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Klein+Hummel O410

Active Midfield Monitors
Published February 2009

Getting the balance right between the benefits and disadvantages of ported and non‑ported speaker designs is a tricky job, and K+H do it better than most with this ported model.

Klein+Hummel O410

The German loudspeaker manufacturers K+H were one of the best-kept secrets as far as the UK's studio monitoring market was concerned, up until just a few years ago. I'd rarely come across them professionally in all my years in the business, but when I reviewed the company's compact, three‑way O300 back in SOS October 2004 I became something of a fan — and that particular monitor remains one of my favourites today. The tiny O110 two-way monitor, which graced these pages in SOS July 2007, also proved capable of punching well above its weight. But this review focuses on a much larger speaker, the O410, which is the most recent to enter the K+H catalogue and only one step down from the company's flagship O500C.

Design & Construction

The new O410 shares many similarities with the larger O500C. They're both large, three‑way, active designs with ported cabinets, but whereas the flagship model employs a 12‑inch bass driver and can deliver up to 123dB SPL at one metre (one percent THD), the O410 has a 10‑inch bass driver and its maximum output is 3dB less (three percent THD).

The smaller bass driver means that the cabinet can also be slightly smaller, of course, but it is still a substantial piece of furniture, with an internal cabinet volume of 42 litres and external dimensions of 330 x 645 x 444mm. K+H recommend a listening distance of 2.5m, with a minimum of 1.5m and a maximum range of 8m. Each cabinet weighs 36kg, and although there are eight M5 threaded mounting‑points on the rear panel, mounting on a floor stand seems a safer option to me! The dense MDF cabinet is painted a dark-grey anthracite colour, but silver is listed as an option. Although the review model wasn't fitted with it, there's also an optional metal grille to protect the drivers.

The magnetically shielded driver set comprises the 10‑inch bass unit, a three‑inch mid-range dome, and a one‑inch tweeter, mounted in a vertical line with a pair of port vents in the two bottom corners of the front baffle (which make useful handles when moving the speaker!). The mid‑range driver and tweeter are mounted on a fully enclosed (sealed cabinet) sub‑baffle with sculpted baffle wave‑guides, which K+H call MMDs, or 'mathematically modelled dispersion' waveguides. The sculpted baffle is made from the same LRIM (Low Resonance Integral Moulding) material as used in the O300, both to provide controlled dispersion over 80 degrees horizontally and 60 vertically, and to avoid edge‑diffraction problems. If the monitor is to be used on its side, perhaps as a centre channel in a surround system, the sub‑baffle can be rotated to suit very easily.

A front‑panel badge is normally illuminated when the speaker is powered (and also shows protection status and, if appropriate, input type and condition), but the brightness can be adjusted and the light can even be turned off completely if required.

The integral amplifier pack at the rear of the cabinet contains four fairly traditional class AB amps, although they are slightly unusual in that the power-rail voltages are reduced when the input signal is low, to help reduce power dissipation. When idling, each O410 monitor consumes just 36W, but when running flat out that rises to 1.3kW. A pair of bridged amplifiers conservatively rated at 340W powers the bass driver, with a third amp delivering 160W to the mid-range driver and the fourth 180W to the tweeter. Protection limiters are built in for each amplifier channel, of course. Unusually, there's no obvious external heat sink to help cool the amplifiers. Instead, cooling air is drawn in through a slot on the right-hand side near the base of the rear panel and expelled at the top left by convection thanks to a clever funnelling design — and it works equally well whichever way up the speakers are. If the speaker is to be flush‑mounted in a wall cavity, the amplifier chassis should be removed and housed in an optional case (supplied with suitable cable harnesses) to ensure that effective cooling is maintained.

A conventional analogue crossover uses 24dB/octave slopes at 600Hz and 2kHz to integrate the drivers, and there's a 12dB/octave subsonic protection filter below 15Hz. The monitor is claimed to produce a maximum SPL at one metre of a very loud 120dB (three percent THD and averaged between 100Hz and 6kHz), with an overall bandwidth of 30Hz to 24kHz (+/- 3dB). Self-noise — essentially amplifier hiss — is less than 25dBA (measured at 10cm), which makes it all but silent for practical purposes.

