I recently was at a home improvement store to buy some PVC pipe to make flutes. The brand of pipe that I normally buy was not available, so I bought 100 feet of what was available. However, when I got it home I discovered that the bore of the pipe was not smooth but slightly dimpled. I was upset, thinking that I was going to have to scrap all of this new pipe, because it just didn’t meet my standards.
Then, I thought about some of the postings on C & F that dealt with the micro-bore boundary with regard to acoustics, and I decided to experiment with this “defective” material. I was shocked to find that a flute made from this material with a dimpled bore did not have the same characteristics as a flute made from a typical smooth bore pipe. In fact, the second octave intonation problems that are usually present on cylindrical bore flutes was not present on the flute made from this material.
I was excited about prospects of this new material so I contacted the supplier of the the pipe in Michigan. I wanted to know whether the pipe that I had purchased was an anomaly or whether I would be able to purchase more just like it. The salesperson was apologetic that this defective pipe had gotten through their quality contol process. They assured me that PVC pipe without a smooth surface was an extrusion anomaly and that I could not count on buying any more just like it.
There is a moral to this story, but I am not sure what it is. What do you think?
i had thought when Casey Burns mentioned this recently that it would be interesting to try different ways of “texturizing” the normally smooth PVC bore. maybe there’s a way to recreate the dimples Doug, or something equivalent. (i’m curious about the dimple details too.)
First of all, the dimples are not quite what Whistlin’Dixie was talking, I don’t believe. Actually, the bore of the pipe looks fairly smooth on appearance. However, when you put your finger in the bore, it doesn’t feel smooth. I called it dimpled for lack of a better word. I am guessing that what happened in the extrusion process is that either the PVC batch or the extrusion dies were not hot enough, causing the bore to be less than smooth, although the exterior of the pipe is quite smooth.
Secondly, I did go back to the store and buy 200 feet of the “special” pipe. So far, I have made two flutes from the pipe. The first one was a 2-piece, tunable flute, which seems much improved in intonation without a wedge, but the tone doesn’t seem as complex as with the wedge. I also made a one-piece, non-tunable flute from the “special” pipe. I was disappointed to find that this flute plays pretty much the same as an identical smooth bore flute, with perhaps some improvement in intonation, but not as much as the first flute. So I haven’t done enough experimentation yet to draw any conclusions. I suspect that there are variations in bore texture between the two bores and that these minor variations are affecting the acoustical properties of the pipe.
With regard to texturing PVC, I have been thinking about that, as well.
Of course, abrading the surface is an obvious first idea. A special tool for sand blasting the bore might also work, but the sand-blasing machine would not fit in my kitchen, I am sure. Obviously, more experimentation is needed. Does anyone have any suggestions about how to texturize the bore of PVC pipe, so that it would have a fairly standard and uniform texture?
Perhaps some 5-minute epoxy could be dribbled down the length of the pipe?
I’m still trying to picture what the “dimples” look like, though… If you cut a length of the pipe in half, Doug, would the “dimples” look like wave crests and troughs alternating down its length? That’s kind of what I’d imagine happening if the extrusion feed rate and/or temperature weren’t quite right. Lengthwise undulations, like a snake?
wow. good thought. and once the pvc is softened up a bit by the acetone all sorts of ways to impress different textures and patterns on the interior present themselves.
if texture impedes airflow in some ways, could more texture toward the foot of the flute simulate some aspects of a conical bore?
oh, and, btw: that was a seriously impressed, but not the least bit surprised “wow”. >
It was an idea from my delinquent youth My mom once had this nice set of acrylic dresser accessories that she loved. One day I “decorated” them with a cotton ball and nail-polish remover. I thought the frosting would just wash off.
It didn’t.
Twenty years later, she still occassionally brings that up!
As long as we are offering SWAG’s (Scientific Wild Ass Guess), here’s mine:
The irregularites of the surface are probaly disrupting laminar flow in the boundary layer. Possibly in a smooth bore there is a difference in the boundary condition between the registers, i.e., laminar in lower and turbulent in upper and this makes tuning in the two registers slightly different. In the lumpy bore, the turbulence may be more uniform between the registers making the tuning also more uniform.
well, actually… the reading i’ve done on flute acoustics suggests that there is some sort of spiral air movement down the flute. while the precise spiral probably depends on pitch, a generally spiral texture roughly alligned with the airflow might have some interesting affects on turbulence & such. might even accellerate the air a bit???
ps- bet this puts me over the top for today’s SWAG allotment!
