Attenuator matching question

Discussion in 'Amps and Cabs' started by scottcw, Feb 6, 2008.

  1. scottcw

    scottcw Low rent hobbyist Silver Supporting Member

    Messages:
    3,455
    Joined:
    Jan 8, 2002
    Location:
    Supportland
    I have an amp with 4 and 8 ohm taps. My cab is 8 ohms. With a 4 ohm resistive attenuator, which tap should I use from the amp?

    Also, can anyone explain the tonal differences between a resistive and a reactive attenuator? This would be in line between amp and cab, not paralell.
     
  2. sickboy79

    sickboy79 Member

    Messages:
    10,418
    Joined:
    Aug 17, 2006
    Location:
    Chicago
    I would set it up like this > 4 ohm amp output > 4 ohm atteunuator > 8 ohm cab. I would not run the amp at 8 into the 4 ohm attenuator - that the same as running it into a 4 ohm cab.
     
  3. localmotion411

    localmotion411 Supporting Member

    Messages:
    3,395
    Joined:
    Feb 1, 2006
    Location:
    Madison, MS
    Okay, say you have two identical cabs, one 4-ohm and one 8-ohm. If you set your amp for 4 ohms, run it into the 4-ohm hotplate, and into one speaker cab, will both cabs sound the same?
     
  4. 908SSP

    908SSP Supporting Member

    Messages:
    5,801
    Joined:
    Jun 22, 2004
    Location:
    Michigan
    I don't know do they sound the same? The attenuator won't make them sound different.
     
  5. drbob1

    drbob1 Silver Supporting Member

    Messages:
    22,163
    Joined:
    Aug 9, 2004
    The reactive vs resistive attenuator thing may be a marketing ploy. The idea is that the impedance of a speaker changes dramatically with frequency, and it's not constant when signal is applied but is highest when the voltage first starts to swing and drops dramatically as the voltage starts to drop (the coil of the speaker acting like an inductor). Since attenuators tend to sound less dynamic (more "cardboard" to my ears at high settings) people have done things from using fans or lightbulbs to actually using a speaker with no cone to try and copy the dynamic character of speaker resistance. That said, most "reactive" attenuators have resistors in parallel/series with the inductive load, and the more attenuation you're using the more resistive it becomes-hence not a lot of difference in sound. I personally like Webers stuff: it's not too pricey, lots of options and sounds good to my ears. I only use a bit of attenuation to protect old speakers, 6-10 dB, so I don't notice any significant tone degradation. If you're really trying to drop volume, you're going to have to try a few different brands to see what works for you. Buy used so you won't lose too much money! As to the impedance matching, it seems to me that the speaker impedance is reflected thru the attenuator, so the 4 ohm attn into the 8 ohm speaker should result in about a 5 ohm load. You'd be safe at either the 4 or 8 ohm tap...
     
  6. Ed DeGenaro

    Ed DeGenaro Supporting Member

    Messages:
    18,728
    Joined:
    Jan 3, 2002
    Location:
    Malibu
    Amp set to 4 ohm, into the 4 ohm attenuator into the 8 ohm cab.
     
  7. localmotion411

    localmotion411 Supporting Member

    Messages:
    3,395
    Joined:
    Feb 1, 2006
    Location:
    Madison, MS
    My question is, will the setup that Ed describes here sound different if you switch the cab to a 4-ohm cab instead of an 8-ohm cab?
     
  8. 908SSP

    908SSP Supporting Member

    Messages:
    5,801
    Joined:
    Jun 22, 2004
    Location:
    Michigan
    My answer is do the cabs sound the same or different to start with? Then they will if they don't then they won't. Your amp and attenuator aren't changing in either case are they?
     
  9. localmotion411

    localmotion411 Supporting Member

    Messages:
    3,395
    Joined:
    Feb 1, 2006
    Location:
    Madison, MS
    I think the consensus is that amps sound different at different impedence settings (some say 8-ohms is louder and more open and 16-ohms is sweeter and more compressed). Just curious if anyone knows whether or not the impedence of the cab will have any effect on tone in the same manner.

    Reason I'm asking is that I have a Komet Concorde and an 8-ohm Hotplate, and I'm assuming that I should wire my 2x12 for 8-ohms. Unless 16-ohms would sound better for some reason. A lot of varying opinions about this.
     
  10. Ed DeGenaro

    Ed DeGenaro Supporting Member

    Messages:
    18,728
    Joined:
    Jan 3, 2002
    Location:
    Malibu
    Most likely yes. Just the same as going from a 4 ohm tap to an 8 ohm cab will sound different then 4 ohm into 4 ohm without an attenuator.
     
  11. Ed DeGenaro

    Ed DeGenaro Supporting Member

    Messages:
    18,728
    Joined:
    Jan 3, 2002
    Location:
    Malibu
    I have yet to hear an amp where I don't prefer a matched load to a mismatch.
     
  12. localmotion411

    localmotion411 Supporting Member

    Messages:
    3,395
    Joined:
    Feb 1, 2006
    Location:
    Madison, MS
    Thanks; that is what I wanted to hear. And I trust your judgment. I've heard others say they prefer a mismatch in certain instances, but I don't necessarily believe that.
     
  13. scottcw

    scottcw Low rent hobbyist Silver Supporting Member

    Messages:
    3,455
    Joined:
    Jan 8, 2002
    Location:
    Supportland
    So in the scenario described - 8 ohm amp tap > 8 ohm Hot Plate > 16 ohm cab, is the amp seeing a mismatch or is the attenuator seeing a mismatch? Seems the amp is getting an 8 ohm load from the HP, no?
     
  14. Ed DeGenaro

    Ed DeGenaro Supporting Member

    Messages:
    18,728
    Joined:
    Jan 3, 2002
    Location:
    Malibu
    The amp is seeing a mismatch, depending on how much you attenuate...odB=16 ohm, load=8 ohm and anything logarithmically inbetween.
     
  15. scottcw

    scottcw Low rent hobbyist Silver Supporting Member

    Messages:
    3,455
    Joined:
    Jan 8, 2002
    Location:
    Supportland
    So you would trace the 8 ohm line below once attenuation happens?

    Same scenario for 4 ohm amp tap > 4 ohm Hot Plate > 8 ohm cab, except trace the 4 ohm line below?

    [​IMG]
     
  16. mlj_gear

    mlj_gear Member

    Messages:
    2,311
    Joined:
    Jul 14, 2006
    Doesn't Weber say you can use a speaker of any impedance as long as the impedance of the attenuator is matched to that of the amp, and that the amp will only see the impedance of the attenuator? I'm almost certain I've seen that on his site from time to time. And if the answer is yes, why is the story from the THD folks so much different. Different design?
     

Share This Page