The rear amplifier-chassis carries all of the signal and mains connectors, as well as some comprehensive equalisation controls. Mains power is input via the usual IEC socket, with switching for 100, 120 and 230V AC supplies. The mains on‑off switch is also on the rear panel, but there is provision for a 12V DC remote control option too. Towards the bottom of the panel are the operational controls, starting with a small, recessed rotary switch that allows the brightness of the front-panel logo badge to be adjusted. There are four settings providing 100, 60, 30 and zero percent.

The analogue input XLR connector is associated with a ground‑lift slide switch, input sensitivity trimmer and output level slide switch. The electronically balanced input impedance is a healthy 14kΩ (a transformer input is available as an option), and the level trimmer spans the range ‑9 to +6dB. The output level control adjusts the overall amplifier gain to provide maximum outputs of either 106 or 120dB SPL. As supplied from the factory, the input trimmer is set to 0dBu and the output power switched to the lower option, such that an input signal of 0dBu will produce 100dB SPL at one metre. In the higher output level setting, an input of 0dBu will produce 114dB SPL.

There's no 'D' version of the O410 (as there was with the O300), but an optional digital input module can be fitted in place of a blanking plate on the back panel. This module accepts AES3, AES3‑id, or S/PDIF signals up to 24-bit and 192kHz. Inputs are connected on either XLR or BNC sockets, and another BNC provides a buffered output for onward connection to a second speaker. A selector switch determines which channel is fed to the amplification (left, right, mono sum or the analogue input).

Remote Control

The rear panel of the O410 includes an 'acoustical controls' section for room calibration, as well as a parametric equaliser.The rear panel of the O410 includes an 'acoustical controls' section for room calibration, as well as a parametric equaliser.

The O410 is the only speaker I'm aware of that supports the new IEC 60958‑1 standard for remote volume control using the data stream user‑bits. This sensible system allows a full-scale digital signal to be connected to the speaker, and the output level of the D‑A converter adjusted in the analogue domain according to the user‑bit data. This ensures the maximum signal‑to-noise ratio is preserved, even when monitoring at low levels. The only problem with this excellent idea is that I don't know of any monitoring controller or consoles that support this use of user‑bits yet... but it's one of those 'chicken and egg' scenarios and I'm sure suitable products will start to appear.

Room EQ

Comprehensive room equalisation facilities are also provided on the rear panel, with three recessed rotary switches to adjust treble, mid-range and bass response, plus a further three (and a bypass slide switch) to configure a single parametric EQ band. The bass control is intended to compensate for boundary loading effects, and its four settings provide attenuation below about 200Hz of 0, ‑2.5, ‑5, or ‑7.5dB. The mid-range control is provided to compensate for early reflections from floor, ceiling and walls, again with four attenuation settings of 0, ‑1.5, ‑3, or ‑4.5dB, centred on 1kHz and spanning roughly an octave either side. The high‑frequency control allows matching for the listening room's HF damping, with shelf EQ options for +1, 0, ‑1 and ‑2dB starting from about 3kHz.

The parametric equaliser can be bypassed, but is provided to help control strong room-mode problems below 200Hz. The three controls adjust the centre frequency between 20 and 200Hz, the gain from +4 to ‑12dB, and the bandwidth between Q values of one (1.4 octaves) and eight (0.2 octaves).


Everything about K+H fills me with confidence. Like all the other K+H monitors, the handbook for the O410 is crammed full of precise technical details and comprehensive measurement plots and figures — far more than is usually provided by manufacturers. It feels like a true professional product designed for professionals, and that has to be a good start!

