I've recently been mulling over two methodologies of bass reproduction: boxless dipole (which I have the pieces for and am going to build) and ELF (which I am designing a transducer for).
With both of these very different approaches in mind, I began wondering about something they share in common--the air they move.
I have heard it said that air, like any compressible medium, is single-ended. That is, its behavior under compression is different from its behavior when rarified.
Common sense has it that a good loudspeaker begins with a linear transducer whose suspension applies constant centering force against both directions of displacement in mirror-image fashion. I'm assuming that all conscientious transducer designers strive for this goal.
However, take that beautifully linear driver and mount it in a box. Now it's compressing and rarifying your room (very compliant, highly damping) on one side, and the enclosure volume (much less compliant, less damping) on the other. Now you've got a nonlinear sum of forces acting on your diaphragm over its excursion. Presto! You're creating even-order harmonic distortion.
For a given diaphragm displacement, the greater the difference between the compliance of your box and your room, the more pronounced the distortion. As I pondered ELF subwoofers, with their tiny, highly pressurized enclosures, this truth sent me off on a tangent to design a *nonlinear* suspension to compensate.
When you're designing a driver for a defined enclosure, it's probably possible to regain decent force symetry with good design. But what about all other OEM drivers, destined for enclosures unknown? It got me wondering if correction could also be applied to the audio signal.
Aside from intentional correction, either mechanical or electronic, it seems to me that only open-baffle dipole or large infinite baffle approaches avoid inherent harmonic distortion.
Your thoughts, flames?
Bill
With both of these very different approaches in mind, I began wondering about something they share in common--the air they move.
I have heard it said that air, like any compressible medium, is single-ended. That is, its behavior under compression is different from its behavior when rarified.
Common sense has it that a good loudspeaker begins with a linear transducer whose suspension applies constant centering force against both directions of displacement in mirror-image fashion. I'm assuming that all conscientious transducer designers strive for this goal.
However, take that beautifully linear driver and mount it in a box. Now it's compressing and rarifying your room (very compliant, highly damping) on one side, and the enclosure volume (much less compliant, less damping) on the other. Now you've got a nonlinear sum of forces acting on your diaphragm over its excursion. Presto! You're creating even-order harmonic distortion.
For a given diaphragm displacement, the greater the difference between the compliance of your box and your room, the more pronounced the distortion. As I pondered ELF subwoofers, with their tiny, highly pressurized enclosures, this truth sent me off on a tangent to design a *nonlinear* suspension to compensate.
When you're designing a driver for a defined enclosure, it's probably possible to regain decent force symetry with good design. But what about all other OEM drivers, destined for enclosures unknown? It got me wondering if correction could also be applied to the audio signal.
Aside from intentional correction, either mechanical or electronic, it seems to me that only open-baffle dipole or large infinite baffle approaches avoid inherent harmonic distortion.
Your thoughts, flames?
Bill