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KLEIN+HUMMEL O 110 COMPACT MONITORS
Hugh Robjohns MIBS tries out some diminutive German monitors.
orst Klein and Walter Hummel set up their Stuttgart company to make studio monitors and PA loudspeakers back in 1945, but my only experience of K+H monitoring to date has been the O 300D system. That particular model a compact, three-way active design, with a sealed cabinet and digital inputs provides seriously impressive reference quality monitoring, despite its modest dimensions. In fact, I was reluctant to return them after a review a couple of years ago, and have been tempted regularly to buy a pair ever since. So when I was offered the chance to audition the O300s junior sibling, I was very eager indeed. Overview The two-way O 110 is a reflex loaded design with corner ports either side of the tweeter. Each 6.5 litre MDF cabinet measures 268 x 170 x 190mm and weighs 5kg so while compact, these are not flimsy at all. The cabinets are finished in a hard-wearing anthracite enamel paint, and metal grilles protect the drivers. The steel amplifier chassis set into the rear carries a K+H O 110 Prices (per individual speaker): Electronically balanced 528.15 Transformer balanced 548.21 Digital Input O 110D 674.42 Sennheiser UK Tel: +44 (0)551 www.sennheiser.co.uk Bag BA/KH-O110D 46.00 KT Systems Tel: +44 (0)0981 www.ktsystems.co.uk All prices exclusive of VAT
modest heatsink, plus the (fixed voltage) mains and signal connectors, and a pair of threaded inserts to facilitate wall mounting. A comprehensive array of brackets and other mounting hardware is available. The speakers front baffle is made from a material referred to as Low Resonance Integral Moulding or LRIM, which has been machined to produce an elliptical waveguide for the tweeter. This ensures mechanical time alignment between tweeter and woofer, while also controlling the dispersion wide horizontally for good imaging; narrow vertically to minimise reflections from the mixing console surface. The magnetically shielded 145mm bass driver has a sandwich-membrane diaphragm which, combined with an unusually long excursion voice coil, is claimed virtually to eliminate harmonic distortion. The 25mm composite tweeter is cleverly engineered too, combining the transparency of titanium with the low distortion characteristics of a fabric dome. Each driver has its own amplifier and both are conservatively rated at a continuous 50W (for THD below 0.1%). Separate protection limiters in each amp are optimised for the characteristics of their respective drivers, and their activity is indicated on the illuminated K+H logo on the front panel. The active crossover is tuned to 2.5kHz with fourth-order slopes, but the LF response of the monitors can be fine tuned to suit the room. The bass roll off can be increased below about 500Hz by 0, 2.5, 5 or 7.5dB, and a gentle bell-shaped cut can be applied to the lower mid with 0, 1.5, 3 or 5dB settings. The overall free field response is given as 56Hz to 24kHz 3dB, which is surprisingly respectable for such a small box, and the published frequency plots are remarkably flat. The waterfall spectral decay also shows a clean, fast decay above 400Hz and very good damping of the port and LF driver. The rated maximum SPL is 107dB at one metre for 3% THD which is more than enough for a nearfield! The review model had an electronically balanced input on an XLR, and a rear panel
control adjusts the sensitivity from +6 to 18dBu. Optionally, an input transformer can be specified, and the D model adds a digital input. I assume this is similar to that of the O 300D, and if so despite the unusual arrangement it works perfectly and with excellent sound quality. Listening I rigged the O 110s alongside a pair of similarly sized PMC DB1 monitors powered by Flying Moles, as a familiar reference, and used them both during a SADiE editing session for a choral CD. I was immediately impressed with the scale, depth and accuracy of the stereo images they produced, and the wide sweet spot listening area they allowed. The sound is detailed and precise, transparent and neutral, without any hyping. Later, I played a wider variety of material through the little K+H monitors and was impressed further with their capabilities. Solo voices are portrayed in a very lifelike way with solid, three dimensional images and a complete absence of colouration. Bass instruments are also carried surprisingly well although obviously without the weight of a larger monitor. Bass guitars are tuneful, not onenote affairs, and kick drums are clearly defined and surprisingly solid. However, this speaker only delivers its best when the monitoring level is above a certain threshold. Like most reflex cabinets, lower listening levels appear to reduce the efficiency of the bass driver significantly, delivering a bass-light balance as a result. The overall tonality of the O 110 seemed to be voiced fractionally brighter than the DB1 at the extreme HF, but this only became a mild distraction when listening at silly volumes, in which case it could sound a tad strident at times. Overall, these diminutive monitors are clean, accurate well balanced and very impressive certainly well worth auditioning. I understand that KT Systems can also supply a padded protective carrying case for those who require a convenient portable monitoring solution.

