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Matching Amp & Speaker Wattage

Discussion in 'Amps and Cabs [BG]' started by RunngDog, Jun 25, 2004.

  1. RunngDog


    Jan 22, 2003
    Chicago, IL
    I'm planning to upgrade from a combo to a head & cab rig, but I'm hoping someone can answer a question. Some material I've read tells me to try to match the wattage of my cabs to that of the amp -- or even to use an amp with 2x the wattage of the cabs. But most of the cabs I'm looking at (Eden, SWR, Flite) are 450-500 watts. Does that really mean that to run 2 such 8 ohm cabs, I need an amp that puts out 800-1000 watts at 4 ohm? If I use a smaller amp (e.g., Eden WT400 -- which puts out 400W RMS @ 4 ohm, will the speakers be "underpowered"? And what exactly does "underpowered" really mean?

    Thanks for the help.
  2. Brian Barrett

    Brian Barrett

    Nov 25, 2001
    Murfreesboro, TN (Nashville)
    Dealer LowEndBassShop.com, Builder LowEndBasses.com
    Ideally you want more power then your cab is rated at. Keep in mind the rating on the back of the cab is RMS, not peak verse the rating on the amp is peak/clip point! So yes you want your amp to be rated higher then your cab is rated at. You want headroom in your amp over what your cab will do. You will notice better performance out of a 400watt cab with an 800 watts amp then a 400 watt amp. I’m not going to tell you to double the output of your amp, but being higher then the cab would be ideal for high volume performance. Now if your never going to run very loud then it really doesn’t matter, because this is all based off the fact that you are running at volume’s of 70 % into the cabinet.
  3. RunngDog


    Jan 22, 2003
    Chicago, IL
    What's confusing me here is that Eden itself recommends using 2 x D210XLT 8 Ohm cabinets with the WT400, although those cabinets are rated at 450 watts RMS and the WT400 total output is 400 watts RMS at 4 ohm -- which suggests that each cab would be getting only 200W or less than half its capacity.
  4. Ba55Man1ac

    Ba55Man1ac Gold Supporting Member

    Apr 22, 2004
    Sydney, Australia
    Hey RunngDog.

    The reason you always use a bigger amp is that when an amp clips (reaches maximum volume) it sends the DC rails straight to the speakers. To DC, speakers are basically a short circuit so heaps of current flows and speaker coils get fried! (look up Ohms law)

    I guess what they're getting at over a Eden is to get you to achieve a higher volume by using more speaker cone area instead of more power. This makes good business sense (they sell more cabs) and also means each speaker isn't working as hard to achieve that volume (and lives longer).
  5. Brian Barrett

    Brian Barrett

    Nov 25, 2001
    Murfreesboro, TN (Nashville)
    Dealer LowEndBassShop.com, Builder LowEndBasses.com
    I have to agree completely, its all about the sale of more gear to them. It was when the company was under eden and it is now for sure since its been bought out. But SWR and others are just the same. The head units they build don’t have the power supply’s to really make the cabs perform and you really waste a lot of money buying the head unit just for the name on it. You can buy a good power amp with twice to three times more power and a lot better power amp section quality wise and still get the same preamp section in the head unit from Eden, Swr, etc. if that’s what you want and save money with the amp/pre set up.

    I’m an advocate for buying used Preamps unless your wanting something of the audio-file quality like a Kern preamp or nice Mic Pre. You can find preamps used all over the place and buy and sell till you find the preamp that voices your rig the way you want. On average preamps sell used between 300-450 for all brands. Where not to skimp is on the power amp and buy New is a good idea with the warranty and all. The power amp is your core to your rig just like a quality cabinet is. The preamp can come and go but the two key elements, at least to me is the power amp and the cabinet. If you pay around $1000 for a killer amp like the Crest (name drop, sorry :) you can see your spending 1300-1400 on a combo and probably less verse a New WT800 cost you 1600-1800 and a third or 4th of what you could of had in Quality and power with no flexibility for the future.

    Hope that helps and again this is my opinions over time working with Pro, Semi-Pro and weekend Warriors and building their rigs.
  6. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Fortunately, that is not a correct description of what happens when an amp clips. ;)
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Amp power is generally rated in continuous average sine wave power, determined by the RMS voltage right at the onset of clipping into a certain load resistance. Reputable amp companies generally don't use "peak" or "music" power ratings.

    Loudspeaker power handling is generally specified as continuous power (AKA "RMS") or program power. A continuous power rating is how much average power the loudspeaker system can take over a period of time. It is essentially a thermal rating, because nearly all of the power put into a loudspeaker is wasted as heat (their efficiciency is roughly equivalent to incandescent light bulbs). So if a speaker is rated for 300 watts continuous power and you put an average of 350 watts into it for maybe a few minutes, there's a significant chance that a voice coil will melt and cause the driver to fail.

    A program power rating is usually about double the continuous rating. It is a roundabout way of saying this is a safe maximum amp power point for most users. Why is it safe to use a 600-watt amp to drive a 300-watt (continuous) speaker? Because the amp isn't putting out full power most of the time. In fact, even if the peaks clip a little (meaning they're hitting just beyond full power), the amp is usually putting out less than 1/3 of full power (more likely, even less than 1/6), averaged out over time. So if you avoid significant clipping, your speaker(s) will be safe.

