The different projects


Frequency Measurement using XTZ mkII

With the mike about 1 cm in front of the cone I get a really nice response. The slope above 4 kHz is an artifact, at a distance of 30 cm (and more) the driver keeps going to 16 kHz and then it drops rapidly.
The dip at the 63 Hz mark shows that the pipe is giving increased radiation resistance and thus reduced output from the driver in the 50-80 Hz range. The dB of driver and pipe can not be simply added as phase and radiation surface come into play.
Below is the output from the pipe, a broad peak around the fundamental at 60-70Hz, a dip of the second harmonic of 125 Hz and a second unwanted peak in the 200 Hz range. I will try to increase the damping material in the first half of the pipe to reduce the harmonics and at the same time keep as much as possible of the fundamental, more to follow...


Added Baffle step compensation and a Zobel link

The bass was light so I added a textbook 6dB baffle step to lower the response above 600 Hz or so to get a better balance.
The green curve is the driver itself.
To flatten the impedance a zobel network is used calculated values are 4.7 Ohms and 36µF, the things I had in the drawer was way off at 6.8 Ohms and 20µF. Still it works well with an impedance ranging from 3.5 to 5 Ohm from 120 to above 10 000 Hz, pink curve where as before it reach 12 Ohm at 10 000 Hz.

Calculated baffle step compensation is a 4 Ohm resistor and a 1.1 mH coil, here I got closer at 4.7 Ohm and 0.7 mH, blue curve.

The sound took a huge step towards a more balanced sound, I am sure that there is room for improvements by tweaking various values. I will perhaps get back to that after tweaking the room accoustics.


Finishing the Midi Trikes

This image shows the internal construction. I have been very liberal with glue and sealer as I had two cartridges that would dry out if I not used them
Dressed up with some BAF wool in the inner tube and some foam glued to the inside of the outer tube. Not shown are some crossbraces close to the open end. I found that it vibrated a bit when playing loud.
I bought some fabric in a style that is typical of the time period 50 years ago when the Trike was concieved. I picked a eleastic fabric and sewd it as a tube that was pulled over the pipe more or less as a sock. Then I used a staple gun to fix the fabric at both ends.

Three outside legs rising the the pipe 1/10 of the diameter (2cm) attached with brass screws completes the construction. I added some modern binding posts. And presto:
Measuring the impedance shows a pipe tuning of 70 Hz with some harmonics 210 and 350 Hz, text book stuff of the third and fifth harmonic ;) The big dark thing to the right is a trike driven by a Peerless 10" alnico driver but that is an other story...
The Philips AD 3701M is a gem, it really sound right in a musical way. With nothing below 60-70 Hz it lack some in the low end but above that it is so nice, Adele sound so nice so the midrange is well taken care of.