overpower or underpower, a hypothetical..

[billfitzmaurice]

I didnt really read through this thread

Then why resurrect it?
The Myth of Underpowering comes up, and is promptly shot down, on average twice a week. You didn't have to go back to a five year old post, you could have gone back no more than five days.

The answer to your question is yes.

Now please, can we let this dead horse rest in peace?

 

[Bachatero36]

Dam ok sheesh just asking a simple question thats all ok thank you though

 

[jaysbassspace]

I've been going through the majority of this thread but haven't read every single post so if i missed this please direct me to the right place. I just bought a GK MB Fusion that (as per the manual) runs 350 Watts into 8Ohms. I have an Eden D112xlt cab that has 8Ohms, 250 Watts RMS written on the back. Will I damage the cabinet by running the MB Fusion through it? Thanks in advance.

 

[HolmeBass]

I would go for the amp with 1500 watts... I would rather have more power in case you want to swap out cabs later. I tend to always go with a 'bigger is better' mentality. I know this isn't always true, but it is my normal habits.

Oddly enough -- I played a show with another band last weekend & their bassplayer was trying to explain to me that if you underpower your cabinets - this is what leads to blown speakers.... which completely seems backwards. I still don't think I understand that scenario.

This "underpowering" myth is a complete canard!! Check the sticky, maybe in the BG amps forum, IIRC.

To OP, I'd say go with either 1000 or 1500, not really going to make too much difference because your cab will probably max out on excursion - the Xmax of your speakers - long before reaching any thermal limits of either 1000 or 1500 watts.

 

[seamonkey]

There's an old saying about Q-tips. "Stop pushing in your ear when you feel pain"
For cabinets - if you hear pain like farting - turn down.

10 more pages to follow

 

[Bob Lee (QSC)]

I've been going through the majority of this thread but haven't read every single post so if i missed this please direct me to the right place. I just bought a GK MB Fusion that (as per the manual) runs 350 Watts into 8Ohms. I have an Eden D112xlt cab that has 8Ohms, 250 Watts RMS written on the back. Will I damage the cabinet by running the MB Fusion through it? Thanks in advance.

You probably won't, but it is possible. It's like asking if you will crash your car.

As long as you don't push too much signal into the cabinet, it should be fine.

It's really up to you.

 

[jaysbassspace]

Thank you Bob. I understand that if you crank any amp you risk damaging the amp and / or cabinet, I guess my question is should I be picking up a new cabinet with higher RMS.

 

[Bob Lee (QSC)]

You should choose the cabinet that you like. The one that sounds and puts out and covers like you want. That's the biggest variable in choosing gear.

Then choose a head or pre+power amp that's appropriate for the cab and has the features (input options, EQ or tone adjustments, limiting/compression, etc.) that you want.

If you don't run your GK into any significant clipping (that could raise the average power beyond the loudspeaker's thermal limits), or pound a lot of deep bass (that could cause overexcursion), you should be fine.

 

[jaysbassspace]

Thanks again.

 

[billfitzmaurice]

Thank you Bob. I understand that if you crank any amp you risk damaging the amp and / or cabinet, I guess my question is should I be picking up a new cabinet with higher RMS.

Only if the cab you have now won't go loud enough. And as the RMS rating of a cab tells you nothing about how loud it will go it's a far more complicated question than just a matter of watts. 99.9% of the time if your cab won't go loud enough you don't need a higher rated cab, you need a second cab, preferably identical.

 

[tanktones]

After reading this whole thread and many similar overpower threads, I think my very basic understanding of electronics and power might help resolve some of the confusion... probably not. I've seen alot of discussion that walked right up to the problem and then danced away, or called it something else.

