Thiel Owners

Tom Thiel,

I have a new speaker rebuild and elected to place the crossover out board for final tuning. It will always be outboard.  Components are mounted on a solid 1/2 inch poplar board and grounded to the floor via threaded 1.5 inch Audio Points.. Originally the 2 8gauge inductors were tied down to the board each with several zip ties. After listening for a couple of weeks I felt the sound was dynamically restrained and cut away the straps, so now the inductors only rest on the board under their own mass and physical size. Immediate improvement was heard in soundstage size, everything was much more dynamic and with much  more acoustic air.

These 2 small inductor values are physically large with a space of about 2.5 inches between them. They are placed 90 degrees to each other. I decided to move 1 another 2 inches from the other. Way different again in performance. I thought that placing the inductors apart and with 90 degrees of separation would eliminate any magnetic field inner play but that is not the case...So my thoughts and observations leads me to question.  What are the magnetic actions and reactions when a crossover is placed inside a cabinet in proximity to a woofer magnet or powerful neo tweeter magnet and or the variable fields under power of confined inductors? 

Today I will be receiving 4 sections of mu metal to place around all of the inductors or a large portion of the facing circumference of each. If this case study of the magnetic field, external to the confines of a cabinet makes for an improvement then why wouldn't the same hold true for crossovers inside the box but even much more than those outboard? TomD

Prof - I ran the painted driver experiment; and I’ll call it a success.

I used Krylon ’Fusion’ because it claims ’5X the adhesion’ (of whatever?). Its solvent cocktail includes acetone, which makes a good scrub agent.Careful. I chose dark oiled bronze because it’s nearly black and so much more visually engaging than 'plain black'. I cut a cardboard mask, laid the speaker on its back and misted just enough paint to knock the aluminum down by perhaps 85%. First measurements were 1 hour later, which showed significant harm, especially in the mid bass and lower midrange with frequency erratica and time domain throbbing. After 4 hours it was much better and after 24 hours is hardly visible. The paint cure cycle is 48 hours.

At 24 hours, the top octave rolls off perhaps an additional 1dB at 20k and there are some harmonic differences. Generally, the 3rd to 7th harmonics are smoothed out and 3 to 5dB lower. On balance I would say the lightly painted cone is superior to the bare aluminum one. It is plausible that a crossover tweak might get that top octave air back, since the CS1.6 has a notch filter at its oil-can resonance. Note: there is none of the typical resonant peak at 28k (etc.) When using my Earthworks QTC40 into a 96kHz interface. The high end of the 1.6 just keeps rolling off around 12dB / octave out to 50k. That’s very nice.

I will experiment with a midrange driver when I get the 2.4s into the studio.

I suggest leaving tweaters alone, at least until we do some real homework.

If you paint cones, go easy. I certainly like the look better and it opens a door to using nylon window screen for a protective grille with far less resistance than Thiel’s polyester - plus a peek-a-boo allure.

By the way, the 1.6 grille shows differences in two areas. In the deep bass from 20 to 50 the grille introduces time domain throbbing, although I can't hear it. The FuzzMeasure sweep goes full power from 1Hz to 48kHz. This grille seems quite transparent up to about 7500Hz where it gradually rolls off the top to about 1-2 Hz at 20k. I like the sound better with the grille.

That's 1-2 dB at 20k.

Tom D - welcome to the rabbit hole. Electrical and electromagnetic fields are a huge issue. In my opinion this issue deserved more attention than Jim gave it. As time went on, Jim's XO position moved farther from the drivers. Note the 3.7's location in a separate chamber in the bottom of the cabinet.

In the development of 1978's 03, we mounted the XO on the cabinet bottom, as far from the woofer field as possible. The interactions are significant. My clearest memory was noting the difference between the breadboarded 3 dimensional rat's nest crossover hanging in space / compared against the conglomerated XO on a board in relative proximity to the woofer (and other drivers) as well as closer to each other. The aural congestion was significant.

I had an aha similar to yours in my work on the CS2.2 a couple years ago using an EMF field meter which showed strong fields extending about 2' behind the woofer. I'm staying outboard when possible, and if not (such as a minimalist upgrade) it's going under or on the outside of the cabinet, in free air, far away from drivers.

Among the issues are vibration, which can be controlled via shock mounting.

Also, heat build-up changes circuit performance.

And there are proximity effects, both between components and in relation to the drivers. Those aspects interact because the coils (especially) must be positioned not only in relation to each other, but in relation to the flux lines of the driver fields, which can be a bigger deal than between the XO parts themselves.

MuMetal, etc. is quite technical and frequency and density related, generally requiring complete cages around components, which can exacerbate thermal considerations and reluctance interactions between the propagation fields in the coil wire. It's a jungle. I have found that physical distance and positioning geometry are more fertile avenues toward global solutions.

Regarding your preference for the sound of unbound coils - be very careful. Motion can induce various interactions with all other elements. Stillness is the goal (IMHO). As a generalization, many kinds of 'distortion' can be seductively appealing; sorting it out is a hard, complex problem. Where I've settled is that coils on rubber feet are strapped to the board. The feet increase and equalize thermal radiation , while mechanical motion is minimized as well as audio vibration frequency decreased to where the coils seem to not be stimulated into motion.

The position of coils can be optimized via listening to noise. The puzzle is hard because virtually all coils affect all others, and there are too many permutations to test (in a complex Jim Thiel crossover.)

There is another aspect that is real, but beyond my understanding, but here goes. Wire, at least new wire, has directional sonic properties. But I've found no reliable way (except Cardas wire) to track the directionality of wire. However, these effects seem to diminish with play-in time. I have chosen to ignore wire direction because I'm using played-in wire, and I can't do anything about it when re-using Thiel coils. In addition to spatial attitude, that leaves feed vs load of the coil. I have demonstrated to my own satisfaction (but contrary to common opinion) that coils are best fed from their circumference and tapped at their core with attention paid to lead wire dressing. I also note that as time passed, Thiel's crossovers tended to migrate toward this (outer to inner) feed direction.

Tom T.

Thanks, Tom Thiel, for your experienced and insightful response.

I have heard the sounds of Barkhausen noise generated by the rapid change in magnetic fields. I know this firsthand in my use and experiments with magnetic materials, varying field strength and geometric shapes within prototypes of my products for acoustic instruments.  

I will take what I learned in close quarters about my devices for acoustic instruments and expand into this speaker project. Hope it is no deeper than a rabbit hole and less than a Minute Man Silo.  Still learning after all these years. TomD