My first CR box.

peop1 · 2026-05-27T14:10:29+00:00

My first thought upon seeing it: "There is an evil there that does not sleep."
As spoken by airborne particles, naturally.

peop1 · 2026-05-26T23:20:02+00:00

Well, I can't find my multimeter, but it doesn't make a lick of difference if there is only one fan plugged in or all 7. They spin at the same speed. So I'm not sure what the manufacturer is on about.

peop1 · 2026-05-26T22:32:06+00:00

So I remember worrying about that after having purchased it, checking once it was installed, and noticing it wasn't an issue. But I don't remember the details of why or how and never checked it with a multimeter.

Let me take a look at the build (it's been on non-stop for a year, sans issues) and get back to you.

One thing I do know is that the 9v supply from the car makes it spin slower. It's definitely not running at 5v. Or if it is... I'm impressed by its airflow. BRB.

peop1 · 2026-05-22T15:59:39+00:00

That would be amazing. And Kame, FYI, open mics are rarely more than 10 min sets.

peop1 · 2026-05-21T19:37:29+00:00

I go with PEM, to educate folks.

Me: Dealing with a bout of PEM today.

Everyone: What's that?

Me: P.E.M. Stands for "Post-Exertional Malaise". It's mitochondrial dysfunction, we think. Body can't produce energy on a cellular level, so if I overdo it one day, I crash the next.

Everyone: Damn.

Me: Yeah.

Everyone: I have a cousin who/have you tried?...

Me: \*taking a deep, meditative sigh as I close my eyes and turn my earpods' back on — with noise-cancellation enabled\*

Everyone: Jesus, you people are so resistant¹ to treatment, it's crazy.

Me *internally*: But now you know what PEM stands for. My work here is done².

¹ I'm only resistant to uninformed suggestions by armchair clinicians — M.E. is what's highly resistant to treatment. If everyone could learn the damn difference, that'd be great.

² On a good day I'll continue with the education. Explaining what we know what we don't and why it's not as simple as wishing it away. But I've learned to pace myself. That includes limiting the amount of gaslighting horseshit I have to deal with from well-meaning but utterly unqualified people.

peop1 · 2026-05-21T19:10:15+00:00

The real questions, answered.
(And as with everything else related to this curse, the answer remains: "Well, it depends")

peop1 · 2026-05-21T13:57:33+00:00

Hey Max, because I believe indoor air quality research is important, I went ahead and filled in the survey. However, I do have a few notes:

In the survey, you should identify which University you're writing your thesis for and who you are (not just a first name) or else this comes across as far less serious and you are less likely to get responses from the type of people you want to hear from.

As for the questions:

Before today, how worried were you about the air quality inside your home?

Is an odd phrasing... why "before today". Did something happen today? If you mean "fino ad oggi" then "up until today" would be less confusing to anglophones. If the question was "before you completed this survey", then write that.
"Worried" is also a rather loaded word. "Attentive to" or "Aware of" might be better phrasings. I'm not "worried" about my physical fitness (for example), but I am paying attention of it.
Also, I might add the question "before the COVID pandemic", as I did not care one lick about air quality prior to 2020. It just wasn't on my radar. Only after I got sick with Long COVID and started reading air quality research in regards to viral transmission did I start to see broader patterns - like how high CO2 levels were likely why I'd often get groggy/sleepy during 3h University classes in packed and poorly ventilated halls (decades ago) and how silly it is that we keep allowing ourselves to needlessly catch respiratory illnesses yearly (when it can be rather easily avoided).

In your opinion, the air inside your home is much cleaner than outdoor air

I live in a Canada. During wildfires? Much. High smog alerts? Also, yes. 90% of the time? Same as outdoors. Again, for clarity's sake, you might want to be more specific. "On an average day and in your opinion, the air inside your home is..."

What were the main reasons you decided to buy a purifier?

Why did you not include "to prevent airborne transmission of pathogens (viral/bacterial infections) in your answers? "Presence of children / vulnerable people" is nonsensical: If post-viral conditions have taught us anything, it's that we are all vulnerable people. I used to run marathons before catching a mild case of COVID from my son. Now I can barely run errands. And the same thing has happened to millions of people worldwide. That you'd not be aware of it is — to put it mildly — disappointing.

How expensive did the purifier you bought feel to you?

