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wattage

Discussion in 'Amps and Cabs [BG]' started by Stingray, Jun 6, 2002.


  1. Stingray

    Stingray

    May 12, 2000
    this is really a question for my guitarist but it should be relevant to te same situation with a bass
    do you have to have an equal or greater than head for a cabinet of say 200w or can you buy one that is less pwerful than the cabinet and still run it safely with the cabinet pulling extra power throug he head that it cant handle. thanks
     
  2. You gotta get the physics straight first.

    The head supplies the power, and it is limited by its nature. A 400 Watt head will only supply up to 400 Watts.

    The cabinet uses the power to produce sound. Its power rating is how much power it can handle.

    A cabinet rated for 500 Watts can handle power from 0 to 500 Watts. You could drive the 500 Watt cabinet with a 400 Watt head, and the cabinet would only see up to 400 Watts, which is under its limit of 500 Watts. So everything is cool.

    This is a simplification, but basically that's how it works.

    Chris
     
  3. ZuluFunk

    ZuluFunk

    Apr 14, 2001
    Pennsylvania
    Just don't go to the other extreem.

    Using too high a rated cab for you head can do damage to the head. The amp can get burned out because you drove it too hard.

    Tha better way to go is have excess power in the head. I go with double the power that your rig can handle a continuous signal. Usually the peak signal the cab can handle is around double the continuous rating. My BagEnds are 4ohm 400-800 and 8ohm 200-400.

    The channel with the 4ohm load on my QSC puts out up to 750watts (into 400-800), the 8ohm load is driven by 500watts (into 200-400). I've never had the need to drive my amp past 12-o'clock on each side, the master on my pre about half-way too. The gain control rarely gets even close to half.
    I'm not pushing the amp anywhere near the limit of the head or the speakers. The sound is huge and very clean all the way down.

    Unless you have all the volume and power control maxed out you shouldn't have to worry about blowing your speakers.
     
  4. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    John, this just isn't true. Your cab rating has nothing to do with how hard you drive your amp. The only way anything can get hurt is if you push your amp too hard (and not always then), and having a lower rated cab does nothing to protect you from that if you don't have enough amp for the job. Using a high-rated cab doesn't harm either the cab or the head.
     
  5. jamminji

    jamminji

    Mar 22, 2002
    It is funny... I have heard many guitar center sales people tell me that I can blow my amp if I hook up a speaker with a higher rms power rating then my head. I do not know who is spreading this rumor but it sure is causing alot of problems when they tell this to newbies and they believe it. You can have a cab that is rated for 1000watts rms and hook it up to your 10 watt practice amp, with no ill effects. Well not "NO" ill effects. The sound will be crap because your little amp will not be able to drive the cab hard enough to get a good tone most likey. BUT you will not blow the head, unless you crank the head to it max and the amp then goes inot clipping. At that point you "could" but not abosolutly blow either the cab or the head or both. You will blow the speakers because the amp is now sending out a square wave (clipped) to the speaker and speakers do not like this. The amp 'could blow because some amps are not designed to run at max levels and will overheat. Now in my example of a 1000w rms speaker and a 10w head, even a clipped signal would probably not cause a speaker problem (just too little power) but you could blow the amp. But not because of the speaker. It would be because you turned the head all the way up. I really wish GC would stop spreading incorrect info.


    jam
     
  6. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Man, I don't know who starts this stuff either. My guess is that it starts with something sensible that through endless repetition and misunderstanding gets turned into errors. For instance, it's perfectly true that you *can* use a 400 W amp with a 250 W cab in many circumstances. It's *untrue* that it's *inherently* safer to do this, across the board, than to use that same amp with a 600 W cab.

    BTW, no personal animadversion toward you is meant, John Z.

    I very seriously doubt that a 10 W amp is ever going to blow the average 1000 W cab, no matter how hard it's driven. If the system has a tweeter, and that tweeter is only rated for 15 or 20 W, then yeah, maybe. But in a box that size, the tweeter would probably carry a rating closer to 100 than to 10.
     
