The Glensound Atomic Helium 2 Feedback Destroyer works by
rapidly varying the audio output by down-shifting it by about 4Hz over
a short fluctuating cycle. This variable frequency shifting is sufficient in a
speech/voice PA system to largely suppress risks of feedback and even 'ringing'. Such a unit should not
be used with music (especially live music) because it noticeably alters the sound of some instruments,
e.g. for keyboards the effect shows up most. But for spoken voice
the frequency shifting effect is not noticeable other than that feedback is ‘magically’
suppressed. This method of ‘Feedback Destroying’ is generally much more effective
with speech than can be achieved by any of the conventional notch filter effects
units, e.g. Sabine or DBX (and certainly enormously more effective than
Behringer’s product!).
The pitch shifting effect itself can be subtle to hear and is
difficult to demonstrate, but see video (where steady tones have unfortunately
been somewhat suppressed by the camera on the phone). In the video the Helium 2
is fed with a steady 400Hz on i/p 1 and its o/p 1 is connected to i/p L of a
stereo speaker. Input R of the stereo speaker is connected directly to the same
steady 400Hz tone. The Helium is then toggled between ‘Freq shift’ and ‘Bypass’.
When the freq-shifted o/p is heard mixed with the clean tone there is a
warbling effect, but when the bypass button is pressed the warbling ceases,
hence the demonstration shows the unit does its job.
The unit is in excellent condition for its age, with the
only marks and slight scratches being on its upper- and under-sides, from being
rack-mounted.
Audio quality is to the usual Glensound level of
excellence, see spec sheet for details. Line level balanced inputs and outputs
are on gold-plated XLRs. Metalwork finish is hard-wearing black anodised with
silver text showing through.
Perfect for use in public speaking situations, e.g. church, town hall, lecture theatre, etc. where spoken word intelligibility will be increased.
All packed carefully ready
to ship with included insurance to a UK address now. Free postage to UK
destinations. I’m prepared to take offers – contact me through eBay if you’d
like to discuss.