Converting Ampeg Cabs From 4 Ohms To 8 Ohms

Discussion in 'Amps and Cabs [BG]' started by TimSterling1981, Jan 22, 2013.

  1. TimSterling1981


    Jan 19, 2012
    Lees Summit, MO
    Endorsing Artist: AmpClamp, InTuneGP, Morley, Rotosound, Spector
    Hey all,

    I will soon be purchasing a couple older Ampeg SVT18E 1x18" cabs for my biamp setup (the "EN" versions with the Speakon jacks). I noticed that these cabs are 4 ohm cabs. I am using Ampeg SVT410HE cabs on top for the high end/mids (currently running SVT15E 1x15"s on bottom). The 4x10"s are 8 ohm cabs, as are my 15"s, so they work fine together with my rig; however, since I'm replacing the 15"s for 18"s, the 18"s need to be 8 ohm cabs as well. Is there an easy way to convert the Ampeg 1x18" to an 8 ohm cab so that it plays nice with my biamping rig (I need to be able to run 4 cabs daisy-chained for a total load of 2 ohms, hence why I need to mod the cabs)? Is it as simple as swapping the stock 4 ohm 18" speaker for an 8 ohm one?

  2. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    Yep. That would get it done. Swap 'em out.

    Get ready for a barrage of why you shouldn't be running different drivers, especially the power division between 4-driver cabs and single-driver cabs. For now, I will spare you.
  3. Yeah, you would need to change the speaker. I don't know if Ampeg have one as stock. While physically any 18 inch speaker should fit, that doesn't mean it'll play nice with the box, would be cheaper and make more sense just to buy 8 ohn 1x18s.

    You may also find that single large area speakers aren't any better for low end than the 10s you have, no real reason to biamp like that. Such a massive mix of speakers is going to be, erm, interesting when it comes to sound wave interference.
  4. You could also run your 118s in series for a total load of 8 ohms on that side. Running that side parallel with the other two cabs, which were parallel to each other, would give a total load of ~2.6 ohms.

    Not sure why the total impedance matters if you are biamping.
  5. wcriley


    Apr 5, 2010
    Western PA
    Assuming you're running the 18s on the low side of the crossover and the 410s on the high side, the power amp would see a 2 ohm load on the channel for 18s and a 4 ohm load on the channel for the 410s.
  6. TimSterling1981


    Jan 19, 2012
    Lees Summit, MO
    Endorsing Artist: AmpClamp, InTuneGP, Morley, Rotosound, Spector
    Oh, I was already prepared for a bombardment of replies that had nothing to do with providing me with an actual answer. ;) LOL. Thanks for a quick one, though!

    I discovered from Ampeg that they actually made two SVT18 cabs...the SVT18 is a 4 ohm cab, while the SVT18E is an 8 ohm cab.

    Yes, I am biamping, but I'm using one head to do so; the maximum load I can put on one side is 2 ohms. I need the ability to expand to four cabs per side (4 top cabs for highs/mids, 4 bottom cabs for the real subterranean lows) in the event of a massive outdoor show.

    Yes I realize it's overkill to most. Yes I understand the physics behind why 10" cabs sound better to most or move more air or whatever the reason of the week is. But it's all about the tone I'm after (and tuning down to low G on a 5-string, I need that extra girth in the low end). If something sounds good and works and fits within the tonal spectrum of the band, then to hell with physics.

    Besides...I don't hear anyone telling Mike Inez that his custom SVT 2x18"s sound like garbage. ;) If you know how to properly run and EQ that type of cab setup, and you know how to tweak it from venue to venue to sound good in that particular environment, then it will sound just as good, if not, better than any head-thru-8x10" rig. It's all about proper EQing and tweaking the mix and volume levels of each set of cabs to that particular venue, be it a massive outdoor stadium gig or a small club deal. The average bass player (not to slag anyone) wants a quick setup; just plug & play. But the great bassists know how to fine-tune a rig to the point where it may seem like an oddball to most (look at the way Billy Sheehan runs his amps).

    Thanks to all for the input, and I apologize if any of my words came off offensively...just trying to be lighthearted with the physics players who will argue about this kind of setup. ;)
  7. wcriley


    Apr 5, 2010
    Western PA
    Oh. Didn't realize you wanted to run 4 cabs per side.
  8. mbelue


    Dec 11, 2010
    Yeah that was somewhat unclear at first.
  9. Ditto.

    Even then, he could still run 4 cabs in a series/parallel arrangement on each side if need be.
  10. TimSterling1981


    Jan 19, 2012
    Lees Summit, MO
    Endorsing Artist: AmpClamp, InTuneGP, Morley, Rotosound, Spector
    Basically, I want to be able to run one full stack (4x10" + 1x18") on each side of the stage for smaller shows, and two full stacks on each side of the stage for the big outdoor ones.

