Salt water to ground the stage..... EPIC.... a brilliant yet so simple solution to a bad problem... It's why I keep coming back, the wisdom shared here is practical, useful yet mind blowing... THANKS!!!!
I'm not buying that story! that's not exactly how RF grounding works. He is probably talking about en.wikipedia.org/wiki/Olympiaturm witch is not one big antenna but there are small short wave antennas on top of a tower Short wave is (was) FM not AM... so maybe the Sound guy version of Sailors' superstitions
Yes that's the tower and scepticism is welcomed with open arms! Here is a more in depth description of the event written the same or following day after the event occurred with more accuracy. Curious to hear your take or alternate possible explanations. www.ratsound.com/cblog/archives/282-Day-402-June-29th-Munich-Show-Day-All-things-Are-Inter-Connected-or-Sometimes-Not-Part-2.html
@@DaveRat Thanks! It just sounded to mush like the magic salt circle witchcraft to keep away the bad RF Ghosts. But on the other hand Every electrical engineer can confirm that RF is basically voodoo or black magic. Antennas are kind of like acoustic resonators. the bigger the lower there Frequency. The frequency from that tower are probably all over ~100MHz and a Antenna would be something like 3 meters or shorter. Also professional gear should be relatively immune to that frequency?
@@lambda7652 yes, as I troubleshoot in the bpg I put the link to, it was not the pro gear that was the issue. The issue was that when the guitar pickups where physically closer to the stage, the RF interference increases. If the guitar was held overhead it got quieter and guitar set on stage was louder. Somehow the metal stage seemed to be saturated in the RF. Guitar pickups can be quite susceptible to RF especially high gain single coil versions. Somewhere I have a recording of the show. Even though the salt water did appear to help, the issue was only reduced but was still audible between songs. I will try and locate it and post excerpts if I do
I’ve heard the cell phone interference several times when it’s next to a speaker, or an unbalanced line. Most often, I’ll hear the noise a few seconds before my phone starts to ring! Thank you for sharing your knowledge, that story was awesome!
Hello from Munich, Germany. Nice story. Yeah, the biggest live sound arena and indoor venue are in the Olympic Park, right next to the tv tower. I had a sound job for a kids soccer tournament in the stadium and could not get one reliable channel of rf for a distance for over 10 meters (with my old shure u4d), them I looked up and knew why. A few hundred meters further at the second event: no problems... Still was a successful and fun event.
An MIT undergraduate recently borrowed a very expensive network analyser. Absolutely Doctor Rat was indeed correct that the designs of tinfoil hats do indeed amplify specific frequencies of EMI, rather than attenuating them. It has been experimentally confirmed. IIRC the boost was anything up to 14dB
Awesome video! Even if I have known the basics of sound reinforcement for years, you still managed to blow my mind with salt-water story! 🤯 I have a story too, with heavy interference and unbalanced lines! Sooo before DJM V-10, all of Pioneer's DJ mixers did not have XLR AES master output, only the RCA one. So we were using an AES-EBU adapter which is basically standard XLR-RCA adapter with pin 1-3 on the sleeve and with 110 Ω of resistance. Guess what. A thunderstorm was coming and the sky started to light up. (The event was indoors.) The situation got really weird really fast. It was like: **Lightning** **immediate earshattering pop from the PA** **thunderroar** This went on, until I hooked up DJ mixer with balanced analog lines. Shielding and faraday cages are always manage to impress me. IDK why.
Bill Whitlock (former owner of Jensen Transformers) had a situation where you couldn't play guitar on half of a stage. It turns out the problem was high current through water pipes below the stage created a magnetic coil that produced 60 cycle hum through the guitar coils. Each side of the building was fed by a different transformer and the pipes was where the ground current would flow. The solution was to galvanically isolate the two sides using a PVC union.
There are different modulation types used by cell phone for the RF connection to a base station. Some are more steady than others regarding power level. What most often is audible is the pattern that the transmitter turns on and off, when the repetition is an audible frequency. GSM (2. gen) was particularly burst-heavy due to it time-divided protocol where each phone gets assigned short time slots to transmit in, where all other phones in the area shall keep quiet, so they transmit one at a time.
The GSM signal had 8 times slots per channel, each about 4.6 ms long. which produced 217 Hz interference (1/.0046). During the phones time slot, the battery current would surge over 1 amp. Shorts bursts of high current through inductive circuits create high voltage spikes. CDMA phones don't experience this kind of surging. However, you have the haptic motors which can create interference when a phone vibrates.
