This could happen as a result of amp failure, if one of the output transistors develops a short circuit, or something else causes the output to develop a large DC offset.
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Common amp myths
- Thread starter JimmyM
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This could happen as a result of amp failure, if one of the output transistors develops a short circuit, or something else causes the output to develop a large DC offset.
The amp belonged to the store and judging by the groaning sound the tech made, I would agree that it was amp failure. It really smoked the speakers. Really! I mean the smoke came out of the cabinets. Smelled bad, too. It was a stereo PA amp. When I called the store, he thought I was doing something wrong and told me to switch the speaker wires and see if it had the same problem. I know I shouldn't have, but I did. Poof! More smoke and that same smell. They still didn't believe me (because the loaner amp was so much more expensive than the cheap Peavey amp I was waiting on). They blew a dual 18" at the store to test it. The tech was not amused at the salesman's testing method. They were still having an animated discussion as I left the store. But at least they fixed the speakers.
bongomania
Commercial User
Ooh, interesting! So, all else being as equal as it's gonna get for now, would the increased voltage be perceived as a louder signal on output from the speaker, even if the wattage was reduced by the amount you suspect?
can we not go back to simple equations
P= IV
V = IR
and then expand on it and use what is lost to resistances across cables and so forth and covert that to mechanical power to drive the speaker using the classical differential equation of a harmonic oscillator
dx^2/d^2t - a(dx/dt) + b^2(x) = K
Solve it using the a,b,k for that given speaker and figure out P from this (watt = J * S and E = 1/2 mv^2 or 1/2m(dx/dt))
Just an idea you can solve for theoretical power from this and then you can use material's data to solve for what stresses will cause damage to the cone.
(fyi I do materials/chemistry so this is why I go this route)
P= IV
V = IR
and then expand on it and use what is lost to resistances across cables and so forth and covert that to mechanical power to drive the speaker using the classical differential equation of a harmonic oscillator
dx^2/d^2t - a(dx/dt) + b^2(x) = K
Solve it using the a,b,k for that given speaker and figure out P from this (watt = J * S and E = 1/2 mv^2 or 1/2m(dx/dt))
Just an idea you can solve for theoretical power from this and then you can use material's data to solve for what stresses will cause damage to the cone.
(fyi I do materials/chemistry so this is why I go this route)
The short answer would be no. If anything the drop in current(amperage) required to maintain the same wattage at a higher voltage would most likely be percieved as a drop in sound level.
-Johnny
You might want to check the "speaker theory" articles at my website, which goes through much of this derivation in detail.
bongomania
Commercial User
That's what made intuitive sense to me, but as we've seen in this thread intuitive sense doesn't necessarily = fact.
So I just wanted to see where fdeck was going with this, and whether I misunderstood.In Loudthud's earlier post on the subject he said:
And Rick replied:Loudthud said:
...And now fdeck is also suggesting that the higher voltage in the one image is not an indication of higher power, and may in fact indicate lower power, which (barring other signal alteration e.g. clipping/compression) indicates less potential "loudness".
If I have understood and followed this correctly (granting that I may not have), then the oscilloscope readings given actually indicate (if not prove) that the "special" interaction between a tube power amp and a speaker load does not account for any increase in loudness.
Thoughts?
I think it will be louder. It is necessary to take a look at how an amp and speaker work together.
Under normal operation, an amp is a controlled voltage source. The output voltage is proportional to the input voltage, under normal variations in output current.
An ideal "flat" speaker is one that produces the same SPL output at a given input voltage over a range of frequencies.
Why prioritize voltage, and not current? The reason is that a cone speaker can be rendered "flat" or nearly so, if driven by a controlled voltage source, not a controlled current source. If driven by a controlled current source, the response curve of a speaker will have a huge response peak coincident with the impedance peak.
An amp that can achieve a higher output voltage in a narrow frequency range, if driven to just below clipping, will sound louder in that range. In the case of clipping, the output voltage is determined by the available current, so the amp is acting in a quasi controlled current mode.
Now the $64 question is: How much louder? It depends on the design of the power supply in the amp. I imagine that silicon rectifiers produce a stiffer supply than a rectifier tube, for instance. But I would leave that to the tube experts to confirm or refute.
I made a plea way back at the start of the thread to keep responses civil and by and large this thread has been good in that respect.
But there's always a few folks around - let's call them cerebrally unsophisticated - who just cannot see something they disagree with without descending into infantile bickering. I've already had to delete a few posts of this nature from several users. If one of your posts has been edited or deleted, it was in this category, or quoted a post in this category.
My moderator colleagues and I have been discussing this and would like it to cease, now. So please, take care. If you can't take part in this discussion without resorting to personal attacks, then you won't be taking part anywhere here at all pretty soon.
