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Author Topic: Choir PA Reinforcement - Low cost, low profile  (Read 761 times)

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Offline voltronic

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Choir PA Reinforcement - Low cost, low profile
« on: December 15, 2018, 10:12:51 AM »
I just finished another series of performances with my choir, and realize it's long past time to give my students some PA reinforcement.  Some background:

This is an elementary school choir which ranges from 50-90 voices.  The big problem is they perform on a tiny stage barely large enough to hold the 4 sections of choir risers, which is in a school gym and then that extends to a cafeteria when we open the retractable wall for performances.  (This is your typical cafe-gym-a-torium found in schools built in the 1960s.)  My students put out a good deal of sound, but it is just getting lost in the lack of acoustics.

A colleague who teaches choir in another building but performs in mine recently consulted the tech guys in our district, who had her buy a pair of NT5s, two boom stands, and a cheap 8-channel Mackie mixer to have a portable setup that connects to the stage PA systems in the schools where her choir performs.  This works well, but I want something more compact.

We have a very good recently-installed PA system that has a 1/8" stereo input and single XLR line level input.


What I want to do is make a low-cost version of the Audix Micro-Boom - a low-profile and portable set of choir reinforcement mics.  I am thinking a simple pair of AT853s used for their original application of choir PA, but not hanging them (not feasible here).  I would make my own boom arms out of standard mic stand bases and these carbon fiber tubes I already use for my DPA 4041 setup.  Instead of the AT power modules, I would use my FP24 as power source and mixer.  It runs great from battery power, already has low cut, 1/8" and XLR outs, and more gain than I could ever need.  Or, if I don't want to use any of my personal equipment and have my school buy everything, I could go with a cheap micro mixer like the Mackie 402.

The trick would be finding 853s without the 4.7k mod, terminated to XLR and without the inline phantom supply.  Sound Professionals has them, but only with short cable lengths.

Does this sound like a good plan?
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Offline heathen

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Re: Choir PA Reinforcement - Low cost, low profile
« Reply #1 on: December 15, 2018, 10:25:24 AM »
I don't have much intelligent to say but your idea of powering the mics with the FP24 raised an eyebrow.  Doesn't that put out more power than the mics are meant for?  When I power my AT853s with phantom, I use the AT8531 modules (without batteries in them).
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Offline voltronic

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Re: Choir PA Reinforcement - Low cost, low profile
« Reply #2 on: December 15, 2018, 11:27:36 AM »
I don't have much intelligent to say but your idea of powering the mics with the FP24 raised an eyebrow.  Doesn't that put out more power than the mics are meant for?  When I power my AT853s with phantom, I use the AT8531 modules (without batteries in them).

I can't find any info on what the capsule polarization of these is, but I am sure it is way lower than 48V.  Does anyone know?
The FP24 can switch between 48V and 15V phantom, but that may be too much as well.

At any rate, it looks like the newer 853r's come with the 8538 power module which accepts standard phantom.
https://www.bhphotovideo.com/c/product/396393-REG/Audio_Technica_U853R_U853R_Hanging_Microphone_Phantom.html

My on-the-cheap thinking was that 15V would be within spec for these capsules and I could buy an unterminated set for cheap and terminate them myself for just a few bucks more.

EDIT: I just remembered that the building I used to work in has something like 6 853a's with power modules, so I may be able to just borrow these as needed, and make my DIY carbon fiber boom arms.
« Last Edit: December 15, 2018, 11:30:40 AM by voltronic »
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Offline Gutbucket

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Re: Choir PA Reinforcement - Low cost, low profile
« Reply #3 on: December 18, 2018, 02:51:27 PM »
I can't find any info on what the capsule polarization of these is, but I am sure it is way lower than 48V.  Does anyone know?
The FP24 can switch between 48V and 15V phantom, but that may be too much as well.

[snip]

My on-the-cheap thinking was that 15V would be within spec for these capsules and I could buy an unterminated set for cheap and terminate them myself for just a few bucks more.

EDIT: I just remembered that the building I used to work in has something like 6 853a's with power modules, so I may be able to just borrow these as needed, and make my DIY carbon fiber boom arms.

Remember that the 3-wire connection between the microphone and it's powering module is not a standard 3-wire balanced microphone connection via mini-XLR, rendering balanced "Phantom" powering directly to the microphone inappropriate regardless of voltage.  You need the powering module to convert the wiring format as well as provide the correct voltage.   Best to use the AT powering modules for unmodded microphones if available.
« Last Edit: December 18, 2018, 02:53:19 PM by Gutbucket »
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Offline voltronic

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Re: Choir PA Reinforcement - Low cost, low profile
« Reply #4 on: December 18, 2018, 09:39:50 PM »
I can't find any info on what the capsule polarization of these is, but I am sure it is way lower than 48V.  Does anyone know?
The FP24 can switch between 48V and 15V phantom, but that may be too much as well.

[snip]

My on-the-cheap thinking was that 15V would be within spec for these capsules and I could buy an unterminated set for cheap and terminate them myself for just a few bucks more.

EDIT: I just remembered that the building I used to work in has something like 6 853a's with power modules, so I may be able to just borrow these as needed, and make my DIY carbon fiber boom arms.

Remember that the 3-wire connection between the microphone and it's powering module is not a standard 3-wire balanced microphone connection via mini-XLR, rendering balanced "Phantom" powering directly to the microphone inappropriate regardless of voltage.  You need the powering module to convert the wiring format as well as provide the correct voltage.   Best to use the AT powering modules for unmodded microphones if available.

Thanks.  I'm going to probably go with the standard 853r that comes with the phantom power module for $189 each at the usual places.

I'll probably get the Mackie 402 so I have some basic EQ.  It remains to be seen if I decide to make some more DIY carbon fiber stands, or just buy she cheap $25 standard boom mic stands.
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Offline goodcooker

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Re: Choir PA Reinforcement - Low cost, low profile
« Reply #5 on: December 18, 2018, 09:57:40 PM »

You can often score the Audio Technica AT935QMRx mics in lots when people clear out their boardrooms or other places where podium mics are used.

It's an unusual AT mic that is basically the XLR phantom power converter + short gooseneck + adapter for increasing the thread size from 9 series to 8 series and a 853 cardioid capsule. I got a few for ~$30 on eBay.
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Offline voltronic

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Re: Choir PA Reinforcement - Low cost, low profile
« Reply #6 on: December 19, 2018, 08:11:20 AM »

You can often score the Audio Technica AT935QMRx mics in lots when people clear out their boardrooms or other places where podium mics are used.

It's an unusual AT mic that is basically the XLR phantom power converter + short gooseneck + adapter for increasing the thread size from 9 series to 8 series and a 853 cardioid capsule. I got a few for ~$30 on eBay.

Cool, thanks for the heads up!  I'll keep a look out for those.
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Offline 2manyrocks

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Re: Choir PA Reinforcement - Low cost, low profile
« Reply #7 on: December 27, 2018, 04:49:01 PM »
Since you aren't hanging them and are dealing with an elementary age choir, you aren't confined to AT853 style mics nor do you really need much more than a standard mic stand for height. 

These aren't bad.  https://www.iskproaudio.com/products/pearl  They have a roll off switch to help with stage rumble, and you'd want to use a shock mount. 

 

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