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overpower or underpower, a hypothetical..

#61
ricplyrz said:
Bob, a musical signal is an ever changing signal right. With hi levels and low levels and breaks in the middle, or pauses for a better term.

Now a "clipped" signal is a high powered, distorted, compresed..(has alot more information in it) signal that does not allow for as much, (let me correct myself) movement in that speaker, as it was designed, for it to propertly cool down. Would you aggree?

This is where the information I got was trying to make a point that it's like a dc signal.(clipping that is)..it may still have alternating peaks a bit...but it is closer to a dc type signal than an alternating one.
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I think that where you are getting hung up is that a clipped signal still flips polarity, just like an unclipped signal. IE, 60HZ sine wave and 60HZ clipped square wave change polarity just as often - the square wave just does it far more abruptly. As such, the square wave signal will still cause cone motion, just like the sine wave. As others have stated, the harmonic content in the square wave can tear up high end gear, and also the additional power of a square wave vs. a sine wave of similar amplitude.

Pure DC never changes polarity - that's why it's called DC!

Clearer? I hope so . . . .

- Tim
 
#63
tadawson said:
I think that where you are getting hung up is that a clipped signal still flips polarity, just like an unclipped signal. IE, 60HZ sine wave and 60HZ clipped square wave change polarity just as often - the square wave just does it far more abruptly. As such, the square wave signal will still cause cone motion, just like the sine wave. As others have stated, the harmonic content in the square wave can tear up high end gear, and also the additional power of a square wave vs. a sine wave of similar amplitude.

Pure DC never changes polarity - that's why it's called DC!

Clearer? I hope so . . . .

- Tim
Click to expand...


It does Tim..and I appreciate the patience you have all showed me....
 
#64
ricplyrz said:
In part, yes..it also relys on the varying amplitude of the signal.
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Varying amplitude of the signal helps cooling only in that lower power input allows the voice coil to cool down. All else being equal, if you go the other way, say, going from a steady X watts in to varying the signal between X and 2X watts in, the voice coil will get warmer because of the additional power.
 
#65
Bob Lee (QSC) said:
Varying amplitude of the signal helps cooling only in that lower power input allows the voice coil to cool down. All else being equal, if you go the other way, say, going from a steady X watts in to varying the signal between X and 2X watts in, the voice coil will get warmer because of the additional power.
Click to expand...

I understand..thanks...
 
#66
Bob Lee (QSC) said:
You're really hung up on the DC thing, and it's clouding your understanding. Forget the DC.

Put an audio signal into a loudspeaker driver, and it'll move, whether the signal is clipped or not. Audio is AC, not DC. If you put DC into a driver, the cone will move out to a position where the pull of the surround and spider equal the push of the voice coil, and it will stop. It will be silent. You may burn it out if you put in high enough power. But it is not audio, and it doesn't resemble a clipped signal.
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Another reason to forget DC is that most power amps don't pass DC.
 
#67
fdeck said:
Another reason to forget DC is that most power amps don't pass DC.
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I understand this, but I think what the author that I am refering to, and posted the link...is saying, is that the signal can be so clipped as to more resemble a dc wave than an ac wave.

I did some further research, and saw a couple sites where a 36 volt signal was so cliped it became 12 volts....thus the original signal was closer to a dc signal by its APPEARANCE..even though it was still alternating.....with much more information inside that signal
 
#68
Everyone should read Bob Lee's, Jerrold Tiers', and tadawson's posts in this thread. These guys know what they are talking about. Herman too.

I won't rehash anything they've said, but I'll just add a couple of points:

When a speaker is presented with a pure square wave signal, it doesn't stop moving entirely at the flat part of the wave. The inertia of the cone will keep it moving in a roughly sinusoidal trajectory. When you consider that real world amp clipping doesn't really ever get to the pure square wave stage, this becomes even less likely.

The primary cooling mechanism for speakers is heat transfer across the gap into the magnet, though in some designs (vented pole pieces) movement is a significant factor as well. However, if the speaker is in a situation where the coil is driven outside the gap (i.e. overexcursion) the part of the coil that goes outside the gap is more subject to thermal damage than the part that remains in the gap. This can occur with clipped or perfectly clean power often way less than rated (especially in vented cabinets). The other effect of too much excursion is mechanical damage (torn surrounds mostly), which, in my experience, is way more common than VC burn. I'd say 90% of cone speaker failures are mechanical.
 
#69
ricplyrz said:
I understand this, but I think what the author that I am refering to, and posted the link...is saying, is that the signal can be so clipped as to more resemble a dc wave than an ac wave.

I did some further research, and saw a couple sites where a 36 volt signal was so cliped it became 12 volts....thus the original signal was closer to a dc signal by its APPEARANCE..even though it was still alternating.....with much more information inside that signal
Click to expand...


No, this is not the case. There is no such thing as a DC wave, for one.

