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Passive Attenuation

Discussion in 'Amps and Cabs [BG]' started by Chris Fitzgerald, Jun 30, 2003.


  1. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    I know this is possible for tweeters on cabs, since many brands and makes have tweeter "pads" which allow you to use as much or as little of the tweeter as possible. But can this be done with an entire speaker cabinet? How, if at all, would adjusting this control affect the impedence load of the amp powering the speaker?

    I'm asking because I've come up with a wonderful setup for DB: an EA iamp 800 powering a VL208 underneath the rack, and a VL108 on top of the rack. The 108 functions as a monitor which aims at my head so that I can hear myself while sitting nearby without having to focus the output of my main cab on my bass, which causes all sorts of problems. (I use the same setup for BG, substituting a CXL112 for the 208 in that case)

    This rig would be just about perfect if I could adjust the volume of the 108 (monitor) independent of the main cab - for DB, this is an issue of balance for convenience, and for BG, it's more a matter of balance to avoid going deaf and blowing up my beloved VL108! So, is a passive attenuation pad possible for the entire 108 in these circumstances, and if so, what would be involved to pull it off? Thanks in advance.
     
  2. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    What you are describing is known as an "L-Pad". They are available in various power ratings and impedance from suppliers such as Parts Express or Madisound. It's function is to maintain a constant impedance load, and dissipate the excess volume as heat. Marshall also makes some large models so that guitar players can push their amps at full power (distortion) into a 4x12 while only allowing a small amount of power to reach the 4x12 to keep the volume down.
     
  3. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    My Gawwwd, why didn't I think of this.

    I'm gonna get an L-pad and put it in a small metal case with both 1/4 inch jacks and speakon inputs/ outputs. Then I'm gonna chuck it in my gig bag.

    The next time I get a case of guitarist De-Ja-Moo (ie I've heard this bullsheit before) regarding his tone/tube drive relationship, I'll pull it out and whack it between his amp and speaker, and turn the speaker down...... brilliant idea if it works. One way to find out.
     
  4. 20db pad

    20db pad

    Feb 11, 2003
    I been everywhere, man...
    None. At all.
    I'm not sure if the L-pads will work with a solid state amp.
     
  5. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    Yeah, but then you still don't have that special distortion you get from cone breakup on the speakers ... there's always a reason for guitar players to play too loud.
     
  6. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Why wouldn't they? Don't get me wrong - I have no idea about this stuff, but why would solid state be different than tube in this respect?
     
  7. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    You're right, it will work either way.

    Many many years ago, I had 2 speakers that didn't work too well together because one was way more efficient. I put an L-pad on the loud one and turned it down until the balance was right. I used it like this for years and was using a SS amp the whole time.
     
  8. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    The problem with using an L-pad is handling all that wattage. It's not a problem with tweeters because the pad is wired in after the crossover, and higher frequencies take up very little of the overall wattage of a signal.

    The biggest L-pads I've seen are rated at 200 watts, and those are pretty uncommon.

    I suppose you could try it. It depends on just how much you want to attenuate the signal. An L-pad is just an adjustable resistor; you adjust how much wattage passes by, and how much is fed into the resistor and converted to heat. Since you're running two cabs already, the one cab will see no more than half of the i-amps output, or 400 watts max. So as long as you're careful and don't try to attenuate the signal too much, you could probably get away with a 200 watt L-pad. You just don't want to have a resistor rated for 200 watts trying to burn off the full 400 watts. Unless you'd like to contribute to the light show.
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    True but that's not usually what the guitarists argue. They talk about tubes and heat and driving the amp.

    Marshall actually make a device that call the "Power Brake" or something like that, which is designed to to exactly what I want to do with the L pad. The difference is that an L-Pad will probably cost $40 Australian and the Marshall device was $900. You could buy a smaller amp for that :)