Benchmark:Shure Brothers Microflex MX391/c Boundary Microphone

Shure Marks its Boundary

Microflex MX391/c Boundary Microphone


Shure Brothers

222 Hartrey Avenue

Evanston, IL 60202-3696

(800) 25-SHURE

We’ve said it time and time again: if you want to make quality video, consider purchasing an external microphone.

Shure Brothers, long known for their high quality sound systems, have introduced a solid boundary mike in the Microflex MX391/c. Aimed at prosumers and professional videographers, who make everything from wedding videos to documentaries to industrial videos, the MX391/c captures a broad range of sounds that would elude handheld or shotgun microphones. Best suited for shoots where there are a number of scattered or different kinds of audio sources or where more than a few people will be talking or singing, the MX391/c would be ideal for weddings, choirs, concerts, plays, distant-learning classrooms or business meetings.


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It’s Got Heart

The MX391/c is a small, cardioid, surface microphone especially designed to mount on flat surfaces like a conference table or lectern. Its high sensitivity and heart-shaped pickup pattern make it especially suitable for picking up speech and vocals in a number of different applications.

We tested the MX391/c using Canon’s ES4000 camcorder. We found that it worked extremely well in a business meeting setting, placed in a middle of the conference table. Its unobtrusive design made it blend in with the other objects on the table while it clearly picked up speech from the five different people seated. Most impressive was that the MX391/c picked up different voices that talked at the same time.

It also passed the old voice versus-music-test. With the stereo playing and two people speaking at a conversational level, the microphone delivered even sound that delivered the background music without drowning out the subjects’ voices.

We also liked this microphone’s overall even pickup pattern and flexibility of applications. If you’re hosting your own public access television show, for example, and you’re conducting an interview, instead of relying on two lavaliere mikes that are clipped on shirts, you could place the MX391/c between you and your guest and hide it behind a plant. The pickup will be clear and it will allow both you and your guest a modicum of freedom and comfort.

The Phantom Menace

You can’t just plug the MX391/c directly into your camcorder and start recording. It needs power to pick up audio. Shure offers an inline battery powered adapter for this mike so you can plug it directly into your camcorder. If you already have a mixer with phantom power, you can plug it into your mixer, then run a line to your camcorder.

For performance sake, the latter is better. According to Shure, the inline battery adapter has a little less power. Plus, you can’t control the input levels. With a mixer, you gain a reliable power source, and the ability to conveniently control the input level.

For our tests, we plugged the mike into a mixer then ran a cable back to the mike jack of our camcorder. The pickup was crisp and clear from 10 feet and closer. From about 20 feet away, the audio was clear, but it competed with the other ambient noises. Although Shure’s advertisements say that the MX391/c is good for stage floors, we found, however, that it picked up the scuffing and stomping of shoes.

Clearly, this microphone works best placed on a table or desk. The cardioid (heart-shaped) pickup pattern is ideal for recording voices from a variety of directions. The fact that you can interchange the condenser cartridge on this microphone makes it versatile. Besides the cardioid cartridge that the MX391/c came with, Shure offers supercardioid and omnidirectional cartridges as well. So depending on your desired pickup pattern, you can interchange whichever cartridge you need. –DC

Tech Specs – Shure Microflex MX391 Boundary

Physical Type: surface mount

Transducer :condenser

Pickup Pattern :cardioid

Frequency Response :50Hz-17,000Hz

Sensitivity: n/a

Filter: n/a

Output impedance :150 [OMEGA Symbol for Ohms]

Max SPL :117dB (less than 0.1% THD)

Connector :XLR (balanced)

Signal-to-noise ratio :71dB

Power Supply :phantom power or battery adapter

Dimensions :5.3cm x 7.9cm x 1.9cm

Weight: 5.9oz


  • good audio pickup, especially when mounted on table
  • interchangeable cartridges
  • strong, sturdy construction that won’t slip or move around


  • needs phantom power or battery adapter
  • needs adapter to plug into camcorder


Good microphone for prosumer and professional videographers who make event or corporate videos.


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