The only way a 36V signal could become 12V under clipping is if the amplifier's power supply sagged to 12V. If the amp's power supply rails are +/-36V (say a perfect amp with no power supply sag) the maximum unclipped voltage is 36V peak. The clipped voltage will also be 36V peak, except in the clipping case the peak to average ratio will be lower. The extreme case is the pure square wave, where the peak value is the average value. It will have twice as much energy as a sinusoidal signal of the same amplitude.

Real amps will sag, some more than others. When the rails sag, it limits the amount of power the amp can put out under clipping. No 12V signal will put as much power into a load as any 36V signal. A 12V square wave has the same heating power as 12VDC. A 36V peak sine wave will have the same heating power as about 25VDC.
 
#70
Not to belabor the issue, but there is another way of looking at it, which is to consider the waveform of cone motion amplitude after being effectively processed through low and high pass filters. Low pass filtering includes DC blocking in the amplifier. High pass includes the 12 dB/octave effect of cone mass, even before inductance is included. The cone motion ends up being anything but a square wave function.
 
#71
Mark Reccord said:
...
When a speaker is presented with a pure square wave signal, it doesn't stop moving entirely at the flat part of the wave. The inertia of the cone will keep it moving in a roughly sinusoidal trajectory. When you consider that real world amp clipping doesn't really ever get to the pure square wave stage, this becomes even less likely.
...
Click to expand...

If a square wave was presented to a perfect fullrange speaker the cone would follow a square wave. And sound like a square wave. The cone, spider, coil, magnet are all balanced to achieve this.

If it's a woofer, then it would roll off highs and move in a more sinusoidal pattern. And not sound like a square wave.

If you added a mid and tweeter, it again sound like a square wave. If you hooked up a mic and watched the waveform it'd be a square wave.

If you take away the mid and tweeter, those frequencies are still coming out of the amp and their going somewhere, they're going to the woofer but be dissipated as heat. If you hooked up a crossover to the woofer and put a dummy load on the highs it would sound the same but the woofer would be cooler.

When an amp clips a sine wave, it produces a bunch of high frequency harmonics and this energy needs to go somewhere. If the tweeter is there it can overpower them burn them out. If there's no tweeter, and even if you can't hear it, it's still part of the equation and comes out as heat.
 
#73
Mark Reccord said:
When a speaker is presented with a pure square wave signal, it doesn't stop moving entirely at the flat part of the wave.
Click to expand...

I'll add that at frequencies above resonance, the voltage is an accelerative force on the cone and not a positional force. So the flat parts of the square wave will actually cause a constant acceleration of the cone. The cone's position ends up being analogous to the integral of the signal voltage.

The primary cooling mechanism for speakers is heat transfer across the gap into the magnet, though in some designs (vented pole pieces) movement is a significant factor as well. However, if the speaker is in a situation where the coil is driven outside the gap (i.e. overexcursion) the part of the coil that goes outside the gap is more subject to thermal damage than the part that remains in the gap. This can occur with clipped or perfectly clean power often way less than rated (especially in vented cabinets). The other effect of too much excursion is mechanical damage (torn surrounds mostly), which, in my experience, is way more common than VC burn. I'd say 90% of cone speaker failures are mechanical.
Click to expand...

Brian Oppegaard of SpeakerPower and others whose knowledge I respect recommend high-pass filtering for protection against overexcursion.
 
#74
hope i didnt hijack the thread... i have a similar issues too

i have a avatar b410 delta, rated at 1400W handling

should i go QSC PLX 1202 (1200W mono, 325W stereo) all 4ohms operation

or PLX 1602 (1600W mono, 500W stereo) on 4ohms..

which should i take?

most likely i'll only use 1 4ohm cab, and add one more on larger venue.

also, other than avatar, i rarely found any 410 cab that handles 1000W or above.. in case that i change cab later on... any help here?
 
#75
I think you'd be fine with either one of those amps but if this statement...

johans said:
most likely i'll only use 1 4ohm cab, and add one more on larger venue.
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...means you're planning to add a second 4 ohm cab in parallel with the first, you'll have to make sure that whichever amp you select is rated to drive a 2 ohm load.
 
#77
Herman said:
I think you'd be fine with either one of those amps but if this statement...



...means you're planning to add a second 4 ohm cab in parallel with the first, you'll have to make sure that whichever amp you select is rated to drive a 2 ohm load.
Click to expand...

yeap
svt4-pro can drive up to 2ohms
if i use 2 4ohms cab, i'll load it stereo, or biamp

also my concern is since avatar has high power handling, what if i change to another 410 cab that sayonly handles 400-450, can i still monobridge into one?
 
#79
Bob Lee (QSC) said:
Brian Oppegaard of SpeakerPower and others whose knowledge I respect recommend high-pass filtering for protection against overexcursion.
Click to expand...

Add me to the list. It helps clear up/tighten up the sound as another benefit.

There is virtually no instrument speaker that can usefully use 30 Hz.... and if there were, your soundman would not thank you for using it.
 

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