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How do you connect an 8ohm and 4ohm speaker cabinet to a 4 ohm amp?

Discussion in 'Amps and Cabs [BG]' started by WinterBass, Aug 8, 2003.

  1. WinterBass


    May 19, 2002
    Hudson Valley, NY
    Endorsing Artist: MTD
    Hello all,

    I just bought a Bergantino HT115 speaker cabinet and would like to occasionally pair it with my Berg HT310. The problem is that my Ashdown ABM amp head will only handle a 4ohm load. The 1x15 is 8ohms and the 3x10 is 4ohms. Putting them together will create a load of 2.6 (I think). Is there anything that can be used to make this work without buying a new amp?

    I have seen this SPEAKER MATE? What does this do to the power coming out of your amp? Does it disperse it equally, or does more go to the 4ohm speaker?

    Any input would be appreciated. Thanks!

    Eric Winter
  2. BruceWane


    Oct 31, 2002
    Houston, TX
    Yeah it will create a load of 2.67 ohms (OK, actually 2.6666666.......).

    You could make a custom cable that would allow you to connect the two cabs in series for a load of 12 ohms. Drawbacks are that your amp won't be putting out nearly the wattage it normally does under an 8 or 4 ohm load, and the 4 ohm cabinet will recieve quite a bit more wattage than the 8 ohm cabinet. No way to balance the volume between the two.

    Dunno about the SpeakerMate. From their website, it seems to automatically configure speaker loads into the optimum series/parallel combination to get nearest to the minimum load the amp will tolerate. Kinda odd that ALL of their examples use exactly equal loads and number of speakers - like 2 8 ohm speakers and 1 4 ohm (you'd wire the 8's in parallel for a 4 ohm load, then wire that to the 4 ohm speaker in series for a total load of 8). Nowhere do they address your problem, which is kinda odd because your problem is pretty common. Give them a call and ask them.
  3. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA

    You don't.
  4. NeedMoreBass

    NeedMoreBass unregistered

    Feb 14, 2003
    The end!!
  5. Fuzzbass

    Fuzzbass P5 with overdrive Gold Supporting Member

    I can't think of a way to help. Which is too bad, because the HT310 and HT115 sound amazing together! At one gig I had to remind myself not to bridge my amp into those two cabinets, because as mentioned, the load is 2.67 ohms and min load for bridging is 4 ohms. But my Stewart World 2.1 can handle a 2 ohm load from each channel, so I use just one channel.

    (My guesstimate is that each channel of the Stew puts 900W into 2.67 ohms... whatever the number is, it's plenty loud enough even for outdoor gigs with no PA support!)
  6. junglebike


    Feb 14, 2003
    San Diego, CA
    I'm staring down the barrel of the same frustrating combination of speaker impedances with my Epi 2x12 (4ohm) and 1x12 (8ohm).

    It's strange because most stereo amps won't bridge below 4ohms, you're stuck with either looking for:

    1. a mono amp (i.e. head) that can drive 2ohms (I-amp, Fafner, Clarus)


    2. an immensely powerful stereo amp that can put a reasonable amount of power from a single channel into 8ohms. Basically PLX 1600+

    Usually, getting big power from a head is much more expensive, but in this case it seems that the pre/power scenario closer to parity.

    Iamp: $1400 new
    PLX 1600: $700
    Good pre: ~$650 new
    (both will put 800+W into the stack)

    Anyway, it's gotten me thinking about using a powerful 2ohm capable head, where before I was totally sold on separates. Bummer the Ashdown can't do 2ohms.
  7. ChenNuts44


    Nov 18, 2001
    Davenport, IA
    In series...or not at all.;)
  8. Fuzzbass

    Fuzzbass P5 with overdrive Gold Supporting Member

    That SpeakerMate™ thingie does look interesting, but that's the first I've heard of it.

    If you like the Ashdown sound, I would suggest building a rack containing an Ashdown preamp (and maybe your head could be used as the preamp) plus a power amplifier. Even if the power amp didn't handle 2 ohms per channel, you could run the 310 off of one channel and the 115 off of the other.
  9. Edwcdc

    Edwcdc I call shotgun!

