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Old 1st February 2013, 10:58 AM   #91
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JMF,
so how do you explain the 35V peaks the tweeter sees?

The original wave form frequency or shape doesn't really matter that much, all I'm saying is that the leading edge of any square wave is of high frequency at full output voltage regardless of the square waves fundamental and Rodd Elliotts example shows that quite nicely unless you are wilfully blind to it.
The fundamental frequency could be 10Hz, 100Hz, 1000Hz or anything else, the only thing that really matters for the extreme peaks is the rise time. The faster the rise time the higher the frequency needed to achieve it.

And this may well lead to failure of the tweeter. Either through overheating or, as djk pointed out, mechanical failure.
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Old 1st February 2013, 02:06 PM   #92
JMFahey is offline JMFahey  Argentina
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And who says the tweeter sees 35V peaks?
A simulation with poorly chosen and contradictory values?
So poorly chosen, that it "shows" the HF content has *higher voltage* than the LF signal, which is impossible in any clipped sinewave.
You must understand something about simulation: you can start with physically impossible values, and of course get physically impossible results.
What's news about that?
There's even an acronym for that: "GIGO" , meaning "Garbage In, Garbage Out".
Quote:
The original wave form frequency or shape doesn't really matter that much,
Really? You are inventing new Physics.
Specially you are ignoring a certain "Fourier" guy, who seems to know everything about this.
Joseph Fourier - Wikipedia, the free encyclopedia
Fourier transform - Wikipedia, the free encyclopedia
Fourier Series -- from Wolfram MathWorld
In particular, he is ***THE*** Authority to study stuff such as this:
Click the image to open in full size.
Quote:
all I'm saying is that the leading edge of any square wave is of high frequency at full output voltage regardless of the square waves fundamental
What you are saying over and over is that it burns tweeters, and it has been proven it's not so.

Fourier says otherwise, and the Math explaining it was posted many times above.
Don't want to overload the post with Fourier's formulas time and again, read them in full in post#50.

Mmmmhhhhh , big doubt.
Who do I believe? Fourier or "Charles Darwin"?
Quote:
Rodd Elliotts example shows that quite nicely
Does it?
From Rodd Elliott's own mouth:
Quote:
The waveform used for the simulation was made up
Quote:
The fundamental frequency could be 10Hz, 100Hz, 1000Hz or anything else,
Yeah, really?
Quote:
And this may well lead to failure of the tweeter. Either through overheating or, as djk pointed out, mechanical failure.
Well, overheating was proven not to be enough.
And mechanical failure was discarded by yourself in post#77
Quote:
breakage due to excess movement is neither here nor there.

Last edited by JMFahey; 1st February 2013 at 02:13 PM.
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Old 1st February 2013, 02:20 PM   #93
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by AndrewT View Post
JMF,
why did you choose a 100Hz signal for your analysis?
Dear Andrew T , "Charles Darwin" himself chose it in post #44 , where he made a wrong statement
Quote:
Charles Darwin said:
It is quite easy to fry a tweeter with a 100Hz sine as long as the amplifier is clipping.
which is haunting him ever since, because *many* Forum Members proved him wrong, from different analysis tools .... which agreed, of course.

That's the beauty of Science: that it's consistent.

I don't understand why he *still* insists on it.

Maybe it's to "save face" or something, but this is not the way.

Read the post #44 in full, where he bases his assumptions on his being able to burn tweeters using his synthesizer, a very uncontrolled "experiment" (if you can call it.)

Then he confesses on not using a pure sinewave but a "kick drum simulation" which of course can have all kinds of harmonics, but is not what we are discussing here.

In a nutshell: he is using poorly understood anecdotal "evidence" to challenge well known Physics answers.

Just to make sure we read his error correctly, and it was not a typo, he repeats it again in post #49:
Quote:
Let's try again:
We feed an amp a sine of 100Hz and drive it into hard clipping,
Incredible !!!

Even worse: not to be outdone, he doubles the bet in post #80
Quote:
I'd use a 100Hz sine and clip it or 50Hz or 20Hz, it doesn't really matter
Double incredible !!!!

By the way, you spoke of a 1000Hz sinewave, driving the amp to clipping, and with a 2KHz crossover.
In that example yes, of course, starting at 10X "Charles Darwin frequency", it's reasonable to deduce that the tweeter will receive 10X the former power, and this will be very bad to its health.

But all this proves is that AndrewT is right and "Charles Darwin" is wrong.

Personally I have been corrected many times, and, if approppriate, accepted it graciously.

I'm here to learn and exchange experiences, like most others.

Thanks.
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Old 1st February 2013, 07:13 PM   #94
djk is offline djk
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"100hz"

Looking at the spectra of pop music this would seem to be in the middle of the band that has the most energy and driving an amplifier into clipping.
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Old 3rd February 2013, 04:29 PM   #95
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JMF,
so because it supports my point Rodd Elliotts work is faulty even though the behaviour shown is pretty much textbook?

Interesting…

Either way you appear to be under the impression that the harmonics occur spread out over time as neatly as they are spread out over frequency ie they happen consecutively.

This is of course wrong, they all start simultaneously.
The effect of this is that the leading edge of a square wave takes on the frequency of the its highest harmonic while the amplitude is closer to F1+F3+F5+F7+F9... and so on until the system runs out of bandwidth and minus a certain amount since the sines of the harmonics do not sit exactly on top of each other. The reproduction of a perfect square wave is of course impossible since it would require infinite bandwidth.
Which is also why it does not matter if the square wave is 10Hz, 100Hz or !000Hz as the steepness and therefore the frequency of the leading edge is limited by the clipping amps bandwidth which might be 50 or 100kHz.


Here is a little gif which should make this very clear, also notice that the leading and trailing edges at all times have a higher voltage than the original.


http://upload.wikimedia.org/wikipedi...SquareWave.gif


PS: I have not dismissed breakage due to mechanical failure as you make out.
The point was that the exact failure mode matters less than the fact that it failed.
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Old 4th February 2013, 12:42 AM   #96
djk is offline djk
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"The point was that the exact failure mode matters less than the fact that it failed. "

Yeah, right.

Very few tweeter actually fail due to the coil burning up, the vast majority are from mechanical failure.

Yet we continue to spread the myth that this is somehow connected to amplifier clipping when it is the increase in stress during the non-clipped portion of the program material that is the culprit.

Get over it.
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