Screaming CUB monitors

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
Post Reply
OneSwitch
Posts: 95
Joined: Tue Nov 22, 2011 5:50 pm
Contact:

Screaming CUB monitors

Post by OneSwitch » Sat May 19, 2018 5:47 pm

Last year I took a CUB monitor as part of a historical exhibit of assistive technology. I thought it was fine, but some of the young people there complained that it was making a horrendous high-pitched squeal. Once upon a time I probably would have agreed with them, but I could hear nothing at all.

This year, I replaced the trippler and some caps, to stop a horrible picture roll. But I didn't think to use a frequency analyser app to see if I'd improved things. Here's what I'm getting now....

CUB 1531 monitor: 15611 Hz at 51dB.
Space Invaders colour monitor: 15590 Hz at 62dB.
Vectrex: 20 KHz at 70db.
Philips TV: 15611 Hz at 56dB (not far off the CUB).

The CUB's the rowdy one out of the CRTs I tested. I'm wondering if this is about normal or a bit of a screamer that still needs to be looked at. Be interested in what anyone else's CUB racks in with.

User avatar
tricky
Posts: 2851
Joined: Tue Jun 21, 2011 8:25 am
Contact:

Re: Screaming CUB monitors

Post by tricky » Sat May 19, 2018 6:23 pm

I don't know about CUBs, but my daughter complains whener I turn on any of my CRTs.
I remember when I was a kid, I could hear most CRTs, but some would start and stop, I don't know why.

User avatar
1024MAK
Posts: 8009
Joined: Mon Apr 18, 2011 4:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: Screaming CUB monitors

Post by 1024MAK » Sat May 19, 2018 6:33 pm

The horizontal/ line transformer and / or the horizontal defection yoke coil(s) vibrate at the horizontal/ line frequency, which is just within the hearing range of non-decrepit humans... [For system I video, it's 15625Hz].

As we get all old and... our ears become less able to detect the higher "audio" range frequency sound waves.

Hence children, teenagers and young adults can hear the sound of the horizontal/ line systems of a CRT, and it sounds relatively loud to them. But older people like us either can't hear it any more, or perceive it less loudly and with less clarity. So it does not sound so bad...

Try the test on this site (make sure you use a decent computer/soundcard and decent audio system).
And here is another hearing test site.

Mark

OneSwitch
Posts: 95
Joined: Tue Nov 22, 2011 5:50 pm
Contact:

Re: Screaming CUB monitors

Post by OneSwitch » Sat May 19, 2018 7:32 pm

Thanks for the replies. I could hear the 15KHz pitch as it was announced in that test when wearing headphones, and it was not pleasant when I could. I think the CUB's just a fraction above my ability to hear it.

Out of curiosity, what sort of dB do other people's CUB monitors kick out? I use the free "Raspberrywood Spectrum Analyzer" on my Android phone. Seems pretty good.

Is 51dB unusual for a CUB monitor, or is it fairly normal? My 20 year old daughter says its fine for her. She can hear it but it's not bad. But she's battered her ears with iPods and IPhones for years.

duikkie
Posts: 2887
Joined: Fri Feb 07, 2014 3:28 pm
Contact:

Re: Screaming CUB monitors

Post by duikkie » Sun May 20, 2018 6:11 am

do the laury / yanny test :lol:
if you hear laury you are old :evil: , if you hear yanny you hear tv's, microwaves, things for dogs /
and a lot of devices =D>

User avatar
tricky
Posts: 2851
Joined: Tue Jun 21, 2011 8:25 am
Contact:

Re: Screaming CUB monitors

Post by tricky » Sun May 20, 2018 7:24 am

Coincidentally my daughter played that for me on friday evening, we both hear laury, but she still complains about my TVs. :lol:

User avatar
sbadger
Posts: 353
Joined: Mon Mar 25, 2013 1:12 pm
Location: Farnham, Surrey
Contact:

Re: Screaming CUB monitors

Post by sbadger » Sun May 20, 2018 9:10 am

I recall a device that they would stick on the side of buildings to stop kids loitering, adults can't hear it but the kids hate it.

https://en.wikipedia.org/wiki/The_Mosquito

In my early 20s I used it to my advantage, I had a high pitched sms tone that my boss couldn't hear! :D
I wouldn't hear it at all now.
So many projects, so little time...

User avatar
Elminster
Posts: 3137
Joined: Wed Jun 20, 2012 8:09 am
Location: Essex, UK
Contact:

Re: Screaming CUB monitors

Post by Elminster » Sun May 20, 2018 9:36 am

Even in my 30s I could hear crt’s I always put it down to wearing glasses most of my life, I.e. rubbish eyesight, good hearing. But not used a crt for well over 10 years. Will have to go round listening to people’s crts at abug south to see (hear) how my hearing has degraded over the last decade.

dominicbeesley
Posts: 654
Joined: Tue Apr 30, 2013 11:16 am
Contact:

Re: Screaming CUB monitors

Post by dominicbeesley » Sun May 20, 2018 4:55 pm

You should try collecting 405 TV's they run at 10Khz which more people can hear. My missus complains if one is on two floors away.

15kHz doesn't seem to bother my 3 year old daughter who watches Peppa pig on my old Decca Bradford TV. Most people became desensitized/used to 15kHz at a young age in the past. People born in the last decade or two may never have experienced CRTs and so find it highly irritating.

Me, pretty much deaf. It's Laurel!

Coeus
Posts: 1080
Joined: Mon Jul 25, 2016 11:05 am
Contact:

Re: Screaming CUB monitors

Post by Coeus » Mon May 28, 2018 6:59 pm

Am I the only one to think trusting absolute values (i.e. relative to 1mPA) from a sound level meter on an Android phone is being a bit optimistic? There are so many models I doubt the writer of the app has tested them all. How many microphones does it have? Are they omnidirectional or something else? How sensitive are they? Are they being summed or is noise cancellation engaged? In theory this could all be addressed with the right API and some calibration data from the manufacturer but I wonder if it is.

For all that, it should be valid for comparisons when the measurement is made by the same phone, in the same orientation, the same distance from the equipment.

Back to the original questions, remembering back to when I was young some CRTs were noticeably noisy and I don't think it was that a particular design was always noisy but that some examples of that design were. I know for laminated core transformers there are strips of metal separated by some kind or lacquer or tar like substance so they behave as one core magnetically, but don;'t suffer from eddy currents. Would how rigidly that whole assembly hangs together mechanically affect the noise output, i.e. the strips are able to move relative to each other then it will generate more noise?

If so, does that mean that insulating layer between the metal could dry out over time and shrink causing the whole thing to loosen up?

User avatar
1024MAK
Posts: 8009
Joined: Mon Apr 18, 2011 4:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: Screaming CUB monitors

Post by 1024MAK » Tue May 29, 2018 3:08 pm

You get exactly the same problem with some mains transformers if they are poorly constructed. I was in an equipment building earlier to day, and two 110V to 12V transformers were making a right racket. All the other transformers were okay. If you apply pressure on the metal mounting in the right place, you can shut up one. But as soon as you let go, it starts vibrating at 50Hz (and at 100Hz) again... And these particular transformers are only two to three years old.

Meanwhile elsewhere in another location, we have a 650V to 110V transformer rated at 35KVA. Yes it makes a little bit of noise, but nowhere as much as the 110V to 12V that I mentioned. Even though it is nearly 50 years old.

The "varnish" used to seal the laminations does not shrink as far as I know. It sets hard. So if you try to take a transformer apart, it flakes as it breaks, it being a bit brittle.

One problem is it may not be the laminations themselves that are making the noise, but instead, the former or fixing that the coils or laminations are mounted on. Part of the reason that the 110V to 12V transformers that I was on about above make so much noise, is that the case and mounting appear to be acting like a sounding board :(

You could try using some epoxy type glue on anything that is even slightly loose, if you can find anything that is loose.

Mark

Post Reply