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Ok, I know this is REALLY been talked about..ohms

Discussion in 'Amps and Cabs [BG]' started by KlarkKent, Jan 24, 2002.

  1. KlarkKent


    Dec 17, 2001
    Los Angeles

    Ok...one more time...most bass cabinets are 4 or 8 ohms. SO ...8 ohm cabs , (from what I have deduced looking at power amp specs), suck up more power(?). For example 460 into 4ohms, and 275 into 8ohms, was what one power amp spec said. So what is the difference other than the power drain, which one is louder, which one sounds tighter/better? AM anywhere close to right on this?

    Then they,(cabs) are rated at different watts, which means what? Is that the least power you can use to drive it? In other words, lets say I have a cab rated at 600 watts @ 8 ohms, do I need at least 600 watts to drive it? If that is the case, what is the desirable,(if I can use this phrase), HEADROOM? I plan on getting a 2x10 cab with tweeter?

    thank you for responding to this super age old question, It shows you have a heart!!
  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    1. 480W are less than 3 dB louder than 275W, that's it. No sound difference per se. It is louder but far from being twice as loud.
    The watts are the power the amp puts into the cab, not the amps power consumption, which is much higher.

    2. A cab that's rated 600W AND HAS AN IMPEDANCE OF 8 Ohms (it's not "600W at 8 Ohm" when you talk about a cab!) was tested and the manufacturer decided that it can handle a signal of 600 W RMS for a prolonged period of time without exceeding the specs (distortion, etc.). The headroom (peak power) handling is probably twice as much, but that can vary. Note: peak power ratings on spec sheets are usually useless since they don't represent a typical working condition. You want high RMS power handling.
    Another thing: Ratings of this kind are done in numerous ways, there is no norm. So check the small print ;)
    The 8 Ohm only tell you that your amp will see it as a load of ca. 8 Ohm and will deliver roughly the power it has been rated at that particular load.

    That's it (I hope).
  3. mgood


    Sep 29, 2001
    Levelland, Texas
    If everything else is equal, like say, one manufacturer makes a 4-ohm and an 8-ohm version of the same cab, the 4-ohm cab should be louder with the same amp. There are still times an 8-ohm cab would be the better choice, like if you want to run two of them and you have a mono amp that will only go down to four ohms.

    Watts and ohms and all that are not the only things that make one cab louder than the other. If you really want to know which is louder, you need to look at efficiency. Some manufacturers have efficiency in their literature or on their websites. Some you just have to call and ask. It is usually listed something like "Sensitivity: 98dB @ 1w @ 1m." That means that if you power that cab with one watt and measure how loud it is one meter away, it will be 98 deciBells sound pressure level (dB SPL). If one cab is rated at 98 dB @ 1w @ 1m, and another is 101 dB @ 1w @ 1m, the 101 is 3dB louder. It will take about twice as much power to make up that difference.:
    The cab rated at 98 dB @ 1w @ 1m will be 124 dB @ 400w @ 1m.
    The cab that is 101 dB @ 1w @ 1m will be 124 dB @ 200w @ 1m.
    That assumes that those power levels are well within what that speaker can handle. It does not take into consideration things like power compression or how well each cab dissapates heat. (We won't get into that right now.)

    The power that a speaker system can handle may be rated several different ways. Mostly though, it is a continuous rating. It means that that speaker can take that much power continuously for a long period of time. Playing music won't give you a continuous amount of power. There will be peaks here and there, but most of it will be well below peak. For that reason, you can get away with having an amp rated at much more power than what the speaker is rated at. Many people like it this way so they have extra headroom. Clipping, or distorting, the amp will kill your speakers faster than overpowerring them will. Having a bigger amp than you need helps to ensure that you never, or rarely, clip the amp. I like to have 1 1/2 to 2 times as much amplifier power available than what I need. What I think I need may be closer to what the speaker is actually rated at. So, for a 400w speaker, I might have a 600-800w amp. THIS IS NOT AN IDIOT-PROOF SYSTEM! If you are running that way, and the peak/clip lights on your amplifier are staying on or flashing constantly, that is BAD! Turn it down or you're going to lose your speakers. Having the extra headroom allows you to run near the full potential of the speakers most of the time, but still have plenty of room in the amp for the occasional louder peak. Your speakers can handle that just fine.

    I'm sure Bob Lee and some others here can explain that better than I can. I'm not sure how clear my explainations were.
  4. KlarkKent


    Dec 17, 2001
    Los Angeles
    ok...thanks guys!!! Looks like if I'm running just a 2x10 cab with about a thousand watt power amp, I'm looking for a 4ohm cab rated at about 600 watts. This should be just fine, right?

    Klark Kent