Frugel-Horn Mk3 Builds & Build Questions

frugal-phile™
Joined 2001
Paid Member
Driver choice is growing steadily. Everyone will have their favorite. Room/amp will also play a role.

Toppsy prefers CHP70, Chris likes FE126eN^2, i'd choose Alpair7eN. Other builds have used A7, FE126En. A7eN, FE126eN^2 are going out with flat-paks sold, and the other will house FE108eS (one of Ed's when he cleared them out :))

We have had EL70eN and CHR70eN in them. And we'll be trying FE127eN and if i can talk Jeff into it (probably not hard), his FX120eN.

You have to weigh price, room, amp, sonics and choose yourself (BTW, EL70, CHR, CHP, A7, FE126/7, FE108eS, and probably FX120 can all be installed in the same cutout if you don't do a rebate).

I have a dedicated break-in bench. Hook the drivers up naked, set the FM station to lowish volume, turn it on and come back a couple weeks later.

dave
 
frugal-phile™
Joined 2001
Paid Member
Here is my version of an 18mm cut plan for 18mm.

Designed to optimize the size of the largest offcut*, and to maintain grain pattern -- i suspect many of these will be natural BB finish.

* one chunk just slightly over 25 x 29", large enuff to make a stabalization base (shown ghosted out in blue)

I have a whole bunch of pages to add to the document, will add this & the other pages over the next day or so, and also try to get a 1st page for the website so that it can be hosted there.

dave
 

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Hello

Thanks Dave.. A couple of queries regards the drawing for the cabinet

1. The drawings suggest the front baffle can sit "on" or 'in' the cabinet, but by design which is correct ? Would a rounded edge to the front baffle be an improvement ?

2. Please confirm that the baffle is at 90 degrees to the base ?

3. For the best practice should the driver sit "in" a recess flush on the baffle front ?

4. There is no mention on the plan about the extent of flaring inside the baffle for the driver as too much would effect of rigidity of the baffle and the driver mounting.

5. Looking at the design the most critical part of the design it seems is the top left hand corner of the cabinet. Would it make more sense to dimension the drawing from that point for each material thickness ?

6. The plan infers that a dimensional accuracy of 0.1mm is called for which is going to be quite a challenge without the use of modern methods! What are the tolerance limits for the design and which are the MOST critical ?

Thanks
Miles
 
frugal-phile™
Joined 2001
Paid Member
Hello
1. The drawings suggest the front baffle can sit "on" or 'in' the cabinet, but by design which is correct ? Would a rounded edge to the front baffle be an improvement ?

Up to the builder. From a structural POV I like the baffle to overlay the sides, but Chris will usually build with it inset. with the 15mm FH3 moving the baffle to go over (at least the top and bottom), allows the entire thing to be (carefully) cut out of a single shet of 5x5 BB.

What we are doing for the flat-paks is to dado all the edges of the sides so that top, bottom, front are inset halfway thru the sides, and the baffle is in front of the top & bottom. inside panels are dadoed into one side to nsure proper placement. The other side buts up to the internal panels. The little bit at the choke point is not inset. This is primarily to make assembly easier. It takes more material, but we are optimizing across a lift of plywood.

Rounding or champhering at least the vertical sides around the drivers, and the top are good sonically. makes venering harder. For optimum wavelaunch one would build a supraBaffle like the Cain & Cain or a RonHorn. I like the elegance of the shape without.

2. Please confirm that the baffle is at 90 degrees to the base ?

The baffle tilts back at 5 degrees, so 85 degrees referenced to the base (to the nearest degree)

3. For the best practice should the driver sit "in" a recess flush on the baffle front ?

The front of the driver bezel is ideally flush with th baffle. This can be done as a rebate or one can add a layer of material over the baffle that makes it flush with the front of the bezel.

4. There is no mention on the plan about the extent of flaring inside the baffle for the driver as too much would effect of rigidity of the baffle and the driver mounting.

