Measure the impedance before anything else. A 50 Ω resistor and two jack leads identify the
driver version and give the real port tuning in minutes (Impedance jig).
Don't copy the 43 Hz tuning for the Aiyima. Aim for ≈ 50 Hz; a 175 mm total port gave
≈ 48 Hz and a flat bass in this box. Cut long, measure, trim.
Place damping by the mode, not by the panel. Thick, loose fill at mid-height for the 350 Hz
mode; wool on the back panel for the ~950 Hz depth mode. One thin layer alone does little.
The budget damping layout works: one layer of sheep's wool fleece on the back panel plus 50 g of pillow
fill in a wool pocket across the middle third of the height.
Build the back panel as drawn — 292 × 482 mm, gasket and screws — and seal the OSB inside.
A friction fit leaks and shifts the bass every time it's refitted.
Stop before the impedance dip disappears. When the dip between the bass peaks is down to
~1 Ω, more damping costs bass.
Make the setup repeatable before you measure the speaker: floor marks, taped knobs, a
loopback reference, fingerprints at every session.
Measurement makes it verifiable; the ears make it final. The curves say the alignment is
right; the listening test says it sounds more balanced. Tuning further would trade evenness
against bass quantity — a matter of taste, not of right or wrong.
Balance, not quantity. For more bass level the levers are placement (closer to a wall, as the
original design intends), a gentle EQ shelf, or loudness compensation — all safe once the
protective high-pass sits at 0.75 × Fb.
The first tube cut landed on target. Partly luck — but the prediction came from the measured
tuning, and three independent checks (port near field, bass sum, impedance) agree on ≈ 48 Hz.