  7. Stingray

    Stingray

    May 12, 2000
    Im not a newbie but i have heard a lot of junk that way before ive jus always use dmy 200watt combo never a cab and head. but when pete my guitarist wanted to buy an amo and thought of goin amp and cab and asked me about it( i guess i have the most sound knowledge out of the entire group) i told him what i had heard i always though it was a loud of bull. i just figured id ask you guys for help because i didnt wanta have him buyin a new amp a day after our next show. thanks for clearin up the wannabe guitar tech sales pitch lingo from the guitar store.
    Anotherquestion though i just though of, is a 200watt combo worse better or the same as compared to a cab and head of the the same watt power give me some pros and cons to both.
     
  8. DBeall

    DBeall

    May 10, 2002
    Vancouver, Wa
    The only way a speaker will blow is through exceeding its thermal handling capabilites...i.e. exceeding the thermal handling of the voice coil...

    This is not necessarily done through clipping (square waves) it can be done through an amp that is rated higher than the woofers receiving the current...If your going to over power your cab, be smart and adjust the gains properly...

    Just because you run square waves to a woofer doesn't mean it will blow...it just means your essentially running a sine wave with upper order harmonics to your woofer...which shouldn't hurt your cab due to crossovers....

    Distortion is not always bad for the cab...just for the ear....

    Exceeding thermal handling on a woofer is bad...but this not always done by square waves....
     
  9. DBeall

    DBeall

    May 10, 2002
    Vancouver, Wa
    My bad I did leave out overexcursion...

    There's actaully 3 ways a speaker can be damaged

    1)Thermal Failure
    2)Mechanical Failure
    3)User Error

    Overexcursion is caused by overpowering your woofer, or improper box design....Both can be fixed on the user end, especially if your building your cab from scratch....

    But...
    If you clip a 300 watt amp, you are doubling the current output of the amp in the form of a square wave with upper order harmonics...these can be negated by the fact that the speakers acts as a mechanical low pass filter...

    ...It is this increase in current that causes failure in the voice coil, or overexcursion...
    ..But not the clipped signal itself...

    A sub rated at handling 1200 wRMS would be able to handle a 300 wRMS amp clipped to all hell....

    It wouldn't sound pretty, but it wouldn't blow....

    Gains are there for a reason.
    .....
     
  10. ZuluFunk

    ZuluFunk

    Apr 14, 2001
    Pennsylvania
    Hey, I'm cool with the way you expressed your point. I agree with what you're saying about GC salemen speading BS. However, to my point, look at it this way (to get what I meant - sice I never go to any GCs ;) ), if I have a 200 watt amp and a 400watt speaker, I will sound fine through that speaker if I'm pushing 3/4 power (150watts). However, for stage settings that I've been in, most 200watt rigs will hardly be heard over the PA or even the unmic'ed drums, so I'll turn up my volume over time to eventually running it maxed out... Now I've got the amp cranked just about all the way. Already my low B is sounding like flatulence and by the end of the second set I can't even hear anything except the PA, and the sound guy refuses to give me any decent push in tone or volume (either because he's an anti-bass snob, or because he's got too low powered a system and I'll suck up all the watts, or he's afraid I'll blow his speakers). So I keep that 200watt amp cranked on stage, eventually, it's going to overheat. Circuitry gets damaged and now I'm out an amp. Now I know that's got nothing to do with the amp-speaker combination per se. However, if I had the watts to push the cab near its continuous rating, I wouldn't be pushing the amp.

    200watt amp with a 200watt cab - that's fine if you're getting over the mix. You could stil be pushing the amp. If you have a 400watt amp with a 200watt speaker, you're not pushing either at 200watts. The speaker isn't going to get damaged with that load. You start running itup toward its peak rating, which is usually double the continuous rating, you'll be looking for trouble. But I'd rather replace a driver than a head or PA (which is "safer" IMO).

    My rationale only. I'm no gear head. I'm just used to my way of doing things on my system and haven't had a speaker problem yet since I started playing in 1982. It may not be the way to go for everyone, but it wasn't based on the advice of a ring-nosed guitar player assigned to the bass dept at GC.
     
  11. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    John, I see what you're saying, and I'm glad you took my point in the spirit in which it was meant.

    I agree that in the setting you describe, using a 400 W amp with a 200 W cab is probably fine. My only point was that--again, in this setting--this combination gives you *no* advantages over using the same 400 W amp with an equally efficient *400 W* cab. None at all. If anything, the latter is more likely to protect you longer if you start getting happy with the volume. The idea being that it's not important that your amp be rated higher than your cab; what's more important is that you have more watts available than you need to do the gig easily.

