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For Sale ► Hygeia Electron Co. Air Motion Transformer (AMT) & Planar Magnetic Ribbon Tweeters ◄

Discussion in 'For Sale: Parts, Strings, and Accessories' started by OscarJr, Oct 30, 2018.

  1. OscarJr

    OscarJr Kneel before Zod! Supporting Member

    Feb 20, 2013
    Laredo, Tx
    TB Users, please note that Admins have approved of this For Sale thread containing multiple personal items of mine.

    I have for sale AMT and planar ribbon tweeters, made by Hygeia Electron/Electrical Co, LTD. Excellent build quality, consistency, and performance, very low distortion. These are "made to order" and are not mass-produced junk that you can find everywhere. Hell I had to fight with them for 5 months just to get this order! If you are familar with "audiophile" speakers from Legacy Audio, you might recognize some of these.

    These air motion transformer tweeters are of the same technology brought forth by Dr Oskar Heil beginning in 1969 under the ESS brand.

    I went in on a group purchase for these for a studio monitor project/speaker projects I have on the back burner, but I have lots of extras from people who backed out, so here they are. I know, I know, this is a bass guitar forum, but even bass cabs need that extra sizzle up top ! :)


    Here you can spot some of them during some testing:


    2. Specs:

    3. Description/Condition:

    Everything is brand spanking new.

    4. Price (quantities & prices subject to change depending on demand, but current as of now :) ) :

    Check/MO/Cashier's check/Paypal.


    Shipping is on the buyer, USPS in the USA is probably the best value, but sometimes FedEx is cheaper for larger packages, from what I've seen

    5. Pictures:

    As you can see, my AMT's have a gorgeous machined aluminum 45° bevel faceplate, not available anywhere else.










    MASSIVE heat sink


    Extra Diaphragms

    Brand spanking new.




    Hygeia RT-50021

    2.7-ish V, two sample set.

    Last edited: Oct 30, 2018
  2. OscarJr

    OscarJr Kneel before Zod! Supporting Member

    Feb 20, 2013
    Laredo, Tx
    Hygeia RT-4001



    Hygeia RT-20051



    Hygeia RT-1101


    Hygeia RT-1104


    SirMjac28 and mikewalker like this.
  3. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion

    Aug 25, 2010
    The Great Midwest
    This is one of the best for sale ads I've ever seen I don't need a tweeter but you've made me think about buying one.
    T. Brookins and yodedude2 like this.
  4. OscarJr

    OscarJr Kneel before Zod! Supporting Member

    Feb 20, 2013
    Laredo, Tx
    Thank you, I appreciate it. Take some off my hands! :) These really are good/unique speakers that sound great, and measure up to par. Some of these are used in $20k+ speaker systems! Including my personal ~ $7k stereo music monitors. You can get a better glimpse of them here in this wider angle shot:


    Would make great replacement tweeters as well, since all of these have a flat linear impedance for all practical purposes. I've done impedance sweeps on them, but what ever resonances do exist don't leave a mark on the impedance graph (increases are usually about 0.05-.15Ω), so they are very easy to integrate into cabs, IMO.

    Oh and I forgot to mention, the planar wavefront from these kind of flat diaphragms/apertures respond nicely to horn-loading and waveguides. In the 2nd picture, bottom right corner, you can see the RT-50021 with a test waveguide on top of it from Parts Express that has been modified to match up to the rectangular aperture. Look at the difference in midrange output (increase), with hardly any loss on the top-end:


    dB difference (gain):
    Last edited: Oct 30, 2018
    SirMjac28 likes this.
  5. OscarJr

    OscarJr Kneel before Zod! Supporting Member

    Feb 20, 2013
    Laredo, Tx
    Updated some quantities left.

  6. CurtWash2


    Jun 18, 2010
  7. CurtWash2


    Jun 18, 2010
    What is the horizontal dispersion for this tweeter?
  8. CurtWash2


    Jun 18, 2010
  9. OscarJr

    OscarJr Kneel before Zod! Supporting Member

    Feb 20, 2013
    Laredo, Tx
    I haven't measured the horizontal dispersion for it, but I get a few measurements and report back.
  10. CurtWash2


    Jun 18, 2010
    I noticed some diaphragms. So you will sell a pair with extra diaphrams included if I understand correctly they are new? I want at least two of the planar ribbon tweeters. (62041). My zip is 40241.
  11. OscarJr

    OscarJr Kneel before Zod! Supporting Member

    Feb 20, 2013
    Laredo, Tx

    Everything is brand new from my receipt of this order in July of this year. Only opened boxes to inspect them for damage and to measure frequency response and distortion with my Dayton Omnimic V2.

    To be perfectly clear: extra diaphragms are not free. They can be purchased by anyone who purchases the tweeters so they can have as extras is they wish to do so. The pricing for the extra diaphragms are listed in my pricing chart, #4 in my original post, towards the bottom of the chart.

    I should be able to get some polar measurements later today after I get off work to depict the dispersion intensity vs angle.
  12. OscarJr

    OscarJr Kneel before Zod! Supporting Member

    Feb 20, 2013
    Laredo, Tx

    Here is the info you request.

    Version 1: Polar response curves

    Version 2: Polar plot

    If you consider -6dB to restrict the beamwidth SPL loss, then I would summarize the dispersion:
    ~120° @ 1,500Hz
    ~90° @ 3,000Hz
    ~80° @ 7,000Hz
    ~55° @ 12,000Hz
    ~30° @ 16,000Hz
    ~20° @ 20,000Hz

    This is with the tweeter's response EQ'd flat using a standard graphic equalizer. Smoothing on the individual polar response curves was 1/24 octave.
  13. OscarJr

    OscarJr Kneel before Zod! Supporting Member

    Feb 20, 2013
    Laredo, Tx
    Curtwash2, what do you think after all?

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