Running Three Cabinets With One Amplifier

Discussion in 'Amps and Cabs [BG]' started by Adam Groves, Aug 12, 2018.

  1. Adam Groves

    Adam Groves

    Aug 12, 2018

    I have an Ampeg SVT-7 PRO with two speaker outputs or:
    600 watts (8 ohm) single output
    1000 watts (4 ohm) double output.

    I have three speaker cabinets:
    1.) Markbass 121H; 8 ohms, 400 watts
    2.) Markbass 102P; 4 ohms, 400 watts
    3.) Ampeg PN 210 HLF; 8 ohms, 575 watts

    Things I already know (please correct me if I am wrong)

    I should never run my amp below 4 ohms overall impedance. By running both outputs I get 4 ohms per side. And to be safe I should use my two 8 ohm rated cabs and nothing more.

    Running the single output I should get 8 ohms from the amp. I understand I can run one 4 ohm cab and nothing else because running another cab (8 ohms) in parallel will drop the recommended 4 ohms to 2.67 ohms and possibly smoke my amp.

    Things I do not know, please help?

    SINGLE OUTPUT (Series)

    Scenario One:
    AMP --> 8 ohm cab + 8 ohm cab = ? ohms or total impedance
    What happens to the total impedance if I run two 8 ohm cabs from a single output "in series" or by "daisy chaining" cabs together and nothing else?

    Is it true I am actually running these cabs in parallel not series? Is it true that I am creating 16 ohms total impedance or 4 ohms?

    Scenario Two:
    AMP --> 8 ohm cab + 4 ohm cab = ? ohm or total impedance
    What happens if I run one 4 ohm cab and one 8 ohm cab together from this single output or by "daisy chaining"?

    Is it true I am actually running these cabs in parallel not series? Is it true that I am creating 12 ohms total impedance or already 4 ohms or less?

    What is the real impedance of combining these cabinets in both scenarios, what overall impedance is my power amp working at from a single output?

    DOUBLE OUTPUT (Parallel)

    AMP output 1 --> 8 ohm cabinet + 4 ohm cabinet (daisy chain)
    AMP output 2 --> 8 ohm cabinet

    What is the real overall impedance of combining these three cabinets, what impedance is my power amp working at--2 or 4.6 ohms? I understand that it should not go below four. Should I simply give up running the four ohm cabinet?

    Thank you for your advice, it's appreciated.
  2. two fingers

    two fingers Opinionated blowhard. But not mad about it. Inactive

    Feb 7, 2005
    Eastern NC USA
    First off, Welcome to TalkBass!!!!!!

    It doesn't matter about the outputs on your amp. You don't get 4 ohms "per output". You get 4 ohms TOTAL.

    As per the manual, they are wired in parallel with each other. The ins/outs on most speaker cabs are parallel also.

    It's safe to say everything we're dealing with is in parallel.

    The total load running two 8 ohm and one 4 ohm cab would be 2 ohms..... and below the minimum safe load for your amp. The math on ohm loads is kinda "backwards".

    Roughly where are you geographically? I only ask because advice for someone here in the US would be different from someone living in rural Australia.

    If you're here in the states, I would advise selling all of your cabs and getting a beefy 4 ohm 4-10 cab..... unless weight is no issue, in which case I would suggest a 6-10 or 8-10.

    But don't hook up all these cabs together. Your amp will suffer.

    Glad you asked here first! :D
    Last edited: Aug 12, 2018
  3. Adam Groves

    Adam Groves

    Aug 12, 2018
    Hi Two Fingers.

    Thanks for the reply. I am in Southeast Asia, originally from the US.

    I used to own an SVT-3 Pro in the late 90's. It lasted me a long time. I paired it with an Ampeg Pro 410 and Classic 15. I blew the 15 after about 10 years of shows and lots of abuse. I loved the 410 but did not like how heavy it was. So when I decided to buy new gear, I first opted for the Ampeg 210 cause of the neodymium factor. I played one here and loved it. The Markbass stuff was a good deal and sounds really good--but it's not Ampeg. I wanted to get the Ampeg PN 115 to pair with my 210, but got two cabs for the same price. I guess that 4 ohm cab I can use at home or for back up. Maybe sell it.

