[ogodei]

I’m starting a build on two triple, OB sub H frames this weekend.  Thought I’d document it here to share the pain and as a self-disciplinary measure to make sure I complete them within a reasonable time frame.    I have a bit of history in starting builds and still having boards stacked against the walls years later.     I’d love to have these done this month but with glue-ups and finishing I suspect it’ll be end of October.  Any later than that anyone reading this is free to start harassing me here.
 
I originally planned to do two doubles and ordered the double-trouble flat packs. Once they arrived I changed my mind and so ordered two more drivers.   The plan now is an MDF core / interior baffles with all drivers facing forward.  The exterior case will be ¾ inch cherry with waterfall corners just to make things difficult. Interior will be black, the cherry will probably get a natural finish. I have a pair of Cornwalls in natural cherry I like the look of.  No rez on the interior surfaces.

I’m still working through a few of the details in my head.  Grills will probably be in-set to the cherry case, black cloth on hardwood frame, but I’m considering a full-face grill because old school.  Either way the grill will be detachable, inset magnets to posts in the MDF.
 
Also pondering how to get wiring out of the subs.  Plan is to run cable to a 4 pole female Neutrik and put put male jacks on the amps (A370PEQs in boxes made from whatever cherry is left over).   To avoid interference from the grills I’m thinking route through the bottom MDF, epoxy a cable gland into the cherry.  I have some Canare L-4E6S star-quad (4 wire, heavily shielded) or I may just run dual wire-twists through a jacket to pretty things up.  The cable run outside the subs will be 12 to 16 inches max, not sure how much interference they’d pick up anyway.

Another thought is an extended bottom panel or heavy runners under the speakers to provide additional support in back.  I’m not sure how back-heavy these get, probably wait to see how solid they are before I build anything extra.  I may go ahead and drill anchor holes in the plates to avoid a trip back to the workroom later.
 
Any thoughts on my proposed design & especially on methods for cable exit when grills are used would be welcome.   Pics and notes to follow once the fun starts …

Steve

[Early B.]

Post a timeline of milestones from today through October 31st so we can track your progress and yell at you when you get behind.

[ogodei]

Ooof, I don't know if I'm that masochistic    I have a tasks/milestones list for maybe 2/3 of the project but a specific timeline would be tough, my available time gets pretty fluid.  Good idea though, I'll work on it.  Honestly I'm hoping to power through a lot in the next several days.

OF which, got to the lumber yard this morning and picked up MDF and cherry. My high-tech sheet goods cutting facility in the driveway



Ready for the trip into the basement



And the cherry is now acclimating but it seems pretty dry already, a couple of days at most needed I think.

[ogodei]

Wasn't interrupted for most of the day



All MDFs for the interior case cut to size



Got through the initial rips OK but my vacuum can't cope with the crosscut sled, got to wear the NIOSH respirator for a couple hours.  I really love working with MDF.  Cleaned up the workspace afterwards then realized I have to route tomorrow, which will create even more of a mess.

The price of progress.

[JWCoffman]

Haven't seen a good build thread in a little while.  These are always fun to watch.
I feel your pain regarding stalled projects.  For me, there always seems to be a point when it just feels like an unpaid job rather than a hobby.  The end product is so worth it though.

[russellberg]

I hate to be the bearer of bad news but I made a pair of XSLS Encores where I clad the outside of the MDF box with ⅝ solid maple that was very dry.  I am not sure how you are planning on to attach the maple to the MDF but I glued it on to the exterior of the MDF box.  I knew this was a risk but I decided to go ahead anyway.  Here's the build thread https://www.audiocircle.com/index.php?topic=171848.0 It looked great and the cabinets where very inert but after about a 6-8 months cracks started opening up in the maple.  Wood is going to move regardless of how dry it is and MDF will not.  Having it glued to an inert substrate means that it is pulling and tearing and that eventually makes cracks.  It didn't happen on every side, for the pair it happened on 3 of the 8 sides and the top.  I used a router and chisel to excavate the crack and then filled it with pieces of purple heart.  The cracking has stopped and I think it looks ok.





Maybe you have a different plan or technique, just wanted to pass on my experience.  If you have more questions let me know.

