Faint LFE channel output, but overpowering when using RCA. - AVS Forum
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post #1 of 8 Old 12-28-2013, 05:22 PM - Thread Starter
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Receiver is a Sony STR-DH820. It has 2 RCA subwoofer outputs.
Sub is a Polk Audio DSW Pro 600. It has RCA inputs and LFE input.

Room was pre-wired with RG6 Coax in the corner for the sub. I believe I have all the connections converted to F type correctly, however when it is hooked up the connection is very weak. This is using one of the subwoofer RCA outs (either one) and the LFE input. After running the auto calibration software in my receiver, it sets my subwoofer channel to +10dB. You have to pretty much max out the subwoofer gain/volume to know it's even there.


Alternatively, If I run a set of stereo RCA cables instead and use the stereo RCA inputs on the subwoofer it's actually a little overpowering. Auto Calibration wants to put -10 dB on the subwoofer, and I can run the volume at 50-60% with very fantastic results. I've since bumped up the channel to -6.5 dB because I prefer move bass. I do not notice any bottoming out or other clipping issues. I'd be happy with this if it didn't mean I'd have to re-run a new wire through top plates and insulation.


So I'm not sure what the problem is. Seems to be the RG6 wiring and connectors, or the LFE input on the sub, or some hidden setting in the receiver.


So are my F to RG6 and back to F connections in question? I get a signal, just a weak one. I believe I have a good connection on the center copper, but not sure if I was supposed to get better contact with the outer shielding/wrapping. I used twist on style RG6 terminals and it's the first time I've ever messed with that, but I'm confident the center copper has good contact.

Or, I'm thinking the Sony subwoofer outputs are not producing the +10 dB LFE spec channel. Auto Calibration software did set all my speakers to "large" so I wonder if that's why the sub channel is weak. I'll try that tomorrow, but I'm using the same outputs. Just a single RCA to LFE (bad) or dual RCA on both ends (good).

Or maybe I'm missing something obvious?

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post #2 of 8 Old 01-10-2014, 02:47 PM - Thread Starter
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So single F/rg6 vs. Dual RCA, any guesses if I screwed up my Rg6 tap (loose connection) or maybe my receiver just doesn't support it? (E.g.the dual subwoofer output is for Rca input only and my dedicated LFE input on my sub is not getting the amplitude it needs?

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post #3 of 8 Old 01-10-2014, 04:46 PM
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It should pretty obvious from the RG6 cable and F-type connectors!

You're trying to run low frequency audio (0-100 Hz) through a cable and connectors designed for TV band radio frequencies (in the MHz band).

Radio frequencies ride on the skin of the conductor, at very low voltage and current, while line-level audio wants a thick cross-section to pass a lot of current without much resistance.

The design criteria are just about opposite for the two situations - the central conductor of a cable for radio frequencies (unless it's carrying a signal strong enough to be broadcast across the landscape) needs very little cross-sectional area and could even be hollow - or else very thin.

You're just going to have to run a good RCA cable. Sorry. The only effective way to send audio over that coax would be by putting a radio transmitter at one end and a tuner and amplifier at the other.

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post #4 of 8 Old 01-10-2014, 04:50 PM
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Quote:
Originally Posted by Philnick View Post

It should pretty obvious from the RG6 cable and F-type connectors!

You're trying to run low frequency audio (0-100 Hz) through a cable and connectors designed for TV band radio frequencies (in the MHz band).

Radio frequencies ride on the skin of the conductor, at very low voltage and current, while line-level audio wants a thick cross-section to pass a lot of current without much resistance.

The design criteria are just about opposite for the two situations - the central conductor of a cable for radio frequencies (unless it's carrying a signal strong enough to be broadcast across the landscape) needs very little cross-sectional area and could even be hollow - or else very thin.

You're just going to have to run a good RCA cable. Sorry. The only effective way to send audio over that coax would be by putting a radio transmitter at one end and a tuner and amplifier at the other.

Is this a serious post?

RG6 will pass an audio signal just fine.
Chances are it's not terminated correctly.
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post #5 of 8 Old 01-10-2014, 05:03 PM
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Quote:
Originally Posted by SAM64 View Post

Is this a serious post?

