overpower or underpower, a hypothetical..

[billfitzmaurice]

The speaker impedance is a static factor that is already figured into the amplifier circuits, and why you have a limited range, usually 2 Ohms - 8 Ohms of options in order to keep the amp biased and functioning properly. It is the amp devices internal R (resistance + impedance) that lowers when you turn up the volume. That volume control does bias that amplifier to conduct more and more voltage and current, and unfortunately when in saturation more current.

Don't fixate on current, as it's not a consideration where the driver is concerned. And as for impedance being static, it's anything but. Understanding the effects of clipping on speakers requires a very thorough understanding of how speakers work, not just how amplifiers do.

 

[JHAz]

My mistake regarding the meaning of fundamental. My experience ended 15 years ago in another electronic field and terminology does differ sometimes.
I did state that I was not addressing the effects of frequency and harmonics in the circuits in order to simplify the discussion and that my knowledge of these factors in the audio range was limited. However, I never mentioned frequency and Ohm's law in the same breath, even though frequency does have an effect on impedance which is part of R in I=E/R. Those topics are better discussed by those with more audio experience than I.
That does not change the fact that available at the output of the amplifier in full saturation, is a power signature that is more current heavy than in the power signature of an amp not in saturation. You are correct that the impedance at the output of the amp does not change, unless you change cabs or # of cabs. The speaker impedance is a static factor that is already figured into the amplifier circuits, and why you have a limited range, usually 2 Ohms - 8 Ohms of options in order to keep the amp biased and functioning properly. It is the amp devices internal R (resistance + impedance) that lowers when you turn up the volume. That volume control does bias that amplifier to conduct more and more voltage and current, and unfortunately when in saturation more current.

But you are killing me... What movie was that from. I gotta know or I'll dwell on it all day.

If all you are trying to say that the RMS power of a square wave, or clipped wave approaching a square wave, is higher than the RMS power of a sine wave, no disagreement. But, still, the amp HAS to deliver the same curent at the peak of a sine wave as it delivers at the peak of a square wave, if the peaks are equal. It's the law. It just delivers that current longer during a square wave sycle than during a sine wave cycle.

Pirates of the Caribbean.

 

[Bob Lee (QSC)]

I'm sorry that you're disappointed, but babebambi made an excellent point about what you seemed to imply, that current is unrelated to voltage. Many non-technical people make that mistake (no doubt helped by questionable marketing campaigns), and that's what it looked like in your post, too.

It is the amp devices internal R (resistance + impedance) that lowers when you turn up the volume. That volume control does bias that amplifier to conduct more and more voltage and current, and unfortunately when in saturation more current.

The volume control only apportions the amount of signal passing through. The signal causes some devices to conduct more and some to conduct less, more or less in porportion to the instantaneous value of the signal (usually voltage). That's because the devices are typically set up as voltage dividers--some pull the output toward the positive and others toward the negative (in a class B amp), or as a variable conductance in series with a fixed resistance (in a class A amp).

 

[JHAz]

I'm sorry that you're disappointed, but babebambi made an excellent point about what you seemed to imply, that current is unrelated to voltage. Many non-technical people make that mistake (no doubt helped by questionable marketing campaigns), and that's what it looked like in your post, too.

Lemme make sure I'm thinking straight. As I understand it, if I know voltage and impedance, I can calculate current. So it seems to me that voltage and current are related. It's just that the relationship, the way I think about it, is mediated by resistance/impedance. Maybe controlled isn't the right word, but I think of the three as immutably locked together. I was responding to what I understood babebambi in an earlier post to be suggesting, that under some conditions, with the same speakers, an amp would output more current with the same signal at the same voltage. I wan't thinking about clipping because, first, I thought babebambi was not talking about average current but instanteneous current, and second, once you clip it's a different signal, and you wouldn't expect the same power envelope for that signal . . .Ready to learn.

 

[Bob Lee (QSC)]

that under some conditions, with the same speakers, an amp would output more current with the same signal at the same voltage.

Here's one scenario: The resistance of the loudspeaker's voice coil will be lower when it is cold than when it is hot, so more current will flow for a given signal voltage. Without changing the resistance (and impedance), though, the current would be the same for a given voltage.

