Hi all again
Sorry for lapsing quiet, too much going on! Hey, at my age, aren't I supposed to be at risk of boredom?
Still puzzling about how we define the low end of the 1st Regime. I unearthed my old Type II Sound Level Meter, and wondered if it would reveal anything. Type II is "industrial grade", whereas Type I is "laboratory grade". Probably good enough for our immediate purposes.
I've talked before about the lab acoustics not really being ideal for sound measurements. So instead of following the classic "1 Metre on Axis" approach, I just put it down on the desk 200mm (8") away from the whistle's window. And not even on axis, as that would make reading the meter harder. If we decided it is a necessary feature in future, I could play with the location of the various items to optimise ease of use and quality of results. But let's see what it tells us, if anything.
Things to note:
- couldn't measure the lowest flow rates, so just marked them <2 and relied on Pressures
- Included a zero flow line, to note the Sound Level Meter's background reading. I'm using it on "slow" and "dBA". A background reading 10dBA lower than any other reading is fine.
- Noted that it rose to 46 dBA Slow or 60dBA Fast while the compressor was running! That's OK, I'm happy to wait!
- I used the Old Gen whistle, note it too has what appears to be a higher pitched Aoelian regime below the start of the 1st, but it's much less noticeable than on the Feadog Mk1 I'd investigated previously. Probably a voicing issue, but not noticeable in use. Nobody blows that low!
- Note when the 1st Regime kicks in, it's again at a very low frequency and volume level, rising a long way in both till it snaps into the 2nd regime.
- I didn't go much into the 2nd Regime, as I was interested to see if we would see Hysteresis going back down in flow rate. It appears that we do, whereas I don't think that was the case with the Feadog. Unless perhaps I didn't investigate that thoroughly enough.
- the point 5L/Min, 8mm Pressure, 571Hz and 71dBA looks like a possible "practical" bottom end of the 1st Regime. But identifying it on the run wouldn't be easy!
Code: Select all
Old Gen D, 6 holes covered, 23 May 2023
Flow Pres Hz dBA Regime
0 0 0 20
<2 2.5 575 52 Aoelian?
<2 3 370 30 1st
<2 4 496 28.5
<2 5 544 39.6
2 5.5 548 42
3 6.5 563 60
4 7 568 63.5
5 8 571 71
6 10 575 74
7 13 578 77
8 17 581 79
9 22 1137 84 2nd
10 29 1147 89.5
9 22 1135 85
8 16 1092 73
7 12 576 76.5 1st
Thoughts anyone?