Here is your final design.
The pdf for you final box is attached.
The woofer is
Peerless 164 WR 33 102 NWP AL LS 8 ohm.
This woofer has a smooth mid band response and a good off axis response. There is a break up mode peak maximal at 4.5 kHz. It is based between 3 kHz and 5 kHz. So this requires a crossover at in the region of 2 kHz.
In the specified enclosure the F3 is 49 Hz. The tuning peaks of impedance are 33 Ohms at 28 Hz and 34 ohms 80 Hz, which gives a null of impedance of 8 ohms at the F3 of 49 Hz, showing optimal tuning of the design.
Vb is 0.56 cu.ft. The port is flared at both ends and 2.5" in diameter and 9.738" long. Vent velocity at max power is 24 m/sec.
The vent and driver displacement is 0.0618 cu.ft. This needs to be added to Vb as well as brace volume and crossover volume. The sum of these will be Vt which is the actual size of the box you need to build.
50% of the internal surface should be covered with damping material such as mineral wool. Areas behind the driver should be covered preferentially. The volume of the damping material is allowed for in the design.
The enclosure should be well braced and as narrow as possible. The tweeter should be as close to the top as possible, the woofer below the tweeter as close as possible. The port should optimally be placed below the woofer. I prefer the front, but rear mounting is also satisfactory. Drivers and port flare should be flush mounted.
To minimize diffraction effects, the corners should be rounded like this.
The tweeter is the
Vifa BC25SG19-04.
This tweeter has a very smooth response over most of its pass band. There is gradual attenuation above 9 kHz which becomes steep around 18 kHz. This is not a bad fault in a tweeter for a small bookshelf speaker, and actually tends to give a better bass/HF balance. I have made no attempt to pull up the response.
Fs is 1060 Hz. So the tweeter should optimally be down 24 Hz at that frequency.
The crossover is centered at 2 kHz. The low pass filter has an electrical third order slope. The HF filter has a second order electrical slope. The combined acoustic and electrical slopes give fourth order slopes, with the woofer being 24 db down at 4 kHz and the tweeter 24 db down at 1 kHz.
There is also diffraction compensation. Because of power limitations, loss of sensitivity and lowering of impedance, 4.5 db of diffraction loss compensation is provided rather than the calculated 6 db. However room gain will almost certainly correct this. The curves shows a rising low end response, but because of diffraction loss the response will almost certainly be flat to within 3 db from 49 Hz to 9 kHz.
The crossover pdf is also attached. L2, L3 and C2 form the third order low pass filter. The values have been tweaked to provide 4.5 db of diffraction loss compensation. Req and Ce form a zobel to correct the woofer frequency dependent impedance rise so that the low pass filter can work as intended.
C1 and L1 form the second order high pass filter. Rp1 and Rp2 form an L-pad to match the tweeter output to the woofer.
All inductors should be good quality air core. The capacitors should be good quality Polypropylene. Resistors should be wire wound 10 watt minimum.
After diffraction compensation and insertion loss of the crossover, sensitivity will be in the range of 84 to 85 db 2.83 volt 1 meter. This is fairly typical for a small bookshelf speakers.
The crossover models as a superior crossover. In addition to a nice flat mid band response, the impedance curve is very flat indicating an easy to drive speaker. X-over pro assumes a sealed alignment so the tuning region impedance curve will be the one in the enclosure pdl. Impedance is 5 ohm over a good deal of the frequency spectrum. I would give this speaker a 6 ohm nominal impedance rating.
The phase response is superior. Tweeter and woofer are only 45 degrees apart at crossover. This is an excellent result.
The speaker if built correctly should have a an accurate smooth response and wide sound stage. Hopefully they will sound bigger than their size, and be pleasing to listen to even without a subwoofer.
Good luck with your build. Take your time and build it carefully.
Please keep us informed as to the progress of your build and the final result.
One final note. While getting involved with this design, I seem to remember Hi-Fi had asked for a crossover design for these speakers. My apologies for having forgotten. Better late than never!