Voltage, current, and resistance/impedance are all interconnected. If you change one, you also change at least one of the others. And all of electronics is about manipulating this three-way relationship. That's why the invention of devices that change conductance based on a control voltage or current--vacuum tubes, bipolar transistors, FETs, et al--made it possible finally to actively, electronically amplify signals, something that couldn't be done with just passive components.

 

[tanktones]

Don't fixate on current, as it's not a consideration where the driver is concerned. And as for impedance being static, it's anything but. Understanding the effects of clipping on speakers requires a very thorough understanding of how speakers work, not just how amplifiers do.

I am addressing the current issue because no one has. It can be an issue when the amp power capabilities and the cabs power capabilities are close, or the amp is slightly higher rated. During normal operation you are right, normal current flow is accounted for and no problems for those drivers. But the topic of this thread is the "underpowered amps" being run wide open trying to be louder than possible with the existing hardware. When this is the operating criteria and you start to approach the limits of those drivers and then add even a little more current, due to the saturation of the amp, the chances for a component failure goes up. Add to that the additional stress on the components from harmonics, heat fatigue and other things I am learning more about daily, and you really start to put those drivers at risk.

Secondly I should not have said impedance is static, I know it is not. I meant to say impedance is a known commodity and already accounted for in the amplifier support circuitry.

Finally I think we are using two terms that are close in meaning but are different. Clipping v Saturation; Clipping only deals with the voltage/signal portion of what happens when an amp goes into saturation. Clipping is of huge importance to you in the speaker biz. Saturation is the cause of clipping and carries with it the knowledge that the amplifier has approached the end of its range and all that this implies (covered earlier).

I am not saying current should be blowing stuff up all over the place, I am just putting out the thought that when you run that amp wide open, bad things can happen and current can be one of many factors.

 

[tanktones]

If all you are trying to say that the RMS power of a square wave, or clipped wave approaching a square wave, is higher than the RMS power of a sine wave, no disagreement. But, still, the amp HAS to deliver the same curent at the peak of a sine wave as it delivers at the peak of a square wave, if the peaks are equal. It's the law. It just delivers that current longer during a square wave sycle than during a sine wave cycle.

Pirates of the Caribbean.

The input signal into the final amp stage no matter what shape it is, only changes the point where the amp starts to go into saturation. If we were talking about a fixed gain amp, everything you guys are saying would be true, however, the amp has a volume control which means this amp has variable gain in its last stage. It does this differently in different types of amps , but the outcome is usually similar. This gain control (volume) can usually allow even a small clean signal to be driven to or near saturation. This is the why and how the saturation I am talking about differs from normal everyday clipping. With a variable gain amp you can have a fully clipped signal and still be nowhere near saturation in that final amp stage.

Thanks, I'd never have remembered Captain Jack.

 

[Bob Lee (QSC)]

Output stages typically are fixed-gain. Volume/gain controls typically are located upstream of the output stage.

 

[billfitzmaurice]

I meant to say impedance is a known commodity

Actually, it isn't. The impedance of a speaker can vary from DCR to DCRx10 or more across its bandwidth. What better amplifier designers consider when calculating power supply and output device current capacity is the worst-case scenario, a load which is DCR across the board. The reason current does not enter the clipping versus woofers equation is that, while high frequency voltage swing goes wildly non-linear with a clipped waveform, impedance rises with frequency, and as impedance rises current drops.

 

[bongomania]

...[when]you start to approach the limits of those drivers and then add even a little more current, due to the saturation of the amp, the chances for a component failure goes up. Add to that the additional stress on the components from harmonics, heat fatigue and other things I am learning more about daily, and you really start to put those drivers at risk.

The thing is though, you may be adding 2 and 2 to get 5. Just because running an amp outside of its rated range for an extended period does increase risk of some sort of failure somewhere in the chain does not inherently mean a chance of blown drivers. I'm not saying it's impossible, just saying one doesn't always follow the other.

Saturation is the cause of clipping and carries with it the knowledge that the amplifier has approached the end of its range and all that this implies (covered earlier).

