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Author Topic: Issues with distortion on QLX-D1 when house is full  (Read 1531 times)

Zachary Sherman

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Issues with distortion on QLX-D1 when house is full
« on: March 12, 2019, 12:39:07 pm »

Hi! This is my first post on the forum, but I've been working on sound for a few years. I'm a senior in high school, and I run sound for our theater productions. We've just finished our run of Seussical, but we had a weird issue I'd like some help resolving.

We now use fourteen Shure QLX-D1 mic packs with mostly Countryman E6 elements. We used to have the ULX system, but we switched because of the T-mobile 600mhz situation. The new mics were installed over the summer, and the frequencies were presumably set by someone who knew what they were doing. We have a Yamaha IM8-32 analog console, which is plenty for our needs.

Before each show, I mic'ed everyone up according to the Countryman manual as I've done for plenty of shows with no issues. We completed mic checks, including having each actor sing their loudest song with the (already too loud and not even mic'ed) live band and had no issues. Afterward, we had a couple groups of actors who usually sing together do their songs, and again had no issues. Last, I turned on all the mics for the actors' vocal warm-ups, and of course, still no issues. I could push them as far as I wanted and, although too loud, they sounded fine.

The house was then opened, and the audience piled in. As soon as each show started, it was distortion galore! It couldn't have sounded any worse. I immediately checked the receivers, and found that they were not peaking. I then checked the board, and no channels were peaking either. Finally, I checked the master monitor, and found no peaking.

A couple more important pieces of info about the setup:
1. Our receivers are placed under about five rows of platform seating. It's a black box theater, so there isn't a better spot.
2. We've never had issues with distortion before when the receivers were placed here. I've done seven other shows in the same theater, including one with these mics.
3. The theater holds about 200-300 people. It's none too big: from all the way upstage to the back of house wall is probably fifty feet.
4. During the show, each receiver indicates full RF signal.
5. The problem usually seems worse when many mics are on (even when their faders are set to ~-20dB and neither the receivers nor the main mix are peaking), but some mics distort by themselves.

Any ideas why this might have been going on? It seemed very weird to me and was certainly incredibly frustrating!
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Russell Ault

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #1 on: March 12, 2019, 01:19:32 pm »

Hi! This is my first post on the forum [...]

Hi! The rules of this forum require that your display Name (it's in your Account Settings) be your real first and last name. No one will answer your question until you've changed it, and this thread will probably be locked in the mean time.

-Russ
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Andrien (No Last Name)

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #2 on: March 17, 2019, 12:07:32 pm »

Do you have networking in place? You can try to use Shure Workbench and see the RF signal on the fly to monitor each QLX-D during shows.
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Russell Ault

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #3 on: March 17, 2019, 01:53:40 pm »

The house was then opened, and the audience piled in. As soon as each show started, it was distortion galore! It couldn't have sounded any worse. I immediately checked the receivers, and found that they were not peaking. I then checked the board, and no channels were peaking either. Finally, I checked the master monitor, and found no peaking.

A couple more important pieces of info about the setup:
1. Our receivers are placed under about five rows of platform seating. It's a black box theater, so there isn't a better spot.
2. We've never had issues with distortion before when the receivers were placed here. I've done seven other shows in the same theater, including one with these mics.
3. The theater holds about 200-300 people. It's none too big: from all the way upstage to the back of house wall is probably fifty feet.
4. During the show, each receiver indicates full RF signal.
5. The problem usually seems worse when many mics are on (even when their faders are set to ~-20dB and neither the receivers nor the main mix are peaking), but some mics distort by themselves.

Any ideas why this might have been going on? It seemed very weird to me and was certainly incredibly frustrating!

Do you have a recording of the distortion you were hearing? Do the TxOL indicators on the receivers ever turn on?

To add to what Andrien said, Wireless Workbench also creates a log of warnings (like audio peaking), so being able to monitor the receivers in software can be very useful for troubleshooting these problems.

That being said, if the QLXD system says it's happy (which it sounds like it is from your description of the problem) I tend to believe it. QLXD packs are some of the easiest wireless to gainstage, and they do a pretty good job letting you know when something is wrong. Also, because of the error checking built in, digital wireless tends to be an all-or-nothing affair: it tends to drop out completely if the wireless signal is too garbled to receive.

