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Klein+Hummel O 100 & O 800

Active Monitors & Subwoofer By Hugh Robjohns
Published November 2002

A versatile and cost-effective modular system which can cater for stereo and surround monitoring in both nearfield and midfield applications.

Whether monitoring in surround or stereo, the convenience of nearfield/midfield satellite and subwoofer systems is very persuasive. Indeed, the vast majority of mid-market monitoring probably conforms to this philosophy these days, even if some users don't initially acquire the corresponding subwoofer.

K+H O 100 & O 800Photo: Mike CameronThe subject of this review is a recently relaunched system from the respected German manufacturers, Klein+Hummel, who have been making PA and studio loudspeaker systems for a very long time. The diminutive O 100 active nearfield monitor loudspeaker was formerly known as the O 104, whereas its accompanying powered subwoofer, the O 800, was previously marketed as the O 818. These are not the only products in the company's range to have been renamed either — much of the range has been retitled, introducing a little more logic to the new structure. So although these are not new monitors, the renaming provides a good excuse to audition these little beauties.

O 100 Satellite

The O 100 is an active two-way compact reference monitor loudspeaker. The small charcoal-grey (other finishes are available to order) reflex-loaded 7.5-litre cabinet vents through a pair of triangular ports in the top corners, above the tweeter. The combined area of these ports is unusually large for such a small cabinet — 170 x 267 x 190mm (hwd) with a weight of just 5.5kg. The specifications claim a frequency response of 60Hz to 20kHz flat within ±2dB, which the supplied plot shows to be accurate, with only a mild lift between about 2kHz and 4kHz. The cabinet is constructed from an exotic composite material referred to simply as LRIM, and is apparently formed in a single moulding process. The cabinet's internal walls are claimed to be non-parallel to minimise standing waves, and two M8 threaded bushes on the rear panel (the metal amplifier chassis, in fact) are fitted as standard to accommodate a variety of mounting hardware.

K+H O 100/O 800 £1183/£1255
  • Smooth, surprisingly extended, and sweet sound.
  • Fine resolution and tonal accuracy.
  • Good build quality.
  • Monitors integrate well with subwoofer.
  • Three inputs to subwoofer enables surround system management.
  • Supplied subwoofer calibration CD
  • Room alignment features well judged.
  • The supplied handbooks were only in German.
A cost-effective, practical, well-built modular monitoring system. The O 100s are very capable active nearfields which can be extended by the addition of the O 800 subwoofer to make an impressive full-range stereo system which is easy to set up and reliable to use. There is also integral support for surround sound applications.


The 25mm tweeter and 145mm woofer are both magnetically shielded to facilitate mounting near CRT monitors or on console meterbridges where moving-coil meters are used. (The magnetic field emanating from unshielded monitors can cause erroneous readings on moving-coil meters in some circumstances.) The tweeter is unusual in that it is constructed from a combination of titanium and fabric — the resulting design is claimed to provide both the detail associated with a titanium dome driver and the low distortion characteristics of a fabric dome. The tweeter is also mounted in (and optimised for) a recessed waveguide formed in the front baffle. This waveguide helps to control the dispersion characteristics and provides greater phase continuity through the crossover region.

The woofer is another specially designed unit protected by a removable metal grille. Its cone is constructed from a composite of several different materials in a sandwich arrangement, the properties of each element being used to combat harmonic distortion. The waterfall decay plot supplied in the loudspeaker's handbook (only supplied in German, sadly), along with a superabundance of other technical test plots and measurements, shows a very fast and resonance-free decay throughout the mid- and high-frequency ranges.

The woofer's large-excursion voice coil has been designed to aid the high-level reproduction of bass frequencies, and the magnetic motor assembly employs flux compensation to help reduce distortion, especially in the woofer's upper frequency region.

Specifications & Adjustments

The specs are certainly impressive with less than 0.5 percent THD above 150Hz at 90dBSPL, and I have to say that they do sound very clean at normal nearfield monitoring levels. The maximum level generated by these little boxes is almost 108dB at one metre, although at this level distortion rises to a still credible three percent.

Controls on the rear panel of the O 100 monitor allow you to optimise its frequency response for your specific room.Controls on the rear panel of the O 100 monitor allow you to optimise its frequency response for your specific room.The line-level crossover section is a fourth-order design (24dB/octave slopes) tuned to 2.5kHz with phase correction for the two drivers to ensure a smooth transition between them. The amplifier chassis incorporates a pair of independent 50W amplifiers (capable of 80W peaks) to power each 6Ω driver separately. The circuitry incorporates protection against thermal overload of both the driver motors and the amplifiers.