30 LINE UP Apr/May 2007

Level Limited

Active Studio Monitor

O 110 D
Installation and Operation

KLEIN + HUMMEL GmbH

Zeppelinstr. Ostfildern/Germany
058-E0017 Version 24-10-2002 Tel.: + 49 - (0)711 - 45893 - 0 Fax: + 49 - (0)711 - 45893 - 35 email: info@klein-hummel.de h t t p : / / w w w. k l e i n - h u m m e l. d e

Safety Instructions

It is absolutely essential that you read these safety instructions carefully before connecting and using this K+H product. Your safety depends on it. Furthermore, failure to follow these instructions voids the warranty. To ensure safe operation for years to come, keep these instructions in a safe place for future reference. K+H has manufactured this product in accordance with IEC 92 (SEC) 39 standards, then tested and delivered it in safe operating condition. To maintain it in this condition, you must: observe all safety instructions, use the product only as described herein, have any maintenance, repairs, or modifications performed only by K+H or other authorized personnel, and ensure that the room in which you use this product is wired in accordance with the local electrical code.
Warning! When the interior of the cabinet is exposed, touching some parts can lead to an electric shock. If you need to gain access to the interior electronics of the unit, always disconnect the unit from any and all power sources first. Any repairs, maintenance, or other service of the unit when its interior compartment is exposed may only be performed safely (in accordance with VBG 4) by authorized technicians familiar with all the risks involved. Even in an unplugged state, a fully charged capacitor in the unit can zap the unsuspecting. Loudspeaker output jacks labeled with the IEC 417/5036 emblem (Fig. A, right) may be carrying dangerously high voltages. If your unit has this emblem, ensure that any connections to be made between these jacks and the speakers themselves are made before powering up the unit, and are done so only with manufacturer-approved interconnecting cables. If you need to replace any fuses, ensure that the replacements are of exactly the same type, value and voltage as the originals, as spelled out in the technical specifications at the rear of this manual. Do not use "repaired" fuses. Fig. A If you do not have any fuses on hand of the specified size, type, and value, do not hot-wire the contacts in the holder by short-circuiting them. Certain areas of the cabinet, cover, and rear panel can achieve extreme temperatures and are therefore marked with a "HOT" label (Fig. B). Refrain from touching any heat sink or ventilation grille. High volume levels are known to cause permanent - i.e. irreversible - hearing damage, especially when listened to without sufficient breaks. The higher the levels, the more frequent and extended must be the breaks. Avoid standing too close to loudspeakers that are being driven at high levels. If you must be exposed to high sound pressure levels over an extended period of time, use hearing protection. Fig. B Mains Connection: This unit is designed for continuous operation. Ensure that the operating voltage of the unit matches that of the local mains current (AC line voltage). Always check before connecting the power cable to the mains socket that the power switch on the unit itself is set to off ("O"). Use the power cable or power supply that came with the unit to connect to the mains socket (wall outlet). Power supply: a damaged power cable may not be repaired. Use a new cable. Avoid plugging the mains cable into a power strip that already has several other power-consuming devices connected to it. Avoid using extension cables. The unit must be connected to a mains socket close to it, and that socket should be freely accessible. Installation: This product may only be placed on a stable, clean, horizontal surface. Do not expose this product to vibration. Do not operate this product anywhere near water or other liquids. Do not use it near a sink, swimming pool, bathtub, or in any damp room or area. Electrical shocks carried through water can kill. Do not place any beverages whatsoever on or near this product, as liquids can kill electronic components. Ensure sufficient ventilation around the product to allow for adequate heat dissipation, especially near the rear panel and the sides of the cabinet (minimum of 8 inches from the nearest wall). The unit may only be installed in a rack if measures are taken to ensure sufficient ventilation and if the mounting instructions of the manufacturer are followed. Do not block or cover any heat sink, fan, or vent. Do not place the product where it will be in the path of direct sunlight, and keep it a safe distance away from radiators and other heaters of any kind. If you bring this product from a cold environment into a warm one (such as from a vehicle into a studio), it is quite possible that condensation will form inside the cabinet. Please allow the unit sufficient time for acclimatisation to room temperature (minimum thirty minutes) before connecting and powering up. To avoid accidents, do not use any accessory equipment with this product which is not approved by the manufacturer, particularly mounting accessories. Do not place this unit on any unstable platform, cart, stand or table. Should the unit fall, it can cause bodily injury to persons, or can be damaged itself. To protect this product from lightning damage during a thunderstorm or from power surges during an extended absence, disconnect the power cable from the wall outlet.

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Active Studio Monitor O 110 D
Active Studio Monitor KLEIN + HUMMEL O 110 D

Installation - Operation

Figure 1: Front view of the O 110 D
Figure 2: Rear panel of the O 110 D

Table of Contents:

Safety Instructions..2 Table of Contents...3 1. Installation and Operation..4 1.1 Operating Conditions..4 1.2 Installation..4 1.3 Connection to Mains Current..4 1.4 POWER Switch..4 1.5 Mains Power Fuse..4 1.6 Input / Room Compensation / Ground Lift.4 1.6.1 XLR Input...4 1.6.2 BNC - Input..5 Active Studio Monitor O 110 D Page 3 1.7 Display Functions..6 1.7.1 Overload Protection..6 1.8 Care of the Cabinet..7 2. Diagrams...7 3. Warranty Information..9 4. Technical Specifications..9 1.6.3 Level ATT(ENUATOR)..5 1.6.4 INPUT SELECT Switch.5 1.6.5 Equalization..5 1.6.6 Ground Lift...6
1. Installation and Operation
1.3 Connection to Mains Current
The amplifier electronics within the O 110 are set up for an AC line voltage of 230 volts, 50 or 60 cycles per second. For export, special versions with other AC voltages are also available. If it becomes necessary to use a different mainscable plug, pay attention to proper grounding when wiring a replacement plug.
It is absolutely essential that you read and observe the Safety Instructions on page 2 before connecting or using this device.

