Is underpowering the right term?

It sounds to me like you have everything right. People shouldn't be worried about any of this if they are not pushing their amp past its limits.

The idea of not supplying enough power to a cab is just a misinterpretation of the original idea that amp clipping can damage speakers, especially tweeters.

The limiting protection on amps are there to protect the speakers but I cannot comment on their effectiveness because I have never blown speakers. (HMMM maybe they DO work!)

 

For all practical purposes, there's no such thing as underpowering a speaker. You can only be underpowered for your playing situation.

And having an amp rated for more power than your cab can handle on a regular basis does not give you headroom. What gives you headroom is having more power than your playing situation requires.

 

+1
Low power does not damage speakers.
Clipping the amplifier can, and often does damage speakers.
If you're pushing your amplifier into clipping, you need a more powerful amp - one that won't have to work so hard to get the volume you desire.

So you might be "underpowered" for that situation. And the clipping amp might damage your speakers.
This results in people saying they were "underpowering their speakers."
Which leads to misinterpretation and a whole load of confusion, including many people preaching the gospel of the underpowered speaker.

 

Underpowering can be good!

Speakers and amps have something in comon. If you push them too hard, they don't sound so good. We seem to understand the concept of clipping the amp and why it's bad, and as such we hear lots of people talking about "headroom" in the amp, but what about the speakers?

Your speaker might be rated for say 700W but how many watts can it take before it starts to suffer from power compression? How many watts can the speaker take before it moves far enough to use up all it's suspension travel? I can guarantee it's a lot less than 700w n all but the most expensive drivers. All the 700w rating tells you it that's how many watts it can take before the glue starts to let go. It gives no indication of the drivers sonic abilities under those conditions.

For this reason, underpowering WITHOUT clipping is actually a good thing. If you can get enough volume without pushing your amp too hard, you're often better off using speakers that have a higher wattage rating than the amp to keep the speakers working within their optimum sonic range.

 

If it sounds good, you're all set. The only time "underpowering" can cause problems is when the amp is distorting to get the volume you're trying to achieve. And even then its hard to destroy them when the cab is rated much higher than the amp. There's probably a sweet spot where the amp and speaker are close in their rated power, and you have a tweeter. That's where you're liable to blow the tweeter. Extra high freq energy involved in clipping the amp exceeds the "normal" clean signal ratio. Your 700W cabinet only comes with a 150W tweeter under normal conditions cause on a normal clean bass signal, very little high freq energy is in the signal. Clipping changes that ratio significantly. All of a sudden your 500w amp is cranking out 250W of highs when clipping vs its normal 100W when not clipping. The rest of the power is in the lower regions, so generally your woofer is safe. Keep that up, the 250W of highs will blow your 150W tweeter with no problem.

So you don't blow the tweeter from "underpowering" it. You blow it by exceeding its power handling capability cause the amp clipped and put out a much greater fraction of its total power in the tweeters frequency range compared to how the power normally splits between the woofer and tweeter when operating cleanly.

Randy

 

I'm not that technological but I hit a situation the other day:

We were practicing at my singers house and I was using my 16 watt (sixteen watt) amp to power his 400watt (2x200-watt 12 inch) cab and he blamed me for blowing the cabs...now he's doing music tech and I'm doing Pop music (ba hons degrees) and he apparently has been told that "the quickest way of blowing a speaker is by either over OR underpowering it"... now, I can't see how 16-watts into 400-watts is gonna blow them (the amp distorts when its on full blast anyway) but he was getting concerned about it...I reckon its a pile of bulls£%$T simply because I was once advised to get a 200-watt cab to go with a 125 watt head I've got so it won't damage the speaker if it gives out more power

WHICH IS RIGHT??? - I'm no tech know it all but I know that 16 into 400 isn't gonna blow it immediately...

 

You didn't blow his cab. Underpowering can hurt tweeters and some midrange drivers, but not woofers.

 

I agree with all of the above information, and would only add that some might refer to "underpowering" a speaker cabinet in discussing getting a nice solid tone from the cabinet. You can power a 700 watt 4x10 cabinet with a 100 watt solid state amp if you want to, but the amplifier may not provide enough power to get the speakers to perform efficiently. This would cause no damage to the cabinet, but the speakers may not sound as punchy, or the lows may not be as deep.

 

If you used hi-fi audiophile speaker cables, that 16 watts could EASILY blow a 400 W cabinet! The higher velocity of the electron flux dampening flow results in more sonic hardness, and if the cab is used to the softer sonic energy of normal cables, which sort of absorbs some of the impact, the increased sonic harness can multiply the impact forces involved substantially when the electricity hits the speaker .

Would you rather get hit with a brick, or a fish? The sonic hardness is overlooked at your own peril!

Randy

 

It's not really about getting the speakers to perform efficiently. Remember, sensitivity tests are conducted with a measly 1 watt. It's really about, do you have the power to get the volume and tone you want in the playing situation you're in? if you're playing a 100 W amp into a 700 W cab, you likely won't have a problem and will sound fine if you're accompanying a cabaret singer at near-conversational volume. You likely *will* have a problem if you're trying to cut through a hard rock band without PA support in a 1000 person club. But that's not because the cab is underpowered, it's because your *amp* is underpowered for your gig. You would have the same problem, or likely worse, if your cab was rated for only 100 W (all else being equal).

The ratio between the max power you have available and the max power the cab can handle, *in itself*, doesn't mean nearly as much as people often think. There is no *inherent* problem in putting a 100 W amp into a 700 W cab. What matters is, first, the ratio between the power you have available and the power you need to play your gig, and second the ratio between the power you're actually using and the power handling of the cab.