    We like to run all over the place when we play, and having bass amps on each side of the stage ensures that everyone hears the bass and can lock into the songs better. We tried running one stack on stage left with some DI bass signal in the wedge monitors; no one liked it. You could hear the notes and the attack and grind from the wedges, but none of the full, warm low end that you get from bass cabs. We just lock in better when we can hear the full tonal spectrum of the bass no matter where we're standing onstage.
  11. mbelue


    Dec 11, 2010
    If you don't need extreme volume from each stack, series-parallel would be a quick fix. Sounds like you are looking more for"coverage" them anything else.
  12. Tuned


    Dec 6, 2007
    I'm struggling to think of a real situation where this sort of stage volume and coverage is practical where there wouldn't already be adequate side fills to do the job.
  13. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Running a speaker system on each side of the stage is going to cause problems with cancellations in different areas of the room. I did this at one time. Then I walked out on the dance floor, during a sound check, to find areas where I was way too loud in the mix and others where I was virtually inaudible. I stick to one side of the stage nowadays.
  14. YuppyPunk


    Oct 21, 2011
    I think you misunderstand people when they say physics. In this case there is no reason to beleive that the 18's produce better lows than the 10's. In fact you get better tone by reversing using the 18's for the highs and the 10's for the lows.

    You use the example of Sheehan, but he runs cabs that are designed for exactly what he's using them for rather than using the conventional wisdom (which is often wrong) of 15's and 18's are good for lows and 10's are good for highs.

    Rather than saying to hell with physics why not use it to produce the sound and volume you want with a minimum of equipment rather than having to throw more equipment to overcome the likely phase cancelling issues that your setp produces. That is unless you like shlepling more stuff that you need to.
  15. YuppyPunk


    Oct 21, 2011
    Sound guys love having stage volume completeing with the FOH...or not so much.
  16. Go for those or another brand, unless you are going purely for image, it seems like a massive waste of money to buy 118s just to replace the speaker in them.

    If you want real subterranean lows, you'd probably be better looking at some subs instead of full range bass speakers.

    What we are trying to tell you is that the best low end probably won't be had with a single full range speaker. To hell with physics if you want, we are just trying to help.

    One of the first pictures of him on image search shows him with an 810, smart guy!

    I'm not saying 18s are garbage, I'm saying you'll face issues caused when mixing speakers and that they might not be what you are looking for.

    I know perfectly well how to EQ properly, I also know the limitations of a stage rig when it comes to gigs, like when outdoors.

    The best players can know how to get it to work without every bit of gear under the sun. From personal experience my 810 pumps out a hell of a lot more low end than my 215 and I certainly have a fuller on stage sound using the 810 than using the 410+215 setup I used a couple times.

    Just trying to help you out, if you don't want advice, don't take it, people trying to help doesn't equal people trying to attack what you want to do. Don't worry, it doesn't come off as offensive, nieve and arrogant maybe.

    I will also re-state that you can run them series/parallel. The 4x4x10s could just be all parallel, as you know. Run the 4 ohm 118s as two pairs, each pair in series (so each pair is a load of 8 ohms), then run those together in parallel bringing total load on that side to 4 ohms. You won't have the full power capabilities of the amp, but the real volume difference would be negligible.

    The problem of interference I was talking about could be pretty evident, depending on the space. You'll likely end up with a number of dead spots around the stage. Not so much a question of tone or spectrum, but a question of coverage.
  17. You can't argue with already proven physics. The word you're looking for is remonstrate: "to present and urge reasons in opposition".

    You can mix drivers all you like but please listen to BassmanPaul about not putting one stack on each side of the stage. If you want bass, no bass, BASS, bass, huh what's up with the guy playing that thick string guitar one string at a time, I can't hear him at all, BASS, go right ahead.
  18. Everyone has an opinion so here's mine. If you are going to run four cabinets off of each side of your amp make sure that you have a big one. Like at least 1000W per side at 2 ohms big.

    If you are going to bi-amp (which I would if I were you) I recommend using a subwoofer. You can get them with amps and crossovers built-in (active) or passive so you will have to use your own amp and crossover. Lots of companies make them like Peavey, Yamaha, Bag End, Carvin, ElectroVoice, JBL, Cerwin-Vega, QSC, etc. Here is a link to what guitar center has. If you are going to use an active subwoofer then your amp does need to be nearly as big.
  19. JHAz


    Jun 29, 2011
    Although the Ampeg 118 is specified to go pretty deep (-3 dB at 35 Hz), changing the speakers to something different provides no guarantee whatsoever that you'd still get the same frequency response. Different speakers, different response characteristics, different results in the same cab.

    Putting bass cabs on opposite sides of the stage can cause problems in the room. A 40 Hz (low E fundamental) soundwave is about 28 feet long. The closer people in your audience are to having the two stacks be 14 feet different in distance from them, the closer they get to having the 40 Hz wave from stack A being exactly out of phase from the 40 Hz wave from stack B, with the result that the two outputs will add up to something like zero in that location, because one is pushing when the other is pulling. 60 Hz wave (about a C) is 18 feet long so a cab to ear difference of 9 feet zeroes out that frequency for listeners in that position . . . .
  20. TimSterling1981


    Jan 19, 2012
    Lees Summit, MO
    Endorsing Artist: AmpClamp, InTuneGP, Morley, Rotosound, Spector
    Correct me if I'm wrong though, but can't I just adjust the phase of one set of cabs to correct this problem?