BIDA Air Quality Measurements

I've been curious for a while how well the ventilation at the BIDA contra dance works. This is actually something that we can measure reasonably well by looking at CO2 levels: outside air has about 400 parts-per-million (ppm), while your exhalation is about 40,000ppm. By measuring the concentration of CO2 in the air inside, we can determine how much of the air you're breathing has been through other people first.

I recently got a Temptop M2000, which measures CO2, as well as particle levels (pm2.5 and pm10) and HCHO (formaldehyde). I got it because I'm interested in running some tests on my ceiling fan air filter idea, but now that I have it I want to measure everything. It logs to one minute intervals, and you can export to CSV.

The dance is in the basement of the Cambridge Masonic Hall, and the main room is 66x48 (3200 sqft) with about a 25ft ceiling (80,000 ft3). There are four ceiling fans which we keep on high. We have two large barrel fans, rated for 15,000 CFM on high. We put one blowing in at one end, and one blowing out at the other. In theory that might give us 11 ACH (60 min/hr * (80k ft3 / 15k ft3/min)) but I would expect to see lower performance than that: there are various obstructions, and there is nothing to stop air coming back in around the fan (the opening is not sealed around it).

Here's what I measured, with the monitor in a back corner where I expect the air is most stale:

Ceiling Fan Air Filter

Filter cubes are a great way to cheaply filter a lot of air, but they're bulky and noisy. Elevating them can get them out of the way if you have a high enough ceiling, but it's still not ideal. What if we built something around a device that is intended to be up there: a ceiling fan?

Let's say your blades are a foot from the ceiling, and sweep a diameter of 52". Shroud the fan with a regular octagon of 12"x24" furnace filters, and the air will flow in through the filters and down:

Microphone on Electric Mandolin

A large portion of what I'm doing when I play rhythm mandolin is percussive: the sound of the pick hitting the strings. After listening back to the comparison between my electric and acoustic mandolins, this is the thing I find most lacking in the sound of the electric. What's interesting, however, is that I don't really notice this when playing at home. I realized a few days ago that it's hearing the electric mandolin acoustically that makes the difference, because the pickups are not really capturing these pick sounds. And if I can hear it acoustically, I can fix it with a microphone!

I made some recordings, and I really like the sound I get when I mix a little external microphone into the main sound from the pickup. I also really like that this means when I run the pickups through distortion or a talkbox the crisp sound of the percussion is unaffected.

Experience on Meloxicam

I continue to have wrist and hand issues, though they are mostly fine as long as I minimize how much I use them. Which mostly means a lot of dictation! Still, it would be good both to understand what is wrong with them and figure out how I can resume some of the activities I enjoy that I've stopped.

On 2022-03-04 I started taking 15mg of Meloxicam, daily with dinner. This is a nonsteroidal anti-inflammatory (NSAID), which often reduces arthritic swelling. I continued for a month, with my last dose on 2022-04-04. Unlike when I tried Methotrexate, I didn't notice any changes either when I started or when I went off.

To understand whether there might be a more subtle effect, I also checked my level of finger swelling each morning on waking by clasping my hands and seeing how tight it felt. I rated this feeling on a scale of 1 to 10, and all days were in the range 6 to 9 inclusive:

Contra Dance Mask Policy

After getting a question in the BIDA Facebook group, I was curious what mask policies contra dances are using. I looked at the dances marked as active on and checked their websites for mask requirements (sheet).

Of the 56 dances that have resumed, 31 (55%) require masks. Of those 31:

  • 2 (6%) require surgical or better.
  • 4 (13%) require a surgical + cloth or better.
  • 4 (13%) require high-filtration masks (N95, KN95, KF94, etc)

Now that high-filtration masks are widely available, it does seem like a weird compromise to require masking but allow low-filtration options like cloth or surgical, especially when I haven't seen anyone wearing a P100. Specifically:

Chording Bass

When using my foot pedals to play bass, I've primarily been using them to specify the current chord. I'll play the same pedal on each downbeat, switching when the current chord changes. There are a lot of things you can do with this, but on a real bass you'd normally play some things that are much more complex.

Consider this traditional bass pattern:

  • A bass note on every downbeat.
  • Odd downbeats get the current chord.
  • Even downbeats get either:
    • If you are staying on the current chord, the fifth.
    • If you are going to a new chord, a half step below the new chord.

Here's an example on piano:

Can we play this with just feet?

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