Speaker Cabinet Joinery

[TheWarrior]

I doubt many of you are familiar with the german power tool company Festool, or their Domino joining system. But the concept is a much stronger wood tenon connection between one butt end of a board to another.

My question is are there any negatives to using 'biscuit style' joinery with speaker cabinet construction? It seems most DIY cabs are just glued ends, sometimes with a channel routed for a tighter fit. This seems like a much more rigid construction option.

What say you Audioholics?

 

[TLS Guy]

I doubt many of you are familiar with the german power tool company Festool, or their Domino joining system. But the concept is a much stronger wood tenon connection between one butt end of a board to another.

My question is are there any negatives to using 'biscuit style' joinery with speaker cabinet construction? It seems most DIY cabs are just glued ends, sometimes with a channel routed for a tighter fit. This seems like a much more rigid construction option.

What say you Audioholics?

Butt joints are bad joints and in my view should not be used for speaker construction. Unfortunately that us what you usually see on this site. I use dado joints.

 

[TheWarrior]

Yes that channel would provide a good snug fit for the back to the sides, (which I might do an exposed domino to really lock it in) but for the front baffle, would that not create an incredibly solid joint that the front baffle would benefit from, given its duties of projecting sound? Or do you promote removable baffles?

And I'm glad you chimed in, a second question would be related to TL's. Using the Thor design, how rigid should the line itself be? Would you Dado channels on each side wall for it as well?

Oh, and no I did not buy Festool so I can build the Thor. My health has not been the best this year so my construction plans for next year are on hold, so to make money I am starting a little garage based cabinet shop over the winter.

 

[Swerd]

I doubt many of you are familiar with the german power tool company Festool, or their Domino joining system. But the concept is a much stronger wood tenon connection between one butt end of a board to another.

My question is are there any negatives to using 'biscuit style' joinery with speaker cabinet construction? It seems most DIY cabs are just glued ends, sometimes with a channel routed for a tighter fit. This seems like a much more rigid construction option.

Biscuit joinery is a big improvement over butt joints in speaker cabinets. I don't see any negatives other than the requirement for another specialized tool. I have a Porter Cable biscuit cutter and have used it successfully in smaller speaker cabinets.

For a larger cabinet, such as a floor stander, rigid construction becomes more important than in smaller cabinets. I would use dado joints on the interior divider/braces of the TL.

 

[TLS Guy]

Yes that channel would provide a good snug fit for the back to the sides, (which I might do an exposed domino to really lock it in) but for the front baffle, would that not create an incredibly solid joint that the front baffle would benefit from, given its duties of projecting sound? Or do you promote removable baffles?

And I'm glad you chimed in, a second question would be related to TL's. Using the Thor design, how rigid should the line itself be? Would you Dado channels on each side wall for it as well?

Oh, and no I did not buy Festool so I can build the Thor. My health has not been the best this year so my construction plans for next year are on hold, so to make money I am starting a little garage based cabinet shop over the winter.

Yes, all boards are grooved including the internals.

 

[TheWarrior]

Thanks! What do you think about mounting the baffle? It seems that routing a channel in the baffle would not be good for sound quality, and it should be butt jointed and secured with domino's/biscuits/hurricane screws only.

And I really want to clarify: the mdf 'line' itself, the board mounted on the interior of the cabinet behind the drivers, should be mounted as rigidly as possible? I question it only because its job is to vibrate. Is it like a reed on a saxophone, or is it taut like a snare drum?

 

[TheWarrior]

Ah TLS we posted at the same time. So even the front baffle should be routed/dado'd/grooved?

 

[TLS Guy]

Ah TLS we posted at the same time. So even the front baffle should be routed/dado'd/grooved?

I use two boards for the front panel glued and clamped together, and yes, it is a dado joint, but the inside board fits all the way inside the opening. So the outer board is 3/4" larger in both dimensions.

 

[Swerd]

Thanks! What do you think about mounting the baffle? It seems that routing a channel in the baffle would not be good for sound quality, and it should be butt jointed and secured with domino's/biscuits/hurricane screws only.

