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- Analogkid455 6:59PM
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Next project / post Iowa
Thanks again JR, JP, and BK for putting together a really great event.
There were sooo many interesting builds, I left with many ideas to think about to potentially incorporate into a ‘next build’.
The ones that hit me from a skill level on execution (and I’m thinking I should say in no particular order) kudos to Brad, Nick, and John. I’m comfortable that I’ll never get to that level of execution (paint, fit & finish) so maybe I can get ‘close’ with interesting designs…
From a sound _and_execution standpoint, and maybe it was that diminutive tw/mid combo (reminiscent, in a positive way, to the rat shack minimus 7) on its slight wedge shaped, exquisitely finished, woofer box, with integrated waveguide / grills, was Nick’s entry (Dayton winner- congrads). Maybe too much info, but my kids have more than once called me a wac-a-mole. As I listened to the many great sounding speakers at the event, what I’m listening for is ‘that something’ that negatively stands out, and Nicks for me, was the exception; not to hot, not to cold, but just right (and with inexpensive Dayton drivers). Well done, VERY well done.
So looking at my box of toys, I have a beyma 5.5in coax (IMO the best coaxial design with extended horn) and I could possibly mate with a side firing 8.5in dayton rss210 ho-4 in a narrowish 6.5 in. width by 12.5 deep and 30 in. tall. The problem with a side firing woofer is the crossover point / directionality with the coax. While the beyma has an f3 of 75 it falls off around 120-150Hz which would be at the limit of integrating with the side woofer. And I’ve concluded not enough (although close) headroom. So I’m left with a more traditional box design, but with flexibility of crossing somewhere in the 220 to 380Hz range, depending upon final driver mounted measurements. Per my recent preferences, the coax will be open backed (or tapered to minimize reverberant waves) and the woofer sealed. Passive coax Xover and active btwn coax and woofer (with a tad bit of eq low extension on the woofer).
Needing that something to challenge, I’m tossing in a bit from Troels Gravesen with his setback on the baffle btwn woofer/mid/tw. With final timing adjustment per the active crossover software. Something I haven’t played with in the past. And I’m revisiting my previous crossover for this coax and leaning towards a 3rd order LP and HP (~3850Hz) per some modeling. I’ve attached a few rough initial ideas (including the narrow tower I had thought about). I enjoy putting pen (and pencil) to paper, its a required process for me. Draw, think, rethink, re-draw…
Comments
I wonder if having those internal cross-braces installed in an asymmetric fashion/angle would make much difference in the back-wave effects upon the cone? Maybe even extend the lower one to the cabinet corner and pack it with pillow stuffing as a trap.
…Or, do I
take the mandatory 5 point deduction against the WAF scoring and turn it so its 12.5 in w X 6.5 in deep and 30-34 in high aka Vandersteen?
That way more flexible with matching the front coax with front woofer. Still looking at open back for the coax and slightly tilted up towards listening position. Debating placement height of woofer - thoughts and suggestions welcome
Looking at the dowel risers (from mid-box to top cap), do you guys see any issues with using a 1 inch wood dowel here (warping / twisting) or should I be looking at using a PVC pipe and fill with a low expansion foam (deadening the plastic pipe)? If the latter I could glue in 1.5 inch plugs into either end for connecting mid box and top.
Also considering going with a ⅞ round-over on the wood sub-box and laying a full length outer corner (about 1/3rd of a 1in pipe ?) of a PVC pipe to provide both a very thin spacing for an outer sock vs the box to avoid showing any transition (assuming I’m less than dead on with the top extension). Of course, slicing the PVC pipe to get a rap-around corner is going to be a real challenge.
OK wood working masters- thoughts on how you may tackle this?
Thanks !
I think you could pull off a side woofer with a closed back mid. The coax will like a off axis listening position which would help with any side woofer to mid high cross over points
.
I would go with wooden dowels on the top section, or alternatively aluminum. As for cutting pcv pipe, it can be done on a tables by attaching the pipe to a board, so that the pipe can't rotate, but keep in mind that the pipe is under stress and will clamp down on the blade while you're cutting, so you'll need to stop part way through and wedge the already cut end open, before continuing the full lengthwise cut.
Not to put a monkey wrench in your plan, but have you considered building a truncated pyramid enclosure? You would then have a narrow top for WAF. Just a thought.
