After rereading, always important for forgetful me, they started talking about 14' being quarter wave of 20Hz BUT they ended up using 12' sections of Sonotube...
Then modified the design for 1 speaker and a 10' section (cut 2' off the end in the box) which they were happy with but was not the ideal design.
Then suggested (last page of article) making 2 six footers from a 12' section of eight inch sonotube and using 8' woofers with a 40Hz resonant Freq.
So there were 3 design experiments. The 8" six footers should go great next to the big boys huh?
I think I can handle the dual eights as I have a loose pair that are currently "between boxes" haha.
oops, driver was pointed wrong way. here is pipe-o
That's terminus output alone. You have to do combined response to see actual response.
BUT with these sonotube transmission lines that have the driver and port so far apart the actual response at any given position could be anywhere between the combined response with 0 path length difference (which only applies if you measure from a spot equidistant from both ends) or the response on the terminus end (as you showed) or the response at the driver end (which is significantly different than both) depending on where you are in relation to the sub. The room will even it out to some degree but it's still a mess.
These long straight (constant csa) transmission lines with driver and terminus so far apart are just a bad idea (IMO). Adding a bit of taper to the line (like your example, although it's also shown as terminus output only) and doing a simple single fold to put the driver and terminus closer together is much better (again IMO). Do that and throw in a bit of stuffing and you can get almost ruler flat response over a much wider bandwith no matter where you stand in relation to the sub, unlike El Pipe-o.
Graph 1 - combined response +300 cm
Graph 2 - combined response 0 cm
Graph 3 - combined response -300 cm
So if you built this, laid it out flat on the ground and measured from different locations in relation to the sub, this is what you would get from the terminus end, the middle and the driver end. As you walk around the sub you would get VERY different response due to the driver and terminus being so far apart. Put it in a room and the room will even this mess out to some degree (and add it's own wild influence to the mix) but it's still a mess and a bad idea (IMO).
Did you read the article? It was just an experiment for fun about 12 years ago.
I read it, and if it had been my experiment I would have chalked it up to experience and moved on. Nellie's as good as they get with amplifier design, but where speakers are concerned he's as much a hacker as I am playing golf. That doesn't mean I'll ever give up playing golf, but I'll never make a living doing it either.