Friday, 6 March 2020

Powered Loudspeakers + DSP...

Wow, it really has been a long time..

I have been working to get this demanded powered-speaker thing going.

Why powered speakers?

Obviously, most loudspeaker boxes will contain individual drivers for maybe high, low, mid frequencies.
So we must provide a way to separate those frequencies.
Commonly this is done with 'passive' components (i.e. inductor / capacitor networks). I could write a post on that one day.
But for more control and that precious phase/time alignment, you will need some DSP.
In pro-audio this traditionally has lead to 19'amp racks filled with amps and  some DSP (maybe like one off those Soundwebs).
Anyway, things get rather bulky fast. So if you need just 1 (euhm, mostly 2 as in stereo) boxes
maybe as a fill-in or delay or just some soundscape thingie, something compact would be nice.
Hence the popularity of 'powered' boxes.

Now for the difficult part:

Most of  the powered loudspeakers in the market are not of a quality level we do appreciate, those plastic boxes will serve a purpose, but not ours...
So here's the design goal: make a powered box with a build in DSP//amplifier (no user controls!)
So first we checked the market to find a ready made 'plate-amp' to fit into our loudspeakers. People into this know the brands,yup I tested them all and I will not state my opinion on either off them .. :)
The main problem is that they are either limited in DSP (no FIR) or highly suffering from unstable software due to featurites.
So phase 1:

Build a DSP unit:

There you go, home brewn DSP with a Sharc SigmaStudio ADAU1701.
Check the mix off through hole audiophile components (WIMA, panasonic) and smd stuff (man, soldering these manually..aaarggh..)

Nothing really new here hardware wise, everybody knows those MiniDSP boards, but this one is programmed with the free Sigma Studio software, so we can do stuff like FIR.

Problem solved?

Hmmm, not really: apparently it is difficult to mix analog and digital circuitry. And those on board ADC's are not the most brilliant.
I did some test with SPdif and i2s inputs, which did improve the sonic quality, but things get complicated fast.

We could use some different DSP with a dedicated AD/DA section, but you will quickly find that the choice off self-boot chips is limited. All the rest will need some MCU to boot and control.
And hey, here's an idea:

Why not use a MCU  (you know like a arduino) to do all processing?
There is a zillion off boards available out there and they are all dead-cheap!

One tiny problem: not that many people are doing audio stuff with them, google doesn't really help

So stay tuned to find out more...