    Jul 21, 2003
    Columbia MD USA
    I checked out the SpeakerMate thingy on HarmonyCentral. It seems like it will work. I am going to try to find out if anyone has written a review on it.
  10. WinterBass


    May 19, 2002
    Hudson Valley, NY
    Endorsing Artist: MTD
    The man from Speaker Mate offered a few suggestions including, rewireing my 3x10 cab. It seems as if the Speaker mate will work with multiple numbers of the same speakers. It doesn't seem like there is much I can do besides add an additional power amp. However I do know that these amps can handle a 2ohm load. Maybe I will have to bite the big bullet.

    EBS 650
    Aguilar 750
    IAmp 800

    Ashdown reworked their ABS heads, but they still do not hande 2 ohms.
  11. rdkill


    Jan 20, 2003
    Years ago I commonly ran a 4 ohm on my side of the stage and an 8 ohm on the other - off a 4 ohm amp. I just plugged them in and didn't worry about it and never had a problem. If you don't think your amp is of marginal design I'd say go for it! :bassist:
  12. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    I really don't recommend doing this. Although it is possible that it will work. It is also possible that you will blow your amp. I'm glad that nothing bad has happened to your amp, but it really isn't wise to recommend that other people do this.
  13. rdkill


    Jan 20, 2003
    Unless your amp is really crappy, the worst that can happen is that it will "shutdown" until it cools off...
  14. Tritone

    Tritone Supporting Member

    Jan 24, 2002
    Santee, America
    I don't mean to be rude, but that's not a good idea at all. Running below minimum will eventually (probably sooner than later) blow up the transformer of your power amp.... "Does anybody else smell something burning?":rolleyes:
  15. rdkill


    Jan 20, 2003
    Jeez, I heard it would just be - like - bad karma, dude! :rolleyes:
    So, who here has any direct experience of "blowing your amp" doing this? Do modern amps really suck this bad? :meh:
  16. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    I know someone that blew the head in an SWR Basic Black by adding an extension cab that was 4 ohms. It can and does happen.

    It is not necessarily because of bad design. If they have to design for every possible wrong thing that a person can do to an amp, then it will increase its cost and affect its performance. By putting on a load that is too small, you have the possibility of running too much current through the output stage. This can blow up the parts before they have a chance to heat up.
  17. rdkill


    Jan 20, 2003
    I looked up that amp - it is 120 watts at 8 ohms and only 160 watts at 4 ohms so I'd concede it is pushing it at 4 ohms already. I could not find this info for the ABM head but it does have some of the characteristics I look for in an amp that can be "pushed" - variable speed fan, torodial transformer, and 50 hz power capability. The later means that at 60 hz the transformer is running much cooler than it would at 50 hz so it has quite a bit of margin when run on US power. Hmm... I see that the Behringer "copy" of this amp is also 50 hz capable - if I wuz still working I'd pick one of those up to "torture" :D
  18. pjleo


    May 27, 2003
    del valley
    Ask ashdowm about the min. load on your amp.
    I have a Eden 330 time traveler that says 4 ohm min. I had the same problem 4 ohm / 8 ohm cab.
    I e-mailed eden and somebody named David answered back that the amp would have no problem handling another 8 or 4 ohm cab.
  19. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Ok, how's this for wierd. I just bought an ART 260W power amp to use in my practice rig. The specs say 4 ohms per channel. However, in one place in the manual, it states that the amp actually can handle a 2 ohm load. And no, it doesn't appear to be an error in the manual because they also acknowledge that this is less than the value in the specification.

    I give up. If manufacturers aren't going to publish accurate specs, what hope do we have of using our gear properly. I still can't recommend using a load less than the published spec, but it does appear that at least in some cases the amp can handle the lower impedance despite not being spec'ed that way.
  20. WinterBass


    May 19, 2002
    Hudson Valley, NY
    Endorsing Artist: MTD
    Thanks for the help. I will e-mail Mark Gooday at Ashdown and Jim Bergantino on this issue. I truly love these products and want to make it work. I might just have to get a small slave amp for those bigger gigs.