Subtle surround anyone, Eno style?

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kalimerox

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Oct 25, 2021
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Thanks MidiMagic, I am still struggling to understand parts of the concept..

The most likely connection to work would be a 5th back speaker with its terminals connected to the + of left back and the + of right back.
wouldn t that reproduce the mono (or center-) signal in the 5th speaker?

sorry for my english, does "strapped" mean balanced, unstrapped = unbalanced? In my case the car radio is some cheap kenwood with "I think" rca outputs? I will see, maybe it s not worth the effort, I definitely would have tried if it would just mean changing the wires or soldering an adapter.
 

MidiMagic

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Jul 5, 2010
Messages
1,329
Thanks MidiMagic, I am still struggling to understand parts of the concept..


wouldn t that reproduce the mono (or center-) signal in the 5th speaker?

sorry for my english, does "strapped" mean balanced, unstrapped = unbalanced? In my case the car radio is some cheap kenwood with "I think" rca outputs? I will see, maybe it s not worth the effort, I definitely would have tried if it would just mean changing the wires or soldering an adapter.
Note that any speaker reproduces the voltage placed across its terminals.
This is the DIFFERENCE between the {+} rerminal voltage and the [-] terminal voltage on the speaker.
Speaker Output = [+] - [-].

Assuming normal stereo amplifiers, the back speakers will have the following signal polarities for the following input signals:

[+] = positive terminal (square brackets indicate a terminal here)

Input F = (R+L) . . . LB[+] = +1 . . . LB[-] = -1 . . . RB[+] = +1 . . . RB[-] = -1
. . . . . B[+] = RB[+] = +1 . . . B[-] = LB[+] = +1 . . . B = no signal . . . (+1)-(+1)=0

Input L (R=0) . . . LB[+] = +1 . . . LB[-] = -1 . . . RB[+] = 0 . . . RB[-] = 0
. . . . . B[+] = RB[+] = 0 . . . B[-] = LB[+] = +1 . . . B = -.71 L

Input R (L=0) . . . LB[+] = 0 . . . LB[-] = 0 . . . RB[+] = +11 . . . RB[-] = -1
. . . . . B[+] = RB[+] = +1 . . . B[-] = LB[+] = 0 . . . B = +.71 R

Input B = (R-L) . . . LB[+] = -1 . . . LB[-] = +1 . . . RB[+] = +! . . . RB[-] = -!
. . . . . B[+] = RB[+] = +1 . . . B[-] = LB[+] = -1 . . . B = R-L . . . (+1)-(-+1)=B

Note that with a normal stereo amplifier, a B speaker connected across L(+) and R(+)
we get the following:

Mono signal (R+L) has no output in B speaker - The exact sane voltage is on both terminals, so no current flows.

Single channel (R or L) has low output in B speaker - One channel has signal, buit the other does not.

Out-of-phase signal (R-L) has max output in B speaker - One terminal is positive while the other is negative.

-----

For some reason I don't know, the convention is that the B[+] terminal connects to R[+] and B[-] connects to L[+].

This convention matches speaker phasing for DQ, EV, and SQ. Only the Dynaco diamond has L[+] connected to B[+].
 
Last edited:

Scott M4

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Jan 3, 2010
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Location
Toronto, Canada
Hi, My contribution to this thread is just a cautionary tale. I began using the 3rd speaker wired across the two + terminals in the mid-Seventies when my band's sound tech (who was a very smart fella) tipped me to the technique. It was fun to get the unexpected sounds coming from the rear speaker and I used the technique for many years.

However... one day in the Eighties I was preparing for a night out and really cranked up Keith Richard's "Talk Is Cheap" (yes, I still remember the album... good songs with a very punchy mix) and got in the shower. When I got out I was surprised that the album was over already... but it turned out that the receiver was blown. The repair person stated that while I could get away safely with the 3-speaker technique on my old transistor preamp, the newer IC receivers could get overloaded, so I abandoned the 3rd speaker as I did like things loud sometimes!

So... if you're trying the technique out, keep the volume under the usual speed limit.
 
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