Need help coordinating 72 Wireless mics

[Jonathan Pitzer]

I work as a teacher at a school that had new wireless microphones installed last year. However, when they did the installations, they treated each system as a stand alone system. However, they are all in the same building and intermodulate with each other and in some cases, the mics are on the same exact frequencies. I do have a spectrum analyzer but I do not have the software that works with it to suggest the best frequency options. I NEED HELP!

I do have a list of frequencies in wireless workbech but the only tutorials that I can find require to have the mics networked to the computer which is not an option because the mics are Shure SLX and Sennheiser e100 G3. The zip code is 75071 and the camups is partially built into a hill so we have no interference at all from television stations. The closest television antenna is about 45 miles away. Please email me at [email protected] to get the frequency list if you are willing to help.

 

[Mike Brown]

My first thought would be to hold the installer responsible for fixing this.

Otherwise, Wireless Workbench will allow you to "add new device" for offline systems, including the SLX. Then you can load in your scans from the spectrum analyzer and calculate new frequencies. If these are classroom microphones and the microphones are fairly close to the receivers I would suggest turning down the transmitter power as much as possible and possibly using attenuators on your antennas.

You may need to relocate some bands and split up the school into "zones" as the receivers which are the most spread out can probably be on similar frequencies without causing issue.

Hopefully they split the microphones up into several different bands, because 72 sources can be a VERY tight fit depending on the spectrum in the area.

 

[Ben Lawrence]

A lot of large production companies have a RF "guy". I wonder if the best solution would be to hire out to have someone come in and do an inspection of what you have going on. Otherwise you are really going to have to dig in with some maps and channel programming.
I also just noticed the line where you said they were installed last year. I would definitely hold the installer liable on them working. 72 installed mics is no small investment. There has got to be a contract with the stipulation of a functioning system.

 

[David Sturzenbecher]

Any installation company that installs that much wireless, and keeps them all on the same frequency does not have the chops to set this up correctly. Yes, you need to have the installation company make this right...which means they need to hire in the RF expert to sort this out for you. Do not accept a simple return trip where the sharpest tack in the box simply moves each wireless to a random different frequency.

 

[Jonathan Pitzer]

I know that we need a wireless coordinator but the reality is that I am going to have to do it myself. This is a school and I am just a teacher. I have mentioned it to our technology department (who oversees the purchase and installation) and they know very little about these things. They also are unwilling to pay for anything else on this project. I do not have any confidence in the company who installed this to be able to fix the issues.

However, I am pretty familiar with the process and although I am generally a lighting guy, I did work in television engineering for 15 years. I have a much higher than average understanding of these issues. I have developed a list of frequencies that I believe will work but I am not familiar enough with Wireless Workbench to have the software tell me if I am correct in my calculations. I have a WWB file but I am not able to get it to re-assign frequencies for me.

 

[Mike Brown]

I know that we need a wireless coordinator but the reality is that I am going to have to do it myself. This is a school and I am just a teacher. I have mentioned it to our technology department (who oversees the purchase and installation) and they know very little about these things. They also are unwilling to pay for anything else on this project. I do not have any confidence in the company who installed this to be able to fix the issues.

However, I am pretty familiar with the process and although I am generally a lighting guy, I did work in television engineering for 15 years. I have a much higher than average understanding of these issues. I have developed a list of frequencies that I believe will work but I am not familiar enough with Wireless Workbench to have the software tell me if I am correct in my calculations. I have a WWB file but I am not able to get it to re-assign frequencies for me.

If you are "just a teacher" (teachers already have WAY too much on their plate) then is this truly your responsibility? It is admirable to go the extra mile (or ten miles) to get this sorted out for them, but they don't seem committed to actually doing things right in the first place, and the amount of time and energy (both physical and emotional) isn't going to be reciprocated in any meaningful way.

They spent more than $40k on equipment to cheap out on $500 worth of consultation?

Let them fail, you've given your advice and it fell on deaf ears.

In the event that you are a better person than I (and you probably are BECAUSE you are a teacher)

Developing your own list of frequencies would be quite the feat, as the calculations for for intermod between channels/around interference are simple but time consuming. You can put in the frequencies in WWB and click "analyze" and see if it comes back as compatible with the scan data (and each other).


