Ended up (active Xover btwn bass and coax) with BW 3rd HP coax, and BW 4th LP ~ 240/260, lets the coax carry 300 up cleanly.
Debating rebuilding the bass w/o the aperiodic vent / line I put in and just go fully sealed. And, w/o the internal line I can chop maybe an inch+ from the height of the bass box.
I’ve been playing around with going fully sealed and relocating the 2nd reversed driver (vs its M&K downward location as in my build) by angling the magnet towards the back bottom corner, and (if my math is correct) looks to save about 0.10 cu ft. for the net sealed enclosure. So I can get ~ same net volume in a bass box that is 10 ⅜ W x 15 1/2 Hx12 ⅜ D (just slightly wider & deeper) vs current build of 10 ⅛ x 17 x 12 (as the bottom 6 inches in that set-up is not actually in the enclosure). The output of the reversed driver would be directed down and back vs down and forward- but with a LP ~240-260 (4th order BW) shouldn’t be an issue. A lot of effort for getting the combo Coax and Bass box to 23 ½ vs 25 in H, and a ratio of top Coax to Bass box of 1:2, but I’m a bit nutz - but since I see / believe a better ultimate control of the sealed vs AV enclosure- why not.
I just ordered some more baltic birch ply (not the best grade ply at ACE / Builders Sq in Clark, CO).
Leaning towards this (latest) re-design for a completely sealed push-pull bass box, targeting a Vb about 15-20% < a Qtc of 0.707. (My wife thinks I’m crazy - only took 35 yrs, to say it out loud anyway…). This design looks to provide the most space efficient configuration (so far) with the inverted driver open fully through the back and bottom of the box).
My thinking is (for what it’s worth) while an aperiodic vent is a good ‘tool’ for a woofer in a tighter/smaller box than .707 targeted Qtc, as it balances the benefit of an acoustic suspension box for control and low-end extension in a passive system. However, with the addition in the system of active eq, targeting Vb a bit below a Qtc of .707 provides additional internal pressure for the re-bounds of the woofer (at the extremes) which can act in helping improve the ‘quickness’ of the diver’s rebound (beyond the driver’s suspension, etc.) and the active eq can offset the additional resistance of the box pressure to get to full extension of the woofer (as long as you do not overdrive).
Hopefully somewhat understandably stated? if not and/or other thoughts please let me know.
Additionally, I’m becoming a big fan of having two 8’s when one would ‘work’, similar to having 300 watts when 150 ‘works’. Having a bit of overhead, vs pushing towards limits, has significant sound quality benefits. Similarly, hearing benefits of having a larger midrange driver to extend to lower range of voice frequencies (depends, of course on transition to tw that you are looking for).
@Steve_Lee said:
AND . . . coaxials sound better than discrete drivers when DSP is used to fix their limitations . . .
That’s what led me to putting a notch/ adjustment before the coax Xover (where appropriate) as it then affects the coax as a unit, minimizing relative (btwn mid and tw) phase affects. It can be passive as well as active, but active is more like a scalpel than a hatchet.
This targets 18% < 0.707 Vb +/- 2% (vs shrinking box experiment which was taken down to 30% below). Bass box @ 15 ¾ ht x 10 ¼ w x 12 ⅝ d (vs 17 x 10 ⅛ x 12 ½) and top box 7 ⅝ ht x 8 ¾ w x 6 ¾ d (vs 7 ¾ x 10 ⅛ x 6 ¾). So, net total ht 23 ⅝ vs 25in, sticking with same stands drops total ht to 28 ⅝ vs 30 inches.
Also making top coax box all back and bringing in width, to match new narrower grill. Sides of bass box coffee stained BBirtch (considering walnut veneer?). That’s about as small as I can get this - all driven by decision to lock up the push-pull 8’s bass box as tightly sealed (vs sealed/ aperiodic vented).