The design also incorporates facilities for the user to fine-tune the in-room bass and mid-range responses, via a couple of four-way switches on the rear panel (marked 0, 1, 2, 3 for the bass, and 0, A, B, C for the mid-range). The bass end can be tamed in 2.5dB steps from zero to -7.5dB and, although the turnover point is not specified, the response charts would suggest the correction is a high-pass filter operating below 600Hz. The mid-range can also be adjusted in four steps between zero, -1dB, -2dB or -4dB, with a bell-shaped reduction centred around 300Hz and extending roughly between 60Hz and 1.5kHz.

The IEC power inlet and switch is also located on the rear panel, of course, as is the electronically balanced line-level XLR input. The powered condition is indicated by the red K+H logo being illuminated, while an overload condition causes the logo to flash. If required, an optional transformer can be installed to provide a fully isolated and floating audio input. In both cases, the input impedance is a conventional 10kΩ, and the system operates with a nominal +6dBu sensitivity, adjustable over a 24dB range (+6dB to -18dB).

O 800 Subwoofer

The rear panel of the O 800 subwoofer has facilities for surround sound bass management.The rear panel of the O 800 subwoofer has facilities for surround sound bass management.This active subwoofer is provided in the familiar form of a cuboid with a front-facing driver and an elongated horizontal slot vent near the base of the front baffle (the vent is actually divided in two). The cabinet has an internal volume of 59 litres, measures 360 x 320 x 510mm (hwd), and weighs a surprising 25kg. The maximum SPL is rated at 115dB at one metre and the response quoted as 30 to 90Hz ±2dB — making it an ideal match for the O 100 nearfield speakers.

The unit's I/O is arranged in a vertical strip on the rear panel (which also carries a huge heat sink) with three XLR inputs. These each have a corresponding XLR output which feeds high-pass filtered versions of the signals on through to the appropriate satellite speaker. The filtering is performed by 24dB/octave Linkwitz-Riley filters set to 90Hz. The integral bass-management filtering can be disabled, though, either via a rear panel switch or, more unusually, via a footswitch connected to a dedicated quarter-inch socket. This function also mutes the subwoofer output, enabling a reliable 'now you hear it, now you don't' comparison to be made with and without the subwoofer's contribution.

This whole I/O arrangement is very flexible and can accommodate a variety of system configurations, including 1.0, 2.0, 2.1, 3.0, 3.1, 5.1 and so on. In many instances the three inputs will be used to handle conventional left, centre and right inputs, filtering the satellite feeds and routing the bass content of all three channels to the subwoofer. Alternatively, the centre channel can be switched to operate as a direct LFE input. In this case, the centre input channel is routed to bypass the internal 90Hz low pass filter (although the bass elements from left and right inputs continue to be processed as before), enabling the user to establish any upper-frequency limit for a bespoke LFE input signal that may be desired.

The three inputs are set up for nominal +6dBu sensitivity again, with an adjustment range for the derived subwoofer level of 18dB. The integral 120W amplifier has sophisticated built-in protection systems which ensure the longevity of the unit regardless of abuse, and a ground-lift facility controlled through another rear-panel switch helps to avoid potential hum loops.

While the upper-frequency limit of the subwoofer's signal is normally set to 90Hz internally, the lower frequency limit is adjustable with a four-position switch offering settings of 30, 40, 50, or 60Hz with a third-order slope. This facility is intended to help fine-tune the unit's integration into the room. A continuously variable phase control (zero to 180 degrees) is also provided, and the whole alignment process is aided considerably by the inclusion of a special test CD with various band-filtered pink noise signals.

The single 16Ω driver is another custom design, with a long ±20mm throw and a 2165mm-diameter cone constructed from a high-tech Nomex/Kevlar composite material. The unit is also magnetically compensated, and is protected by a removable metal grille similar to that of the O 100. The cabinet shares the same charcoal-grey paint finish as the O 100 too, but is constructed from MDF rather than the exotic composite used in the satellites.

