On magnetic systems of planar transducer

I will try to write briefly and clearly about what I have been working on in my planar transducer designs for the last few years.

There will be several articles. First I will write about magnetic systems, then about diaphragms, and also about corrugation of diaphragms.

So, about magnetic systems. At least since 2013, working with TDS-15 mods and thinking about the design of my prototypes, my research was mainly aimed at obtaining more efficient and more perfect magnetic systems. That is, the basic ideology was that first it is necessary to build a good magnetic system with good magnetic and acoustic properties, and for this case to design some optimal planar membrane, which at that time seemed to me quite perfect.

The sequence of steps in the designs was approximately as follows.

First, I noticed that the magnetic and acoustic parameters of magnetic systems literally contradict each other. For example, the best uniformity and density of the magnetic field is easiest to achieve if you make a lot of magnets and arrange them densely enough.

But the acoustic properties inevitably suffer:

• Excess pressure inside the transmitter due to insufficient openness, which leads to diaphragm overdamping;
• Significant flat surface area of the magnets, which leads to specific distortions (especially in the HF region);
• Lack of openness of the radiating area, which leads to a cutoff in the HF region, etc.

The basic idea was to find a certain optimum between the magnetic and acoustic properties of magnetic systems. In doing so, I operated:

• The sizes of the magnets and their proportions;
• The distance between them and the relationship to the proportions of the magnets;
• Mutual arrangement of magnets (different versions of unilateral and bilateral magnetic systems; “partial” magnetic systems, magnetic systems with different sizes of magnets.

As some intermediate result with very good parameters I got a magnetic system with magnets like in figure 1.

In short, the cross-section of the magnets, in the form of such a “vertical” rectangle allows you to keep the parallelism of the magnetic field isolines at greater distances between the magnets than on those variants that are traditionally used. The result is greater acoustic openness while maintaining magnetic field uniformity parameters.

The second major step was to experiment with the shape of the magnets themselves. Dozens of variants of magnet cross-sections were tested in conjunction with the proportions of the magnetic system from item 1.

As it turned out, the cross-section of the magnets themselves also greatly affects both the magnetic and acoustic properties of magnetic systems. When I was working on this, I noticed that I was not the only one who paid attention to it.

Here are 3 examples in modern headphones where there are some similar ideas in the technical solutions:

• The so called “phasors” in the firm’s headphones Though not affecting the magnets themselves, the acoustics slightly improves the system in the HF area.
• Magnets with a semi-circular section in the Kennerton Odin headphones (well done guys).
• Sennheiser’s patent for a system with cylindrical magnets, though in the form of a commercial model of headphones, never implemented…

I should note that at the time of preparing the patent application for my technical solutions, except for “phasors”, there was nothing yet. Well, in my headphones, which I started to make, I use magnetic systems where the magnets are in the form of vertically arranged ellipses. This gives both improvement of magnetic field parameters and acoustic properties (Fig. 2).

The key elements of these findings are documented in the form of utility model № 158852 of 22.05.2015 and are used in headphone models Si-1, Si-2, Si-3.

To date, this approach has produced a sound with less distortion than any other currently known planar driver design. Does this solution have disadvantages? Of course there are. Designing and optimizing such a system is much more difficult. It is much more expensive to precisely manufacture the magnets. It is also much more difficult to implement in the design of radiators for mass or serial production. And, of course, all the advantages of such a transducer can be spoiled by a specific implementation and an unsuitable acoustic design.

In the next article I will write about what I am working on in the membranes.

Author’s article (c) Snorry (Sergey Glazyrin)
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