    I also played an Orange 410 with a Protaflex head and loved it. But the dealer wouldn't sell it for some reason and ordering that specific Orange cabinet from here can take 3-6 months.

    I miss having a 410 but mobility is hard to turn down. For now I guess I am going to run the 121 and the 210.

    Thanks again. Wondering if there are other views out there about my set up. But what you say sounds right.
    two fingers likes this.
  4. Jazz Ad

    Jazz Ad Mi la ré sol

    You get to plug one 4 ohm cab or two 8ohm cabs, that's it.
    Nothing more to it.
  5. Even though a lot of people successfully run a 4x10 with a 15, there are also good arguments for not doing so. You may have been a victim of one, or a combination of these factors.

    A 4x10 will typically be louder than a 15 so the 15 is harder to hear. And in a band situation, with all of the other music, it is even harder to hear the 15. Now, for some reason, people have a tendency to put the 15 on the bottom of the stack. This places it further away from your ears... again making it even harder to hear.

    Now consider the case of two 8 Ohm cabs. One is a 15”, the other is a 4x10. Since both cabs are the same impedance they will equally share the power from the amp. In the 15, half the power is going to one speaker. In the 4x10, the other half of the power is further split 4 ways between each driver in the 4x10 cab. This usually means that at high volume levels, the speakers in the 4x10 are loafing along while the 15 is getting a real workout.

    Now consider that cab power ratings are electrical. They tell you how much a voice coil can take in terms of heating. The cab ratings usually ignore the mechanical power limits because those power limit ratings are much lower and that makes it harder to sell cabs. The mechanical power rating is about how far things can move before reaching a limit.

    Finally, if you EQ you amp for a lot of bass, you bring the mechanical issues into play sooner than you would if you were more conservative with the low end EQ.

    Any one of these factors may explain the demise of the 15. Start combining them and you are rapidly increasing the chances of sending the 15 to bye bye land.
  6. Adam Groves

    Adam Groves

    Aug 12, 2018
    Hi Old Garage-Bander,

    I did switch my 15 to sit on top the 410 after I replaced the speaker that blew-out--only after I destroyed my gear.

    I have always been very simplistic about EQ. I tend to go mid-heavy. But I think that's because I stacked the 410 equal to my chest. So when I would play a basement or living room, the 410 just punched me so hard and I loved it! But you're right, I could not hear the 15', and I took it for granted.

    Another thing might be due to its rating, and I mean watts (all 8 ohms). The PRO 410 was rated higher (maybe 400 watts?), and the 15' rated lower (maybe 200 watts?) cause it was a "Classic" viz Portaflex Series today. So I hear you about the marketing thing. I just grabbed what I could and then experimented. We plugged anything into everything.

    But I still want to challenge the conventional wisdom here, if you don't mind. And I suppose my conceit is that I want to experiment with these three cabs.

    Do you have any stories like that?

    Just curious. And thank you for the generous replies.
    Old Garage-Bander likes this.
  7. One thing you might think about is the fact that you get more bang for the buck by adding speaker surface area as opposed to adding more power.

    In general, doubling the speaker surface area makes things seem roughly twice as loud.
    But it takes something on the order of a times ten power increase to seem about twice as loud.
    Now consider 4 vs 8 Ohm operation of your amp. 600 at 8 Ohms, 1000 at 4. You’re not even doubling the power, let alone having a ten times increase.

    Given the three cabs you have, this is what I would try... though it will take some custom speaker cable wiring to achieve. Hopefully you are up to that, or can get up to speed on parallel/series speaker wiring schemes.

    What you will do is connect the two 8 Ohm cabs in parallel which is normal. This combination will give you 4 Ohms.
    Now treat the two 8 Ohm cabs together as if they are one 4 Ohm cab.
    Now comes the custom wiring...

