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Double Bass amp wattage - does it need to be higher than the cabinet's?

Chris Paget

Chris Paget

Sep 1, 2008
116
2
#1
I've heard this before when buying a 350 watt cabinet - that it would be ideal to pair it with an amp w/ a higher wattage (I ended up with a 450 watt amp). I'm currently looking at the pairing of an 800 watt head with an 800 watt cabinet, so wondering if I'd need a more powerful head to get the best use from the setup.

Obviously there is a limit to how much higher the amp wattage can be, but just wondering if this is a general rule. Thanks!!
 
#2
The ratings on most speakers are usually for "continuous" wattage; most are capable of handling peaks of considerably higher wattage (some cabinets even include a separate peak rating).

And your instrument creates the need for peaks - loud bursts of sound or low end above and beyond the "average" loudness. The amp will, in turn, create a peak burst of energy to recreate that sound - if it can. Having extra wattage in reserve to handle those peaks is called headroom; without it, the amp will overload and likely distort (especially with a solid state amp, this won't be pretty.) So if you're running a 200w head into a cabinet rated for 400w, and you have the amp pretty much dimed, when you start pushing hard, the speaker may "fart" as the amp simply "runs out of gas" and starts distorting. This type of distortion is BAD for speakers (and my SWR 2x10 that started to smoke something fierce when I lent it to another bassist will attest to just how bad).

So, within reason, having an amp with a higher power rating (than your speakers) can be to your advantage, especially if you're USING that wattage by playing loudly - near the amp's capabilities - often. (If you're playing lower volume gigs, it likely won't matter much either way.)
 
#3
Mark is correct that, generally speaking, it is better to pair a cab with an amplifier that has a continuous power rating that exceeds that of the cabinet.

I'd like to clear up/correct a few concepts. As I posted here a while back, "headroom" has a specific definition. It's one of those terms that's more often used incorrectly than correctly. Having extra continuous wattage available is not what headroom is, technically speaking.

What causes woofers to "fart" is not amplifier clipping. Rather, that sound is caused when the amplifier overdrives the speaker. In other words, that sound is caused when the woofer is clipped. It is a sound likely to be caused by too much amplifier power. The good news is that you get a warning and you can back off the gain.

More damage is caused by underpowered amplifiers than by overpowered amplifiers. That's true for any cab with a tweeter. When an amplifier is driven into clipping, massive amounts of energy are "splattered" to high frequencies. That'll fry a tweeter very rapidly. No warning.

So, in the end, the safest course is to have an amplifier with a continuous power-rating that exceeds that of the speaker cabinet.

Alternatively, you could have an amplifier that matches the continuous power-rating of the cab but which has a hefty amount of headroom (as properly defined). Most musical instrument amp manufacturers do not specify actual headroom. Because of this, most of us buy on the basis of continuous power ratings. That's really not a great state of affairs. It would be nice to see actual tests of headroom. If those were commonly available, some amp manufacturers might be forced to change their design philosophies when the shortcomings of their circuits were made apparent. Most of this ground was covered decades ago in the home "hi-fi/audiophile" world. It resulted in testing and specification standards. It would be nice if the musical instrument amplifier world would catch up!

Finally, keep in mind that every 3 dB corresponds to a doubling of power. Musical peaks can easily exceed 3 dB beyond the continuous or average level. 10 dB corresponds to a ten-fold increase in power. Many might be surprised to learn how little power is used on a continuous and/or average basis. It's typically only a few watts. That's why an amp with a reasonable (even modest) amount of available continuous power, but plenty of (actual) headroom is so desirable.
 
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#6
I have read that when pairing cabinets with amplifiers, your power handling on the cabinet should always be at least 1.5x the power of the amplifier. So if you are looking into an 800W head, your cab should be 1200W or more. If you want to keep it at an 800W cab, you're probably looking at a 550W or less head.
 
#7
Guitarist95 said:
I have read that when pairing cabinets with amplifiers, your power handling on the cabinet should always be at least 1.5x the power of the amplifier. So if you are looking into an 800W head, your cab should be 1200W or more. If you want to keep it at an 800W cab, you're probably looking at a 550W or less head.
Click to expand...

