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Old 13th January 2013, 07:05 PM   #41
JMFahey is online now JMFahey  Argentina
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Yes, on sinewaves.
But what djk refers to is something else.
I've also read the JBL led study (have it stashed somewhere ) about listeningbto music at loud volumes.
Basically what they say is that we listen to music at an average level way below that of what would be sinewave clipping, when only some music peaks may clip sometimes, because that does not sound "ugly".
When we don't care much about that (typically a DJ environment) we start raising volume, louder portions of music start to clipo more, but we tend to "forgive" that (we are having fun, aren't we?).
That causes the *average* level of music to rise spectacularly (I couldn't believe it when I saw the graphs); bass (which is what usually clips first) does not rise much (it's clipping-limited) but mids and highs continue to raise *a lot*.
Even if not clipped themselves, the much higher levels burn tweeters.
Bass *is* clipping the way you describe, but it's too many octaves (even their harmonics) away from what would channeled into the tweeters.
Yes, in a "let's blast the neighbouthood with my boombox" distortion you'll reach squarewaves at every frequency (ugh!!) but what worried JBL was their Hi Fi stuff being blown at home parties and such, where the system sounds loud but still is perceived as "basically clean"
If I find the study I'll post it here.
If somebody finds it first, he's welcome to do so.
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Old 13th January 2013, 07:09 PM   #42
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"What do you think clipping is, it's the increase in average power when the top of the sine wave is cut off almost approximating a square wave. "

Read my post again, you totally missed the point.

The difference between a sine and a square wave is only a 3dB increase, the increase in average power reaching the tweeter of program material driven 10dB into clipping on the brief music peaks is trivial compared to the 10dB increase in long-term average-power during the majority of the time the amplifier is not clipping.
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Old 13th January 2013, 07:27 PM   #43
sreten is offline sreten  United Kingdom
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Hi,

Even with Phons the issue is sidestepped. Phons are equally spaced
at 10dB power intervals at 1KHz. From there they are equal loudness
curves, there is no attempt to establish relative loudness levels.

rgds, sreten.
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Old 13th January 2013, 07:34 PM   #44
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Waveforms are funny things.

It is quite easy to fry a tweeter with a 100Hz sine as long as the amplifier is clipping.
I assume a passive multiway speaker is being used.

A (perfect) sine is a pure tone with no harmonics at all but the moment the amp is clipping it produces a square wave which contains all the sines which fit inside it.
So if I drive a 200W amp into clipping it will produce, for example, 10 000Hz at the full 200W. I don't know of (m)any tweeters which will cope with that for very long.

This can easily be shown to be true with an analogue modular subtractive synth like the one I've got. Just take the output of a low frequency sine generator and feed it into a filter. The result is extremely boring as the tone either passes unmolested or is filtered out resulting in silence. But if you take the same sine, run it through an amplifier module and drive that into clipping before going into the filter things are very much different.
Suddenly there are plenty of harmonics for the filter to get its teeth into and the result is very, very similar to feeding the filter a square wave signal instead of a clipped sine.
Btw usually amplifier modules have an adjustable output level so that the signal which reaches the filter is of the same level as before the amp.

Bottom line a clipping amp produces vast amounts of harmonics at full power which are not present in the unclipped signal. No crossover will be able to save the tweeter.
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Old 13th January 2013, 09:28 PM   #45
JMFahey is online now JMFahey  Argentina
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Quote:
It is quite easy to fry a tweeter with a 100Hz sine as long as the amplifier is clipping.
So if I drive a 200W amp into clipping it will produce, for example, 10 000Hz at the full 200W. I don't know of (m)any tweeters which will cope with that for very long.
Would you please make up your mind and choose just one?
100Hz and 10000Hz not exactly the same.

To clear things: I very much doubt a 100Hz squarewave can burn a regular tweeter, even less a Driver+Horn. Talking about passive crossovers, of course.

And if you are talking 10000 Hz, well, *any* waveform at that frequency and 200W will burn any tweeter I can think of.

We are talking the kind which uses a coil and a magnet.
Piezos are something very different.

PS: and if you are saying that "the 10000 Hz harmonic of a squarewave clipped 100Hz frequency, when produced by a 200W amp, will burn a tweeter connected to its output through a passive crossover", the answer is: I very much doubt so.
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Old 13th January 2013, 09:47 PM   #46
cotdt is offline cotdt  United States
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I agree, it is not going to fry a modern tweeter.
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Old 13th January 2013, 11:04 PM   #47
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Simple math: 100 Hz, clipping or square wave. Assume the tweeter crossover is about 1.6 KHz. Only harmonics 17th and above get to the tweeter. Assuming 200W of power from the amplifier, that's about 4.5 watts to the tweeter. So although Charles' math is incorrect, some(*) tweeters may overheat after a few minutes at that power level.

(Also assume perfect square wave and crossover, and zero inductance tweeter.)

(*) Tweeters intended for systems rated at about 50 watts or below, and assuming the tweeter sensitivity matches the midrange driver and doesn't require padding.)

