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Author Topic: line or mic level distribution?  (Read 2372 times)

Peter Kowalczyk

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line or mic level distribution?
« on: March 30, 2018, 02:42:25 pm »

Greetings,

My system design calls for a few remote inputs to the main mixer/amp (using Ashly PEMA).  In a few of these locations, I'd like to have both a microphone and an unbalanced 'aux' input for user's ipods, etc.  Ashly recommended the Whirlwind MIP series of input wall plates ( MIP3 ).

This device is a DI box on a wall plate, soit attenuates the line level signal to mic level for distribution.  My simple mind is concerned about noise and crosstalk while distributing mic level instead of line level for 100' - 200', adjacent to Amplifier output, Cat5, and other signals.

The 'MIPAI' variant ( MIPAI ) outputs line level, but it's an active device requiring external power and more complex wiring.

Am I right to be concerned about distributing mic level signals instead of line level, or are my concerns more theoretical than practical?

Are there other similar devices to these MIP-series wall plates that provide both XLR Mic input and Aux inputs that I should consider?

Thanks!
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Kevin Rudolph

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Re: line or mic level distribution?
« Reply #1 on: March 30, 2018, 07:19:47 pm »

I think you may be overlooking the primary function of a direct box - it will take your unbalanced signals and output a balanced signal.  Is it better to distribute line level balanced?  Absolutely - the 1v is going to be less susceptible to noise ingress than .001v.  The CMR properties of the balanced line will take care of the vast majority of interference regardless of the level. Still best to avoid dimmers, lighting balasts, etc regardless of line or mic.

As far as cross talk is concerned - Iíve run line level sends, mic level return with phantom power, and dmx on the same sheilded cat6 cable and it works fine.  All balanced signals.
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David Sturzenbecher

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Re: line or mic level distribution?
« Reply #2 on: March 30, 2018, 07:26:30 pm »

Greetings,

My system design calls for a few remote inputs to the main mixer/amp (using Ashly PEMA).  In a few of these locations, I'd like to have both a microphone and an unbalanced 'aux' input for user's ipods, etc.  Ashly recommended the Whirlwind MIP series of input wall plates ( MIP3 ).

This device is a DI box on a wall plate, soit attenuates the line level signal to mic level for distribution.  My simple mind is concerned about noise and crosstalk while distributing mic level instead of line level for 100' - 200', adjacent to Amplifier output, Cat5, and other signals.

The 'MIPAI' variant ( MIPAI ) outputs line level, but it's an active device requiring external power and more complex wiring.

Am I right to be concerned about distributing mic level signals instead of line level, or are my concerns more theoretical than practical?

Are there other similar devices to these MIP-series wall plates that provide both XLR Mic input and Aux inputs that I should consider?

Thanks!

Hundreds of concerts happen every day with 20+ mic level signals going down 100ft-200ft snake cables with no issues of crosstalk or signal degradation.  Most often those snake cables are bundled with power, cat5s, intercom etc. I wouldn't be concerned.

Another alternative would be to go digital, with a wall plate from atterotech or similar.
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Peter Kowalczyk

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Re: line or mic level distribution?
« Reply #3 on: March 31, 2018, 05:01:29 pm »

Thanks folks.

I do absolutely understand the concept and need to balance the signal for distribution.  I just have a theoretical concern about attenuating them 40 to 60 dB in the process!  Thats just bad gain structure ;-)  The datasheet for the amplifier (Ashly PEMA 8250) doesn't give a CMRR spec, but i'm sure it's adequate and my concerns are probably overblown.  Since these line inputs will most always be used with compressed MP3 sources in a noisy restaurant environment, any difference is probably academic.

I made the decision to avoid digital distribution for cost reasons, both at the amp end and the input module end...

I'm curious about Kevin's point of using Cat6 cable for audio distribution - never done so.  I see it's 4 twisted pairs, and I gather that impedance must be tightly controlled for it to work properly at gigabit speeds.  Do you use individually shielded pairs, or do they all just share a common drain wire and shield?  Does that controlled impedance help in a meaningful way in the audio band? 

Cheers!
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Tom Burgess

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Re: line or mic level distribution?
« Reply #4 on: April 02, 2018, 10:57:40 am »

Greetings,

My system design calls for a few remote inputs to the main mixer/amp (using Ashly PEMA).  In a few of these locations, I'd like to have both a microphone and an unbalanced 'aux' input for user's ipods, etc.  Ashly recommended the Whirlwind MIP series of input wall plates ( MIP3 ).

This device is a DI box on a wall plate, soit attenuates the line level signal to mic level for distribution.  My simple mind is concerned about noise and crosstalk while distributing mic level instead of line level for 100' - 200', adjacent to Amplifier output, Cat5, and other signals.

The 'MIPAI' variant ( MIPAI ) outputs line level, but it's an active device requiring external power and more complex wiring.

