Become a Site Supporter and Never see Ads again!

Author Topic: Need a way to block cell phone noise  (Read 535 times)

0 Members and 1 Guest are viewing this topic.

Offline Karl

  • Trade Count: (0)
  • Taperssection Member
  • ***
  • Posts: 363
Need a way to block cell phone noise
« on: February 09, 2018, 03:51:30 PM »
I record a lot of marching band type competitions. Recently, the judges at the competitions have been using multiple wifi hotspots to communicate their scores etc. This causes a lot of radio noise type interference with my recording set up. Is there anything I can add to my set up to help filter out the interference? Attached is a picture of my set up. They are AT-853 mics into Samson phantom power adaptors into the Tascam DR-100 mkii.
My portable rig:

AT853>Tascam DR100 mkii

Offline rumbleseat

  • Trade Count: (0)
  • Taperssection Newbie
  • *
  • Posts: 43
  • Gender: Male
Re: Need a way to block cell phone noise
« Reply #1 on: February 10, 2018, 10:40:46 AM »
I am not an expert in RF interference, but I've read that the Neutrik EMC connectors do a good job of rejecting RF noise.

http://www.neutrik.com/en/xlr/emc-series/nc3mxx-emc

In your case, you'd need to try inserting a pair of EMC cables between your Samson PM4 adapter and the recorder.  If this works, great.  But, it's possible that the interference gets converted to an audio signal before the recorder (i.e. inside the Samson adapter or further upstream), and in that case, the EMC cables wouldn't help.  A new set of mics with XLR connectors plus the EMC cables would be the next thing to try.

You need only one EMC connector per cable - the most common configuration is the connector that mates with the recorder (Neutrik NC3MXX-EMC).
If you want to tackle this yourself, be aware that these connectors are more challenging to solder than standard XLR connectors.  Might be worthwhile to have one of the TS guys make you a nice set of cables.

You might also try wrapping the DR100 and the Samson adapters with a single piece of aluminum foil.  Maybe that will do the trick!

AKG C480B CK61 cards >  Canare L-4E6S with Neutrik EMC > Tascam DR-680 MKII > memories

Offline DSatz

  • Site Supporter
  • Trade Count: (23)
  • Needs to get out more...
  • *
  • Posts: 2414
  • Gender: Male
Re: Need a way to block cell phone noise
« Reply #2 on: February 10, 2018, 12:35:01 PM »
These problems can be quite difficult to solve. If the RF source is close to your equipment and you can't increase the distance (or can't increase it sufficiently), it may prove impossible to solve the problem, though you may be able to reduce the effect of the interference.

It all depends on where the interference is being "detected" (converted into audible signal energy); there may be more than one such point in the circuit. Increasing the distance between the source of the interference and your equipment is the first thing to strive for. As a close second, keep the connections among all your items of equipment as clean, short and direct as possible. Try reorienting cables and other pieces because the angle of signal incidence may affect the strength of the received signal. It is basically like trying to improve reception of a distant radio station that you want to listen to, except exactly in reverse; you want to arrange the worst possible receiving setup for the signals you're receiving in this case.

As mentioned, Neutrik EMC connectors on your XLR-3 cables can definitely help; Schoeps' XLR-3 microphone cables use these; I'm amazed that everyone else's do not (and I'm a bit dismayed that Schoeps' XLR-5 to XLR-3 "Y" cables don't use them). Sescom, by the way, sells XLR-3M to XLR-3F barrel adapters with these connectors, unfortunately only one per unit (i.e. there is one unit available with the EMC XLR-3F and a conventional XLR-3M, plus another unit available with the EMC XLR-3M and a conventional XLR-3F; even Sescom's engineers couldn't explain why when I asked them). You might also try tightening any screws that could be any part of the connections among shields on your cables, microphones and recorder.

Ultimately, though, sorry to say, no one can guarantee a solution. Most audio equipment today, particularly in the consumer and "prosumer" ranges but including a lot of professional equipment, simply wasn't designed to handle the kind of interference that modern cell phones and related equipment can generate. Typical designs and production methods are often quite problematic (try doing a Google search on the "pin 1 problem"--even some top brands of studio equipment have had it, and much if not most "prosumer" equipment still does to this day). A new generation of design engineers, with a stronger awareness of electromagnetic interference, may will have to supplant today's generation of production designers before things get much better.

