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Author Topic: Using RG6 Quad for line level signal to RCA fed subwoofer  (Read 17777 times)

Michael Martin

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Re: Using RG6 Quad for line level signal to RCA fed subwoofer
« Reply #10 on: September 05, 2012, 12:08:07 PM »

Jeff,
RG6 is a video cable, and not generally recommended for audio, although that doesn't mean it won't make the connection and work.
A low capacitance 22 gauge (or a 18-20 gauge for the longer run) would be the correct wire for this sub run.

Michael
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Marty McCann

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Re: Using RG6 Quad for line level signal to RCA fed subwoofer
« Reply #11 on: September 24, 2012, 04:30:16 PM »

We recently had a customer that used the Quad cable in a similar hook up to a powered sub.  The Quad cable professes to offer better EMI rejection, but RFI is an entirely different animal.  The system was picking up RFI and when the interconnection was re-patched using a standard low Z mic cable, the problem went away.
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Hal Bissinger/COMSYSTEC

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Re: Using RG6 Quad for line level signal to RCA fed subwoofer
« Reply #12 on: September 24, 2012, 09:21:20 PM »

We recently had a customer that used the Quad cable in a similar hook up to a powered sub.  The Quad cable professes to offer better EMI rejection, but RFI is an entirely different animal.  The system was picking up RFI and when the interconnection was re-patched using a standard low Z mic cable, the problem went away.

Interesting. Did you simply replace the RG6 with the mic cable or did you also convert to low impedance balanced?
 
-Hal
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Marty McCann

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Re: Using RG6 Quad for line level signal to RCA fed subwoofer
« Reply #13 on: September 26, 2012, 12:05:28 PM »


Interesting. Did you simply replace the RG6 with the mic cable or did you also convert to low impedance balanced?
 
-Hal

The power Sub had a balanced input so it was indeed balanced to balanced.  When heavy gauge copper is used in a Quad configuration, it only takes a few millivolts more of induced RF in one of the two balanced inputs to not be adequately rejected by some CMRR circuits.   The cheaper methods using an IC as the differential input may boast a -60 DB CMMR for Hum/Noise or other induced EMI, if they use 0.1 % resistors to null or balance the feedback networks.  However within the substrate of the semi-conductor material itself within the IC, the integration process uses back-biased diodes to set the gain of subsequent stages.  The best tolerances of these substrate diodes is 10%.  Diodes act as detectors for RF.  Thus in cheap products with cheap CMR stages, the best S/N for RFI is more like -20 dB.   -20dB of CMRR may get you by in many environment, but not necessarily in a venue next door to a radio tower.   The beauty of a quality balanced line transformer is that it simply can not pass any RF.
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Hal Bissinger/COMSYSTEC

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Re: Using RG6 Quad for line level signal to RCA fed subwoofer
« Reply #14 on: September 26, 2012, 11:26:44 PM »

Perhaps we are understanding quad cable differently. What the OP is talking about is a length of quad shielded RG6 coax in an unbalanced configuration. If your inputs were balanced how did you connect the RG6? Center conductor to one side and shield to the other side and ground or two runs? If so I can see why you would have problems. I do agree with your assessment of balanced inputs using op amps.
 
-Hal
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Re: Using RG6 Quad for line level signal to RCA fed subwoofer
« Reply #14 on: September 26, 2012, 11:26:44 PM »


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