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300w vs 500w head with 450w cab?

#41
If amps are putting out AC to the speakers then it cannot change to DC just because a sound wave clips. DC is direct current like a battery you have a positive and negative terminal and the electricity flows in one direction. AC is alternating current like the plug in your house you have a hot wire and a grounded wire(neutral) the current goes back and forth through the system(not one direction). So please explain the speaker situation to me I'm not a sound engineer just an electrician so maybe its over my head.
 
#42
CL400Peavey said:
Can you please explain how that is any different than the signal presented to a speaker when using distortion?
Click to expand...

Not trying to be smarmy, but it's the old deal - all clipping is distortion, but not all distortion is not clipping. Before a preamp or power amp stage clips, it will begin generating lots of harmonics, or harmonic distortion, and that's normally the kind of desirable distortion guitarists and bassists go for. If you go beyond that the signal begins clipping, but it is happening in very short durations, so it is not keeping the voice coil in any one position long enough to burn it. The kind of clipping we're talking about that will damage the speaker is when the power supply of the amp totally runs out of gas trying to achieve the desired output, and it (sorry guys) presents a long duration non-varying, or DC voltage to the speaker, in which case the voice coil moves to one position, stays, and burns.
 
#43
Freight Train said:
It has nothing to do with DC being present on the output of an amp. That's a power supply issue. Here's the deal - a music signal is constantly varying in amplitude. To oversimplify let's say it's changing levels at the rate of anywhere between 20 and 20,000 times per second. It is an ALTERNATING CURRENT. A.C. = Alternating Current. When a musical signal clips, the top of the waveform is chopped off, and the amp is putting out a CONSTANT voltage, which moves the speaker coil to one position and stops, and if it stays there too long it burns the voice coil. A CONSTANT voltage is a CONSTANT or DIRECT current. D.C. = Direct Current. Please check the link I posted, don't believe me.
Click to expand...

Can you point out to me exactly where the article you posted says that a speaker coil will move to one position and stop?
 
#44
I believe Freight Train is honestly trying to help, and dispensing info he believes to be true. Sadly, he is also incorrect, and adamant about proving himself right. The OP's question has been answered, either amp is a fine choice, but using your ears to listen for signs of over excursion are important, no matter what any piece of gear is "rated" at.
 
#45
254 stringer said:
If amps are putting out AC to the speakers then it cannot change to DC just because a sound wave clips. DC is direct current like a battery you have a positive and negative terminal and the electricity flows in one direction. AC is alternating current like the plug in your house you have a hot wire and a grounded wire(neutral) the current goes back and forth through the system(not one direction). So please explain the speaker situation to me I'm not a sound engineer just an electrician so maybe its over my head.
Click to expand...

No Stringer, what you're saying is correct, but when the alternating current clips, it does present a constant, non-varying current, or direct current. If that happens in a short duration it doesn't hurt the speaker. But the longer the duration the more likely it will burn the voice coil. Look at the link I posted - that site does a very good job of explaining and showing how it happens.
 
#46
Freight Train said:
Not trying to be smarmy, but it's the old deal - all clipping is distortion, but not all distortion is not clipping. Before a preamp or power amp stage clips, it will begin generating lots of harmonics, or harmonic distortion, and that's normally the kind of desirable distortion guitarists and bassists go for. If you go beyond that the signal begins clipping, but it is happening in very short durations, so it is not keeping the voice coil in any one position long enough to burn it. The kind of clipping we're talking about that will damage the speaker is when the power supply of the amp totally runs out of gas trying to achieve the desired output, and it (sorry guys) presents a long duration non-varying, or DC voltage to the speaker, in which case the voice coil moves to one position, stays, and burns.
Click to expand...

:rollno::eyebrow:

No im sorry this is wrong. Its not that the signal is clipped, its that you have pushed the speaker past its mechanical limits, transient spike or not. This is what kils woofers. Tweeters is another matter. A distorted signal can very quickly push them past their limits even at lower power than you expect.
 
#47
Freight Train said:
No Stringer, what you're saying is correct, but when the alternating current clips, it does present a constant, non-varying current, or direct current. If that happens in a short duration it doesn't hurt the speaker. But the longer the duration the more likely it will burn the voice coil. Look at the link I posted - that site does a very good job of explaining and showing how it happens.
Click to expand...