Woah, that story of Munich reminds me of a venue in Utrecht (NL) where I worked as an intern long ago, that was located right next to the headquarters of the police and the fire brigade of the city, with a big antenna where all the communication and also the 1-1-2 (like the 911 in America) emergency calls were coming on. So in some cases during soundcheck, we could pick up these signals with a guitar pickup through an amp. Not clearly enough to hear what people were saying, but still.. It was pretty insane.
I once hooked a giant marine antenna (30') to an old cell phone and it got really hot and the cell stopped working. It smelled of burnt components afterwards. The experiment was worth an old brick phone, for like 10 seconds I had crazy good service and then none. :) Something else I've discovered over the years is I live in a valley and there is a giant antenna array on the tallest peak in the hills. There are different places that anything with a VU meter (like a CB) will redline even if it's not hooked to power. I've also experienced this exploring military land about 40 miles away except that is mobile while the other is in fixed locations. My neighbor was messing with his brothers boat the other day and it was causing interference everywhere. Turns out his sonar unit was engaged (not good on dry land), it's one that has twin leads that can detect a screwdriver about 2 miles down made for exploration and salvage I guess. It's all super interesting, now that I point all this stuff out I'm wondering if I should shield my house, LOL Totally rad video, the stage story is epic! Thank You. :)
@@stuungar3390 I don't know much more than it was for salvage operations and they really shouldn't be used above water, LOL I do know it created a lot of interference, :)
Wow guys... i mean... just wow.... That story was awesome, thanks for sharing Dave! Absolutely love your videos. How can I get into those zoom chats u mentioned? You are trully inspiring and I thank you for that. And what was Sammys instagram again? I checked but didnt found it!
Sammy is Samufacturing on instagram. The Zoom chats can be accessed by RU-vid channel members. Its like $5 a month and I do one a week and also a bunch more videos that are not public. ru-vid.com/show-UC_nJM07b0k7C9CvcM-9OH6wjoin I'd be awesome for ya to join. Also I post all the older zoom chats as well
I could be totally off base here, but I feel like you're not getting much of the phone interference in the (un-common mode) signal path because the signature clicky sound -- resulting from TDMA rectification -- tends to have a greater effect on the biasing of transistors in power amplification circuits. So you're more likely to notice its affect an active system with speakers or a mixer with lots of amp stages, rather than through a recorder. Again, I don't know this in depth.. just a theory.
Totally saw that stage grounding story coming when you said there was an antenna near it. I've never had to deal with that size of an interference issue under that kind of pressure but I have had to ground amplifiers with tire irons beat into the ground, mobile studios with buried hammers and run 12ga wires between wall receptacles to form a star as a Christian youth group looked at me as if I was summoning demons lol. You do what you gotta do.
How would you solve RF in a studio in Times Square ? In having these same issues and cannot find a viable solution please ! Would love your help! Thank you both for all this information .
What a bizarre engineering job, where a massive grounding task is easier to complete with bottles of water and salt than actually acquiring some copper and ground stakes. Great story, thanks!
Awesome and in the description I added a link to a more accurate account of what happened that I wrote soon after the gig with photos. The stage was on metal plates seperated by wood blocks. The salt and water was to connect the stage to the plate.
As a long time tin foil had wearer, I must say it generally has to do with keeping the juices in. You don't want your brain to get flaky and dry so an little butter, some seasoning salt some good quality tin foil and... Wait, what were we talking about? I'm hungry now... :)
@@DaveRat It's a nice format and great family chemistry. Maybe someday you two could make a masterclass type video on all the info... but family-friendly, meaning no drinking :)
Hmmm, I got into this business so I could hang out with friends, listen to music, have a beer and play with tech stuff. As soon as it stops being fun or there are rules to follow, I will move on to other adventures
Aaah. It's a bit out of my realm of actual experience as I've not dealt with loads of RF issues. But if you go to AES.org website and lookup their paper for recommended XLR wiring to deal with RF there are documents that show you how to optimize that. I believe it's something like putting a 10 Pico ferret capacitor between pin 1 and the shell on both ends. Cheap and easy
My father used to work in telephone control of the police department decades ago in the analog days. His coworker answers a call on speakerphone and it's some really high ranking guy (can't remember exactly) absolutely furious "DO YOU HEAR THAT? I CAN'T MAKE A _____ CALL WITHOUT THIS _____ SPORTS RADIO STATION BLEEDING IN ON THE TELEPHONE LINE!!!!!!!". His coworker jokes "Can you stop talking a second? I'm trying to hear last nights score...". Well, the guy didn't find it so funny. He absolutely lost it. When they went there to install a filter on the line they also had to replace the phone smashed in a million pieces. Lol
