Bonding (a couple of pins set and strapped clamped) the 1/8th in ply (3ply BB) to the front curved edge worked out - and fairly easily. I initially thought I had done a solid job cutting and sanding- but I could feel a couple of small imperfections. Absent a CNC machine, I’m happy with this as a guide for the side pieces. (the dark line between the ⅛ in and the board is the pencil line)
I built a test 'box' for the coax to run some initial comps for different open back-ish configurations. I won't be doing a full open baffle as this unit will sit on top of the woofer box, and being a low-ish floor stander I kept a top on as well. I ran the tests with the mid driver (compression driver not connected). Hard to see, but the baffle angles upward 10 degrees.
The box internals were lined with felt, and each configuration (A,B, C, and D) has at a minimum the baffle, top, and bottom. Not so unexpected, the more open the higher the fs, although each fairly close. The Qts went down (not sure if that makes any difference for this build). I used DATS for the impedance measurements. OK not really free-air in these 'boxes', but I wanted to see what the differences would be.
Additionally, I measured frequency at 18inches inline with the ctr of the coax. (Again, only the mid is being driven). Not surprising the low end falls off sooner as the open back 'box' becomes more open. I hadn't expected the peak rising before the fall. A real issue shows up with configure C which is a box without the back creating ripple-wave (dip). Configure A seems easy to work with (my goal was to have the mid play down through 360-380Hz before beginning its rolloff. D may be workable, I just may need to adjust my goal upward a tad, as a HP will manage the rise ~500hz and it doesn't exhibit the ripple issue of the configure C.
I went back to take a look at a vented design I had used awhile back with an Audio Nirvana 6.5in. Similar to config A, but just extended to create a ~tapered vent.
I tried to duplicate my previous measurements (not exact, but close) and the yellow line is shown with the previous config A and B measurements. Clearly extended through what now is a vent more so than opening. Measures Fs 87.2 and Qts 0.6555.
So, where I'm looking to cross down to woofer I may have some options. I'm leaning towards a non-port option.
Edit: I listened to music with a 1st order HP 190 (tgt down -0dB 380Hz upwards) which may benefit from a shelf to further limit the low energy to the mid. Image w and w/o LP.
Morel 1058s going back - returned one biz measured a bit out from specs, and its replacement keeps getting delayed (initially ordered Nov ‘24). BTW PExpress has been great to work with. So I’m going to pull my DA RSS 210 HOs 8ohm from a previous project, and now going with a 3 ½ way. The design will give me options for testing the top coax open back - I may end up with one or both sides open with the back - depending on measurements, wanting the mid to play extended.
Saves me some serious ca$h, so going with Russian PIOs for C1 in a 3rd order HP (coax passive), 8 in woofers crossed active with LP air coil on the back/ lower woofer. Here is the latest (I’ve clearly been around the block with ideas - sorry).
In a couple weeks I hope to start making sawdust and get on with it- finally. Couldn’t unfortunately get comfortable with a curved baffle, side, or back in the design.
@tajanes said:
Morel 1058s going back - returned one biz measured a bit out from specs, and its replacement keeps getting delayed (initially ordered Nov ‘24). BTW PExpress has been great to work with. So I’m going to pull my DA RSS 210 HOs 8ohm from a previous project, and now going with a 3 ½ way. The design will give me options for testing the top coax open back - I may end up with one or both sides open with the back - depending on measurements, wanting the mid to play extended.
Saves me some serious ca$h, so going with Russian PIOs for C1 in a 3rd order HP (coax passive), 8 in woofers crossed active with LP air coil on the back/ lower woofer. Here is the latest (I’ve clearly been around the block with ideas - sorry).
In a couple weeks I hope to start making sawdust and get on with it- finally. Couldn’t unfortunately get comfortable with a curved baffle, side, or back in the design.
What is the plan or idea or concept with the two woofers sharing an enclosed volume (if I am reading the sketch correctly), I assume firing in-phase so that there is a slug of air inside the box moving back and forth without compression?
What is the plan or idea or concept with the two woofers sharing an enclosed volume (if I am reading the sketch correctly), I assume firing in-phase so that there is a slug of air inside the box moving back and forth without compression?
Bipole.
Generally .5 woofers are brought in relative to BSC, and of course to supplement the low end. My goal here is to let the coax mid play extended and bring in the front woofer accordingly (which will include baffle step). The coax will be passively crossed / one amp channel, and the woofers crossed active with a second amp channel. Active and DSP will provide flexibility to manage filters, letting the mid be primary and the woofer supplemental (up to max ~380Hz). Currently expecting (at this point pre-measurement) that the back woofer will just supplement the lowest end- maybe with an inductor targeting ~80-140Hz 1st order LP. Sort of an active-passive radiator (but with a gentle frequency rolloff of a closed box), 4pi radiating pattern at those low frequencies. While I understand it is problematic to have differing drivers (i.e. mid with woofer) sharing a box, I'm not concerned here for a couple of reasons> same drivers with the bottom woofer just fading its upper ranges 3db relative to front woofer. And, if this actually makes the front driver more sensitive in these upper ranges (i.e. attenuated back relative pressure to the front driver in this range) the active system can easily manage this bipole arrangement.