Last edited by Don Hills; 13th January 2013 at 11:14 PM.
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Old 13th January 2013, 11:17 PM   #48
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just install and listen in your bathroom

ought to make any system sound louder


yes, i am bad.
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Old 14th January 2013, 01:04 PM   #49
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Quote:
Originally Posted by JMFahey View Post
Would you please make up your mind and choose just one?
100Hz and 10000Hz not exactly the same.

To clear things: I very much doubt a 100Hz squarewave can burn a regular tweeter, even less a Driver+Horn. Talking about passive crossovers, of course.

And if you are talking 10000 Hz, well, *any* waveform at that frequency and 200W will burn any tweeter I can think of.

We are talking the kind which uses a coil and a magnet.
Piezos are something very different.

PS: and if you are saying that "the 10000 Hz harmonic of a squarewave clipped 100Hz frequency, when produced by a 200W amp, will burn a tweeter connected to its output through a passive crossover", the answer is: I very much doubt so.
The 10 000Hz was merely an example as it certainly is a multiple of 100 and a nice round number.

Let's try again:
We feed an amp a sine of 100Hz and drive it into hard clipping, the result is the amp puts out a 100hz square wave. Now lets just say the amp produces an output of 30V at that point. This square wave contains all possible multiples/harmonics of 100 at the full 30V.
If the tweeter xover is at 2000Hz the tweeter will now try to reproduce 2000Hz, 2100Hz, 2200Hz, 2300Hz etc all the way up to 20K and beyond at 30V.
Obviously in real life the first few frequencies above 2k will be attenuated due to the crossover but the tweeter does at least see all those above 4kHz at the full voltage minus any crossover insertion losses.
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Old 14th January 2013, 05:20 PM   #50
JMFahey is online now JMFahey  Argentina
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Quote:
Let's try again:
We feed an amp a sine of 100Hz and drive it into hard clipping, the result is the amp puts out a 100hz square wave. Now lets just say the amp produces an output of 30V at that point. This square wave contains all possible multiples/harmonics of 100 at the full 30V.
If the tweeter xover is at 2000Hz the tweeter will now try to reproduce 2000Hz, 2100Hz, 2200Hz, 2300Hz etc all the way up to 20K and beyond at 30V.
Obviously in real life the first few frequencies above 2k will be attenuated due to the crossover but the tweeter does at least see all those above 4kHz at the full voltage minus any crossover insertion losses.
Ok, then let's disregard any mention of 10000 Hz since it's misleading.
What you say is that we have a 100Hz wave, we clip it into a squarewave, will have a ton of harmonica ans the higher ones will reach the tweeter.
Fine. So far so good.
I don't disagree in that, but on the actual threat to its integrity.
Another part you wrote in a confusing way is that:
Quote:
If the tweeter xover is at 2000Hz the tweeter will now try to reproduce 2000Hz, 2100Hz, 2200Hz, 2300Hz etc all the way up to 20K and beyond at 30V.
To begin with the worse offender:
Quote:
at 30V
Written that way, without qualifications, it can be read as a statement that each and every harmonic will be 30V.
Fact is, if the 100Hz signal is 30V , harmonics will always be a lot lower than that, depending on "distance" from 100 Hz.
There's also another misstatement mentioning:
Quote:
2000Hz, 2100Hz, 2200Hz, 2300Hz etc.
In fact we will have only odd harmonics, meaning 2100, 2300, etc , but not 2000, 2200, etc.
But this is only a minor statement compared to the first one.

Mind you, I agree that high harmonics will reach the tweeter, but not on their perceived power.
Let's calculate at least the most powerful ones.
One easy to grasp formula (so as to make it more intuitive) is:
Click the image to open in full size.
It's clear that if we are talking about an Nth harmonic, its voltage will be 1/N that of the fundamental.
And remember that Power is proportional to V squared, so 1/3 the voltage is 1/9 power, and so on.

To ease calculations, and ajusting values in your favor, let's consider 40V instead of the 30V suggested.
Why?
Because it represents 200W into 8 ohms, a common speaker impedance.
Also let's consider a perfect crossover filter, which applies no attenuation above the crossover point.
All in your favor, as I said, because I consider more power and less attenuation.
Now let's see what the poor tweeter will have to stand:
the first harmonic of 100 Hz reaching that tweeter will be 2100Hz, the 21th harmonic.
Its voltage will be 40V/21=1.9V , so its power will be=(1.9^2)/8=0.45W
the next will be 2300Hz , the 23rd, so V=40V/23=1.73V and P=0.38W and so on.
We see that we start with a very weak harmonic and each higher one is rapidly losing power, so even adding all them up will result in power that will hardly damage a Teeter of the type that would be used in a PA type cabinet.
Which is what we are talking about.
In the Hi Fi world , they might use a very weak silk soft dome tweeter with hair thin VC wire, which of course will be easier to damage, but there clipping is a definite no no and although some brief peaks will inevitably clip if used "somewhat loud" their duty cycle will be low or music becomes unbearable.

Last edited by JMFahey; 14th January 2013 at 05:24 PM.
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