If the wireless seems happy, and the console seems happy, is it possible that you're overdriving something further down the line, like PA processing or something like that? Things getting louder when the audience comes in is a pretty common occurrence (both because singers never sing as loud during soundcheck as they do during a show, and because the audience is absorbing a significant amount of sound energy that your PA now has to make up for). This might also explain why the problem seems worse the more mics you have on. Does the distortion show up if you listen to the output of your sound board on headphones?

-Russ
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Mike Caldwell

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #4 on: March 17, 2019, 05:37:26 pm »

Did PFL and listen to any of the individual mics to see what they sounded like?

Did any other wireless equipment get fired up at show time...that your were aware of other than the 200 cell phones that walked into the room?

After you recovered from the show did you test it again with the system at the same levels to see what you had then?

Ike Zimbel

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #5 on: March 17, 2019, 05:57:47 pm »

Hi! This is my first post on the forum, but I've been working on sound for a few years. I'm a senior in high school, and I run sound for our theater productions. We've just finished our run of Seussical, but we had a weird issue I'd like some help resolving.

We now use fourteen Shure QLX-D1 mic packs with mostly Countryman E6 elements. We used to have the ULX system, but we switched because of the T-mobile 600mhz situation. The new mics were installed over the summer, and the frequencies were presumably set by someone who knew what they were doing. We have a Yamaha IM8-32 analog console, which is plenty for our needs.

Before each show, I mic'ed everyone up according to the Countryman manual as I've done for plenty of shows with no issues. We completed mic checks, including having each actor sing their loudest song with the (already too loud and not even mic'ed) live band and had no issues. Afterward, we had a couple groups of actors who usually sing together do their songs, and again had no issues. Last, I turned on all the mics for the actors' vocal warm-ups, and of course, still no issues. I could push them as far as I wanted and, although too loud, they sounded fine.

The house was then opened, and the audience piled in. As soon as each show started, it was distortion galore! It couldn't have sounded any worse. I immediately checked the receivers, and found that they were not peaking. I then checked the board, and no channels were peaking either. Finally, I checked the master monitor, and found no peaking.

A couple more important pieces of info about the setup:
1. Our receivers are placed under about five rows of platform seating. It's a black box theater, so there isn't a better spot.
2. We've never had issues with distortion before when the receivers were placed here. I've done seven other shows in the same theater, including one with these mics.
3. The theater holds about 200-300 people. It's none too big: from all the way upstage to the back of house wall is probably fifty feet.
4. During the show, each receiver indicates full RF signal.
5. The problem usually seems worse when many mics are on (even when their faders are set to ~-20dB and neither the receivers nor the main mix are peaking), but some mics distort by themselves.

Any ideas why this might have been going on? It seemed very weird to me and was certainly incredibly frustrating!
Hi Zachary, welcome to the forum, and good on you for posting such an informative and detailed request.
I don't have a lot to offer here except that Russ' theory that you're overloading something downstream from the mixer seems like a good one to pursue. What happens when you play pre-recorded tracks through the system?
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Eric Snodgrass

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #6 on: March 17, 2019, 07:59:13 pm »

To add to this speculation -
Your singers might be overloading the E6 mics.  That wouldn't show up on the meters of either the pack or the receiver.
Mic placement for the E6 mics is critical.  As was mentioned in a previous post in this thread, singers (especially amateur singers) almost never sing out full during sound check.  Mic check might have gone well, but then they put on their costumes and mic placement can change.  The E6 mics are typically long, physically.  Getting the mic element past the cheek and into the front of the mouth area is really easy and not at all desirable with the E6 as a strong singer will tend to overload the mic element.  It's one of the reasons Countryman makes a shorter version of the earset mic, the E2.  Even adults can have head diameters too small for the E6 to sit behind the mouth (to avoid overloading and breath noises).  I have a corporate gig that I do occasionally where the host must wear an E2 because the E6 is too long for her. 
The E6 also comes in different sensitivities.  No colored band on the mic means it's going to be best for general speaking.  A blue band on an E6 means that mic's output is attenuated - these are much better for loud speech and most singers.  A purple band has the most attenuation and are suited for the loudest vocalists. 
So, if you have E6 mics with no colored bands on powerful singers and the elements are too close to their mouths then they will overload and distort. 
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Zachary Sherman

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #7 on: March 17, 2019, 08:46:08 pm »

Thank you all so much for your help!

