Oe, what’s all that? Great of you to join. Welcome
Let’s start with the questions right away then
:
- Generally we see these systems with closed boxes. But what about enclosures what are leaky, like we see for directivity control purposes (like D&D)?
- What about driving multiple woofers? If we have two of the same, how well would it work to only use a single accelerometer?
Ok, 07:02, all fresh and shiny
Motional Feedback - often referred to as "servo drive" - attempts to mimic the physical cone movement to the electrical input signal which in a nutshell explains why it sounds so distinctly better then most bass systems as it eats away the damping influence of the drivers suspension and enclosure. See
EVE for more info.
The very cleverly designed D&D 8C uses dsp to
LT the twin woofers at the back, I did an experiment with replacing the DSP LT with an analog servo loop but found the results to be of less commercial interest. Unless they decide on doing a "mini" 8C with half the metric volume of the 8C I don't foresee much gain. With regards to it's "leaky" front driver, that could work as long as the leak is purely resistive - i.e. independent of frequency - as any port frequency will mess up the control loop. But the biggest issue with adding a servoloop to midbass drivers like the 8C front unit is with the extended polepiece / phaseplug which effectively rules out using centrally placed accelerometers like my StarBass sensors. Using alternative placements like can be done with ClingOn types also won't work because the added weight messes up the lightweight cone symmetry. I would try a negative output impedance (current drive) amplifier first.
With regards to using primary and secondary drivers, unless you are sure all drivers are within tight production tolerances and all "see" the same enclosure load the highend way forward remains individually looped drivers. Having said that, I did witness great results from an impulse compensated master / slave setup done by
RmsRob so definitely do give it a try !
As for the boards displayed in my xmas card above, the grown/up is a 3way system I have under development and planned for feb 22 launch depending on whether it's
coax mid-high unit is delivered on-time. The Little/Sub is geared towards the bass deprived
LS3/5a Lovers community
Both SDBH2D and SDB1D DIY boards are on hold due to global chip shortages but will eventually come combined with an accelerometer allowing the DIY community to build their own servo systems.