drivers resonant frequency... (This is the lowest impedance that a driver will reach in normal operation). It's the easiest way to specify the impedance of a cabinet/driver...
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    OK I believe you. Can one of you put all this new info into perspective by applying it to the original problem - ie adding a tweeter or horn to a combo amp.

    Would my original assessment of the situation be OK if I'd used the term "nominal" when I refered the the speakers impedance?
     
  11. Bigwan

    Bigwan

    Feb 22, 2002
    Ballymena (hey)
    The easiest way has already been suggested...

    Simply hook a piezo horn up in parallel with your existing speaker and your impedance will be uneffected (I plan to do this with the cab I'm in the process of building - some piezo horns require a resistor in series with them before the parallel connection with the original driver....)...

    A crossover is not required as piezos are not affected by lower frequencies than they can produce (unlike other Horn types which would just go POP after a short but interesting life!). It will mean that you'll have to control your treble output without using an L-pad though...

    I didn't know until recently that most cab manufacturers only use high pass crossovers to filter out the low frequency component of the signal for the horn/tweeter - they don't actually filter off the high frequency component from the low frequency driver/drivers as it/they just wouldn't produce them anyway!