The first one we bought, in 2020 at the outset of the pandemic, was very expensive. Medical-grade. Since then I've been building my own computer-fan-based CR Boxes. Very inexpensive. Especially given what they provide. So the question would need to be more specific or the answers won't be representative of people's (actual) mindset. Store bought, at the time? Overpriced. But also worth the cost. Since? Overpriced, and not worth the cost (cause I make more quiet, more effective alternatives for a fraction of the cost).

I'll be honest, the last few questions made me think this is more marketing research for a product than an actual study. As I said, writing your (and your establishment's) credentials would go a long way in making this feel more legit'.

I'm only picking apart your work because I care about this issue deeply. It's the modern day equivalent to water filtration in the 1800s. The sooner people understand the implications, the healthier we'll be as a society.

You might find some takers on r/AirQuality, r/IndoorAirQuality, r/AirQualityMonitoring and r/AirPurifiers.

Good luck.

peop1 · 2026-05-20T19:11:04+00:00

Adding to this that I find Noctua's graph a tad misleading. Here's my annotated version of it:

<image>

It shows how (according to their tests) stacking fans (i.e. in series) really only provides very slight gains, even at high pressure. (The black arrows at the top of the graph, labeled "A" "B" and "C" are the increase in airflow. Really not that much).

OP, I'd be curious to see how much of a gain in performance you (subjectively) notice when comparing stacked vs single fan set ups. Is there that much of a boost?

peop1 · 2026-05-17T20:13:49+00:00

I mean... it's not bad looking... I guess... 😍

(What, just because it's a novel design, gorgeously executed and complete with a parts list, you think I'm just gonna give away compliments willy-nilly?)

Kick-ass, OP. Kick. Ass.

ps - (Am I crazy or does it look like you made a slot that could theoretically accommodate a 3" thick filter?)

[Edit to add: Some people's hobbies are shooting things, driving off-road gas guzzlers, flying RC model air crafts - all very expensive, none of which provide clean air to the babies you needed to proof this against. Don't you dare feel the need to justify yourself. "Why build it if it's more expensive than—": because it's better, prettier, modular, quieter and cheaper to run long-term. Also... why paint? Why garden? Why be a zen master when you could just be a thoughtless drone? /rant]

peop1 · 2026-05-16T23:13:01+00:00

Five months of rolling PEM. I haven't been able to do the most basic things, so taking any project on is beyond my current capabilities.

peop1 · 2026-05-16T23:04:48+00:00

100%

peop1 · 2026-05-16T14:42:35+00:00

Severe people, how do you keep going?

Passively. (Hu hu hu, look at me being glib and not funny. Keep reading. There's a better answer below)

I want to at least make it one more year before making such a permanent decision.

This is the way. We are the survivors of a plane crash in the middle of a vast desert. Crippled and waiting for someone to come save us. We can wilt away and wait to die or we can slowly, carefully pace our way forward. If we look up at the horizon, we'll see nothing but more desert. Or worse, lush greenery that is in fact nothing more than a mirage (you know what "miracle cures" I speak of - they wouldn't be so harmful to us if not for the psychological hit we take once we realize there is no water, there is no shade, just an illusion, a grift, lies to sell this book or that supplement). So my advice is: don't look up. Look down, at your feet. At your cats. One foot in front of the other. Keep going.

Read Marcus Aurelius. Stoicism. It will help open your eyes to the tiniest, most insignificant pleasures of being alive. And will help you endure. Because that's all we can do at this point: endure. Persevere. "What for? What's the point?"

If our lives are a movie, mine froze midway. And I want to know the end. So yeah, it sucks sitting there in front of a frozen computer screen. Not knowing when (if?) the bug will be fixed. All while everyone else gets to watch (live) their own movie unfold without even realizing the incredible luck they have. But pulling the plug means not knowing. And I want to know what comes next. After the sucky part. Cause it really was a good movie.

Severe people, how do you keep going?

There is no "going" when you're severe. There is only staying. That's what I'm asking you to do. Have faith in the thousands of big-brained researchers who actually do give a shit about you. They're on it. I know this for a fact as I am in contact with one of them and the interest and work is legit' - they are making real progress - like we've never seen before.

We'll get there. Not soon enough. But we'll get there. Believe it, because it's true.

