Well, with a 1/2 WL closed pipe use .25, etc. and .33, etc.; ditto 'open' when both ends have equal boundary loading, so try measuring with it weighted/clamped to the floor.
Some of my best performing subwoofers (I use the term to mean low end 'fill' apps) were 8" frame in 8" center tapped open pipes, i.e. two 1/4 WL 8" drain pipes 'sandwiching' the driver and clamped to a plank (way before I ever heard of B*$3), then weighted to the floor since some of us folks moved around a lot back then for one reason or another and some had to make a hasty 'retreat' (thankfully not me) with little room for a bulky speaker whereas the pipes became storage bins for clothes, etc.. 🙄
Some of my best performing subwoofers (I use the term to mean low end 'fill' apps) were 8" frame in 8" center tapped open pipes, i.e. two 1/4 WL 8" drain pipes 'sandwiching' the driver and clamped to a plank (way before I ever heard of B*$3), then weighted to the floor since some of us folks moved around a lot back then for one reason or another and some had to make a hasty 'retreat' (thankfully not me) with little room for a bulky speaker whereas the pipes became storage bins for clothes, etc.. 🙄
Inside the pipe, these were literally just clamped together using four threaded rods running the whole length with dense cardboard gasketing on each side of the driver frame and some 'L' brackets at the open pipe ends, tension'ed to 'taste'/critically damped and because the pipe came in 4 ft increments it was acoustically ~8 ft.
Would have preferred longer, but the rooms they went in were pretty small and didn't know about adding 90 deg bend extensions to make half square wave tuners till decades later.
Would have preferred longer, but the rooms they went in were pretty small and didn't know about adding 90 deg bend extensions to make half square wave tuners till decades later.
This previous thread might be of interest.
https://www.diyaudio.com/community/threads/bose-wave-cannon.294199/
https://www.diyaudio.com/community/threads/bose-wave-cannon.294199/
Another thing to consider is to not end the pipe abruptly, but instead make it a pipe which gradually opens up the further away the pipe extends from the speaker driver. Karlson used such a thing for loading tweeters in his Transylvania tubes. This will spread the resonances over a range of frequencies.
I made a tapped subwoofer which I intend on doing this too. Not only can this method reduce the amount of severe resonances which are caused, but it can be used to vent the lower frequencies into varying parts of the room, thus, helping to avoid room modes. Of course, such a thing would be awkward to implement in a living room, but not so much in a dedicated listening space.
Retsel
I made a tapped subwoofer which I intend on doing this too. Not only can this method reduce the amount of severe resonances which are caused, but it can be used to vent the lower frequencies into varying parts of the room, thus, helping to avoid room modes. Of course, such a thing would be awkward to implement in a living room, but not so much in a dedicated listening space.
Retsel