Assembly hall XLR sound only

[SteveB_NI]

Having a 'mare at the mo with sound in assemblies - which annoying was not an issue until recently.

 

Basically our sound set up is an XLR jack, back to a sound desk in a side store (which is opposite where the mobile projector needs to be unfortunately) otherwise I'd do a direct connection from laptop to sound desk.

 

The laptop outputs via HDMI to the projector. Then I run a XLR -> phono L + R cable to the projector sound output. I can only get either music, or speaking (i.e. left or right channel) but not both. I also get a constant buzzing / feedback sound if I connect my XLR > 3.5mm jack cable directly to the laptop.

 

The issue remains even if I use another device, such as a MS Surface etc.

 

Any suggestions? I have to place the projector at the side of the hall that only has an XLR back to sound desk, so limited somewhat! I'm thinking until I get this sorted just using a set of portable speakers but that is definitely not ideal.

 

Thanks

[steveg]

Is it worth trying something like this https://www.amazon.co.uk/Neoteck-Extractor-Optical-Converter-Splitter-DAC-1080P/dp/B01GH4MEYC/ref=asc_df_B01GH4MEYC/?tag=googshopuk-21&linkCode=df0&hvadid=309953091299&hvpos=&hvnetw=g&hvrand=9948125115123843603&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045117&hvtargid=pla-562707718451&psc=1 in case it is an issue with the output from the projector?

[3s-gtech]

It sounds like the change from balanced to unbalanced audio, across different devices too, could well be an issue.

 

This can be hugely exacerbated if the laptop is plugged in to charge.

 

Is it worth using a bluetooth audio receiver on the sound desk? Or a USB sound card on the laptop (with balanced output)? Both of those should eliminate the issue.

[Andrew_C]

You have two issues by the "sound" of it . (SORRY). The XLR input to your desk is mono. To combine left and right on it you will need to have a lead made specifically to do that or use a sub mixer. Then you have a "ground loop" which is causing your buzz. Use either a DI box, or a cheap isolator like this one.

[DavR]

XLR to phono jack cables almost always cause a heck of a buzzing sound, because of the ground issue, that's fundamental I'm afraid.

 

Thinking out loud, if an XLR line is the only route from projector side to sound desk side, could you make up a couple of adapter cables? Phono L to one XLR pin, phone R to another XLR pin, and then mirror at the other end? Assuming your sounds desk take phono inputs of course. That would, in theory, change a balanced XLR mono, to an unbalanced stereo phono.

 

Others smarter than I might tell you why that won't work, though....

[Andrew_C]

XLR to phono jack cables almost always cause a heck of a buzzing sound, because of the ground issue, that's fundamental I'm afraid

 

Others smarter than I might tell you why that won't work, though....

 

That's not quite it. You can use a balanced cable with XLRs to extend a stereo pair. Pin1 is earth, pin 2 R, pin 3 L. Not really a problem ; however, if you are running the cable any distance the chance of picking up interference is high.

 

The buzz is much more likely to be cause by the way the laptop PSU behaves. You need to isolate the device from the 'ground' that the audio system is using. No other way to fix it. DI box, isolator like the one I link to above, or an external USB sound device. That might be best actually - get one with a balanced output and send low level signals on the XLR. Pad at the amplifier end if required.

 

eta - I forgot you are trying to come out of the projector. DI or isolator, or take sound from Laptop and run fresh cable to amplifier.

Edited October 15, 2022 by Andrew_C

[dhicks]

The laptop outputs via HDMI to the projector. Then I run a XLR -> phono L + R cable to the projector sound output. I can only get either music, or speaking (i.e. left or right channel) but not both. I also get a constant buzzing / feedback sound if I connect my XLR > 3.5mm jack cable directly to the laptop.

 

As others have suggested, a USB audio interface for the laptop might be an idea. I find the Behringer UM2 quite okay, and affordable compared with other devices at around £40:

 

https://www.amazon.co.uk/Behringer-U-PHORIA-UM2-Computer-Interface/dp/B00EK1OTZC/ref=sr_1_2_sspa

 

That will give you a 1/4" stereo headphones output and left/right phono outputs - probably connect your existing twin-phono-to-XLR cable to the left/right phono outputs.

[Davit2005]

If going for an external audio interface I'd go for one that has it's own power supply and does not take power from the PC USB connection as well. Same with USB hubs these days, I had noise issues with a Blue Yeti to the point it was unusable, fixed by getting a decent powered USB hub.

[SteveB_NI]

It sounds like the change from balanced to unbalanced audio, across different devices too, could well be an issue.

 

This can be hugely exacerbated if the laptop is plugged in to charge.

 

Is it worth using a bluetooth audio receiver on the sound desk? Or a USB sound card on the laptop (with balanced output)? Both of those should eliminate the issue.

 

Thanks for all replies everyone. I like the idea of the bluetooth audio receiver. Is there any that you recommend in particular?

[3s-gtech]

Something like the Logitech 980-000913. Very simple. Range should be adequate but of course this can vary!

[SteveB_NI]

I've been trying different things to sort this at every opportunity. The final solution which bizarrely works is to have HDMI from laptop to projector, then only use 1 of the 2 phono outputs on the projector to an XLR socket back to sound desk.

 

I tested it with different videos, songs etc and it seems to be ok now.

 

It will do till I get a better set up lol - thanks for advice all

[psydii]

To solve the buzzing and get stereo you need this:

 

https://www.interspaceind.com/av-audio-products/product/28-pcbb%C2%B2/category_pathway-41.html

 

It plugs into a consumer-grade 3.5mm line out, and coverts it to Left and Right channel XLR sorting out any earth loops in the process.

 

Keywords I've heard in connection with this are PC Balance Box, Earth Loop / Ground loop eliminator / Earth Lift.

[SamanthaD]

Sorry, late to the thread as always!

 

One of these would sort you out - Behringer DI120 - sorts both of your problems in that it has ground isolation and can mix stereo to mono by using the link mode. Connect it to your projector by using 2 x phono > 1/4" jack leads, then 1 x XLR back to your wall plate. If you have phantom power on your desk then power it through that (be sure to mute the channel or turn the amps off before connecting / disconnecting though to avoid the pops!) or power it via 9v battery.