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Author Topic: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna  (Read 18477 times)

Bob Charest

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Hi,

We've got 6 Sennheiser G2 stereo transmitters (500MHz) going through a Sennheiser AC3000 (bought used a number of years ago) sending the combined signals to a single Sennheiser omni-directional paddle antenna (A1031-U) located in the back corner of stage right.

We've had this in place for a number of years. Usually performance is good with minimal dropouts. Venues are inspected with a TTi handheld unit, and wireless mics and IEM units are all coordinated using IAS.

Lately, the number of dropouts and intermittent "whoosh" noise events in the IEM mixes has increased. I'm nearest to the paddle antenna, and find that sometimes I have to put my IEM receiver in my coat pocket nearest the antenna - having my body between the antenna and the receiver seems to create to much of a barrier to the transmitted signal. That doesn't seem right at all...

Our stages are small - usually no bigger than 24' x 12'.

I really don't want any bad stuff when listening, so here are my questions:

1.) Might the AC-3000 be bad or going intermittently bad? Is there any way to test other than disconnecting all IEM transmitters from the AC-3000 and testing that way?

2.) Might we be better served by having two paddle antennas for coverage - one on each side of the stage? We used to use a Sennheiser A 2003-UHF directional antenna. Might two of those provide a more drop-out resistant method?

3.) Is it possible that some of us (like me) are too close to the paddle antenna?

4.) If I want to use two antennas and if I use a "T" coax connector, what is the method to calculate signal loss due to the "T" connector?

5.) Lastly, given that we were to stay with our Sennheiser transmitters and receivers, do any of you have other suggestions for a combiner other than the AC-3000?

The goal is to have an absolutely rock-solid listening environment. Please let me know if you think I'm expecting too much from our IEM setup, or if you have any suggestions at all, I'd love to hear them.

Thanks!
Bob Charest
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Mac Kerr

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #1 on: December 26, 2014, 02:15:31 PM »

I really don't want any bad stuff when listening, so here are my questions:

1.) Might the AC-3000 be bad or going intermittently bad? Is there any way to test other than disconnecting all IEM transmitters from the AC-3000 and testing that way?
I would not expect the AC-3000 to go bad, although various cables in the system may be the culprit
Quote
2.) Might we be better served by having two paddle antennas for coverage - one on each side of the stage? We used to use a Sennheiser A 2003-UHF directional antenna. Might two of those provide a more drop-out resistant method?
No. You should not use multiple transmit antennas. This will cause much greater interference problems.
Quote
3.) Is it possible that some of us (like me) are too close to the paddle antenna?
It is possible but if it hasn't been a problem in the past it seems unlikely to be a problem now. It is easy to test by moving further away to see if it gets better. Needing to have your receiver closer to the antenna says this is not the problem.
Quote
4.) If I want to use two antennas and if I use a "T" coax connector, what is the method to calculate signal loss due to the "T" connector?
You don't want to use 2 antennas.
Quote
5.) Lastly, given that we were to stay with our Sennheiser transmitters and receivers, do any of you have other suggestions for a combiner other than the AC-3000?

I think the best combiner on the market right now is the Radio Active Designs TX-8, and it is what I would prefer, but I think your problem lies elsewhere.

Does the problem happen equally on all packs? Is it effected by moving around the stage? How much bandwidth are you leaving between wireless mics and IEMs? They should be separated by about a couple of MHz at least. If the antenna is offstage you might try a directional paddle instead of the omni. You don't need coverage farther offstage I think. You might also try a helical if you think maybe the pack position (horizontal vs vertical) is part of the problem. Is the transmit antenna nice and high, like well above head height, with no obstructions and not near large metal structures?

The first thing I would replace is all the patch cables hooking up the transmitters to the combiner, and the cable from the combiner to the antenna. That is the cheapest easiest thing to replace and should be the starting point. Since you have a TTi you can measure the output of the system. Look at the output with all your transmitters and see if any of them have significantly lower output that the others. If there is an outlier move it to a different input to the combiner and see if it changes. Then take one transmitter and measure it on every input to the combiner to make sure every input of the AC-3000 is working the same. Do this with the same set of cable so there are as few variables as possible.

