The open baffle has been sidetracked yet again. This time by a generous gift by Rockolga who gave me two Voigt pipe speakers. An updated version from the Danish High Fidelity designs from the 70s.
They had cutouts for 8” drivers (good) and E-V T-35 horn Tweeters (not so good). I have some really good Peerless 8” 861832 drivers that work well in Voigts and then I also have some piezo tweeter horns that fitted in the horn cut outs after some elbow grease.
The speakers were undamped apart from having 175 gram of BAF fiber stuffed in the closed end of the pipe. Based on B Börjas article I stuffed 80 gram BAF in the first section and 45 grams as a wedge around the first bend and then behind the driver in a wedge like fashion (after removing the initial 175g that is). It worked out quite well. According to Börja I should have added rock wool and fiber glass wedges here and there. As I am not to keen on working with fiberglass I used some 20mm thick sheets of dense BAF (Biltema) and used that to cover the walls in the section of the bass driver.
The upper partition is seen to the left in this picture
I then measured with omnimic just in front of either the driver or the pipe opening
Driver (black undamped pipe and blue trace with 80+25 gram BAF.
The damping at 200 Hz is atributed to the BAF, a thing to note is the weak dip at 50 Hz. Usually the pipe gives a sharp dip in driver output at the fundamental resonance of the pipe. The finding suggest a leak somewhere. (Later I added some plumbers putty behind the Piezo horn and the potentiometer)
The BAF reduces the peaks by about 5 dB. That the pipe peaks in output around 60 Hz indicates that something is wrong. It should be below 50 Hz.
The sealing and the BAF sheets lowers the tuning by 10 Hz from 50 to 40 Hz. Good But the dip at 40-45 Hz is not as strong as I would like to have it. (lower two panes)
The impedance looks like this
Time to look into the tweeter issue.