This is the only reference to driver damage that I can find in the article you linked:

Given the right (or wrong) signal and sufficient clipping, there is the real risk that a loudspeaker driver may even be damaged. The voicecoil may be slammed into the rear polepiece of the magnetic circuit, suspensions may be stretched and the assembly's alignment compromised. This will lead to eventual driver failure.​

That hardly sounds like a description of a voice coil that has "moved to one position and stopped."
 
#48
Febs said:
Can you point out to me exactly where the article you posted says that a speaker coil will move to one position and stop?
Click to expand...

It doesn't. I will give him one thing--the article does show how an asymmetrical signal has an offset of averages that can be described as DC, which could displace the "center" position of the driver by a certain amount. However the only way damage could occur from that is if that displacement was continuous, i.e. the exact amount of asymmetry was unchanging. But a bass guitar signal presents a constantly changing wave, and even if it clipped on many peaks all night long, the amount of asymmetry would not be the same from one microsecond to the next, never mind the "stays in one position" image he's relying on. The article does not support that idea.
 
#49
Febs said:
This is the only reference to driver damage that I can find in the article you linked:

Given the right (or wrong) signal and sufficient clipping, there is the real risk that a loudspeaker driver may even be damaged. The voicecoil may be slammed into the rear polepiece of the magnetic circuit, suspensions may be stretched and the assembly's alignment compromised. This will lead to eventual driver failure.​

That hardly sounds like a description of a voice coil that has "moved to one position and stopped."
Click to expand...

What the article describes sounds exactly like over excursion...
 
#51
To be clear, the linked article does not support any of these statements:
Freight Train said:
...not only is a square wave being presented to the speaker - meaning it is moving the voice coil to one position and burning in there - but when the amp clips it is no longer presenting an rms averaged music signal, but a full peak-power DC signal to the speaker.
Click to expand...
 
#52
Russell L said:
I'll just say this: watch out for the speaker running out of excursion. Too many lows and a hard attack at too much volume can cause it. Turn it down some and it may be ok, or roll off some lows to tame it. If you hear a loud click it's probably happening.

I don't know enough to comment on the other stuff.
Click to expand...

I've had this happen . . . confused it with hitting the pickup with over-enthusiastic slapping. That'll teach me to use an octaver!:D

Seriously though, listen for signs of stress.

jeff7bass said:
I would go with a 500w head over a 300w head as long as there’s a pre-amp control like GAIN, or in the Carvins case, DRIVE. By keeping the MASTER down and pushing the DRIVE up, you can get the overdriven sound of a less-powered amp (somewhat) at lower volumes.
With a 300w amp, you won’t have the advantage of additional clean volume at higher levels (or driving more speakers) so it’s better to have more power.
Keep in mind that you can buy both a Carvin BX500 and a BX250 for the price of some other amps. That way you can choose, plus you’ll always have a backup head. '
:bassist:
Click to expand...

I've heard about this. It's basically word for word why I'm looking at 500W micro heads...:hyper:
 
#58
I finally took time to read the link.

The highest DC voltage I saw mentioned anywhere in the article was less than 5 volts. And even that was in the case of a purely DC coupled amp. I doubt there are any such amp designs in use in the SR or MI world.

I fail to see how a few volts DC (less than 1/2 volt in most of the cases cited) will damage a voice coil that's designed to handle 70 or more volts AC. (If I get bored, I'll hook a speaker up to a flashlight baterry tonight and see.)
 
#59
pan1k said:
THATS WHAT I WAS TRYING TO SAY. :hmm:
Click to expand...

You are taking one thing you read and applying it out of context.

The 3015LF drivers are an exception, in that they are limited thermally; while most commercial bass drivers are limited mechanically.
In short, that is why most commercial cabs will not be able to use as much power as they are "rated" for -- much less, more power...
 
#60
AFAIK, ultimately, 'clipping" is a somewhat variable term. With PA power amps, they might call it clipping at .1 or .5 or 1 percent distortion. Once the amp hits the knee where THD starts to rise, THD rises relatively fast but power does too. But even 10 percent THD doesn't present anything like a pure square wave, and unless your compressing the bejesus out of your signal, it hits really hard (say a 10 or 12 dB peak) for something like a 20th of a second or less, then settles into its sustain at the lower level, quickly fading (from a power perspective) to well less than half the original power of the sustain (leaving out the transient attack at 10 times or more the power of the beginning of the sustain). There's a good example of this in the bassgearmag.com review of the TC Electronics 450, and there was a great thread that occurred before I started coming here showing the power envelope of lots of basses. Bottom line is unless you're going for a very harsh end of the world industrial accident sound and compressing the heck out of it, you're not at max even a 10th of the time AFAIK.
 

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