Otherwise, your workflow for WWB will be generally:

1. Add devices to inventory (leave the frequencies blank)

2. Load Scan Data

3. "Select Frequencies from inventory"

4. "Calculate"

5. "Assign and Deploy"

6. "Deploy To Inventory"

7. Print or export PDF of frequency list and manually reprogram all transmitters and receivers.

8. Wargame

9. Drink beer

If WWB isn't calculating frequencies, it generally means that it can't find enough clean frequencies. You can switch your tolerances to "More Frequencies" and you can use "Zones" to take wireless devices that are far apart and lower the tolerances that way as well.

Again, I would also look at lowering the RF output power of each transmitter as much as possible.

 

[Brian jojade]

According to the manufacturer's sites, the Shure SLX system is designed for up to 12 systems in a single band, or 20 across dual bands. The e100 G3 system is capable of 32 systems. Even if magically, they didn't interfere with each other, that leaves you a maximum theoretical capacity of 52 systems. You somehow have to get 72 to play nice together.

Sorry to break it to you, but it's pretty unlikely that you're going to ever make this work correctly. There simply aren't enough frequency options available in the systems. Even with the best coordination, if they are all in the same building, there's going to be interference.

You can try, but I'm thinking you're going to be spending a lot of time at step 9 on Mike's workflow...

 

[David Karol]

Working in schools gets incredibly rough. Installations go out to the lowest bidder, and you get what you pay for in quality. Contracts calling out for a "functioning system" are too vague, and there's usually stipulation that future service comes at a cost. It's also not easy for a school / public institution to go out and drop $500 for an RF guy to stop by-- chances are the 'RF guy' is not on the state's approved vendor list.

Mike Brown's advice should get you going. Philip LaDue and I used to put together more than functioning systems with less. It'd won't be as rock solid as the Super Bowl, but I'm sure you'll make it work.

 

[Kevin Maxwell]

I work as a teacher at a school that had new wireless microphones installed last year. However, when they did the installations, they treated each system as a stand alone system. However, they are all in the same building and intermodulate with each other and in some cases, the mics are on the same exact frequencies. I do have a spectrum analyzer but I do not have the software that works with it to suggest the best frequency options. I NEED HELP!

I do have a list of frequencies in wireless workbech but the only tutorials that I can find require to have the mics networked to the computer which is not an option because the mics are Shure SLX and Sennheiser e100 G3. The zip code is 75071 and the camups is partially built into a hill so we have no interference at all from television stations. The closest television antenna is about 45 miles away. Please email me at [email protected] to get the frequency list if you are willing to help.

As has already been said with what it sounds like you have, it will be impossible to coordinate all of these wireless systems to work all at once if there were all in one room. But since they are spread out there might be hope. Are there different bands (frequencies) in each manufacturer’s wireless that you have or are all the Sennheiser’s in one band and all the Shure’s in one band?

In general with wireless the strongest thing wins. Since this is a school and not something high profile, like a concert or show you can get away with a few things that you normally wouldn’t want to even chance. If these are in every classroom and the receiver is always on and the feed from that is always up into the speakers that could create problems. If things are turned off or down when not in use then you might be able to make it all work with a lot less problems because as I said the strongest thing usually wins.

I think the first thing that you need to do is figure out how far in this environment the transmitters will reach. You will need to map it all out. And by this I mean will hear a transmitter signal while listening to a receiver in one room as someone walks around the place constantly talking with a transmitter in their hand. This will be time consuming. The person walking needs to be telling you exactly where they are at all times. I would suggest that you have a whole bunch of printouts of the floor plan of the school possibly one for each receiver location. You then need to map out (mark on the floor plan) where the person was that was talking when you received them. This will tell you how far and where the coverage pattern is. Due to the shape of MBHS you might find that the outer wings where they curve in in the front may be in the coverage pattern of each other, even though they are the farthest away from each other.

If this is of any help and if I can walk you thru using Shure WWB let me know and maybe we can talk.

BTW I was doing a big conference in a big hotel and at some point I discovered that someone had tuned some wireless to frequencies that would have been a problem. But because they were far enough away from each other and due to the construction of the building it wasn’t a problem.

 

[Jeff Babcock]

Sorry to hear about your situation.
I have dealt with plenty of these types of scenarios in the corporate world, and there is almost always a way to sort it out without making it YOUR problem.