Or perhaps, since this problem doesn't affect most people most of the time, and most people don't shop specifically for equipment that's known to meet high standards of resistance to electomagnetic interference, the broad mass of equipment sold to the general market may never improve its resistance to EMI. Or the market may continue to muddle through as it has all these years, hoping that no one will blame them as from time to time we all, or nearly all, have recordings ruined in this way without there being anything much that we can do about it.
« Last Edit: February 10, 2018, 12:45:23 PM by DSatz »
music > microphones > a recorder of some sort

Offline nassau73

  • Trade Count: (3)
  • Taperssection Regular
  • **
  • Posts: 74
Re: Need a way to block cell phone noise
« Reply #3 on: February 10, 2018, 01:03:16 PM »
I'm not an rf knowledgeable person either. But ferrite beads might help.

https://www.rfvenue.com/blog/2015/05/06/how-to-prevent-cell-phones-from-interfering-with-audio-equipment

Offline Walstib62

  • Trade Count: (26)
  • Needs to get out more...
  • *****
  • Posts: 2364
  • Gender: Male
Re: Need a way to block cell phone noise
« Reply #4 on: February 10, 2018, 01:06:12 PM »
Balanced audio signal paths are more resistant to interference than unbalanced. You could possibly reduce the noise in your setup by placing the phantom adaptors closer to the mics, (shorter length on the mini-xlr cable, which is unbalnced) and using an XLR-XLR cable to extend the length between the adaptors and the recorder. Copper foil is also a good shielding material, but would need to be properly installed to be effective. Using well shielded cable is also necessary.

Offline Walstib62

  • Trade Count: (26)
  • Needs to get out more...
  • *****
  • Posts: 2364
  • Gender: Male
Re: Need a way to block cell phone noise
« Reply #5 on: February 10, 2018, 01:12:48 PM »
I'm not an rf knowledgeable person either. But ferrite beads might help.

https://www.rfvenue.com/blog/2015/05/06/how-to-prevent-cell-phones-from-interfering-with-audio-equipment

You could try that. It is better to put a loop in the cable so that the loop passes around the side of the ferrite core. (the cable passing through the core twice)

Offline Karl

  • Trade Count: (0)
  • Taperssection Member
  • ***
  • Posts: 363
Re: Need a way to block cell phone noise
« Reply #6 on: February 12, 2018, 09:48:14 AM »
Thanks for the replies. I will see what I can do.  Annoying for sure!
My portable rig:

AT853>Tascam DR100 mkii

Offline kleiner Rainer

  • Trade Count: (0)
  • Taperssection Regular
  • **
  • Posts: 125
  • Gender: Male
Re: Need a way to block cell phone noise
« Reply #7 on: February 18, 2018, 04:17:55 AM »
Hello all,

my day job includes EMC testing and compliance. If your recorder has a CE or FCC sign, it should have been tested to comply with the relevant standards - and that includes RF immunity. My suspicion is the problem originates in the passive components connected to the recorder: mic and wiring.

Point in case: my speciality is recording steam trains. Here in Germany. that often means contending with catenaries for electric traction, 15000V at 16 2/3 Hz. Unless your shielding from mic to recorder is 100%, you get massive hum problems. I found out the hard way that shielding of audio cables must be low-ohmic, and cover the signal conductors close to 100%. After measuring the shielding resistance of the offending cable, I built my own with much lower shielding resistance -> problem solved!
The reasoning is simple: lower resistance means more copper in the shield. And copper is expensive, so the probability that someone saved a few cents per meter in a ready made audio cable is high.

Recommended reading:

http://audiosystemsgroup.com/publish.htm -> "Hum, Buzz, and RF Interference -- Written for Audio Professionals"

In another case of hum, I could help a friend who plays bass. To solve the hum problem, I recommended using double shielded RF coax and high-quality connectors - Neutrik in this case - hum gone!

Another secret weapon is using ferrite beads to suppress RFI - but as with all secret weapons, you must be knowledgeable about your weapon - it takes years to master the art of EMC... using the wrong kind of ferrite at the wrong place can make your problem even worse!

So here comes tip no. 1:

Dont save on wiring and connectors! If you build the cabling yourself, go for quality in material and workmanship. My problems with connectors dropped to near zero after using only Neutrik or REAN. Soldering is an art - overheating wires and connectors leads to trouble sooner or later. Invest in a temperature controlled soldering iron. Use good quality rosin core solder. Learn to use your tools.

Testing for EMC issues is simple - a GSM Phone is sufficient. The pulsed RF it emits will point to problems immediately.

Good luck!

Greetings,

Rainer
recording steam trains since 1985

 

RSS | Mobile
Page created in 0.145 seconds with 31 queries.
© 2002-2018 Taperssection.com
Powered by SMF
Website Design by Foxtrot Media, Inc., a Baltimore Website Company