DMLs don't create measurable 3rd order harmonic distortion

In this article we'll talk about what 3rd-order harmonic distortion is, and why DMLs don't create measurable amounts of it.

What is 3rd order harmonic distortion?

With a traditional pistonic driver found in a point-source loudspeaker, the goal is for the cone of the driver to move as a single unified unit. When the cone is pushed too hard, it loses its shape—this is called "cone breakup." This deformation is unintentional and occurs at specific frequencies, creating high peaks of harmonic distortion because the material is essentially "fighting" the motor. This distortion is essentially the loudspeaker making sound that was not in the original content (in other words, distorting the original content.)

Why is a DML different?

With a DML, the bending or distortion of the driver isn't a failure of the material; it’s the intended mechanism. The panel is designed to support a massive number of uncorrelated vibration modes across its surface. Physicists call this "Bending Waves."

Our transducer is made of a carbon fiber over Nomex core - this structure, combined with the off-center placement of the group of exciters help to spread out the resonances across the entire surface,

 

  • Traditional Driver: Has a few dominant, high-amplitude resonant peaks that define the characteristic of the drier, and are what generates clear 2nd and 3rd order harmonics.

  • DML: Has hundreds of small, low-amplitude resonant modes.

 

Because these modes are so dense and distributed, they don't collect into the distinct, measurable harmonic peaks we hear as coloration with a traditional driver. These very small peaks and valleys essentially bury themselves. below the noise floor.

Another factor that contributes to DMLs not having measurable distortion, has to do with the fact that the very large surface area of the transducer panel moves very little - even at high SPL (about 1MM at full rated power.)

 

  • To produce a 100Hz tone at high volume, a small 5-inch traditional driver has to move back and forth quite a distance - and increases with SPL. The further it moves, the more it encounters opportunities for the surround or the cone to to deform, and for even the spider to flex.

  • A DML panel uses its entire surface area (which is usually much larger than a cone) to move air. Because the surface area is so large, the actual physical displacement (the "bending") required to achieve the same volume is incredibly small—often measured in microns.

Because the DML panel is not called upon to make large movements, it retains rigid and in its original form, keeping harmonic distortion exceptionally low. Our pane's material are specifically chosen for their high stiffness-to-mass ratio

All of these factors combine to allow us to safely state that DML500 does not create any measurable 3rd order harmonic distortion, even beyond its rated power. Or as we often like to say, if you are hearing distortion in your DML500, it's likely coming from the signal chain, and not the DML itself.

This is part of what makes a DML500 sound pristine at both low and high SPL - and it's also why we recommend higher end 96k DSP amplifiers, and we also recommend that you plan your amplifier with plenty of headroom, to keep the amplifier well below it's maximum output, where it might be more likely to introduce distortion into the signal.