Fonken-- my 4th build

[Jim Shearer]

OK, I guess it’s time for me to start reporting on my Fonken build. I work so slowly that I hesitate to say anything until I’ve made significant progress. For the benefit of newbies or those who need a little encouragement to get started, I will pontificate at length on some details. If the experienced builders have suggestions for improvements, by all means, chime in. Just remember that this is an approach for one who doesn’t have a wood working shop & can’t afford one.

What is a Fonken? A small near aperiodic cabinet with a Fostex FE127e driver designed by Dave Dlugos (Planet10-HiFi.) See:
http://www.planet10-hifi.com/fonken.html

The Fonken is my fourth build. I had originally planned to get at least one more under my belt before starting in on the small (but somewhat fussy) project. Build number 3, a Triska sub, didn’t fill the slot I intended: the XO in the plate amp doesn’t cross as low as it says; as a result, it doesn’t blend well w/ my FE108eSigma Metronomes. Hopefully, it will match the more bass challenged Fonkens. (If not, then I’ll need a better plate amp.)

For those who haven’t tried building yet, let me set the stage w/ a few bits of wisdom that the old timers may forget to say (‘cause it’s second nature to them so they don’t think about it anymore.)

1) Trust NO ONE, not even yourself! Maybe the old timers don’t need this, but making full size drawings and triple checking every measurement reduces my error rate. :thmbsp:

2) That sheet of plywood may be premium quality, but it isn’t square. :scratch2:

3) Plan the work, then work the plan. Once you start pouring glue, it’s too late to rethink what you’re doing. :nono:

4) In the end, the only way to be sure you never make a mistake is to do nothing! When you do mess up, chalk it up as a learning experience--however painful that may be. :tears:

I found that I can buy Baltic Birch ply at the Curtis Lumber. At Home Depot and Lowes they had no clue what I was talking about. At the time I was looking to buy materials for the Fonkens, I couldn’t find any good ply at either HD or L. What they did have was either too warped or too beaten up. So I went to Curtis. They don’t have BB in the store, but can get it from their warehouse.

The BB I got is flat & in good condition, but the edges tend to chip out or fray, no matter what I use to cut it. So after I get the Fonkens tuned to my satisfaction, I plan to take them apart again and veneer them in red oak--which will match the stands I built for them.

End Part 1.

 

[Jim Shearer]

Part 2:

Having planned the work, including full size drawings, it’s time to make saw dust!

My table saw is too small for me to cut a full sheet of ply, so I use a guide and circular saw to cut the 5x5 sheet into slightly over-width strips. Then get the fence set on the table saw and cut those strips to precise width. Don’t change the fence until all pieces of a given width are cut!

Now cut the strips into appropriate size making sure that you get them square. If you don’t have the benefit of a table saw or need to make odd shaped pieces (like for a Metronome) you can make one piece as close to perfect as you can, then use a router with pattern follower or flush trim bit to replicate it. And keep the flush trim bit handy for later! A router is great for cutting holes, but it’s the flush trim bit that makes it indispensable to me.

I apply finish to all surfaces, inside and out, with the exception of areas which will be glued. I was quite sure that wood glue doesn’t hold on finished surfaces, but I did try it just to be certain I wasn’t ‘missing out’ on sealing glued areas. Yes, I was able to break apart pieces finished with polyurethane and then glued with wood glue.

One reason I am so slow in assembling is that I am applying stain/finish to surfaces before gluing, so that excess glue will wipe off easily. Prior experience tells me that no matter how hard I try, if glue gets on a fresh wood surface, I can’t clean it off well enough to get it to stain properly.

 

[Jim Shearer]

Part 3:

The difficult part of the Fonken is building the ports in the side panels. After cutting the exterior and interior pieces of plywood, I applied finish to one side of each piece.

Then I found some 3/8” birch for the port spacers. I cut the 3/8” birch into strips 0.996” wide (as close to 1” as I could get, as measured with a vernier caliper.) Next cut the strips to length, adding an extra 1/32” so they are just slightly long.

Find a scrap piece of the BB ply and clamp it onto the rear of the outer side piece where the back panel will be when you finish. Take a couple other small scrap pieces and cut them to 3” wide (port width,) mine ended up 3.020”.