Let us know what you find.

Mac
« Last Edit: December 26, 2014, 05:48:57 PM by Mac Kerr »
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Jamin Lynch

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #2 on: December 26, 2014, 02:42:28 PM »

Hi,

We've got 6 Sennheiser G2 stereo transmitters (500MHz) going through a Sennheiser AC3000 (bought used a number of years ago) sending the combined signals to a single Sennheiser omni-directional paddle antenna (A1031-U) located in the back corner of stage right.

We've had this in place for a number of years. Usually performance is good with minimal dropouts. Venues are inspected with a TTi handheld unit, and wireless mics and IEM units are all coordinated using IAS.

Lately, the number of dropouts and intermittent "whoosh" noise events in the IEM mixes has increased. I'm nearest to the paddle antenna, and find that sometimes I have to put my IEM receiver in my coat pocket nearest the antenna - having my body between the antenna and the receiver seems to create to much of a barrier to the transmitted signal. That doesn't seem right at all...

Our stages are small - usually no bigger than 24' x 12'.

I really don't want any bad stuff when listening, so here are my questions:

1.) Might the AC-3000 be bad or going intermittently bad? Is there any way to test other than disconnecting all IEM transmitters from the AC-3000 and testing that way?

2.) Might we be better served by having two paddle antennas for coverage - one on each side of the stage? We used to use a Sennheiser A 2003-UHF directional antenna. Might two of those provide a more drop-out resistant method?

3.) Is it possible that some of us (like me) are too close to the paddle antenna?

4.) If I want to use two antennas and if I use a "T" coax connector, what is the method to calculate signal loss due to the "T" connector?

5.) Lastly, given that we were to stay with our Sennheiser transmitters and receivers, do any of you have other suggestions for a combiner other than the AC-3000?

The goal is to have an absolutely rock-solid listening environment. Please let me know if you think I'm expecting too much from our IEM setup, or if you have any suggestions at all, I'd love to hear them.

Thanks!
Bob Charest

Have you re-scanned your frequencies? There may be some "new" interference that as cropped up somewhere.

May want to try a properly placed directional antenna. Could help reject unwanted interference from the rear side.

Although the body packs don't have to be line of sight, it is preferred to have them on the same side of your body as the antenna.
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Andrew Broughton

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #3 on: December 26, 2014, 04:19:31 PM »

I think the best combiner on the market right now is the Radio Active Designs UV-1G, and it is what I would prefer, but I think your problem lies elsewhere.
I think the link you were going for was the TX-8. ;-)
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Mac Kerr

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #4 on: December 26, 2014, 05:47:49 PM »

I think the link you were going for was the TX-8. ;-)

Uhhh... Yeah. I fixed the link.

Mac
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Bob Charest

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #5 on: December 26, 2014, 10:09:29 PM »

Hi Mac,

Thanks for all the good ideas.

The trouble doesn't happen to all the packs at the same time except on very few occasions quite a while ago. It does seem to change in severity when one moves around, but not in a predictable re-producible way.

Regarding the coordination and spacing between frequencies, I've attached a jpeg of our IAS coordination report and a jpeg of my IAS options.

We used to use the directional antenna, but I thought that an omni approach would be better for us. The antenna is usually between the corner of the stage and 1/3 of the way along the back edge. I wouldn't think that placement in that area would be critical to cover such a small stage.

Helical is definitely under consideration, as I hadn't yet thought about polarity as an issue. Members mount the packs all sorts of ways so solving for some might introduce problems for others I thought...

One thing that might be important is height. I'm currently mounting the antenna on a mic stand fully extended, but that only raises the antenna to about 6' 2". Maybe it should be mounted on the stage right light tree crossbar about 7' up... I'm definitely going to check that out as it would be easy to do.

