# Are rear channels of a head unit simply parallels of the front?



## MikeT1982 (Jul 6, 2011)

Hey guys what's up? I have been gone forever and apologize...I've been trying to keep my mind off audio to save money and on my cheaper hobby of vintage lighting LoL! I never stop thinking audio though lmao! Anyways I hope everybody had a great holiday and such I don't think I've posted here since around turkey day or something. But I jussst remembered a question I never asked and quickly forget. In a traditional head unit like from our oldschool times (mine were mid to late 90's) I always wondered if the rear channel RCA preamp outputs were simply the exact same information as the fronts (left rear a parallels to left front and right rear a parallel (wired off of) the front right internally if you know what I mean. My old Alpine deck also had sub outputs which I would assume are a third parallel copy, but front, rear, and sub outputs (6 jacks) all on their own attenuation controls (front rear left right). Orrrr are they similar to Dolby multichannel audio with different tracks all carrying different information....I am guessing not due to a CD just having two channels (I could be wrong). This all would be relevant someday in my dream setup which involves a cut through s10 time machine I don't own yet and on highs a 4 channel amp with the front driving dash speakers and the rear driving the doors....basically if there indeed does exist "rear channels of audio" more than simply left and right information, this would spell for a "weird sounstage and improper imaging" LoL! I can't wait to hear the real answer!  I probably should have posted in general but feel more comfortable in our little forum, hope that's alrite .

Thanks guys!!!

Mike T


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## Justin Zazzi (May 28, 2012)

I cannot speak for oldschool car audio gear, but what is common in modern car and home audio is when there is an algorithm for creating false surround channels or rear fill or some other kind of processing, the manufacturers love to highlight that as a feature and give it a name and a logo. Dolby as you mentioned has ProLogic. DTS has something called NEO6. Car audio has many different ones like CircleSurround and Logic7. If the head unit has any of these technologies, it is always proudly labeled on the faceplate or somewhere else really visible.

It is a reasonable bet that older or very inexpensive gear (that does not have licensed technology like above) simply sends the same signal to the front and rear like you described. In that case, you can use the "front" channels to drive your front stage, and "rear" to drive your subwoofer. Or whatever combination works best for you.


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## MikeT1982 (Jul 6, 2011)

Thank you very much for the explanation! I got curious and followed your link and saw your transmission line sub!! I really like that as I'm currently working on a set of Frugal Horn backloaded horns for the Fostex Sigma 3" full range drivers and a small tube amp! (My other hobby, the audio I actually practice now lol!). A transmission line....I would love to hear one, what does it act like and sound like? I am thinking/imagining it would act like a very large ported box with a narrow but very deep tuning frequency, hence little cone support out of the tuning frequency (need stiff suspension woofer) but very powerful in it.... I really wish I could have heard yours, beautiful design  I guess you could say I'm kind of fascinated with them and would love to build a set of small transmission lines to have next to my frugal horns to demo either! I still have yet to hear a backloaded horn and that is the goal of building them as no one here has any I can listen too and I can't wait to see if its true that the 3" full range driver can eminate highs and mids from the front and I truly get a small sub like effect out of the horn mouth! I can't wait, it's too cold now to finnish the woodworking though lol. (16F as I type this) lol.


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## Justin Zazzi (May 28, 2012)

The user here Patrick Bateman is one of the most active when it comes to horns and transmission lines. Look up his work for more details.


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## smgreen20 (Oct 13, 2006)

A simple answer to your question... It is just as you think/describe it to be. AM/FM/CD are all in stereo /2ch. Unless you're running a processor that specifically states it is creating some sort of surround, assume what you posted.


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## MikeT1982 (Jul 6, 2011)

Thanks man


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