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Fuses do affect sound, the question is how much

mansr

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The fuse is in series with the loudspeaker so the voltage change appears across the fuse linearly to the resistance change. Its a simple voltage divider. There is no carrier signal, just the original signal so there cant be a modulation. Modulation requires a carrier signal. There is none. The term modulation is being used incorrectly.
The resistance of the fuse is modulated by the signal.
 

scott wurcer

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The fuse is in series with the loudspeaker so the voltage change appears across the fuse linearly to the resistance change. Its a simple voltage divider. There is no carrier signal, just the original signal so there cant be a modulation. Modulation requires a carrier signal. There is none. The term modulation is being used incorrectly.

This is still wrong a poor resistor such as a carbon comp has a relatively high TC and the resistance has a component that varies as V squared run two sine waves through it (at sufficient amplitude) and they intermodulate. The experiment is easy to do, you could use a thermistor to exaggerate the effect.
 

DonH56

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The fuse is in series with the loudspeaker so the voltage change appears across the fuse linearly to the resistance change. Its a simple voltage divider. There is no carrier signal, just the original signal so there cant be a modulation. Modulation requires a carrier signal. There is none. The term modulation is being used incorrectly.

No, that is not what happens. There is no need for a carrier, you are thinking of mixing, whereas this is more like AM applied (at a very low level) to the signal and that causes distortion. We are not talking about modulating an RF carrier but essentially changing the attenuation with signal, and it is a nonlinear thing. It is not a simple voltage divider; it is a voltage divider that changes with signal.

Modulation is inducing a variation in a signal, or exerting control on a signal, per my dictionary and my old textbooks. It is not restricted to signals riding on a carrier. Maybe we just have different definitions.
 

3dbinCanada

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No, that is not what happens. There is no need for a carrier, you are thinking of mixing, whereas this is more like AM applied (at a very low level) to the signal and that causes distortion. We are not talking about modulating an RF carrier but essentially changing the attenuation with signal, and it is a nonlinear thing. It is not a simple voltage divider; it is a voltage divider that changes with signal.

Modulation is inducing a variation in a signal, or exerting control on a signal, per my dictionary and my old textbooks. It is not restricted to signals riding on a carrier. Maybe we just have different definitions.

Just to get a grasp on your definition....... filters such as low , high and bandpass modulate a signal? I didn't see the word modulate until I cracked Communication Electronics and carrier waves were introduced. . Even amplifier theory never used the term modulation until two different signals were introduced. That's my back ground.
 
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DonH56

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Just to get a grasp on your definition....... filters such as low , high and bandpass modulate a signal? I didn't see the word modulate until I cracked Communication Electronics and carrier waves were introduced. That's my back ground.

No, assuming they are LTI, at least to first order. To bring it more out of the weeds and stay with audio and play into my musical side, back in the 70's analog synthesizers modulated amplitude, phase, and frequency to create vibrato, tremolo, flange effects, adjust attack/decay times, etc. No carrier waves involved. Or I could say I am modulating the volume by adjusting a potentiometer -- no distortion to speak of, and no carrier there either. Definitions vary. The general definition is just to control or vary something.

Maybe I don't know what I'm talking about -- I used to ask my teens to modulate their tone when they got mad at us, and that never seemed to work...

I was headed toward a PhD in Com until Life and Work got in the way. Got too busy with the boys in sports and Scouts with a full-time-plus job and dropped it halfway through the course work. Bummer, only time in my life I had straight A's going... Grad com theory would've taken care of that, though! Someplace I have my spread-spectrum theory book I used to pull out to explain why I quit -- it has some long nonlinear quadruple integral equation with exponentials and sinusoids in the middle of it that make most poor hairy-knuckled engineer's eyes glaze. What scares me is I understood it, once, for a few minutes...
 
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3dbinCanada

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No, assuming they are LTI, at least to first order. To bring it more out of the weeds and stay with audio and play into my musical side, back in the 70's analog synthesizers modulated amplitude, phase, and frequency to create vibrato, tremolo, flange effects, adjust attack/decay times, etc. No carrier waves involved. Or I could say I am modulating the volume by adjusting a potentiometer -- no distortion to speak of, and no carrier there either. Definitions vary. The general definition is just to control or vary something.

Maybe I don't know what I'm talking about -- I used to ask my teens to modulate their tone when they got mad at us, and that never seemed to work...

I was headed toward a PhD in Com until Life and Work got in the way. Got too busy with the boys in sports and Scouts with a full-time-plus job and dropped it halfway through the course work. Bummer, only time in my life I had straight A's going... Grad com theory would've taken care of that, though! Someplace I have my spread-spectrum theory book I used to pull out to explain why I quit -- it has some long nonlinear quadruple integral equation with exponentials and sinusoids in the middle of it that make most poor hairy-knuckled engineer's eyes glaze. What scares me is I understood it, once, for a few minutes...

I got as far as triple integrals used to describe a radiation pattern of an antenna. Weird stuff and like you, I understood it way back then :) ..Now its just a distant fog.

I guess we'll just have to agree to disagree on the term modulation. To me, I see your example as interesting as it is as wave shaping, a cool thing in itself. Oh well. It is what it is. :)
 

scott wurcer

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No one is saying this effect is anything but very small, but it is real. The 7.5A speaker fuse in my PA is .0125 Ohms typically pure metals or simple alloys are ~3000ppm/C so at 100C (well below the melting (fusing) point) the resistance is 25-30% higher, so yes you don't play music this loud but a careful experiment could measure the effect. BTW resistance can only go up with power so the polarity of the current does not matter and the effect is like a VERY small compression (third order).
 