I will do the measurements with the TTi. That will most certainly provide the most useful information.

I'll run down the troubleshooting when we set up for NYE and let you know what I find. Also, understood: Don't use multiple antennas  :)

Thanks again,
Bob
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Bob Charest

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #6 on: December 26, 2014, 10:21:23 PM »

Have you re-scanned your frequencies? There may be some "new" interference that as cropped up somewhere.

May want to try a properly placed directional antenna. Could help reject unwanted interference from the rear side.

Although the body packs don't have to be line of sight, it is preferred to have them on the same side of your body as the antenna.

Hi Jamin,

Thanks for the reply!

We check our environment on a pretty regular basis, and I download the RF database for my copy of IAS on a regular basis as well. Our TTi comes in pretty handy for checking things that may not be reflected in the downloaded database as well.

We had used a directional antenna originally, but went with an omni because, with a small stage, I thought an omni would reach all the members more completely that a directional antenna would.

Best regards,
Bob
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Tim Padrick

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #7 on: December 27, 2014, 12:22:26 AM »

First, disconnect and reconnect every BNC a few times.  Wireless connections can get dirty too, yes?

It could be that the pack antennas are shot.
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Bob Charest

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #8 on: December 27, 2014, 07:33:29 AM »

First, disconnect and reconnect every BNC a few times.  Wireless connections can get dirty too, yes?

It could be that the pack antennas are shot.

Hi Tim,

I've replaced a couple of the pack antennas that were bad - The signal would mess up if you wiggled the antenna at all. That doesn't make a difference with this problem though.

All connections will be getting exercised when I check everything out in a few days.

Best regards,
Bob
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Henry Cohen

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #9 on: December 27, 2014, 10:40:27 AM »

A few thoughts:

- Why are you checking for 5th order IM products, but not 3 transmitter 3rds? I would check for the latter before the former, especially given the number of IEM frequencies.

- Where is your IEM TX antenna relative to either/both of your mic RX antennas?

- Where and how are the IEM receivers placed on the performer relative to the mic transmitters?

- IEM TX antennas should definitely be positioned higher, and aimed downward, so every IEM receiver has an opportunity at the least obstructed line of sight path to the TX antenna. 8' to 10' high at a minimum. Hanging an omni overhead, above center stage, often works well.

- A helical is a highly directional antenna; that sounds like exactly what you don't need, but I'm not sure where your intended antenna position is relative to the desired coverage area. That said, it does sound like a more directional antenna, such as an LPDA versus an omni, located in the proper location, would be a better choice than the omni. A quick sketch of the stage area would help.

Henry

The trouble doesn't happen to all the packs at the same time except on very few occasions quite a while ago. It does seem to change in severity when one moves around, but not in a predictable re-producible way.

Regarding the coordination and spacing between frequencies, I've attached a jpeg of our IAS coordination report and a jpeg of my IAS options.

We used to use the directional antenna, but I thought that an omni approach would be better for us. The antenna is usually between the corner of the stage and 1/3 of the way along the back edge. I wouldn't think that placement in that area would be critical to cover such a small stage.

Helical is definitely under consideration, as I hadn't yet thought about polarity as an issue. Members mount the packs all sorts of ways so solving for some might introduce problems for others I thought...

One thing that might be important is height. I'm currently mounting the antenna on a mic stand fully extended, but that only raises the antenna to about 6' 2". Maybe it should be mounted on the stage right light tree crossbar about 7' up... I'm definitely going to check that out as it would be easy to do.

I will do the measurements with the TTi. That will most certainly provide the most useful information.

I'll run down the troubleshooting when we set up for NYE and let you know what I find. Also, understood: Don't use multiple antennas  :)
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Henry Cohen

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Re: IEM Dropouts & "Whoosh" Sennheiser IEMG2, AC3000 Combiner, A1031-U Antenna
« Reply #9 on: December 27, 2014, 10:40:27 AM »


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