Cogito wrote:
tomp wrote:
Very true, but the servo if properly designed and executed it is another tool that can help get better results. The fly in the ointment is the cost of producing a good servo is often more than the cost of an additional driver. The servo is not going to work properly when the excursion puts the VC beyond the XMag point as the motor strength has dropped significantly. A good servo design takes that drop into account otherwise the amp would be directed to put destructive levels of power into the driver which cannot correct because there is insufficient motor strength. The voice coil at that point becomes a toaster. So the range of correction available to the servo is limited by the characteristics of the driver.
On the other hand, starting with a good driver, the distortion should be below 1% until you approach XMax. By using the money spent on the servo, you can usually buy a second driver which will give you double the linear volume displacement before the distortion rises. The second driver can be put in the reversed position and driven 180 degrees out of phase so the acoustic output is in phase. You get lower distortion, more linear displacement, higher sensitivity but wind up with double the enclosure size. It is always a trade off.
Adding a second driver firing in the reverse direction is not going to correct the non-linearities of the driver of either driver, but it spreads the non-linearities to both phases and mask them with linear content (from driver firing forward), which might be less objectionable.
BTW, we are not saying HAL's drivers have the non-linearity issues.
Shashi:
I don't think that is correct. As I said I am not an expert on the mechanism but you might want to look at this patent:
US 5537479 A
Here is what the author claims. I can't verify that myself. It might be an interesting test if I ever get time.
This push-pull configuration is a prior art concept in which the major even-order distortion harmonics (which contain the 2nd harmonic, usually the largest of all distortion harmonics) are greatly reduced because they are intentionally caused to be precisely out-of-phase as radiated, as between a normally mounted driver (or drivers) and an axially inverted mounted driver (or drivers)