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MXL 604 Dual-Capsule Microphone

Marshall Electronics, best known for its range of inexpensive and versatile MXL-series tube microphones, expanded its small-diaphragm condenser line with the introduction of the MXL 604 at the AES show in October.

Fast FactsApplications: Studio

Key Features: Pressure gradient small-diaphragm (20mm) condenser microphone; interchangeable omni and cardioid capsules; transformerless FET amplifier design; 10 dB pad and 6 dB/octave 150 Hz high-pass filter; includes wooden case, mounting clip and foam windscreen

Price: $179

Contact: MXL Microphones at 800-800-6608, Electronics, best known for its range of inexpensive and versatile MXL-series tube microphones, expanded its small-diaphragm condenser line with the introduction of the MXL 604 at the AES show in October.

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The MXL 604 ($179) builds upon its predecessor, the cardioid-only MXL 603, by adding interchangeable cardioid and omnidirectional capsules plus selectable high-pass filter and 10 dB pad.


The MXL 604 pressure gradient condenser microphone features interchangeable omni and cardioid capsules with 20mm gold-sputtered diaphragms and a transformerless FET amplifier design; internal wiring uses Mogami cable. The all-metal etched satin silver mic housing measures 22 mm by 133 mm and weighs in at 130g.

The MXL 604 system includes the microphone body, cardioid and omnidirectional capsules, wooden case, mounting clip and foam windscreen. In addition to its interchangeable capsules, the MXL 604 also features a selectable 10 dB pad and 6 dB/octave 150 Hz high-pass filter.

According to the manufacturer’s frequency response chart, the mic exhibits a slight rise in the 70 Hz to 300 Hz range, a dB hump from 600 Hz to about 2 kHz and a broad high-end boost of 3 dB – 4 dB from around 3 kHz to 11 kHz. As only one chart is provided, I assume this chart corresponds to the cardioid capsule, as it also closely matches my in-use findings. The mic exhibits very little, if any, high-end boost when used with the omni capsule (more on this later).

Manufacturer’s specifications state a sensitivity of 10mV/Pa, output impedance of 200 ohms, A-weighted signal-to-noise ratio of 80 dB and a maximum SPL handling of 134 dB (for 0.5% THD).

In Use

For this review, I was provided a pair of the MXL 604 microphone systems plus optional shockmounts.

The first thing I wanted to test with the 604 was the difference between its interchangeable omni and cardioid capsules, as this is the main new feature compared to its cardioid-only predecessor, the MXL 603. For this test, I set up the mics in close proximity to each other, pointing at a 45-degree angle towards the sound hole of an acoustic guitar from about the twelfth fret. The mics were situated about nine inches away from the guitar. The two resulting tracks recorded from the same performance were strikingly different, and not just in the way one would expect from the two different polar patterns.

The cardioid mic was bright, slightly aggressive and full, while the omni was fairly flat (even a bit dull) and about 5 dB lower. Concerned that the mics were not well matched, I repeated the test using a single mic, performing the same strumming chord figure once with the cardioid capsule and again with the omni. The results were very similar to the simultaneous two-mic set up.

This in itself is not a bad thing – in a way it’s like getting two completely different mics for the price of one. I was just surprised at the stark difference in frequency response and output. In no way is swapping out the cardioid for the omni simply opening up the polar pattern. As a means for comparison, I repeated the cardioid/omni test using the same configuration, but this time using an AKG 451 alternating between its CK-1 cardioid and CK-2 omni capsules. In this test, the resulting recordings were very similar save for the differences in patterns.

Once I knew what I was working with, I went on to use the pair of MXL 604s on a variety of applications appropriate to their character. Ultimately, my favorite use of the cardioid 604 was on acoustic guitar (as well as mandolin), where its top end really shined, and enabled easy placement of the instrument in mixes without EQ. The high-pass filter came in handy for taming its fairly strong proximity effect, though moving the mic back another six inches or so worked equally well in certain situations.

The cardioid 604 also proved to be a fantastic tom mic (with the 10 dB pad in, thank you), yielding a classic full-bodied sound with plenty of attack. I found the mic in cardioid configuration to be too bright and uneven for overhead miking, though it worked nicely in omni mode as an overall percussion pair. The pair in omni also fared well in a closed-top piano used in a live ensemble.

Overall, the omni capsules worked well in spaced-pair applications where the high end did not need any additional emphasis, and the cardioid capsules worked best on single-mic applications where extra high-end detail and focus are called for. One thing to note: the 10 dB pad and 150 Hz high-pass filter are on the same slider switch – you can only use one or the other at the same time.


In my various studio and live duties, I enjoyed having the MXL 604s on hand, and frequently managed to find a place to use them even when more expensive mics were available. The MXL 604s fit squarely into the “you can never have enough mics around” category: they excelled in specific applications (especially acoustic guitar and toms), the interchangeable capsules provided a range of versatility, and at an incredible street price of around $99, it’s hard to justify not having two or more of these guys in your bag of tricks.