Ohm F's Refurbished

[W9TR]

My first real high end audio purchase was a pair of Ohm F loudspeakers in 1975. I first heard the F’s at a Tech Hi-Fi store in the Chicago driven by some big SAE amps. They sounded like nothing I’d ever heard before. I was smitten. I emptied my meager bank account and bought a pair. They became the centerpiece of my system for over 10 years.

Ohm F’s are Walsh drivers – single, full range omni-directional loudspeakers with no crossovers. The highly tapered cones act as transmission lines, the voice coil ‘plucks’ the cone, launching a wave down the cone where it is then radiated into space. Lincoln Walsh’s patent #3,424,873 explains the design in detail. The inverted cones are made of ultra-thin Titanium and Aluminum foils and a paper cone section that forms a transmission line driver. Internally, the Titanium section is treated with a clay-like damping material, and the Aluminum cone section is damped by open cell foam. The paper cone has four rows of long slits around its circumference at different heights. It is one of the most complex electro-mechanical systems I’ve seen. Today, German Physiks and MBL make similar designs

Ohm F’s proved to be hard to live with. As omni-directional radiators, they have to be positioned very carefully away from room boundaries to sound their best. They consume prodigious amounts of power, and were prone to failure. The old joke was it took 200 Watts to get them to sing, and 201 watts to blow them up! I blew mine up at least three times, maybe more. Big parties and Ohm F’s just don’t get along! I had some voice coil separations that were not abuse related. Finally, Ohm stopped supporting the rebuilds and provided an upgrade path to their newer model, the Walsh IV. Without another option, I switched to the Walsh IV. It had much better efficiency, but some of the Ohm F magic was gone for sure.

Fast forward 37 years. A little voice kept saying….wonder what it would be like to have F’s in the house again? So I started researching the options for refurbishing a pair, and found an active but small community of admirers that are keeping the design alive.

I found a one owner pair on CL, from a gentleman who was going into an assisted living facility and couldn’t bring them with. The cabinets were in great condition, but the drivers needed major refurbishment. I contacted Bill Legall from Millersound in Lansdale, PA, and arranged to have Bill rebuild the drivers. I flew from Minneapolis to Philly with the drivers to meet Bill and discuss refurbishment

The spiders were sagging, the surrounds shot completely, and all the inner cone treatments failing. But the cones themselves were in good shape. So we agreed on a complete refurbishment, with new voice coils, spiders, surrounds, and inner cone treatments. Bill’s knowledge of Ohm F’s is very deep and I could tell he is an outstanding craftsman. You can learn more about him here: http://www.6moons.com/industryfeatures/forbidden/forbidden_9.html

Bill explained to me that Ohm F’s were shipped broken from the factory. The petroleum binder in the Ferrofluid used in the motor assembly migrated out of the gap and attacked the adhesive that held the voicecoil to the cone. He demonstrated this on one of my drivers by simply pulling the voice coil away from the cone. There was no adhesive left! He also said the original spiders were too soft, causing the cones to sag almost immediately. This pulled the voice coils out of the gap, reducing efficiency dramatically. That’s why most people had trouble keeping them running. I left his shop confident that my speakers were in good hands. I was in good hands.

While I was waiting for Bill to finish the drivers, I hand rubbed the cabinets with five coats of teak oil, cleaned the grills, and repainted the driver mounting boards. I also replaced the cheesy binding posts and re-wired the cabinets with Kimber 4TC.

This is a picture of the reburbished driver. When the drivers arrived, I mounted them, re-assembled the cabinets and moved the F’s into position in my room. Bill made a lot of changes - adding dynamat extereme to the basket ribs and surfaces. He covered the spider with felt to prevent treble re-radiation onto the cone, and covered the motor assembly with felt to keep down reflections. These are now truly better than new!


How do they sound? They sound just like I remembered them. They truly fill a room with music. They have deep and prodigious bass, clear and clean vocals. The treble is smooth, although not as extended as some more modern speakers I’ve owned. The overall tone is excellent – these are tone-meisters for sure. They sound beautiful.

After some experimentation, I’ve moved them out about 5 feet from the back wall, about 10 feet apart.

Bill said it would take about 60 hours of break in for them to sound their best. I’m now at about 40 hours, and they are sounding great. They are starting to image more precisely. Will they replace the Sophia 2's? I don't kow. They are more of a contender than I expected them to be, for sure. This was a lot of fun, a little work, and I got to meet Bill and Loretta along the way - both great people dedicated to the enhancement and preservation of audio.

Tom