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Help needed making microphones more sensitive

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Help needed making microphones more sensitive

Postby Camman595 » Tue May 21, 2019 7:46 pm

Our organization holds meetings in hotel banquet rooms 3 times per year and I got tired of paying their outrageous prices to rent audio equipment. So, I purchased the equipment below to help us save money. We use the house sound system but with our equipment.

2 X Shure SM57 microphones
1 x Behringer Micromix MX400 Ultra Low-Noise 4-Channel Line Mixer
1 X Peavey USB Audio Interface
1 X Behringer MicroHD HD400 Ultra-Compact 2-Channel Hum Destroyer

I purchased the mics based solely on the fact that is has been used for the Presidental Podium for 30 years.

The mics don't seem to be sensitive enough for our needs. The 1st time we used this setup, we had to turn up the volume so high that the hum was unbearable. We just ended up not using mics and everyone had to speak loudly. (This is also why we purchased the Hum Destroyer)

This last time, the volume wouldn't go loud enough to be useable without holding the mic very close to the mouth (which is not a good solution when trying to do presentations). So, we had to rent the mics from the hotel.

Can you help me find a good (and cost effective) way to use our current mics but louder? If not, what do we need to change? Also, hauling around our own powered speakers is not an option.
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Re: Help needed making microphones more sensitive

Postby Hugh Robjohns » Tue May 21, 2019 8:27 pm

You haven't said how you're connecting that pile of equipment together, but we can't really help without knowing the full details.

The SM57 is not a very sensitive microphone, but it can be made to work well given the right knowledge and equipment.

I suspect the fundamental problem is that your mic preamps -- presumably the Peavey interface -- just don't have sufficient gain to cope with the relatively distant podium mic placement I assume you're using.

If that's the case there are lots of ways of improving the situation with a better (but inevitably more expensive) interface, or a high-gain mic preamp, or possibly a cascade mic booster like the Royer dBooster or Cloudlifter (there are others).

The hum problem is a separate issue probably related to a ground-loop between your equipment and the house PA -- although there are other possibilities. If it is a ground-loop between your kit and the house PA the hd400 should cure it, but only if connected and sited in the right part of the signal path to break the relevant ground-loop.

Can I ask the purpose of the MX400 line mixer?
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Re: Help needed making microphones more sensitive

Postby Camman595 » Tue May 21, 2019 9:17 pm

Can I ask the purpose of the MX400 line mixer?
I am using that to mix the signals and control the volume. From your reply, I'm guessing that this may be my weak link.

I suspect the fundamental problem is that your mic preamps -- presumably the Peavey interface -- just don't have sufficient gain to cope with the relatively distant podium mic placement I assume you're using.
Sorry for the confusion. The Peavey USB Audio Interface is used to bring computer sound into the mix (for videos)
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Re: Help needed making microphones more sensitive

Postby blinddrew » Tue May 21, 2019 9:38 pm

So are you plugging the microphones directly into the MX 400 and then that into the house PA?
If so you're basically missing a mic pre-amp in the chain. The MX400 is designed to handle line-level sources, which are louder than microphone-level sources.
So it's not surprising that you're running into problems there. It's not so much a 'weak link' as the wrong tool for the job. You need a mixer with mic pre-amps, something like this: https://www.behringer.com//Categories/B ... rans(en|en) will do the job at the budget end.
The line-level output from that mixer can then run into some line level inputs on the house PA.
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Re: Help needed making microphones more sensitive

Postby Camman595 » Tue May 21, 2019 9:44 pm

So are you plugging the microphones directly into the MX 400 and then that into the house PA?
If so you're basically missing a mic pre-amp in the chain. The MX400 is designed to handle line-level sources, which are louder than microphone-level sources.
That is what I was doing. And your explanation shows where I went wrong. Thank you.

Can I replace the MX400 with the 802?
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Re: Help needed making microphones more sensitive

Postby blinddrew » Tue May 21, 2019 9:49 pm

I would expect so, but it would help if you could just set out your exact current set up. What's plugged into what, end to end.
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Re: Help needed making microphones more sensitive

Postby Camman595 » Wed May 22, 2019 12:53 am

Currently, both mics and Peavey USB Audio Interface are plugged directly into the MX400. The output of the MX400 is plugged into Hum Destroyer and from the Hum Destroyer into the house wall.
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Re: Help needed making microphones more sensitive

Postby CS70 » Wed May 22, 2019 8:01 am

What Drew says. The line mixer expects a line level signal, which is much stronger than the microphone signal that it's getting. Hence your problem - there's no way the poor line mixer can amplify the mic signal properly, as it's too weak.

