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Watts and headroom

Discussion in 'Amps and Cabs [BG]' started by xb100, Mar 18, 2005.


  1. xb100

    xb100

    Mar 24, 2004
    NH, In
    Hey guys i was looking around at bass cabs and reading loads of stuff, and it seems that if you have a cab rated at 400 watts RMS then it would be good to power it with a 500 or 600 watt amp at the cabs ohm rating. Well i was looking around and i'm really digging the kustom groove bass head, and i was thinking of cabs to go with it, so i went and looked around and got a deal on a gk sbx 410. It's rated at 400 watts rms @ 8 ohms, and the kustom is rated at 500 watts@8ohms so i figured ok awesome. Then i went and read some avatar reviews and looked at em, and i can basiclly get 2 avatar cabs for the price of one gk 410 sbx. I was looking at the 210 models and all of em are rated well above 500 watts, and what i dont want to happen is to have the speakers in the avatar to clip because im pushing the rated amount of watts into.

    Wouldn't 500 watts into a cab thats rated to handle 700 be bad? Or maybe i mis read something. Anyways could anyone help me out here?

    I was also looking at the sb112 and its 500 watts @8ohms and since the grove bass is rated at 500 watts be a good combo or a bad combo.


    thanks for your help.

    rob
     
  2. What really destroys a speaker is clipping the signal and creating more or less square waves. This can happen easier with running a low wattage amp at or near max. It is suggested by some that you use a larger rated amp so you do not have to run the amp to the point of clipping. As long as you watch your preamp clipping light and keep the amp at a sane level you will not have a problem (that is if your cab can handle the wattage). You can blow a speaker by putting more wattage than it can handle or by heavily clipping the signal, especially at higher wattage levels.
    Either way...you stand to loose the speaker. So I have trouble with the guy who listens to others and gets a 700 watt amp running into a 500 watt cab and runs it at 600 watts. Use common sense. Don't overdrive a cab and don't clip the signal.
     
  3. The idea behind headroom is to use the most power available, not the least amount of speaker handling possible. A 600watt amp will work with a 400watt cab, but it will also work with a 1000watt cab.

    If you use a 400watt cab it would be much better to have a 600watt amp and not need it all than a 200watt amp and drive it all the way up to achieve the same volume. Now, if the 200watt amp turns out to be enough you could still use the 1000watt cab with no problems.

    I don't know if I helped or made an unreadable, confusing statement. Basically get the biggest amp you would need and a cab of at least half the power rating. More handling is fine.
     
  4. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    I think you may be misunderstanding his question. It seems to me that he's getting the 500 W amp. I don't think he's asking what amp he should get. What he appears to be worried about is, he's somehow gotten the idea (probably from the whole underpowering myth) that he's at more risk using 700 W cabs with that head than he is using a 400 W cab with it. Which is completely wrong. If 500 W is enough with a 400 W cab, it's enough with a 700 W cab of equal efficiency, and in fact safer. If 500 W is not enough with a 700 W cab, it won't be enough with a 400 W cab of equivalent efficiency either, and is likely to start damaging the latter *sooner*, if anything.

    So the answer is, of course that amp can be used with a 700 W cab just as well as with a 400 W cab, provided that the 700 W cab is at least as efficient.
     
  5. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Yes, this is exactly the point. When you use a 1000 W amp into a 500 W cab, any benefit you get comes from using a bigger amp *than the job requires*, not from using a bigger amp than the cab is rated for. If 1000 W is more than enough amp for the job, using a 500 W cab has no advantage over using a 1200 W cab, all else (such as efficiency) being roughly equal.
     
  6. TheChariot

    TheChariot

    Jul 6, 2004
    Boston, MA
    oy.... yeah, your definately missing something dude. I think you need to take a search of the forums... maybe "headroom" and "clipping" are where you should start.

    SImple answer for you.... 500W will be fine for any of Avatar's 210 cabs. Anywhere from 200W to 1200W would probably be fine for the 210Pro.... and the 210Delta would be fine at about 1000. You can overdo it a little more if you want, but then the risk factor comes into play and you could fry something.

    I recommend just getting the B212 in 4ohms. Then you'll get 800Watts into a very diverse cab. The 212 would hit way better lows and fill a room better than any of the 210's would, and isnt much more expensive. You'll probably never need anything again... and if you did, you'd get the full 1200Watts. Voila!
     
  7. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    you'll be fine with those avatar cabs. you can't "underpower" a cab, just be underpowered for a given situation. you dont clip speakers, you clip a power amp, which in turn sends a clipped signal to the speakers. this isnt dzngerous in and of itself, but a clipped power amp can generate up to a theoreticl maximum of twice its power rating. thus clipping a 500 watt amp into a 700 watt cab can give the cab up to 1000 watts to deal with, which ain't good.

    the idea behind headroom is to have "power to spare" you generally don't use anywhere near the full wattage of an amplifier, but transient peaks may be closer to full output. in a system with a good amount of headroom these peaks may be from a quarter to half power or so, which still gives you 3-6 dB of headroom above that.
     
