First Steps

If you look at the FH3 document, at the link above, there are several cut sheets for different types of plywood: 15mm, 18mm, 4' by 8' and 5' by 5'. The problem with these sheets is that they assume that both sides of the plywood are sanded and clear. If, like me, you have limited access to plywood types finding two sides clear is not an option. I have been building shop cabinets with cabinet grade plywood from Home Depot ($29. a sheet) which is really nice void free plywood; however, it is not hardwood. The other local choice I have is Blonde wood from Lowes which does have some small voids. Forget Birch from HD or Lowes.

Above is a cut sheet for 4' by 8' 18mm plywood panel which works for one sided sanded. This layout has two purposes: to put the side panels at the corner of the sheet which is already square and to allow cutting at the home store for easy car transport.

To be continued.

Introduction

Many years ago I built an ultra-linear tube amplifier, Heath Kit pre amps and speaker cabinets with Electro Voice speakers. I thought those days were gone, but then my son sent me a picture of a horn speaker enclosure saying here is your next project.

The picture my son sent.

 That got me searching the Web and there was the Frugel Horn FH3 using a 4" driver which looks like a great project and maybe some great sound. I wonder what "In the Wake of the Wind" will sound like.

From the DIYAudio forum, Frugel Horn Mk3-paks

Some months ago I started the design of a CNC router and before I got very far into the project it was clear that my shop was a disorganized mess. I started by building a lot of storage, mainly wall cabinet and specialized cabinet for my power tools, drill press, miter saw, etc. At this time I am completing a router table and cabinet all of which can be found on my workshop projects blog, see links. One thing my shop needs is some great sound, before I get back to the CNC router project.


Documentation:
             http://homepage.mac.com/tlinespeakers/FH/beta/frugel-hornMk3-1v0b-300911.pdf

Sources:



Drivers:

1. Fostex FE126En, 4.7", 8 ohms, Fs=83 hz, Qts=.3, Vas=.3, $50. from Madisound
2. MarkAudio CHP-70.2, 8 ohms, 4", Fs=72.3 hz, Qts=0.52, Vas= 4.7L, $36. from Madisound
3. MarkAudio CHR-70.3, 8 ohms, $36, from Madisound
4. Tang Band W4-1879, 4", 8 ohms, Fs=55, Qts=0.43, Vas=9.1L, $60. from Parts Express
5. CSS EL-70, 4", 4 ohms, Fs=64, Qts=0.55, Vas=6.1L, $39 Creative Sound Solutions

So far 10 different drivers have been test in the Mk3 and discussed on the DIYAudio forum. I posted a question concerning the musicality of these different speakers with a recommendation of the EL-70 by Planet10. The EL-70's have a 4 ohm voice coil and since I will use these Mk3 with a Pioneer 50 watt receiver, the EL-70 may overload the amplifier. For the initial build we will use the CHP-70.2. If you are looking for great bass try the W4-1879.

Materials and Parts:

The material cost including drivers should be less than $150. for a pair of Mk3's. Though the development builds are done with baltic plywood, which I do not have access to, we will use the cabinet grade plywood from HD. I have built several cabinets with this plywood which is great plywood and void free. As an alternative the Lowes Blonde 18mm (23/32") plywood could be used.

Cutting Driver Hole with Jasper 400 Jig

The Jasper 400 was mounted on a Ryobi RE175 plunge router using two of the pre-drilled mounting holes. From many of the reviews of this product, the following points are important to prevent cracking the base:

1. Do not over-tighten the mounting screws
2. The pivot hole must be perpendicular to wood surface, so the plate will sit flush on the wood.
3. No more than 1/8" deep cuts should be made in each pass to prevent stress at the pivot.
4. Use a dry lubricant on the pivot pin like Dupont No Stick.

This product which is not a production jig is made with acrylic, Plexiglas, not Lexan or a phenolic plastic and can be damaged unless care is taken.

Step by Step:

1. Determine the hole size and insert the pivot pin in the proper hole of the Jasper 400
2. At the center of the driver hole, drill a 1/8" hole at 90 degrees to the wood surface. Use a drill press, drill guide such as the Wolfcraft or a jig as shown below. (Note 1)
3. Set the plunge router for 1/8" deep cut.
4. Put a dry lubricant on the pin, Dupont No Stick.
5. Insert pin in pivot hole, plunge router and rotate router around pivot slowly
6. Continue these steps until driver hole is completed.

Note 1: It is critical to drill the pivot hole 90 deg to the surface. This can be done by using a drill press or a drill guide clamped to the surfase. A simple drill guide can be made by drilling a 1/8" hole in a piece of oak with a drill press or a guide such as the V-DrillGuide from Big Gator Tools can be purchased. See picture below.

Jasper Circle Jig mounted on Ryobi RE175 router.

V-DrillGuide from Big Gator Tools.