Sumo is one of the coolest names anybody came up with for an amp line…somebody should revive that name and make a new tough looking amp.
- ...
- 264 posts total
Of course the real point is that EMI is not magnetic field. Which is what my original post was addressing. I.e., that shielding is effective for RFI/EMI but not for either external magnetic fields such as those produced by transformers or induced magnetic fields such as produced by current running through cables and wires. I used to work on the ELF program which transmits at 75 Hz so yes, I’m quite familiar with low frequency radio frequencies. Just because some people might not consider it a radio frequency it actually IS a radio frequency.Its apparent to me that you did not look at the Wikipedia link I posted earlier for your convenience. EMI really is a magnetic field and one that can occur at almost any frequency. So is RF, as they originate from the same principle of electricity. We usually use 'RFI' to refer to higher frequency phenomena (an example might be an oscillation in a circuit) but its just a polite nomenclature. What is generally different about the two is that for audio purposes, RFI **usually** originates via an antenna (driven by an RF source), whereas EMI generally does not (likely instead radiates from a power transformer or power lines, or any source that is powerful enough to radiate directly without the need for an antenna, although power lines might well be argued to be antennae. I recommend you take a look at the link I posted or ask your colleagues at the ELF station. |
Actually radio frequencies are electromagnetic waves. I realize it sounds repetitive but RF is not magnetic fields, which are stationary fields. It should be obvious that magnetic fields are not the same thing at all as electromagnetic waves. If they were the same then magnetic fields would be flying all around the room at light speed, which of course they are not. They’re stationary. Recall the experiment with iron filings and a magnet? The magnetic lines of flux are stationary. Everyone and his brother knows that the intensity of the magnetic field is inversely proportional to the distance from the conductor in the case of induced magnetism. This is not true for radio waves. And the fact radio waves don’t attenuate like magnetic fields allows extremely low frequency radio waves like ELF at 75Hz to be used for long distance communications. The last time I looked nobody is using magnetic fields for communications. Even the units are different, V/meter and Gauss. Thus, when setting out to eliminate or reduce magnetic field intensity one requires high permeability materials, not shielding. |
Thanks Dracule1 For pointing out there is no such thing as "neutral" in the recording/listening chain. Any musician like you, or myself, or any recording/sound engineer can tell you that...how do you measure neutral? What are the standards utilized to measure it? Every room is different, every combo of equipment is different, the electric signal varies from home to home, minute by minute and so on infinitely. Talk about a "moving target"...this is it. Best, Rob |
Well you got the first sentence right. The rest of it seems to point to the area of confusion. You might want to think about the fact that radio waves can very much metals.... An example that most of us know about are microwaves. I think maybe where you are having the disconnect is this: Recall the experiment with iron filings and a magnet? The magnetic lines of flux are stationary.What you are talking about is a simple magnet- much like what would happen if you put DC into a field coil. But that does not cause EMI- but if you use AC as a source now it can. IOW a simple magnet does not cause EMI only because it operates at DC. As best I can make out that must be where your confusion lies. An example of an AC source powering what otherwise might be considered a magnet is a tape head degausser. It is an electromagnet; different from a power transformer in that the core is the load rather than a secondary winding. If you get it near the tape head you will see a prodigious signal through the playback electronics if they are on. But you might be surprised to find out that if you take a simple magnet and bring it near the head the same thing will happen- not because the magnet is creating a field so much as the act of moving it is putting the field in motion and inducing something in the head as a result (thus the use of the term V/meter instead of Gauss). RF most definitely follows the inverse square rule BTW. The reason ELF works is that the ground wave can extend around the planet whereas at higher frequencies (FM for example) don't. Take a look at this Wiki page: https://en.wikipedia.org/wiki/Ground_wave_propagation I really recommend you read Wiki pages at the links I have posted!! |
- 264 posts total