Since you don't seem to have any mic preamp in your current setup, you need some. Since you have more than one mic, the easiest way is to get rid of your line mixer and replace it with a mixer which contains preamps.

Alternatively you could keep the line mixer and purchase individual mic preamps for each microphone, but that's way more expensive normally.

If your USB interface had preamps, another alternative would be to rely on the computer to do the mixing; or you get rid of what you've bought, get a computer interface with enough preamps, and use a software mixer on the computer to produce the final result; the line out of the computer will then drive either active speakers or a the power amp+passive speaker combination.

This latter setup tough would depend on the computer being turned on and seems a little too complicated for the simple task at hand, so I wouldn't recommend it.

In any case you don't need the Hum destroyer - the noise you're experiencing is the result of trying to use the line mixer to amplify the too-weak microphone signal.
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Re: Help needed making microphones more sensitive

Postby Hugh Robjohns » Wed May 22, 2019 9:34 am

CS70 wrote:In any case you don't need the Hum destroyer - the noise you're experiencing is the result of trying to use the line mixer to amplify the too-weak microphone signal.

I wouldn't be quite so certain of that at this stage. Ground-loop hums are quite likely when connecting between the podium mic equipment and the venue's PA equipment, and the 'Hum destroyer' is the right tool to deal with that should it occur.

But that's a completely separate issue to not actually amplifying the signals from the mics, which must be resolved with a proper mic mixer or similar...

H
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Re: Help needed making microphones more sensitive

Postby Arpangel » Wed May 22, 2019 11:16 am

Can I suggest simplifying the system, replacing the MX400 with a small Behringer USB mixer would eliminate the Peavy interface, and therefor, possibly, a potential hum problem. One less piece of gear to worry about.
I would also use a couple of short shotgun condenser mic's, Rode or Beyer, they'll have a healthier output than the dynamic mic's you're using. The hum destroyer may be useful, but hum shouldn't be there anyway, and these boxes add complexity and potential problems yet again. Carrying things around like an ART Cleanbox, can help with interface issues between balanced and unbalanced systems, you just have to do a bit of research on how best to apply these things, and know clearly what type of inputs the house PA will have.
Plugging your equipment into a wall socket or extension lead that isn't on the same outlet as the house PA could be a cause of hum, you might create a hum loop, so sorting things like that out from the off maybe worth the effort.
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Re: Help needed making microphones more sensitive

Postby CS70 » Wed May 22, 2019 4:06 pm

Hugh Robjohns wrote:
CS70 wrote:In any case you don't need the Hum destroyer - the noise you're experiencing is the result of trying to use the line mixer to amplify the too-weak microphone signal.

I wouldn't be quite so certain of that at this stage. Ground-loop hums are quite likely when connecting between the podium mic equipment and the venue's PA equipment, and the 'Hum destroyer' is the right tool to deal with that should it occur.

But that's a completely separate issue to not actually amplifying the signals from the mics, which must be resolved with a proper mic mixer or similar...

H

Good point, so worth waiting to sell it just in case..
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Re: Help needed making microphones more sensitive

Postby Camman595 » Wed May 22, 2019 6:09 pm

CS70 wrote:What Drew says. The line mixer expects a line level signal, which is much stronger than the microphone signal that it's getting. Hence your problem - there's no way the poor line mixer can amplify the mic signal properly, as it's too weak.

Since you don't seem to have any mic preamp in your current setup, you need some. Since you have more than one mic, the easiest way is to get rid of your line mixer and replace it with a mixer which contains preamps.


Thank you. This is the way that I will go.
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Re: Help needed making microphones more sensitive

Postby Bob Bickerton » Wed May 22, 2019 9:29 pm

Regarding ground loops, all equipment connected to the sound system should be run off the same power point.

Once that is done the likely culprit will be the laptop and a good idea is to run it through an AV DI such as the Radial ProAV2 2-channel Passive A/V Direct Box. If you do this though, you may them require a mixer with four microphone inputs as the DI presents microphone level impedance outputs.

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