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2 amps 2 cabs 1 amp 2 cabs

Discussion in 'Amps and Cabs [BG]' started by matzingerz, Sep 11, 2019.


  1. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    That is not correct. Doubling the drivers, given the same output that a tube head delivers, results in a theoretical +3dB. Other things happen with doubling drivers as well. Due to coupling, lower frequencies benefit more, so there will be added low end response as well. That is why the standard recommendation of how to get more perceived volume is to double the drivers instead of doubling the power.

    Now if the user was using an SS head, and doubling the drivers created the scenario of going from a 8ohm load to a 4ohm load, you can pick up an additional 2~3 dBs depending on the specifics of the head for a net increase of 5~6dB.
     
    HolmeBass likes this.
  2. Double E

    Double E I ain't got no time to play... Supporting Member

    Dec 24, 2005
    Cleveland, OH
    The 3db increase for doubling power is an industry standard calculation for configuring audio systems... the same 3db increase does not apply to multiplying your driver area by a factor of 2... furthermore the OP is specifically asking if using two amps would produce more volume and I still stand by my answer that, given the equipment involved, the answer is YES!
     
  3. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    That is simply false.

    What do you believe it to be?


    We have already agreed that the OP would see a 3dB gain in perceived volume with his plan.
     
  4. Double E

    Double E I ain't got no time to play... Supporting Member

    Dec 24, 2005
    Cleveland, OH
    Is it still false when you are doubling both power and driver area?
     
  5. I actually didn't know the fridges were split in halves! Thanks for the correction guys :)
     
  6. sowilson

    sowilson

    Jul 5, 2013
    4 heads into two cabs would be loud, fairly compact, and look very, very cool - tubealicious
     
    BigBear77 likes this.
  7. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    -Doubling the power adds 3dB.

    -Doubling the drivers adds 3dB. Plus the added benefit of increased low end response due to better coupling of those lower frequencies.

    Example: SS head that is 300 watts into 8 ohms, and 600 watts into 4 ohms.

    Base rig is that SS head into a 115/8ohm cab.
    Double the drivers so you now have a 215/4ohm cab, and the SS head can now deliver 600 watts. You gain a theoretical 6dB in perceived loudness because you have doubled the power AND doubled the drivers. (If the SS head was 300 into 8ohms but 500 into 4ohms, the net gain would be a bit less, approx 5dB)

    Tube heads are different. In the case of a tube head, the power does not increase as the ohms load drops. The SVT is always 300 watts. So going from a 115/8ohm cab to a 215/4ohm cab is still 300 watts, but since the drivers doubled, there is a theoretical gain of 3dB.

    @Double E, again, what dB gain by doubling drivers have you been going by?
     
    Last edited: Sep 11, 2019
    Downunderwonder and ctmullins like this.
  8. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    Sort of. Doubling drivers has the added benefit of increased low end response due to better coupling of those lower frequencies.

    But the practice here at TB has always been to recommend a second cab as the better/easiest way to get more perceived volume before one looks at their head.
     
    buldog5151bass likes this.
  9. Stevorebob

    Stevorebob Well... I Am Here, Aren't I? Supporting Member

    Sep 29, 2011
    Los Angeles
    More power, same cab is easier to load — the back-saver way to get more dB. Well, maybe not with SVTs, but certainly with class D amps.
     
  10. Or 1 folded Horn cab
     
  11. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    You only get 3dB by doubling the power. That’s generally accepted as being barely detectable by the average listener. But it greatly increases the chance of driver damage. No thanks.
     
  12. H Nighttrain

    H Nighttrain

    Feb 12, 2018
    Let's say I have a Bob amp and a Fred cab. Then I get another Bob amp and another Fred cab.

    That should be the very definition of doubling the output (+10dB), but in reality it's only +6dB?
     
  13. Double E

    Double E I ain't got no time to play... Supporting Member

    Dec 24, 2005
    Cleveland, OH
    Well... I was already aware of the power to dB gain ratio but I didn't think that it would equally apply to driver area... mainly due to my own personal experiences playing on bass amps for years but I have no canned response for an exact amount.

    You speak as someone who actually knows what they are talking about so I will not argue the point except to pose this: If, in addition to the baseline 3dB increase based on the arithmetic, doubling the speaker area enhances coupling and produces more low end gain then this can be a pretty big factor in perceived volume. Especially for a bass guitar rig where low end response plays quite a key role.
     
  14. Blackjac97

    Blackjac97 Supporting Member

    May 27, 2012
    Maine
  15. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    Bear in mind, the gain factors are all theoretical. No substitute for actual field testing. But you can take it to the bank that the +3dB factor applies to doubling power as well as doubling drivers. That’s pretty much the starting point for the musicians, engineers, and designers who frequent here. And in addition to low end coupling gain from multiple drivers, there is baffle step comp which deals with the combined area of the baffle surfaces and it’s ability to keep more waves directed forwards towards the listeners.

    One thing to note, is that +3dB is not a huge increase in perceived volume. Detectable by the average listener yes, but a huge increase, no. If one wants something to be perceived as twice as loud, that needs +10dB. And that translates to 10X the power or 10X the drivers or combination thereof.

    I learn something new here everyday too!
     
    HolmeBass likes this.
  16. Rip Van Dan

    Rip Van Dan Supporting Member

    Feb 2, 2009
    Duvall, WA
    Normally you are right on. However, my understanding is that some of the SVT 810's actually are two separate 410's enclosed in the same cabinet with separate inputs for each 410 section. That's why you used to see a lot of that "back in the day" with two SVT810's each having two SVT heads driving them. I remember a concert the Stones did where everyone was using SVT's and they had this huge wall with two heads on each 810 cab. But that is not true of all SVT's...@JimmyM would know the specifics

    Now...if you managed to run both amps into just one of those inputs, then you'd fry one section and perhaps the amp too. And if you hook two amps into any other cabinet that I know of, then it absolutely would be "magic smoke release" time.
     
    BioWeapon likes this.
  17. I've used 2xSVT + 2xFridge, and it was really nice.
    had one on each side of the drummer.

    didn't really matter though because the stage was pretty large, and really I only heard the wedges and side fills.
     
  18. BigBear77

    BigBear77 Supporting Member

    Aug 30, 2017
    Think the question is Why not?
     
    Coolhandjjl likes this.
  19. DrewinHouston

    DrewinHouston Not currently practicing Supporting Member

    Apr 20, 2009
    Houston Heights, Texas
    Disclosure: I am not a great bass player
    SVT-II Pros run at 4 ohms or less, you shouldn't connect them only to one half of an 810, that would only put an 8-ohm load across it.

    EDIT: so you shouldn't can't have four SVT-II Pros and two 810 cabinets.
     
    Double E likes this.
  20. el murdoque

    el murdoque

    Mar 10, 2013
    Germany
    I meant that a tube amp delivers 300 Watts into a 4 ohm load as well as into a 2 ohm load.
    If you have a scenario with a tube head and one cab vs two cabs, the wattage will remain the same, therefore the gain will be +3dB for doubling the speaker surface when adding a second cab.
    Most SS heads will roughly double their output power when the attached load is halved.

    So a 300W SS head with one cab attached will put out something between 130-170 Watts with one cab and
    the full 300W into both cabs, resulting in +6dB from doubling both the power and the speaker surface.
     
    Double E likes this.

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