RG6 will pass an audio signal just fine.
Chances are it's not terminated correctly.

I could be wrong - that's not unprecedented.

The answer to whether this cable can do the job can be determined very easily with an ohmmeter (and very long probe cables!). If the resistance from end-to-end is high, reinstall the connectors and try again. However, if it reads a dead short but little audio still gets through, use RCA cables.

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post #6 of 8 Old 01-10-2014, 06:13 PM
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The cable can pass audio as well as DC and RF, no ohm meter is necessary to determine that.
An ohm meter will tell you if the cable has been terminated properly, which I suspect it hasn't.
Quote:
but not sure if I was supposed to get better contact with the outer shielding/wrapping

Yes, you need a good connection to both conductors in the cable, both conductors are needed to complete the circuit.
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post #7 of 8 Old 01-11-2014, 02:32 AM
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My JBL ES150P with the cheapest jack-RCA cable, output from PC, does almost the same thing. I never suspected the cable cause how could the cable be the problem when it has no problems if I attach a RCA splitter to fill both inputs on the sub ... its still the same cable and the same signal only difference is I connected both inputs.
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post #8 of 8 Old 01-11-2014, 05:49 AM
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Quote:
Originally Posted by Johnny Mnemonic View Post

Receiver is a Sony STR-DH820. It has 2 RCA subwoofer outputs.
Sub is a Polk Audio DSW Pro 600. It has RCA inputs and LFE input.

Room was pre-wired with RG6 Coax in the corner for the sub. I believe I have all the connections converted to F type correctly, however when it is hooked up the connection is very weak. This is using one of the subwoofer RCA outs (either one) and the LFE input. After running the auto calibration software in my receiver, it sets my subwoofer channel to +10dB. You have to pretty much max out the subwoofer gain/volume to know it's even there.


Alternatively, If I run a set of stereo RCA cables instead and use the stereo RCA inputs on the subwoofer it's actually a little overpowering. Auto Calibration wants to put -10 dB on the subwoofer, and I can run the volume at 50-60% with very fantastic results. I've since bumped up the channel to -6.5 dB because I prefer move bass. I do not notice any bottoming out or other clipping issues. I'd be happy with this if it didn't mean I'd have to re-run a new wire through top plates and insulation.


So I'm not sure what the problem is. Seems to be the RG6 wiring and connectors, or the LFE input on the sub, or some hidden setting in the receiver.


So are my F to RG6 and back to F connections in question? I get a signal, just a weak one. I believe I have a good connection on the center copper, but not sure if I was supposed to get better contact with the outer shielding/wrapping. I used twist on style RG6 terminals and it's the first time I've ever messed with that, but I'm confident the center copper has good contact.

Or, I'm thinking the Sony subwoofer outputs are not producing the +10 dB LFE spec channel. Auto Calibration software did set all my speakers to "large" so I wonder if that's why the sub channel is weak. I'll try that tomorrow, but I'm using the same outputs. Just a single RCA to LFE (bad) or dual RCA on both ends (good).

Or maybe I'm missing something obvious?

Reality is that the terminations (connectors) on any cable are the reliability/installation error hot point.

Electrically there is no practical difference between a F connector and a RCA connector in home use.

If you want to test a cable's signal-handling ablities, you can use either an ohm meter or a cable checker.

Ohm meter - general purpose tool:

http://www.amazon.com/Digital-Multimeter-Resistance-Capacitance-Tester/dp/B00A117OE8



Usage:

http://www.tigerstop.com/tigertamer/Using_an_Ohm_Meter.htm

Cable tester - special purpose tool:

http://www.monoprice.com/Product?c_id=105&cp_id=10524&cs_id=1052401&p_id=8129&seq=1&format=2



The above is the best kind of specialized tool for checking cables because it does not require connecting the identical same piece of equipment at both ends of the cable. The tool snaps apart into 2 pieces that you attach one of to each end of the cable. One end indicates whether or not the cable is good and the other is a remote sensor. It works for both network cables and coax, and works great with RCA cable if you add the proper adapters which are also economically offered by Monoprice.

http://www.monoprice.com/Search/Index?keyword=rca+f+adaptor

Example - priced at $0.99

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