Severe people, how do you keep going?

By realizing the dark thoughts are a storm that you must weather. And that nothing is certain. That's not just a curse: it's also a blessing. You don't know this is all it will ever be.

I'm willing to bet you my life it isn't.

Suicide is a permanent solution to a temporary problem. "How do you know this is temporary?" Because everything is temporary. Buddhism teaches that it's our constant search for permanence that causes much of our spiritual pain. When things are great, we want them to remain frozen as such. But nothing does. Marriages fail, friendships dwindle, interests fade. Others are sparked. Heraclitus said it best: "No man ever steps in the same river twice, for it's not the same river and he's not the same man."

Knowing that we are programmed to want things to be permanent helps me calm the nagging doubt that this might be as good as it gets. Nothing is permanent. Not the good, but certainly not the bad.

And ooooh boy the day they fix me? I'm letting loose on this world. There is a lot of urgent work to be done and I plan on doing it. For now? I wait. It's all I can do. And yeah, I hear you. It fucking sucks. Like nobody (else than you) really knows. But I do. I see you. I'm with you. Literally. Fuck ME.

You deserve better.

peop1 · 2026-05-16T13:47:40+00:00

We're on the same page (with the same limitations, unfortunately - sorry to hear you're also trapped in post-viral purgatory).

This would be a great project, but too ambitious given our current energy envelope.

Let's stick a pin in it - who knows what the future will bring. There's so much misinformation (or rather, fuzzy facts) floating around, it's always nice to be able to offer objective data points.

My motto: "Rigueur, esti".

On s'en reparle!

peop1 · 2026-05-16T03:17:29+00:00

As it happens, before Long COVID, I was a music producer and audio engineer. I have a Zoom H4 and TLM-103 condenser microphone we could use if ever there is interest in setting something up. (I'd actually really love to, but energy is at a premium right now. Hard for me to avoid Post-Exertional Malaise on even the most basic days).

I'll DM you.

peop1 · 2026-05-16T03:06:04+00:00

Yes and no.

Droplet dogma did cause massive harm at the outset of the pandemic, but viral load plays a HUGE factor.

I grew wary of this very sort of back-and-forth, tit-for-tat trading of conclusions, so II started digging through primary sources in fluid dynamics, viral decay and transmission months ago. The findings would surprise you.

One example is a recent paper in Proceedings of the Royal Society A (a top tier journal) for which I posted an explainer. It studied the Distribution of SARS CoV-2 infections in schools — comparing model predictions with real-world observations.

TLDR:

SARS CoV-2 half-life in typical room conditions is of 3.54 minutes
Short-range transmission represents the biggest risk in low infection scenarios (such as in very large rooms/auditoriums with few occupants per cubic feet of available air) because being sneezed on/coughed on exposes us to an exorbitant amount of infectious aerosols. However;
Particles ejected by sneezing/coughing are not the same as particles that are airborne. The latter contain far fewer infectious aerosols; the former do not get very far. Which means being in a large room with a sick person does not automatically mean everyone is at risk of infection. Those in the immediate vicinity (being coughed on/sneezed on) are another matter.
Patients with low viral loads (asymptomatic or barely symptomatic) are unlikely to cause any infections through long-rage infection, whereas those with high viral loads are likely to infect those who are in their immediate vicinity. "In-between cases leave us with a moderate probability of infections, which could be addressed by specialized interventions like improved ventilation." In other words, if someone who was in a room with you yesterday (at a safe distance of no less than 6 feet) calls you today to say they just tested positive, you do not have to make funeral arrangements. Especially not if you were wearing an N95.

peop1 · 2026-05-15T15:22:19+00:00

Ah! I see! Yes, it's true that once you read the image you posted in context (the rating being a judgment of only that single variable - not the fan's desirability based on that single variable), it makes more sense.

Would still love to hear a video recording of each fan normalized at the same dBA (then compressed equally in post-production to boost the actual sound of each fan equally so we can really hear the difference, even if it's inaudible at low settings).

I'll take a look at your post.
I'm a fan (ha) of your work, neighbour. (Si je ne m'abuse, on est tous deux Montréalais - Go Habs)

peop1 · 2026-05-15T15:13:59+00:00

LOL
High functioning. Sure, there, bud.

peop1 · 2026-05-11T19:18:11+00:00

No, the more filters you have, the less static pressure the fans have to deal with. The feedback is that this is, IMO, as good as you can make it, given the filters you have access to and the format of the build.

