. . . it's probably almost impossible to predict how a bamboo will whistle, even when all bamboos look and perform the same, tiny differences can change their sound significantly. What they could do is to test these bamboos and discard the loud ones.
Any smaller or bigger ones would be manufactoring errors.
Theres no bamboo that doesn't whistle, all of them do, just differently with peaks at dirrefent draw speeds and some of them are loud . . .
. . . the hole size on the bamboos does vary considerably. I dont think its manufacturing error, i think it's that they have a wide tolerance in manufacturing; the units will work with variable sized holes. I do think hole size effects the whistle, among all the other factors; I don't see how it couldn't....
If they fix the bamboo issues on the evo, I'd use it more though. I think they're concentrating on growing the company, not tinkering with the Evo anymore though . . .
. . . they said they've decreased the manufacturing tolerance with EVOs.
I think so too, if different bamboos whistle differently and the hole positions have little effect on that, the size variance seems to be the only possible factor . . .
Just fwiw, maybe to add a tad more clarity . . .
First, as a reference point, in my previous life GE Medical was a client of mine. GE's imaging equipment used glass tubes which were hand-blown. GE could not develop a method to automate the process. Even though there was a tolerance range, the reject rate was still quite high. The cost of the poor yield was of course baked into the pricing, which fortunately for GE, was possible due to the nature of that particular market and GE's position in it.
The first EVO's delivered to the "Fanatics" incurred a number of complaints regarding the whistle (the units were exchanged). I talked with Seibo about the bamboo design and manufacturing process. Similar to GE, the bamboo had to be hand made. A tolerance range was defined, and a tool devised to manually measure the orifice diameters. My observations at the time were (a) The glass heat chamber design was central to the EVO's convection performance and its marketing message, (b) there are 2 orifices that affect air flow along with the draw, (c) the tool had to be very precise, and (d) a manual measurement process would inherently induce some errors. My net impression was that VXL had a problem similar to GE's, but without GE's advantages.
So . . . VXL apparently made a cost/benefit business decision, as all manufacturers do all the time. In this case, the perceived customer satisfaction costs were outweighed by the perceived costs of design changes and/or lower margin and/or higher prices. These latter costs were not financially sustainable; like most small cottage-industry companies, VXL was operating on a shoestring. (Recall that it needed advance customer funding just to bring the EVO to market, not to speak of the later heavy ancillary production costs VXL incurred due to its inexperience.) The EVO's market performance would seem to justify its decision, although that of course is little consolation to those customers for whom the whistle issue could not be resolved.
So IMHO the short of it is that both of you are correct on most of your points.
The whistle is the result of the force of air in/out of the heat chamber orifices, all of which vary. There are multitude permutations. While some units did not whistle, most did but across a rather wide range of pitch, the perception of which also varied considerably from one user to another. The whistle and variance is not a flaw, but a design decision. Personally, I don't expect that to change, unless it is in a new product generation.
There is one other likely variable that hasn't been mentioned: The glass. IIRC, the few HT's at release had fairly similar airflow. I can't speak to later HT's; I don't have any. Certainly using a whip will change the dynamics. I used my EVO with a number of 3rd-party pieces and my perception is that the glass could have a major affect. But since I have a non-whistling unit in the first place, I can't confirm that.
@Brewervapesalot, I wonder, might this be a solution to your problem?