  8. ErnieD

    ErnieD

    Nov 25, 2004
    Atascocita,TX.
    What can cause the actual clipping? A few years ago I ran a GK1001RBI into a Ampeg 4x10 HLF cab. On two different occaisions I fried 2 different 10" speakers in this cab. I thought the 4 ohm cab could handle the 540 watts from this amp, IIRC the cab was rated at 1000 RMS peak. It did well at most gigs but then at two larger rooms warehouse-like,
    (never any PA support for me) is where I damaged the speakers. I did turn the amps gain/volume knobs up more but it was not 100% cranked. Was I underpowered with this amp so that it clipped when I turned up the settings? I also did this with a 1 month old, Peavy 4 ohm cab with a BW-15", later that year. Since I started using 8 ohm cabs no blown speakers for at least 3 years now don't know if that had anything to do with it or not. Now I have a GBE 600 and 2 SWR cabs, Goli III 4x10 & SOB 15"( 8 ohms), 425 watts @ 4 ohms from this amp and I am playing outdoors later today. Have not used both cabs with this amp yet, will the 425 watts be ample? What should I be careful of, maybe sending too much lows form the EQ of the amp or bass, for starters?
     
  9. msquared

    msquared

    Sep 19, 2004
    Kansas City
    First, read this: http://en.wikipedia.org/wiki/Sine_wave

    The above example of a sine wave is what a perfect "clean signal" at constant frequency and power looks like in a lab environment. When your amp is clipping, the output of the amp looks like the sine wave with the tops and bottoms cut off. This is what people are saying when they refer to a "square wave". Clipping is caused by the amp getting a signal that it's not able to cleanly reproduce. This can mean that the signal coming into the amplifer is already "dirty" (in which case it's not the amp itself that's clipping) or it can mean that the amplifier cannot reproduce it without squaring the wave to some extent.

    What happens when the power from your amp goes to your speaker is that it causes the speaker to move back and forth, several times per second. You can very loosely compare this to being on a roller coaster. Imagine riding a roller coaster which looks like a sine wave. It would just be up and down. Pretty tolerable, right? If it wasn't ridiculously fast, you could probably ride that coaster all day with no problem. With a sine wave, this is "healthy" because it's a smooth movement.

    Now imagine riding a roller coaster that looks like a squared-off sine wave. You would get to the top, hit a corner, and get jerked into a path that's parallel to the ground. You'd sit there for a few seconds, then get jerked violently back down toward the ground. When you got to the ground, you would be thrown against the ground for the other part of the square until it was time to go back up again, at which point you are probably singing "Whiplash" by Metallica and looking for your nearest lawyer.

    This is about what your speaker is going through when it sees a clipped signal. After a few hours of some clipping, the drivers aren't feeling so well. What's happening to them is that as they are moving outward toward the end of their excursion, they are hitting that corner of the square wave and being jerked into a fixed position for the top of the wave. They have had power applied to them and are moving out, but then they have to stop. The battle between kinetic energy and electrical energy results in a build up of heat somewhere around the voice coil area of the driver. The heat buildup is the speaker equivalent of you getting your neck cracked repeatedly by the square wave rollercoaster. Of course heat buildup happens naturally, but it's much worse with square waves, and at performance volume it's even worse yet.

    Here is the tricky part: You can't always hear that your signal is clipping, and if you can, it actually sounds kind of cool to some people. Unless it's at a high volume, it's not some easily discernable clatter that makes you immediately stop and adjust your equipment. Certainly in the heat of the moment of a live show, you've got other things you're concentrating on so a subtle distortion in your sound isn't always going to register with you. This is why amps have clip lights, so you can glance back and see that hitting that low B with your thumb is causing problems.

    But as you can see, sending unclean power to your amp is bad news. This is why people like to hook up a 1000 watt head and turn it up 3/4 of the way. With a good amplifier, it almost guarantees that there won't be clipping anywhere in the signal chain.

    Note that it is absolutely possible to destroy a cabinet with a big enough power amp. A 2000 watt amp hooked up to a 1x10 cabinet and turned up all the way will fry that cab in short order. But that's not what happened in your case. In your case your amp was either turned up too loud or you were overloading the input stage of the amp somehow.

    This is almost certainly what did it. GK stuff is decent enough, but you don't have to 100% crank it to get it to clip.
     

  10. You stated very eloquently what I was trying to say...
    Thanks for making it more understandable.
    Gary
     
  11. Check out this link to a thread Iron Mike wrote to help us knuckle heads out.
    It's great. If you read later in the post headroom is discussed.
    Ohms FAQ