Tell your tech department (not the local tech guy, someone in senior management, preferably the person who signed the original contract) that the vendor failed to install the systems correctly, that it has the potential to be very disruptive, and that this problem should be able to be fixed WITHOUT the school board having to pay for anything - they just need to make a few calls or have a meeting. Provide all of the details and offer to be available for any follow-up questions.

Without knowing your org structure for your school board management team, I will just say that it is critically important that you reach out to the right person, someone who has a sense of ownership/accountability for ensuring that these types of projects for your school board are successful. If it's not the tech dept then keep looking.

I'd suggest that you recommend this approach:

1) Have this person review the terms of their contract with the installation reseller/VAR regarding its language around deliverables and dispute terms etc and see what grounds you have there. Keep this in your back pocket in case you need some leverage beyond goodwill with my 2nd point below.

2) Contact the installation reseller/VAR to explain the issue and negotiate a reasonable remediation plan (free of charge).

3) If the vendor fails to cooperate or are unqualified to help, reach out to the regional sales representatives for Shure and Sennheiser to explain the situation. Neither of these vendors want to be associated with this type of reputational mess and they will definitely have access to a technical resource who can likely assist in remediating the situation as best as possible (acknowledging the technical limits imposed by the installation reseller's poor choices), again, free of charge. Make sure they are aware of the problems with the installation reseller...... they will want to know about poor resellers.

4) If you are unable to have ANY success with these aforementioned things (highly unlikely), consider the solid advice Mike B provided..... but DON'T do that unless all else fails. This should not be your responsibility and it should be fixable through normal corporate vendor relationship management 101 type practices.

Best of luck!

 

[Mike Caldwell]

It sounds like these 72 mics are spread out through the entire building, as already mentioned that will give you a chance of maybe making something kind of sorta work!

Are these wireless mics used in each classroom as part of a hearing assistance system where the teacher wears a headset or lapel mic?

If that is what there used for there are products to do just that, they use wireless IR (infer red) light to transmit the audio. Those systems can have their own set of issues but room to room RF issues are eliminated.

If these are indeed classroom systems I hate to say it but the wrong equipment was installed from the start.

 

[Brian jojade]

In general with wireless the strongest thing wins.

If only it were that simple. The problem is that it's not. Something with a lower power can interfere enough to muck with the signal to noise ratio enough to cause a drop out of the main system without being the strongest signal. Harmonics can also do this, which is why simply using different frequencies isn't enough. Harmonics are less powerful than the original signal, but certainly can disrupt a microphone nearby that is operating on full power.

With mics spread around the building, it may be possible to get things to work to some degree, but it's never going to be a reliable system. The advice of going back to the contractor that poorly installed this is probably the best advice.

 

[Kevin Maxwell]

If only it were that simple. The problem is that it's not. Something with a lower power can interfere enough to muck with the signal to noise ratio enough to cause a drop out of the main system without being the strongest signal. Harmonics can also do this, which is why simply using different frequencies isn't enough. Harmonics are less powerful than the original signal, but certainly can disrupt a microphone nearby that is operating on full power.

With mics spread around the building, it may be possible to get things to work to some degree, but it's never going to be a reliable system. The advice of going back to the contractor that poorly installed this is probably the best advice.

It is a generalization and admittedly an over simplification. But in real life situation like this is I stand by my reply and if you read it all you will see I gave a lot of caveats. But there are a lot of details left out by the OP so we don’t really know what he is dealing with. If you didn’t take my reply out of context you will see that with all of the conditions I spelled out, all the information I gave is correct. Not the best way to do it but for the OP it may be the only way. I hope it isn’t.

When I am dealing with a bunch of wireless in a concert venue or theater I am extremely picky as to my coordination. I have been told that I am actually taking it much farther then I need to. But I can’t remember the exact quote. It was from a well-respected RF guru. But as I said this isn’t a high profile situation that he is talking about, so he can probably get away with things I would never accept.

I don’t know how this has fallen on the OP to try and make this work but I made the assumption that he knows the powers that be and with that knowledge he feels that the best thing to do is to try and make it work. Maybe he will bring the whole thing to the attention of someone that has some power to make the original installer (or seller) make things right.

Maybe the specifications were bad and the installer bid on what was asked not what was needed. I have seen that done multiple times. But I refused to have any part in a mess like that. It isn’t good for your reputation.