Listening Tests

I was supplied with a complete surround sound system comprising five O 100s and one O 800. I started the review with a simple stereo nearfield system using a pair of O 100s, progressing to a full-range stereo system by adding the sub, before moving on to a full surround rig. Listening to the stereo pair in a nearfield situation, I found them to be clean, detailed, and very quiet when 'resting'. In fact, the residual amplifier noise level is claimed to be just 2dBA (at one metre) which is very impressive! Moving around the speaker in the horizontal plane revealed that the frequency response changed very smoothly and progressively, without any nasty surprises or obvious colorations. In practical terms this equated to a broad and stable sweet spot, and the sound energy emanating from the sides and rear of the cabinet (which is typically reflected back into the room to combine with the direct sound) should integrate smoothly.

I found the vertical dispersion a lot narrower, as you would expect given the shape of the waveguide, but also a little less progressive. As is usually the case, the most critical area was around the crossover frequency, and it certainly paid to set the tweeters at ear height for the optimum stereo imaging. It would also be very unwise to position these speakers on their sides on a meterbridge, for example.

Given that proviso, I found the O 100s worked very well indeed, with a very precise, detailed (but still sweet) treble, and very crisp, stable stereo imaging. Although these are small boxes, the frequency range was well extended and controlled in the lower register. Whilst the absence of the lowest two octaves would be a concern in some applications, the quality and resolution of low-frequency information that the O 100s presented made up for any lack of quantity, particularly in a true nearfield environment.

Introducing the O 800 to the system was simple, with the replugging of a couple of cables and a few minutes messing about to find the optimum position for the cabinet within the room. I finally settled on a more-or-less central location slightly behind the plane of the O 100s — but this will obviously vary considerably with different rooms. Having the ability to tune the phase alignment makes an appreciable difference to the integration of the subwoofer and satellites. Compared with many such systems, I would say that setting it up was a little quicker than usual, thanks in part to the useful alignment CD which, in conjunction with a sound level meter, took a lot of the guess work and subjectivity out of the process.

The combined system performed very nicely, with well-judged crossover slopes making the whole system sound acceptably homogenous, once the levels were matched correctly. In this arrangement I found these K+H speakers to produce a very neutral and refined presentation of the source material. They were also easy to listen to over long periods without fatigue, yet retained the detail and transparency essential of a monitor-class speaker. At this price level there is considerable competition, including the lower-end Genelecs, active Dynaudios, and Mackies.

Extending the stereo rig to a full surround sound array was most rewarding. The wide horizontal dispersion and very tight unit matching allowed the O 100s to create a very stable, solid 360-degree sound field. Using a test disc with a surround panning band-filtered pink noise source, the signal's progression around the array was very smooth and linear, with only small shifts in coloration caused by room boundary effects.

For this test I used the O 800's integral bass management facilities as well as providing a direct LFE signal using my own surround controller to apply bass management. K+H suggest using multiple subs in situations where there is considerable bass energy, one specifically to handle the bespoke LFE signal and a second for the main channel's low-frequency content. This was not very practical in my room, although I can see the logic, particularly in film or TV post-production environments where there is typically far greater low-frequency energy to cope with.

Such was the consistency of these speakers that panning specific sounds or instruments anywhere in the surround environment, or moving a source continuously, was no problem at all in terms of fidelity. The character of a source remained highly consistent regardless of surround positioning, which is certainly not always the case with some systems. The overriding impression of the O 100/O 800 system in any configuration was always of clarity, accuracy, and detail without fatigue: a welcome combination.


As an active speaker, the O 100 seems to represent good value in the UK, and is certainly worthy of auditioning and comparison with similarly priced offerings from other manufacturers. The O 800 subwoofer is also well priced in comparison with its rivals and offers some well thought out facilities, particularly in terms of the I/O functionality, bypass switching and room tuning features. Despite their price, the build quality of these units inspires confidence and, while the use of some exotic materials may seem gimmicky at first, it is all backed up by impressive test measurements and documentation.

I enjoyed using these speakers and found them easy and reliable to work with. Listening to mixes made using them on my own reference PMC IB1 three-way speakers, the balances transferred very well and there were no surprises. This is as I would expect and hope, and I feel confident in recommending the K+H O 100 as a practical, reliable, and capable nearfield monitor. Extending a pair with the O 800 subwoofer expands the system's capabilities considerably and makes a useful upgrade path which will support further expansion to surround sound — either through the addition of more O 100s, or moving the original O 100s to the rear and adding the company's three-way O 300s at the front for a truly impressive, high-class monitoring system.

infop.gif O 100 active monitors £1182.52 per pair; O 800 active subwoofer £1254.79. Prices include VAT.
infot.gif Beyerdynamic +44 (0)1444 258258.