This won't work. In addition to what others have said about different points in the room having different distances to the fan and speaker, there are other issues:
1. The fan's fundamental frequency isn't perfectly stable, so even if you are in a spot where there speaker's tone cancels with it, the fan will probably wander around that frequency enough that the cancellation won't work well.
2. The fan isn't just a fundamental tone + noise. There are also a whole series of harmonics above it. You'll need to cancel those out too. Even if you do cancel out the fundamental, you'll still "hear" it because of the missing fundamental effect [1] otherwise. Cancelling those overtones out gets harder and harder because the higher the frequency, the more precise you need to be with phase to get proper cancellation.
3. Obviously, none of this will help with the atonal noise components of the fan's sound, which are significant. Though arguably, if you get rid of the droning tonal part, the remaining whooshing noise might actually be a nice sound.
I believe the most effective fixes here are:
1. Get a better, quieter fan that produces less noise to begin with.
2. Move the fan farther away. You don't necessarily need to filter the air from the window closest to you. Put it in a farther window. Or go all the way and get a whole house fan that puts the fan in the attic.
"1. Get a better, quieter fan that produces less noise to begin with.
2. Move the fan farther away. You don't necessarily need to filter the air from the window closest to you. Put it in a farther window. Or go all the way and get a whole house fan that puts the fan in the attic."
This might work for homeowners, but is an ineffective solution to renters like me. Our furnace/air conditioning blower is loud AF. The utility closet is next to the bedroom and it is nearly impossible to hear the TV when it is running. It is so loud that we even have to turn up the TV in the living room, around 25 feet (7m?) away and around two corners.
I am CERTAIN that other renters, like myself, would like to know how to actually cancel out this droning nuisance via noise cancellation.
Is the drone of a fan harmonic? I would’ve thought it’s more like a repetition pitch so its overtones would not be harmonic and would not exhibit a missing fundamental.
Agree with the broader point, just curious if there’s some interesting physics that creates a harmonic sound.
Overtones are about timbre, not harmony. The fan isn't playing a chord (well, probably not). But the tone the fan plays isn't a pure sine wave either. It will have overtones that are integer multiples of the fundamental that give it its characteristic sound.
It's the same reason that a flute and saxophone can play the same note but sound different. The fundamental is the same, but the amplitudes of the overtones are different.
Unfortunately, this is not possible with such a simple approach. In 2 and higher dimensions, the problem is that any attempt to create a cancelling wave from a position other than the source of the wave will not cancel the wave. Instead it will create a network of places where it cancels and places where it constructively interferes, depending on the wavelength and their relative positions, and there is no way to make the entire space be cancelling in such a short space. You can only get various arrangements of cancellation but also constructive feedback.
(Some other things happen as you get a large number of wavelengths away from the source, but given the wavelength of the audio in question, being in a room with it means you get that local behavior, not long-range behavior.)
Probably somewhere on the internet is a fantastic interactive diagram that would clearly demonstrate this for you, but I couldn't google one up. Links solicited. (I got a lot 1D stuff but this phenomenon doesn't show up in 1D. 2D is adequate, 3D just adds more nodes in more dimensions.)
The way noise cancelling headphones work is that they know where they are relative to your eardrum, and as such, they can arrange it so that for all incoming audible frequencies, your eardrum is in a cancellation location for that frequency, ignoring a lot of details. They'll still unavoidably create locations of constructive interference, you just won't have your sensors there.
In principle you may be able to do this with some very precise location of where your ears are, where your mics are, where your speakers are and the exact characteristics of all of these things, and some very clever coding; I've seen people kicking this idea around but I haven't yet heard of anyone pulling it off. I can say it's still yet harder than it sounds at first, because you have things like echos and all kinds of other fun effects to deal with. In theory it should be possible to echo cancel at a distance, but you'd be getting into super high end audio processing, not just a weekend project where you record a microphone or two and "just" invert it with a couple of speakers. You might need something as fancy as https://youtu.be/UPVcwDzhBZ8?t=463 just to get started, and an accurate room model, and all kinds of things, and you might still get something that only works as long as nothing in the room moves, including you or even parts of you. In practice, I'd guesstimate this at the level of difficulty of doing a PhD in audio processing at a minimum... but not necessarily impossible.
