Wireless mic issues only when there's an audience in the space?

[Ravenbar]

I'm the lighting guy, so know little of the audio side of the space. I've done their lighting for a decade. It seems every year, no matter how much testing and prep goes into it, the wireless mic system experiences all kinds of issues once we get an audience in the space, but is fairly reliable during rehearsals and testing.

It's a fairly new system, with 28 wireless mics spread over ~80mHz of band, from ~470 up to 540. As I'm a ham radio guy, 28 signals spread over 70mHz(likely 12.5kHz bandwidth) seems like interference between the mics isn't the issue. I've considered buying a TinySA spectrum analyser to watch the frequency spread during the performances, but I doubt it covers 70mHz spectrum in one go.

The space also is 60-yrs old, has no sound deadening, and the walls are 30' tall and drywall/plaster mounted to 4" vertical trusses, so the walls tend to act as speakers from the vibrations. The orchestra is also very LOUD, depite the music directors attempts to hold them back, so the mics are cranked up to an almost painful level to be heard over the orchestra.

I only work on this one show per year for them, that closed tonight. I'm trying to talk them into some space mods, including adding sound deadening to the vertical walls(which would hopefully cut down on the reverberations and mute the pit somewhat), and some much needed structural repairs to the ceiling, as well as a booth relocate.

Thoughts on why the audiences presence might be affecting the wireless mic system?

 

[themuzicman]

It's a fairly new system, with 28 wireless mics spread over ~80mHz of band, from ~470 up to 540. As I'm a ham radio guy, 28 signals spread over 70mHz(likely 12.5kHz bandwidth) seems like interference between the mics isn't the issue. I've considered buying a TinySA spectrum analyser to watch the frequency spread during the performances, but I doubt it covers 70mHz spectrum in one go.

The TinySA isn't instantaneous but it does have adjustable RBW so you can adjust to the needs of your scan. A low RBW value will give you higher resolution scans at the expense of speed, a higher value will give you increased speed at the expense of resolution. A scan is only useful if you know how to interpret it which could mean taking several scans and comparing them - the empty room without any transmitters, the room with no audience and transmitters on, and then again with the audience.

Has anyone done an actual coordination of the mics, against both external (TV stations) and internal sources (intermod) of interference or are they just turning things on and hoping for the best? Do your microphone receivers have the ability to connect to a network and do a scan to a computer? If they have the ability to do this, I'd do a scan with all transmitters off, export the scan data, and then run a coordination in Soundbase.

The space also is 60-yrs old, has no sound deadening, and the walls are 30' tall and drywall/plaster mounted to 4" vertical trusses, so the walls tend to act as speakers from the vibrations. The orchestra is also very LOUD, depite the music directors attempts to hold them back, so the mics are cranked up to an almost painful level to be heard over the orchestra.

I only work on this one show per year for them, that closed tonight. I'm trying to talk them into some space mods, including adding sound deadening to the vertical walls(which would hopefully cut down on the reverberations and mute the pit somewhat), and some much needed structural repairs to the ceiling, as well as a booth relocate.

If the issues are related to RF this is not going to fix those problems, it'll just make the audible issues with microphones less apparent

Thoughts on why the audiences presence might be affecting the wireless mic system?

I'd say correlation isn't causation, if the audience affected wireless microphones no arena show would happen reliably. 99 times out of 100 when I have issues with the audience it is because someone brought an unauthorized wireless microphone system into the space, which if it is happening to you should be easy enough to be on the lookout, but probably unlikely?

Is it safe to assume this is an amateur/community group? My initial inclination is that on show days traffic patterns change and perhaps what was an attentive cast sitting in the room during rehearsals now has folks outside of the stage house during the shows and things are punched up on the console that shouldn't be up so you're getting noise you are unaccustomed to.

 

[kenact]

Just a couple of thoughts. Unless I missed it, you indicate where the receivers are, in relation to the transmitters. Again, unless I missed it, you didn't indicate what types of problems you were experiencing with the wireless mics. You did go into some detail regarding the frequency bands, so is it safe to assume you getting interference, causing drop outs?

 

[TimMc]

I'm the lighting guy, so know little of the audio side of the space. I've done their lighting for a decade. It seems every year, no matter how much testing and prep goes into it, the wireless mic system experiences all kinds of issues once we get an audience in the space, but is fairly reliable during rehearsals and testing.

It's a fairly new system, with 28 wireless mics spread over ~80mHz of band, from ~470 up to 540. As I'm a ham radio guy, 28 signals spread over 70mHz(likely 12.5kHz bandwidth) seems like interference between the mics isn't the issue. I've considered buying a TinySA spectrum analyser to watch the frequency spread during the performances, but I doubt it covers 70mHz spectrum in one go.

The space also is 60-yrs old, has no sound deadening, and the walls are 30' tall and drywall/plaster mounted to 4" vertical trusses, so the walls tend to act as speakers from the vibrations. The orchestra is also very LOUD, depite the music directors attempts to hold them back, so the mics are cranked up to an almost painful level to be heard over the orchestra.

I only work on this one show per year for them, that closed tonight. I'm trying to talk them into some space mods, including adding sound deadening to the vertical walls(which would hopefully cut down on the reverberations and mute the pit somewhat), and some much needed structural repairs to the ceiling, as well as a booth relocate.

Thoughts on why the audiences presence might be affecting the wireless mic system?

Intermodulation products, and actors in different places that during rehearsals can add to the IM. Addition of additional transmitters (of any kind) in or near your operating spectrum, creating new, different IM products on day of show.

