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wiring dis-similar cabinets in series

Discussion in 'Amps and Cabs [BG]' started by townsley, Feb 2, 2004.


  1. townsley

    townsley

    Nov 10, 2003
    Portland, OR
    I'm thinking of creating a special cable/break-out box in order to wire 2 cabinets in series to avoid putting too much of a load on my amp. I've read some posts that this should only be done if the cabinets are exactly the same, but can it be done with a 1X15 and a 2X10? What are the drawbacks of wiring different cabinets in series (given that the watts and ohms are the same)?

    Any help greatly appreciated Oh Ye Bass Gods.
     
  2. ostrzoskrzydly

    ostrzoskrzydly

    Jul 1, 2003
    Actually I have my old physics notebook where I have notes on that subject in my hand, and I can't really see why wouldn't you be able to do that....
    The main difference is that in serial connections, voltage is constant, and amperage varies based on impedance (sorry for lack of proper terms in english ;) ), while the opposite is true with parallel connections. The power division stays the same, assuming you use same impedance cabs.
    If you use different ones, cabs with higher impedance will get a bigger portion of the power, completely opposite to connecting them in parallel.
    So, in reality...
    BUMP ;)
     
  3. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Sounds about right. Never can remember this stuff without rereading for clarification - series, parallel effects, etc. As long as you don't drop your cabs below the ohm rating of your amp, you're okay regarding damaging anything. But the the more powerful cab will in deed have higher output. You can for example run an 8 0hm speaker off a 4 ohm amp but the output would be half of what an equivalent 4 ohm speaker would be.
     
  4. The real issue here is impedance. The impedance of a speaker changes widely over its frequency range. It gets especially whacky around the resonant frequency of the cab, where impedance peaks to about 4 to 10 times the rated nominal impedance. So an 8 ohms 115 cab may have a 50 ohms impedance at 50Hz, while a 210 may have its peak at 80 Hz. This means, the 115 will eat away all power at 50 Hz, leaving nothing fot the 210 and at 80 Hz, the 210 will draw most power. To complicate matter even more, ported cabs have 2 peaks: one just below the port frequency, and one just above.

    This unbalance will cause problems in the total frequency graph and may rule out certain ranges on either cab. When one cab peaks, the other goes almost silent. This can't be undone, unless you equalize the impedance peaks, which is close to impossible to accomplish at "bassist" power levels.

    In other words: in a series connection the cabs will influence each other. You may like the resulting sound; then again, you may not.

    Series connection is not harmful for an amplifier, be it tube or solid state.

    Parallel connected cabs don't have all these problems.

    I hope this answers your question.
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Thanks Joris. Great info.

    Can I ask why you're trying to give your amp a helping hand? Is it over heating?
     
  6. miccheck1516

    miccheck1516 Guest

    Feb 15, 2003
    Ireland
    Go get the physics book again, and check up before you have this guy blow a speaker by accident, the power output at 8 ohms is about 2/3 of what it would be at 4 ohms. :)
     
  7. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    It's maximum power might be, but at any given level below clipping, the amp's output power will be double into 4 ohms compared to what it is into an 8-ohm load.
     
  8. miccheck1516

    miccheck1516 Guest

    Feb 15, 2003
    Ireland
    I dont really understand this, could you elaborate?

    The way i read it it seems like i would have to have my 65W@8ohm amp Clipping before i would actually get 65W out of it????
     
  9. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    If the amp's not putting out full power, it's not putting out full power.

    If at some given instant the amp's output voltage is, say, 20 volts RMS, then:

    • if the load impedance is 4 ohms, the power it's putting out is 100 watts.
    • if the load impedance is 8 ohms, the power it's putting out is 50 watts.

    Power = voltage^2 / impedance.
     
  10. miccheck1516

    miccheck1516 Guest

    Feb 15, 2003
    Ireland

    Im still none the wiser :confused:
    Would the equation you gave not be true for an amp putting out its maximum power?

    For example, my amp is 65W @ 8ohms, i know it wont put out 130W into 4ohms so the equation must change in some way???


    Perhaps im out of my depth in electronics here :meh:
     
  11. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Into 4 ohms, it'll clip at a lower output voltage than into 8 ohms. That's why its maximum power rating into 4 ohms wouldn't be double its 8-ohm rating.

    Most of the time, though, an amp is operating well below full power. Or at least it is if you chose your amp and speaker(s) right. In this case, halving the load impedance will double the power the amp is putting out.
     
  12. miccheck1516

    miccheck1516 Guest

    Feb 15, 2003
    Ireland
    Thanks for clearing that up, i understand it now. :)
     
  13. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    LOL! That thing again!!!! :rolleyes:
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Joris this part of your post has me a little confused. The frequency/impedance behaviour you described makes sense and I always thought that all cabs were subject to that. If I understand correctly, cabs connected in parallel distribute power evenly if they have the same nominal impedance, even if the actual impedance varies. Am I on the right track?
     
  15. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio

    Pete, parallel-connected cabinets all get the same voltage across them from the amp. As long as the amp has a very low output impedance, as most do, the impedance variations of one cabinet has practically no effect on the others.

    In series-connected cabinets, however, each one's impedance variations influence how much power the others get as well.
     
  16. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Thanks Bob.

    TB rocks!

    :)
     
  17. Dell

    Dell

    Apr 7, 2005

    So if you had two cabs exactly the same and wired in series to the head you would not get these problems becuase the resonanent frequencies of the cabs would be the same, meaning their impedence will always be the same as each other so they would always draw the same power as each other. Is that right? Would there be massive peaks and troughs in volume at different frequencies if this was the case?
    Would it matter if the head was lower powerd than the cabs could take? say at the resonent frequencies of the cabs they draw 100W instead of say 50W at other frequncies, would it make a 100W head clip at this frequencie but sound fine on lower and higher notes?
     
  18. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Joris has it right....

    Two of the same cabinet in series will act like one cabinet (more-or-less) of a higher impedance. The power of the amp isn't really part of the issue, that just afffects how loud it can get.

    Remember, lots of cabinets have internally series connected drivers. That is really the same issue, but you never see it because it is internal.

    Joris' point is that because different cabinets respond differently, one may "choke back" the other at certain frequencies if the two series cabinets are different. It may be that neither one will act like or sound like it would if used alone.

    Two of the same cabinet will tend to BOTH do the SAME thing together, so they are "in synch" and don't change the sound very much.

    Connecting in parallel is usually better, because each cabinet will work much independently, not affecting the response and character of the other one.