I may be an idiot... but is under-powering a load of ballcocks?

[Magic Matt]

Ok, I totally get that when you drive a low powered amp up high, it clips. I've seen it on a scope, it looks ugly, heard it, and it sounds ugly.

Here's the thing though... if the speaker can handle more power than the amp can put out, how is that any different to playing music through it that's been hard-limited, or a sound from a keyboard that's basically a square wave?

Seems to me that this whole under-powering thing is just a load of nonsense... so what I am I missing? ...or aren't I?

[bumnote]

I think Bill F said it was an old wives tale

[Dad3353]

[quote name='Magic Matt' timestamp='1410377714' post='2548836']... so what I am I missing? ...or aren't I?
[/quote]

[size=4]Not sure to fully understand the question, really, but...

The speaker (or cab...) doesn't care about amplifiers or whatever. If a signal comes in, it'll reproduce it. If the signal is 'clean', the cab will be 'clean'. If the signal is clipped, the cab will sound 'clipped'. A clean signal will be well-treated up to the mechanical limit of the cones, when the clean signal becomes distorted. If this 'overload' continues too long, the speaker could well be permanently damaged, or even fail through over-heating or such. Not Good.
If the amp starts clipping before this physical speaker limit, however, the speaker will just put out what comes in, ie : a clipped, distorted sound. Not Good. This 'clipped' signal will not do any good to the speakers, either, as the more 'square wave' signal will push them harder than nice clean bass tones.
Under-driving a speaker, then, is not, in itself a problem. Only if one is trying to get high volume from a tiny amp will clipping occur (as you say, it sounds awful, too...). The speaker won'y mind, but your ears will. If the clipped signal from the amp increases in power, however, damage could occur to the speaker.
Not sure if this answers your question, though...[/size]

Edited September 10, 2014 by Dad3353

[BassTractor]

Cool question! Very good!

I'm not the specialist that Bill is (the person you talked to on the other thread), but lemme just say that "underpowering" is a lame concept that is misunderstood and misused to boot.

Mostly, amp vs cab is like a gas pedal in a car: one does not have to press it all the way all the time.

"underpowering" does get some (some) validity if by that one means that the cabs are fitting for the needed volume, but the amp is not.
Also, some amps do not have the control over the cabs that the wished for output quality needs, and one ight on that case also misuse the word "underpowered"

As to the square waves from a synth, they most probably are far from as square as the square ones that are the result of ss circuits clipping, but if they indeed are close, I think there is one important issue: some gear is made especially to be able to handle that synth. Most traditional bass gear probably is not.


At this point I recognise I'm really to exhausted for this, and bid you farewell. I hope others will answer better.

[Bill Fitzmaurice]

[quote name='Magic Matt' timestamp='1410377714' post='2548836']
if the speaker can handle more power than the amp can put out, how is that any different to playing music through it that's been hard-limited, or a sound from a keyboard that's basically a square wave?[/quote]It isn't.
[quote]Seems to me that this whole under-powering thing is just a load of nonsense... so what I am I missing? ...or aren't I?
[/quote]Clipping can toast tweeter voice coils, because what makes a square wave square is harmonics not present in a clean signal. Those harmonics can increase the power seen by a tweeter tenfold over normal, and that's what toasts the voice coil: overpowering, not under-powering. BTW, this document is the source of the under-powering myth:
http://www.jblpro.com/pub/technote/lowpower.pdf

With the re-telling of the tale, probably by the first wag to do so, the key phrase 'high frequency components' was omitted, and the myth was born.

[Beer of the Bass]

And as any fuzz user will tell you, hard clipping sounds bloody 'orrible into a tweeter! This is why guitar amps never have them. Square wave synth sounds usually have some kind of low-pass or bandpass filter on the output, as an unfiltered square wave is surprisingly unmusical.

[Magic Matt]

With computer games, square wave output was all we had back in the early 80's! No fancy filters etc. just a square wave generator... or if you were really lucky... 3 of them... and if you were in luxury land you might also get one that generated pink or white noise! LOL!

[Quote]
[color=#282828][font=helvetica, arial, sans-serif]Clipping can toast tweeter voice coils, because what makes a square wave square is harmonics not present in a clean signal. [/font][/color]
[color=#282828][font=helvetica, arial, sans-serif][/quote][/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]Are we talking harmonics that are still lower than the fundamental frequency of the square wave, but which could be pushing the tweeter beyond its Xmax, even though the woofer may be quite happy?[/font][/color]

[Bill Fitzmaurice]

[quote name='Magic Matt' timestamp='1410382508' post='2548928']
[color=#282828][font=helvetica, arial, sans-serif]Are we talking harmonics that are still lower than the fundamental frequency of the square wave[/font][/color]
[/quote]Harmonics are multiples of the fundamental, so they're always higher in frequency, never lower.

