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Today I finally had my set of testing reeds delivered from Harmonikas.cz and I have made some simple test recording. It is available here: https://soundcloud.com/martynowi-cz/reed-tests The reeds tested are: 1.DIX reed on an alluminum plate; 2.DIX reed on a brass plate 3.DIX reed on a zinc plate 4.Tipo A Mano alluminum reed 5.Export Durall alluminum reed 6. Old russian alluminum reed salvaged from a cheap russian CBA (it was the only valved reed in this test) Some important notes: all DIX reeds were identical in size, standard accordion reeds were larger but both in the same size. Old russian reed is a bit smaller than Tipo A Mano and Export durall reeds and has old leather valves (one of which has obviously blocked a lot of airflow). From what can be heard "live": alluminum reeds were louder and brighter. When played "in mouth" brass and zinc reeds had significantly more honky sound, a bit like trumpet or other reedles brass instruments. DIX reeds have somewhat distorted, slightly more buzzing sound than standard reeds. From the three, the alluminum one was the brightest and most susceptible to pressure variations and more volume modulation can be obtained than in brass and zinc ones. Those were more stable and subtle, with zinc one having fewest of the higher harmonics in the falloff stage (but only slightly less than brass one and both had significantly less than alluminum one). As a testing setup I have used my DIY bellows and beech, single block reedpan. There is no additional reflections dampening, the setup was completely open (no endplates, no valves, no hole pads or action).
Recent discussions on leathers and leakage prompted me to think about doing some tests. I was particularly interested in questions like why we use chamois leather as a gasket when we know it isn't airtight. Does clamping it between two flat surfaces solve all its problems? And I thought I'd make it more fun for me and you by having you looking over my shoulder, putting forward helpful hints, coming up with bright ideas, making cruel and unnecessary jibes .... I thought I'd start by making up a general purpose test rig, which I could also use to test bellows, reed pans etc for leakage. One piece was like the end cap of a concertina, except no button holes or vents, other than a hole in the middle to attach to the leakage detector. The other piece was just a flat plate of the same concertina-like dimensions. Put them together and you have a thin, airtight, empty, hexagonal box. Both were made from 12mm (1/2") MDF, sometimes called craftwood. Smooth, dense, flat - just the thing. So I make up my two pieces and clamp them together with 6 big spring clamps where the 6 bolts of a concertina end would normally go. First test is to confirm that they form an air-tight cavity. Plug in the Magnehelic leakage detector, et voila - hmmm, leaks like a sieve. Indeed, the Magnehelic dropped from its setup point of 8 when open to atmosphere, to about 7.8. My test rig was essentially transparent to it! A failure of stupendous proportions! What an excellent start to our journey! Aha, I thought, clamping isn't enough - air is getting out through the gap between the two pieces. I can prove that by wrapping it around in duct tape. Hmmm, absolutely no difference. About now the true horror is sneaking in. MDF might be dense, smooth and flat - but it ain't airtight! Hey, this science stuff is cool - we've learned something already! But can I prove it, and what am I going to use for a test chamber? The answer is clearly: - let's render it airtight by doping it. So, I've lacquered all surfaces of both sections with a layer of PVA glue. That's going to take some time to dry, and it's getting late down here. We'll pick up the story tomorrow. Terry
Wondering if concertina repairers ever resort to pressure testing the seating of pads? Pad seating is critical in flutes, but it's pretty easy to do a suck test, so most flute repairers just do that. Being somewhat of a fetishist, I use a Magnahelic Flute Leakage meter to refine that test. The Magnahelic is essentially a combination of a small air pressure generator (an aquarium pump in reality), a regulator to reduce the pressure further, and a Magnahelic differential pressure meter, which is what gives the unit its name. The Magnahelic is set up to read 8 with the end of the tube open, and ideally should register 0 when the end of the tube is closed. In a whole flute, it's OK to be as bad as 2, but any worse that that is likely to weaken the response. Obviously each pad individually has to be a lot better than 2 if that is to be the whole flute result. The meter is sensitive enough to detect airflow through the whorls of one's fingerprint - you need to wet your fingers before testing a keyless flute. I tried out the Magnahelic on the pads of the concertina I'm looking at at the moment, and found most pads registered around 4. One was much better at around 2, some worse around 6. One even scored an 8 - when I opened the pad, I could see that the seat impression ran right up to the edge of the pad at one point. Enough flow to startle the Magnahelic, but obviously not enough to make the reed vibrate. Now that's possibly not a problem for a high pressure, low flow instrument like the concertina, although it would spell doom for the high flow, low pressure flute. I haven't tried it out on other concertinas, and wondered if anyone has had experience here? Is it just a point of interest, with no practical import? Or should one get obsessive and use such tools in the search for perfection? Terry
I suddenly find myself in the position of needing to evaluate a couple of concertinas to see what work they need. It made me wonder if anyone has produced (or could be tricked into producing) a checklist of issues as a guide to assessing the condition of a concertina. Some things of course jump out - notes that don't play, pads that don't seal, etc. Others you pick up in playing, for example on one instrument the buttons protrude too far, wobble badly in the out position, dip too far and require far too much pressure when pressed. Some need investigating to find, like end screws with only a turn or two of useable thread or action cover sides held in place only by the screws, as the glue joints have come apart. Hmmm, if I go on like this for much longer, I won't need a checklist. But if anyone has one.... Terry