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Trying to get a quick cab fix...

Discussion in 'Amps and Cabs [BG]' started by Sundogue, Mar 5, 2006.

  1. Sundogue


    Apr 26, 2001
    Wausau, WI
    I've got a bit of a dilemma.

    I have a 410 cab with at least one blown speaker. I know I have at least two good speakers in it.

    Here's my problem. The speakers in the 410 are 4 ohm speakers and it's wired up as a 4 ohm cab.

    I also have a 210 cab (which sounds great, but not nearly as loud). The speakers in that cab are 8 ohm (also wired up as a 4 ohm pair).

    My question is, could I put the two 8 ohm speakers in the 410 along with two of the 4 ohm speakers? Could I wire up the two 8 ohm speakers in series so they are 16 ohm, and then wire up the two 4 ohm speakers in series so they are 8 ohm...and then connect the two pairs together?

    I can't go below 4 ohms. If I wired them up that way, what would my ohms result in (16ohm plus 8 ohm)?

    I know the current configuration of my 410 is that each pair of the 4 ohm speakers are wired in series to give each pair an 8 ohm load and then they are paralleled to result in the final 4 ohm load.

    Is it possible, or advisable to do this (pairing up two 8 ohms as 16 ohm, and two 4 ohms as 8 ohm...and then combining them into ? ohm)?

    What about wiring up my two 4 ohms as an 8 ohm load, and then the two 8 ohms as a 4 ohm load and then combining them? Would that give me somewhere between 4 and 8 ohms total?

    OR...what about wiring it up this way. The two 4 ohm are wired up parallel (giving me a 2 ohm load) and then the other 8 ohm speakers are wired up parallel, (giving me a 4 ohm load on those). Then the two pairs wired together in series to give me a total 8 ohm load (4 X 2 = 8).

    OR...I could load my 410 cab with all the speakers but disconnect two of them and have my 410 cab only have two 4 ohm speakers wired up as a 2 ohm load. Then keep the 8 ohm speakers in my 210 cab wired up as a 4 ohm load. Can I run speaker cables from my amp to each cab (one now a 4 ohm and one an 2 ohm)? Will that give me a total load on my amp of 8 ohms? Or should I wire up my 210 as a 16 ohm load and connect both cabs to my head (with my other one wired up as a 2 ohm load) giving me an 8 ohm total?

    I know it's a strange question...and I'm even confusing myself here. I'm just looking for any wiring scenario using my two cabs and speakers to give me more volume but stay at or above 4 ohms total.

    Any help is appreciated.
  2. Sundogue


    Apr 26, 2001
    Wausau, WI
    OK...I've been re-thinking this.

    I have 1 blown speaker so I only have 7 speakers to work with (three 4 ohm, and two 8 ohm).

    What I would like to do is this...

    210 Cab...
    Load two of my 4 ohm speakers into my 210. Wire them up as an 8 ohm cab.

    410 Cab...
    Load two of my 8 ohm speakers in my 410 cab and wire them up in parallel so they have a total 4 ohm load on one side. Then on the other side of the 410, load both of my 4 ohm speakers, but have one disconnected. The single 4 ohm speaker on this side would be wired to the other side of the cab.

    4 ohm load on one side of the 410 (the two 8 ohm speakers) and a 4 ohm load on the other side (the single 4 ohm speaker) wired together to make this 410 (actually a 310) an 8 ohm cabinet.

    Then I could plug both 8 ohm cabinets into my head for a total 4 ohm load.

    Does anyone see how this can't work? Anyone?
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You'll have a power mismatch no matter how you wire them. Just get another 4 ohm woofer, and make sure its T/S specs are quite close to those which you already have.
  4. Sundogue


    Apr 26, 2001
    Wausau, WI
    I realize I will have a power mismatch (wattage-wise between the three speakers anyway), however...I just need this to work temporarily without worrying about blowing my head (which can't go below 4 ohms).