[HowieBass]

[quote name='Magic Matt' timestamp='1410382508' post='2548928']
[color=#282828][font=helvetica, arial, sans-serif]Are we talking harmonics that are still lower than the fundamental frequency of the square wave, but which could be pushing the tweeter beyond its Xmax, even though the woofer may be quite happy?[/font][/color]
[/quote]

I think he means 'harmonics that are lower in volume than that of the fundamental frequency of the square wave'.

[Guest monsterthompson]

Under-power is bunk. I will say I've found lower power amps don't push hard enough to get good tone. For example, I had a Crown XLS 1000 power amp, and I could tell when it was in bridge mode (for more watts) because the speaker reacted differently, and the sound was fuller even if the volume was roughly the same (I wasn't using any form of measuring device). I'm not sure what was going on in the guts that made it that way, but it was noticeable.

[Magic Matt]

[quote name='Bill Fitzmaurice' timestamp='1410387651' post='2549028']
Harmonics are multiples of the fundamental, so they're always higher in frequency, never lower.
[/quote]

I meant lower amplitude, rather than frequency...

[Sonic_Groove]

Does this all mean I can safely run a 12inch wizzy (no tweeter) cab with my Hotone Thunder Bass 5 watt without fear of damage?

It sounds great and is pleanty loud enough for home, but been worried "what if it clips"

Brendan

Edited September 10, 2014 by Sonic_Groove

[Dad3353]

Worry no more. If it clips, you'll hear it, and will turn it down. I doubt that [size=3]the 12" would budge[/size][size=4], even fully square waved, at full belt. Your ears would bleed, though. ([/size][i]Children: don't do this at home without adult supervision[/i][size=4]...).[/size]

Edited September 11, 2014 by Dad3353

[Magic Matt]

[quote name='Sonic_Groove' timestamp='1410393251' post='2549089']
Does this all mean I can safely run a 12inch wizzy (no tweeter) cab with my Hotone Thunder Bass 5 watt without fear of damage?
[/quote]

Check the impedance and make sure your amp is happy with that rating.

What dictates volume is sensitivity rather than watts. If your 12" wizzy is as sensitive as the speaker in your Hotone it will sound about the same volume (ish), if not then it wont. I would be surprised if the sensitivity was the same though - bigger speakers = more mass to move = more energy needed to move it.

As far as I can tell, the only thing really relevant about watts on a speaker is how much heat it can dissipate before something bad happens.

If it clips it'll just sound like bad 80's punk.

[Magic Matt]

Also, speakers can't produce proper square waves - your clipping will be dampened by the speaker mass and momentum. No matter how good the speaker is, you can't change the laws of physics. It's going to have to accelerate, and decelerate, at each "end" of the waveform, and trying to stop instantly is probably going to introduce artifacts into the sound.

[Kevsy71]

A question possibly related to this: I have a Genz Benz Shuttlemax 12.2, which incorporates two power amps with a separate output for each: [color=#000000][font=Helvetica, Arial, sans-serif][size=3]Power Output - 375W/8 ohm x 2, 600W/4 ohm x 2[/size][/font][/color]

[size=4][font="Helvetica, Arial, sans-serif"][color="#000000"]I run this into two Baer ML112s (8 Ohm each). Will there be any difference if I connect one Baer to each power amp output, and hence use both power amps at 8 Ohms each, versus daisy chaining the Baers and presenting 4 Ohms to one of the power amps, i.e. just using one power amp? And if so is one approach recommended over the other? [/color][/font][/size]

[size=4][color=#000000][font=Helvetica, Arial, sans-serif] [/font][/color][/size]
[size=4][font="Helvetica, Arial, sans-serif"][color="#000000"]Cheers! [/color][/font][/size]

[Chienmortbb]

[quote name='monsterthompson' timestamp='1410390748' post='2549061']
Under-power is bunk. I will say I've found lower power amps don't push hard enough to get good tone. For example, I had a Crown XLS 1000 power amp, and I could tell when it was in bridge mode (for more watts) because the speaker reacted differently, and the sound was fuller even if the volume was roughly the same (I wasn't using any form of measuring device). I'm not sure what was going on in the guts that made it that way, but it was noticeable.
[/quote] if you bridge an amp you will get 3-6db more power output at the same settings on the preamp comlared to a single channel.