For the reasons I've given above and in the links provided and for the reasons also noted by Mark Gollihur, I don't think that's a reasonable rule of thumb. By the way, one can always place a fuse at the input of a cab to protect against extremes, although, in most cases, it's not necessary at all.
 
#8
First of all, cab power ratings are basically meaningless. The rating is the thermo limits of the speaker. When pushing low frequencies a speaker can reach its maximum excursion long before its thermo limit. The whole under powering a cab is a total myth. I push two 410 Neo cabs with a 700rb. Thats 1600w of cab ratings being pushed by a 480w amp. If the under powering nonsense was true my cabs would already be dead.

Also clipping and distortion does not damage speakers, if that were true everyone with a fuzz pedal would have blown cabs.
 
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#10
Hopkins said:
First of all, cab power ratings are basically meaningless. The rating is the thermo limits of the speaker. When pushing low frequencies a speaker can reach its maximum excursion long before its thermo limit. The whole under powering a cab is a total myth. I push two 410 Neo cabs with a 700rb. Thats 1600w of cab ratings being pushed by a 480w amp. If the under powering nonsense was true my cabs would already be dead.

Also clipping and distortion does not damage speakers, if that were true everyone with a fuzz pedal would have blown cabs.
Click to expand...

Power ratings are not meaningless at all if they are true measures. Many companies supply meaningless numbers but that does not make the enterprise meaningless if done properly.

It is true that many low-frequency speaker cones, i.e., woofers, will reach their excursion limits well before they reach their thermal limits. That's when you "clip" the woofer (just as I mentioned in post #3 above).

There is no such thing as under-powering a cabinet. One can supply as little power as one wishes, all the way down to zero! :)
The damage occurs when an amp is driven into clipping and, as I described in detail, when tweeters are involved. The spectral splatter produced by hard and prolonged clipping is extreme and dangerous to a high-frequency driver. The power rating of the cab hardly matters in such a case. When you clip the amp, the tweeter will likely die.

So, it seems that you've misunderstood what is the issue of "under-powering." Your 4 X 10 cabs can handle 800 watts each so, of course, they will not be bothered at all by handling less power. If, however, you run your 480-watt amp into clipping and if you had tweeters, you'd likely fry them within milliseconds (literally). As I mentioned above, if no tweeter is involved, you can clip your amp all day long and your woofers are not likely to care.

So, in the end, the two things to avoid are clipping the amp and over-driving a cab.

Here's a pretty good summary, although it's not entirely correct.
 
#12
Hopkins said:
If what you are saying is true, than anyone using a fuzz pedal with their tweeters on will damage them.
Click to expand...

Wrong again. It's not the case that any distortion will fry a tweeter. Tweeters are made to handle high-frequency content. The energy produced by hard and prolonged clipping is radically different from that produced by typical effects pedals.

Many of the seemingly "expert" articles that you'll find on the internet about this are substantially flawed. For example, one article I just looked at suggested that it's not high-frequency harmonics that fry tweeters but, rather, the energy generated by clipping. Of course, that energy is made up of high-frequency distortion products.
 
#13
Exactly.

To sum up

If amp is honestly more powerful than speaker can handle, speaker will eventually die if amp is at highest output but NOT CLIPPING. Could be woofer or tweeter.... more likely woofer. If amp is lower than max output then speakers will not die as soon... maybe never.... its a gamble.

If speaker can handle anything the amp can drive it with, which means amp has equal or lower power output than speakers can handle, you are fine if amp is at or lower than highest output but NOT CLIPPING.

In EITHER case, if you push power amp into clipping you will eventually kill your tweeters and possibly overheat your woofers due to effectively pushing square wave ac through them.
 
#17
Major Softie said:
Hopkins, you seem to missing the distinction between "any distortion" and "some distortion."

Drurb is saying that there is distortion which can harm a speaker. You keep repeating that he is saying that any or all distortion will harm a speaker, which he is not. They are not the same.
Click to expand...

High frequency is high frequency. Whether it comes from a square-wave synthesizer in a keyboard, a fuzz-type distortion applied to a bass, or a clipped waveform at the output of an amplifier is irrelevant.
 
#18
Im saying that clipping doesn't damage speakers. Over powering them does. The thing about an under powered amp being driven to clipping causes speaker damage is a myth.
 

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