Again, not necessarily. For examples:
--Saturating tubes is done all the time, in amps around the world, resulting in a wide range of clipping, with zero risk to anything aside from drivers that can't handle the power (rated too low, or simply inadequate, i.e. overpowered).
--Guitarists drive their amps and speakers into distortion all day, every day. They are not all destroying their amps.
--The square waves from a synthesizer, pipe organ, woodwind, or fuzz pedal are all shaped the way people imagine the worst case of clipping looks like, yet they can all be amplified without fearing for drivers that can take the power.

Again I'm not saying what you said is "always wrong", far from it; just pointing ways that it is not always right.

 

[tanktones]

I'm sorry that you're disappointed, but babebambi made an excellent point about what you seemed to imply, that current is unrelated to voltage. Many non-technical people make that mistake (no doubt helped by questionable marketing campaigns), and that's what it looked like in your post, too.



The volume control only apportions the amount of signal passing through. The signal causes some devices to conduct more and some to conduct less, more or less in porportion to the instantaneous value of the signal (usually voltage). That's because the devices are typically set up as voltage dividers--some pull the output toward the positive and others toward the negative (in a class B amp), or as a variable conductance in series with a fixed resistance (in a class A amp).

Bob, I realized after rereading the postings a few more times that you were not calling me a moron and that I was being over sensitive. Sorry for the confusion.

If I read you right, you are saying the volume control is basically a voltage divider that changes the amps inputs and not the gain. This may be true, I've seen applications like that. Since I do not have a schematic of an audio amp handy, I will defer. I have seen a few actual variable gain applications also, but most of those were low power applications in RF situations, some of those were op amp setups and some power applications. If the final stage is a fixed gain setup with a variable signal input then most of my theory does not apply. See, I knew you were smart. Now I really do feel like a moron.

 

[tanktones]

Here's one scenario: The resistance of the loudspeaker's voice coil will be lower when it is cold than when it is hot, so more current will flow for a given signal voltage. Without changing the resistance (and impedance), though, the current would be the same for a given voltage.

Just 1 last note before I slink away with my tail between my legs, beaten and stupid. :scowl:

I do believe resistance usually declines as a conductor heats up, unless you are talking a SUPER conductor. Otherwise thermal runaway would not be a problem. I'm sure this was a typo and not a mistake.

 

[Bob Lee (QSC)]

Bob, I realized after rereading the postings a few more times that you were not calling me a moron and that I was being over sensitive. Sorry for the confusion.

If I read you right, you are saying the volume control is basically a voltage divider that changes the amps inputs and not the gain. This may be true, I've seen applications like that. Since I do not have a schematic of an audio amp handy, I will defer. I have seen a few actual variable gain applications also, but most of those were low power applications in RF situations, some of those were op amp setups and some power applications. If the final stage is a fixed gain setup with a variable signal input then most of my theory does not apply. See, I knew you were smart. Now I really do feel like a moron.

The gain control sets the gain (voltage multiplication) of the overall amp channel. In a power amp, typically there's a fixed-gain input section, a gain control (usually set up as a variable attenuator), and a fixed-gain output section. Because they are multiplicative, the overall gain is Ginput​ × Gatten​ × Goutput​.

 

[Bob Lee (QSC)]

Just 1 last note before I slink away with my tail between my legs, beaten and stupid. :scowl:

I do believe resistance usually declines as a conductor heats up, unless you are talking a SUPER conductor. Otherwise thermal runaway would not be a problem. I'm sure this was a typo and not a mistake.

In metals, resistance increases with temperature.

Thermal runaway is a bipolar transistor phenomenon, in which the hfe increases with temperature, the increased current flow that results pushes the temperature higher, which further increases hfe and increases current, and so on.

 

[tanktones]

In metals, resistance increases with temperature.

Thermal runaway is a bipolar transistor phenomenon, in which the hfe increases with temperature, the increased current flow that results pushes the temperature higher, which further increases hfe and increases current, and so on.

Damn, I can't get anything right this week. I quit while I'm way behind, before this costs me money or something worse.

 

[billfitzmaurice]

I do believe resistance usually declines as a conductor heats up

It increases. This fact is the cause of thermal power compression in drivers, due to the heating of the voice coil. It's also how light bulbs work as tweeter protection devices. When excess voltage is applied the filament heats, resistance increases, and current flow through the tweeter/bulb decreases.