1" PVC pipe for the corner risers with some 1/4" all-thread rod down it and counter sink with flat washers or hurricane nuts/threaded inserts on the top board and lower cabinet. Wrap the sock and then cap the top with a finish board.
Cut some plugs for bushings with a hole-saw to stuff into the PVC pipe [if needed or recess the PVC pipe for stabilization].
Use a band saw if slicing the pipe in a V shaped jig if going that route.
Just some thoughts . . .
Thx. It does look to be close, but I’m going thru my open back mid period…
Thx for bringing up the issue with slicing PVC. While I was thinking attaching to a flat board - I hadn’t thought of the need to support the cut section. Aluminum, if I can find it, may be the best (and safer) way to go.
Thx
Thx for ideas. The connection to top and box with plugs probably the way to go- getting everything to line up smoothly (for the grill sock) is a concern - hence thinking about the full length corners (and aluminum may be the approach).
You could try creating a Vandersteen style box by first making a full length frame out of 3/4" PVC pipe as shown in the pic below. The pic is actually the DIY frame that I made to hold 30 gallon leaf bags in position during leaf bagging operations, but the concept should work for speaker building as well. Bill
So I’m debating the pro’s and cons of a Vandersteen tower type build vs the more standard compact box.
I can get both designs’ coax (tw) aimed at listing area - small(er) box via an angled low floor stand, and the tower via angled coax within the tower.
So, looks like I’m really trading off ‘compact’ for possible advantages ~Vandy tower design with a narrow baffle for the coax box ???
While I’m somewhat in the camp that a narrow(er) baffle for the coax combo (mid/tw) as in the Vandy design gives better imaging and dispersion characteristics (then when on a wider/bigger baffle), my question is: is it really an advantage?
The attached pics: std box with dimensions approximately 10w x 18.5ht x 12 inches deep.
Vandy type tower dimensions approximately 11.75w x 34ht x 6.625 inches deep.
As much fun as it is to draw and develop concept builds - I generally come back around to my senses (what’s left of them) back to KISS.
Since I’m active btwn woofer and coax - I don’t really need to set the coax back from the woofer (the dsp can adjust timing/positioning) and while going with a small narrow box for the coax (as in the Vandy tower design) probably presents a better imaging presentation- it potentially suffers from equidistant tweeter positioning to box edges.
However, what could make a difference is possibly going overboard with baffle felt around the coax, and experimenting with the triangle cuts around the coax (seen around tweeters as in the Wilson’s) and sticking with the more conventional, relatively compact box.
I like the tower idea, but the coax naked.
Ah, to have a man cave…
Damn it JR, I can’t get those Beston’s out of my mind. Especially when I came across the concrete open baffle pics (reposted pic here).
I’m wondering if I can take my current build - the bass unit with rs210 ho8s and replace the top coax unit with some sort of a horn / waveguide ? Looks like the 210’s may be able to cross up towards 850 to 1.2kHz ? The Bestons may not handle that Xover range - but maybe a ribbon with a horn-ie waveguide? Is that a) asking too much of the rs210’s, and suggestions for the top driver? Possibly Heil ESS air motion driver ?
Latest twist: 3 way with DA RSS210HO-4 8in woofer sealed, either a MarkAudio CHP-90 or Fostex FF125WK vented / open back, and a Beyma CP21/F 1in slot tweeter with waveguide wings. Sticking with active btwn woofer and mid (thinking 3rd order ~220Hz) and 1st order passive btwn mid and tw- rolling off the mid somewhere btwn 8Khz and 12Kz. The slot loaded tweeter with ‘wings / waveguide’ will sit on top of the W and Mid box, with a single front grill. Tgt box 15h x 10w x 12d, with total height (with the tw) 20in.
My first go-to for the mid is Fostex, but leaning towards the MarkAudio it looks to have a stronger lower-end (and more Xmax) and power handling. If anyone has experience with either mid driver and/or suggestions plz let me know.
And suggestions on how to make the wings. I do not have a printer, but that may be the best way to go- any printers for hire?
Thx !
Those wings remind me of the profile of the old style streamline door and window casing
I would touch base with Jason here for 3D printing, he might have the bandwidth to help.
Personally, I would go with the Mark Audio driver for mid duty.
...and no, I think the big Beston is probably limited to 1500 or higher and is already deeply horn loaded. I should really get them measured on Brad's big board.
may be a good place to start- thx
Looks like the 2nd one made of Douglas Fir has sufficient thickness to add an additional round-over to smooth the difraction smear . . .
