e-mail links for Tom Brandau and David Waelder
accounts of production experience on set and on location
view photos, resumes, download PDF files, link to our other sites
return to the tools index page
for your information: a collection of articles we find interesting, useful, or amusing
return to Home page
Radio Systems Test Graphs

Frequency Response Traces Measured in Anechoic Conditions

In conjunction with the radio mic test, it seemed reasonable to look at the Sonotrim mic head itself. There are many lavalier mics out there to choose from but the Sonotrim seemed like a good place to start. Since microphones do change their characteristics over a period of time, we allocated a brand new microphone for these tests. It has never been used except in testing so the results are reasonably consistent and typical for that type of mike. The mike was tested in an anechoic chamber and its response was measured in different configurations without moving the mike.

Thanks to Dave Missal, Ed Somers and Marc Lesonsky at LSC. The frequency ID marks didn't print on this Audio Precision graph but the identities can be confirmed by reference to the graph below.
Sonotrim microphone plotted, above, in an anechioc chamber, connected to a PSC power supply, hard wired. This is a brand new, never used microphone and this graph is our reference standard of how the mike is intended to operate. The gradual presence rise starting around 1 kHz is a normal characteristic of this mike.

Thanks to Dave Missal, Ed Somers and Marc Lesonsky at LSC.
This graph, above, is the same Sonotrim microphone operating through an early series Lectrosonics185 VHF radio transmitter/receiver. The bottom end is no longer flat but the response otherwise is a reasonable approximation of the hard wire pattern.

Thanks to Dave Missal, Ed Somers and Marc Lesonsky at LSC.

Lectrosonics 195 Series transmitter/receiver set plotted with Sonotrim microphone. Note the fall-off of nearly 5 db @ 100 Hz. The presence rise around 1.5 kHz is consistent with tests of the microphone connected directly to a power supply. The low frequency attenuation is an artifact of the radio set.

We have been inclined to think of these results as an anomalie. Listening to the radio, we hear more bottom end than in with the VHF radios and would expect to see a flatter graph. We have since rerun the test with a different Lectrosonics 195 radio set. We can report that the new test shows much better response at the low end and a more accurate trace throughout.


Thanks to Dave Missal, Ed Somers and Marc Lesonsky at LSC.
This is the Lectrosonics 190 Series transmitter/receiver set plotted, above, with a Sonotrim microphone. It's interesting that this is the lower cost, narrow band UHF radio set intended for news work rather than high quality recording for films yet the low end is much flatter than the 195 Series. The presence rise is much broader, starting just above 1 kHz and rising a full 5 db. Altogether rather good performance from an economy radio set.

Thanks to Dave Missal, Ed Somers and Marc Lesonsky at LSC.
This is the Audio Ltd. transmitter/receiver set plotted with a Sonotrim microphone. It is a very nearly identical match to the output of the microphone when connected to a hard-wire, PSC power supply. If one holds the two graphs up the the light and superimposes them, the trace lines lie exactly on top of one another. A demonstration of audio excellance available with unlimited money.
© 2004 by Production Recording