Recent content by hollowman

  1. H

    Permanent magnets and "permeance"

    Thx. It would still be helpful if there were a more definitive or rigorous description or quantification -- beyond the somewhat roundabout terminology thrown around this thread, like "permeance". Maybe the "magnetic stuff" or "magnetic mass" of a NATURAL permanent magnet is something like the...
  2. H

    Permanent magnets and "permeance"

    Going over some web articles, it's possible that the bike's ferrite magnets were, over time, also affected (demag'd) by the Earth's mag. field.
  3. H

    Permanent magnets and "permeance"

    Another thing to note is that in engineering (especially industries related to permanent magnets/magnetism, like TDK), "permeance" is used as follows: "in calculating a magnetic circuit, permeance P, which is the reciprocal of magnetic resistance R" ...
  4. H

    Permanent magnets and "permeance"

    And/or "Coercivity", https://en.wikipedia.org/wiki/Coercivity " also called the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized"
  5. H

    Permanent magnets and "permeance"

    Another way to think about the issue would be, all else held equal, how long to would magnetic domains remain "in static position" if the fridge magnet or audio cassette tape were isolated in some remote, inter-cluster corner of the universe?
  6. H

    Permanent magnets and "permeance"

    I meant exactly what I said: permeance And I think it applies to permanent magnets, including magnetic recording tape. In engineering; https://www.arnoldmagnetics.com/resources/technical-publications/calculators/magnetic-field-permeance-coefficient-calculations-for-rectangular-magnets/...
  7. H

    Permanent magnets and "permeance"

    I have an indoor recumbent exerciser bike that uses a non-contact magnetic "clutch" for resistance. There is permanent-magnetic fulcrum assembly that pivots on a hinge. And a heavy iron flywheel that spins when pedaling. The arc moves toward/away from flywheel based on resistance setting...
  8. H

    Harmonics in the "electrical" domain

    On a related note... Watch the following YouTube video (it's about spectral analysis of the 1985 digitally-recorded Beach Boys album, which was released on vinyl): The vlogger concluded that post-22khz content is "inaccuracies in vinyl" or "cartridge mis-tracking". But I'm not sure I buy...
  9. H

    Harmonics in the "electrical" domain

    I'm not sure this was pointed out ... but I've dwelled on the topic a bit and the explanation may be this simple: The tape recorder/player is band-limited. Let's say, 18khz is the highest freq. it can record/playback. We record a very high-freq sound ... for the sake of argument, let's invent...
  10. H

    Harmonics in the "electrical" domain

    I posted on a somewhat related issue WRT "image frequencies", here: https://www.physicsforums.com/threads/image-frequencies.931256/ When creating digital pulses, note that images (err... "harmonics"?????) are created purely in the "electrical domain". For the topic in this thread [Harmonics in...
  11. H

    Harmonics in the "electrical" domain

    There is some controversy as to why the spectral content of vinyl records contain frequency "information" above what the analog tape recorder was capable of capturing. A thought experiment: If I have a piano that has a key which plays 15khz (primary freq. of that key's piano string), what...
  12. H

    Thermal ballast (or whatever it's called!)

    Thermal mass .. yes! Wiki categorizes this first under HVAC ... maybe why I couldn't find it (I was looking under Thermodynamics) . Wiki does relate TM to heat capacity, which is covered extensively. About interior sources of heat ... besides people/pets, hot water and cooking stuff, my biggies...
  13. H

    Thermal ballast (or whatever it's called!)

    During weather-based heat waves or cold snaps, a completely sealed house with all windows/doors shut (but using no HVAC, heating-ventilation-AC) will take "a while" to cool down or heat up. If the heat wave or cold snap is quick (e.g., 24 hrs), a resident inside the house will experience almost...
  14. H

    What Do Smart Phones (Partially) Replace?

    FIRE! If you take it apart, you can short the batt. wires (single strand) to create a red-hot "burner". Touch some kindling, and ... FIRE! Also, the battery itself (with Li) can be made to ignite (YouTube the topic) ... sometimes w/o help (Samsung Note 7)
  15. H

    Image frequencies

    I assume you mean in during the A/D process: i.e., use an anti-aliasing filter before the ADC. Actually, modern ADC systems (e.g., as used for digital audio) use an analog anti-aliasing filter before the A/D converter (an IC chip). Then, following the A/D converter, an oversampling digital...
Top