1st Topic - Input,
The signal coming from a preamp, eq, or some effects box, (no matter how clipped) does NOT in its self cause an amp to blow up stuff. It will change the point on your volume dial where the power amp goes into saturation (start clipping). The more clipped or over driven the power amp input, the lower on the master or volume dial the saturation will start. Conversely, the cleaner and more under driven the power amp input, the higher you will be able to set your volume without pushing your power amp into saturation. You can run a square wave (representing total distortion) through most power amps at low volume, through most cabs and probably not have any problem for a long time. It will sound terrible but not harmful. Provided your not doing something stupid like using a 1000 watt head and a 50 watt cab or at a extreme frequency. This is theory, I'm not going to get into head/cab matching.

2nd Topic - Normal Operation,
The reason it is likely not to damage the amp or cab is because the power amp is running in its stable and designed range of operation. Your power out of the amp will have a normal power signature with your output signal (aka ac voltage) TIMES a nominal amount of amperage (current) generating the power expressed in watts. As you increase your volume you push that amp to put out higher voltage (taller signal) and proportionally higher current, meaning more watts.

3rd Topic - Over Driving Amplifier,
Once you start pushing that amp into saturation, things start to change. The harder you push that amp into saturation, the quicker you push that amp into a different more damaging power signature. When you turn up the volume past the point of saturation, the amp is told to put out more power, but, it is limited by its supply voltages, how high it can raise its ac voltage output (output signal), then saturation occurs. The more over driven the amp is, the harder the amp works to put out the required wattage, but with no ability to add ac voltage to the output, it will start to pass more CURRENT to the output to generate the power it is being asked to produce, The harder it is driven the more CURRENT the amp sends to the cab.

4th Topic - CURRENT is the KILLER!!!
Both physically and to electronic components.
If you were to measure the power output of this hypothetical saturated (over driven) amp, you would see a higher wattage, but more importantly, you would also see a disproportionally elevated CURRENT level. And again ....... ... ...... CURRENT THE KILLER! (looks like me after one of the many times I got tickled by a tiny encounter with CURRENT THE KILLER).

From the first days of electrical class in jr. high school, through 3 yrs high school electronics classes (we had good schools), all the way through electronic tech school, and over 20 yrs in the high end applied electronic industry, including 15 yrs with an ultrasonic equipment manufacturer as a system to component level field tech, and now, reading about the details of the damage some of these heads have done to these cabs reminds me that...CURRENT IS THE KILLER.
Heat is only a very destructive byproduct of excessive current flow. That is why the power amp is usually the one bolted to a heatsink, and why that heatsink is usually really hot when problems strike. When CURRENT itself runs amok resembles arc welding, leaving melted metal and vaporizing things. Of course we are talking about alot less CURRENT here, but voice coils and tweeters can be more delicate esp. in lower rated models. Higher rated cabs have heavier components, tweeters, mid range and all voice coils and crossovers, ect. and can stand more current but they have their limitations too.
This CURRENT heavy power signature when in saturation can be true for both tube and SS amps, but MUCH more so with the SS amps. However a leaky or shorting tube can cause a lot of damage when pushed.

It is really hard for me to say accurately which amps will blow up what cab or better yet which amps will sing beautifully through which cab with all the punch you could want, which after all is said and done is what all of us really want, isn't it? That's up to the real geniuses in the audio/music industry and your own ears. I'm just an old solder jockey putting in my 4 cents (I went on a whole lot longer than I meant to).

Hope I added some insight without boring you or humiliating myself. It does seem that the deeper I go into this the more questions I generate.

Please correct my theory or any other mistakes, I'm sure I made a few. Be eazy on my ramblings all you Big Brains out there.

I'm new to TB and hope I didn't come off as rude or anything. I like the tech talk and humor mix.

JAM ON!

 

[MuzikMan]

If you had
an Avater 2x12 cab rated for 1200 watts rms, and the choice of two power amps (I already have a good pre).

Would you take the amp rated for 1000 watts or the amp rated for 1500 watts?

Thanks

I would take the less expensive one. It is likely that the Avatar 2x12 drivers will be at full output before it gets 1000 watts. At that point the extra 500 watts won't get you anything useful.

