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Ohm confusion??Help

Discussion in 'Amps and Cabs [BG]' started by monroe55, Mar 17, 2009.

  1. monroe55


    Mar 17, 2009
    What would be the best way to be louder when on a gig? I play a Fender Jazz through a Hartke 7000A into an 8ohm D.Eden XLT-210. I kow you're gonna say the 2x10 is not enough so I recently got hold of an 8ohm Aguilar GS112 to go with it. Im not sure if this combination makes sense but Im really limited to what equipment I can have( financially) so I take what I can get. My confusion starts when running 2 seperate cabinets off one amp head. The hartke has a bi-mono switch which I know somehow relates to running two cabinets but my guitar player started explaining how wattage changes when doing this and that I should keep it on mono or stick to one bigger cabinet and how the difference in ohms changes, something about running parallel...blah, blah, blah. Does the set up i described ( Hartke+Eden210+Aguilar112) make sense or should I be looking for alternative equipment before my next gig? Also, I like the idea of using 2 smaller cabinets rather than dragging one huge 4x10 muthha F'er around.
  2. lug


    Feb 11, 2005
    League City, Tx
    Keep it in mono. The bi-amp function is to split certain frequencies between cabinet types but it looks like you want to run full frequency spectrum to both cabs. This should give you a 4 ohm load which is the lowest (and therefore allows the most power transfer) the amp is spec'd for.

    If you don't have a manuel, here's a link...

  3. CosmicRay

    CosmicRay Supporting Member

    I also keep my amp in bridge/mono. I run two 8 ohm cabs together giving the amp a 4 ohm load. That's about as loud as you'll get it. You will loose some volume in bi-amp mode.
    In ohm world 8+8=4
    Connect the two cabs together, then into the Hartke.
    Also the amp should be at least 500 watts so you can move some air.
    Also go to the mfg. websites, they should have some info on speakers and how to connect them...
  4. monroe55


    Mar 17, 2009
    Holy sh*t! Im a new member here and Im so glad to get these responses. Thank you guys so much for your help. I spent a lot of time today reading about ohms and amps and I was still a bit foggy. But the most helpful info I got was from CosmicRay. "8+8=4". You truly understood me. Awesome!!!
  5. SanDiegoHarry

    SanDiegoHarry Banned Supporting Member

    Aug 11, 2008
    San Diego, CA
    You have your ohms matched up right, as CosmicRay points out... In fact, this is a similar setup to what I have (Epifani 2x10 / Ag GS 2x12).

    But the truth is, if your band is LOUD - as in crazy metal loud, I suspect you'll need mo speakahs, bruthah. Keeping up with double-bass and marshal stacks can be *tough*...

    Wear your ear plugs!
  6. CosmicRay

    CosmicRay Supporting Member

    Thanks monroe55, glad I can offer some help. But as BigOldHarry says, you may(probably) need bigger speakers.
    I use a 410 and a 115 with an 800 watt amp
    I'm in a Grateful Dead cover band and need to pump out some low freq's
    More feeling than hearing at times...
  7. monroe55


    Mar 17, 2009
    Another question. Each of these cabinets I have are 350 watts a piece. Does that mean I should find an amp that can push @ 700 watts or is that too much for each speaker cause their only @350 watts. In other words, does joining the cabs mean I now have 700watts to safely push?
  8. CosmicRay

    CosmicRay Supporting Member

    According to the SWR website, each cab gets half the power of your amp. So in that regard the answer would be yes.
    But it's also ok to push the speakers somewhat. It's worse if the speakers are underpowered....
    Here's what SWR says....
    "Since the two cabinets are of equal impedance, each will receive half the power your amp can deliver. If your amp puts out 200 watts RMS at 4 Ohms, then each cabinet will receive 100 watts RMS maximum under clipping. (Clipping is the point where the power amplifier runs out of headroom and begins to distort.)"
    I suggest that you look around on Eden, SWR, Aguilar, and as many websites as you can
    for tech info. Most times they're helpful...
  9. CosmicRay

    CosmicRay Supporting Member

  10. Monroe55

    Please look closely at the amp and the manual, If I read them right you have two...separate power amps... rated at 350 watts each if you are running a 4 ohm load on each power amp. These power amps are not bridged ( or combined) when you are in the mono mode, they are just receiving the same full range signal.

    If you attach one 8 ohm speaker to each power amp you are probably getting 150 - 200 watts max to each speakerbox.

    If you want more put a 4 ohm speaker on each power amp to get the full 350 watts per side. You could actually put two 8 ohm speakers per power amp on this and get full power as well and be really loud due to the extra speakers as well, but it would mean getting two more 8 ohm speakers.

