Mid-side for ceiling speakers - AVS Forum
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post #1 of 12 Old 07-23-2010, 09:16 PM - Thread Starter
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I came up with an idea that I'd like to try out... Curious what you guys think.

I have a split-level house with the kitchen and living room upstairs. The LR is medium size, tall ceiling, and will have seating on maybe three of the four walls. There's a fireplace, lots of light, and is generally a great place to hang out alone or with company. I have no intentions of putting a TV or proper stereo system in there, and mainly just want music for entertaining, casual listening, background, and so on.

I'm strongly considering ceiling speakers. The attic is directly above, so enclosed cans would be fine. But with ceiling speakers, especially when there's no "correct" orientation to sit, having good left-right imaging seems somewhat of a burden to try and achieve. I would still like the sense of spaciousness (in the sound) but I'm far more concerned with something that sounds 'nice' rather than 'accurate'.

Given that, I thought of having a center speaker in the middle of the room, and then maybe two others flanking it, or four in a box or diamond around it. The four would be tuned to sound as loud in any given area as the center, and instead of using L and R feeds, I would put the stereo audio through a Mid-Side encoder and send the Side channel to the four.

For those of you not familiar with M/S, it's basically like the Center and Surround channels from Dolby Pro Logic, but contains 100% of the audio and can be converted back and forth losslessly with simple mixing and phase inversion.

So... Thoughts?
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post #2 of 12 Old 07-24-2010, 01:46 PM
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Interesting;

What are you using to do this Mid-Side encoding?
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post #3 of 12 Old 07-24-2010, 01:54 PM - Thread Starter
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Haven't figured that out yet. Probably throw something together with a couple op-amps if there isn't a cheap box to be found online somewhere.
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post #4 of 12 Old 07-24-2010, 04:17 PM
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Quote:
Originally Posted by SirNickity View Post

Haven't figured that out yet. Probably throw something together with a couple op-amps if there isn't a cheap box to be found online somewhere.

Ah, ok, I tought perhaps you were using something new I was unaware of.

In that case you should be able to use Smart CS-3X Jr's to accomplish what you want, I use several of them in my test system.

You can see what I did a while back in this thread it might give you some ideas;

http://www.avsforum.com/avs-vb/showthread.php?t=982996

BTW;I still have this system intact, only rearranged to encompass the whole bedroom with some better speakers, a large HDTV display and love it!
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post #5 of 12 Old 07-25-2010, 12:01 AM - Thread Starter
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Unless I missed something, that box takes the sum of two channels. That would give me the Mid channel, but I still need a difference for the Side. :-)
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post #6 of 12 Old 07-25-2010, 07:21 AM
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Quote:
Originally Posted by SirNickity View Post

Unless I missed something, that box takes the sum of two channels. That would give me the Mid channel, but I still need a difference for the Side. :-)

No, it gives you the difference between two channels;

For example; if you want left and right mid channels then you use two of those boxes, for the left mid channel use your front left as main left input and surround left as the main right input and the center output on the box for your left mid channel. Then do the same with the second box to create your right mid channel using front right and surround right as inputs and the center out on it.

This will accurately place the correct sound at the mid point between your fronts and surrounds for a smooth transition front to back and back to front.

Another example would be if you want a single center overhead channel at the listening position; you would use one box and the left and right surrounds outputs as the main left and right inputs on the box and use the SP1 out on the box for the overhead channel. Or you can use both SP1 and SP2 outs for dual mono overhead channels.

Or go even further like I did where my overheads are all stereo the sky is really the limit with this.
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post #7 of 12 Old 07-25-2010, 02:09 PM - Thread Starter
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I think we're talking about different things. Mid and Side aren't referring to physical placement, it's regarding the phase relationship between two input channels and the processed output.

Mid is the audio that is correlated between two inputs. This looks like what the CS box does. Great for filling the gap between two sound sources like in your setup, as it represents the commonality between the two.

Side is the exact opposite and represents the audio that isn't common between two inputs. Whether that's because the audio is Left-only, Right-only, or common but out of phase.

With the two, you represent every bit of the original audio still in two channels, just in a different form. VHS, vinyl, and FM radio all use this technique to present a mono channel, for compatibility, plus a "difference" (side) channel to provide all the information necessary to re-create the stereo field without having to explicitly carry L and R in addition to the Mono channel.

Am I still missing something? :-) Correct me if I am.
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post #8 of 12 Old 07-26-2010, 05:22 AM
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As for the “Side” I would have no clue how to isolate or extract it so only it could be sent to separate speakers.

Also I would think these anomalous sounds emanating from separate speakers at least if not placed just right would distract from the surround sound rather than add to it.

But if you are looking to squeezes out every bit of audio information out the surround sound audio it may be worth a shot.

If that is what you are after you also might want to consider going with dual sub’s; one hooked to the sub out, and one hooked to a multichannel bass management controller using the multi channel audio outs (except the sub out) on your receiver or pre-amp in between it and the amp/amps, to extract every bit of bass.
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post #9 of 12 Old 07-26-2010, 12:17 PM - Thread Starter
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It's not for surround sound. It's designed as a music-only system. I'm just looking at an alternative to stereo, but still using two channels and multiple overhead speakers.

A true stereo image requires being between two speakers. I don't want to give up on spacious sound and go mono, but I don't think the flexibility of a group of people being able to sit anywhere in a common area lends itself well to traditional Left-Right imaging.

So I'm looking at a centrally mounted speaker (Mid), and up to four peripheral speakers located around it, all playing the same channel (Side), but at a lower volume, and spread out to cover their local areas. I'm wondering how this would pan out (no pun intended), providing some depth to the sound.

I can come up with something to do the processing, but as I don't have the equipment set up to do a demo yet, I'm fishing for ideas on the theory itself from anyone who has maybe thought of or tried something similar.
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post #10 of 12 Old 07-26-2010, 01:49 PM
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Then why not still use a 5.1 surround sound receiver set the surround sound output to 5 channel stereo, use the center as your main and front left, right, and surround left and right as your peripheral speakers and lower their volume as you see fit?
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post #11 of 12 Old 07-26-2010, 06:34 PM - Thread Starter
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I guess that would be an option, but it seems a bit overkill. I had counted on using a little 2-channel amp mounted in the wall (like the Boston Acoustics LCAi220 over at Parts Express, for e.g.) 20w or so would probably be plenty. Multiple amp channels would only be useful if I found that each of the four 'ambience' speakers needed different level settings. Otherwise, a serial/parallel configuration would probably suffice.

I had actually started out considering matrix surround, though I would imagine your presentation at any point in the room really wouldn't be very predictable - especially with some of the steering artifacts caused by Pro Logic decoders. PL-II Music mode would probably work alright... but I doubt it would be better than a simpler alternative. That's when I started thinking along the lines of M/S.

I appreciate the sounding board - even if so far I still suspect I'm probably headed on the right path. Sometimes the true brilliance or utter stupidity of an idea only surfaces when you try to explain it to someone else. ;-) We'll see which way this one goes...
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post #12 of 12 Old 07-27-2010, 11:55 AM
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Well whatever you come up with post about it here I would be curious as to what you devise.
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