    That doesn't mean that you must use that much power. If you use less power but can get the sound you want without clipping, that's fine, although it may mean that you bought more speaker than you actually need. ;)

    You are underpowered if your amp doesn't have enough power to achieve the sound levels you want without clipping. But there is no such thing as "underpowering" a loudspeaker.
    triode6L6a likes this.
  8. RJN1999


    Jan 9, 2014
    I have a seismic audio 3x10 cab that's rated at 300 rms but it's peak is 600 watts I was wondering if I could use a behringer bx4500h with it, and that head has 450 watts will this work well??
  9. swamp_bass

    swamp_bass I love it when a groove comes together

    Nov 20, 2013
    North Cackalacky
  10. Uli has his own way of optimistically rating the power of his units. I wouldn't be too worried.
  11. Hi.

    Welcome to TalkBass RJN1999.

    ~9,5 year bump as the first post, not bad.
    10 years is the treshold for the honorary mention and the star sticker though ;).

    You obviously did use the search function though.
    If You hadn't done that, and posted a new thread about cab vs. amp matching, somebody would've told you to do a search :).

    +1 to Bob Lee's post about power ratings.

    +1 to that as well, but not much unlike Peavey ;).

    In any case, use Your ears, just going by the numbers chosen by the marketing department is often a sure way to blow a speaker.
    Especially with ported enclosures below the tuning frequency.

  12. tdbass2


    Jul 18, 2009
    Dallas Texas

    This pdf from JBL Clarifies the amp watts to speaker watts conundrum.

    "...C. For musical instrument application, where
    distorted (overdriven) output may be a musical
    requirement, the system should be powered with an
    amplifier capable of delivering only one-half of the IEC
    rating for the system."
    More information here:

    EIC ratings are explained in the pdf, as I understood it, to mean your speaker's RMS rating, so if you're driving your 400w RMS speakers with an 800w RMS cab amp, you could easily fry your cab. Just sayin.
    Last edited: Apr 21, 2014
  13. chris_b


    Jun 2, 2007
    I prefer clean and full sounding bass and have never damaged a speaker.

    I know nothing about the technicalities of this, but my rule of thumb is that if I'm running the amp at over half it's volume then I need a bigger amp and I always have more watts in my cabs than the amp is rated for.

    I aim for headroom in my cabs as well as the amp.

    Currently I'm running less than half of a 500 watt amp into 700 watts of cab. Sounds fantastic.

    IMO, IME
  14. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    The JBL reccomendation is for systems with passive crossovers where hf elements will be fried by clipping due to the power in the harmonics produced. It has no application to woofer only type systems, if it did, guitar amplifiers wouldn't work.
    Steve Dallman likes this.
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    This recommendation white paper aplies to drivers used for musical instrument applications specifically. Has nothing to do with tweeters in the deratings recommendation.
  16. Once again resurrecting a dead thread!

    So from my understanding in this thread, its ok to have an amp rated higher than than the Cab's rating.

    I have an opportunity to buy a 2nd SWR GoLight 210 - 8 ohm.
    For an amp, I am looking into getting the Peavey MiniMega.

    However, the seller of the cab says he doesn't recommend 1000W into two of those cabs.
    Why would that be?

    Please please please correct me if I'm wrong here.
    1000W at 4 ohm, into two speakers rated at 400W, wouldn't that split to be 500W into each cabinet?

    Wouldn't that provide decent headroom, or am I missing something obvious?
  17. Headroom is only headroom if it is USEABLE. The cabs "limit" the headroom to 800 watts combined, the extra 200 watts (1000 watt amp) is for destroying speakers, NOT headroom. I have 8 foot ceilings in my living room but there is light years of headroom above that I can't use.

    To be completely honest I would not push 800 watts into the two cabs of bass guitar. Low frequencies are much harder on speakers than white or pink noise testing.
  18. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    If you are running the amp with two of those cabinets, the each cabinet would receive 1/2 the rated power that amp delivers at 4 ohms, or 500 watts per cabinet. I would recommend caution when operating any 8 ohm 210 or 4 ohm 410 (the equiv. of 2 x 8 ohm 210's) that way because often expectations exceed the ability of the cabinet to deliver without placing the cabinets in danger of mechanical damage from too much power. This is especially true of compact cabinets when used with an amp that has a very low high pass filter as Bobby described on your amp. The power handling of any ported speaker actually decreases as frequency drops below the -3dB point and is often about 1/2 the rated power at the -10dB point (though there are exceptions).
  19. I guess I should mention you can run a 100 watt cab with a 10,000 watt amp IF you know how to process the signal and are very good at controlling the system and yourself. You still only have "100 watts" of "headroom" and I would NEVER sell a system like that to anyone (much less trust myself with one).
  20. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    All it takes is one " enthusiastic" song...

    I always recommend going the other direction; Cabs rated for twice (or at least more than) the amp power. With an amp rated for 1000 watts, I'd want a seriously hefty pair of cabs, preferably in the 600+ watt range rating. Sure, use your ears, keep the volume in check etc, but you CAN still wreck a "400 watt" speaker with a 200 watt amp if you go bass heavy. No driver is indestructible. Common sense wins this game.

    Also consider that every knob on the amp is kind of a "volume" control... If you go boosting eq knobs, or using boost switches, you're still turning it up; even if you never touch the actual volume control.
    squidtastic and B-string like this.