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les_maverick
Lokahi
USA
238 Posts |
 Posted - 07/18/2011 : 10:16:50 AM
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Lawarence:
We have been experiencing a hum in the speakers. This was with the cables that came with the speakers and mixer from Guitar Center.
But I had to use a 1/4 inch to dual rca jack to go to line in on the speakers.
Last night I took those cables out and used a cable with XLR into the line in on the speaker.
On the other end, I had to use a XLR to 1/4 adapter to plug into the mixer Main out jacks.
Guess what...... Hummmmm gone !!
Now I have to go buy some XLR to 1/4 cables for the speakers.
I also need a similar one for my DI to mixer.
Thanks for all the help. |
Edited by - les_maverick on 07/18/2011 11:19:50 AM |
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rendesvous1840
Ha`aha`a
USA
1055 Posts |
Posted - 07/20/2011 : 06:23:18 AM
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The sleeve portions of the TRS cables, and one terminal of the XLR plugs in those cables, goes to a braided wire tube that completely encloses the two shielded wires from the other connectors. This braid defeats the efforts of magnetic fields to create interference in the signals. This is the source of the hum you were getting, and why it went away when you changed cables. It's not that your other cables had a defect, just that they are susceptible to picking up a hum from electronic stuff. It could be as simple as fluorescent lights in the area. Motors and generators can also cause hum. Sometimes just relocating equipment can help, but it isn't always possible to move everything on a stage. Plus you have to figure out which piece is the culprit. So much easier to change cables.
Unko Paul |
"A master banjo player isn't the person who can pick the most notes.It's the person who can touch the most hearts." Patrick Costello |
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Lawrence
Ha`aha`a
USA
1597 Posts |
Posted - 07/20/2011 : 06:56:13 AM
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quote:
This braid defeats the efforts of magnetic fields to create interference in the signals.
Yes- except that the word "reduces" rather than "defeats" would be more accurate. The "shield tube" is not nearly 100% effective at eliminating magnetic interference but is very effective at eliminating electrostatic interference. And of course this also depends upon the quality of construction of the shield. There are cables available that have one braided shield inside another forming a dual shield and these are even more effective at reducing interference but still do not eliminate it entirely.
This is the reason balanced signal connections were developed. You have a device at the receiving end of the wire (either a differential amplifier or a transformer) that can take two opposite polarity signals, effectively invert one of them, and then add them. Any interfering signal that gets through the shield of the cable will cause the SAME signal (not an opposite signal) to be introduced onto the two wires inside the shield. These interfering signals will then get CANCELLED when one of them is inverted and then added to the other.
So with some increased expense, (three wires instead of two and either a transformer or a special "inverting and subtracting" a.k.a: differential amplifier), interfering signals can be very greatly reduced.
Sorry for the somewhat technical talk, but this is the reason for using balanced cables and devices in professional audio applications, especially for very low level signals (such as microphones).
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Mahope Kākou...
...El Lorenzo de Ondas Sonoras |
Edited by - Lawrence on 07/20/2011 06:58:16 AM |
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wcerto
Ahonui
USA
5052 Posts |
Posted - 07/20/2011 : 10:40:44 AM
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| See you guys, I told you Lawrence is the "Sound Man Extraordinaire"!!!!! Don't you just love how he talks? |
Me ke aloha
Malama pono,
Wanda |
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les_maverick
Lokahi
USA
238 Posts |
Posted - 08/16/2011 : 5:15:08 PM
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| Yes Aunty. Paul and Lawrence have been a big help !! |
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DI Box help