> Probably somewhere on the internet is a fantastic interactive diagram that would clearly demonstrate this for you, but I couldn't google one up. Links solicited.
Interestingly, the wavelength of sound and the wavelength of wifi signals are in the same ballpark. 900MHz electromagnetic waves come out to ~30cm waves, which is about 1000Hz in sound-in-air.
My thought immediately jumped to beamforming / phased speaker array.
What's more problematic is that its not the lower frequencies that are annoying (the 312Mhz drone), but the mid and high range. Think about it like this: fridge compressors suck to hear with their 2500Hz high-pitched electrical buzz, but once the compressor turns off, the gentle but deep slosh of the liquid being pumped around isn't annoying at all.
It would be possible if you had a matrix of speakers covering all walls & ceiling. In that scenario you could control the entire sound landscape across the board, and cancel out or simulate arbitrary sound sources in the room.
So it could be possible if the cancelling came from the source of the wave, such as making the spinning fan or its enclosure the speaker?
I guess the 'fan as the noise cancelling speaker' idea could be reworded as 'a fan with active stabilization that doesn't vibrate', making no mechanical noise.
A friend with a recording studio solved their problem by putting the fan at the end of a length of ducting with a couple of 90 degree bends, lined with foam.
Yes. I believe this is used in some high-end applications. It's really hard though. You need a near-perfect model of what the sound will be slightly in advance. I doubt a fan would be amendable to that.
Since all comments seem to agree that noise cancelling wont work, 3 practical tips:
1. use the Bernoulli-Effect, aka get "up to 50+%"(depends on fan model) more airflow by placing the fan 0.2(0.5) - 1.5m away from the window.
2. Blow air out of the window, dont try to suck air in.
3. To avoid noise: Put the fan in another room and open the window in the room where you are.
> The way noise cancelling works is that a microphone picks up the sound-wave, and then another speaker plays a slightly delayed version of that wave, which cancels it out.
I always thought noise cancelling worked by playing an inverted version of the sound wave rather than just a delayed one.
In fact, wikipedia seems to back me up on this:
> A noise-cancellation speaker emits a sound wave with the same amplitude but with an inverted phase (also known as antiphase) relative to the original sound.
If you have a single amplitude wave then a delayed playback could be inversion of the wave. Not very sophisticated, but good enough for canceling a single frequency.
The original post stated unequivocally that noise cancellation works by playing a delayed version of the sound before deciding it was only going to cancel a single frequency.
So either the text has been re-ordered or OP is under the mistaken impression this would also work when dealing with a mix of frequencies.
Those Lasko fans have pretty raw edges on the blades of the fan itself, which I think contributes a lot to the noise. If you take the cover off, sand down the nubs and bits of flaking plastic, and reassemble, I think that will take care of a lot of noise.
A 20" Lasko box fan is about as cheap as they come - and, consequently, noisy and inefficient. The thing retails for $20, the budget for quieting measures is $0. In particular, especially when placed at a window (where it's expected to generate a pressure differential) you get a counterflow effect in the corners, and the 5 blades create individual pressure pulses as they move near to the 4 flat sides of the enclosure and then out into open air.
A quality high-volume, low-speed industrial drum or axial HVAC wall fan costs a whole lot more than $20 but the quiet, low-frequency noise is so much less intrusive.
Another mechanism (if you don't want a 36", 1/2 HP galvanized industrial contraption on your desk) is to concentrate the airflow near the user. Less power, but more concentrated. I've got a big fan that helps in the morning and evening to exchange air through the entire house, but on my desk I've got the biggest PC case fan I could find (a 230mm monster) wired to a speed controller cable and then directly to a 12V wall wart. At ~300 RPM, you can almost keep up with the motion of a single blade with your eyes, at 500 or 800 RPM it's barely perceptible... but it's only about 8x8x1" and keeps the air moving over your skin!
This begs the question of what is the most quiet fan(s) on the market? If all of us sat down in a room together and had this mission, what would it look like? An electrostatic fan (using electrohydrodynamics) would be pretty silent, but provide very little airflow. It's a fun problem to solve and would love to see a company create better products than those overpriced Dyson fans (which are junk IMHO).