Lay the outer side piece against a flat, vertical surface (like the fence on a table saw.) Now apply glue to the first of the 3/8” strips and place it onto the side piece using the BB ply piece and the fence (or whatever) to insure correct positioning. I used 1/2” wire nails (brads) to hold the strip in place, making sure that the brads are not within the area to be cut by the corner bevel (critically important!)

Using the 3” spacers, glue the next strip in place and nail it. repeat twice more. Now wipe off excess glue and ‘clamp’ with a flat board and weights. The bottom strip was about 0.06” beyond the edge of the ply, so I trimmed it off with the router and flush trim bit.

Apply finish to the interior surfaces of the ports--both sides. Use masking tape to protect the surfaces which will be glued. Photo below shows the two pieces which will make-up the port assembly.

To make sure the interior side piece attaches to the exterior side (with port spacers) correctly, I used dowel pegs. Lay the top of the exterior piece against the table saw fence. Place the interior side piece onto the port spacers in proper registration. Use masking tape to mark the 1/4” drill bit so you can go in slightly more than 1” but know when to stop! (see photo below.) Drill two holes (one top, one bottom) for the dowel pegs in the side pieces (making sure you avoid hitting the wire nails in the port spacers.) Clean wood chips from the holes.

Apply glue to the port spacers. I used a small paint brush to spread a thin layer of glue over their entire surface--insuring full coverage with minimal excess. Place the interior part onto the assembly, apply glue to dowel pegs, and pound in dowel pegs. Wipe off excess glue. I used a stiff bristled artist’s brush with a long handle to remove/smooth the excess glue inside the ports. Clamp with flat board and weights.

Apply finish to the bits of port spacer extending to the back panel and to the interior edge of the plywood.

Use the flush trim bit on the router to insure that the front edges of the assembly are flat/square and the excess length of port spacers is removed on the front.

Final photo shows parts ready to begin glue up.

 

[gmilitano]

What is a Fonken? A small near aperiodic cabinet with a Fostex FE127e driver

I don't think it is a near aperiodic cabinet. Here is some info on Aperiodic Speaker Cabinets.

 

[Jim Shearer]

I'll let you argue the semantics w/ Dave. His design, his description.

BTW- For anyone interested, the name Fonken comes from a contraction of Fostex and Onken.

Cheers, Jim

 

[chasaboo]

Hey Jim, thanks for posting and nice pics. I built a pair of the mFonkens awhile ago and they're amazing. :thmbsp:

 

[Jim Shearer]

Glad to hear you like the mFonkens. Haven't heard many comments on them yet. Do you use a sub with them? If so what do you set the XO at and how do they blend?

Maybe I should consider using some of my excess 12mm BB ply for a pair of microFonkens. Then I could get rid of the cheapie speakers I have on one of my computers. The price is right! :yes:

 

[Jim Shearer]

Part 4: How to assemble W/O clamps

I don’t own furniture clamps--can’t justify the cost for the little I would use them. (If I bought the clamps, then I wouldn’t have the money to build anything with them!)

Most of the time I use screws. Sometimes I use dowel pegs. But the Fonken is made w/ 1/2” ply, which seems to me too thin for screws or pegs to go in edge-wise.

I finally settled on nails in a temporary mode. First I drilled 1/16” holes diagonally through the corners of the front baffle and one side assembly. Set these onto the bottom piece and extend the holes from the front & side into the bottom. Add another hole from the top of the front into the side. A sharp, new drill bit is essential here. Insert 1.5” long 17 gauge wire brads to insure proper fit-up. Don’t pound them in! Just slip them in w/ fingers, leaving a generous amount for pliers to grip when you remove them.

Now glue the front baffle onto the bottom, locking it in place w/ the wire brads. Glue up the side and fasten w/ brads. When the glue is dry, pull out the wire brads with pliers.

My next step was to glue in the 1/2” x 1/2” strips for extra hold along the bottom of the back. Then add the driver brace. Next come the other side assembly and the back. And finally, the top.

You may find it easier/better to assemble in another order (or a whole other way,) but this is how I plan to do it.

I should have mentioned that the lining needs to go on the parts prior to assembly. I decided to use 1/2" acoustic foam from Parts Express (p/n 260-520.) I have used this foam previously with good results; and haven't found any wool felt locally.

Photo below shows the driver brace installed with its fuzzy coating: 1/4" poly batting on each side. We'll see if this works as well as the recommended 1/2" of felt on one side. You can also see that this time I used a wood joiner to hold the brace for glue up rather than a wire brad.