Comments
Ended up (active Xover btwn bass and coax) with BW 3rd HP coax, and BW 4th LP ~ 240/260, lets the coax carry 300 up cleanly.
Debating rebuilding the bass w/o the aperiodic vent / line I put in and just go fully sealed. And, w/o the internal line I can chop maybe an inch+ from the height of the bass box.
I’ve been playing around with going fully sealed and relocating the 2nd reversed driver (vs its M&K downward location as in my build) by angling the magnet towards the back bottom corner, and (if my math is correct) looks to save about 0.10 cu ft. for the net sealed enclosure. So I can get ~ same net volume in a bass box that is 10 ⅜ W x 15 1/2 Hx12 ⅜ D (just slightly wider & deeper) vs current build of 10 ⅛ x 17 x 12 (as the bottom 6 inches in that set-up is not actually in the enclosure). The output of the reversed driver would be directed down and back vs down and forward- but with a LP ~240-260 (4th order BW) shouldn’t be an issue. A lot of effort for getting the combo Coax and Bass box to 23 ½ vs 25 in H, and a ratio of top Coax to Bass box of 1:2, but I’m a bit nutz - but since I see / believe a better ultimate control of the sealed vs AV enclosure- why not.
If you have the time and resources, building this stuff is always fun.
I just ordered some more baltic birch ply (not the best grade ply at ACE / Builders Sq in Clark, CO).
Leaning towards this (latest) re-design for a completely sealed push-pull bass box, targeting a Vb about 15-20% < a Qtc of 0.707. (My wife thinks I’m crazy - only took 35 yrs, to say it out loud anyway…). This design looks to provide the most space efficient configuration (so far) with the inverted driver open fully through the back and bottom of the box).
My thinking is (for what it’s worth) while an aperiodic vent is a good ‘tool’ for a woofer in a tighter/smaller box than .707 targeted Qtc, as it balances the benefit of an acoustic suspension box for control and low-end extension in a passive system. However, with the addition in the system of active eq, targeting Vb a bit below a Qtc of .707 provides additional internal pressure for the re-bounds of the woofer (at the extremes) which can act in helping improve the ‘quickness’ of the diver’s rebound (beyond the driver’s suspension, etc.) and the active eq can offset the additional resistance of the box pressure to get to full extension of the woofer (as long as you do not overdrive).
Hopefully somewhat understandably stated? if not and/or other thoughts please let me know.
Additionally, I’m becoming a big fan of having two 8’s when one would ‘work’, similar to having 300 watts when 150 ‘works’. Having a bit of overhead, vs pushing towards limits, has significant sound quality benefits. Similarly, hearing benefits of having a larger midrange driver to extend to lower range of voice frequencies (depends, of course on transition to tw that you are looking for).
I think you're crazy.
...if you don't build it.😈
AND . . . coaxials sound better than discrete drivers when DSP is used to fix their limitations . . .
Effortless speakers just sound better.
That’s what led me to putting a notch/ adjustment before the coax Xover (where appropriate) as it then affects the coax as a unit, minimizing relative (btwn mid and tw) phase affects. It can be passive as well as active, but active is more like a scalpel than a hatchet.
Agreed !
This targets 18% < 0.707 Vb +/- 2% (vs shrinking box experiment which was taken down to 30% below). Bass box @ 15 ¾ ht x 10 ¼ w x 12 ⅝ d (vs 17 x 10 ⅛ x 12 ½) and top box 7 ⅝ ht x 8 ¾ w x 6 ¾ d (vs 7 ¾ x 10 ⅛ x 6 ¾). So, net total ht 23 ⅝ vs 25in, sticking with same stands drops total ht to 28 ⅝ vs 30 inches.
Also making top coax box all back and bringing in width, to match new narrower grill. Sides of bass box coffee stained BBirtch (considering walnut veneer?). That’s about as small as I can get this - all driven by decision to lock up the push-pull 8’s bass box as tightly sealed (vs sealed/ aperiodic vented).