    You will have to make a specially wired adapter so that when connected to the two 8s as a 4 Ohm combination and your 4 Ohm cab, they will be in series with the amp. This will give you a total of 8 Ohms. Your amp will operate at 600 watts but will have increased speaker service area. The other advantage with this arrangement is that you will have more speaker headroom. This allows you to push the amp harder while not pushing the speakers as hard.

    I know it may sound complicated to describe the wiring arrangement in words, but I’ll let you take it from here.
    You may up with my description which is great. If not, there is plenty of info on the internet. Apologies for not being in a position to make a drawing at this time, or I would. Perhaps someone else will step up and do that.

    FWIW, there was a thread a while back about running speakers in series. Some folks were trying it and liking the results. What I propose is a bit more complicated, but really just an extension of series speaker wiring.
    Last edited: Aug 12, 2018
    bassmeknik and Adam Groves like this.
  8. Adam Groves

    Adam Groves

    Aug 12, 2018
    That's a great lead. Thanks!

    I have been reading a lot about wiring individual speakers. So I am willing to try new things. I think caution is a good so I am not just eager for loudness but truly interested in speaker surface. The amp hasn't become warm when I run the 4 and 8 ohm cabs from one side--but that does not mean something is wrong, it could be.

    I don't want to devalue the advice others have given, I think it's valuable. But I do like experimenting--part of me thinks that is part of the fun. However it's hard to argue with the facts. The problem is neither Markbass or Ampeg offer much (officially) about how they wire their cabs. So I have to open them up and see. There's a lot of info about wiring individual speakers on the web and Two Thumbs was pretty convincing about the 4 ohms output. That doesn't mean individual situations might be different, as he seem to imply.

    I look forward to other ideas and will keep you updated if I get brave and try.

  9. abarson


    Nov 6, 2003
    Santa Cruz
    Instead of "conventional wisdom" which can sometimes be wrong, study Ohm's Law. It is called a law because it is unchanging. It is a scientific fact and not fake news. You are more than welcome to ignore it, but you will destroy equipment in the process of trying to prove it wrong.
    After Ohm's Law, study how speakers operate. Find reliable published sources, as not everything on the Internet is accurate.
    Experimenting is all well and good but you must understand the fundamentals first. An experiment is rooted in science, in contrast to just randomly trying stuff.
  10. Adam Groves

    Adam Groves

    Aug 12, 2018
    Thanks Abarson,

    I get it, I won't be changing Ohm's law or the idea of any 'law' by playing with my amp. But I do wonder if the material changes in the speaker cabinets (beyond noise cancellation in a 410 versus 210 or 2 / 210's) might have a part to play in it? Or simply the improvements in the materials that go into these things today might lead to new things? Maybe there's something to that? Maybe not. It's fun for me to wonder and try. I know I am being speculative.

    As I mentioned earlier, there is clear common sense about ohms and cabinets and I respect that. And I agree with you, I don't believe everything on the web, which is why I am a bit confused.

    Maybe it's just the musician trying to be an electrician's muse? Not sure. If the speakers in my 4 ohm rated cabinet are wired differently than conventional wiring, maybe there is a chance? But maybe finding out leads me to something else--beyond having three cabs work? Who knows?
  11. abarson


    Nov 6, 2003
    Santa Cruz
    I don't know what "material improvements " mean. I guarantee that your 4-ohm Markbass 102P consists of two 8-ohm drivers internally wired in parallel and not two 2-ohm drivers in series, as the 2-ohm variant doesn't exist. Changing the internal wiring from parallel to series on it would produce a 16-ohm cabinet, but why do that?
    Manufacturers are going to stick to proven formulas and market dictates. None of them are going to suddenly start offering 3-ohm drivers, for instance. There are improvements in design and build, but some "standards" like even valued driver impedance won't change.
    Adam Groves likes this.
  12. BadExample


    Jan 21, 2016
    Welcome to TB Adam!

    Hey, I spent quite a few years in that region.
    Adam Groves likes this.
  13. Tim Skaggs

    Tim Skaggs

    Sep 28, 2002

    It is generally safe to assume everything manufactured (not home-made) has all connections wired in parallel at the jack.

