Audio interference projector/speakers

[Matt Strickland]

Hi all,

Slightly different topic, we've been refreshing some classrooms and we still use a variety of projectors (ceiling/short throw) and run HDMI, with speakers wired to the projector location.

Usually we mount a small amplifier and connect via to the projectors audio to the ceiling speakers. I often install an audio isolator in-case of ground loops (tho everything on the same circuit)

But in this recent install, I just can't rid of the noise with both panasonic/epson projectors and the amps I have. As soon as the audio out from the projector is plugged into the input of the amp, terrible high frequency noise (not a ground loop buzz) more a SMPS noise (LED controllers, fire system loops etc)

Has anyone got a source of good quality, low power audio amplifiers? Ideally small enough to sit on a projector.

Ill try some commercial amp gear tomorrow to rule out the projectors outputs (this is while they are turned off)

Matt

[Ben Green]

In years past, we have had the occasional combination of projector and amp/speaker that made squealing noises - but only when the projector was off/in standby. Sorry to say we never solved these (other than by eventually replacing the gear). Like you say it wasn't a ground loop issue.

We switched to wall-mount powered speakers and never looked back.

Currently standardised on these: https://www.edifier.com/product-r1280t.html

On same circuit as projector, no ground loop isolator, utterly silent when not in use.

Yes powered speakers need a power outlet in a suitable location, but you need one there anyway to power the screen.

- Ben.

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From: 'Matt Strickland' via Techies for schools <techies-f...@googlegroups.com>
Sent: Wednesday, 27 July 2022 7:38 pm
To: Techies for schools <techies-f...@googlegroups.com>
Subject: [techies-for-schools] Audio interference projector/speakers

 

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Christchurch Boys' High School phone: +64 3 348 5003 address: 71 Straven Road, Riccarton, Christchurch 8014 postal: PO Box 8157, Riccarton, Christchurch 8440 web: www.cbhs.school.nz

[David Keenleyside]

Have you considered using a TOSLink adaptor for the audio?

This would disconnect the devices electrically and most AMPs have TOSLink in, or you can use another converter.

(The fibre cabling can be quite long.)

An alternative to the above is a wireless audio transmitter and receiver.

David Keenleyside, BSc CS & IS, CTech

ITP Associate

EFF Member

ICT Technician

Glenfield College

PO Box 40176 (Kaipatiki Rd)

Glenfield, Auckland City 0629

Ph:       +64 9 444 9066 ext 677

DDI: +64 9 441 9779

Email:    d.keen...@gc.ac.nz

https://itp.nz/CTech/NZ160799

https://www.linkedin.com/in/david-keenleyside-626871/

The Three O’s of Backup: Online, Offline, Off-site.

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[Alistair Baird]

I had one projector do that, eventually tracked it down to a bad earth or loop earth on the backplate of the projector. Projector used to cause real grief when some staff tried to just project, I used to spend the period reinstalling drivers etc until the bell went, yet my laptop never gave problems (mind had an external VGA, the others all used either a USB-C or HDMI to VGA adaptor). Speakers would range from hum to growl, motorboating even, but got worse over a term. Was using extension cords to try different power outlets etc, but when I put in new Epson projector [EB10] all was good in the hood.

From: 'Matt Strickland' via Techies for schools <techies-for-schools@googlegroups.com>

Sent: Wednesday, 27 July 2022 7:38 pm

To: Techies for schools <techies-for-schools@googlegroups.com>

Subject: [techies-for-schools] Audio interference projector/speakers

Hi all,

Slightly different topic, we've been refreshing some classrooms and we still use a variety of projectors (ceiling/short throw) and run HDMI, with speakers wired to the projector location.

Usually we mount a small amplifier and connect via to the projectors audio to the ceiling speakers. I often install an audio isolator in-case of ground loops (tho everything on the same circuit)

But in this recent install, I just can't rid of the noise with both panasonic/epson projectors and the amps I have. As soon as the audio out from the projector is plugged into the input of the amp, terrible high frequency noise (not a ground loop buzz) more a SMPS noise (LED controllers, fire system loops etc)

Has anyone got a source of good quality, low power audio amplifiers? Ideally small enough to sit on a projector.

Ill try some commercial amp gear tomorrow to rule out the projectors outputs (this is while they are turned off)

Matt

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Christchurch Boys' High School phone: +64 3 348 5003 address: 71 Straven Road, Riccarton, Christchurch 8014 postal: PO Box 8157, Riccarton, Christchurch 8440 web: www.cbhs.school.nz

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Kind regards,
Alistair Baird
IT Manager

P  06 354 4198 stpeterspn.school.nz   @stpeterspn 1 Holdsworth Avenue, Milson Palmerston North, 4414

[Matt Strickland]

Thanks all,

I tried my cheap home fosi audio amp as a direct replacement and no audio issues - no isolator needed.

Ideally it would be nice to see projectors offering HDMI/ARC or TOSLink, or perhaps even balanced outputs.

I'm sure at the better end of the market they do.

I'm going to change the amplifiers. Seems the particular ones I got pickup lots of noise (around ~1khz noise but with a blip/cycle of 1.5sec...)

Matt

From: 'Matt Strickland' via Techies for schools <techies-f...@googlegroups.com>

Sent: Wednesday, 27 July 2022 7:38 pm

To: Techies for schools <techies-f...@googlegroups.com>