Start with a full freq coordination (Shure Wireless Workbench, Sennheiser WMS, or Soundbase {on line}) and see if current freq assignments are IM-free to start with. My guess is 'no'. If you ain't testin', you're guessin'.

 

[Ravenbar]

The TinySA isn't instantaneous but it does have adjustable RBW so you can adjust to the needs of your scan. A low RBW value will give you higher resolution scans at the expense of speed, a higher value will give you increased speed at the expense of resolution. A scan is only useful if you know how to interpret it which could mean taking several scans and comparing them - the empty room without any transmitters, the room with no audience and transmitters on, and then again with the audience.

Has anyone done an actual coordination of the mics, against both external (TV stations) and internal sources (intermod) of interference or are they just turning things on and hoping for the best? Do your microphone receivers have the ability to connect to a network and do a scan to a computer? If they have the ability to do this, I'd do a scan with all transmitters off, export the scan data, and then run a coordination in Soundbase.



If the issues are related to RF this is not going to fix those problems, it'll just make the audible issues with microphones less apparent



I'd say correlation isn't causation, if the audience affected wireless microphones no arena show would happen reliably. 99 times out of 100 when I have issues with the audience it is because someone brought an unauthorized wireless microphone system into the space, which if it is happening to you should be easy enough to be on the lookout, but probably unlikely?

Is it safe to assume this is an amateur/community group? My initial inclination is that on show days traffic patterns change and perhaps what was an attentive cast sitting in the room during rehearsals now has folks outside of the stage house during the shows and things are punched up on the console that shouldn't be up so you're getting noise you are unaccustomed to.

It's a HS auditorium. The entire system was installed as a package as part of a capital project, so I'd assume the all the frequency coordination was done at that time. The building is out of town about 3 miles, so not much odd RF from low power devices other than what the school has.

Part of the issues, particular feedback issues, are happening because the volume coming out of the speakers has to be turned up so high to overcome the excess un-mic'd volume of the pit(musical productions). They also have students running the console under the guidance of a teacher.

Just a couple of thoughts. Unless I missed it, you indicate where the receivers are, in relation to the transmitters. Again, unless I missed it, you didn't indicate what types of problems you were experiencing with the wireless mics. You did go into some detail regarding the frequency bands, so is it safe to assume you getting interference, causing drop outs?

Recievers themselves are in the back of house in the sound booth, I'm unsure if that's where the antenna are, or if they're fed from somewhere else closer to stage.

Drop outs, static, feedback, ect. It seems as if it's a random mix of everything.

All the mics were tested by the sound person before sound check, then actors ran all over the space during their mic check and groups that seem to have issues when onstage together are also called to test mics together, and other than an occassional loose connection that gets fixed things check out fine.

Intermodulation products, and actors in different places that during rehearsals can add to the IM. Addition of additional transmitters (of any kind) in or near your operating spectrum, creating new, different IM products on day of show.

Start with a full freq coordination (Shure Wireless Workbench, Sennheiser WMS, or Soundbase {on line}) and see if current freq assignments are IM-free to start with. My guess is 'no'. If you ain't testin', you're guessin'.

Other than the audience, everything is staying the same.

 

[kenact]

Recievers themselves are in the back of house in the sound booth, I'm unsure if that's where the antenna are, or if they're fed from somewhere else closer to stage.

Most installations I've seen, have the receivers near the stage, with a snake connecting them to the booth. The greater the distance between the transmitter and receiver, as well as physical obstructions, the greater the chance of interference. With 28 wireless mics, I assume you're in a fairly large space.

 

[themuzicman]

It's a HS auditorium. The entire system was installed as a package as part of a capital project, so I'd assume the all the frequency coordination was done at that time. The building is out of town about 3 miles, so not much odd RF from low power devices other than what the school has.

Things change over time, doing coordinations every now and again is best practice - at least checking for new sources of external interference and making sure students haven't changed frequencies from the initial setup when the system was commissioned is a solid start.

Part of the issues, particular feedback issues, are happening because the volume coming out of the speakers has to be turned up so high to overcome the excess un-mic'd volume of the pit(musical productions). They also have students running the console under the guidance of a teacher.

Well now we're getting somewhere, feedback is an issue not mentioned in the first post! Feedback is just as much about reducing the sound of your orchestra as it is about optimal placement of your speakers. With a fixed installation I am assuming your speakers aren't movable to more ideal locations, so not much help can be had here unless you physically move your orchestra. Really only 3 fixes can be done here: Move current speakers, add more speakers, or move your band (if they are already playing at the lower limits of their volume).

Drop outs, static, feedback, ect. It seems as if it's a random mix of everything.

All the mics were tested by the sound person before sound check, then actors ran all over the space during their mic check and groups that seem to have issues when onstage together are also called to test mics together, and other than an occassional loose connection that gets fixed things check out fine.

An audience of humans are a fantastic way to inhibit the path of travel of your wireless signal and acoustic audio signals alike. You're getting feedback with an audience when you had none without because an audience both raises the general noise floor of the room and large bags of water soak up acoustic energy.

The same thing happens to your radio signals if your receivers are at the back of the house with sub-optimal antennas and distribution. Your mic packs are already trying to power thru one human when onstage if the mic is on their backs, let alone an entire audience and possibly walls if your receivers are in a booth with stock whip antennas.

Additionally, if groups of students do have issues when onstage together I would also suspect intermodulation issues which ties directly back to re-doing and verifying an RF coordination.