 

[babebambi]

3rd Topic - Over Driving Amplifier,
Once you start pushing that amp into saturation, things start to change. The harder you push that amp into saturation, the quicker you push that amp into a different more damaging power signature. When you turn up the volume past the point of saturation, the amp is told to put out more power, but, it is limited by its supply voltages, how high it can raise its ac voltage output (output signal), then saturation occurs. The more over driven the amp is, the harder the amp works to put out the required wattage, but with no ability to add ac voltage to the output, it will start to pass more CURRENT to the output to generate the power it is being asked to produce, The harder it is driven the more CURRENT the amp sends to the cab.

4th Topic - CURRENT is the KILLER!!!
Both physically and to electronic components.
If you were to measure the power output of this hypothetical saturated (over driven) amp, you would see a higher wattage, but more importantly, you would also see a disproportionally elevated CURRENT level. And again ....... ... ...... CURRENT THE KILLER! (looks like me after one of the many times I got tickled by a tiny encounter with CURRENT THE KILLER).

Pardon my arrogance, but how do you pass more current withing out raising the voltage, with a specific impedance ?

 

[billfitzmaurice]

Pardon my arrogance, but how do you pass more current withing out raising the voltage, with a specific impedance ?

You don't.
When an amp is pushed to clipping voltage swing is increased in the harmonics, but not in the fundamentals. Therefore an abnormally high voltage swing is applied to tweeters, which can toast them. The voltage swing applied to the woofers remains no higher than what they normally see, so they are not damaged.

It is doubtbul that the Avatar 2x12 drivers will be at full output before it gets 1000 watts

A pair of Delta12 LF are displacement limited to no more than 300 watts in the 50-80Hz range. More power than that will give more headroom before the amp can clip, but won't give a single dB more output.

 

[Bob Lee (QSC)]

Pardon my arrogance, but how do you pass more current withing out raising the voltage, with a specific impedance ?

+1 It's always good when someone shows an understanding of Ohm's Law.

 

[Bob Lee (QSC)]

You don't.
When an amp is pushed to clipping voltage swing is increased in the harmonics, but not in the fundamentals.

The fundamental actually increases but the harmonic artifacts increase at a greater rate.

 

[JHAz]

+1 It's always good when someone shows an understanding of Ohm's Law.

It's a law? I thought it was more guidelines than an actual law . . .




(contractually-required smiley onaccounta this is supposed to be a joke [not to mention being, in fact, a lame movie reference]).

 

[tanktones]

Pardon my arrogance, but how do you pass more current withing out raising the voltage, with a specific impedance ?

No arrogance at all. I was expecting to have further discussion, that is why I commented in the first place.

First, which impedance are you talking about?
If you are asking about the impedance out side of the amplifier circuit, I am not addressing that because there are to many variables for me to deal with here. I'm trying to keep this to discussion length and not into dissertation length.
The impedance inside the amplifier is more crucial to my discussion. By the nature of amplifiers, as you bias an amplifier more on, the internal impedance and resistance of the amplifying device, decreases, allowing for more current and signal flow. In other words as you turn up your volume, the amplifier output wattage goes up in a linear pattern until you get to saturation. Saturation occurs when the amp basically runs out of new voltage due to designed power power supply limitations.
Example;
Now a guy with the small cheap amp head and some slightly higher rated cabs is playing in a bigger venue and he turns it up to "11" to be heard. As he cranks that volume well past saturation, he keeps biasing that amplifier more and more open to fullfil the demand. Open here means like opening a valve, which is what those geniuses that invented the vacuum tube amplifier called it a "valve". They called it that because it would allow you to combine a signal source and a power source and give you a larger signal and you could control the signal/power flow like turning on and off liquid flow through a "valve". The worst part about overdriving an amp way past its saturation point is, that the more you turn that amp up past saturation, the current path goes up in a logarythmic value compared to voltage. Meaning more current quicker. Check out the data sheets for your favorite amp package. At the top end of the [current out/votage(signal) out] charts you will usually see a straight almost 45 degree LINEAR line that ends with a little curl up at the top end. This curl is the DANGER ZONE, where CURRENT THE KILLER is now a larger percentage of your power output signature. I would have posted a graph myself but several years ago my wife tossed out all my data and reference books in a freak spring cleaning accident.
Today almost all of the amp packages have built in current limiters and thermal protection so they don't burn them selves up because, CURRENT is the KILLER, but the limiter still allows a nice jolt before it saves it self.