Theirs probably isn't silent, but you certainly could figure out how to make this very quiet and gentle sounding, building tension in a spring between strokes with some kind of silent linear actuator
This is intriguing and I assume the mechanical and balance (force distribution) have been addressed with strange, extremely light but strong materials. I think it's the parent comment, but someone mentioned Dyson fans, criticizing them as junk. I haven't owned one due to cost, but have been impressed with air/noise ratio.
I once knew a rogue architect who rode a bicycle, wore broken glasses mended with tape and lived in a home in south Florida (warm humid summers). He had dug trenches beneath his house, which he explained were for air circulation intended to work in harmony with interior modifications which I can't remember.
Unfortunately the city condemned and demolished his house. But I've been intrigued by solid state cooling methods since. The Japanese fan, though of questionable mechanical efficiency, ispires me as an example of easily overlooked but formidable design. Neat!
Most all ceiling fans I've had make no noise until you are on the "blow all the papers around the room" setting. For the ones that do make noise usually it's merely a balance issue.
Essentially they make the same sound, but 100's of times lower in audible volume, just as they move 100's of times less volume of air per second. (It may not be linearly scaled, but it's definitely proportional.)
As others mentioned this will only work in the right spot in the room.
This was an experiment in my high school physics, where our teacher played a constant tone from two sources and students were to walk around the class room searching for dead spots where the phases would cancel each other out.
It was quite surreal to take a step and suddenly the tones went quiet.
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1. The fan's fundamental frequency isn't perfectly stable, so even if you are in a spot where there speaker's tone cancels with it, the fan will probably wander around that frequency enough that the cancellation won't work well.
2. The fan isn't just a fundamental tone + noise. There are also a whole series of harmonics above it. You'll need to cancel those out too. Even if you do cancel out the fundamental, you'll still "hear" it because of the missing fundamental effect [1] otherwise. Cancelling those overtones out gets harder and harder because the higher the frequency, the more precise you need to be with phase to get proper cancellation.
3. Obviously, none of this will help with the atonal noise components of the fan's sound, which are significant. Though arguably, if you get rid of the droning tonal part, the remaining whooshing noise might actually be a nice sound.
I believe the most effective fixes here are:
1. Get a better, quieter fan that produces less noise to begin with.
2. Move the fan farther away. You don't necessarily need to filter the air from the window closest to you. Put it in a farther window. Or go all the way and get a whole house fan that puts the fan in the attic.
[1]: https://en.wikipedia.org/wiki/Missing_fundamental
2. Move the fan farther away. You don't necessarily need to filter the air from the window closest to you. Put it in a farther window. Or go all the way and get a whole house fan that puts the fan in the attic."
This might work for homeowners, but is an ineffective solution to renters like me. Our furnace/air conditioning blower is loud AF. The utility closet is next to the bedroom and it is nearly impossible to hear the TV when it is running. It is so loud that we even have to turn up the TV in the living room, around 25 feet (7m?) away and around two corners. I am CERTAIN that other renters, like myself, would like to know how to actually cancel out this droning nuisance via noise cancellation.
Objecting to the proffered solutions doesn't make the unworkable one workable.
Agree with the broader point, just curious if there’s some interesting physics that creates a harmonic sound.
Overtones are about timbre, not harmony. The fan isn't playing a chord (well, probably not). But the tone the fan plays isn't a pure sine wave either. It will have overtones that are integer multiples of the fundamental that give it its characteristic sound.
It's the same reason that a flute and saxophone can play the same note but sound different. The fundamental is the same, but the amplitudes of the overtones are different.
(Some other things happen as you get a large number of wavelengths away from the source, but given the wavelength of the audio in question, being in a room with it means you get that local behavior, not long-range behavior.)
Probably somewhere on the internet is a fantastic interactive diagram that would clearly demonstrate this for you, but I couldn't google one up. Links solicited. (I got a lot 1D stuff but this phenomenon doesn't show up in 1D. 2D is adequate, 3D just adds more nodes in more dimensions.)
The way noise cancelling headphones work is that they know where they are relative to your eardrum, and as such, they can arrange it so that for all incoming audible frequencies, your eardrum is in a cancellation location for that frequency, ignoring a lot of details. They'll still unavoidably create locations of constructive interference, you just won't have your sensors there.
