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How many watts to spare?

Discussion in 'Amps and Cabs [BG]' started by needmoney, Feb 28, 2005.


  1. I'm about to purchase a couple of cabs for my Eden WT-400 and i'm just curious, how many watts should I have spare, for example, is 500 watts (4 ohms) handling enough for the WT-400 to run safely at high volumes?
     
  2. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    EAW recommends that your amp be rated at 1.5 to 2 times your speaker rating. You've got it backwards. Let's say you get just one D-410XLT, rated at 750 watts. That means that, as you turn the amp up, it will begin to clip long before you reach the power-handling capability of the cab. Bad karma. Speakers hate clipped signals.

    On the other hand, with plenty of headroom at the amp (Say a 1,000 watt amp), you won't be clipping it at 750 watts output. The danger here is that you can blow the speakers by sending 1,000 watts continuous, especially if it has a large low-frequency component. The extra headroom is for short peaks in the signal. The D-410XLT probably can handle 1,500 watts or so for short periods. Just don't crank it all the way up.
     
  3. Hmmm gotcha, I'm actually thinking of getting 2 cabs both with a rating of 250 watts RMS each at 8 ohms, Is this a bad thing?
     
  4. Sundogue

    Sundogue

    Apr 26, 2001
    Wausau, WI
    Not necessarily. As Munji said, ideally you'd like to have your amp put out more watts than your cabs can handle. Your Eden head (I own the same one) will put out 400 watts into a 4 ohm load.

    So if you have one 250 watt, 4 ohm cab, your Eden will put out 400 watts and you'd have 150 watts of headroom. But you can still get two 250 watt 8 ohm cabs. Just don't drive them hard.

    I either run a single 8 ohm 210 cab (rated at 150 watts) where my Eden head puts out 225 watts into that 8 ohm load (which gives me only 75 watts of headroom...but I don't push it too hard usually). Or I run it into a 4 ohm 410 cab and my Eden WT400 puts out 400 watts into that 4 ohm load. My 410 cab handles 350 watts, so I only have 50 watts of headroom. But again I don't push it very hard (not that I really need to).

    If you find that you are playing at very high volumes and the Eden WT400 just isn't enough power, you can always use another power amp to give you more watts and use the WT400 as a pre-amp, so you'd still get that Eden sound.

    But unless you are really in a very loud cranking band, those two 8 ohm cabs with your Eden head should suffice. Just don't go cranking it.
     
  5. Okay, so what happens if I drive them hard (the two 8 ohm cabs)? The amp starts to clip? Isn't it worse to have it at the same volume with a cab that can't handle it? Which makes for the easiest way of blowing the speakers? I'm a little confused.
     
  6. nastyn8c

    nastyn8c

    Feb 7, 2005
    Tampa, FL
    Why don't you consider a pair of 8 ohms Eden 210XLTs? Great cabs, plus you can use one for smaller venues and both for larger.
     
  7. TheChariot

    TheChariot

    Jul 6, 2004
    Boston, MA
    If you clip a 100Watt amp into a cab rated 800Watts RMS, there is a significant risk of speaker damage. Clipping is really horrifying for speakers, no matter what your clipping at. Limiters may dull you down a little bit, but I'd rather pay for a little more power than clip at all :eek:

    Munji pretty much laid it down really well on the power rating topic. I would think you should aim to power your cabs with about 1.5X the RMS rating of your cab(s). You dont need that, especially if you have efficient speakers... but it would give you as much extra headroom as you can load onto your speakers without getting carried away. So since your looking at a pair of 250Watt cabs, I'd recommend about 650-750Watts @ 4ohms.
     

  8. This is just not true. It is just about impossible to damage a 800W rated cab with a 100W no matter how much you clip it. It just can't produce enough power to damage a cab rated that much above it. Yes, I have tested this experimentally

    Now make that a 600W amp in hard clipping and you might be getting into the damage range with an 800W cab. But it's because a '600W' amp will produce considerably more power than that when clipped.

