Newsgroups: rec.audio.tech
Subject: Re: Attach speakers digitally
References: 
Kevin Boergens  writes:

> I have an idea and I'd like to hear your opinion about it: I'd like to
> build digital speakers. That means that even the bus to the speakers
> in is digitals. Making the signal analog will be done within the boxes.
> 
> Is there anyone selling such boxes? If not, what kind of bus would you
> use? 

In the computer world there are speakers out there that attach with
USB and perform the D/A conversion and amplification within the speakers. 

There are also speakers for example in professional monitor speaker 
market with S/PDIF digital interface (for example GENELEC 2029A).

> I'm not sure whether S/PDIF is the right thing for me because I
> have to transport only one channel. 

I think that S/PDIF is the right thing to use. 
It is well standardized, there is wide selection of suitable 
ICs for handling the signal, equipment with digital output 
most often give this kind of signal output directly. etc. 
S/PDIF sounds like a pretty good idea to me, even though 
you only use half of it's bandwidth per speaker. 

> And even if, I still need to split
> the signal before going to the boxes and chips with are capable of
> decoding the stream.

You need the decoders in the boxes, that's for sure. 

You don't need any fancy special splitter for going to both boxes. 
Baically you can build the system in such way that you always 
feed the same full stereo signal to both speakers, and the 
speakers just pick up the channel you want to play out through 
it and forger everything else coming in. You cna foe example 
have two identical speakers with S/PDIF input and switch on the back 
to selec which channel audio to play back (just set left speaker 
to left channel and right speaker to right channel and things work). 

For splitting the audio from one source to two speakers, you bascially 
need some form of passive signal splitter or active splitter amplifier 
that can run two outptu cables from one signal source. 
Passive splitters will do if you don't have too lign cables or have 
sensitive enough S/PDIF signal receivers to get slightly weaker 
than normal signals. Passive splitter for coaxial S/PDIF if just 
simply a tranformer with one primary coil and two secondary coils 
(with slightly less turns than primary), that does the impedance 
matching. Active solitter would be something quite similar to 
a vidoe disribution amplifier or s/ODIF inut amplifier + two S/PDIF 
driver circuits.

For optical Toslink interface, I quess that a simple optical signal 
splitter would work well (I quess I have seem somethign like this for sale 
somewhere quite cheaply). 

> Any help appreciated,
> 	Kevin

Hopefullymy tips helped you.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/