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Klein Hummel M 52 D Digital Active Control Monitor

When taken in whole, the combination of Georg Neumann GmbH microphones at one end, Klein + Hummel monitors at the other and Sennheiser’s broad base in the middle created an encompassing, formidable pro audio entity.

(click thumbnail)In 2005, Sennheiser extended its pro audio reach with the acquisition of high-end speaker manufacturer Klein + Hummel. Calling the pairing “a match made in heaven” might be a bit over the top, but it certainly was a match made in Wedemark, Germany, where both companies started in 1945. When taken in whole, the combination of Georg Neumann GmbH microphones at one end, Klein + Hummel monitors at the other and Sennheiser’s broad base in the middle created an encompassing, formidable pro audio entity.

Klein + Hummel released its M 52 “active control monitor” at the beginning of this year. The diminutive monitor, which supersedes the original M 50 model, is built like a tank and boasts features that make it versatile enough to be put to use in studio control rooms, editing suites and in-the-field broadcast applications.


The Klein + Hummel M 52 D model ($1,150), reviewed here, adds digital inputs to the analog-only M 52 ($850). Digital signals with sample rates from 32 kHz to 96 kHz are sent to the M 52 D’s 24-bit delta-sigma D/A converter via a BNC (S/PDIF, AES 3id) or XLR (AES/EBU) connector. The same XLR jack also serves as the monitor’s transformer-balanced analog input.

The M 52 D’s magnetically shielded aluminum enclosure measures a mere 6.8 x 4.7 x 4.6 inches, and weighs in at a substantial 6.2 pounds. Behind the M 52 D’s perforated metal grille is a specially designed long-excursion three-inch woofer, meaning lower distortion in the low-frequency range, according to K+H.

Just below the grille is a volume attenuator knob (infinity to open) that also doubles as a standby switch. A corresponding LED indicates active (green) or standby (red) status. A four-position rotary switch selects either analog input or demutliplexed left, right or summed L+R digital signals.

In addition to the aforementioned XLR and BNC connectors, the rear panel has a mains on/off switch and standard fused IEC A/C jack, plus a four-pin XLR connection for external power supply input (12 – 20 volts DC).

The M 52 D’s internal amplifier is capable of 24 watts continuous (at less than 0.1-percent THD) and a peak output of 40 watts. Manufacturer’s specifications include a free-field frequency response of 100 Hz – 20 kHz (+/- 5 dB), a common mode rejection ratio greater than 50 dB at 15 kHz, and a maximum SPL, averaged between 100 Hz and 6 kHz, of 103 dB (in half space and 3-percent THD at 1 meter).

In Use

Admittedly, I have not had many opportunities to spend quality time with Klein + Hummel studio monitors. To date, my only mixing experience with K+H monitors was with a mid-field model (or small mains in this case). This was in Europe — well, England — and it some time ago, but I remember liking what I heard. When presented with the opportunity to review a pair of K+H speakers in the comfort of my own studio, I eagerly accepted, sight unseen.

Fast FactsApplications
Broadcast control rooms and TOCs, editing suites, post-production houses, field producers/engineers, music production studios, OB vans/trucks

Key Features
Transformer-balanced/floating analog input on XLR; AES and S/PDIF digital inputs (XLR and BNC); select source from analog, or left, right or summed digital signals; powered by standard IEC AC cord and external 12-20 VDC 4-pin external input for field use; analog attenuator control; magnetically shielded

$1,150 per speaker

Klein + Hummel | 860-434-9190 |



  • Ultra-compact
  • Durable build quality
  • Impressive power and 100 Hz-and-up performance for its size
  • Very good as real-world reference


  • Lacks external Word Clock support
  • Attenuation knobs not stepped, making accurate stereo balancing difficult
  • Steep price point

Recommended for broadcast control rooms and TOCs, editing suites, post-production houses, field producers/engineers, music production studios and OB vans/trucks.The next day, a single modest-sized box (1 x 1 x 1.5 feet) arrived on at my door. My first thought was that the other box must have gone missing in transit. My second thought was that the single speaker that did arrive couldn’t be any larger than a NS-10, if that. To my surprise, packed within the confines of this single box was in fact two diminutive K+H powered monitors. My third thought: I pulled down the Westlake Lc8.1’s a bit prematurely.

