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Power Amp Question

Discussion in 'Amps and Cabs [BG]' started by xring, Sep 30, 2003.


  1. xring

    xring

    Sep 16, 2003
    Ohio
    Hello. I will soon be putting together my rig, and so far it will consist of the BBE BMAX pre, and either a QSC RMX 1450 or Mackie M1400.
    My cabs will be one of the following configurations: Avatar 212 and 210, or to start, just a 410 with another cab later if deemed necessary. My dilemma is, the cabs are offered in 4 or 8 ohm. If I commit to 4 ohm cabs, I would have to run 2 channels at 4 ohms each for the best wattage from the amps. (around 450-500w per).
    I could go 8 ohm on the cabs, but would have a marginal 280-300w per, unless I bridged the 2 - 8 ohm cabs (which is 4 ohms bridged right?) which would give an optimal 1400 watts. With the 410 cab (either 4 0r 8 ohm I could bridge from 900-1400w which would be plenty).
    So is it better to run this rig at 2 channel 4 ohms each or bridge the cabs (8 ohm) for a total 4 ohms?? I read somewhere that it might be best not to bridge as it changes the tone? My thought is that with different cab configurations, one could have different levels at the amp in order to even the volume level at each cab. Am I making sense and would you please set me straight and give some advice? I do realize that going 4 ohm cabs limits use of a regular amp head - not a problem. I did search the threads, and while close, I never found this exact question. SSL, thanks for all help! Randy:confused:
     
  2. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    Where are you playing? 600W is not marginal for most venues, it's plenty. IMO, you're overthinking this. Just buy the gear and hook it up a few different ways and see which sounds best to you. I've got the Mackie 1400i and like it a lot except for the weight.
     
  3. xring

    xring

    Sep 16, 2003
    Ohio
    Well I did hear that the Avatars sound better with more watts. I was just thinking that at moderate volumes the most efficient use of the amp would allow it to idle more, hopefully reflecting in the quality of the bass reproduction. The 212 is rated @ 1000, the 210 700, not to mention the 410 @ 1400. 4 or 8 ohm cabs? I think it's more than a coin toss! r
     
  4. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    Go w/ 4 ohms if you are *never* going to want to daisy chain it w/ another cab, go 8 ohms if you are. I run at 8 ohms a side for a total of 400-500w and have never run out of headroom. I don't use Avatar cabs, but I can't think they are *that* ineffecient.
     
  5. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    warning will robinson
    danger
    if you bridge a power amp into 1 8 ohm cabinet each side of the power amp will "see" a 4 ohm load (notice how the bridged into 8 ohms is equal to twice the wattage each side puts into 4 ohms?)
    but..........
    if you "daisy chain" two 8 ohm cabinets together or otherwise run them in parallel their combined impedance is 4 ohms and each side of the bridged power amp will "see" a 2 ohm load
    i dont think the mackie is rated for that
     
  6. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    The Mackie runs fine bridged into 4 ohms or stereo/parallel into 2 ohms per side. I'd go for 4 ohm cabs run in parallel mode so you can balance the sound of them to suit your tonal preference/compensate for any efficiency differences. If you want to add more cabs you can always daisy chain two 4 ohms cabs to each side for a 2ohm load per channel, or connect them in series parallel bridged for a 4 ohm load.

    Alex
     
  7. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    No, you're wrong about this. When bridging, don't try to figure out what each side is "seeing", just don't go below the minimum rated impedance for bridge mode. You can't bridge the Mackie into 2 ohms but you can put 2 ohms on each side. You can bridge it into 8 or 4. The manual is on their site.
     
  8. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    Are you 100% sure on this? I was under the impression that running is 4 ohms bridged was very similar to running in stereo at 2 ohms.

    Alex
     
  9. It is exactly like that. That's the reason why the minimum impedance for bridged mode is always twice that of the minimum impedance for each channel But you don't really need to think about it because the ratings for brdge mode are given to you.
     
  10. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    This is exactly correct! There should be no reason why there would be a difference in tone by using one channel or the other vs bridged. If there is an amp out there that sounds 'different' in bridged mode vs stereo them something is wrong.

    I would go with 8 ohm cabs. The Mackie can be run bridged into 8 or 4 ohms and this is the route I decided to go. I use the amp bridged at all times. I have an 8 ohm cab and I have the option to add another for bigger venues. Also if you are using the same cabs then you should not have to compensate for one or another using different volume settings on either channel.
     
  11. :)