[ogodei]

Haven't seen a good build thread in a little while.  These are always fun to watch.
I feel your pain regarding stalled projects.  For me, there always seems to be a point when it just feels like an unpaid job rather than a hobby.  The end product is so worth it though.

It's more me getting stalled than the projects if you know what I mean.  I also have a tendency to start new projects before the current work is completed. I'm trying to overcome that these days and I have a pretty high desire to get these completed.

... Wood is going to move regardless of how dry it is and MDF will not.  Having it glued to an inert substrate means that it is pulling and tearing and that eventually makes cracks.

Thanks for reminding me of this. I rarely work with MDF or do these types of panels so while I theoretically know this it wasn't top of mind during design. You are absolutely correct, semi-rigid glues (white or yellow Elmers, Titebond) or rigid glues (epoxy, urea formaldehyde) would eventually crack the cherry.  This is plainsawn stuff so if firmly adhered it will expand sideways and rip itself off at some point. The expansion chart indicates a 14 inch wide board might expand by .26 of an inch over the course of the seasons (although I'm never sure about those charts).

I'm wondering about using a flooring or construction adhesive like Bostik GreenForce or SikaBond.  It's engineered to stay stretchy.  They use this stuff to glue wood to concrete or hardwood floors to underlayments which is pretty much the same as I'm doing here. Place a center line of dowels to hold the cherry centered on the MDF, the glue lets it expand towards the open front and back. I could also pre-seal the back of the Cherry & MDF before glue up meaning less (but still some) water absorption\expansion over time. I might try an experiment with it before giving the design up entirely.

Nice build thread and speakers, BTW.   I agree, I dont like straight polyurethane over maple because of the plastic-y look. I just did some audio stands in maple (though not as pretty as the maple you seem to get in Canada) and finished them at 600 grit with Waterlox "Tung-Oil," which is actually tung oil and alkyd resin I think.  It buffs up very nicely.   




   

[russellberg]

Construction or floor adhesives might be a good idea!  I hadn't thought of that.  Let me know how it goes.  I so prefer solid wood for speaker boxes but MDF is so inert that you really want to end up using both.  I know that my XSLS's are very dead but maybe the best combination is a solid wood box, cherry, maple, etc. with No-Res on the inside.  That stuff is magic.  I just built a pair of NX-Otica's and I just did them in flat black MDF with No-Res and the results are pretty remarkable.  I am in the process of doing a little experiment to test that.  I'll let you know how it goes.  I built an Open Baffle H Frame https://www.audiocircle.com/index.php?topic=173562.msg1834381#msg1834381 out of 2" thick cherry and I am pretty sure that it is moving more than the just ¾" of MDF with No-Res.  I will let you know.

[BobRex]

I keep reading about not using solid wood for cabinets due to dimensional stability.  Yet I have solid cherry and oak furniture made up of glued up pieces that have never shown any cracks, splits or other distresses.  This is 35 year old furniture (from Pennsylvania House and Ethan Allen) that has been in multiple houses with different environments.  Daedalus seems to do fine with solid wood too.  So what's the secret?

[WGH]

I'm wondering about using a flooring or construction adhesive like Bostik GreenForce or SikaBond.  It's engineered to stay stretchy.  They use this stuff to glue wood to concrete or hardwood floors to underlayments which is pretty much the same as I'm doing here. Place a center line of dowels to hold the cherry centered on the MDF, the glue lets it expand towards the open front and back. I could also pre-seal the back of the Cherry & MDF before glue up meaning less (but still some) water absorption\expansion over time. I might try an experiment with it before giving the design up entirely.

Attaching any 3/4" thick wood to anything (MDF, wood, plywood, metal) will self destruct over time. Using a stretchy glue will make it happen faster.

Pre-sealing the back of the wood will do nothing. The problem is the two sides of the 3/4" board will absorb room humidity at different rates. Take a sample cherry board and place a wet towel on one side and watch what happens, the board will curl. If the relative humidity of your house is 20% during the summer and drops to 8% in winter then the wood will shrink, but it can take months for the entire 3/4" board to reach 8%. The outside will then shrink, the glued side with higher moisture content will not and the flexible glue will let the cherry pull away from the MDF at the edges. Not a good look.

I have been veneering with solid wood for 30 years without a failure. The maximum thickness I use is 3/16", any thicker will start acting like solid wood and de-laminate over time.

The mesquite veneer I made for my Salk speakers

[WGH]

Daedalus seems to do fine with solid wood too.  So what's the secret?

The solid wood sides move in harmony with each other, the grain runs around the box. The dovetail corner construction locks the corners together. The front baffle is usually quartersawn which minimizes movement plus walnut is not as hard as some woods (cherry) and moves less when properly dried. Cherry planks can move a lot and keep moving with the seasons. I would guess Daedalus ages the wood for at least a year before using it, the boards that crack are used for smaller pieces. The mesquite I used was aged 1 year for every 1" of thickness, usually longer. 

[ogodei]

...The outside will then shrink, the glued side with higher moisture content will not and the flexible glue will let the cherry pull away from the MDF at the edges...

So the issue is cupping and bowing, not edge-to-edge expansion which is what I wanted to allow for with the glue.  That's a good insight, thanks.  How does hardwood flooring deal with the issue?  Thinner (less wide) planks?  Air flow under the boards? Possibly that's why commercial flooring planks have ridges on the bottom?

What if I air-gapped the glue up with striations on the back of either the cherry or the MDF?  Its no longer a pure lamination, there could be an air gap 40-50% of the board with air access from under the speaker.  That gets more structurally complicated yes, probably enough for me to move to a full hardwood solution, but I'll have to think about it when I'm a little more awake.

Steve

[russellberg]

I have made solid wood cabinets for speakers with lock miters for the corner joints.  These have had no issues as I made sure that the grain was all running the same direction so that when the wood expands or contracts the whole thing just expands or contracts together.  If you dislike working with MDF and veneer, as I do, I think this method with No-Res is a good solution.

[WGH]

How does hardwood flooring deal with the issue?  Thinner (less wide) planks?

Yes, narrow planks that float. A wide pine plank floor will have some cupping.

there could be an air gap 40-50% of the board with air access from under the speaker.

sure, with tiny fans moving the air under the boards.

And hamsters running the fans
And cats to keep the hamster population in check

This is why I always worked alone. A shop partner would always come up with some hair brained idea that I would have to explain why it wouldn't work. I have been woodworking since 1975 and have seen a lot of disasters. There is never enough time to do a project right the first time, but there is always enough time to do it over.

[ogodei]

I've got all that already except the hamsters.  I'm not sure what the WAF of hamster wheels attached to the speakers will be, I'll have to check with her on that.

Steve

[emailtim]

Nice sled.  Speakers aren't bad either !!!   

[ogodei]

This is why I always worked alone. A shop partner would always come up with some hair brained idea that I would have to explain why it wouldn't work. I have been woodworking since 1975 and have seen a lot of disasters. There is never enough time to do a project right the first time, but there is always enough time to do it over.

I was actually already adjusting my plans based on your input.  No need for disparagement or continued explanations if they pain you.

I'm still thinking hardwood but would have to wait longer to start the build unfortunately.  And find a use for the cherry already purchased but that shouldn't be too hard.

Steve

[Early B.]

I'm still thinking hardwood but would have to wait longer to start the build unfortunately.  And find a use for the cherry already purchased but that shouldn't be too hard.

Why not stick with MDF? There's no sonic benefit to using real wood. Seems wasteful for subs. Besides, you have tons more options with paint or veneer. Save the solid cherry for the main speaker build.

[WGH]

Instead of using solid cherry for the sides, 3/4" cherry plywood glued to the 3/4" MDF would work. ApplePly is available in pre-cut sizes that will survive shipping. A 4x8 sheet will usually have a big scrape or dent from shipping. I had a good distributor that let me sort through plywood sheets for the ones that didn't have any damage. Hobbyists buying at lumberyards are usually told to pull from the top with no sorting. At $175 per sheet they have to sell the damaged sheets to somebody and it won't be their steady commercial customers.

ApplyPly is available in White Maple, Walnut, White Oak, Birch, Teak, and Cherry. Usually Ships in 3 to 5 Days
https://www.buyappleply.com/

The solid cherry can be used for edge banding. All the custom cabinet makers I know use solid wood edge banding because it survives bumps and dents better. The solid edge banding is clamped on using yellow glue so it is permanently attached and won't peel off like the veneer strips with hot melt glue backing.