Sarang S. Dalal sarang.da...@uni-konstanz.de wrote:
> I would like to construct a higher-order sound system, ideally with >consumer-level (and consumer-priced) components. I don't need a big dynamic >range, high power, or the best sound fidelity possible, I just need a working >prototype. > Sure. It's really easy to do if you don't care how much money you spend. Oh, but you do care! Even inexpensive PCs have so-called 7.1 channel outputs. My most recent PC, which cost less than $400, has an audio subsystem based on the RealTek ALC892. In the past I've put together a number of PC audio systems for various professional systems. One thing that I learned from those is that it's difficult to get high quality audio from a computer unless you have the converters be remote from the computer itself. Still, there is that claim of 8-channels of audio output from my computer. Those audio output jacks have been lurking on the back panel but I haven't investigate them until now. I just routed those outputs to my audio analyzer and ran some tests on them. I'm able to independently address all 8 outputs from the audio output selection in Plogue Bidule http://www.plogue.com/?page_id=56 I ran frequency response measurements on all 8 channels and they are all within +/-0.1 dB, 20 Hz - 20 kHz. The dynamic range, as measured per AES 17 is from 90 dB to 95 dB depending on the channel. Realtek claims 103 dB, but I can't credit that, not even with A-weighting. Still, 90 dB is really quite good. Remember, this is with a mini phone plug on the source end and and RCA jack on the other end. Looking at the dynamic range from full scale all the way down to -120 dBFS, there's a little bit of funny business for signal levels of -95 dBFS, but not too bad. Overall this is really quite impressive considering that it's free... Backing up just a little bit, one needs all of the items below to make a computer audio Ambisonic system: 1. Computer 1. PC 2. Mac 3. Laptop 2. Decoder 1. Stand-alone i. Blue Ripple ii. Harpex 1. Plogue Bidule 2. Max MSP 3. Pure Data 4. 1. Soundcard 1. Inbuilt 2. External, high-end 3. External, cheap 2. Distribution cables 3. Power Amplification 4. Loudspeakers The computer and OS is presumably whatever you have. I like working with Bidule because it makes all the file I/O and audio I/O transparent from my point of view. It's a VST host, if one were to go with using any of the several VST plugs that do Ambisonic decoding. If an internal sound card doesn't do the trick, another possibility is the M-audio FastTrack Ultra. But it costs just as much as my PC! I wish it were a little less expensive. Power amplification and loudspeakers are certainly an issue, as is the problem of mounting all those eight loudspeakers. You need to find a source of good cheap loudspeakers and don't forget the loudspeaker stands. As a rule of thumb it seems that there are many good loudspeakers available at about the $100 price point. As an example, I've just checked on the current pricing on the Infinity Primus 163 and they go for about $83 in the US. The primus 153 goes for $75. So eight of those is $600. Is this system going to be Periphonic? You say 3D so I guess the answer is yes. That means that you will be mounting loudspeakers both above and below the horizontal plane. I've never found a really satisfactory solution. It's easy to spend almost as much mounting the loudspeaker as the speaker itself cost. That just doesn't seem right! It's difficult to mount speakers down close to the floor, too. For the 'Up' speakers, there are speaker mounts available in the $10 price range, but they don't support heavy speakers and they don't allow the speaker to be mounted very far away from the supporting structure. Remember that the speakers need to be pointed at the listening area. Almost every speaker I've ever measured has serious frequency response discrepancies for angle above and below the central axis of the speaker. Amplification; The idea of using a surround receiver is a good one, although there are some serious problems. 8-channel analog inputs are only available on a few higher end units. I'm not saying that you shouldn't go that way. It's just that most gear ends up not doing what you want. A few years back you could have found a surround receiver with six power amplifiers and an analog volume control Not so easy today! I think that I would still pursue a multichannel power amplifier solution. The trouble is that those are almost all expensive. A quick search shows that there are a number of 8-channel power amplifiers but almost all of them are over $1000. Hmm. I see a nice Marantz Mm8003 8-channel amp for only $2400. Not what you wanted! I'm gonna back up again. I don't know what your budget is. But let's say that I want to put together an inexpensive 8-channel system. I'm going to use my PC, because I have it and because it has 8-channel audio output. What I really need are 8 channels of amplification and 8 channels of loudspeakers. So here's my budget computer free audio I/O free (use what I have) cabling to power amp free (I scrounge from my parts scrap box. But that assumes that I have a scrap box) Amplifiers 8X Pyle PMSA20 at $37/each ~$240 Speakers 8X Infinity Primus 153 ~$600 Speaker cables Zipcord (lamp cord) free (everyone better watch out because I've scrounged the cord off their lamps) speaker stands home built from plywood and 2X4s $100 (but this assumes that I have access to things like saws and hammers) So now I've built a system for $940. Probably more like $1000 since I may get caught in the act of stealing those lamp cords. And I'm not too confident about those Pyle power amplifiers. Hmm. I just spotted the Behringer EPQ304 which is a 4-channel power amplifier that goes for $200. That's 8 channels for $400. A lot of folks don't like Behringer but I find that they give good value for the money! Now my system is $1100 but I feel much better about the power amps. My solution (use the computer that I have) leaves out the problem of the volume control. One can actually do without a volume control, but it's also possible to just do it in your software. It's necessary to calibrate the system in such a way that the output levels from the DAC match up with the sensitivity of the power amplifiers to give you a system with a minimum of noise. It may occur to you to cheap out and use less expensive loudspeakers. I really wouldn't go to far down that road. $75 loudspeakers have maybe 50 Hz bass response. You can do a lot with that. Computer loudspeakers tend to be limited to 200 Hz or so. If you route all of the LF below 200 Hz to a subwoofer you end up loosing two important octaves of localizable audio. There's lots more that could be discussed here, but so much depends on what you can find locally in .de. Eric Benjamin _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