Edited September 11, 2014 by Chienmortbb

[HowieBass]

[quote name='Kevsy71' timestamp='1410426992' post='2549258']
A question possibly related to this: I have a Genz Benz Shuttlemax 12.2, which incorporates two power amps with a separate output for each: [color=#000000][font=Helvetica, Arial, sans-serif][size=3]Power Output - 375W/8 ohm x 2, 600W/4 ohm x 2[/size][/font][/color]

[size=4][font=Helvetica, Arial, sans-serif][color=#000000]I run this into two Baer ML112s (8 Ohm each). Will there be any difference if I connect one Baer to each power amp output, and hence use both power amps at 8 Ohms each, versus daisy chaining the Baers and presenting 4 Ohms to one of the power amps, i.e. just using one power amp? And if so is one approach recommended over the other? [/color][/font][/size]


[size=4][font=Helvetica, Arial, sans-serif][color=#000000]Cheers! [/color][/font][/size]
[/quote]

I'd be inclined to make both sides work equally hard by having them both run a single 8 ohm cab and in theory it'll be a bit louder (375+375=750 watts) than daisy chaining the cabs off one side (600 watts) assuming of course that the cabs are happy taking all that power (though I imagine it'd be bloody loud and you'd give up before the rig did).

[Dad3353]

I'd go with balancing the channels, 1 cab each. I doubt that 1 channel/2 cabs or 2 channels/1 cab each would sound any different. The change comes if you later wish to add another pair of cabs. Then the 2 channels/2 cabs each would allow the full potential to be realised. I wouldn't want to stand too close to such a monster rig, though (1200w..? Good gracious..!)

[Bill Fitzmaurice]

[quote name='Magic Matt' timestamp='1410422288' post='2549201']
Also, speakers can't produce proper square waves...It's going to have to accelerate, and decelerate, at each "end" of the waveform, and trying to stop instantly is probably going to introduce artifacts into the sound.
[/quote]Logical, but that doesn't occur. On reason why is because voice coils are inductors, and like all inductors they are low pass filters. That being the case, a goodly portion of the harmonics that make a square wave square are filtered out. When you break down a square wave into its basic components it's not intrinsically different than any other complex wave form, and drivers have no more issues with them than they do with any other complex wave form.

[Magic Matt]

Surely acceleration and deceleration are an issue whatever the waveform? If it's a low frequency sine wave, the movement required is slow. Lets use a 4mm travel for example - 100Hz sine wave, so the speaker can gently rock to and fro over that 4mm travel 100 times a second. No problem. A square wave isn't like that though - 100Hz square wave would require the speaker to move over that 4mm distance instantly, then stay there motionless for half a cycle, then instantly jump back, stay motionless for half a cycle, etc.... impossible! Speakers have mass, and require a force to move them, so there will always be a slight delay as it accelerates, moves, then decelerates - if the travel movement is fast enough, there will also be some bouncing due to the springy nature of the speaker cone material etc. - ok, only a little, but enough to prevent accurate reproduction of a square wave - what you get is a smoothed/rounded square with a little wobble.

I'm not sure what you're saying by "breaking down a square wave into its basic components"... square waves are the basic component! So much so that many battery-backup devices use square waves combined at different frequencies to artificially recreate a sine wave (DC to AC).

[Bill Fitzmaurice]

[quote name='Magic Matt' timestamp='1410451921' post='2549598']
100Hz square wave would require the speaker to move over that 4mm distance instantly, then stay there motionless for half a cycle, then instantly jump back, stay motionless for half a cycle, etc...
[/quote]That's part and parcel of the myth. It doesn't happen. Where a speaker is concerned there is no such thing as a square wave as seen on an oscilloscope.
[quote]
I'm not sure what you're saying by "breaking down a square wave into its basic components"... square waves are the basic component![/quote]That's also part of the myth. A square wave is a sine wave with all of its harmonics present with equal power density. Run a square wave through a brickwall low pass filter, its corner frequency set slightly above the fundamental, and you are left with the original sine wave.
Further reading:
http://forum.qscaudio.com/forum/viewtopic.php?f=29&t=2736

[Chienmortbb]

Bill is correct. A square wave is like an infinite collection of sine waves in its purest form. If you gave square wave going into a speaker it will sound awful but will not damage a speaker per se. It becomes a problem when approaching the thermal limit of a speaker. At that point you could be putting approx 40% more power through the speaker than if you were putting a pure sine wave into it.

Of course unless you play bass flute or whistle through your system, you will not be putting a sine wave through your system.
I can find you many men who bash their heads against walls every day for years and some if them will escape brain damage. Overpowering your speaker is the same, some will last years but some will fail the first time you go to 11.

Edited September 11, 2014 by Chienmortbb

[Magic Matt]

Read the comment about clipping being DC and cracked up! LOL! How could anyone think clipping is D.C.!?!?

[Bill Fitzmaurice]

[quote name='Chienmortbb' timestamp='1410452743' post='2549614']
Of course unless you play bass flute or whistle through your system, you will not be putting a sine wave through your system.
[/quote]Nor then. All instruments save electronic have harmonic content, and no one I know of plays a synth patch that's a pure sine wave. The only instrument I can think of offhand that might play pure sine waves is the Tannerin (that's what's on [i]Good Vibrations[/i], not a theremin). I say might, as how pure the wave is depends on the quality of the oscillator and the attendent circuitry, and the speaker as well.