Lambda 001 Motor

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The Lambda 001 motor is the first in a long line of low distortion designs from Lambda Acoustics Inc.  Designed over the period from 1997~1999 by Nicholas McKinney, tremendous effort was given to create the lowest distortion possible while keeping the costs affordable.

 

 

Nicholas McKinney with one of the first 001 prototypes

 

 

The ultimate motor design for low distortion should have the following characteristics;

 

(1) Linear magnetic flux levels across the entire VC movement range.
(2) The flux should be fixed permanently and not move, this is however not the case in 99% of speakers.
(3) High heat absorption properties as close to the VC as possible.  The VC if allowed to heat significantly will lower the speaker output Spl very quickly.
(4) Linear inductance as the VC moves through its entire range if the driver has to contribute ANY output above the impedance minima above the Fs of the driver.  This is not just at the crossover point, this is any output that is not -48dB down in our opinion.  The only way to accomplish this is to keep the CORE of the VC the same at all excursions.  The VC is after all an inductor, however this is the only inductor in the whole audio system that varies it's value with low bass excursion.  The low bass creates massive excursions that at the same time changes the parameters of the driver at higher frequencies with every deep in and out stroke. 

 

 

 

To accomplish the above only one motor design comes close immediately, the Underhung

 

 

(Photo courtesy Bob Stout's LDSG)

 

 

Here you can see;

 

(1) The flux level is the same as long as the VC stays in the gap.
(2) There is a lot of steel pole to absorb the VC heat.
(3) No matter where the VC is in the gap, it still has the same steel core forcing it's inductance to stay linear with xmax.

 

 

However the Underhung has 3 problems immediately to consider;

 

 

(1) It needs a wider VC diameter, this makes the higher frequency response worse, and also raises the costs significantly.
(2) It needs a much larger motor assembly to get the same motor strength as the Overhung.  This again raises the costs significantly and is the main reason more companies do not use Underhung designs.
(3) Once the VC leaves the gap, the Bl drops very quickly, and the driver immediately compresses the output.

 

 

And most importantly;

 

We still cannot keep the flux from moving in the gap even with the Underhung

 

This is a sever distortion problem in loudspeaker motors.  The magnetic flux in the gap is stationary only when the VC is stationary.  There are 2 ways of lowering this effect;

 

 

(1) We lower the electrical conductivity of the magnetic pole pieces.  The excellent ATC drivers were the first as far as we know to incorporate this technique.
(2) Or we can permanently mount a highly conductive layer that is not magnetic between the VC and one of the poles.  This cannot be a moving piece like an aluminum VC former!  Rather it has to be mounted rigidly in the motor, and also be much thicker than the typical 0.005" VC former is.  

 

 

 

With this permanently mounted highly conductive layer, any flux movement creates large currents (Eddy Currents) that can now short themselves out.  Rather, the magnetic flux lines are electrically shorted to their original location and cannot move now.  Hence the devices used for this are called Shorted Turns or Faraday Rings.

 

Another benefit of this is that if the shorted turn is highly conductive, it has to be made of either copper or aluminum (or silver but remember the cost aspect)  Copper immediately becomes the perfect material for this.  It is low cost, highly electrically conductive, and also highly thermally conductive.

 

You see, steel while being able to absorb heat quite well, does not like to do it rather quickly.  The VC needs to quickly dump the heat that it generates or else the power compression will come up.  When the power compression goes up, we need to put more power into the VC to keep the output the same.  Hence we start this chain reaction that we will never win against.  The VC at some point absorbs double (3dB) and even quadruple (6dB) the input power for no gain in output Spl.

 

So our "perfect" motor has to then have a large piece of copper designed in such as way that no matter where the VC is located, the copper is right there to absorb the heat.  The copper serves as double duty this way by also keeping the flux field from moving no matter where the VC is.

 

Thus the Lambda 001 motor was born.  This overhung motor was designed to give the low distortion and high power handling of an equivalent Underhung, but with the smaller VC diameter and lower cost.  The steel pole has been extended well out of the gap to create a large "fringing field" of magnetic flux.  This helps to keep the Bl higher when the VC leaves the gap completely, and hence the output is not compressed as quickly as in the Underhung.

 

  In the following picture you will find a full color cutaway of the motor design.  Notice the size of the full length copper Faraday and pole piece in relation to the VC.  This copper piece is one seriously large heatsink that serves 4 duties;

 

 

(1)

Lowers the gap flux movement no matter where the VC is located.

(2) Quickly absorbs the heat from the relatively smaller VC and directs it into the large steel pole over a much larger area than the VC could have done on its own.
(3) For wide bandwidth use, the VC is always surrounding the same CORE no matter where the excursion has taken it.  This is very important to understand as the VC is in fact an inductor, hence it is very sensitive to what the core material is at any given location.
(4) The copper effectively short circuits the inductance of the VC to an incredibly low level.  This further lowers the influence of the inductance variance on the high frequency response of the driver.  Also it forces a flatter phase curve for the driver.  The main difference between electrostatics, ribbons, and VC driven drivers has always been the inductance.  Here we can finally get a woofer to mate with these other drivers as closely as possible.

 

 

 

 

Lambda 001 Motor

 

   

 

 

 

The following shows the VC relation in the motor at maximum rated xmax

 

In-Stroke

 

 

 

 

Out-Stroke

 

 

 

Also shown above is the attention to detail in regarding the air movement in the motor.  All venting schemes include very generous radius, and also venting of the gap chamber is included as well.  The pole top is also severely radiused to lower the reflections into the dustcap.  The thick top plate of 10mm also forms a good heat sink for the outside diameter of the VC.  This heat is then absorbed and dissipated by the thick cast aluminum basket which has a close proximity to the VC.  At first appearance it might look quiet simple, but hopefully you will realize that every specification in material size and shape works together in a truly beautiful harmony.  Every 0.001" has been stressed over, designed and redesigned in the above, now we offer it to you for pure musical enjoyment. 

 

Copyright Ó 1999, Lambda Acoustics Inc.