    Example; an amp with two speaker output jacks will have the same impedance load if you;

    1. connect two cables, one from each of the amp speaker output jacks, to two separate speaker cabinets, or

    2. if you connect one cable from one of the amp's speaker out jacks to one cabinet, and connect a second cable from the first cabinet to a second cabinet.

    Both are parallel connections.

    You could build a series speaker cable that connects two cabinets in series.


    1. connect an 8 ohm & 4 ohm cabinet together with a series cable to make a 12 ohm impedance an connect that cable to one of your amp's speaker jacks.

    2. Connect an 8 ohm cabinet to you amp's other speaker jack with a regular cable.

    The amp would then have an impedance load of 12 ohms in parallel with 8 ohms, or a total impedance of 12x8 divided by 12+8 or 96/20= 4.8 ohms.

    The single 8 ohm cabinet would receive 66.6% of the power from your amp, and the two cabinets in series would receive 33.4% of the power from your amp. That 33.4% power would be divided between the 4 & 8 ohm cabs wired in series at a 2:1 ratio, with the 4 ohm cab dissipating twice as much power as the 8 ohm cab.

    So 1000 watts would divide up about like this.

    666 watts into the single 8 ohm cabinet

    334 watts into th 4 & 8 ohm cabs in series, with the 4 ohm dissipating 222.26 watts and the 8 ohm getting about 111.3 watts.

    This got way too long, but is "a way" you could run all three of your cabs with one amp that has a minimum impedance rating of 4 ohms.

    I doubt you would gain much doing this, and would have to really be adept at keeping polarities straight to avoid getting something out of phase, which would nullify what you are trying to gain.
    Last edited: Aug 12, 2018
    Adam Groves likes this.
  14. Haroldo

    Haroldo Supporting Member

    Aug 31, 2005
    North Shore, MA
    Howdy, Adam,

    First off, welcome to TB.

    Secondly, what sort of gigs (and music) do you play? Big rooms? Small dives? Wine bars? Do you have FOH support? All these questions are aimed a finding out if you need a lot of loudness. (I'm guessing you think you do, but maybe not.)

    As others (especially @two fingers, I think) have pointed out, you cannot run below a 4 Ohm speaker load with your amp. So that limits your options if you keep the 3 cabinets (and amp!) your already have.

    Either the 102P by its lonesome (where you run the risk of cooking it by the amp (1000W -> 4 Ohm, 400W cabinet); OR the 151H + PN 210 HLF in combination (again, 500W -> each speaker cabinet, as they are in parallel). You are pushing the limit of what the 151H can tolerate. Do the 151H and PN 210H HLF sound good together? OR either of the 8 Ohm cabinets by their selves (600W -> 400W for the 151H, 600W -> 575W for the PN 210 HLF). It seems the safest choice is running the PN 210 HLF by itself. Does that meet your loudness & tone criteria? If not, re-configuring your rig might warrant some consideration.

    Thirdly, it sounds as though you are preferring something lighter these days. (Maybe a new, less powerful Class D amp, for instance.)

    Batting fourth, what's your budget? (If in fact re-sculpting your rig is something you want to do.)

    Good luck.
    Adam Groves likes this.
  15. MDBass

    MDBass Supporting Member

    Nov 7, 2012
    Los Angeles, CA
    Endorsing Artist: Dingwall-Fender-Bergantino-Dunlop-Tech 21-Darkglass-Nordstrand
    The cabs decide whether your ohms are, not the amp.

    That amp is stable down to 4ohms, so you can either run two 8 ohm cabs or a single 4ohm cab: you can try other combinations, but you’ll quite literally be running the risk of setting your amp on fire and/or melting it.
  16. Rip Van Dan

    Rip Van Dan DNA Endorsing Artist Supporting Member

    Feb 2, 2009
    Duvall, WA
    As noted previously your amp has two parallel outputs, not two separate channels. If you plug your 8 ohm cab into the back along with your 4 ohm cab, that comes to a 2.67 ohms load, which can easily damage your amp - hopefully the circuit protection will turn it off before it goes up in smoke.

