On 10/10/2011 10:42, Neil & Marcia Adams wrote:
Who is old enough to remember the Keith Monks 'Phaserite' Checker
http://dl.dropbox.com/u/14586505/Keith%20Monks%20Phaserite.pdf ? I last saw one 'in the flesh'
30-odd years ago.
If you live in Europe or U.S. you might be able to locate one, or maybe they're
still made?
I have to admit I remember when this first came out - the modern equivalent is the Optogate
<http://www.optogate.com/html/phasee.html> which is about 110 ukp. We couldn't justify buying a
Phaserite way back then but it did inspire me to knock up something I named the "in-phase".
Basically a sinewave generator (discrete transistors!) feeding a half-wave rectifier so that only
the positive peaks come out. With a scope, a microphone and a bit of care, it's possible to check
speaker polarity (or cable/amp/whatever polarity). The box, being small and battery powered, still
regularly gets used for quick'n'dirty checks on systems.
These days I'm tending to include a Raised Cosine Pulse generator in my plugins - in code it's
easier to make RCP's with separations that are much greater than than the pulse width which in turn
makes it easier to spot polarity on speakers. You still need to be careful to allow for the fact
that some cross-overs use driver inversions to even responses in the cross-over region, because this
can really confuse the issue. If used for checking microphone polarity, and you don't have a known
unit with positive electrical out for positive pressure in, you need to use a battery (or similar)
applied directly (but via a current limiting resistor) to the speaker terminals to determine that
the cone is going out (increasing the pressure in the room) for positive voltage in, before you use
the RCP generator - don't forget to use a scope to check that the pulse polarity at the input to the
speaker is correct!
All that having been said, a clicker is easier! I used to have one that was given out at a trade
show (AES?? APRS?? - can't remember) as a "Free Acoustic Tester" but it eventually collapsed on me
and I keep meaning to get a new one but, as yet, I haven't replaced it.
Dave
--
These are my own views and may or may not be shared by my employer
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