Santa delivered early this year - how does he know ???
The beyma compression slot tweeter is built like a tank. And the MarkAudio CHP-90 should be an interesting driver to work with - greater Xmax than I’ve seen with the Audio Nirvana or Fostex drivers.
I’ll probably have to wait until after Xmas to start the project…
Santa knows what HE likes/wants . . .
Reminds me of the old JBL 2405 slot tweeters. Loved those things. Didn't love replacing the diaphragms.
The beyma is listed on US Speakers as a replacement for the 2405's.
This has me pondering a HP filter; frequency and order. While I'd like to 1st order with the MarkAudio CHP-90s (somewhere in the 10 to 16kHz range) to extend the narrowing horizontal pattern of the CHP-90s, I'll see what the drivers are 'saying' when I get around to measuring in and on box... Tom, any specific suggestions you have regarding your experience with the JBLs would be appreciated.
Most of the damaged ones I saw back in the 80s & 90s were from being cooked for hours at festivals or not using a protection cap and asking them to play too low when using an active crossover. Pretty much operator error most of the time.
Looking into the Beyma CP21/F slot loaded tweeter (replacement for the JBL 077/2405s) for use and implementation ideas (filter orders, crossover frequency, etc) I came across two somewhat interesting posts.
One by Troels Gravesen, and one by Nelson Pass. Troels suggests a couple of mods to the Beyma (similar to porting and polishing cylinder heads for us car nuts) which, while I'm not thrilled about removing the cover ring, it does clean up the response (air flow ~ sound propagation, not sure about improved HP- jk).
Nelson's article was on his re-do of a crossover network for a JBL L300 (which used the 2405s). He ended up going with a 1st order HP on the tweeter (vs 3rd) and lower orders and adjusted crossover frequency points elsewhere as well. And, a little stuffing for the port (not a sock, though...). I've attached a link to his article biz he's a sound over measurement guy. A good read, imo.
https://www.firstwatt.com/pdf/art_l300.pdf
Not getting a solid buy-in (from the much better half) for placing the super tweeter on top of the WM box (even with a full front grill), I’m looking at either a WMT, or a WTM with the Markaudio broad range above the super-Tw, and off-setting that pair (sTw and Mid) a bit to a side.
In searching the older Mission speaker designs, I came across this sage bit of advice rel to T M vs MT:
The difference is an inverted polar pattern on the MT vs TM arrangement, as well as different baffle diffraction. The audible difference will be subtle, but I'd like to think that placing the mid on top would be beneficial in creating an off-axis null that angles towards the floor rather than to the ceiling. Listening straight on it may be difficult to differentiate between…
dcibel Jan 2010 post
As mentioned above, Troels Gravesen took the beyma's apart and did / recommends a couple of mods to clean up the edges of the horn mouth (especially the vertical narrower exit edges) and filling some gaps in the throat. I was a bit hesitant, but in view of his pre / post measurements, and after taking them apart, the flow should be fairly significantly improved - especially when we are dealing with very high / short wavelength frequencies relative to the needed mods.
I've attached a few pics, and will be going back with another layer of glue to make sure the gaps in the throat are all filled and smoothed out. I'm not taking pre / post measurements as I'm thinking Troels' would be better than mine.
pic 4486 edge pre-filed, 4488 edge post-filed, 4485 throat gap pre-filled, 4490 gap post-filled (hard to see biz of clear glue), 4480 under the knife, 4484 driver base / horn pieces
I will take pre / post frequency sweeps (vertical and horizontal) when I get the box built to compare surface mounted with and without my ~winged waveguides.
modeled
1st order series ‘works’ but looking at the mid frequency response / slope, I’m thinking off-axis is going to be funky.
Keeping with series (and the Lpad for the super tweeter) but going with 2nd order LP with 1st order HP looks to provide more balanced slopes.
We’ll see what in-box actual measurements show.
You mean series second order highpass, 1st order LP.
I think the second order version could be improved a bit more by making the Mark Audio circuit second order to engage the tilt and flatten it. Place a coil on the bottom line between the cap and MA negative terminal. You'll likely have to increase the pad to the tweeter, and maybe invert the tweeter's polarity. Start with a 0.15mH coil, and maybe step up the tweeter pad to 6-8 ohms in series.
This is all spitballing off the cuff, YMMV.
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