Yes, the front baffle should be routed/dado'd/grooved or biscuited. I don't understand why you say that routing a channel in the front baffle would not be good.

And I really want to clarify: the mdf 'line' itself, the board mounted on the interior of the cabinet behind the drivers, should be mounted as rigidly as possible? I question it only because its job is to vibrate. Is it like a reed on a saxophone, or is it taut like a snare drum?

No, the interior divider of a TL cabinet (the mdf 'line' as you call it) must be rigid. The same for all the interior and exterior panels of the cabinet.

The air inside the TL is meant to vibrate, not any of the panels. An acoustic transmission line is a column of air long enough to vibrate at the intended bass frequencies. The length of that line is ¼ wavelength of the bass tuning frequency. Its easy for that length to become awkwardly large, so the air column is often folded over inside the cabinet to achieve the intended length in a smaller cabinet. The mdf 'line' is there to create such a fold.

 

[TheWarrior]

Ohhhhhh. Yeah thats a good idea! Ok, I know you made the Thor previously, what thickness would you make the front baffle? But in having the front baffle extend to the interior of the speaker cabinet, would I need to change the side wall dimensions so that the line is the correct distance from the baffle?

 

[TheWarrior]

Yes, the front baffle should be routed/dado'd/grooved or biscuited. I don't understand why you say that routing a channel in the front baffle would not be good.

It could be my bad memory, but I recall reading information about the baffle needing to be one solid piece, so that itself vibrates/resonates correctly. I believe it went so far as to explain the benefit of round overs or chamfering the interior route for the drivers, as well as the outside edge of the baffle.

No, the interior divider of a TL cabinet (the mdf 'line' as you call it) must be rigid. The same for all the interior and exterior panels of the cabinet.

The air inside the TL is meant to vibrate, not any of the panels. An acoustic transmission line is a column of air long enough to vibrate at the intended bass frequencies. The length of that line is ¼ wavelength of the bass tuning frequency. Its easy for that length to become awkwardly large, so the air column is often folded over inside the cabinet to achieve the intended length in a smaller cabinet. The mdf 'line' is there to create such a fold.

That was the best explanation of the science behind a TL I have read so far. Thank you!

 

[Swerd]

Ohhhhhh. Yeah thats a good idea! Ok, I know you made the Thor previously, what thickness would you make the front baffle? But in having the front baffle extend to the interior of the speaker cabinet, would I need to change the side wall dimensions so that the line is the correct distance from the baffle?

A 1" thick front baffle is a good idea. You can make it by gluing two ½" thick panels as TLS described, with the outer panel larger than the inner panel, creating rabbited edges. If glued (you can use biscuits between panels) and clamped during assembly, it will as rigid as a single 1" thick panel.

Yes, with a thicker front baffle you would have to increase the side wall dimensions to achieve the interior dimensions as shown in the plans. The interior dimensions, port dimensions and location, and speaker locations are essential to keep as shown in the plans. The exterior dimensions can vary with your construction methods.

TLS built a Thor. I never did.

 

[TheWarrior]

Beautiful, thank you Swerd. That answered everything.

 

[Swerd]

Beautiful, thank you Swerd. That answered everything.

One more hint. I've tried Hurricane nuts and T nuts in the past. I hate them, especially with MDF. I've had much better results with threaded inserts like this:

Don't use this kind (they work in hardwood but not MDF or plywood):

And frankly, for those 7" drivers in the Thor, I would skip the threaded inserts and screw directly into the 1" thick front panel with #8 black pan-head screws with a coarse thread like these:

I don't have a drill press, and when I used threaded inserts, I found it difficult to drill 6 perfectly perpendicular holes for the inserts. When I drove in the bolts, the last one in never lined up correctly. With wood screws, you have a little more latitude, and they are plenty strong for a 7" woofer. I use the threaded inserts for heavy woofers bigger than 8".

Edit:
When I mount woofers or tweeters, I pre-drill holes for the screws. I would never trust myself power driving screws. One slip and you buy a new woofer. I also try to always use screws that can accept a square drive tip. Again, it's too easy to slip with a flat blade or Phillips head screw driver and punch a hole in the speaker cone.

