Dan's is clearly the most qualified person to summarize what is known about these mics, but until he has time to do it better, I will sketch-out a few things including some questions we are still puzzling-over.
According to the manufacturer, the model WL183 is one of three "lavalier electret condenser microphones designed for use with a wireless body-pack transmitter." As such, they are designed to operate on the low voltage power supplied by the wireless transmitters--typically 1.5 to 10 VDC. The WL184 and WL185 heads are super-cardioid and cardioid respectively. All heads are interchangeable on the C122 cable which includes the FET amp.
Dan reported about his 183s, "I bought them from Sound Professionals wired...to a mini-stereo plug. They (SP) have discontinued the item, inexplicably, IMHO it was one of the best products ever for field recording. My first pair was mismatched in gains, I sent them back and got a well-matched pair."
With Shure's spec sheet and Dan's units to examine, a straight-forward wiring diagram for operation on Minidisk (MD), DAT Walkman and Hi-MD other "Power In Plug" (PIP) recorders could be drawn-up. Its also possible to wire them to preserve the TA4F connectors that come with the WL183's on the ends of the C122 cables.
Within weeks, a number of recordists were trying WL183's in the field and the list of impressed users began growing steadilty. See right sidebar links to sound file examples.
How does this mic compare?
Very favorably to all of the elecret mics I have ever used over the last 25 years. Its self noise of 23dB(A) matches that of the highly-respected DPA 4060 . The 183s high output of 29mV/Pa can produce recordings with less noise when used with noisier mic preamps. Although 23dB(A) self-noise is less than ideal for recording ambience in quiet settings, it is a step above other mics in its class. Nature recordists describe the contour of the low-end as "smooth" and "well-suited for natural settings."
Mounting & Application Flexibility
Field recordists are always on the look-out for small, omni-directional mic s becasue they are so easy to mount and versatile in application. The "omni" polar patterrn is more evenly sensitive to high frequencies from all directions than cardioid and super-cardioid mics. As a result the 183s are very popular for binaural mounting on headphones and with head-like barriers. The spatial imaging is powerfully accurate when monitored on headphones. Their small size makes them easier to mount and wear without "handling-noise." See right sidebar for links to some of mounting designs recordists have developed for the WL183's.
The "Botttoming-Out" Problem
The WL183 can be prone to distort when exposed to loud, low frequency sounds such as busses, trucks, thunder, and loud effects with certain recorders. The problem does not present itself in most recording situations and some recordists with Sharp MD recorders do not experience the problem at all. Jeremiah Moore found the distortion to be much less evident with the Sharp IM-DR580/DR80 (2003) recorder than with his Sony MZ-R37. Curt Olson and Richard M found some evidence that the mic preamp in Sony Hi-MD could be a contributing factor and Klas Stranberg has suggested that the mere .42 volts supplied by HiMD PIP circuits might be another factor.
Secrets for Shure
In summer 2005, by chance, a Shure salesperson noticed me recording with a compact WL183->HiMD rig at an amusment park near Chicago. When I told him the mics were Shure183's he replied, "Our techncians have been wiring-up 183's for their own portable recorders too! They call it the best secret mic in the industry."
A couple of people have asked Sound Professionals if they would consider selling 183's again but ,so far, have not expressed an interest. I have noticed that the number of dealers showing WL-183's in their product lists has increased. Until Eric Benjamin's discovery of the value in the omni-directional AT-3032 mics, the 183's may have been the best omni mics under $350/pair available of any size/type. Witht their small profile, PIP operability and binaurally friendly omni patterns, more recordists are choosing 183"s for their first pair of mics when portability is a hgh priority. May 2006.
Dan Dugan WL183 recording: French Gulch Hotel Frogs