Megamini the active little beast
I have designed and built a very small active speaker using the same technology as my Macaroni, but this time with AMP11.
It is housed in an aluminum die-cast enclosure, the connections in the back are enclosed in another die-cast enclosure so to make sure that not only dust, dirt or water can't enter the amp/speaker assembly, the speaker is also well sealed off. Normally the connections are as leak as a basket causing it to produce all kinds of hissing and puffing sounds.
Again I have used a much smaller input cap (150nF) to make sure the little driver survives the violence of AMP11. I have also again modified the AMP11 to start working from 9Vdc and up, so you can connect anything between 9 and 32Vdc....
Have a drool:
Nice handles now too:
You don't wanna know how hard it was to get the bull-bars on, I bought them from IKEA and hoped they would fit, but they were just about 4mm too short. Than I decided to weld a piece in between to make them exactly aligned with the screw holes. So although you don't see it there are two welds in the middle of them....
For me the big advantages of the Monacor SPH-30X drivers are the water repellent materials (dust proof) and the light magnet. When these features are not important there are literally thousands of good alternatives. I render the Monacor driver therefore to be quite unique.
A friend and I have designed a new filter circuit that makes the response very linear, it makes the high frequencies much smoother (less sharp) and makes the mid-bass region nicely punchy. Now it starts to sound very very hifi!
Here's how it measures without any filtering and without the grill:
Than with grill:
There's a large dip in the most sensitive frequency area
Then the old filter with grill:
After some listening to this old configuration of the filter it became irritating that the higher frequencies were too sharp...
So I tried adding an RC high cut filter:
But it became dull and the midrange area became too pronounced again...
Than I went a whole other route. Instead of filtering the 2Khz bump I wanted to boost the lower end a bit to pull it up to the same level. This way the whole area would match the 10K bump better where the old filter would make everything right except the bump, made it even worse because the bump there would stick out even more. With the present configuration the peak at 10K is really not irritating anymore and the whole band sounds really well in balance...
Here's one of the simulations with this program:
The present filter:
The filter circuit works quite neat!!
Made my own grilles, no effects on the curves and very robust...
Not bad looking either if you ask me...