 

[TheWarrior]

Thats a good point about using square drive screws, I've used those on my decks with great effect! But for the baffle I think I will follow the plans and just have a removable base, and mortise and tenon the baffle to sides as well as use the rabbet edge. Over built, yes, just the way I like it! And although my knowledge of TL's is limited, I definitely comprehend the need to keep interior dimensions to spec. TLS Guy and I had have had a few chats about that as well. You guys both have been a big help. I look forward to showing off my handy work whenever I can get around to it!

 

[lsiberian]

I don't know a woodworker who hasn't heard of Festool. They make great tools that I'd love to own. All my speakers use butt end joints with PL Construction Adhesive which seals the speakers very well. I've considered using hardwood corners and cutting rabbets and round overs on the boards. I simply don't have the space for it right now. Sealing the joint is more important then strength IMO. Especially if you overbuild like most of us.

 

[jinjuku]

I'm going to take a counterpoint view. You don't need extensive joinery. I cut my corners at 45's. I dado my braces for a few reasons one of them being a third hand whilst building.

Even my subs are just buttjointed and glued with bracing, back and front walls dado'd in and the overhang flush cut with a bearing guided router bit.

 

[TheWarrior]

lsiberian you make a good point about the construction adhesive, I could see applying a bead of that on the interior joints. However the need of this speaker to contain those two 7 in woofers means I want it as rock solid as possible. I also have a track saw so cutting the boards to make a rabbet will be quite easy.

And Jinjuku, if you like 45 degree angles you would LOVE this saw. My first time using it I sliced up some scrap plywood and made a box with 45 degree joints that fit together perfectly. Each cut is glue ready! And with the parallel guide I could mass produce each side panel with ease..... hmm, maybe its time to start a speaker company! Oh wait, I know carpentry, electrical engineering is still a work in progress...

 

[lsiberian]

lsiberian you make a good point about the construction adhesive, I could see applying a bead of that on the interior joints. However the need of this speaker to contain those two 7 in woofers means I want it as rock solid as possible. I also have a track saw so cutting the boards to make a rabbet will be quite easy.

And Jinjuku, if you like 45 degree angles you would LOVE this saw. My first time using it I sliced up some scrap plywood and made a box with 45 degree joints that fit together perfectly. Each cut is glue ready! And with the parallel guide I could mass produce each side panel with ease..... hmm, maybe its time to start a speaker company! Oh wait, I know carpentry, electrical engineering is still a work in progress...

Does the track saw do stacked dado blades? It's been a while since I saw the demo. I actually considered a Festool before I bought my table saw.

I went table saw for 3 reasons
1. Repeatable cuts(Measuring out repeated cuts for my straight edge circular saw combo is a pain.
2. Protect my knees. It gets tiring cutting over the top of boards.
3. Cost. My table saw cost half as much.

I didn't use the adhesive just for a bead. I used it to join the boards together and create an airtight seam. It is not an easy glue to work with, but I got a case of it on the cheap. My biggest concern was having an unseemly external gap. I already had to use it to adhere the interior panel to the peel-n-seal. It is not nearly as easy to work with as titebond.

 

[TheWarrior]

Dado is about the only thing the TS 55 and TS 75 can't do. But that is even more easily accomplished with a Festool router as it can utilize the track in the same way the saw does.

Repeatable cuts, such as rips from a 4x8 are accomplished with the Parallel Guide. Larger pieces can be cut with a jig and the track saw fixed on a Festool work table, or a DIY one with the rear bracket to lock the track on to. The track is then able to pivot vertically, so that it lifts out of the way, a new piece can be situated and then you just drop the track back down, place the saw and cut!

I think the biggest advantage over a table saw are the flawless, glue ready cuts that are made. Zero tear out, even on a bevel cut. But for me, what these tools provide are the elimination of the big stationary machines used for cabinetry as I will be switching gears this winter and will build up an inventory of kitchen cabinets to be sold online next year. So there in lies how I justified the cost. And then of course a couple speakers might get built too...

Back to construction adhesive, that makes perfect sense even more today now that I consider how porous mdf is, it would need to be sealed to use wood glue. I trust the construction adhesive eliminates this?