    And few of us have a problem with having extra power on tap, right?;)
     
  12. jamminji

    jamminji

    Mar 22, 2002
    yes Rich, that is why I bought my GK 2000rb. It has 500W per side at 2 ohms or 340W per side into 4ohms, OR 1000Watts bridged into 4 ohms. When I run bridged i go through a 350watt 4-10 and a 300 watt folded horn 18. Notice that my cabs are rated lower then my head, but I have NEVER had to turn up past about 1/2. The most protection is when your speakers are rated higher then your head. But if your head is under powered you WILL turn it up (You know you will) and that causes most of the problems with both heads and speakers for all the reasons above. Headroom is the key. With a large head you will get nice clean power becasues you are not maxing the head and if you turn it up too loud you will hear the speakers starting to distort (if you can not then maybe you need help...hehe) and you will know to turn down before you hurt the speakers.

    jam
     
  13. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    I agree with most of what you say--especially about the value of lots of amp power!-- but personally I'd prefer not to rely on listening for speaker distortion to protect the cab. Mainly because by the time you can actually hear the speaker protesting, you could be getting close to doing it some damage, if you haven't already. Ideally, I'd rather be in a position where I know I'm not gonna push *either* the amp *or* the cab near the limits.
     
  14. jamminji

    jamminji

    Mar 22, 2002
    Absolutely Rich, that is the idea way to protect your cab and your head. But if I had to choose, I would always go with more amp headroom before a cab rated at more then the head. Example: Option 1; 500watt head 300watt cab or, Option 2; 500watt cab and 100watt head. I would go for the Option 1 unless I knew for SURE that I would NEVER need more power. Of course there are always exceptions...hehe

    jam
     
  15. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    PBG, I know you like the rock like I do - can you elaborate as to why this is? I'm so sick of large arena rock shows being all about the vocals, clicky kick drum, and thin, tinny guitars. Probably why I don't go to big shows anymore... I can't stand the sound!
    Rolling it off at 50Hz is fine by me, most of the time when you actually CAN hear the bass, it's so boomy and thumpy that you can't even distinguish one note from the next anyway... Why can't they just mic everything up, leave it all flat, and turn it up? It's almost like they eq everything for maximum volume - to hell with what it sounds like, as long as it's loud!
    I must say though, the best 'big show' bass tone I've ever heard was Timmy C from Rage... sounded exactly like his tone on the records, just loud.
     
  16. ZuluFunk

    ZuluFunk

    Apr 14, 2001
    Pennsylvania
    But like I said, I'll never get anywhere near surpassing 150watts continous with my signal. But a 200watt amp will sound like crap when pushed at that level for a long time. My gain is always very low; just enough to get a strobe when I'm hitting hard on the low B. The I turn up the power on the PA then master volume on the pre.

    I like my set up and my rig can be heard very clearly without damaging any equipment yet. Knock on wood. I'm not trying to steer anyone the wrong way. Take my advice, don't take my advice...talk to the service guys at QSC, Ampeg, BagEnd, or whoever you're buying from like I did and get their feelings on your potential set up. I really think you can run a risk either way. Maybe I can find a 1200watt 8ohm cab and a 2400watt 4ohm cab. Then I'd be happy.

    I think most sound guys are raised to bury the bass because they want to save their cabs. Some just think it sounds better. Very few will stick with what you force on them during sound check. I always go out into the audience area during full checks too. I've rarely delt with a guy who will even get me at rehearsal levels. Maybe I just suck and they are doing me and the audience a favor!!!
     
  17. Rockbobmel

    Rockbobmel Supporting Member

    I went to a Metallica show a few years ago, and they were so ovr the top. They must have done the sound check at lower volume with an empty house, then cranked it way up without further EQ. On the other hand, I saw part of Ozzfest lasst year, and Marilyn Manson was incredibly loud, BUT, WELL balanced. You could hear everything perfectly. Like monitors in the studio.

    Salute to you for addressing the anti-bass people. I sometime struggle with my drummer (band leader) about hearing myself at practice. One time it was bad. I was pissed and stopped playing for half the song, and was not missed!

    I will say, however, our demo came out excellent (drummer is recording engineer too). The bass was killer. He really surprises me.

    As for live, I rule the sound now. My SVT is finally working, and I;m using it with a D410 xlt and D118xl. Daisy chained off the 4 ohm tap.

    WE WILL GET RESPECT!!