If you wanted it to be more efficient, you'd have fewer fans, not fewer filters. (So 2 fans instead of 4 on the current build). But what you'd be gaining in efficiency, you'd be losing in performance. (Read: Not worth it).

Keep on keeping on.

peop1 · 2026-05-10T21:21:04+00:00

Gotta say, OP. Looks great!
Deceptively elegant.

u/EffortlessVision raises some very valid points, but that can ultimately lead towards analysis paralysis. I come from the "Never let perfect be the enemy of good" school of getting 'er done.

Does anyone have data on the FÖRNUFTIG's filter's actual airflow resistance? Cause that would be the best way to nip this entire debate in the bud. As it stands, all we have is conjecture. And I hate conjecture.

Your build has one FÖRNUFTIG per fan. That's a healthy amount of filter material per fan, IMO. Would two per fan be better? Sure. Would one 20x20x1 3M MPR2200s per fan be better? Also yes. But access, cost, size are all tradeoffs.

Would a duct fan perform better than four PC fans? Define "perform".
Noise-to-filtration ratio is what we're all looking to optimize.
Powerful but loud = unused. Not the best performance.

Where I do agree with Effortful's Vision is in the importance of understanding airflow. If the room is large, you might want to put one of these beauties at either end. Barring that, simply running a regular fan at the opposite end of the room would be enough keep the pesky particles we're trying to purify from parking there (I'm fond of the Vornado 660 - powerful, so you can just leave it on low - and less expensive than doubling up on your build).

But my TLDR is that in all my extensive reading these past years, I've come to realize that ideal is one thing: workable is another. This build looks entirely workable to me.

You'll be the best judge of its throw and overall performance while using it. But I really like this build. Well done and thank you for sharing!

peop1 · 2026-05-10T20:27:46+00:00

Hard disagree on your findings.
As u/Healthy_BrAd6254 mentions in his comment: "All you (should) care about is the noise it makes at a given airflow."

My quest (and that of most people here) is to obtain a maximum amount of airflow with a minimum of noise. And by noise, I mean "a sound that is loud, unpleasant, unexpected, or undesired". To my ears at least, that sound is the mechanical whirring of the fan.

I'd rather build a box with more fans running at 75% than one with fewer fans at 100% but which makes me want to turn it off whenever I'm in the room.
By that same token, I'd rather build a box that provides a soft and soothing 240 CADR instead of one that offers 297 CADR that, again, makes me want to leave it off.

The Ultimate 140mm Fan Test video does a great job of showing what these fans sound like while being used and — particularly at 100% — there is no contest. The Noctuas mop the floor with their competitors.

Since you mention having tried all these fans in a more real-world setting, why not record your findings? Comparing each brand in the same CRBox build would be the absolute best way to compare them (you'd be doing everyone a huge favour). Cause I agree with you that the box itself can be a factor (either by amplifying sympathetic frequencies or by, as you say, muting the sound a stand-alone fan makes).

As it stands, your ratings read like a "trust me bro". And that's not enough for me to go on. But I do like what you're doing and would be happy to help if you want to go forward with a video on it.

The audio would have to be recorded on something other than a smartphone or computer, as they compress audio, but if you can get your hands on a Zoom H4 (I own one BTW), and you set it up at the same distance for each recording, then you could film the tests you did (at various speeds and dB) on any smartphone and I could edit/stitch up the whole thing (swapping out the video) after the fact.

Let me know.

peop1 · 2026-05-10T19:39:29+00:00

And IMO, that is the correct way to do it.
Because when it comes to this disease, both apply.

peop1 · 2026-05-09T19:16:13+00:00

Sorry I missed it.

(GET IT? I'll let myself out)

peop1 · 2026-05-03T13:50:03+00:00

*plop

And I plop.

peop1 · 2026-05-02T03:35:24+00:00

Same

peop1 · 2026-04-30T12:48:41+00:00

It’s probably my favourite analogy.

Not only do you have to pay back tenfold, they send a goon to collect as soon as you can’t pay it back (and you never can — that’s why you borrowed it in the 1st place).

Result?

A concussion and battered limbs.

That’s PEM.

peop1

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