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Not finding anything in any manual about the 'extra' output from the sa 10 and watching the extra little light light up on the front panel, I couldn't help but hook that output to A speaker. There is sound there. It does not seem to duplicate the surrounds or rear. So I have to ask .... What is it? Has anyone else used the extra channel? If so what is the speaker placement? Judging from what I hear it sounds like it could be a ceiling placement
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The SA-10 is just applying Pro-Logic to the surrounds. Pro Logic will make 4 channels from 2. On a Stereo setup, you get Left, Centre, Right and Mono surround.
In a Surround-EX you feed LS and RS in and you get Left side Surround, Right Side Surround, Back Surround (the centre channel) and... the Surround's Surround, which is the out of phase sound from the LS and RS.
Schematics (https://www.film-tech.com/warehouse/.../DOLBYSA10.pdf page 23) say that the Extra channel is going via a 50Hz HPF, a delay and a B-Type NS. It's then labelled as "future use". While the "centre/Back Surround" channel is derived without big limitations, the surround in a Pro Logic decoding is limited in frequency so I guess that's why it wasn't used straight away but left wired as "future use" which never happened.
What you hear is the out of phase sound between LS and RS - I'd imagine that is minimised in a proper EX track but it's basically sound which is not intended to be played anywhere.
I wasn't aware of that Extra channel, last time I played with an SA-10 was many years ago!
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Thanks for answering Marco. So where is the speaker placement for the extra?Comment
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there is no placement. It's "future use". The pro-logic decoder outputs 4 channels. Dolby decided to wire the 4th output anyways, in case there was a further development which never happened.Comment
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I put the extra on the ceiling and it sounds great!Comment
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Perfect! Silly cinemas who never wired that channel to the ceiling speakers!Comment
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