Not to belabor the size thing, but by my rough calculations, I think I could stack nine or 10 M 52 Ds inside one Lc8.1 cabinet. Out of respect for these speakers and deference to the manufacturer, I shouldn’t use M 52 D and Radio Shack Minimus-7 in the same sentence, but that’s about the size of it [A comparison to the Fostex 6301s would be more appropriate, says the manufacturer. — Ed.] But size is the only thing they have in common, as I quickly found out upon using the M 52 Ds as alt speakers in the studio for the first time.

Within the armor—like exterior of the M 52 D, K+H has packed an impressive amount of power and quality. While the low-end frequency response is predictably limited, the 100 Hz-and-up range is impressive in overall quality for a three-inch speaker. More impressive, however, is its capable power versus expected distortion and resonance issues (or lack of, more precisely). Make no mistake, the M 52 D is not a speaker on which a critical mix should or can solely depend, but it does make a terrific companion to full-range favorites. (On a related note, I must extend praise to Steinberg Nuendo’s excellent control room functionality, through which I was able to quickly set up mono/stereo alt-speaker busses to the M 52 D that were level-balanced with the mains, and all without affecting my existing stereo, surround and alt busses.)

In addition to alt-speaker duties on music mixes, I also employed the M 52 Ds on several radio PSA and video postproduction projects, for which I found the K+H monitors to be ideally suited. Given their portability, the M 52 Ds proved useful in live broadcast applications, as I found out during a last-minute news conference at the National Press Club involving a bi-directional satellite link with high-ranking government officials in Sudan. When these crop up, we often find ourselves setting up a makeshift audio-video control room in the back hallway off a conference room, due to packed schedules in the actual studios.

In this instance, I had no trouble relying on the M 52 Ds (used on the digital outputs of a Yamaha O2R-96) because of my prior experience in the studio, and the fact that they are ideal for voice-only applications where low end should be shelved off anyway.

Besides the steep price point of $1,150 per monitor I only had a couple of minor complaints, the first of which is the position of the BNC digital input (less than .5-inch from the top edge in the upper left corner of the rear panel). When linking two M 52 Ds together via S/PDIF coax and a BNC T-connector as described in the manual, the location of the BNC spigot makes it unavoidable to have characteristically inflexible 75-ohm coax cables jutting out several inches beyond the top or side of the speaker (depending on which way you rotate the T-connector). Beyond the aesthetic aspects of having two cables sticking out into space, it also caused a clearance problem with placement within a rack (for truck use) and prevents placement directly next to near-field monitors (unless you don’t mind a six-inch curve of coax sticking out from the top).

The other two items are for my wish list. Firstly, I would appreciate external word clock support (but to be fair, I can raise the same issue with just about every monitor with a D/A, and to K+H’s credit, its D/A supports its sample rate range, as opposed to forcing asynchronous sample rate conversion like other “high-end” monitors). And lastly, because the attenuation knobs are not stepped, and cannot be linked in any way, the only surefire way to achieve functionally equal levels is to run the analog attenuation knobs fully open and use upstream analog or digital attenuation.


On the whole, I found the Klein + Hummel M 52 D monitor to be quite impressive, especially where it counts the most: sound quality and power. Despite its ultra-compact size, the K+H engineers pulled off some stunning accomplishments in build quality and versatility that inspired in me the confidence to immediately put the M 52 D to good use as an adjunct reference speaker in music and postproduction mix sessions, and in mission-critical live broadcast situations both at the National Press Club and in the field.

The fairly high price point may preclude certain buyer segments from purchasing M 52 D monitors. But it actually falls right in line price-wise — and actually can be considered a bargain, given its versatile and reliability — for broadcast control rooms and TOCs, editing suites, postproduction houses, field producers/engineers and music production studios. So to all of those I would not hesitate to recommend these little gems.