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Old 28th January 2013, 12:36 PM   #81
JMFahey is offline JMFahey  Argentina
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Fine.
I chose that value on purpose to show *one* case in which the VC would burn with no mechanical stress involved.
And being a pure sinewave, would make crossover slope irrelevant.

Now, if you use a 100Hz sinewave, which *is* what we are discussing here, you won't kill the tweeter with its harmonics.
It was already shown in earlier posts, with accompanying Math.
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Old 28th January 2013, 01:15 PM   #82
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Quote:
Originally Posted by Charles Darwin View Post
I have no intention to start off with a 6kHz wave.
I'd use a 100Hz sine and clip it or 50Hz or 20Hz, it doesn't really matter as long as it is well below the crossover point so that none of the original, unclipped signal would ever reach the tweeter.
No crossover has the power to infinitely attenuate. Even a 4 pole filter will let something of the original sine wave through.
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Old 28th January 2013, 01:48 PM   #83
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Quote:
Originally Posted by JMFahey View Post
Fine.
I chose that value on purpose to show *one* case in which the VC would burn with no mechanical stress involved.
And being a pure sinewave, would make crossover slope irrelevant.

Now, if you use a 100Hz sinewave, which *is* what we are discussing here, you won't kill the tweeter with its harmonics.
It was already shown in earlier posts, with accompanying Math.
Then there are two possibilities: Either there is something wrong with your maths or with your interpretation of the results because I can do what I described in reality without any problems at all.

You can also over-stress tweeters with a bass drum whose fundamental is usually around 80-120Hz while the loudest part, the transients, are more in the region of 8kHz.


As for the filter issue Kesh mentioned if we stick to a 100Hz sine wave and a crossover point of 2000Hz the original signal would be attenuated by over 96dB using 24dB filters. Which is close enough to nothing for me.
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Old 28th January 2013, 08:42 PM   #84
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Quote:
Originally Posted by Charles Darwin View Post
Then there are two possibilities: Either there is something wrong with your maths or with your interpretation of the results because I can do what I described in reality without any problems at all.
...
There is a third possibility: that your understanding of the mechanism involved is incorrect. Your rejection of the well-understood laws of harmonic progression lends weight to this possibilty. If you're burning out tweeters by feeding them a 100 Hz square wave you need to look for another reason - for example, an incorrectly implemented crossover. For example, a "crossover" with a single series capacitor might let through enough of the lower harmonics to overheat or over-excurse the tweeter. This would tend to be the case in lower-spec speakers with poor-quality tweeters.
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Old 29th January 2013, 10:04 AM   #85
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Quote:
Originally Posted by Charles Darwin View Post
As for the filter issue Kesh mentioned if we stick to a 100Hz sine wave and a crossover point of 2000Hz the original signal would be attenuated by over 96dB using 24dB filters. Which is close enough to nothing for me.
If we have 4 pole filters then we've pretty much made our tweeters safe from this issue, so we're missing the point, which is how tweeters fail.
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Old 29th January 2013, 10:20 AM   #86
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On the other hand if our square wave has a rise time of 0.000015 sec from zero to 40V we actually have a 20kHz 40V sine right there.
(rise time of a sine being roughly 0.3 x period)

Which could very well lead to tweeter failure, be it thermal or mechanical.

Shorter rise times lead to higher frequency components but 20k seems appropriate in these days of digital audio as it is about the fastest rise time digital with a 44.1k sample rate can produce since it is low pass filtered at around 20k.
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Old 29th January 2013, 04:12 PM   #87
JMFahey is offline JMFahey  Argentina
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Quote:
Charles Darwin said:
On the other hand if our square wave has a rise time of 0.000015 sec from zero to 40V we actually have a 20kHz 40V sine right there.
(rise time of a sine being roughly 0.3 x period)

Which could very well lead to tweeter failure, be it thermal or mechanical.

Shorter rise times lead to higher frequency components but 20k seems appropriate in these days of digital audio as it is about the fastest rise time digital with a 44.1k sample rate can produce since it is low pass filtered at around 20k.
You didn't read earlier posts, did you?

In post #63 I explain:

Quote:
2) To analyze it from another point of view (which confirms my earlier statements, the beauty of Science is that it's consistent):

* Suppose the 100Hz squarewave has a leading edge which rises within 50uSec.