There will be a page with examples. A 45 degree champher is best*, but round over is often used... my personal caveman approach is to take a big rasp to it (but Chris doesn't lt me in the shop except to look)

* actually, best might be a 3mm (or so) aluminum subbaffle, a 45 degree champher on the cutout and the driver mounted from the rear. This is then set into a big square or rectangular hole in th baffle, and bolted in from the front.

5. Looking at the design the most critical part of the design it seems is the top left hand corner of the cabinet. Would it make more sense to dimension the drawing from that point for each material thickness ?

I am probably going to do something like that. Input is appreciated.

6. The plan infers that a dimensional accuracy of 0.1mm is called for which is going to be quite a challenge without the use of modern methods! What are the tolerance limits for the design and which are the MOST critical ?

Dimension accuracy to a mm or 1/16 inch is desirable, but ven that is bing anal. Dimensions are taken out further than that so that you know which way you are off. Plans so far are for 15 and 18mm material and the dimensions are rationalized for metric, when 5/8 and 3/4 plans are done they will be rationalized for imperial.

In every case it is up to the builder to confirm th actual thickness of his material.

dave

PS: some good points for the FAQ, someone on that?

PPS: the "e" key on my laptop is getting recalcitrant, there are probably some missing.
 
Hello

Thanks Dave.. A couple of queries regards the drawing for the cabinet

Miles - I'm not Dave, but hope my comments might help

1. The drawings suggest the front baffle can sit "on" or 'in' the cabinet, but by design which is correct ?
Keep in mind that the FH3 is designed for DIYers to experiment with -there is no "correct" with respect to thickness of front baffle or fabrication techniques - just which ever is easier for each individual

The "recommendations" for materials and assembly are based on a combination of iterative experience with a variety of enclosure designs, and my personal exposure to working in a commercial cabinetmaking shop, where material yield is not necessarily as important as ease and speed of assembly, - not always the case for a DIYer.

That said, I've long ago determined by my own very non-scientific analysis ( i.e. just simply listening), that high quality plywood (i.e. high density ply count / voidless such as Baltic / Russian Birch, "Apple Ply" etc) is definitely highly recommended. Use whatever material and fabrication techniques you like, but don't stray far from the design dimensions, and don't be surprised if enclosures built from different materials sound vastly different.

Would a rounded edge to the front baffle be an improvement ?
If you're concerned about mitigating edge diffraction, for a radius to have a substantially audible effect it would be much a larger than available at the intersection of side panels and front baffles, even with 3/4" material.


2.. Please confirm that the baffle is at 90 degrees to the base ?
the front baffle of the FH3 tilts back at approx 5 degrees

3. For the best practice should the driver sit "in" a recess flush on the baffle front ?
yes, but slightly harder to achieve with pin-cushion shaped frames such as Fostex FE126En - unless you have access to a CNC router, or are well practiced with pattern templating (for me the former)

4. There is no mention on the plan about the extent of flaring inside the baffle for the driver as too much would effect of rigidity of the baffle and the driver mounting.
Yes, the combination of rebating for flush mounting (particularly with drivers with thick flanges such as the Mark Audios, or Fostex FX120, F120A, FE108eZ), and the flare does make things a bit tricky, which is why I like to upgrade to 18mm for the front baffles. Of course, I have ready access to any required material thickness, and the ability to amortize the expense over many projects. As pointed out previously not all DIYers can justify the expense of a second sheet of material just for the front baffles of the FH3.



5. Looking at the design the most critical part of the design it seems is the top left hand corner of the cabinet. Would it make more sense to dimension the drawing from that point for each material thickness ?
Dave can answer that

6. The plan infers that a dimensional accuracy of 0.1mm is called for which is going to be quite a challenge without the use of modern methods! What are the tolerance limits for the design and which are the MOST critical ?
Yup, unless you're cutting / routing everything in a CAD/CAM CNC environment, .1mm accuracy is hard to read on your tape or consistently cut. My own cutting is a combination of CNC and by hand on table saw - I'm happy with keeping a 1mm tolerance on all parts, and have certainly been known to adjust parts to fit with belt or RO sander. ( air powered sander and 80g paper come in very handy)
 
Hi all,

Yippeee!!!! :)

Thanks Colin,

That's a great way you did that cutting sheet. I do hope you don't mind I've re-drawn it so that it can be printed off without using 1/2 a tank of black ink :) and the bloke at the the Do It Yourself shed can cut it;

My idea being that the 4 off 140 strips are cut first, the remaining piece turned through 90 degrees and the other 140 strips cut while the 140 stop is set then the remaining pieces in the same fashion.

