Pretty Persuasions - InDIY Coax Build Thread

[JavadS]

Javad, I have never done kerfing, but plan to do so soon. Could you post the link to the online calculator you mentioned? Also, you mentioned you only used it to get into the right ballpark, how was it overall... Did it get you pretty close to where you needed to be or were your manual refinements pretty significant?

You bet see https://www.blocklayer.com/kerf-spacingeng.aspx I’m confident the Calculator is Accurate mathematically, the trick in real life is to get all the dimensions to match the Calculator exactly, which is why doing some test cuts and getting a set up Locked in then will allow you to make that particular set up accurate until you have to do it again later. I’d recommend getting oout in theshop and doing some testing, you’ll get a great feel for what works and what doesn’t after a little bit

[a4eaudio]

Javad, I have never done kerfing, but plan to do so soon. Could you post the link to the online calculator you mentioned? Also, you mentioned you only used it to get into the right ballpark, how was it overall... Did it get you pretty close to where you needed to be or were your manual refinements pretty significant?

[JavadS]

Tom thanks for the comments and thoughts! You think like I do, sequentially from one issue to another as they relate to each other.

I think like this for weeks leading up to a project and all through it testing ideas in my head before I ever actually try them.

There is some Faceting but it’s very light and it is sandable, so Poplar is really an ideal material here and performed much better than plywood and MDF during my tests. MDF is very weak too when it’s thin (corners too) so I’d use it very carefully.

Yes I’’ve thought that a pointed blade would be amazing for kerfing but haven’t seen one on the market, a blade that formed an angle would be great as it would allow the kerfs to miter together which would also be stronger.

You’’ll notice the shape of this speaker closely resembles my Strafi speaker so this is another experiment in creating a speaker baffle with a generous roundover (3”” radius).

Thanks for the conversation Tom!
Javad

[tomzarbo]

Hey Javad,

Nice work so far, I enjoy watching your progress as you go along.

I have a question on the kerf cuts. I've done a few of these in the past and have had issues with what has since been called "Faceting," or flat spots (similar to the facets on a jewel) showing up on the areas which have not been cut. These are amplified when a glossy finish is applied.

I don't see any on your project, and was wondering how you avoided it? My father tells me of a "Kerfing" saw blade he saw a woodworker use when he was young.....which was tapered so that the tip of the blade was more narrow in width, getting thicker, farther away from the cutting edge... designed specifically for doing just this. I stopped using this technique for curves, so I never looked further into it.

I've done a few things with kerf cuts in MDF, and if you just bump one of those little strips of wood the MDF just flakes apart, basically making it no better in those areas than 1/16" MDF, which isn't going to be very strong as we know. I'm sure solid wood performs much better in that regard.

It seems to me that since you are using solid wood, you could do a light sanding to 'round' the curve to perfect anyway if there was any slight faceting going on. Now that I'm thinking about it, the fact that your curve is perpendicular to the grain is really giving it some resistance to keep the curve rounded and not crease on the corner of the cut. Trying to bend what looks like about 3/32's of an inch of poplar against the grain would probably be hard to do without cracking it if it were not for the fact that the 'backer' pieces are keeping things held together. Sorry, just thinking out loud here...

Also, It's nice that the construction adhesive you used actually provided enough strength to keep the "C" shape in tact without any other support. That's gotta give you a nice feeling that it's going to help strengthen things up.

Anyway, basically what I'm trying to say is.... it looks fantastic so far. I'm a big fan of using real wood, though I almost never do!

Happy new year!
TomZ

[hardcorecap]

amazingly gorgeous build. nice job.

[JavadS]

I tested several adhesives to glue the kerfs including media filled epoxy (was overkill and messy to work with), wood glue(too runny) and Loctite construction adhesive which I ended up using. It was thick and didn’t run, squeezed nicely into the voids to support the “veneer surface”, and had great adhesive strength.

Since the cabinet would be heavily braced, ultimately there will be very little load on the kerfs, I think even with proper construction you wouldn’t even have to glue the kerfs, the bracing and ribs of the enclosure will hold everything to shape. It’s also interesting to note how much spring pressure there is on a kerf like this, it takes substantial pressure the bottom out the kerfs and hold the shape so really gluing is a great idea.









I built some spacer blocks to set the final width out of MDF, and used a combination of straps and bar clamps to hold everything while the glue dried for about three days. After 3 days the clamps essentially fell off and all the spring load of the kerfs was gone, a good sign.





While the glue was drying I decided to work on the midrange sub-enclosure, I used a technique I’ve done before in my Rally Sports and also the 135Hz horn, the reverse horn, The idea being to reduce the number of parallel surfaces and allow the backwave to diffract and be absorbed better than in a simply square or rectangle or enclosure.

