Mixing 8 and 4 ohms cabs in same rig.

Discussion in 'Amps and Cabs [BG]' started by semborg, Jun 15, 2005.

  1. Okay, I have given up my search for a 1x15 cab at 4 ohms.

    Is it possible to use a 1x15 8 ohm cab with 2x10 4 ohm cab?

    Will the 1x15 be more quite?
    Bad volume balance?

    Thank you very much as hell :rolleyes:
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    in order to do that you need either a mono head that can handle a load down to 2 ohms (you'll be using 2.67), or a stereo head that can handle 4 ohms per side.

    in the mono head scenario the 4 ohm cab will get 2x the power of the 8 ohm cab. if both cabs are exactly as loud as each other (which depends upon overall voicing, not just sensitivity which is only measured at 1 KHz) the 8 ohm cab will be 3 dB quieter, which is just noticeable.

    in the real world you have no idea until you try it. one 15" speaker is a bit larger than two 10" speakers in the amount of air it moves, so the two cabs might be very close in volume, but there are way too many variables to be sure until you try it.
  3. Aha, cool.

    So it's mostly often not any big difference between 4 ohms and 8 ohms cabs?

    So probably I can run on 2x10 4 ohm and one 1x15 8 ohm and get good balance?

    Yes my head can go down to 2 ohms bridged.
  4. xring


    Sep 16, 2003
    I may be mistaken, but I thought that by mixing an 8 ohm and a 4 ohm cab (mono) - you're drawing 6 ohms - not 2.67??
  5. paintandsk8

    paintandsk8 Pushin' my soul through the wire...

    May 12, 2003
    West Lafayette, IN
    nope 8 and 4 in parallel is 2.67
    8 and 4 in series is 12
    8 and 4 never equal 6
  6. xring


    Sep 16, 2003
    Yikes! I read somewhere the basic "formula" for mixing cabs was:
    8+4=12 divided by (2) cabs= 6 ohms.
    I better be more careful!
  7. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    Is your search ended because you simply can't find a 15" cab in 4ohm, or because you can't find one you like?

    Avatar has a 15" Neo cab in either 4 ohm or 8 ohm for $239 plus shipping. Look here: http://www.avatarspeakers.com

    I was using a SWR 210T 4 ohm + Avatar SB112 8 ohm cab together in parallel for several months with excellent results. It was near impossible to tell the difference in volume while standing at the amp, and even harder when in the audience.

    And while your amp may handle a 2 ohm load, the real question is whether it handles it well and is happy with it. My SWR will do 2 ohms, but it is much, much happier with a 2.67 ohm load. YMMV of course.

  8. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    i think it's a "what's available in sweden" thing.

    anyhow, to answer the 2nd question, it's hard to say. it may work well, or one cab may dominate the other volume wise. you just have to try it. I use a 4 ohm 210 and 8 ohm 115 on a mono head that can handle 2 ohms from time to time. the 15 has a sensitivity of 103 dB, and the 210 has 100 dB. they end up being about equl volume. however, the sensitivity is kind of moot as the overall voicing of the cabs plays more of a role in the apparant voluem than how loud the cabs are at 1 Khz.
  9. Jazzin'

    Jazzin' ...Bluesin' and Funkin'

    Nope, it's not an average. It's Total Resistance = 1 / ((1/R1)+(1/R2)+(1/R3)etc...)
  10. I've been using this 4Ohm/8Ohm combo for about 15 years,
    and I've never had any problem. I had a stereo head that I bi-amped
    until last year, and now I use a pre/power amp rig and just
    send the signal from one side of the power amp to the 4Ohm speaker,
    and the signal from the other side of the power amp to the 8Ohm speaker.
    Seems to work just fine. Unless I'm doing something I'm not
    supposed to do?

    I have a related question. If I have a power amp that
    bridges at 8Ohms but I want to run it bridged into a 4Ohm cab,
    am I going to get not all of the amp's watts? Or am I
    going to get something terribly worse(like damage)?
    Sorry if this is considered "hijacking" the thread.
  11. Its okay.
    But I cannot answer your question.

    My reason for searching for a 8 ohms 15" is that I can't find any 4 ohm 15 that I think I am gonna like.

    And It sounds that mixing 2x10 4ohm (Yamaha, they don't tell the sensitivity :() and 8 ohm 15" (Think Gallien Kreuger) probably would ending upp well.
  12. popinfresh


    Dec 23, 2004
    Melbourne, Aus
    May I just ask, what 15's have you looked at? There are MANY 4ohm 15's...
  13. Peavey's - too heavy
    Behringner - Heard to many bad things about behringer
    EBS - Too expensive - (for me atleast)
    Ampeg - WAAY to heavy

    But if it is better to have a 2.67 load instead of 2 and the volume balance between the 2 cabs will be equal I go 8 ohm 15".
  14. Funkengrooven

    Funkengrooven Turn it down? You gotta be nuts!!

    I have the same issue (not problem) with my rig. My 18"JBL is a 4 ohm model and my 2x12 cabinet is 8 ohms.
    My SWR 550x doesn't really like 2.67 ohms even though I have run it like that. So my solution at the moment is to hide the 2x12 cabinet from the amp by using a passive crossover on the 2x12.
    This is in the form of a capacitor rated about 145 uF @ 250 volts. Actually it is (2) 250 uF in series. Their measured capacitance is 288 and 293 respectively. These are big electrolytic caps. The crossover frequency works out to be about 180 Hz. This is a 6 db/octave crossover so the lower end is still there by virtue of the slope, it is rolled off gradually enough so the your ears still think the low end is coming from the 2x12.

    We have all talked about roasting our outputs with too little load. This is mostly because (I am gonna get corrected here I am sure of it) the speakers are in the DC path ot the outputs.
    If the speakers are not in the DC path (via the cap) then that should not be effected. I think. My old Acoustic 360 had a 4700 uF cap coupling the output to the speaker (remember the turn on thump?) and the DC path was not thru the speaker. So...
    I figured....let's try it.....Gig this weekend..I'll let you know.
  15. Thor

    Thor Moderator Staff Member Gold Supporting Member

    I remember that thump real well! Happens every time I turn on my Acoustic 140 head and the 106 cab.

    That is an interesting solution, love to hear about how it
    worked out.
  16. 8x4/8+4= 2.67 ohms

    The 4 ohm cab will get 2/3 of the power and the 8 ohm cab 1/3
    So the 4 ohm cab will be noticably louder. I tried this with 2 15" cabs, one 4 ohm and the other 8 ohm. I did not like the results. My amp distorted easily at 2.67 ohms and the 4 ohm cab was louder than the 8.

  17. Semborg, I sent you a private message concerning your cab situation.
  18. I think it makes sense to run a 2 speaker cab at 4 ohms and a 1 speaker cab at 8 ohms. All three speakers will be getting the same amount of power. BTW I do this with my 4 ohm B212 and 8 ohm B115 with good results.
  19. I never thought of this.
    You are right, every speaker gets same amount of power.