* Suppose it reaches 40 V.
(as you see I am so sure about what really happens that I accept all your premises)

* Peak power will be 40*40/8=200W (you must be smiling by now )

*BUT* that narrow pulse will repeat every 10000uSec (we *still* have those pesky 100Hz as base frequency )

Duty cycle will be: 10000/50=200 .

So average power dissipated by that poor voice coil will amount to 200W/200=1W.

Piece of cake.
Repeating this calculation with your 20KHz front edge , created by a rise time of 0.000015 sec (your numbers) we now have a duty cycle of=
0.000015 sec/0.01Sec (meaning 100Hz frequency)=0.0015=0.15% (PLEASE check the Math) so the average power dissipated by that voice coil will be= 200Wx0.0015=0.3W .

Another misconception you write:
Quote:
we actually have a 20kHz 40V sine right there.
No, the amplitude of a harmonic is:
Click the image to open in full size.
so, the "20KHz sinewave", being the 20000/100 th harmonic=200th harmonic, and its *voltage* will be 40V/200=200mV which amounts to a power of: 0.2V x 0.2V / 8 ohms= 5 milli Watts.

By the way, djk says about the same, only using dB instead of % , in post #59 .

Now that I reread older posts, I see that all this was already explained to you.
What's the point of wasting our time repeating the same 1000 times just because you cover your ears and shout "I can't hear you .... I can't hear you .... "
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Old 31st January 2013, 11:32 PM   #88
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Why Do Tweeters Blow When Amplifiers Distort?


Scroll down to 'moderate clipping' and you'll see what I mean.
The amps full range output is 24.7V rms in this case, the woofer receives 20.5V rms and the tweeter 8.9V rms.
But the voltage peaks the tweeter receives exceed 35V on this scale while the woofer only sees peaks of 30V.
The spikes in the tweeter voltage are the leading edge of each squared off wave.
Even that is visible in that measurement.
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Old 1st February 2013, 02:49 AM   #89
JMFahey is offline JMFahey  Argentina
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You don't read what you cut and paste, do you?

We have been discussing from the beginning *your* statement that harmonics of a 100Hz squarewave , even with the fastest rise time possible, and with a 2KHz crossover can burn a tweeter coil ..... and demonstrated by many different methods that it does NOT happen.

We calculated the power of all harmonics and in no case they added up to a dangerous level .... by a LONG way.

Now you refer to a test which you clearly do not understand and *think* it proves your point ... which it does not.

Instead of the original clipped 100Hz waveform we are discussing, you refer to a Rod Elliott's study which is absolutely unrelated.

He does NOT analyze a clipped 100Hz frequency but a MIX of frequencies, arbitrarily chosen, from 160Hz to 13 KHz

And the intensities are also arbitrarily chosen at very high and unrealistic values.

Example: in our example of 100Hz base frequency, the 2KHz component amplitude would be 1/20th the amplitude of the fundamental , so for 40V peak we would have 2V peak=-26dB or 0.5W *peak*


BUT Rodd Elliott arbitrarily sets the 2KHz signal 3 dB below the lowest frequency one.
He assumes a 20 dB higher level, 100 times the power !!!

And that talking of *undistorted*, below clipping signals!!!

Of course, *all* high frequency signals will rise even more after clipping.

So what? It's not a 100Hz signal, the original one discussed (and accepted by you) but a completely different (and artificial) thing.

Talk about cheating !!!
No doubt you now want to include this absolutely unrelated signal!!!

To show what you are NOW referring to (and which is not what we are analyzing here):
Quote:
Rodd Elliott said:
Example Power Waveforms

The following diagrams illustrate the above. The waveforms below are the result of simulation, but 'real life' will show exactly the same things as described. The waveform used for the simulation was made up from the following signals ...
Frequency Peak Amplitude (V) Relative Amplitude (dB)
160 10 0
400 10 0
1k0 8 -2.0
2k0 7 -3.1
3k5 6 -4.4
5k0 5 -6.0
9k0 3 -10.5
13k0 2 -14.0

Table 1 - Test signal Composition

This waveform is not an attempt to reproduce any musical instrument or section of music - it is simply a batch of frequencies
that make up a suitably interesting waveform
So, next time you bring a witness in your behalf, at lest choose one who speaks about what we are discussing here.
Thanks.
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Old 1st February 2013, 09:24 AM   #90
AndrewT is offline AndrewT  Scotland
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Default Signals reaching the treble driver

JMF,
why did you choose a 100Hz signal for your analysis?
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regards Andrew T.
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