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acme b2 4 or 8 ohm - second guessing advice

Discussion in 'Amps and Cabs [BG]' started by amac, Jun 16, 2004.

  1. amac


    Oct 9, 2002
    Commerce, Georgia
    This could be considered a continuation of a post I started a few months ago(http://www.talkbass.com/forum/showthread.php?t=113760), but here goes...

    I ordered an acme b2 yesterday and Andy suggested that I get the 4 ohm instead of the 8 ohm, to have more watts when I run a QSC PLX 1602 in stereo (500 @ 4 vs 300 @ 8). I mentioned that I was planning on running the 8 ohm bridged and also wanted the 8 ohm cab so if I added another later I could run them bridged and have 1600W (two 8 ohm daisy channed = 4 ohm). But he thought that wouldn't work or be the best idea and suggested the 4 ohm and I went with it. I'm now having my doubts.

    Would 500 watts be good enough to push this cab? Or should I call him back and change my order to the 8 ohm since I may acquire another b2 in the future (1 cab = plx 1602 bridged @ 8 ohm w/ 1100 watts or 2 cab = plx 1602 bridged @ 4 ohm w/ 1600 watts). Running two 8 ohm cabs off a bridged amp @ 4 ohms works, right? Thanks guys.
  2. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    I think Andy is a) concerned that people using way more power than the cab is rated at will blow things up and cause him problems re warranty claims and blaming him for suggesting lots of power, and maybe b) doesn't realise how a surfeit of power really opens up his cabs and lets them play seriously loud.

    I used to use a Mackie M1400 delivering 425W into each cab. I now use a PLX3002 delivering 900W into each cab. The volume difference is such that I can leave one cab at home most of the time.

    If I were you, I'd change your order to 8 ohm cabs, run the PLX bridged and be careful with your bass boost and demanding too much from one cab. You can clearly hear when the Acmes are being pushing tpo hard, the woofers start growling/farting as they over excurse.

  3. I think Andy is also, besides the things Alex mentioned, thinking it's better, when possible, not to run the amp in its most stressed-out mode. When you bridge at 4 ohms, you're running the amp at about the limits of its ability to handle low impedances (it's equivalent to running 2 ohms/side). It isn't always a problem to do so--many people do it all the time without a care in the world--but sometimes it can be. Especially since it seems that Acmes when new--i.e., before they're broken in--can tend to dip toward the low side in terms of impedance and thus present the amp with a slightly lower load than you think you're getting. (Andy himself told me this when I was having a problem bridging into my 4 ohm B-2.)

    Personally, I'd split the difference in a way. I'd prefer to run the Acmes stereo at 4 ohms/side, as Andy suggests, but I'd get a somewhat bigger amp, like Alex, so that even in stereo rather than bridged mode, each Acme could get plenty of power.
  4. amac


    Oct 9, 2002
    Commerce, Georgia
    would 500 watts be enough for this cab? Andy said it would be a nice compliment to the cab. I've got a 1602 on order, so... I could bridge it at four and push it with 1600, but if I want another cab later, would 500 do?
  5. Lonnybass

    Lonnybass Supporting Member

    Jul 19, 2000
    San Diego
    Endorsing Artist: Pedulla Basses
    I think 500 watts would do the trick for one B2. Of course, this depends greatly on the application - it's not going to cut the mustard vs. two Marshalls and a loud drummer no matter how much power you throw at it.

  6. I had the same thoughts when I placed my order for 2 Low B-4's...and I opted for the 8 ohmers for the same reasons you have. I've got a PLX 3402, and bridged at 4 ohms will send 1700 watts to each cabinet. I realize that's WAY overkill, and Andy about 5hit a firetruck when he heard I bridged into 1 8 ohm cabinet (2200 watts). But, I kept the power amp gain in check, put my limiters and filters on, and didn't crank the bass. All was well, but after his reaction, I went stereo, sending 700 watts to one cab and I was still loud enough to fill a 200 person venue with no PA support.

    But, since I got my 2nd cabinet, I will be bridging them and bringing the full fury of the 3402 down upon them.

    I say go with the 8's, and if, at any time in the future, you want to change up power amps (either more per side at 8 ohms, or less bridged at 4) then you can do it with confidence.
  7. Can't really answer that question. The question is really, "enough for what?"

    500 W is fine for a B-2 if you don't need to play that loud. Just because you can use more power with it, that doesn't mean you have to. If you want to play louder, you'll need more power, that's all. Or, perhaps better, more speaker. Keep in mind that, roughly speaking, 500 watts into two B-2s (or one B-4) is like 1000 W into one B-2.
  8. At 500 watts per side, a second cab also get you a +3 dB boost from the coupling effect. So you would be producing something in the mid 120s which is VERY LOUD.

    OTOH, if you need VERY LOUD, I have to agree with the guys who say more power is better, if only for the headroom. This insures that you get no changes in your sound across the frequency range when you get loud. The other side of this coin is that it also puts the responsibility of protecting your speakers on you. I regularly run 1000 watts bridged into my B2, but I also use a low freq filter and a limiter. The set up Richard Lindsey suggests makes a lot of sense to me and will be the way I go if I add a second B2.
  9. amac


    Oct 9, 2002
    Commerce, Georgia
    from the varying responses, I think I'm going to switch it to 8 ohms and be careful about my levels. If and when I add another cab, I'll have more headroom with two 8 ohm cabs.

    I called and left Andy a message. I'll try and put up a review when everything comes in.
  10. amac


    Oct 9, 2002
    Commerce, Georgia
    Andy already called me back and switched my order to 8 ohm!