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effect of underpowering a cab?

#22
FuzzBoxVoodoo said:
So you can damage a speaker from using too small of a amp if you push it.That is what I have thought all along but decided not to dive into one of these threads,until now.
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I never usually answer these threads, but I think this is all theory, if you had a low powered amp really cranked, causing ugly square wave distortion enough to theoretically damage the speakers, it would sound so horrible even the drummer would notice how bad it sounded and stop playing long before any speaker got damaged.
 
#23
joeyjoejoe said:
but a square wave is not a dc signal.
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By definition, a square wave has components of a DC signal.

The flatted peaks on both sides of the null-point are at a voltage that are held for x/moments and that effectively is a partial square wave.

One can see that any repeating, non-sinusoidal waveform can be equated to a combination of DC voltage, sine waves, and/or cosine waves (sine waves with a 90 degree phase shift) at various amplitudes and frequencies. This is true no matter how strange or convoluted the waveform in question may be. So long as it repeats itself regularly over time, it is reducible to this series of sinusoidal waves. In particular, it has been found that square waves are mathematically equivalent to the sum of a sine wave at that same frequency, plus an infinite series of odd-multiple frequency sine waves at diminishing amplitude:

Then ::: As noted step by step from here - it's rather obvious what it is we're creating in musical wave form.

In this first plot, one can see the fundamental-frequency sine-wave of 50 Hz (an slightly sharp-tuned G1) by itself. It is nothing but a pure sine shape, with no additional harmonic content. This is the kind of waveform produced by an ideal and perfect musical note, although for purposes of argument, the 50 Hz is not normally a tuned note :
22013.png

Pure 50 Hz sinewave.

Next, we see what happens when this clean and simple waveform is combined with the third harmonic (three times 50 Hz, or 150 Hz - all very common in a stringed instrument). Suddenly, it doesn't look like a clean sine wave any more:
22014.png


The sum of the 1st (50 Hz) and 3rd (150 Hz) harmonics approximates a 50 Hz square wave.

The rise and fall times between positive and negative cycles are much steeper now, and the crests of the wave are closer to becoming flat like a squarewave. Notice what happens as we add the next odd sinusoidal harmonic frequency:
22015.png


The most noticeable change here is how the crests of the wave have flattened even more. There are several more dips and crests at each end of the wave, but those dips and crests are smaller in amplitude than they were before. Watch again as we add the next odd harmonic waveform to the mix:
22016.png


The sum of 1st, 3rd, 5th, and 7th harmonics more aptly approximate a square wave.

Here we can see the wave becoming flatter at each peak. Finally, adding the 9th harmonic, the fifth sine wave voltage source in our circuit, we obtain this result:
22017.png


The sum of 1st, 3rd, 5th, 7th and 9th harmonics approximates a true square wave.

We can get into the Squarewave for SPICE/Fourier analysis, but you can see that at almost any time a note is struck on a string, it generates a certain quality that approximates a square wave with all the primary, secondary, tertiary harmonics, etc.

You are almost always attacking the speaker(s) with these semi-square wave or their equivalent in form by mass acceleration/magnetic hysteresis/field collapse, subtrahention and reversal and REMF anyway.

I too once agonized over the causative damage (via distortion boxes and stomp pedals) to the speaker cones and voice coil windings, but with ample heat radiation/conduction/convection and the resulting damage induced into the delicate micro windings in the coil and the fact that paper burns at Fahrenheit 451, I can see that there might be some concern about square waves.

Just don't hold a note for more than 1.4 seconds and you'll be alright! <sarcastic smiley>
 
#24
Jaco who? said:
As far as tonal differences, it won't hit the "sweet spot" where it sounds full and open at the right amount of volume for what you need it for. I might not with 4 ohms either though, so don't worry about it and play.
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Is this so called "sweet spot" the point where the voice coil begins to leave the flux gap and speaker compression and self noise increases radically.
because if so I vastly prefer the "underpowered" loudspeaker sound.
If you find you have a loudspeaker that sounds thin and weak at anything less than full bore, then this is obviously a very poor suspension/cabinet
design and should be immediately consigned to the trash.
And then see if you can purchase one with a nice wide range of dynamics.:ninja:
 
#25
Even the drummer would notice? Now there's a myth in the making!

It's funny how the TITLE of the thread sparked the underpowering/square wave/dc discussion again, when the real question was how does it affect the tone.

So, does every cab have a sweet spot, volume wise, where it seems to "open up"?
 
#27
FuzzBoxVoodoo said:
My take on the under powering a cab is pushing a small amplifier into a square wave (DC volts/distortion) and that is how you can damage a speaker due to lack of power.
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Square wave is not DC in real audio frequency terms and has never damaged a woofer within the limits of its power handling.
There is really no such thing as harmful under powering and
overpowering just shortens the life of woofers from a few years to a few seconds depending on how much overpowering you use.:ninja:
 
#28
Right, I hope people can take the discussion back to the tone question actually asked by the OP, because the myth of square waves and DC and all that junk has been debunked so many times now that seeing it again and again makes me nauseous. Anyone who believes "clipping = square wave = DC = overheated speaker" has decided to believe something that sounds plausible but that is not actually reality. Threads that go down this road usually get closed by a mod, because the FAQ covers this issue. Now, back to the OP's question of tone...
 