    If you ran both of your 8 ohm speakers off of one of the power amps you would get the full 350 watts out of that power amp, but probably less over-all power per speaker box then if you split them up one cab per power amp, plus, running both poweramps allows you to balance out the volume/sound between the two cabs.
  11. monroe55


    Mar 17, 2009
    Thanks so much BadGrandad and CosmicRay. I dont know why I have so much trouble grasping these concepts. I think Im finally getting it though. I definately need a bigger/more powerful ( more watts ) amp. The sound setup I have now just gets buried by my guitar players when I play out. I feel the speakers are good enough, there's just not enough power to push them. I now have questions about power amps but I will start a new thread for that. Thanks again, this site is F'n awesome!!
  12. UncleBalsamic


    Jul 8, 2007
    That's not true at all.
  13. Fourboardplayer


    Dec 19, 2006
    Here's a real situation that's somewhat of a corollary to monroe55's original question. I play thru a Markbass LMII 4 ohm 500w head thru a Markbass 8 ohm 4x10 cab (104HR) and like this setup very much; serves my needs well. Issue: when I bought this, I thought I'd be adding the 1x15 8 ohm cab (Markbass 151P) as well, which, in my plan would've matched up nicely (8+8=4). Except I'm 99% confident 1 year and a dozen gigs later I've found I absolutely do not need the extra-cab anymore:smug:. I put out plenty of air and good sound. I don't like being mismatched in my head 4ohm/cab 8 ohm. Based on the anecdotes here at TB it seems I'm playing basically a 300W rig, correct?

    Any ideas? Anyone want to swap my Markbass 4x10 104HR 8ohm cab for the exact cab but the 4 ohm version:help:? (btw, with a bad back at 45 years old, I'm a huge believer in this lightweight quality gear; hence, the less the better:hyper:).
  14. monroe55


    Mar 17, 2009
    So if Im using these two 8ohm cabs mentioned earlier, I'll need like an 800watt(@4ohms) amp to get the most out of them and having lots of head room to spare?
  15. CosmicRay

    CosmicRay Supporting Member

    Monroe55 -
    Yes, as long as you run the amp in bridge/mono. I use an Eden WT800C (newest version) in bridge/mono mode along with an Epi 410 & Epi 115 - both @ 8 ohms each. I plug the 115 into the 410 and then from the 410 into the bridge/mono out. The rig kills. On smaller venues I only use the Epi 410. I just have to crank the amp a little more. But since it's a smaller venue to begin with, the decibel level is adequate.


    P.S. The Epi 410 is soon going to be replaced by a Bag End Q10BX-D....The Epi 410 is a UL cab, and it just a little too mid-range for me.

    Good Luck!
  16. monroe55


    Mar 17, 2009
    Ive been looking at the WT800s and thinking of gettin one. Im a bit confused about the description of their watts. Each amp=400watts @4ohms. Bridged/mono into 8ohms = 800 watts?? Why? What if its bridged mono into 4ohms? I thought that two 8ohm cabs =4ohms thus meaning that you're only gettin 400watts off this amp. Wouldn't it be better just to use one 8ohm cab, briged, and get all 8oo watts? I like the idea of using two small cabs ( eden2x10, aguilar 112). Is this a good choice amp for those size cabs? Sorry if Im driving you crazy with these ridiculous questions. Are these WT800s trustworthy to buy used?
  17. Bridging a stereo amplifier means that you connect your speakers between the hot terminals of each channel. The power amps are then fed with identical signals except that they are 180 degrees apart from each other in phase. Thus while one amp is amplifying the positive going signal the other is amplifying the negative.

    This equates to four times the power of a single channel into the same impedance. If your amp is rated at 400W @ 4Ω/channel then it will give 800W into 8Ω bridged. If the amp is rated to work into 2Ω loads per channel then you can safely bridge into 4Ω. If not and you try, your amp will be destroyed.

  18. CosmicRay

    CosmicRay Supporting Member


    Here is what Mr Eden says,
    880 watts into 8ohms
    1100 watts into 4ohms,
    which is what you will get using two 8ohm cabs :8+8=4
    One 8 ohm cab will get you 880 watts
    That's using the new C version.
    The lower the ohm (resistance) = more watts

    And when you purchase used stuff, it's always a gamble...but they are built very well and should hold up.

    "Since its introduction 12 years ago, the WT-800 World Tour has been the number one choice of our touring endorsers. Our new "C" version now boasts an improved cooling system and more power. Conservatively rated at 440 Watts (4Ω) per side with both channels driven, and 880W bridged into 8Ω and a whopping 1100 Watts bridged into 4Ω (with a minimum of 3dB of headroom), the WT800C is still the perfect choice for the touring professional. Standard features include: switchable automatic compression, mute, five-way semi-parametric tone control, electronic crossover, pre and post effect loops, stereo aux inputs, DI out with ground lift, level and pre-/post-EQ select, headphone out, tuner out, and a thermostatically controlled fan."

    Also read what Epifani has to say....http://www.epifani.com/support/faq#faq_12

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