Timeline for Where do overtones in a 555 generated square wave come from?
Current License: CC BY-SA 4.0
11 events
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| Oct 22, 2019 at 9:01 | comment | added | Stack Exchange Broke The Law | at 2.5kHz, complaining the square wave can't be square is a bit like complaining your car's wheels can't be round because they're made of atoms. | |
| S Oct 22, 2019 at 8:01 | history | suggested | Melebius | CC BY-SA 4.0 | typo fixed, formula formatting |
| Oct 22, 2019 at 7:21 | review | Suggested edits | |||
| S Oct 22, 2019 at 8:01 | |||||
| Oct 22, 2019 at 1:13 | comment | added | hobbs | @JShorthouse in large part you're right. An ideal square wave has infinite bandwidth and two discontinuities every period, and so can't be realized by any physical system. Only various approximations of it can. But that doesn't have an awful lot to do with why these answers are correct. | |
| Oct 21, 2019 at 15:23 | comment | added | Stack Exchange Broke The Law | @JShorthouse It's not that square waves can't be fundamental, but the job of a spectrum analyzer is to analyze things in terms of sine waves, so that's what it did. When you analyze a wave in this way, of course you will see that only sine waves are "fundamental" according to this kind of analysis. | |
| Oct 20, 2019 at 23:34 | comment | added | Russell McMahon♦ | @JShorthouse You can't have it both ways :-). You wrote "Using an oscilloscope I adjusted the 555 to generate a 2.5kHz square wave." You know you didn't, of course. A 555 makes a "squarish wave". Other devices more-squarish (or less). But just as the true square wave needs an infinite sum of declining magnitude sinewaves (and so extra terms are unimportant at somewhere around the noise level) so too viewing, analysing , ... is going to run into non-ideal or non-infinite aspects. A speaker is not constrained to follow a single sinusoid - but any path folows is describeable by a set of sinusoids | |
| Oct 20, 2019 at 21:34 | comment | added | nanofarad | @JShorthouse Indeed, a model of a speaker may include a sort of "low-pass" characteristic. It doesn't change the answers here significantly. Sines simply remain useful eigenfunctions for analyzing linear time-invariant systems; a square wave is an infinite series of those sinusoids (a fundamental plus harmonics), and the "imperfection" of a square wave that makes it curve-like can often be described by the application of a suitable low-pass filter to the harmonics mentioned before. | |
| Oct 20, 2019 at 21:32 | comment | added | JShorthouse | @ζ-- Perhaps "constrained" is the wrong word, what I'm trying to say is that since a speaker cone has mass and momentum its movement is always going to be in a "curve-like" way, it's physically impossible for a speaker to replicate a mathematically perfect square wave. | |
| Oct 20, 2019 at 20:38 | comment | added | nanofarad | @JShorthouse Electrons and speakers are not constrained to move in sinusoidal patterns. That constraint only arises for certain particular systems (e.g. harmonic oscillators). It so happens that sinusoids happen to be a convenient basis for analyzing systems that are linear and time-invariant, but you're reading too far into things. | |
| Oct 20, 2019 at 12:31 | comment | added | JShorthouse | Is the answer here really then that a "square wave" isn't really a wave at all? I suppose that a true square wave can't exist within the laws of physics, it would require a speaker cone to teleport between two positions and electrons to teleport within a wire. Therefore because both electrons and speakers are constrained to moving in sinusoidal patterns, the only way to construct a square "wave" is by combining a bunch of sine waves together? | |
| Oct 20, 2019 at 12:01 | history | answered | Russell McMahon♦ | CC BY-SA 4.0 |