This design build would be problematic for full passive, and understandably there are diehard passive only builders in this hobby, but I see advantages of a balance of bi-amping, passive components for the mid-tweeter filters, and active for the woofer(s).
Edit: I could possibly be convinced to have separate enclosures for the woofers...
Comments
Bonding (a couple of pins set and strapped clamped) the 1/8th in ply (3ply BB) to the front curved edge worked out - and fairly easily. I initially thought I had done a solid job cutting and sanding- but I could feel a couple of small imperfections. Absent a CNC machine, I’m happy with this as a guide for the side pieces. (the dark line between the ⅛ in and the board is the pencil line)
I built a test 'box' for the coax to run some initial comps for different open back-ish configurations. I won't be doing a full open baffle as this unit will sit on top of the woofer box, and being a low-ish floor stander I kept a top on as well. I ran the tests with the mid driver (compression driver not connected). Hard to see, but the baffle angles upward 10 degrees.
The box internals were lined with felt, and each configuration (A,B, C, and D) has at a minimum the baffle, top, and bottom. Not so unexpected, the more open the higher the fs, although each fairly close. The Qts went down (not sure if that makes any difference for this build). I used DATS for the impedance measurements. OK not really free-air in these 'boxes', but I wanted to see what the differences would be.
Additionally, I measured frequency at 18inches inline with the ctr of the coax. (Again, only the mid is being driven). Not surprising the low end falls off sooner as the open back 'box' becomes more open. I hadn't expected the peak rising before the fall. A real issue shows up with configure C which is a box without the back creating ripple-wave (dip). Configure A seems easy to work with (my goal was to have the mid play down through 360-380Hz before beginning its rolloff. D may be workable, I just may need to adjust my goal upward a tad, as a HP will manage the rise ~500hz and it doesn't exhibit the ripple issue of the configure C.
Purple squiggle for the win?
I went back to take a look at a vented design I had used awhile back with an Audio Nirvana 6.5in. Similar to config A, but just extended to create a ~tapered vent.
I tried to duplicate my previous measurements (not exact, but close) and the yellow line is shown with the previous config A and B measurements. Clearly extended through what now is a vent more so than opening. Measures Fs 87.2 and Qts 0.6555.
So, where I'm looking to cross down to woofer I may have some options. I'm leaning towards a non-port option.
Edit: I listened to music with a 1st order HP 190 (tgt down -0dB 380Hz upwards) which may benefit from a shelf to further limit the low energy to the mid. Image w and w/o LP.
Morel 1058s going back - returned one biz measured a bit out from specs, and its replacement keeps getting delayed (initially ordered Nov ‘24). BTW PExpress has been great to work with. So I’m going to pull my DA RSS 210 HOs 8ohm from a previous project, and now going with a 3 ½ way. The design will give me options for testing the top coax open back - I may end up with one or both sides open with the back - depending on measurements, wanting the mid to play extended.
Saves me some serious ca$h, so going with Russian PIOs for C1 in a 3rd order HP (coax passive), 8 in woofers crossed active with LP air coil on the back/ lower woofer. Here is the latest (I’ve clearly been around the block with ideas - sorry).
In a couple weeks I hope to start making sawdust and get on with it- finally. Couldn’t unfortunately get comfortable with a curved baffle, side, or back in the design.
Congrats on settling on a design - rethinking projects frequently keeps me in stasis too . . .
What is the plan or idea or concept with the two woofers sharing an enclosed volume (if I am reading the sketch correctly), I assume firing in-phase so that there is a slug of air inside the box moving back and forth without compression?
Bipole.
Generally .5 woofers are brought in relative to BSC, and of course to supplement the low end. My goal here is to let the coax mid play extended and bring in the front woofer accordingly (which will include baffle step). The coax will be passively crossed / one amp channel, and the woofers crossed active with a second amp channel. Active and DSP will provide flexibility to manage filters, letting the mid be primary and the woofer supplemental (up to max ~380Hz). Currently expecting (at this point pre-measurement) that the back woofer will just supplement the lowest end- maybe with an inductor targeting ~80-140Hz 1st order LP. Sort of an active-passive radiator (but with a gentle frequency rolloff of a closed box), 4pi radiating pattern at those low frequencies. While I understand it is problematic to have differing drivers (i.e. mid with woofer) sharing a box, I'm not concerned here for a couple of reasons> same drivers with the bottom woofer just fading its upper ranges 3db relative to front woofer. And, if this actually makes the front driver more sensitive in these upper ranges (i.e. attenuated back relative pressure to the front driver in this range) the active system can easily manage this bipole arrangement.
This design build would be problematic for full passive, and understandably there are diehard passive only builders in this hobby, but I see advantages of a balance of bi-amping, passive components for the mid-tweeter filters, and active for the woofer(s).
Edit: I could possibly be convinced to have separate enclosures for the woofers...
I thought The Tubes-Store in Canada had these PIO’s in stock… It may be an interesting delivery
The K40Y-9 PIO are all over Ebay. So are the K71-4 polystyrene etc.
InDIYana Event Website
I’m thinking gov’t knock, knock, knocking at my door for supporting the cause…