An easy way to build one is to cut your parallel top and bottom angles on the tablesaw, for this I chose about 20°, then create a fixture to hold the piece at that angle in the radial chopsaw, and in this case I cut 45° angles to create a three-dimensional trapezoid or a four sided pyramid.





Each time a cut is made the board is flipped and cut the other way



And this is easily glued together with tape







I wanted to add a little more volume and depth so I created a small riser block of 1.5 inches high





To finish it off I added another small deflector at the bottom flat part of the enclosure, just to interact with any higher frequencies





Since my back panels now had angles, I wanted to the square them to each other so I can simply add a back without having to cut any fancy angles. For this I used my handy new cross cut sled that I built, and simply fixtured each enclosure on the sled and easily made the cuts.





Gluing up more panels for the back top and bottom of enclosure



Next up I’ll document the bracing.
Thanks!
Javad

[4thtry]

That is one cool looking kerf corner. Good luck with the glue up and finishing process.

[Millstonemike]

Convinced me

[scottvalentin]

Excellent - has been too long since a JavadS build thread!!! Thanks for sharing, looking forward to following along.

[Derekj]

Looking forward to more!

[JavadS]

Fabulous! Love the concept. I'm also very curious to hear your impressions of those MCM woofers.

Thanks for following along Tom! Yes will do, seems like a very nice unit at a rock bottom price.

[tom_s]

Fabulous! Love the concept. I'm also very curious to hear your impressions of those MCM woofers.

[JavadS]

Ok time for a new build thread!

I’’ve been planning my “Keeping up with the Jonzes” build for some time and am finally getting splinters from it!

So let’s start with the name, it’s a “coaxial” driver build, or coax, to coax is to be persuasive, these cabinets will be very beautiful and one of my favorite bands R.E.M. have a song called “Pretty Persuasion”. Marketing had a fit over it, they said it was too convoluted so I fired them all and now it’s just me in my garage doing what I want. Makes sense? Alright!

Cost of drivers per cabinet must be under $300 and there are a few other rules as well, check the official thread.

My choice of drivers are the FaitalPro 6HX150 coax ($179 was from online source) combined with the MCM Audio Select 55-5670 8” woofer ($40 each). These model well together and the 8” will have strong response down to 30hz ported and is efficient enough to keep up with the very efficient Faital.







Crossover will be passive as the contest dictates. Mainly I’m going to be focusing on the enclosure construction for the next few posts.

If you’ve been following along my projects over the last year or two, you’ll notice I’m constantly experimenting with new enclosure designs, construction and styles, this project will be no different as I’ll be diving into the world of Kerfing which I’ve never done before.

When I interact with a concept I usually like to do something special with it or something I haven’t seen too much before, and this time I’ll be kerfing solid popular to create a one piece baffle, the enclosure will look veneered but in reality it will be solid wood which I find special/notable.

I did a fair amount of testing initially, but this is a piece I did successfully with poplar, my goal here was to determine the optimal kerf depth so that the wood would bend without breaking





This is another test piece, this was more representative of the actual speaker ID building, however it was with plywood, but it gave me an idea of the curve depth with and spacing and what radius curve it would generate. I used an online calculator to get me in the ballpark, then I fine-tuned using this type of experimentation





This is the wood I’ll actually be using For the speakers, as you can see I found two boards so that the grain will be continuous from one speaker to the other from left to right, as you can see the boards are matched across both speakers. This is very beautiful Poplar heart wood.





Cutting the boards to their rough final length, the length is determined by the baffle width, the circumference of the radiuses, and the lengths of the sides.



To create the height of the speaker, these boards were glued together and reinforced with biscuits











The glue up,I used Titebond type III which sets up a little slower in case I want work on the alignment, noticed the clamping techniques ensuring the boards are tight against the clamp bars Once the glue dried after about 45 minutes, I square one end in my panel saw, them the whole panel in the table saw, I have this set up to cut perfectly square and it does a great job





Getting ready to cut the kerfs, this is a little fixture I built to reference the fence and allow for subsequent fence movements when Kerfing



After the first cut is made, each subsequent cut is spaced 5/16 of an inch using this drillbit, then the next cut is made. Stop block is slid over to the fence and then it’s once again space with the drill bit



And so it goes. The kerfs are all the same distance from each end which locks in the baffle width which will be about 12 inches wide. Kerf depth results in about 1/16” material left.





First board curved and cut, final angle is about 95° which is intentional to gives the sides some rake





Both curves done on both sides, again the middle piece is the baffle and the end pieces are the sides



I created some spacer boards to go in the back to lock in the final dimensions, there will be three for each glue up



Here you can see how perpendicular the assembly is, with some like clapping it’s sits perfectly flat on my workbench



Next up some glue!

Thanks!
Javad