    For testing purposes, my 410 cab now has two 8 ohm speakers wired in parallel for a total of 4 ohms (on one side of it). The other side of the 410 now only has a single 4 ohm speaker wired to the other side. Then both sides are wired together. This should give me an 8 ohm cab, correct? If I had two 4 ohm speakers wired in parallel (2 ohms) on one side...and just another single 4 ohm speaker on the other side, it would not work...but I'm trying two 8 ohm speakers one side...so each side wired in parallel is 4 ohms each (though one side has only one 4 ohm speaker instead of the two 8 ohm configuration). I still have the blown speaker in there, but it is not connected...it's just filling the opening.

    Loading my other 2 (good) 4 ohm speakers (wired in parallel) in my 210 cab will give me another 8 ohm cab. Two 8 ohm cabs will give me a 4 ohm total load to my head.

    I realize this is not ideal...but I'm in a pinch. What I'd like to do is build your Omni 10 for my two 10" BP102's. But by the time I'd get funds transferred to my PayPal account to pay for your plans...and then get the wood, I wouldn't have enough time between now and my next gig to build it. I'm in a bind no matter what. I'm tapped out this week financially, so I couldn't get a replacement speaker even if I wanted to go that route.

    I just want to get through my next gig with enough volume (because even though my 210 cab sounds great...it is not quite loud enough for this next gig). I'm hoping your Omni 10 will give me a bit more volume out of my BP102's than my current 210 cab...because my current 210 works for all but the larger gigs.
  5. Petebass


    Dec 22, 2002
    QLD Australia
    16 ohms + 8 ohms in parallal comes to 5.3 Ohms. As you know, the 8 ohm speakers will only get half the watts of the 4 ohms speakers, so unless they're considerably more efficient, you might not even be able to hear them.

    A 2 ohm cab in series with a 4 ohm cab is a 6 ohm total (4+2=6. Impedances for Series connections are simply added together) Wiring two cabs together in series requires special cables.

    Running cables from your amp to each speaker = parallell connection, not series. you'll end up with a 2 ohm cab and a 4 ohms cab in parallel = 1.3 Ohms. Don't do it. Your maths is a little shakey. I'm not sure where you got the 4*2= 8ohms formula but it's not correct.

    (1/R1)+(1/R2) = Parallel Impedance

    So for a 2 ohm cab and a 4 ohm cab:-

    (1/2)+(1/4) = Parallel Impedance

    (0.5)+(0.25) = Parallel Impedance

    0.75 = Parallel Impedance

    1.33333 = Parallel Impedance

    Ignoring cabinet volume considerations for a second, yes your impedance calcs here are correct. The "310" (ie 410 with one speaker not connected) is running at 8 ohms.

    Close. Don't wire the two 4 ohms speakers in parallel. That's 2 ohms. You know that but you're probably confusing yourself. You probably meant to type series and the 210 will be an 8 ohm cab. That's a total of two cabs at 8 ohms each for a 4 ohms overall.

    The impedances work. We've given no consideration to cab volume and porting etc, so you might need a little luck to get through this without more damaged speakers.

    Can't you just use the 4 ohm 210 as is, and ask the band as a favour to turn right down for this one gig. Or perhaps borrow or hire a 410 from somewhere?
  6. Sundogue


    Apr 26, 2001
    Wausau, WI
    Thank you so much for the answers! That is exactly what I was looking for.

    Wiring and re-wiring multiple speakers gets a little confusing. Thanks for clearing some things up (and yes I did mean "series" rather than "parallel", in that one statement about my 210 using the 4 ohm speakers).

    I tried my 310 cab configuration...and it sounds a little deeper than the 210. But the 4 ohm 210 has better tone. Turns out, I really have two blown 10's from my 410. One is just way more obvious. I messed around with it all day.

    I'm going to go with what you suggested...that is, I'm just going to run my 210 with the two 8 ohm speakers at 4 ohm. It isn't quite as loud as I'd like...but I'll live with it.

    I'd like to build the Omni 10 and load my 210 speakers in that. I'm very interested in how that sounds (both in tone and volume) compared to my current 210.

    Thanks again for your help Petebass. I appreciate it a lot.

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