 

Sensitivity tests are a measure of a speakers/cabinets efficiency. As you have mentioned, 1watt produces so many db at a certain distance from the speaker, usually expressed thus, [email protected] 1W 1M. Not all speakers have the same sensitivity, and thus will not sound the same given an equal number of watts. My point was not about overall volume, rather I was referring to the tone a given cabinet will produce given a certain number of watts. A cabinet may produce [email protected] 1W 1M, but this is not across that cabinets full frequency range. Using the cabinet I have taken these specs from, an SWR Goliath III, at 40Hz the sensitivity rating is [email protected] 1W 1M. Of course, 105dB is only slightly louder than 102dB, but to achieve that 3dB increase requires a doubling of the wattage.

All this techy talk aside, I know from experience with this particular cabinet, I have one in my bass rig, that the tone is significantly more present and pleasing when run with a higher power amplifier, and I don't mean louder. There may not be an "inherent" problem in running a 700 watt cabinet with a 100 watt amplifier. It just may not sound as good as that same cabinet, running at the same volume, using a 1000 watt amplifier. The added headroom allows for a more balanced frequency response, independant of overall volume.

 

I think you have been reading too many boutique cable threads.

The way I like to think of underpowering is actually overtaxing the amp.

 

FWIW:

My speaker repair guy (instrument and hi-fi) said most speakers he repairs are from guys cranking low watt amps into speakers that will handle wattage rating far beyond what the amp put out - clipping

He said the best case scenario is to have a 1000 watt amp set on a fraction of the power to drive 300 watts (whatever) of speaker - far better than the reverse (given the assumption it gets you the desired volume). That's SS, for tubes often you're dealing more with a sweet range in tube output - as usual, tubes are different.

It's also a lot easier to get by with guitar in a setup like you're talking about because the need to crank up to get power consuming low frequencies to useable levels isn't much of a factor.

The problem with bass is big amps typically cost big money (tend to be bigger/heavier as well) so it becomes a compromise for a given situation.

 

I would like to know about this specifically with regard to bass amplification speakers, rather than home hi-fi speakers. I think that hi-fi and PA speakers see a much different type of general usage (full range signals) than bass amplification speakers (primarily low frequencies).

I can see why hi-fi tweeters would be especially damaged by clipping from low power amps, while I have a harder time seeing significant damage caused to high power woofers with low power amps.

Given the low power handling of most woofers in the fundamental range of bass guitar, below 100 Hz (often 25% or less of full power), I have a hard time accepting that 1000W at 31 - 41 Hz is a good idea for a 300W woofer.


Perhaps Bill can comment here?

 

Right, and Randy already touched on this. In hi-fi the signal content that a tweeter might have to deal with is perhaps 5% of the total system power, so even a 10 watt tweeter voice coil is plenty large enough for a 100 watt system. But if you power the system with, say, a 50 watt amp, and push it hard enough into clipping so that the high frequency content consists of 15 watts of square waves, the tweeter is toast. Do so with a woofer with a 100 watt coil and it's of no consequence. It just growls a bit. But if you do run with a tweeter and like the growl you'd best be sure that the high-pass filtering on that tweeter is adequate to protect it.

 

It certainly wouldn't be a good idea to actually push 1kW into a 300w voice coil, but the reailty of the situation is that you wouldn't, as the distortion would be so bad that you'd turn down anyway. Think mega fart. The advantage to having that much reserve power available is that the amp can work effortlessly, perhaps too much so for most tastes.

 

FWIW:

Instrument and hi-fi. Instrument includes bass guitar speakers. But to my knowedge, there's no problem running bass through PA speakers that will take the power/frequency, at least I haven't had any.

The assumpition was you wouldn't put 1000 watts through a 300 watt cab if the most you'd need would be a 300 watt cab. If the need was for 1000 watts of output, then cabs that would handle that would be in order.

I believe the point he was making was that a speaker is more capable of handling a more powerful clean signal than a lower powered distorted signal, not to run 1000 watts of amp through a 300 watt cab.

 

This is half right.

It surprises me that so many people who repair speakers don't fully understand how they work.

First off, speakers don't care about waveform. There's nothing in distortion that's inherently damaging to speakers.

In order to clarify, let's talk about voltage and not power for a second. When an amp reaches clipping, the output voltage cannot increase any further. So an amplifier just at the edge of clipping puts out the same voltage as it does at 100% THD. However, they will not be putting out the same power. There is more energy in a clipped waveform than in a non clipped one of the same voltage (amplitude). A pure square wave will develop twice as much power as a pure sine wave at the same peak voltage into a particular load. So a seemingly low powered amp in clipping will actually put out more power that it is rated for. So you could see how a 300W amp could damage a speaker rated for 500W under severe clipping. However, there is a point where this is no longer an issue. If you have an amp that's rated at less than half the rated power of the speaker it's driving the chances that you could damage the voice coil are pretty low and the less power the amp has, the less likely it is to be able to damage the speaker. You'd have a better chance of getting hit by a satellite than blowing a 400W speaker with a 16W amp.

Another thing that's often totally ignored is that the way a cabinet is set up and tuned can derate the driver's power handling capabilties. For example at the tuning frequency of a ported cab, the air mass effectively stops all cone movement, which significantly derates the amount of power the driver can take at that frequency. You can melt a voice coil with perfectly clean power way less than rated in that situation.

My experience is that about 90% of all speaker damage is mechanical in nature (ie overexcursion). People should be more concerned about this than melting voice coils.

EDIT: Me not Tarzan, me add 'is' to "This half right."