 

[Jim Shearer]

Part 5:

Don’t forget to check the fit of the driver to the brace before installing the second side!

I found that the separation between the back of the driver and the brace increased slightly with the glue added. When doing the dry fit up, I found that a thin piece of cotton fabric was the right thickness for correct contact--firm contact, but no great stress. After glue up, I’m using a piece of slightly thinned poly batting.

 

[vinylkid58]

Maybe I should consider using some of my excess 12mm BB ply for a pair of microFonkens. Then I could get rid of the cheapie speakers I have on one of my computers. The price is right! :yes:

They work very well for computer duty, even without a sub. I would build a pair if I didn't already have a pair of FE127's that need a new home. Coincidently, the 127's were my first Fonken driver.

Jeff

 

[karlo]

anyone ever compare these to the Frazier super midget speakers ,of similar
design (helmholz) ?

 

[Jim Shearer]

Part 6:

With all the sides on, it’s time to make final adjustments before gluing on the tops. First photo below shows the labor intensive process of tiny adjustments with wood file and sand paper, trying to get the fit as good as I possibly can. Good joints are essential if the cabinet is to reach its full potential!

After several hours of fiddling around (including adding poly batting down the center covering holes in brace,) I poured the glue. I use a cheap paint brush to get the glue spread over the entire joint surface.

Here’s what I’m talkin’ about! (See photo of joint.) Not all the joints come out this good, but this is the goal. :yes:


As I worked on the Fonkens, the FE108eSigma Metronomes were playing Diana Krall’s Live in Paris. In front of the Mets are Fostex F120A’s which I’m breaking in for next year’s build(s).

Do I see light at the end of the tunnel? :scratch2:

 

[Jim Shearer]

Part 7:

With the tops glued on, I used the router with flush trim bit to clean off the edges.

Time to cut the 45 degree chamfer on the ports!
To keep the sawdust out of the cabinet, I covered the driver & binding post holes and stuffed pieces of foam into the ports (being sure to get them in far enough that they won’t get caught by the saw blade.) The foam will be removed later with fine pointed forceps (tweezers.)

Note: for improved WAF, I want to mount the drivers diagonally, i.e. so that they look like a diamond shape, rather than a square. If I make a 45 degree cut, the front baffle will be just a little too narrow to accommodate this arrangement. So, I changed the angle by 5 degrees. This is the sort of detail which is easily worked out with the full sized drawings I spoke of earlier.

I was worried that my little 3 HP Sears table saw might not be up to the task of cutting the chamfer, but by going slowly, it made it--although there was a distinct aroma of burned wood. I did hold a piece of scrape wood on the end so that when the saw blade emerged it wouldn’t shred the top or bottom surface of the cabinet (too badly.) The ports did suffer some chip out, but what can you do?

Next up will be patching the chipped out areas, sanding, and another coat of finish. (The exposed ply edges are still bare.)

Then I can install drivers and proceed to sound tests.

And when all is good sonically, then I will take them apart again and veneer the cabinets.

 

[Jim Shearer]

Part 8:

The finish is now ready for veneering. I filled & sanded to cover the chip out, then gave the cabinets another complete coating of polyurethane, so all edges are sealed. This is important not only for cabinet stability and sound, but also because I use peel & stick veneer, which won’t bond properly with bare wood.

But before veneering, it’s time for ‘first sound’ to check the cabinets, and decide on BSC (baffle step correction.) So I installed the drivers, binding posts, and wiring. First photo below shows the drivers going in. I used washers (Nylon in this case) between the driver and the cabinet to prevent stressing (bending) the driver basket. I think this idea came from Bob Brines; (correct me if I’m wrong guys.)

Here they are, ready to go on the oak stands I already built. (photo 2) I’m using a Toshiba SD-3980 DVD/CD player and a classic (1972) Sansui 4000 receiver. Wire is 16 gauge lamp cord.

The drivers only have 45 hours on them, but the sound is pretty good. I’m hearing nice mids, decent bass extension, and a rising high end. Probably will want to use 2-3 dB of BSC. The Fonkens are providing more bass than I expected. Time to get out the RS SPL meter and Stereophile Test CD. Graph below shows what I measured at my listening position. The bump at 80 Hz and the sag below it are room effects. WOW! Response down to 40 Hz. How did that happen? I thought Fonkens were supposed to run out of gas around 80-90 Hz.