Originally Posted by subwoofery View Post
Would like to know what can you tell us about MMS. A strong cone with low MMS VS a strong cone with high MMS - big difference in testing and sound?
For all practical purposes, MMS is only a tool to get a given set of parameters that best fit the design. There is always talk about how MMS has a factor in how fast or slow the driver is. There is really no validity to that statement. I can take an IB15AU and measure the impulse response which shows how fast it starts and stops. I can then go and add mass to it, even a substantial amount and it will not affect the position of the impulse, only the magnitude of the pulse. Putting more power back in to get the pulse level equal to the original makes them essentially the same. It is really only an issue of level and not time delay starting or stopping.

There are several papers out there that verify it. This one is the original from Lambda Acoustics talking about how it is inductance, not mass that affects the "speed" of a woofer.

Bl/Mms = Nonsense

The paper Adire wrote that is hosted on Stereo Integrity's site now also explains the same.


Often people don't really realize the amount of force the magnet can put on the coil. The magnet in a woofer has so much strength that any amount of moving mass that can never realistically be put in a woofer will have little affect on the amount of control the magnet exerts over it. You can get a small magnetic door lock that has enough strength to keep a 200lb man from even being able to even budge the door no matter how hard it is pushed or run into. Consider now the difference between 100-200grams on a woofer being controlled by the magnet vs the force that is controlled by the door magnet.

The one thing that is a factor though in MMS is where it comes from. Adding physical mass has no effect. Adding windings to the VC to create more mass will. It is not the mass that is creating the effects though. It is because the more windings in the VC, the stronger the electromagnet becomes, and the more it can move the permanent magnetic field. This gets back to the distortion issues of inductance again. This factor is the reason why people often think that high mass woofers sound "slower" or less controlled. It isn't because they are heavier, it is because they have more inductance.