I can cut the 5 degree angle and the curve with me little jigsaw on one piece and use that to mark the other three.

Thats Reely Grate thanks a million.

Jim
 
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After much frustration in searching for 1/2 " ( 12mm ) cotton or wool felt I found an unlimited supply at my local auto junk yard. The carpet backing from 1990's Fords is 1/2 inch thick, works great and costs nothing. Had it not been up for sale I would have scavenged my own Mustang but instead I found a F150 donor which surrendered enough felt for a herd of horns.
 
Taking Colin's diagram, here is how I would one-man it out of a 4x8 panel.

0. Build yourself a T-square cutting guide out of scrap material. You can find the instructions out there on the Internet.

00. I have a 3'x6' sacrificial table top on a pair of saw horses. I can still manage to get a 4x8 sheet of plywood on it, but I can no longer get a sheet of MDF on it. For MDF, I just drop the sheet on the driveway and put 4 2x4's under it.

1. With a circular saw, cut off the 4 140mm pieces.

2. Cut between the remaining doubled pieces.

3. Now you can rip the individual pieces on a table saw as long as you can rig some kind of outflow table. I have a jig that fits my router table so that it can double as an outflow table for the table saw. Of course, if you don't have a table saw, you can do this with a circular saw and the rip fence you made above.

You can get the two cross cuts done at Lowes'/HD (speaking to the USA now), but my experience is that their panel saws are not square in any axis and I have to re-cut the ends. Also, the utility blade in their saw really tears up the cut. I have a 60 tooth blade in my circular saw that does an acceptable job. Not as good as the 80 tooth blade in my table saw, but acceptable.

That's my technique. YMMV.

Bob
 
Jim (Jemraid),

Apologies for my poor image. It was exported from my original AutoCad drawing file so quality was poor. Normally I would print the image onto A4 paper then scan that print, but my printer ran out of black ink. BAH!

One small amendment to your revised image cutting list. For 18mm material the 456mm dimension should actually be 458mm.

To be pedantic should be 458.5mm. But who builds to 0.5mm, hey :rolleyes:
 
Another tip for cutting sheet goods on saw horses......

Go to your nearest hardware store buy a 2'x4' pc of 2 or 3" white styrofoam and a roll of duct tape.

Cut the stryo to match the top of your saw horses......use the duct tape to
fasten it around the top of the horse.

You can now cut your sheets with out hanging them over the saw horses.
Just cut thru the styro.....make sure your styro is deeper than your saw cut.
When the styro gets beat up...remove and replace.

This method is used on jobsites all over to cut large panels.
 
frugal-phile™
Joined 2001
Paid Member
I am also adding Colin's variation of the cut to the plans for those who have the local lumber shop do the basic cuts (certainly makes them easier to stuff into the VW).

My drawing shows less scrap than Colin's (or maybe just moved around as i've allowed for a 5 mm trim/kerf

attached for comment & comparison

dave

edit: attachment updated to add some of Jim's comments from post below
 

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Hello all and Hello Colin,

Thanks for clarifying that Colin.

Here is the new and irrevocably final cutting drawing for the FH3 builders like me who have few tools, but do have the will to do it come what may.
An externally hosted image should be here but it was not working when we last tested it.


The idea is to use the cutting service of one of the Do It Yourself sheds [I will use B&Q in Chesterfield] the first cuts being the 140mm ones, the sheet is then turned 90 degrees and the other 140 cuts made while the 140 stop is still in place. Then the 4 sides can be cut in the same manner.

When I have made cabinets in the past I found that a talk to the cutting bloke with an emphasis on getting the cuts parallel has resulted in good cuts.

Warmest wishes - Jim

Edit; wow thanks Dave I'm Beta Builder :)
 
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