A CAM member was selling off some little Bravox 3.5” 12ohm woofers a while back. These are the same drivers Parts Express had a buyout on several years ago and even provided a crossover that was designed by Vance Dickason. My design pairs the Bravox drivers with a 1” Dayton ND28FB-6 in a MTM configuration. It was supposed to be the round version of tweeter ND28F-6 but Solen sent me the wrong version by accident and it wasn’t worth the effort to send them back.
 |
 |
Plugging the Bravox T/S specs into any box software will result in a small sealed design. Since these will be used with a minimum active crossover of 120hz set in the processor I went with a ported box. The ported design can maximize power handling without running into over excursion and group delay issues down to the crossover setting. Asking them to play anything below 120hz will be pure garbage.
Total internal volume of 4 liters gross and tuned to 100hz. Baffle width is 5” and total height is 11”. The tweeter is offset from center by .5”. Driver spacing is 2.5” center to center. The woofer cut outs were chamfered on the backside of baffle with a 45deg router bit to promote airflow behind the woofers. To increase the WAF, end caps made from ½” mdf were made to overhang the box by 1/8” on all sides. The edges were rounded over and painted with black truck bed liner. The rest of the cabinet will be wrapped with speaker cloth to form a sock.
Crossover is 4th order acoustic at 2.6khz. The woofers have a nasty peak at 1200hz which make for a more complex crossover than hoped. The good news is it can be built with less expensive components. All caps are basic electrolytic bipolar. The inductor in high pass circuit is a 22 gauge air core from the parts bin. The .62mh inductor in low pass is a 20 gauge steel core and the DCR should be .30 ohm or less. The inductor in notch filter is critical and must be .24mh with a DCR between .2 and .25ohm. A 18 gauge air core works great here. Resisters are standard issue sand cast.
Average entry level receiver should not have any issues driving them. Aside from being a 4ohm design they do not have any low impedance dips or awkward phase angles to worry about.
 |
 |
 |
 |
Center Channel
Center is same box design as the mains just turned on its side. Crossover changed slightly to work with the different driver layout. The typical off axis dip in midrange is present but is quite decent, only losing 3.5db at 20deg off axis.
Crossover is 4th order acoustic at 2.5khz. Again basic ie. cheap crossover components are used. For some reason I had a single 5.6uf poly cap hanging around so I used it up. The inductor in high pass circuit is a 20 gauge air core from the parts bin. The .55mh inductor in low pass is a 22 gauge steel core and the DCR should be .40 ohm or less. The inductor in notch filter is slightly less sensitive then in the mains. You can get away with .21mh to .23mh and the DCR can be between .2ohm and .3ohm. I used a .22mh 18 gauge air core.
 |
 |
 |
 |
 |
 |
| Prototype for the main crossover | Center |
 |
 |
| Front | Mock up with sock. Needs some extra finish work. |