Line-Level Cable Alternatives

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I'd like to install one or two Bass Shakers in my basement viewing area (two couches). I need no more than 50 feet of line level cable from the AVR to the Bass Shaker and (satellite) amp location (probably more like 30 feet). I plan to route it through a 4mm (wide) by 8mm (deep) expansion joint cut in the concrete slab floor.

Cables I'm considering:

- one or two twisted pair(s) stripped from Cat5e cable or better. (Stripped due to space limitation.)

- a thin shielded line-level cable (RG-174?)

- one run of Cat5e or Cat6 cable (not stripped), but I don't think it will fit in that joint.

Any thoughts you have on cable selection or otherwise would be appreciated.
 
A twisted pair is good for signal connection.

But the quality of the signal arriving at the Receiver is more dependent on the Source parameters that send the signal.

You need a low source impedance and you need sufficient current drive.

I would suggest that <= 100ohms source impedance and >=8mApk of current will be good enough.

If you have high interference, then you may need to consider going to balanced impedance for the connections.
That uses the same cable, this time you would need a new Receiver. Wait till you test your installation. Then decide if you need to buy a new Balanced Impedance input as a Receiver.

It is very easy to convert the output of your source to Balanced Impedance and it would cost less than $10 per channel. See Jensen app note an003. B.Putzeys adopted this as the output for his balanced volume control.
 
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The overall length is 30ft. I assume/understand the subwoofer line-out is (unbalanced) high impedance and the line-in to the plate amp for the subwoofer is (unbalanced) high impedance.

For 30ft do you agree RG174 (unbalanced) would be an ok choice for this application considering signal loss and potential for interference. Most importantly, I think the cable will fit in the expansion joint. (As a reminder, this is a Bass Shaker.)

If balanced transmission would be far superior I would envision this:
Code:
sub line-out [unbalanced]=>balun=>[balanced]line to plate amp=>balun=>[unbalanced]sub line-in
Is that correct?

If I use a Cat6 cable for the balanced line can I deconstruct it (keeping all the pairs with their twists intact) so I can fit it all in the route or will that invite interference and defeat the purpose?

If I use a Cat6 cable for the balanced line how does that work? Do I use one pair (soldering both conductors to the terminal) for V+ and another pair for V-? or -- do I use one conductor of a pair for V+ and the other conductor of that pair for V-?

Where/how is the ground/shield connection in the balanced configuration made? There's four pairs of conductors in the Cat6 cable. Do I just connect one pair to the ground post and leave the fourth pair unconnected?

Can you help me with balun selection? That is, what would the correct balun(s) for this application look like or consist of? Thank you.
 
pgreenwood said:
I assume/understand the subwoofer line-out is (unbalanced) high impedance and the line-in to the plate amp for the subwoofer is (unbalanced) high impedance.
The line out should be low impedance. The line in should be high impedance.

For 30ft do you agree RG174 (unbalanced) would be an ok choice for this application considering signal loss and potential for interference.
That depends on the output impedance of the line out, and how electrically clean is your environment, and how much interference rejection you need.

If I use a Cat6 cable for the balanced line how does that work? Do I use one pair (soldering both conductors to the terminal) for V+ and another pair for V-? or -- do I use one conductor of a pair for V+ and the other conductor of that pair for V-?
Use one pair i.e. the latter arrangement.
 
you need two wires to make a signal connection.
That can be the screen and core of a coaxial cable. Both parts carry the signal.
or
you can use a twisted pair. again both parts carry the signal.
If you go to balanced impedance connection then you have the choice to use unscreened twisted pair (UTP) or screened twisted pair (STP).
Balanced impedance connection generally uses a 3pole plug and socket. Pin1 carries the screen to Chassis at both ends. Pins 2 & 3 carry the signal on the twisted pair.
One twisted pair is needed for one channel.
 
...If you have high interference, then you may need to consider going to balanced impedance for the connections.
That uses the same cable, this time you would need a new Receiver. Wait till you test your installation. Then decide if you need to buy a new Balanced Impedance input as a Receiver.
....

I see your reference to Jensen app an003 and thank you for that. I will read (and re-read....) In terms of cabling, then, I understand that unbalanced may suffice but balanced will [always?] be better.

So in case I end up needing balanced transmission, I should install a two-conductor with shield cable (something like this). Correct?

If one uses one pair of UTP for balanced transmission of the signal, then is the screen implemented via a third conductor (from another twisted pair, for example)? Many thanks.
 
The line out should be low impedance. The line in should be high impedance.

Please disregard this post. I'm going to read up more on impedance.

[strikeout]It is my understanding the (remote) plate amp "wants" a high impedance source. That would be the signal coming from the cable. Right? So the signal is low impedance when it leaves the AVR; then how does it "become" high impedance when presented to the remote plate amp? Is it just that "high impedance" and "low impedance' are relative terms? Is the cable simply "high impedance" in that it has no current, only resistance, as it lays lifeless on the floor? I would expect that if I just RCA-plugged a short (3M) unbalanced shielded guitar cable between the subwoofer line-out at the AVR and the RCA line-in at the plate amp connected to the sub, everything would be hunky-dory. Many thanks.[/strikeout]
 
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PRR

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Joined 2003
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At least one end of the line probably should be low impedance. By long-standing convention (in many electric fields), we do lo-Z source and hi-Z load. Simple resistor-divider sketches will show some advantage.

A more elaborate sketch including crap leaking in will generally show another advantage of low-Z: less crap voltage.

The bass-amp does not "need hi-Z drive"; indeed it surely expects lo-Z but isn't real fussy.

You may be over-thinking. Throw a long RCA cord across the floor and listen. I have done just that, with moderately critical audio (live concert recording), with little trouble. Better here because you actually propose to shove the wire IN a crack in concrete on dirt. Concrete is not the world's best shield but it is probably a lot quieter in that crack than strapped to your main power line or the circuit to the vacuum-cleaner.

_I_ would use CAT-? network wire (cheep!!) as unshielded stereo pair. Just that worked well in multiple situations far more than 30 feet and not down a crack. And in your case, if that does not work, you do not have angry performers demanding instant fix, you can go back for shielded cable or proper balanced line drivers.

Minor work-saver: adapters to put unbalanced stereo audio on CAT-cable are a standard thing in install-sound work. On a DIY forum, this is cheating.... but you just want your bass, not a Project.
 
Thank you PRR (and others). I'm new here and greatly appreciate the feedback. Overthinking? Most definitely. But in my youth I didn't do enough thinking and I'm now approaching a time in life where I want to take my time, learn and [maybe] do it right the first time. Last night I soldered up a long test cable using one (only) twisted pair from a sacrificial Cat6 cable. I will do some seat-of-the-pants A-B testing tonight against a short, "real" shielded RCA cable and expect there will be little if any audible difference.
 
I am obsessing about this cable because (1) the route has limited space (approximately 3mm x 5mm--too tight for an intact CAT cable) and (2) the route will be covered in flooring before too long. Aside from the fact that I can't be sure where my wife and the designer will finally decide to locate the seating, I won't be able to easily go back and install an alternative cable, so I want to install ingredients that can later be balanced if necessary.
 
if you think that interference is a problem then use shielded twisted pair. It can be used unbalanced and the shield attenuates the interference. Or can be used balanced, if that proves to be necessary.
This early experiment comparing UTP to coaxial should show whether there is an interference problem.
 
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