AT3000 Wireless Mic Feedback

[mikekars]

I used an Audio Technica 3000 series wireless handheld unit as an MC mic last night and had some difficulty getting adequate gain before feedback. I have used these before and always felt they were a little morel likely to have feedback problems than the SM58 or Beta58 vocal mics I typically use. But at this event there was a rather dramatic difference between what I could achieve for GBF between a Beta58 and the wireless mic.

 

I say dramatic because the talented but aging lead singer was pretty hard of hearing and required probably the hottest monitor mix I have ever delivered. She got 2x SRM450's daisy chained in a 45 degree sort of setup, one on each side, with pretty much just her vocals in her mix. If I had to guess I would estimate the 450's were running at 3/4 their maximum capacity and they were at least as loud as the mains. From her singing position this was definitely painfully loud for me and my "average" 60 year old ears. This was in a carpeted room with a low (8') ceiling with about 150 ppl.

 

During sound check we got the monitors up pretty high before the SM58 she requested on her rider started ringing a bit. Swapping out for a Beta58 with it's more appropriate rejection pattern got us up to her desired monitor volume without feedback. But both the sm58 and the Beta58 were very manageable in what I considered a fairly challenging GBF situation.

 

All that is background for the comparison to the AT wireless handheld. Putting the MC in her singing position, with none of the MC mic in the monitors, I could not get the volume in the mains as high as desired without little tweaks of feedback. And that volume in the mains was not as high as here singing and between song speaking volume. The feedback was at both high frequencies, say 3-4kHz, and mid frequencies, say about 800Hz.

 

Both the Beta58 and the ATW-T341b MC mic had fairly flat EQ curves on their channel strips. Both seemed to have reasonable gain structure. The handheld transmitter was set to the 0db audio input level.

 

So, from those of you that have used the ATW-T341b handheld mic would you say it is just more prone to feedback than the sm58 and beta58? Was there something I was perhaps doing "wrong" to add to the problem? One thing I probably did wrong was the vocal mic was still hot while the MC mic was in use.

 

 

 

 

[agedhorse]

Unfortunately, there are differences in polar pattern with the standard dynamic head that make it a little more feedback prone than the sm58 and in your application especially, the B58.

 

 

 

The advantage of the 3000 system is the superior wireless link over just about everything in its class. It's part of the tradeoffs, and generally I would take freedom from noises and dropouts over slightly less gain before feedback because turning down slightly is a positive cure for the feedback but there isn't any cure for an unstable RF link.

 

Or, you spend a lot more money on a wireless system with a b58 head that provides a more stable wireless link.

[trevcda]

One thing I probably did wrong was the vocal mic was still hot while the MC mic was in use.

 

Without taking an already too hot live vocal mic out of the equation, anything else was probably futile. That aside, the one thing I would question would be the interaction between the two SRM450 speakers, being used for monitors, at the vocal mic position. The "Ultra-wide, smooth dispersion via multi-cell horn aperture and HF waveguide" may not have been doing you any favors, particularly with them on their sides and with a very low ceiling.

 

With a properly deployed system I don't usually have any issues with my AT3K wireless systems. There are definitely mics that have better pattern control but they're not so horrible that you can't get a usable signal out of them.

 

 

[dboomer]

 

Both the Beta58 and the ATW-T341b MC mic had fairly flat EQ curves on their channel strips. Both seemed to have reasonable gain structure. The handheld transmitter was set to the 0db audio input level.

 

 

There is your problem. They did not have the same gain ... that's the definition of feedback. The mic feeding back had more gain.

 

Now finding what cause than might be difficult. Could have been the settings on the board, or the pattern of the different mics or the compression added by the wireless. But somewhere you got more gain on the wireless mic (at least at some frequencies).

 

 

[mikekars]

Don - As you have detailed in some of your excellent posts over the years on this subject: "gain is gain". It seems like it should not matter whether the capsule was hotter if the rest of the signal chain was set lower and the overall volume produced was lower.

 

There are a couple of additional gain stages on the AT3000 including an input sensitivity that can be set to -6dB, 0dB, or +6dB, and an output trim from the receiver to the mixer input. The output trim was set at 12:00 o'clock which is midway in the adjustment range. I think the head amps in each input channel were the same and my observation of the input metering on the MC channel strip led me to be believe the input to the mixer was within a reasonable range.

 

The other gain variable I suppose is that the MC was not on his mic like the lead singer was and did not project as well. That I suppose was a big factor.

 

A couple other details - when the MC was in the back of the room I could push his channel fader up to the same level as the lead singer's channel fader and I was able to get comparable volume with no feedback.

 

However, when the MC went on stage, in the same location as the lead singer, this is when I had to significantly reduce the channel fader (volume) to avoid feedback. Recall that the MC mic is NOT in any monitor. The mains were really close though - about 3 feet in front of the MC at the edge of a 16' wide stage and only about 7' up in the air.

 

Like Trevcda and others confirm, those AT3000 mics generally do OK. Aged has commented on their relatively good performance / cost ratio in old posts. I have also had good results with them in the past even with one singer jumping off the stage and into the crowd during a pretty loud outdoor concert. That was really strong singer though that stayed right on the mic.

 

Maybe a combination of poor mic technique on the part of the MC, me leaving the lead vocal mic un-muted during the MC announcements, and perhaps a wider or less even polar pattern on the wireless mic all added up to a feedback tendency. I was taken by surprise by how little volume I could achieve without problems. Just when I thought I new what I was doing, too!

 

The flip side is that I am pretty amazed at how stable the sm58 and Beta58 were in this situation.

[dboomer]

Don - As you have detailed in some of your excellent posts over the years on this subject: "gain is gain". It seems like it should not matter whether the capsule was hotter if the rest of the signal chain was set lower and the overall volume produced was lower.

 

There are a couple of additional gain stages on the AT3000 including an input sensitivity that can be set to -6dB, 0dB, or +6dB, and an output trim from the receiver to the mixer input.

 

Compared to what? Unless you are making measurements, these numbers don't have any real meaning. Remember decibels are ratios. You have to know the starting number to make them mean anything compared to a third thing.

 

But yes, poor mic technique and the simple fact that you switched another mic on will change the feedback points. And if anyone is walking around moving the mic placement it starts all over again. If you had muted the vocal mic you would have gained roughly 3dB GBF. By not turning if off you lost 3dB GBF (assuming everything was actually balanced out).

 

And even if everything was perfectly balanced you need to remember that analog wireless is almost constantly under a few dB of compression any time you are speaking or singing into it.

 

 

[agedhorse]

Or a few dB of expansion depending on the net calibration.

 

Companding is a 2 step process, either end can mistrack such that the error can be EITHER compression or expansion depending on which way the error nets out.

[mikekars]

I read elsewhere (gearslutz?) that the companding would always have a negative impact on GBF. The writer asserted if you have high gain at the mic, before the companding, this will exacerbate the GBF problem. He was saying that if you have a sensitivity adjustment at the mic (like the AT30000) you should run it as low as you reasonably can and make up the gain at the mixer.

 

Any credibility to that approach?

[agedhorse]

No credibility, sorry!

 

Stability depends on overall gain and phase at any point in time and at any frequency.

 

The reason (perfect) companding makes no difference is because say for 2:1 companding, the corresponding 2:1 expansion yields exactly 1, which falls out of the loop stability equation. The only companding terms that remain are those due to mistracking, which are usually +/- a couple dB. Note that it can be either way, so it won't always make the GBF worse.