First optimizer port test
I tested the Subwoofer shown previously:
It's an old sony 8" woofer mounted in a big 50 liter enclosure with a port dimensioned with the optimizer spreadsheet for a tuning of 37 Hz.
I tested it without and with filling in the form of a cheap ikea polyester cushion:
before showing the graphs an interesting observation:
when simulating the enclosure in hornresp (with a corresponding straigth tube port in a simple bass reflex chamber), we can see that the tuning frequency does not exactly correspond to the port output peak. The combined output has a "local peak" at the tuning frequency.
FIrst the undampened enclosure measured and simulated:
the first enclosure resonance at just below 300 Hz is quite similar. further resonances are slightly off. I suppose my enclosure cannot exactly be modeled in hornresp. the 880 Hz peak is the port resonance, not very prominent in the simulation - not sure why this is so.
the helmholtz tuning corresponds very well, as far as I see for now, see impedance valley bottom.
the wiggles between 60 and 100 Hz are room modes. those disappeared in the next measurements, where I lifted and moved the speaker to the room center.
the port and the driver are quite near so there is quite some bleed form one to the other in the measurements.
Dampened enclosure:
The enclosure resonances are almost gone. the port resonance is still there, of course.
please note that the absolute levels of the measurements are not exactly comparable, the mic distance changed slightly between the measurements!
I also tried to get the port to start chuffing or blowing, but no chance - the driver starts to distort very badly and is probably compressing heavily at 20 V input, corresponding to an estimated SPL of 94 dB/1m (4pi) or 100 dB/1m (2pi) as simulated in hornresp above. The port is still working perfectly.
More measurements will follow, but for today I am quite happy how this turned out.
Last edited:
