I used my router table to rabbet the edges of all the panels, with the rabbet on the front panels fractionally wider than deep. After assembly (alignment helped by the rabbet) I then used a flush trim bit to clean up the edges.
Rabbet - Wikipedia
Rabbet - Wikipedia
Mike,
I have built quite a few Mets. The top & bottom pieces I get by measuring the angles on a scaled drawing. Cut them on a table saw set to the measured angles, but make them slightly over sized. I measure the size after the sides are glued to the baffle. Then I try fitting the top & bottom pieces to judge how much they need to be cut down to make a perfect fit, and to check the angles. Back to the table saw & trim them--slowly & carefully. I put a straight edge (thick metal ruler) across the side edges to see if the part is too wide for the back to fit properly. Any small amount too large I take off with a sanding block. I wish I had pictures to show, as it's easier to see how it works than to use words!
I have built quite a few Mets. The top & bottom pieces I get by measuring the angles on a scaled drawing. Cut them on a table saw set to the measured angles, but make them slightly over sized. I measure the size after the sides are glued to the baffle. Then I try fitting the top & bottom pieces to judge how much they need to be cut down to make a perfect fit, and to check the angles. Back to the table saw & trim them--slowly & carefully. I put a straight edge (thick metal ruler) across the side edges to see if the part is too wide for the back to fit properly. Any small amount too large I take off with a sanding block. I wish I had pictures to show, as it's easier to see how it works than to use words!
So, is there anything I can do to help overcome the negative side of MDF? If I line it with adhesive 1/8 inch foam? If I spray it with truck bed liner? Anything?
I haven't built for others before, so what might you guys offer as advice if I do this again? Actually, I don't even know what to propose as far as cost. I was figuring putting a dollar amount on the time spent, maybe $20-$30/hour, add that to the cost of materials, and use that as a cost guideline. Is that reasonable. I just like to help out a guy who doesn't do any woodworking but wants decent speakers.
Thanks,
Mike
I haven't built for others before, so what might you guys offer as advice if I do this again? Actually, I don't even know what to propose as far as cost. I was figuring putting a dollar amount on the time spent, maybe $20-$30/hour, add that to the cost of materials, and use that as a cost guideline. Is that reasonable. I just like to help out a guy who doesn't do any woodworking but wants decent speakers.
Thanks,
Mike
Longitudinal bracing is good.
If possible, laminate the panels to 1 1/8in - 1 1/4in thick, which will at least push OA panel stiffness to something ~ equivalent to 3/4in of a quality void free plywood (although at considerably higher mass) so some of the gains are offset. Still worth it if possible.
The truth is MDF is not ideal for bass cabinets but it's also a heck of a lot better than nothing at all, especially since wideband drivers aren't likely to be putting the same kind of energy into the structure as a dedicated big HE woofer, so if it's that or no speaker, I know what I'd be doing.
If possible, laminate the panels to 1 1/8in - 1 1/4in thick, which will at least push OA panel stiffness to something ~ equivalent to 3/4in of a quality void free plywood (although at considerably higher mass) so some of the gains are offset. Still worth it if possible.
The truth is MDF is not ideal for bass cabinets but it's also a heck of a lot better than nothing at all, especially since wideband drivers aren't likely to be putting the same kind of energy into the structure as a dedicated big HE woofer, so if it's that or no speaker, I know what I'd be doing.
For those of us that don't have the time and tools to create an intricate, interlocking bracing scheme, the easiest, cheapest IME is to increase panel thickness to get an average 1/2" thick MDF's ~527k psi MOE up to a ~ 3/4" thick no void [BB, apple, marine, etc.] plywood's ~1.8 mil psi MOE, i.e. gluing on a 1/2" thick MDF 'skin'.
Actual build would normally be to affix the 1/2" thick panels to the inside and size them to be ~71% of the inside area, leaving a ~uniform gap since corners already are high tension ['hot spots'] and much better to use glue blocks in lieu of screws.
You can also leave a gap where the driver mounts to create a simple chamfer, allowing the driver to 'breathe' without having to router out a >45 deg taper in a 1-1/4" thick baffle.
If any bracing is required with the no void plywood, then so will the MDF.
In one way this construction is superior to the plywood in that its extra weight will give it much more mass loading.
GM
Actual build would normally be to affix the 1/2" thick panels to the inside and size them to be ~71% of the inside area, leaving a ~uniform gap since corners already are high tension ['hot spots'] and much better to use glue blocks in lieu of screws.
You can also leave a gap where the driver mounts to create a simple chamfer, allowing the driver to 'breathe' without having to router out a >45 deg taper in a 1-1/4" thick baffle.
If any bracing is required with the no void plywood, then so will the MDF.
In one way this construction is superior to the plywood in that its extra weight will give it much more mass loading.
GM
To be honest when mdf came along it looked like the ideal panel. Smooth faces no voids easy to mill...and heavy. We wanted heavy. Then the down sides became apparent. It still has its uses, but not for some of us with way too much exposure to the dust already, and there's the heaviness issue.
I thot about this for awhile… anything i could think of is more expensive in the end than just using good plywood (and a couple of the responses take a cost out of your back).
Before i discovered plywood i used HDF (15mm IIRC, imagine a sheet of 18mm MDF squished together until its 15mm) and then laminated both sides with plastic laminate (ie arborite, forminca…) and then brace heavily.
dave
Hi Mike David Sundby here in Ft. Collins . I visited you a few years ago and heard your
wonderful Continuums. I proto'ed a pr. of mets with dual el70s. I never did finish them as
I thought the bass very excessive and the treble nonexistent. I had the cabs cnc'd of 18 mm. plywood and only had the inner brace extend down halfways. This probably contributed to the bass as the lower cab was singing along.
my contribution is to leave the inner brace shy of the driver and use a giant screw in the
brace so one can fit the driver tightly against the brace without over tightening. Very fine adjustment is now possible.
If you make these out of mdf they are going to be a ton. I would use a full length brace
with LOTS of holes to lighten it and damp the panels with Frostking duct insulation
(foil backed from Home Depot). And stuff the hell out of the cabinets. Maybe in this way you will not get too much bass. hopefully they are for a very large room. Perhaps tuning the cabs with a longer port would diminish the incredible bass augmentation of this design. Maybe an amp with lots of damping would be in order.
everything comes down to a best guess. good luck and keep us posted.
wonderful Continuums. I proto'ed a pr. of mets with dual el70s. I never did finish them as
I thought the bass very excessive and the treble nonexistent. I had the cabs cnc'd of 18 mm. plywood and only had the inner brace extend down halfways. This probably contributed to the bass as the lower cab was singing along.
my contribution is to leave the inner brace shy of the driver and use a giant screw in the
brace so one can fit the driver tightly against the brace without over tightening. Very fine adjustment is now possible.
If you make these out of mdf they are going to be a ton. I would use a full length brace
with LOTS of holes to lighten it and damp the panels with Frostking duct insulation
(foil backed from Home Depot). And stuff the hell out of the cabinets. Maybe in this way you will not get too much bass. hopefully they are for a very large room. Perhaps tuning the cabs with a longer port would diminish the incredible bass augmentation of this design. Maybe an amp with lots of damping would be in order.
everything comes down to a best guess. good luck and keep us posted.
I have a fellow that has built at least 5 pair (with Pluvia 7 after the EL70 became NLA). Friends kept coming over, borrowing then and refusing to give them back. The amount of bass is easily adjustable with the amount of damping used… best done in room, with the amp being used. Too much bass will almost always lead to the perception that the top is MIA.
Even more so if you consider that a better box can be built with 15mm quality plywood than can be out of ¾” MDF (19.05mm).
dave
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