Taperssection.com
Gear / Technical Help => Cables => Topic started by: SClassical on February 17, 2012, 03:27:59 PM
-
Hi Have this cable:
http://www.fullcompass.com/product_image.php?imageid=20930
I record stereo (L an R) in the field and don't want to carry 2 cables so i was thinking of connecting 2 XLR connectors on both sides (balanced way) to a single cable.
There are 2 reds, 2 blacks and a shield in my cable...so I would like to connect 1 red to one connector and the other red in the other connector. I also will like to connect the black the same way. The shield will be shared with all the connectors...Would this be possible and would the cable be balanced? I know the red and black cables will be fine on both ends but is it ok. Will I get any audio issues with my cable if it is about 25 feet long?
Thanks!
-
or do this(or have me or another put a set together)
(https://public.blu.livefilestore.com/y1pzJXbl1v_I4WkLIVy5qX4F4hIOxofZ6LCCYRiKsqu_G0-xB4T6fdPhWPONW6_uzMg_vQmCAxXmpDUn_CqjREKFQ/DSC00843.JPG?psid=1)
-
Not recommended. Possible but it would not be completely shielded. Better off to snake together a pair like Robb suggested.
-
As was pointed out to me by another forum member, it is generally not a good idea to run L & R channels through the same cable. Crosstalk is possible if the impedance are not equivalent at both ends. We are still trying to fully understand this, but clearly a pair of techflexed cables is a better idea and Darktrain or Gak can make you an excellent pair.
-
You can get 2 pair audio cable with shielding if you want the extra protection. http://www.gepco.com/products/proav_cable/network/genpurp_2prshielded_M.htm (http://www.gepco.com/products/proav_cable/network/genpurp_2prshielded_M.htm)
Strain relief and keeping the pairs twisted after it leaves the common jacket will be where you need to be careful.
When built my cables I used 2 single pair cables. Instead of Techflex I did it the cheap way and used an inch of heat shrink every few feet to hold the two cables together. not as pretty but it works.
-
Wow... that was a great explanation. I am still trying to process it, but thank you Jon!
-
I use 4 conductor + shield all the time with my stereo mics without a problem. My standard mic cable has a 5-pin XLR on each end. As you say, it cuts down on the number of cables and weight you need to pack, and speeds up setup/teardown time. I made 3-pin to 5-pin XLR Y adapters; that way I can hook together as many 5-pin cable I need and terminate it with a Y to get back to the 3-pin world.
Many stereo mics has 5-pin connectors, but the pinout is not standard so I sometimes need to use a 5-pin to 5-pin adapter to get the correct pins connected together.
I have never had a problem with crosstalk or noise with my system. Most stereo mic manufacturers supply their mics with a single cable that carries both L & R channels without a separate L & R shield. It ain’t the shield, it’s the CMR that makes it all work.
-
As was pointed out to me by another forum member, it is generally not a good idea to run L & R channels through the same cable. Crosstalk is possible if the impedance are not equivalent at both ends. We are still trying to fully understand this, but clearly a pair of techflexed cables is a better idea and Darktrain or Gak can make you an excellent pair.
Crosstalk won't be a huge problem as it should be at least partially common-mode (and thus rejected), but even if not a stereo pair is going to have acoustic crosstalk no better than 30dB or so. Also consider that crosstalk occurs because of capacitance between signal leads, which also exists from signal leads to shield, so if crosstalk was a problem then high frequency loss to capacitive loading would also be a problem. You are looking at about 1nF, given 250 ohm source impedance (hopefully worst-case) the corner is about 600kHz, which if I did the math right is 30dB crosstalk at 20kHz (less at lower frequencies, -6dB/octave), *ignoring* common-mode rejection.
Which we shouldn't ignore; star quad cable will have the four wires in a constant relationship, so the L+ and L- signal should leak equally into both R+ and R- (canceling the interference), and also R+ with respect to R- (yielding common mode rejection).
The short ends that aren't perfectly shielded aren't critical either; common mode rejection is *far* more important than shielding. Just make sure the signal leads stay twisted.
I would worry more about the mechanical strength; be generous with heatshrink.
Geek! :P
-
You can also buy a 2-channel snake already made (i.e. two star-quad cables in a single outer shell. See this thread for discussion, description, photos, and links to buy the cable:
http://taperssection.com/index.php?topic=111443.0;all
Also note that in that thread, at least one person mentions that they use a standard star-quad cable for two channels, with no issues.
-
Same as said before. Use starquad and run two balanced stereo signals to my stereo mic or to the mics in a stereo pair. 5 pin XLR-s in each end. I have a few different lenghts of these stereo cables. And breakouts for each end into 3 pin XLR-s. Never had an issue.
// Gunnar