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Question about running two cabs and wattage

Discussion in 'Amps and Cabs [BG]' started by Wownirvana, Apr 28, 2003.


  1. Wownirvana

    Wownirvana

    Jul 7, 2002
    Athens, GA
    I am planning out the next few pieces of gear I'm going to buy and I've decided to upgrade my amp. I have a Mesa Powerhouse 2x10 and I'm going to go buy the 4x10 this summer. The 2x10 is rated 300W at 8 ohms and the 4x10 is rated 600W at 8 ohms. I know that I can get a head that runs at up to 600W@4 ohms and be safe, since 300W would be getting sent to each cab, but is it possible for me to get a 900W@4 ohms cab and it still be safe, even if I cranked it?
     
  2. i feel comfortable putting up to 500W on a 300W cabinet. depending upon the cabinet, some people will put up to 700W amplifiers on 300W cabinets.

    i can explain why that is if you want, but it's apparently too early still. i just tried to write it out, and i couldn't get it to make sense without using terms like "duty cycle". :eek: usually i'm much better at explaining than that. :rolleyes:

    robb.
     
  3. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    Oh, go on, have a go! If "duty cycle" is as hard as it gets at least some of us will understand it.

    Alex

    P.S. You do realise that it's your fault that I'm intending to start putting over 700W through each of my Acme Low-B2's, don't you?
     
  4. You're wanting to know if it is possible to use a 900 watt 4 ohm cab with your existing 2x10-300 watt-8ohm cab? It really depends what impedance load your amp can push. Pairing a 8 ohm with a 4 ohm in parallel makes 2.66 ohms. Many single unit amp heads will operate at 2 ohms but many won't. Most stereo power amps will operate at 2 ohms per side in stereo or parallel mono mode but few can operate below 4ohms in bridge mode. So, you're gonna have to be careful if you decide to go the root of 1x8 ohm and 1x4 ohm. Being that you already have the 2x10 you might consider a single 15 (1x15) cab to add with it. This combination with a 600 watt head is very popular and for good reason, It Kicks!....:bassist:
     
  5. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    If I understand you correctly, yes, you can use an amp that puts out 900 W at 4 ohms with those two 8 ohms cabs. Each cab will have a max of about 450 W available to it under normal operating conditions (i.e., not driven into clipping). Many people use this kind of setup with no problems. But no, of course we can't guarantee that it will be OK "even if you crank it." If you need to crank your rig, you probably need more amp AND more speakers. One of the best things you can do *not* to damage your speakers is DON'T CRANK THE AMP. The whole rationale for getting those big amps is precisely that you don't have to crank them.
     
  6. bah! alex, you're the "some people" of "some people will put up to 700W on a 300W cabinet". i think the acmes are up for it, too.

    ok, it's a little while later, and i've just finished watching the scintillating peavey stu hamm/BAM210 videos, so here goes...

    speakers have two ratings -- RMS and peak. the peak rating specifies how much instantaneous power you can put on the speaker without damaging it. this is largely determined by the voice coil and the excursion the cone is capable of.

    the RMS rating is a little different. it specifies how much power you can put on a speaker over the long term, an average if you will. this is more a measure of the speaker's ability to dissipate heat -- more heat dissipation equals greater power for a long time.

    thinking that way, the peak rating of a speaker is an exclamation point -- a warning not to exceed. the RMS rating, however, is really a guideline. who actually puts a sine wave of power continously through their bass rig? no one does. they play bass guitar through their bass rigs.

    bass guitar (or any music for that matter) is mostly dynamic content -- it is made up of quick peaks without a much lower sustain. in fact, most music is only 10% duty cycle -- the quick peaks that require the most energy only make up 10% of the total signal. therefore, even though you have a 300W amplifier, you're averaging much less over time. if you turn it up to get more out of the other 90%, you're going to risk clipping and other nastiness that nobody likes. (and some would argue a 300W clipped signal is much worse for a speaker driver than a 500W undistorted signal.)

    you can't know for certain what a speaker's limits are without the specifications (and mesa doesn't specify peak power handling), but i would never hesitate to put 500W of amplifier rating into 300W or speaker rating.

    i don't know, that doesn't flow to well for me, but hopefully it works for you. how did i do, alex?

    robb.
     
  7. A compressor set as a peak limiter will also help protect your speaker investment, and will allow you to utilize your amp to drive to a higher average volume. At the volumes some of us play at, dynamics are lost anyway; the ear's transient response is poor in a high-volume situation.

    And please -- wear hearing protection at those levels.
     
  8. Wownirvana

    Wownirvana

    Jul 7, 2002
    Athens, GA
    Thanks for all the responses, they really helped me out. I'm probably going to go ahead and buy a GK 2001RB, since I plan on owning two Mesa Powerhouse 4x10 cabs in the future, until then I'll just make sure to keep the volume low. I still might go for the 1001RB, depending on my money issues though~Josh