    So the short answer is you can't run both cabs from your amp at the same time. If you only want to run one cab, then you can run a single 4 ohm cab from it. If you want to run two cabs, they both need to be 8 ohm cabs. With a parallel connection (the industry standard), 8 ohm + 8 ohm = 4 ohm load, which will get the optimum amount of power out of your amp.

    If you plug one cab into either input in the back and plug the other cab into the first cab (daisy chaining it), the amp sees that exactly the same as plugging both of them into the back - 2.67 ohm load which can and will damage your amp.

    The only way to run both of your current cabs off that amp is to get a serial box. Plug cab #1 into the amp and into the serial box. Plug cab #2 into the serial box. Now you are running a serial connection between the cabs, which adds the ohms of each cabinet together - 8 ohms + 4 ohms = 12 ohm load with a serial connection. That 12 ohm load will drop the power output from your amp by about 1/3, but may end up giving you more volume just because you have more speakers pushing more air than either single cabinet can do by itself.

    I did that with a GK amp I had. It was their Backline 250 (125-watts) with a minimum ohms rating of 8 ohms. It came with a GK 115bpx cab and I needed more than just that 115. I just happened to have an old Sunn 212 cabinet that had both a parallel and a serial output. So I plugged the Sunn cab into the amp and the GK115 cab into the serial output of the Sunn cab. That worked just great. Although it dropped the 125-watts output to about 85-watts (more ohms = less current delivery) adding two 12" speakers to the 115 more than made up for the loss in volume. I continued to run that until I bought an 8 ohm 410 cab.

    Now, my current amp is an Eden WT500/800 (WT500 upgraded to 800-watts bridged), which is a dual power-block amp. That means it literally has two separate power sections. When I was running both the 115 and the 410 I would plug one into the left side and the other cabinet into the right side. Then I would use the power knob on the front to adjust the balance of power sent to each cab to end up with the best sound. Since both were 8 ohm cabs, they were both getting the same amount of power. And, since that GK115bpx was a very boomy cabinet, I just turned that balance knob about about 3 to 4 clicks towards the 410 to tame the boominess of the 115 and give me a good overall sound without needing to drop the Bass EQ, which I had to do with my single power-block amp.

    I have since purchased a DNS-410 which is clearer, more articulate, and much louder than my 410/115 stack was. So I run it bridged at 800-watts into a single 8 ohm 410 cab. Bridging internally sends the power from my right power section into the left power section and then out the bridged output jack, effectively doubling the available power by summing the 2 power sections.

    You really have to be careful when adding cabs. If you run an ohms load lower than the amps minimum, at worst you can really do some damage to it. At best, it will cut out on you while you're playing a gig because it is overheating from trying to generate more power than it can handle.
    Adam Groves likes this.
  17. Stumbo

    Stumbo Guest

    Feb 11, 2008
    You just discounted all the knowledge bestowed upon you by the Ohm Kings of TB.:thumbsdown:

    There's no holy grail to be discovered by keeping yourself ignorant.

    If you only learn by sticking your finger in the light socket instead of applying what you've been taught, your money tree must be bearing lots of fruit.
    Lobster11 likes this.
  18. Just to be certain that I was clear. (For the benefit of all.)
    I was not suggesting to re-wire the cabs internally, just how to wire the hook the cabs together with the amp.
  19. By unconventional, if you mean not the way the manufacturer wired it, then unconventional = wrong.
    Certainly worth looking into just to be sure, if you are not the original owner.
    Pretty much the combination you should find in a 4x, 4 Ohm cab would be 4, 16 Ohm drivers all in parallel.

    There are numerous combinations of three or more cabs that can be connected together and remain at, or above, the amp’s minimum impedance rating. Getting a little Ohm’s law under your belt will help you to sort out these combinations. For purposes of these calculations, Ohm’s law for Resistance, also works the same for Impedance.
  20. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Running that amp below the minimum rated 4 ohm load is a very good path to an expensive (very expensive) repair. The guys who designed your amp might know a thing or two about its limitations as well, hence the minimum rated load.