I disagree. It's not that you pinpoint exactly which frequencies are usable at any given time, but I believe that you reference the used frequencies (TV, Radio) in the area and see where you have space. I'm almost positive that there is a way to figure this out. In fact, if you check back in my posts, there should be a thread where someone does just that (asks for zip code and gave me three sets of four frequencies that should be good.) Either way, if they aren't perfect, you can always adjust them to find optimal RF signal.
Yes, bad frequencies meaning bad signal/interference from existing stations and other things at the same frequencies
I also disagree. While you are right in that selecting bulletproof frequencies would require being on-site with a spectrum analyzer (which costs thousands of dollars and requires an experienced operator), it is possible to select frequencies that do not conflict with local television stations and which are not likely to have intermodulation problems.
Ben, I need to know what frequency range your units use. The Evolution units came in three bands in the US: 518-554, 626-662, and 740-776 MHz. Knowing this, I can select some channels for you to use.
Exactly. If frequencies are not planned out properly, it is possible for them to mix together and generate noise on new frequencies in the mic receiver. For instance, if you have two units running at A:600 MHz and B:602 MHz, you may find interference at 598 (2A-B) and 604 (2B-A) MHz respectively. The number of products increases exponentially based on the number of frequencies in use. This is why any system using more than a few mics should be planned out by an expert or with the aid of computer software. One program that is especially useful is called SIFM by Sennheiser. It runs on Windows only, and is available here:
My point was, the same way you determine frequencies used by the public and are unusable to you, you can determine the frequencies used by TV and radio. Furthermore, in the time it takes to find which frequencies are recomended on the web, you can randomly try a frequency and stand a decent chance of having it work.
Or you could take a little more time and see who has what frequencies licensed and what ones are in use, and save yourself more time when taking a stab in the dark and setting your frequency in the morning to what works and go to turn your mics on for an evening performance and find out that the frequency is then being used and finding out you need to reset all of your mics so that they don't interfere with each other.
Indeed. That happened to me during the very first show I ever ran. The sound designer and the light designer just started randomly setting frequencies, and none of them worked well. We switched them several times during tech, and once during the run of the show. It was not good. Even with the recievers under the stage, they had reception issues.
This past year, for Wonderful Town, I took some time to do the research a bit (with the help of this here forum) and the frequencies worked perfectly. Not only that, but we managed to run them from the back of the house, right next to the board, so that I could moniter AF and RF during the show.
An interesting story- for anyone using Sennheiser ew100's. The first generation, not the G2's. We used four of those along with seven Shure ULX's and one Shure LX. (The 8th ULX that we rented from a school was a J1 transmitter with an M1 reciever- I don't think that they realized that when they purchased it to replace the broken one from the previous summer.)
So, the point is, the ew100's were all just weak. They didn't have the energy to penetrate through people dancing, and as a result were cutting in and out.
It wasn't the frequencies, we checked all of the good frequencies in the area... and it wasn't interference, we had the other three off and it was still too weak to push through people. The AF was hot, but the RF didn't like to be useful.
We determined that it was the transmitters themselves, which was kind of annoying.
Antenna placement: Stage right, inside of a false proscenium (the signal had to go through or around a 2x8 sheet of luan, vertical, and some burlap/duv.) To fix that, we ran a couple of bnc runs out to the front of the stage. That didn't work. We then moved one to another location, that didn't work. We finally moved them up high inside the false pro., above the luan, and it still didn't work. It was only a problem when someone stepped into a certain spot directly between the transmitter and the antenna.