Those of you who know me as a mod know that I don't usually get irritated by stuff much, but I'm irritated now.
If you've any comments on this post or the thread in general, please PM me.
But there's always a few folks around - let's call them cerebrally unsophisticated - who just cannot see something they disagree with without descending into infantile bickering. I've already had to delete a few posts of this nature from several users. If one of your posts has been edited or deleted, it was in this category, or quoted a post in this category.
My moderator colleagues and I have been discussing this and would like it to cease, now. So please, take care. If you can't take part in this discussion without resorting to personal attacks, then you won't be taking part anywhere here at all pretty soon.
Those of you who know me as a mod know that I don't usually get irritated by stuff much, but I'm irritated now.
If you've any comments on this post or the thread in general, please PM me.
No, I got those results because that was all that amp was capable of producing - I can assure you that I know how to make the most out of an amp's gain structure and EQing - I've probably played several thousand gigs in my lifetime - over 75 last year, actually...
- georgestrings[/QUOTE]
But what does playing gigs have to do with understanding how amplifiers work?
That's like saying that the fact that you played a lot of gigs makes you an expert in music theory. You could be, but the act of playing gigs doesn't necessarily make it so.
Specious argument. But then, I think that nothing is going to change your mind.
billfitzmaurice
Commercial User
- Sep 15, 2004
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This goes to the heart of the problem when one equates power with volume. Power into a load varies with the impedance of the load. Since a speaker has a variable impedance with respect to frequency the power delivered also varies with frequency.
More to the point, the output of a driver is directly proportional to the excursion of the cone, and excursion is directly proportional to voltage applied, not power.
For this reason the entire concept of quantifying SPL at 1 meter/1 watt is intrinsically flawed, as SPL is never measured with a constant power input, always with a constant voltage input. By the same token rating amplifier output using power as the standard is intrinsically flawed, since it's voltage swing that determines how loud a speaker may be driven. The situation isn't at all dissimilar to light bulbs, where the assumption was long made by the consumer that wattage, not lumens, was equivalent to brightness.
Regarding the underpowering speakers myth...
At what point is underpowering the speakers dangerous for the amplifier? I don't understand why a 5 watt Epiphone can drive a guitar half stack (or a bass 8x10 for that matter) without burning out, when using a 100 watt SS could very easily burn out trying to power an 8x10.
I used to play my Mesa 412 with an ampeg B2R, and it was clip city. Yet I've seen bassists use the SVT-III or the GK800RB with big rigs no problem.
At what point is underpowering the speakers dangerous for the amplifier? I don't understand why a 5 watt Epiphone can drive a guitar half stack (or a bass 8x10 for that matter) without burning out, when using a 100 watt SS could very easily burn out trying to power an 8x10.
I used to play my Mesa 412 with an ampeg B2R, and it was clip city. Yet I've seen bassists use the SVT-III or the GK800RB with big rigs no problem.
bongomania
Commercial User
There is exactly no point at which "underpowering the speakers" will ever be harmful to the amp. Clipping does not damage the amp. Now, conceivably the amp may be "underbuilt" such that running it at maximum gain for a certain time would cause the components to overheat and self-destruct. But that has nothing to do with the speakers, except insofar as you have to have some kind of load on the amp in order to make it produce wattage at all.
alexclaber
Commercial User
There is an infamous listening room in Italy using horn subwoofers containing eight 18" woofers in each sub, driven by single-ended valve amp of less than 10W power. By using lots of speakers and very little power you get a very accurate low distortion high SPL sound.
Amps don't care how powerful your speakers are! Underpowering does not exist - save for your rig being underpowered (in terms of max SPL, not wattage) for your gig.
Alex
Amps don't care how powerful your speakers are! Underpowering does not exist - save for your rig being underpowered (in terms of max SPL, not wattage) for your gig.
Alex
Top thing I learned from your signature:
No one can defeat the quad-laser.
If you underpower your drivers...
"the explosion will be of extraordinary magnitude"
[Invalid or Expired Link Removed]
Just to make sure I've got this right.
Say I have an deal, perfectly tuned cabinet - completely flat response, but with a typical impedance curve, say 20Ω at 100hz, and 8Ω at 200hz. I put 10V on the speaker terminals at 100hz, it has X-excursion.
If I raise the frequency to 200hz still maintain 10V and it will have the same excursion?
I think the danger in saying a constant voltage input is when the amplifier has a higher output impedance. Say 1Ω (as an extreme example). When the driver impedance is 20Ω the effect is 1/20, when it's 8 ohms it's 1/8. You'd need to be sure to measure and add adjust the voltage at each frequency.
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