Another hair-brained idea!

One of these days, I’ll get around to re-wiring my house, however there are a number of obstacles in the way … the largest being the 2ft of clearance between my crawlspace and my floor joists.

Along with plenty of 20a rated outlets to go around and ethernet glaore, one thing I’d like to have is music in every room, well, nearly every room. I’d especially like to have audio in the kitchen, work shed (attached), bedroom and dining room. The bedroom would be a special case, I’d like to have the audio system, and an additional thin/fat client for full AV usage.

My idea for the audio system revolves around using a linux server. Here’s the basic idea … each room would have a small LCD screen and some buttons (or maybe old pda’s?). So I’ll call that the interface, whatever it ends up being. Each interface will be able to select the source (perhaps four or five source channels, whatever I can get away with, plugging cheap sound cards into my linux box). If the source is digital, i.e. mp3, the interface should be able to pause playback, next track, previous track, random track. The interface would also need to present a pre-programmed list of Internet radio stations (my main source of music, I have a very small cd/mp3 collection). In the case of internet radio, the interface should let me select the previous station, next station, random station, play, pause, etc. When using a live source, cable, tivo, etc, I dont want to mess with an inter-device interface, so, the only option would be mute. For any source, the interface will also provide a local volume control.

MPG321 and the linux kernel modules apparently have support for multiple DSP audio devices, so a rather simple script should allow for a specific input (file or live) to be routed to a specific output. For mixing of sources, that is, two rooms want the same source, I plan to use a series of analog multiplexors, designed for just this application. These simple ICs can be controlled by the server, and connect specific analog ouputs to specific analog inputs. For example, a 8 channel mux arranged as 2×4 will allow a single stereo output to select from a choice of four inputs. So one IC is required for each stereo output, allowing each source channel to select any of the four sound cards as inputs. A similar IC setup would be used to allow the sound cards to share live-output sources (tivo, cable) as inputs, connecting their line-input to any live source available.

I’m not sure about distribution. I could either go with matching transformers, and send line level signals over cable to the room, and use local amplification… or, I could go with central amplification and just use some heavy speaker wire to drive speaker jacks in the rooms. My house isn’t huge, so there wouldn’t be any runs more than 50-70 ft, so inexpensive 14ga speaker wire should serve nicely … I’m not looking for killer sound while I’m stir-frying … just want to be able to hear the tv or shoutcast stream without having to blast my stereo at the opposite end of the house. The advantages I see of central amps, I can build up a big power supply using old computer psu’s, and drive inexpensive car-audio DC amps, one for each source. The server could control the power to the amps, turning off unused sources. Secondly, line level signals are really low voltage… trying to send them over a long run of wire seems to be asking for trouble … unless I use something expensive like RG58 or RG6. Local amplification also means I need to locate an amplifier somewhere in the room, and provide power for it … not that big of deal I suppose.

This project is a long ways off, but its something that keeps crossing my mind, so I figured I should write it down.


5 Replies to “Another hair-brained idea!”

  1. You can simplify your life on this one. If you have a sound card for each room (or a firewire interface with enough ins and outs to cover you), you can have the routing all done in software thanks to ALSA’s advanced capabilities. For the long haul of your line level audio, dont worry about cable quality so much — just use balanced audio. Some firewire intergaces can output it directly or you can convert unbalanced to balanced with an audio transformer. Your audio will go a lot farther with almost no noise. You could probably even run it inside the same cable that will run the serial interrface for your LCD.

  2. Just found this Blog. I’ve had in the back of my mind something similar. I just want sound im living room where my sterio is and other rooms including the back porch. I haven’t read up on it to know if it is feasible, but I thought that Zigbee might be a reasonable didtribution method. What say you?

  3. Bill, the zigbee line of rf modems are for low bitrate serial packet data (like rs232, etc) .. there’s not nearly enough bandwidth to transmit 2 channels of CD quality sound.

    there are other options if you want to go wireless, but most of them are analog, and in very crowded bands … I used to use a 2.4ghz video sender to beam 2 audio + 1 video channel across the house, but now with wifi everywhere, there is too much interference.

    hard-wired is the way to go for audio

  4. Not a hair-brained idea in any way. I’ve done something very similar to what you want to do. Check out my site: if you get a chance. I currently have 4 zones up and running. I have the speakers for a fifth, but haven’t had the time to install them. I have a sixth zone wired, but no speakers yet (backyard). I’m using remote amps and ran speaker wire all over the house. System is controlled via PPC…pretty cool. Good luck to you.

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