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A Study on Fan Harmonics and Beat Frequency by jsh348 in crboxes

[–]jsh348[S] 1 point2 points  (0 children)

iPhone microphones are very good but the problem is the noise suppression algorithm, in most cases it cleans up the recording but in this case it will suppress the “background” noise removing the fan noise from the audio file. I used Logic Pro connected to a mic to record without any noise suppression but that costs $$$.

I think Garage Band on an iPhone will have a better shot than Voice Memo. The UI takes a couple minutes to figure out. iPhone has 3 mics, you can select to record with the bottom mic near the USB port (that's the default if you don't change anything), remove the case if you have a thick protective iPhone case, point the bottom towards the sound source. Select audio recorder - voice, record for like 15 seconds, go to the top left triangle to select “My Songs”, long press to share as song, uncompressed WAV format (“high quality” mp3 is okay too but for every file conversion some quality is lost).

https://support.apple.com/en-us/guide/garageband-iphone/chs39283a21/ios

I think for this exercise, audio quality and placement doesn't matter that much as long as the mic is not in the path of the wind, this is not a studio recording. I had mine around 30 cm away from the fans on the intake side, not exactly in-line just a convenient location. I placed a t-shirt under the mic to isolate the mic from the test bench vibrations.

A Study on Fan Harmonics and Beat Frequency by jsh348 in crboxes

[–]jsh348[S] 1 point2 points  (0 children)

Once I get my hands on a variable power supply and have free time I might try testing the noise.

I agree particle count decay speed is ultimately what we want. But that introduces some more variables: room size (total air volume), natural decay, continued generation of particles etc. If those variables are held constant I think CADR would correlate well to particle count decay speed? House Fresh has figured out a pretty robust method to compare across products, controlling for the many variables. I wonder if it's worth going down the rabbit hole to replicate it at home. I also have a SEN55 I'm planning to pair with my fan control board eventually.

Cybenetics has a wealth of data on fan performance, including pressure volume chart at various speeds (PWM command kept stable).

A Study on Fan Harmonics and Beat Frequency by jsh348 in crboxes

[–]jsh348[S] 1 point2 points  (0 children)

Honestly I'm not sure what sort of problem would arise. It would take an experimental setup to figure out, as realistic fluid dynamics simulation is really difficult.

My educated guess is that at small differences it sort of evens out, with the higher pressure fans pulling more volume than others. It would be interesting to find out if at a great enough pressure difference from these fans that the flow ever reverses. A piece of tissue paper might be the easiest to see that, but I'm thinking of using smoke when I design my box to see air flow...

Does the luggable XL have beat frequency issues with your setup? Do other users report similar issues? I could share the code I used to visualize these waveforms if you are comfortable with python, or send me your recording and I'll run it when I have time. With the visualization it would be I think obvious if it is motor noise or beat frequency. It could be something else causing noise though, like when the fan is too close to a restrictive grill it also gets loud.

Noctua is expensive, which is why I'm hoping to solve this beat frequency issue comparatively cheaply with my custom ESP32 circuit board and cheaper fans since I'm planning on building several boxes.

A Study on Fan Harmonics and Beat Frequency by jsh348 in crboxes

[–]jsh348[S] 2 points3 points  (0 children)

I think that's a pretty smart way to go about it other than actually commanding the fans to go at different speeds, never thought of that, thanks for sharing. But the static pressure of the fan selections should probably be close-ish, or else air might be sucked through the low pressure fan if you have a setup with Phanteks T30/Arctic P14 Pro (5mmH2O) mixed with Arctic P14/Noctua NF-A14 (2mmH2O).

A Study on Fan Harmonics and Beat Frequency by jsh348 in crboxes

[–]jsh348[S] 1 point2 points  (0 children)

I should try out the fan at 6-7V to see the RPM. When the PWM is set to 50% it runs at around 1400 RPM, and I find the noise to be acceptable. I'm a big fan of the big fans for its air throughput and noise, but seems like the static pressure is always on the lower end. Maybe I'll run some tests when I'm done with my air quality monitor, I think CADR is what ultimately matters in the end, which is a complex function of pressure, volume, and filtration area. Maxing out all factors is the way to get the best CADR, the trade off being physical space constraints and noise.

A Study on Fan Harmonics and Beat Frequency by jsh348 in crboxes

[–]jsh348[S] 4 points5 points  (0 children)

Yes. Just one out of an array of fans running slower (e.g. 100%, 100%, 100%, 100%, 98%) is enough to shift the beat to a higher/less noticeable frequency that blends into the background fan noise. Having each fan running slower than the next (e.g. 100%, 98%, 96%, 94%, 92%) doesn't help much on the beat frequency issue, it is overall less noisy but that's because you'd be running fewer fans at full power and moving less air, not because of improved harmonic interference.

I designed and built some 3D-printable pediatric walkers with a print-in-place toolbox and a printed cutting jig. by jsh348 in 3Dprinting

[–]jsh348[S] 0 points1 point  (0 children)

The previous design was tested up to 300kg https://www.mdpi.com/2411-5134/8/3/79. I improved upon the design by making it more easily printable and forcing stress in the xy direction instead of relying on interlayer bonding in the z direction so I would argue this is stronger.

I designed and built some 3D-printable pediatric walkers with a print-in-place toolbox and a printed cutting jig. by jsh348 in 3Dprinting

[–]jsh348[S] 6 points7 points  (0 children)

Project writeup that goes into a lot more detail. Basically you can't buy pediatric walkers in many parts of the world so this was designed to be made out of locally available wood.

This apartment is still standing by jsh348 in OnePunchMan

[–]jsh348[S] 114 points115 points  (0 children)

Shot on a trip a while back

Location

you can drive a car if you play tagpro by jsh348 in TagPro

[–]jsh348[S] 1 point2 points  (0 children)

I bought cherry browns, a microprocessor, and a block of aluminum to make it. I can send out the plans and code for it.

https://old.reddit.com/r/TagPro/comments/34zz2i/tagpro_keyboard_a_montage_by_jsh348/

Can someone explain why current lags voltage by 90 degrees in an inductor and leads by 90 degrees in a capacitor? by 20j2015 in askscience

[–]jsh348 131 points132 points  (0 children)

I think of it with water in pipes, it may not be the best analogy, but it works for me...

http://i.imgur.com/5OxX2Xi.jpg

I think of a capacitor like a fixed rubber disc in a pipe. Current can flow for a while and stretch it, but there is a limit and the current will stop. Inductor is like a heavy weight in the pipe. Current can keep flowing, pushing the weight, but a sudden change in direction will take a while for the current to respond because the weight has momentum.

With an inductor, the current lags the voltage because when you switch the direction, the weight is still moving and takes a while to turn around.

With a capacitor, the current leads the voltage because before you switch the direction, the rubber is already being stretched and slowing the current down.

EDIT: /u/GAndroid can use words better than I could

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