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Frugel-Horn Mk3 Flat-Pak Mock Assembly Instructions

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Note: 15-july-2018.
With Chris’ retirement we no longer have access to the shop, so barring some new, different arrangements we are suspending flat-pk manufacture.

I do have some stock of small flat-paks.

This assembly will serve as a generic frugel-horn assembly guide.


[december 26 2011 -- subthread copied into its own thread here]

Flat-paks include precut cabinet panels of 15mm utility grade baltic birch, with an 18mm baffle Baltic Birch plywood (rebated and dadoed for easy assembly). drivers (optional, 10% discount if bought with flat-pak), terminals (5-way posts, 2" hole, good for sonics, tight for fat fingers, damping, wire (24g copper (from CAT5 cable)) for a pair of speakers. You will need to provide glue, screwdriver, soldering iron, drill & need to finish them. Clamps are useful & recommended, but a slow methodical assembly can usually be done with tape (masking usually -- anything that leaves a residue should be avoided)

Standard rebates for Fostex FE126 (FE127 & FF125wk) Mark Audio CHR/CHP/EL70, Alpair 7.x (with & without decorative bezel), or blank. One went out for FE108eS so that can be ordered. Others, we'll try (really helps to have a driver on hand to do it).


Related Downloads

Chris came up with a clever way to deal with the choke point.

1/ the rebated side with the choke point
2/ fitting the back
3/ back & internal divider in place

Note: the fitment here ranges from tight to really tight depending on actual panel material thickness, If real tight just take it slow & steady

4/ the extra little bit to provide more glue surface and proper spacing
5/ clamped up for the 1st "wait for the glue to dry".

Note: it is very hard to install these and not have them perpendicular, but you should check anyway.


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Addendum: despite somewhere, somewhen recently posting that it was hard to precision CNC BB, be very careful handling the pieces. Corners are sharp enuff to cut (i had all sorts of nicks after we did pre-pack bundling on the kits... and if you get a sliver, you will be screaming.

Addendum 2: in the pictures in the previous post, you;ll see numbers on the pieces in some of the pictures. These were to keep track of pieces to try to get the best matches for surface character

Attached is a stack of paks (3 had already been taken away, and 2 sets of sides are still embedded in the sheets of plywood -- haven't been CNCed yet)


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a couple of notes, probably to be included in the "full documentation set", but several kit builders could be finished before that happens:

The plywood is machined by CNC, and contrary to opinions expressed elsewhere, the edges can be as sharp as those on similarly machined MDF - as Dave if you can cut yourself -with the added benefit of some slivering on long or obliquely cross-grain directions. Some of those little buggers can be very thin, short and hard to find.

We've found a great nitrile glove that reduces this problem quite a bit. They are thin enough to permit dexterous handling, and are also much more durable than thin latex exam gloves when applying solvent based stains and finishes.


Widely available - Home Depot, KMS Tools (Canada) and probably most major auto parts suppliers.

next turorial post >
Top, baffle & bottom put into place (in that order). The baffle is the longest piece in the kit, and some of them may have a bit of a bow. Masking tape should be sufficient to pull everything into place and hold it till the glue drys. You don't need much pressure. (do not use packing tape, the glue on it sticks to the ply after the tape is removed, and is a bitch to get off)

If the baffle bows out at the middle a clamp may be helpful.

Don't forget to check with the square. Leave to dry.


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All the panels now in place, time for the damping.

All the felt pieces have been rough cut. Width will need checking, and you'll need to cut out the sides. I posted a full size template earlier in this thread, but you probably want to double check against your install. Make sure that the sides are mirror images (if you forget it is easy enuff to peel off the black backing) The felt can be fixed in place with glue or hot melt. The black backing on the cotton felt makes this a cinch.

Back 1st, then the divider panel (if you haven't done it earlier). then one side. Now the fluff -- tease it very well. The sandwich bag of fluff should get to be a BIG pile once teased. Consult the damping plan.

(Note: the fluff we used to illustrate placement is not well teased and or of a quality that makes it actually useable)

The pointy part of the line gets one of the 30g packages. You are trying to distribute equal amounts along the length. Since it is pointy at the bottom this means a decreasing density as you approach the fold.

For FE126 you should be good (there is an extra 40g of fluff if you need to fine tune)

For the Mark Audio drivers there is a 40g bag of fluff for the wider part of the line below the driver. This part tunes the amount of bass. If you want big fat rounded bass you can start with none. Using all of it will give a full halfd-pound per cubic foot. You may want to do something to keep the fluff here from drifting to the bottom of the cab. Door screen mesh, a couple long screws sticking out, a piece of low thread count cotton or other acoustically transparent material like double knit, the hook side of some velcro on the walls.

It is easier to start light and insert more thru the driver cutout than reach in and pull it out.

Now it is time to install the other felt side. Just float it on top of the fluff, making sure it is clear of any of the gluing surfaces. After the other side is solid you can reach in and make sure it is solid against the side. A couple spots of glue should do to hold it in place.

Tweaking of damping fluff can be done thru the driver hole, add or subtract from the back top or under the driver. Low density amounts can be placed right behind the driver.


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The other side.

It should drop right into place with the internal bits tight up against the dadoes on the side.

Some clamps are useful here (use some sort of clamping aid to distribute the force and protect the sides -- we used 2x4s in the picture) Alternately, masking tape and the big pile of weights, books, 4 litre plastic milk bottles full of water.

Chris: comments, corrections, suggestions?

Did i mention you want to use yellow carpenter's glue?


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Chris's comments would include

Some clamps or weights during the first assembly stage - i.e. before damping padding - ( or even braid nails), wouldn't hurt

White glue ( Weldbond, etc) is great for attaching the Ultra touch insulation, but I'd recommend yellow carpenter's or polyurethane (Gorilla, etc) for the panels

Note that moisture cured polyurethane glues requires substantially longer curing time, and can definitely swell exterior panels out of alignment- so clamping is required - and it will stain, so if your finishing plans are for clear coat, I'd suggest yellow glue and masking/pre-finishing of interior faces of side panels before glue up

/end tutorial
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