Am I right to be concerned about distributing mic level signals instead of line level, or are my concerns more theoretical than practical?

Are there other similar devices to these MIP-series wall plates that provide both XLR Mic input and Aux inputs that I should consider?

Thanks!
Couple of questions...
Do you need the iPod playback to be stereo?  Will there ever be a need to run the XLR and iPod inputs simultaneously and / or with separate level control?
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Kevin Rudolph

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Re: line or mic level distribution?
« Reply #5 on: April 02, 2018, 08:13:04 pm »

I'm curious about Kevin's point of using Cat6 cable for audio distribution - never done so.  I see it's 4 twisted pairs, and I gather that impedance must be tightly controlled for it to work properly at gigabit speeds.  Do you use individually shielded pairs, or do they all just share a common drain wire and shield?  Does that controlled impedance help in a meaningful way in the audio band? 

Cheers!

Various manufacturers have adapters for cat5 snakes. Iíve always rolled my own but now Redco has a premade option thatís pretty affordable.

Iíve always used plain old black FTP.  Mostly for temporary deployments of various lengths, but installed a couple times on super small churches with non existant repair budgets. Not super fun to solder.  Dirt cheap.

None of this is to imply that I think this is best practice for installation. Only as an example, when using cabling designed with high twist per meter (good CMR), cross talk between various signal types is really quite minimal.

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Keith Broughton

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Re: line or mic level distribution?
« Reply #6 on: April 02, 2018, 08:30:57 pm »

Thanks folks.

I do absolutely understand the concept and need to balance the signal for distribution.  I just have a theoretical concern about attenuating them 40 to 60 dB in the process! 

I'm curious about Kevin's point of using Cat6 cable for audio distribution - never done so.  I see it's 4 twisted pairs,

Cheers!
You could replace the transformer in the wall plate with one that doesn't attenuate the level.

As for CAT cable, I have a buddy that does Indy car racing events and has run a condenser mic down 1000' of CAT 5 and says it worked fine.
CAT6 usually has a common shield as opposed to individual pairs shield.
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Joseph D. Macry

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Re: line or mic level distribution?
« Reply #7 on: April 03, 2018, 11:25:58 am »

Thanks folks.

I do absolutely understand the concept and need to balance the signal for distribution.  I just have a theoretical concern about attenuating them 40 to 60 dB in the process!  Thats just bad gain structure ;-)  The datasheet for the amplifier (Ashly PEMA 8250) doesn't give a CMRR spec, but i'm sure it's adequate and my concerns are probably overblown.  Since these line inputs will most always be used with compressed MP3 sources in a noisy restaurant environment, any difference is probably academic.


I find that most portable mp3 players don't really put out line level, but rather a "hot mic" level. Even with device volume cranked, you may find it lower than average CD player. Consider it a mic signal where you don't need much gain.
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Peter Kowalczyk

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Re: line or mic level distribution?
« Reply #8 on: April 03, 2018, 02:48:22 pm »

I don't need stereo, but I do wish to sum unbalanced Left and Right into a balanced mono signal.  Separate level control would be nice, but not absolutely essential; the single level control on the line input of the Whirlwind MIP3 would be adequate since I'll have overall channel level control through the amp's UI.  I would like to ensure that both mic and line inputs can operate simultaneously, but the mic input will only be used occasionally; the line input is primary.  I really only need the mic input in one or two out of several locations. 

The RDL D-J3 and companion D-J2 actually looks appealing, though it would require running a second line and using another separate input for each mic channel.  However, that puts both level controls in the same interface, which is more elegant.

Thanks for your collective comments on audio over cat5 or cat6.  Whirwind explicitly describes connecting the MIP-AI variant I mentioned earlier using a single cat5 for two signals plus power.  I remember hearing once that our nation's wireline telephone network was connected at the local level with UN-shielded twisted pair, relying solely on the CMRR of the receiving devices.  Electronics are cool  8).
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Dennis Wiggins

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Re: line or mic level distribution?
« Reply #9 on: April 05, 2018, 02:28:16 pm »

...I remember hearing once that our nation's wireline telephone network was connected at the local level with UN-shielded twisted pair, relying solely on the CMRR of the receiving devices.  Electronics are cool  8).

A Category 3 cable (Cat 3 cable) is a type of unshielded twisted pair (UTP) cable that is used for voice and data communications in computer and telecommunication networks. It is an Ethernet copper cable defined by the Electronics Industry Alliance (EIA) and Telecommunication Industry Association (TIA).

It was also used for Ethernet distribution (10/100 Mb/sec) until around Y2K, when CAT5(e) came to town and allowed 1Gb/sec.  (b=bits)

-Dennis
« Last Edit: April 05, 2018, 02:32:45 pm by Dennis Wiggins »
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