    Speakers don't care about waveform as such, they care about LF energy (excursion) and power (heat). If clipping in and of itself was directly responsible for damaging speakers you wouldn't be able to use a distortion effect. Distortion and/or overdrive is clipping.
     
  9. I should also say that using an amp rated at 1.5-2x the cab's rating is appropriate if you're wanting to squeeze maximum performance out of the cabinet. This is pretty essential for PA purposes.

    However, there's nothing wrong with using an amp less powerful than the cab's rating, if the combo of the amp and cab is loud enough for your purposes without driving the amp really hard. If you need to get the amp into clipping to get enough level, you need more power, more speaker or both. Unless you're using a tube amp and are looking for distortion....:D
     
  10. TheChariot

    TheChariot

    Jul 6, 2004
    Boston, MA
    Well, you definately win that one, since you've tested it. I honestly am basing most of my opinions on minimal experience (thankfully) with clipping, as well as a lot of horror stories I've read on here. Looking back, The "100W to 800W" comparison is pretty ridiculous :p. But the theory I've been playing by (which I mostly developed through TB) is that clipping poses a major risk of damage to most any speaker, despite the power ratings either of them poses. Now, that theory has to be somewhat elastic, cuz if a cab can handle 700% more than the amp is rated at.....

    ... but hey, good to know. Anyone else know any more on this scenario (even though I'm sick of talking about clipping).... maybe in the mood to prove me wrong a little bit further. :p
     

  11. There are a lot of factors at play (of course :p) in the mechanics of damaging speakers and a lot of it is heavy on engineerspeak (of course :p). The upshot of it is that there are ranges of amp-speaker power ratios where clipping the amp most certainly can damage drivers. This is mostly because the amount of power an amp can put into a speaker increases beyond the rated power of the amp as it goes into clipping. Under extreme clipping (ie 100% distortion) an amp will put out almost twice its rated power..... So you see how a 600W amp might damage an 800W cab under hard clipping, because it will put out more than 600W under those conditions.... But a 100W amp could only source about 170-180W under hard clipping, which an 800W speaker can easily handle...

    Of course there are also things that derate a speaker's power handling capabilities, like cabinet tuning.....You can melt a voice coil with perfectly clean power way less than the speaker is rated for if you concentrate that power at the cabinet's tuning frequency because the acoustic suspension will just about stop all cone movement at that frequency. Stopping cone movement reduces the amount of power the driver can dissipate.....

    etc, etc.....

    So it's not a real simple problem....:D
     
  12. Well i'm pretty sure i'll never have to drive the amp into serious clipping, so I should be okay. Thanks for all your help!
     
  13. remo

    remo

    Jan 15, 2005
    I'm looking at getting 2 Avatar cabs: a B210PRO (1000watts) and a B212 (1000watts)... would a QSC PLX 3402 (1100 watts into 4ohm stereo) be a good safe match for these cabs? With a MXR M-80 Bass DI as a pre?
     
  14. amper

    amper

    Dec 4, 2002
    US
    I love it when this topic comes up.


    The big problem with all of this is that most manufactures are somewhat disingenuos with their ratings. For example, when a loudspeaker system manufacturer rates their product, is the rating a thermal dissipation rating, or an excursion limited rating? And is that a peak rating, or a "program" rating? At what frequency (particularly relevant for bass)?

    When an amplifier manufacturer rates the output of their product, is it peak rating or continuous RMS output? At what distortion level?

    Things to remember are the fact that a fully clipped amp (100% distortion) theoretically produces twice the power of it's output at 0% distortion. This may or may not be double the figure the mfg. puts on it.

    And, if your loudspeaker system or driver is rated with a thermal dissipation limit, even if you're running your amp at 100% distortion, if you're not exceeding the thermal dissipation rating, your driver *should* be fine. That said, it should be mentioned that drivers usually rely on transducer movement for cooling, so don't expect your driver to work like a light bulb for very long.

    This is why it's unlikely that you will damage a speaker rated at 800W with a 100W amp, no matter how clipped it's running.

