An idea to increase magnet strength in a speaker driver

[bumpy]

Its now relatively cheap to buy small neodymium magnets.

Equally, speaker driver manufacturers have magnet strength as one of the mayor selling points.
In addition vintage drivers will have gradually lost strength since first being built.

So my idea is to stack these small magnets on the rear of the driver magnets to boost their strength. Stronger magnetic field in the coil gap equals better control, drawing parallels with field coil drivers that do just this.

This idea was triggered for me by finding the magnetic front door sensor on my house alarm was giving occasional false alarms after 20 years. Two small neodymium magnets attached to the back of the existing magnet cured the problem.

Thoughts?

[Gregje]

You could do that BUT you probably will need to redesign the crossover.
Adding magnets is easy. Redesigning the crossover less so.
But you know this as one does not buy Endorphin P17 in your local HiFi outlet ;-)

[bumpy]

OK I accept that, but for my current speakers the mid/tweeter is running full range and the bass low pass is set by mini DSP. Just wondering if the suggestion has been explored by people before. In the right circumstances it seems a simple cost effective way to improve performance - a bit like having Alnico magnets re-magnetised.

[Gregje]

Troels Gravesen has one or two older projects where he adds an extra magnet (same size as the original) at the back of the woofers.
It gets him 1.5dB extra sensitivity out of the whole system.

[bumpy]

Troels Gravesen has one or two older projects where he adds an extra magnet (same size as the original) at the back of the woofers.
It gets him 1.5dB extra sensitivity out of the whole system.

Interesting thanks

[Barry]

It might sound like a good idea, but I'm not sure if it would work.

Clearly all magnets have two poles and the idea is for the design of the magnet to be such that the magnetic flux is concentrated in the gap where the voice coil operates.



Referring to the above diagram, the magnetic flux is directed radially between the coaxial poles: N pole (inner) and S pole (outer). At the rear of the magnet, where you propose to fit additional neodymium magnets, the flux is radially directed between the inner and outer poles. It is therefore unclear how this flux would be supplimented by attaching additional magnets; as their flux would be at right angles to that of the existing magnet and so have negligable effect.

In order to arrange the additional flux to add to the existing flux, you would need rows of the neodymium magnets arranged radially on the back of the existing magnet (looking a bit like this:*), but since to increase the overall flux, the new magnets would tend to repel and would have to mechanically forced to stay in place. If you reverse the direction of the neodymium magnets, they would attract and adhere, but in doing so would reduce the overal flux.

[Pharos]

That last point is right Barry, a similar magnet would have to be forced to stay on the back of the existing one, perhaps glued on with a strong glue and left setting for long time.

[Gregje]

Definitely the extra magnet has to be forced to stay on the back of the existing one.

[Gregje]

http://www.troelsgravesen.dk/C17mk4.htm