3dbinCanada

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This is still wrong a poor resistor such as a carbon comp has a relatively high TC and the resistance has a component that varies as V squared run two sine waves through it (at sufficient amplitude) and they intermodulate. The experiment is easy to do, you could use a thermistor to exaggerate the effect.

Are you stating that you will create f1-f2 and f1+f2 harmonics based on the input signal carrying multiple frequencies?
 

3dbinCanada

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No one is saying this effect is anything but very small, but it is real. The 7.5A speaker fuse in my PA is .0125 Ohms typically pure metals or simple alloys are ~3000ppm/C so at 100C (well below the melting (fusing) point) the resistance is 25-30% higher, so yes you don't play music this loud but a careful experiment could measure the effect. BTW resistance can only go up with power so the polarity of the current does not matter and the effect is like a VERY small compression (third order).

I'm arguing the practicality side of this, not the experimental side. I agree that resistance change occurs with power, not polarity. As you can see, I still have issue with the term modulation.
 

scott wurcer

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Are you stating that you will create f1-f2 and f1+f2 harmonics based on the input signal carrying multiple frequencies?

Yes easily (sort of) measured. As I said use a thermistor at low frequencies to exaggerate the effect. You do get mostly the odd order products.
 

Cbdb2

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Chainging the gain of a signal is modulating it. Your multiplying the signal by another signal which results in new freqs. ie THD. This is com theory 101. What happens in a resistive divider if one of the resistances is changing? The signal level is changing. Its being modulated. Doesnt matter if the level changes slowly.
 

Cbdb2

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The shape of the attack/decay maybe one of the reasons different compressors sound different. Different shape of modulation ( linear vs exponential attack/decays ) will create different spectra ( Fourier ) and might sound different. Only of interest to recording engineers and guitar players.
 

3dbinCanada

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Chainging the gain of a signal is modulating it. Your multiplying the signal by another signal which results in new freqs. ie THD. This is com theory 101. What happens in a resistive divider if one of the resistances is changing? The signal level is changing. Its being modulated. Doesnt matter if the level changes slowly.

Where is the 2nd signal coming from since there is only one source across the speaker terminals?
 

scott wurcer

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How does a crystal radio demodulate the audio? There is no LO. Hint: the diode is a non-linear resistance.
220px.png
 
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3dbinCanada

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What is LO? Are you saying that a fuse, a metallic strip is doped such that it allows current flow in one direction only like the diode? Replace the diode with a fuse and see how well your Xtal radio works. Hint...It won't.

This is a bad anology as AM has two distinct frequencies, a carrier frequency and a the signal frequency used to modulate the carrier wave. There is no carrier wave in an audio amp's output. Its a complex waveform yes but its not riding on the back of a carrier. There is no modulation or demodulation occuring.
 
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Cbdb2

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If you run a 1k sine ( the carrier) thru your amp and then fiiddle with the volume, your amplitude modulating the 1k. You dont need 2 signals, anything that changes the gain of that sine is modulating it. This is the fundamental that AM broadcast is built on, but its done electronicaly. And modulating creates new components, distortion.
 

scott wurcer

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The fuse is a non-linear resistor at high current. If you don't recognize LO as local oscillator (absent in a crystal radio) I suppose anymore discussion is pointless.
 

DonH56

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I ran a very simple simulation using a single voltage source with ideal 0.1-ohm output resistance, an ideal 8-ohm load, and a series resistance of another 0.1 ohms using a SPICE H-source and series 0-V voltage source to emulate a resistor whose value changes (to avoid "is modulated by") the current through it. This is a common way to model an ideal noiseless resistor in simulation so is something I've done "forever" when I need such a thing (for instance to get circuit noise without source/load resistors).

Schematic:
1588792680356.png


Result with H1 (ideal resistor) set to fixed 0.1 ohms (spurs are high because I did not bother trying to tighten tolerances and such):
1588792843874.png


Repeated with H1 changing with current to model a simple fuse'ish, no time constant/cap, just to show what can happen -- notice how the second harmonic has popped up:
1588793095221.png


This is not a real-world situation but is just to show that a series resistance changing (varying, "modulating") with signal current can add distortion.

HTH - Don
 

mansr

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This is not a real-world situation but is just to show that a series resistance changing (varying, "modulating") with signal current can add distortion.
How is that not as evident as the sun rising in the east? Oh, well...
 

3dbinCanada

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I ran a very simple simulation using a single voltage source with ideal 0.1-ohm output resistance, an ideal 8-ohm load, and a series resistance of another 0.1 ohms using a SPICE H-source and series 0-V voltage source to emulate a resistor whose value changes (to avoid "is modulated by") the current through it. This is a common way to model an ideal noiseless resistor in simulation so is something I've done "forever" when I need such a thing (for instance to get circuit noise without source/load resistors).

Schematic:
View attachment 62182

Result with H1 (ideal resistor) set to fixed 0.1 ohms (spurs are high because I did not bother trying to tighten tolerances and such):
View attachment 62183

Repeated with H1 changing with current to model a simple fuse'ish, no time constant/cap, just to show what can happen -- notice how the second harmonic has popped up:
View attachment 62187

This is not a real-world situation but is just to show that a series resistance changing (varying, "modulating") with signal current can add distortion.

HTH - Don

Thanks Don. I appreciate this and learned something new.
 
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