    All things considered, I really don't know where people get the idea that you should run an amp that's capable of twice the power your speakers are capable of handling. A more useful reference, IMO, would be to reverse that and use speakers capable of handling at least twice the rated output of your amp. As long as you're not clipping your amp to get the volume you need, you'll be hard pressed to damage those drivers.

    If your amp can put out twice the power your speakers can handle on a continuous basis, it's quite easy to fry your drivers simply by turning it up louder. You'll never know you're near the limit unless your speakers start to distort, and by then you have very little between you and a recone job. Also, that amp will probably be putting out peak levels well in excess of what the speakers can dissipate, so they may blow even if you don't hear any distortion. I've done this myself, running a 220W tube amp into a driver rated for 150W. There was no warning whatsoever--just no more sound.
     
  15. stropsrats

    stropsrats Owner: www.kennedyaudio.com

    Feb 14, 2005
    Valders, Wisconsin
    Three cheers for amper! With more posts like that one above, we can all start to dispell the myths and cobwebs and start learning about the good stuff on talkbass. I have my two cents to add of course, studies done here (I'm a manufacturer/reseller) show without doubt that flat wire edge wound speaker are very much harder to blow out, so the wattage rating is again, like amper said first, not the thing to go by at all uness all equipment is from the same source. Maybe that's where the idea of having more output than input power came from. Let's kill this myth for good. You have to consider the speaker damping too if you are going to run near max capacity and the amp's cooling.
     
  16. easy

    easy

    Mar 16, 2005
    seattle
    man, I'm just getting confused, the more I read about this stuff. My head makes 300w at 4 ohms. I'm using two cabs, each one handles 200w at 8 ohms, so my speakers, in total, handle 400w at 4 ohms. I thought underpowering my speakers is best. am I wrong? Am I going to hurt my head by underpowering my speakers? or do I have it right?
     
  17. Jmaginnis

    Jmaginnis

    Mar 15, 2005
    I don't wanna hijack here, but what *exactly* is clipping? I mean, I know what clipping is and does to speakers, but what exactly is happening that causes the clip?
     
  18. Passinwind

    Passinwind I Know Nothing Supporting Member

    This topic had been here done countless times, and it invariably turns contentious. Here's a link in the Amp Forum FAQ, for instance: http://www.talkbass.com/forum/showthread.php?t=91962

    amper: All things considered, I really don't know where people get the idea that you should run an amp that's capable of twice the power your speakers are capable of handling.

    Handling for how long? Peak or RMS? At what frequency and how close to the drivers' Xmax or Xmech? Solid state or tube? What crest factor do you run at with your gear and musical style? It's a can of worms, as you say, but to answer your question, they get the idea from the multitude of manufacturers' websites and pro sound reinforcement sites and manuals that espouse it. It works really well for a great many of us, too. Go through the search ordeal, you'll find every viewpoint well-considered and articulated somewhere in the morass. :cool:
     
  19. stropsrats

    stropsrats Owner: www.kennedyaudio.com

    Feb 14, 2005
    Valders, Wisconsin
    I have to admit I am struggling with explaining the watts thing on my website pages, in spite of having collected a large number of sources. Some of the things I had to say make less sense the more I think about them. But one thing I did learn is that matching watts continuous to speaker rated watts invites thermal problems. These can be engineered around too of course. On the other hand, not matching by using heavier duty speakers really reduces the volume in general. I surmize it often comes down to how long you play at high volume and how long your break time is for cooldown.
    Impedance is like these little icons that jump around, right?
    But seriously, my personal solution: I only use 16 ohm speakers so the extra dampling factor takes care of all the 'fudge factor analysis' for me.
     
  20. stropsrats

    stropsrats Owner: www.kennedyaudio.com

    Feb 14, 2005
    Valders, Wisconsin
    The engineer actually does not even want to talk about some things, so I'm on my own. He does claim to have an amplifier that is tested at .25 ohms continuously, by adding cooling to the amplifier directly. Because it's so risky, I slapped a price on the cooling package, but it can be done on an 'at your risk' basis. If anybody out there wants to review such an idea, let me know with plenty of advance time. It would work best if you had an old amp that nobody cares about. I would outfit it and run to failure, more fun too! :hyper: