When i am in any house i can hear this "hum" of a CRT TV turning on from a distance. Even if i enter a house i will know if the TV is on through that sound. What is that sound? Where does it come from? Is it the Electron Gun (because the TV is old)?
What is that weird sound i hear from regular CRT TVs?
Exactly, it has an electron gun. and what you are hearing is probably the audible frequency at which the tube is firing. note that not all people hear this. I for instance never heard it. But it does exist and is audible for some people. like you for example.
Thanks for the reply. But what drew me to say if it was the electron gun was because now that i have a CCFL LCD TV there is no sound from it. So the thing that is inside the CRT making a noise should be energetic like the electron gun.
Yeah most ppl if not all dont even hear it like i asked all the family at home and non noticed it. Could it be some ppl like me could hear more or less the audible frequencies by a small percentage?
Note: I knew J4D would be the one to first reply.
Yeah most ppl if not all dont even hear it like i asked all the family at home and non noticed it. Could it be some ppl like me could hear more or less the audible frequencies by a small percentage?
Note: I knew J4D would be the one to first reply.
- Edited
J4D is partially right, it may be the electron gun's firing of electrons onto the phosphor target in the vacuum tube (which when put together forms the cathode ray tube or CRT). But the fired electron beams need to be accelerated towards the screen via a high voltage electric field: new CRT screens (developed in 1990s and later on, that is) have coils which generate magnetic fields to deflect the electronic beams (magnetic deflection). What you are hearing might be the coils' hums when they are generating the magnetic fields. In both cases, the sound emitted by an electronic gun or operating coil is not audible to most people (frequency as low as 50 to 90 Hz).
Thanks for the info mesa177.
I still remember in grade 11 my physics teacher told us about the high voltage in the tube could reach thousands of volts!
Also, is it true that there is a thing(i think transformer) which actually alternates between positive and negative charges to attract to repulse electrons that will be on screen?
I still remember in grade 11 my physics teacher told us about the high voltage in the tube could reach thousands of volts!
Also, is it true that there is a thing(i think transformer) which actually alternates between positive and negative charges to attract to repulse electrons that will be on screen?
- Edited
[Edit]Not a regular transformer but there's a flyback transformer: regular transformers are coils with two winding forms that allows the AC (alternating current) voltage to either be boosted up or bucked down; a flyback transformer is used to generate high saw-tooth current signals at high frequencies. For the case of a CRT screen, the flyback transformer is one of the deflection coils (one that deflects the horizontal electronic beams)[/Edit]:kareem_nasser wroteAlso, is it true that there is a thing(i think transformer) which actually alternates between positive and negative charges to attract to repulse electrons that will be on screen?
Regular Transformer:
Coil (deflecting coil in CRT):
Yes, the coil is subjected to an alternating current, which leads to magnetization and demagnetization of the coil and consequently generates an alternating voltage at the coil's terminals: this alternating voltage allows the attraction and repulsion of the electrons from the electron beams (emitted by electron gun) to phosphor layer on screen, hence generating the lines seen on the screen. There are actually two coils: one controls the horizontal deflection (horizontal line view on screen) while the other handles the vertical deflection (vertical line view on screen).
This is a detailed diagram of a CRT tube:
Number 1: electron gun + Number 4: deflection coils (Number 7: phosphor layer, Number 8: closer view of layer):
I hear it too and it's been bugging me since I was a kid. My brother, being an electronics technician, introduced me to the "canon d'electrons."
It's nifty to use it as a trick with friends, but really it's mostly annoying. I have to unplug my TVs before I sleep. And I work in a film post-production suite with several CRT monitors... so I hear it all day.
It's nifty to use it as a trick with friends, but really it's mostly annoying. I have to unplug my TVs before I sleep. And I work in a film post-production suite with several CRT monitors... so I hear it all day.
When my parents open the door of the house i used to tell them while there that the TV is on, of course they wont believe me. But i am like 95% of times right that the TV is on because the sound it makes. I guess i am one with electronics ;).
@mesa177: The info is awesome i have a lot more....
Note to Admin and Mods:May i continue using this thread to ask questions about CRT TVs or i should open another one?
@mesa177: The info is awesome i have a lot more....
Note to Admin and Mods:May i continue using this thread to ask questions about CRT TVs or i should open another one?
No reply so i will continue.
@mesa177: Does the way that a CRT TV operate justifies its inability to progressively scan frames?
@mesa177: Does the way that a CRT TV operate justifies its inability to progressively scan frames?
Yes, actually there are two ways to scan frames:
1) Progressive (non-interlaced) scanning where the lines on each frame are drawn (i.e. displayed) in sequence
2) Interlaced scanning where the odd lines and the even lines are drawn alternately <= case of a CRT screen
In short, progressive scanning uses one field (odd and even lines of display at the same time) to create a frame while interlaced scanning uses 2 fields (odd and even lines of display at two different times) to create a frame.
It should be noted that interlaced scanning is possbile only for CRT screens due to their electronic scanning process (firing horizontal and vertical electron beams from the electron gun onto the phosphor screen) which is described as follows:
1) Progressive (non-interlaced) scanning where the lines on each frame are drawn (i.e. displayed) in sequence
2) Interlaced scanning where the odd lines and the even lines are drawn alternately <= case of a CRT screen
In short, progressive scanning uses one field (odd and even lines of display at the same time) to create a frame while interlaced scanning uses 2 fields (odd and even lines of display at two different times) to create a frame.
It should be noted that interlaced scanning is possbile only for CRT screens due to their electronic scanning process (firing horizontal and vertical electron beams from the electron gun onto the phosphor screen) which is described as follows:
The last line actually describes the refresh rate (30 to 60 Hz respectively). A clear picture is achieved with higher refresh rate. The drawn lines are more apparent for lower refresh rates or damaged screens.ehow website wroteColor images are produced by putting three electron guns together. One of the guns is red. The other two are blue and green. The inside of the CRT is coated with different colored phosphors when the beam from the cathode strikes the colored phosphor on the inside of the tube, that phosphor glows and we get a color image. According to Columbia ISA, these phosphors are chemical compounds that are "excited" when the electron gun scans them and they glow for a short time each time they are scanned by the electron gun. The scanning process is called "painting" and electron guns paint the screen thirty to sixty times every second.
So it is exactly as a i thought. What LCD does to display an interlaced frame is to use a technique called De-interlace.
2 years later
mesa177 wroteJ4D is partially right, it may be the electron gun's firing of electrons onto the phosphor target in the vacuum tube (which when put together forms the cathode ray tube or CRT). But the fired electron beams need to be accelerated towards the screen via a high voltage electric field: new CRT screens (developed in 1990s and later on, that is) have coils which generate magnetic fields to deflect the electronic beams (magnetic deflection). What you are hearing might be the coils' hums when they are generating the magnetic fields. In both cases, the sound emitted by an electronic gun or operating coil is not audible to most people (frequency as low as 50 to 90 Hz).
Has anyone measured the frequency coming from a CRT TV?
Cause 50-90 Hz does not seem like what I'm hearing when a CRT TV is on. It is an incredible high pitch sound with a lot of volume to it.
When I was in 3rd grade I first realized I could hear something that no other person around me could hear. I could tell if they were going to show a video in class from well outside of the room. If it were 50-90 Hz at that volume everyone should hear it. It is not a faint sound.