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Underpowering Cabinet Question?

Discussion in 'Amps and Cabs [BG]' started by Frankenwill, Dec 8, 2011.


  1. jnewmark

    jnewmark Just wanna play the groove. Supporting Member

    Aug 31, 2006
    Stax 1966
    Third St. Cigar Records staff musician.
    Why do you say SS amps don't get along as well with sealed cabs as they do with vented ? I've brought this up in another thread and nobody seems to agree with this notion.
     
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The average impedance of sealed cabs is lower than that of vented. SS amps don't care for low impedance loads. Sealed cabs are also less sensitive in the lows, and that can result in stressing the current capacity of SS amps in general and those with switching power supplies in particular. By the same token tube amps don't care for high impedance loads and can be bothered by ported cabs.
     
  3. seamonkey

    seamonkey

    Aug 6, 2004
    SS amps are more of an ideal voltage source.
    They do better in all respects of loads.
    There are no systemic problems with SMPS and loads.
     
  4. jnewmark

    jnewmark Just wanna play the groove. Supporting Member

    Aug 31, 2006
    Stax 1966
    Third St. Cigar Records staff musician.
    Would this also apply to the Thuderchild, with both port plugs in ? The reason I am asking, ( and not to get too OT here ), is that I have been fooling around with a TC and a GB 9.0 head, with both ports plugged, and really like the results I am gettin, over the both ports unplugged. Have'nt used it on a gig yet, though.
     
  5. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The permutations are too complex to make a long distance diagnosis, you should just be aware that the possibility for problems exists. Ampeg ran into a major problem with the combination of the Micro VR and two sealed SVT210AV cabs. I haven't seen an official confirmation from Ampeg that it was an impedance issue, but that's what I suspect.
     
  6. Hmmm, no way - how can a cabinet design change the impedance?
     
  7. BurningSkies

    BurningSkies CRAZY BALDHEAD Supporting Member

    Feb 20, 2005
    Syracuse NY
    Endorsing artist: Dingwall Guitars
    Because a speaker is pushing against air (in both directions), that air has an impedance and the speaker impedance reacts or interacts with it, which shifts its own impedance in a given frequency range.
     
  8. +1

    As a magnet moves through a coil it creates current. This current generation changes the impedance seen by the amplifier. Now if the ease of movement of that speaker changes because of a sealed/ported cab, it will also change the impedance see by the head.
     
  9. Skies - can you please provide me with the test documentation that supports this theory? Thanks
     
  10. Oh and why with SS only and not tubes again? Thanks
     
  11. BurningSkies

    BurningSkies CRAZY BALDHEAD Supporting Member

    Feb 20, 2005
    Syracuse NY
    Endorsing artist: Dingwall Guitars
    No test documentation needed. Just to a quick search on free air impedance, feel free to cross search with 'speaker' or 'audio' to clarify further. :)
     
  12. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Nor is this a 'theory'. :rollno:
     
  13. I’ll be darn, thanks Skies.

    I think I’m running on slow today - I read impedance but I was thinking resistance (brain fart). But in any event I just learned something new (cool). Hey, by how much can a sealed enclosure change the impedance and what is the mathematical equation, formula? And I think I need to learn more about peak impedance - you wouldn’t happen to have a good link would you? And I still don’t understand why there could be a problem with SS only and not tubes - can you explain it better?
     
  14. Bassmec

    Bassmec

    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    Tube amps with ultra linear output stages tend to deal with ported cabs better in the low end, after all you don't want flutter on your bottom do ya!:D
     
  15. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    It actually produces a voltage, which may cause current to flow if there is a complete circuit for it to flow through.
     
  16. will33

    will33

    May 22, 2006
    austin,tx
    Easy way to see it is to look at the cab design pdf's at eminences site for the DeltaliteII2512. Compare the impedance curves between the sealed and vented designs as well as the impedance curve for the driver tested in free air. Then compare those to the in box curve for a driver that isn't recommended for sealed enclosures at all. The differences will become obvious.
     
  17. Hey Bob Lee, what is your take or understanding about possible problems with SS amps used with sealed cabinets as appose to tube amps? Thanks
     
  18. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Anything that influences the loudspeaker mechanically or electrically will be reflected in the impedance. Press your thumb on the cone? It'll change the impedance curve. Block the port(s), that'll change the curve also. A tear or slice in the cone will show up in the impedance curve, too.

    Thiele_equiv_circuit.

    (From Thiel_small_analysis)
     
  19. Thanks Will - I just saw you post and I'm soaking it in now.
     
  20. will33

    will33

    May 22, 2006
    austin,tx
    Sure. Some of the math is beyond me, I just know it happens and that's an easy way to see the results of it.
     

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