In principle you may be able to do this with some very precise location of where your ears are, where your mics are, where your speakers are and the exact characteristics of all of these things, and some very clever coding; I've seen people kicking this idea around but I haven't yet heard of anyone pulling it off. I can say it's still yet harder than it sounds at first, because you have things like echos and all kinds of other fun effects to deal with. In theory it should be possible to echo cancel at a distance, but you'd be getting into super high end audio processing, not just a weekend project where you record a microphone or two and "just" invert it with a couple of speakers. You might need something as fancy as https://youtu.be/UPVcwDzhBZ8?t=463 just to get started, and an accurate room model, and all kinds of things, and you might still get something that only works as long as nothing in the room moves, including you or even parts of you. In practice, I'd guesstimate this at the level of difficulty of doing a PhD in audio processing at a minimum... but not necessarily impossible.
Here's one: https://apenwarr.ca/beamlab -- as well as the author's writeup: https://apenwarr.ca/log/20140801
The author is focused on beamforming WiFi signals, but the principle is exactly the same whether it's a radio wave or a sound wave.
Interestingly, the wavelength of sound and the wavelength of wifi signals are in the same ballpark. 900MHz electromagnetic waves come out to ~30cm waves, which is about 1000Hz in sound-in-air.
What's more problematic is that its not the lower frequencies that are annoying (the 312Mhz drone), but the mid and high range. Think about it like this: fridge compressors suck to hear with their 2500Hz high-pitched electrical buzz, but once the compressor turns off, the gentle but deep slosh of the liquid being pumped around isn't annoying at all.
You'd have to run realtime 3-D FFTs on the sound in the system, at approximately a few kHz.
I guess the 'fan as the noise cancelling speaker' idea could be reworded as 'a fan with active stabilization that doesn't vibrate', making no mechanical noise.
A friend with a recording studio solved their problem by putting the fan at the end of a length of ducting with a couple of 90 degree bends, lined with foam.
I always thought noise cancelling worked by playing an inverted version of the sound wave rather than just a delayed one.
In fact, wikipedia seems to back me up on this:
> A noise-cancellation speaker emits a sound wave with the same amplitude but with an inverted phase (also known as antiphase) relative to the original sound.
https://en.wikipedia.org/wiki/Active_noise_control
https://graphtoy.com/?f1(x,t)=sin(x)&v1=true&f2(x,t)=sin(x-%...
So either the text has been re-ordered or OP is under the mistaken impression this would also work when dealing with a mix of frequencies.
A quality high-volume, low-speed industrial drum or axial HVAC wall fan costs a whole lot more than $20 but the quiet, low-frequency noise is so much less intrusive.
Another mechanism (if you don't want a 36", 1/2 HP galvanized industrial contraption on your desk) is to concentrate the airflow near the user. Less power, but more concentrated. I've got a big fan that helps in the morning and evening to exchange air through the entire house, but on my desk I've got the biggest PC case fan I could find (a 230mm monster) wired to a speed controller cable and then directly to a 12V wall wart. At ~300 RPM, you can almost keep up with the motion of a single blade with your eyes, at 500 or 800 RPM it's barely perceptible... but it's only about 8x8x1" and keeps the air moving over your skin!
Theirs probably isn't silent, but you certainly could figure out how to make this very quiet and gentle sounding, building tension in a spring between strokes with some kind of silent linear actuator
I once knew a rogue architect who rode a bicycle, wore broken glasses mended with tape and lived in a home in south Florida (warm humid summers). He had dug trenches beneath his house, which he explained were for air circulation intended to work in harmony with interior modifications which I can't remember.
Unfortunately the city condemned and demolished his house. But I've been intrigued by solid state cooling methods since. The Japanese fan, though of questionable mechanical efficiency, ispires me as an example of easily overlooked but formidable design. Neat!
Essentially they make the same sound, but 100's of times lower in audible volume, just as they move 100's of times less volume of air per second. (It may not be linearly scaled, but it's definitely proportional.)
This was an experiment in my high school physics, where our teacher played a constant tone from two sources and students were to walk around the class room searching for dead spots where the phases would cancel each other out.
It was quite surreal to take a step and suddenly the tones went quiet.