To sum things up, the guy with his/her amp @ "11" has been playing for a good long time in the Danger Zone with that toxic power (higher Current levels) are HEATING everything up real nice. The solo comes up and every thing is peaked with maybe an added effect switched in that finishes squareing off the input signal. He steps into the light, hits a low B or E and ... POP ... silence or worse. At this point though silence is probably better than that mashed toneless mechanical sound that was coming out of those poor cabs.

You don't.
When an amp is pushed to clipping voltage swing is increased in the harmonics, but not in the fundamentals. Therefore an abnormally high voltage swing is applied to tweeters, which can toast them. The voltage swing applied to the woofers remains no higher than what they normally see, so they are not damaged.

Actually 2 of the 3 fundamentals don't change too much once you are in saturation, you are right about Voltage being held somewhat constant. There is a small increase in Power, however I believe I've shown that there is indeed an increase in CURRENT THE KILLER, that makes up the entirety of the Power increase.

As far as harmonics, frequency response, heat, vibration, speaker coil specs., impedance matching, make & model choices, special circuitry, outside influences, speaker construction and what that finger smells like...(just seeing if you're really reading this). , is outside my expertise and I will leave that to the learned bass aficianado here at TB. There are alot of factors that are different in the audio field than my experience with ultrasonics and RF. Example: impedance is barely a factor between 1 MHz -50 MHz with RC coupling. I DEFER to their immense brains but just wanted to add a technical view point I did not see yet.

+1 It's always good when someone shows an understanding of Ohm's Law.

OH REALLY.
Bob, I've been reading your posts and find you to be an intelligent man, which made it that much more disappointing when, after reading my post with my history, you found it necessary to insinuate I had a lack of understanding of Ohm's Law. And you can read more into it, but I won't. I'll write it off to blogitis and blog attitude and move on.

The fundamental actually increases but the harmonic artifacts increase at a greater rate.

Now Bob, either the fundamentals don't change and I don't understand Ohm's Law or they do change and I do understand the old I=E/R and E=P/I.
Sorry, just a friendly nudge back.

Actually the harmonics you are talking about adds to my original reason for writing all of this was to illustrate one of the dangers of severely overdriving any amp too hard for too long.

I welcome all corrections and further discussion. Lets play nice and maybe we'll all be better with more input not less.

JHAZ- It's a law? I thought it was more guidelines than an actual law . . .

very funny...what movie is that; Blues Brothers , Super Troopers , Ghostbusters ...I know I've seen it.

Thanks,
I needed that.

KEEP THUMPING

 

[JHAz]

The fundamental tha Bob Lee is talking about it the fundamental frequency. As you push an amp into clipping harmonics increase. Ohm's law has zero to do with the frequency content of any signal. SO yo're kinda off base there.

Whatever is going on inside an amp, its current output is going to follow Ohm's law . . . so it will be controlled by the voltage swing and the impedance presented by the speakers. It is not possible (onaccounta the thing bein' a law and all) for it to be otherwise.

 

[tanktones]

The fundamental tha Bob Lee is talking about it the fundamental frequency. As you push an amp into clipping harmonics increase. Ohm's law has zero to do with the frequency content of any signal. SO yo're kinda off base there.

Whatever is going on inside an amp, its current output is going to follow Ohm's law . . . so it will be controlled by the voltage swing and the impedance presented by the speakers. It is not possible (onaccounta the thing bein' a law and all) for it to be otherwise.

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.