#29
Vanceman said:
So, does every cab have a sweet spot, volume wise, where it seems to "open up"?
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Good question. I think this is all part of the myth, too.
As a guitar player, the sweet spot in the amp (for blues players and rock players, mainly) is where you're beginning to push the power tubes into saturation. For guitar players, this "sweet spot" also applies to speakers. This is why the 15 watt Celestion Alnico Blue is so highly regarded in the guitar world.

For bass, I guess if you're going for that 60's stadium rock sound where your old SVT/Fridge combination is being pushed so hard it sounds like it's about to catch fire, then the sweet spot argument may apply.

But for solid state amps (or even tube amps) where distortion is not the goal, there really is no sweet spot. As a bass player, I can't imagine a scenario where I'd like the sound of a speaker being pushed to its limits.
 
#31
Bassmec said:
Is this so called "sweet spot" the point where the voice coil begins to leave the flux gap and speaker compression and self noise increases radically.
because if so I vastly prefer the "underpowered" loudspeaker sound.
If you find you have a loudspeaker that sounds thin and weak at anything less than full bore, then this is obviously a very poor suspension/cabinet
design and should be immediately consigned to the trash.
And then see if you can purchase one with a nice wide range of dynamics.:ninja:
Click to expand...

Oh jeeze. I was refering strictly to the harmonic content from an amplifier where it happens to sound best, nothing at all to do with speakers. Nothing like the celestion speaker sound that a Marshall cab might make with a guitar player. I haven't used the MB stuff much, just going by what others had mentioned about the LMII 8 ohm operation. OKEY DOEKEY? I'm gonna' go play my bass now.
 
#33
capnjim said:
I never usually answer these threads, but I think this is all theory, if you had a low powered amp really cranked, causing ugly square wave distortion enough to theoretically damage the speakers, it would sound so horrible even the drummer would notice how bad it sounded and stop playing long before any speaker got damaged.
Click to expand...

There have been a bazillion threads on this topic. If square waves were damaging to speakers all by themselves, then synth players and guitarists would blow speakers all the time. But they don't.

Speakers are blown by TOO MUCH POWER, end of story.
 
#36
Devo-lution said:
My question is related to the effects on the sound when giving a cab less than half of the watt-amount it can take. So, does it make for tonal differences? If yes, which ones?

I personally do like the sound I get, but a chance of improving my tone is always okay... I do wish to note that I go for a relaxed, clean sound usually in my rig.
Click to expand...

If you like the sound from your rig, then there's nothing to worry about: as you know, you're not gonna hurt anything. The only problem with running a 300 watt head into an 800 watt speaker cab would be if you played a loud gig and needed more power than the head could deliver. In that case your tone would become dirty, which again is not harmful, but it is not what you want from your rig.

If you get all the volume you need from your rig and you're happy with the tone, then you're set!
 
#39
Eric Moesle said:
Underpowering is a myth.

The wattage rating of a cab is simply the point at which the voice coil will melt, causing permanent failure.

Just because an amp is rated at 500 watts doesn't mean its putting anything near that to the speakers when driven at "normal" levels. You would have to have everything on "10" as well as a proper input level for the speakers to see the full 500 watts, and even then the speakers would most likely blow from overexcursion LONG before they would fail because the wattage rating was exceeded.
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you're kinda sorta there, but not quite, eric.

an amp that's rated at 500w rms has approx. twice that in what's called peak power, which is the amount of power it has after the onset of distortion. so that 500w rms amp would be rated for 1000w peak.

the underpowering myth says that an amp that's rated lower than the cab can take can clip and take out your speakers. if you buy into that, then if i took my b-15n (25w rms, approx. 60w peak) and hooked it up to my svt 810 and turned up all the way, it would blow the 810's speakers. but i have plugged my b-15n into my 810 and turned it up all the way several times and my speakers are still intact. myth busted.

if a clip takes your speakers out, then the clip OVERpowered the speakers by going into your peak power and using wattage beyond the rms rating. if the peak power of your amp is enough to take your speakers out, then you have to worry about clipping, but only then.

as for dc, yes, there is a dc component to square wave distortion, but your speakers never see it. if they do, then you need to take your amp to the shop because there's something very very wrong with it. a working amp will NEVER leak dc to the speakers.
 
#40
FuzzBoxVoodoo said:
So you can damage a speaker from using too small of a amp if you push it.That is what I have thought all along but decided not to dive into one of these threads,until now.
Click to expand...

If you damage a loudspeaker with a "small" amp, you'll damage it with the same amount of power from a "big" amp, too.
 

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