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Klein Hummel O300D Powered Loudspeakers

German-manufacturer Klein + Hummel has been making loudspeakers since the 1930s. Its products have always had a high-end pedigree (and expensive) reputation. Having heard them at several European trade shows over the last few years, I was glad to hear that the company now has distribution in the U.S.

German-manufacturer Klein + Hummel has been making loudspeakers since the 1930s. Its products have always had a high-end pedigree (and expensive) reputation. Having heard them at several European trade shows over the last few years, I was glad to hear that the company now has distribution in the U.S.
Product PointsApplications: Recording studio, post production, broadcast station, mastering

Key Features: Three-way; 8-inch woofer, 3-inch midrange and 1-inch tweeter powered by separate discrete amp sections; analog and digital inputs with 24-bit 96 kHz DAC; tone-tailoring/boundary compensation/gain controls; limiter; optional controller, XLR and BNC digital inputs

Price: $6,400 per pair

Contact: Klein + Hummel North America at 866-417-8666, Web Site.
My first direct sampling of a K+H product is the O300D, an ultra-compact, closefield active monitor reviewed here, priced at, gulp, $6,400 per pair. After the shock of the price wears off, and you listen to them, you soon discover that they may be some of the most accurate small monitors you are likely to hear.


The O300D is an unusually compact, three-way closefield monitor – measuring 10 inches high x 15 inches wide x 11.5 inches deep. It sports an 8-inch specially-designed, polypropylene woofer, 3-inch treated, fabric dome midrange, and a 1-inch fabric dome, titanium tweeter. Like more and more speakers, these days the O300D can operate with a digital or analog input. The D/A is a 24-bit converter that takes up to a 96 kHz sampling rate.

Factory-rated frequency response is 40 Hz to 20 kHz at an amazingly tight plus, -2 dB window. Maximum SPL at 3 percent distortion is 112 dB. The crossover frequencies are 650 Hz (woofer to midrange) and 3.3 kHz (midrange to tweeter) with a 24 dB-per-octave slope per each crossover.

Each driver is powered by a discrete separate MOSFET amplifier (150 continuous watts for the woofer; and 65 continuous watts for the midrange and tweeter amps).

Like most higher-end powered speakers, the O300D includes room-matching controls including EQ, boundary compensation, driver attenuation and subsonic filter. A limiter also prevents grossly distorted sound and potential damage to the drivers.

Rear panel features include an on/off rocker switch, balanced XLR connector for analog or digital input, analog/digital input selector switch for the XLR connection, 75-ohm BNC connection for digital input/throughput, and room compensation EQ switches for bass, midrange and treble: flat, -3 dB, -6 dB and – 9 dB for bass; flat, -2 dB, -4 dB and -6 dB for midrange (designed to correct anomalies from meter bridge placement), and +1 dB, flat, -1 dB and -2 dB for the treble.

The subsonic filter has a cutoff frequency of 30 Hz with a 6 dB per octave slope and is not defeatable. The O300D can be operated with the Pro C28 optional outboard controller ($5,500) that has its own filtering, digital converter and limiters all done in FIR. According to the company, activating the controller disables the built-in EQ, limiter and D/A and allows the unit to connect its functions directly to the power amps. Connection is via a 7-pin female XLR.

As its price would dictate, the speaker is impeccably made with its enamel finish over the very solid, inert MDF cabinet, Weight is a manageable 32 pounds each.

In Use

I tested the O300Ds in my studio, driving it with a number of sources — digital and analog — and listening from a number of different positions including workstation monitors on stands next to a wall and free-standing monitor placement in the middle of the room on Apollo custom speaker stands. I tested the unit with DAT and CD demos, 24-bit/96 kHz DVD-V demos, commercial DVD-As and SACDs, and a live console feed from a Midas Venice 160.

In the free-standing floor set up, I tried the speaker with a number of high-res SACDs and DVD-As and DVD-Vs. In any location, the speakers are recommended to be placed horizontal with the tweeter to the outside. Driving the pair with a Legacy high-current preamp from its balanced outputs with Alpha-Core solid silver balanced cables, I sampled several 24-bit, 96 kHz DVD-V high-res guitar demos that were recorded using Audix SCX-25s and a vintage Martin D-35.

My first impression was how tight and real the bass was. I am a big fan of sealed boxes, which tend to sound less plump than many ported designs, and the K+H bass was tight, but still had ample output down to 40 Hz. The midrange and treble were seamlessly integrated, but unlike many powered monitors I have heard, no hype at all on the top-end.

In fact, I can predict that some engineers may reach for the treble boost because they don’t like the flatness of these monitors, but in reality these speakers are super accurate on the top-end, The sweet presence of the Martin via-the-Audix mics was there, but in their “smooth-is-real” splendor. Imaging was very good with the ability to read the soundstage with its plucked ambiance of the guitar.

Switching to a Bel Canto Pre6 preamp, I sampled several commercial SACDs. On vocals, I thought the speakers were good and the timber accurate, but the voices of several singers that I knew well did not seem as up front as other speakers I have used. I ended up mounting the speakers vertically and thought the vocal image benefited from the position change. K+H North America’s George Weber said that studios that have purchased the speaker have reported the same result with the vertical placement.

On every analog setup I tried with every kind of music, the result was the same. Great tight bass, pinpoint imaging and smooth midrange and treble without coloring the sound. This may be one of the best powered three-way speaker I have ever heard that synergizes its three drivers to the point that the speakers are not part of the sonic equation. Other speakers I have tried that are close include the ADAM S3A ribbon speaker and the Genelec S30D ribbon and the Tannoy Ellipse, all which have been reviewed in PAR.

I also listened to the O300D via the digital inputs, feeding a Fostex DV40 via its digital XLR output. The digital selection switch allows the option of taking in a standard AES/EBU stereo signal, in which the second channel is fed to the other speaker’s digital input via a BNC connection Each speaker can also be fed a single channel digital input. S/PDIF unbalanced signals are fed to each speaker via the BNC digital inputs.

The sound from the digital input, D/A converter was just about as good as the analog, but I did detect slight differences when listening to subtle ambiance; after repeated listenings the difference was slight when compared to my reference Bel Canto and Benchmark DACs that were used in the analog setup. The difference became less and less as I went from 16-bit 44.1 kHz versions of the recordings to 24-bit 96 kHz. And most important, the converter did not sound harsh with violins, trombones and other brass instruments, which can be somewhat strident with lesser converters.

Quibbles? The K+Hs sure are expensive for little monitors. Although there are many setups where a direct digital input makes sense, I would like to see the digital as an option, which maybe could lower the price of the speaker for those who only want analog connection.

Still, if you play in this range of quality, a passive set of really top-notch monitors and a superb amp could cost you near the same. Especially if they are from Europe.

My other small wish-list item is a set of unbalanced analog connectors for those who wish to connect in such fashion. I have a number of high-end preamps that have unbalanced outputs, but make great monitors preamps.


Although I still prefer separate amp and passive speakers, (it is difficult to put the best amp in small integrated package on the back of a speaker) the K+H O300D proves that the distance is shrinking. If you don’t want plumped up bass or upper mid/treble hype and what you do want is sonic honesty, the O300D can fit right into any studio — from a serious home project set up to big time post facility.