Adrien:
- We don't, although it's something I would love to do! I might ask our school's IT department if they've got a 16 (or more) port switch and a laptop I can borrow, since we've got 14 mics. Since I'm graduating this year and the students I was training haven't done sound stuff before this year, I'm not sure it's something I want to leave them with, but it certainly would be cool. It's kind of like how I would have loved to a digital board for this production to fix EQ and help mix using an iPad without the trainees having me over their shoulders. It would've been great, but it's definitely not something the new students will properly know how to use without taking advantage of it.

Russell:
- Unfortunately, I didn't record the distortion. During this show run since I was training new students to do sound, I wasn't able to record while (attempting to) fix problems and helping them mix.
- As for overdriving something later down the line, I doubt this is the case because we've had so many other shows where volume has been no issue. We usually can raise it farther than as high as is comfortable without any noticeable audio issues.
- I tried to monitor with headphones, but unfortunately all I had with me was a crappy pair of earbuds and an adapter, so the mix didn't sound right through that anyway. I believe I remember hearing the distortion through the headphone port, but unfortunately, I can't remember for certain.

Mike:
- As far as I know, we didn't start up any other wireless devices at the beginning of the show. All of lighting's lights were wired to my knowledge, and we have all wired ClearComs.
- My music teacher thought phones entering the room might have something to do with it, but I'm skeptical, since we've had so many other successful shows with phones in the room. Also, the phones should theoretically be transmitting and receiving at 2.4GHz (Wifi and 4G) whereas the mics are on the 500MHz band.

Ike:
- We didn't try pre-recorded stuff at loud volumes, but the sound effects and intermission music (which were played loud enough to be heard over the actors) sounded fine.

Eric:
- We were wondering about this as well. Before each show, while the house is filling up, the actors scream backstage as part of their "pre-show rituals." The director was wondering if the mics were being "blown out" during this. What do you think?
- I've been following the Countryman instructions for placing the mics. I've attached a picture of roughly how I mic up actors so you can verify whether or not I'm doing it right. As I mentioned, I've done this for many other successful shows, so I don't think it's the issue, but it's definitely good to think about. In the picture, the black line is the mic, and the yellow squares are medical tape that we use to ensure the mics stay on while actors act.

Again, I really appreciate everyone's help. Hopefully we can get this sorted out!
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Eric Snodgrass

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #8 on: March 17, 2019, 10:15:16 pm »

The mics aren't being "blown out", but they could easily be distorting.  Check your E6 mics and see if they have small, colored bands on them near the cable connection.  If they don't, then it is most likely that the singers are overdriving the mic elements because the mics are too sensitive for the level produced by the singers.
Here is a link to a .pdf about the E6.  In it is an explanation and picture of the different color bands.

After you have positioned the mic on someone, have them smile.  If the mic is sticking in front of the corner of their mouth then it will definitely be more susceptible to sybilance and plosives (popping from wind generated by the mouth, typically on consonants such as P or B).  Also, taping the mic to the cheek where you are doing it puts the mic too tight to the mouth.  I recommend putting the tape back near the ear (avoiding any little hairs).  This will allow for you to pull the mic away from the mouth a bit, helping somewhat with plosives and sybilance.  It also gets an unsightly piece of tape off of their cheek and hides the tape better.   
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Kevin Maxwell

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Re: Issues with distortion on QLX-D1 when house is full
« Reply #9 on: March 18, 2019, 02:18:46 pm »

Listen to what everyone is saying about the E6 mics and bout the actors singing a lot louder when there is an audience present. I donít know if your wireless transmitters can be padded down enough to fix this problem. Did you check to see if there is a band (blue?) on the E6. If they arenít one of the reduced gain version of the E6 whoever sold you this stuff doesnít know what they are doing. If this was purchased new and this is the first show you have done with these E6 mics the school needs to get in touch with the supplier and tell them they had better take these back and get you the right mics.

Also while we are on the subject of tape we use 3M Transpore tape and then use a concealer makeup stick to take the shine off of the tape and make it blend with the actors makeup. DO NOT use the type of concealer that sprays on a foam pad it will dissolve the glue in the tape, I think the liquid type is also bad. Be careful with the mic cable, if there is any stress on it (too tight) it may break internally. Be sure to have spare cables on hand.   

Do you have any more performances or is the show over? Do you have an antenna distribution system or are you just using the antennas on the back of the receivers? We always put the receivers in the pit or backstage with the antennas up high with a clear shot at the stage.
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