Wednesday, February 27, 2019

MYWIFIHIFIBIPI (Wi-Fi and bluetooth playing bi-amped hi-fi system based around a raspberry pi and 5.1 receiver) or: Another abandoned project

I first was given my aunts old Onkyo TX-SD696 5.1 receiver. Then I found a pair of JBL ARC 1000's on the local classified ads. Then I went crazy.

See the rub was that several reviews of the loudspeakers mentioned that they really shine when bi-amped. I did a little research and learned what that means and that most people who think what that means don't actually know what that means.

Since I can't help but show off my new-found knowledge I'll share it. Bi-amp, etymologically just means 2 amps, but there are bountious ways to use 2 amps incorrectly. Bi-wiring is an orthogonal idea where you run 2 lines (4 conductors) instead of 1 (+- only).  You really need both to gain any advantage AND you need a preamp crossover. This is where the real advantage is to be gained: by allowing the amps to focus on amplifying their respective audio band (woofer or mids & tweeter) without the other band taking any headroom. Also the amp drives the horns directly without the other drivers electrically coupled in. The passive crossover is still there, but since all the content managed by each amp is in the passband of the channel its driving, it shouldn't have much any effect on phase or amplitude of the signal reaching the speaker. I'm not an audio expert but that jives well with the signal processing & circuit theory I learned in school. Interestingly they say these crossovers are always active, though I don't see any reason why they HAVE to be (as long as your input source has enough oomph).

Since its probably a stereo system (though I did recently acquire the traditional mono version of Pet Sounds) you actually need 2 crossovers, 4 amps, and 8 wires (4 +- pairs)! Not to mention you need speakers with 4 posts on the back and not just 2.

Well, with these new (to me) speakers, the 5.1 receiver, and some salvaged speaker wire I have most of those things. I don't actually have 4 amps, but I have 5 amp channels, which I can utilize.

What about the crossovers?!

Setting up a Raspberry Pi 3 as a Bluetooth Speaker with NO Pulseaudio...

I really don't have much against pulseaudio. I use it daily on my daily computing machine. But believe it or not, I don't do my daily computing on a bluetooth speaker. No, I'm of the persuasion that pulse is a great desktop audio system (though I have high hopes for pipewire), except for when it isn't. For pro-audio (making my own music) I use JACK and it's awesome, and you already know I use pulse for daily web browsing, music listening etc, but neither of these cases are very much like a bluetooth speaker, are they?... We need an audio system that's basically going to serve as part of an appliance. But what else is there?!


No, there is not oss.
I mean, there is, but it was replaced for good reason.

ALSA. I'm trying to lead you to alsa. Alsa is actually the audio driver behind both JACK and pulseaudio so its lower level, but you've got a headless system for crying out loud that just connects bluetooth and streams the audio, what do you need high level stuff for?