I rigged the monitors in place of my roughly similar sized PMC IB1s, and checked that all the switches were set to their default or zero positions, before starting to work my way through a broad range of familiar and challenging listening material. My initial reaction was that the O410 is a very clean‑sounding speaker indeed, with extremely low levels of distortion, immense resolution of low-level details through the critical mid-range, and a beautifully open and clear high end. The horizontal dispersion is very well controlled too, creating quite a large 'sweet spot' with a smooth, stable frequency response and spacious stereo imaging. The on‑axis frequency response is extremely well controlled, without any obvious peaks, dips, coloration or character — this is a very neutral-sounding speaker indeed. In my room it was also delivering useful output right down to 30Hz.

However, whereas the high end and mid-range were extremely accurate and precise, I found that the bass end exhibited hints of typical 'reflex speaker' character — a subtle ringing or resonance below about 50Hz that worked to smear the attack and precision of bass drums and other LF instruments. Some people are far more sensitive to this aspect of speaker design than others, and it's an inevitable trade-off: reflex cabinets allow greater bass extension for a given cabinet size, but poorer transient response. While the O410 balances that compromise extremely well — and much better than a great many other high‑end ported speakers I can think of — it's still evident, albeit to a small degree. The seriously impressive (to my ears at least) O300 avoids the problem completely by using a sealed cabinet, but the side‑effect of that is a relatively restricted SPL figure (only 112dB SPL for three percent distortion). My PMCs get around the same problem by using an 'advanced transmission line' design approach — but there are always disadvantages to balance the advantages, and the best compromise ends up largely being a personal decision.

The wide range of equalisation adjustment, and the inclusion of a parametric band, makes integrating the O410 into a control room relatively easy, and the balanced off‑axis response ensures that the results are consistent throughout the room. Some monitors seem to be better suited to particular musical genres work, which I find rather disturbing in the context of a studio reference monitor, but I found the O410 to be equally informative regardless of the kind of music I listened to. I worked my way through choral, orchestral, chamber, small ensembles, jazz, pop, rock, electronic... the O410 reproduced it all with precision and accuracy that allowed me to hear deeply into the mixes.

I then moved on to remixing some familiar material through the O410s, which was a pleasure. Small changes of EQ and level were obvious, particularly across the mid-range, and effects like reverb were easy to judge. As with most reflex speakers, I found that there was an optimum listening level — because the sensitivity of the bass end fell away relative to the mid-range and high end as the level was reduced — but this was a comfortable volume, and I experienced no fatigue problems, even during extended listening. Another good sign!


I've never been disappointed with a K+H speaker yet, and the O410 doesn't change that. It is a superb monitor that does exactly what it is supposed to do: present the source sound cleanly and accurately so that you can hear what you need to hear when balancing and tweaking a mix. It sounds less like a ported monitor than most — which is a good thing, to my ears — and it manages a very attractive balance of physical size, maximum SPL and sonic precision. This is definitely a new class leader in the making here, and I'd enthusiastically recommend an audition if you're in the market for a monitor of this size and capability.  


Monitors at this price point rarely disappoint, but there are distinct differences and resulting personal preferences. Alternatives include the larger ADAMs , such as the S4a and S5a, the ATC monitors (SCM50A/100A), Blue Sky Big Blue, Dynaudio's Air 25 system or more conventional M3Ps, the remarkable Geithain RL903k and RL944ks, the larger Genelecs such as the 1037C, the Harbeth M40s, the PMC IB1/IB2, and the Tannoy Ellipse 10 iDP.


  • Superbly accurate and clean mid-range.
  • Beautifully open and detailed top end.
  • Well controlled and extended bass.
  • Flexible room EQ tools.
  • Analogue and digital input options.


  • Monitors of this quality don't come cheap!
  • Mild reflex‑port lag.
  • I don't have room for any more monitors!


These large, three‑way, reflex monitor speakers are designed and built with K+H's impressive technical precision and sonic neutrality, and I feel they're class leaders in the making.


£6780.50 per pair including VAT.

Sennheiser +44 (0)1494 551 551.

$13996 per pair.

Sennheiser USA +1 860 434 9190.