1.1 Operating Conditions

The K+H model O 110 D active studio monitor is intended for use over a range of ambient temperatures from +10 C to +40 C (+50 F to +104 F). During transpor t or storage, temperatures from -25 C to +70 C (-13 F to 158 F) are permissible.

1.4 POWER Switch

When you switch power on, there is a 7 second delay before the amplified signal is sent to the loudspeakers. This delay avoids the loud popping sounds that otherwise are generated by prior devices in the signal chain as they are switched on. You will find this arrangement particularly useful if your studio uses a master switch to power up all the equipment at once. When power on the O 110 D is turned off, on the other hand, or if there is a general power failure in the area, the signal flow to the speaker is immediately stopped, preventing any loud pops.

1.2 Installation

The loudspeaker chassis used in the O 110 D are magnetically shielded, allowing these loudspeakers to be mounted side by side with a video or computer monitor without adversely affecting the screen. One of the finer features of the O 110 D active studio monitor is its unusually uniform off - axis directivity, which results in a very wide sweet spot. Preferred placement of the cabinet is in the upright position, for the dispersion in the verical plane was intentionally kept narrower than in the horizontal. In certain cases, for example if there are hard, reflective surfaces both to the left and right of the loudspeakers, it would make sense to operate the loudspeakers on their side. The reduced horizontal directivity in this position would then be helpful in minimizing any phase cancellation caused by comb - filter effects. When considering placement, please take into consideration the possibilities offered by both of the room compensation switches described in section 1.6.5. On the back of the unit you will find two M8-style threaded bushings for use with various mounting options. These holes are labeled Speaker mount option. The bushings will accommodate either the LH 32 wall bracket adapter or the LH 31 mounting bracket for use with additional mounting accessories. The plastic screws that occupy these threaded holes from the factory may not be used for the actual mounting of a loudspeaker under any circumstances.

1.5 Mains Power Fuse

Should you ever need to replace the power fuse, please ensure (first of all that the unit is unplugged from the mains!) and that only the following type and value of fuse is used: For 230-240 volts AC: 1 A Slo-Blo (5 x 20 mm) For 117 volts AC: 2 A Slo-Blo (5 x 20 mm) For 100 volts AC: 2.5 A Slo-Blo (5 x 20 mm)
1.6 Input analog-digital / Level / Room Compensation / Ground Lift
1.6.1 XLR - INPUT ANALOG / DIGITAL - AES/EBU
The sensitivity of the electronically balanced input is rated at +6 dBu (1.55 volts). The three - pole female XLR jack is wired in the standard manner (pin 1 = ground, pin 2 = +, pin 3 = negative). If you are connecting unbalanced sources, you will need to solder a bridge between pins 1 and 3:
Please ensure that these threaded holes are always plugged so that the volume of air sealed within the cabinet may only pass through the precisely calculated bass - reflex openings. Page 4
unbalanced balanced as seen from solder terminals of male XLR Figure 3: Pin layout of input connector In digital mode, this same XLR input accepts the digital signal according to the AES/EBU specification (110 Ohm balanced). Active Studio Monitor O 110 D
1.6.2 BNC - Input DIGITAL INPUT / THROUGH
This digital input, configured as a 75-Ohm BNC connector, is intended to receive signal sources in S/P-DIF or AES 3id format. The incoming digital signal line requires one 75 -Ohm terminator at the very end, as the O 110 D has no internal termination. The XLR input and the BNC input are wired in parallel across a transformer. The fact that the termination is wired externally allows you to make connections in a wide variety of ways: 1.6.2.1 Source 1x AES/EBU, monitors connected with each other via BNC cable
1.6.2.4 Source 2x S/P-DIF or 2x AES 3id

1.6.3 Level ATT(ENUATOR)

Directly beside the input XLR jack you will find the ATTENUATOR pot, which allows for smooth, gradual damping of the input signal by anywhere from 0 to 24 dB in both analog and digital modes.
1.6.4 INPUT SELECT switch
Use a screwdriver to change the position of this recessed switch in order to select analog or digital mode of operation. Since one digital input carries both stereo channels, the input selector has three additional positions for establishing how the monitors are assigned to the channels. This works as follows: To obtain an output voltage of 1 Vpp at the BNCoutput connector (with 75 - Ohm terminator), an input voltage of 5 Vpp at the AES/EBU input is required. This complies with the rules for AES/EBU level. If the input level varies, the output level does so accordingly. 1.6.2.2 Source 2x AES/EBU Position A = Analog mode (XLR input) Position R = Digital mode right channel Position L = Digital mode left channel Position M = Digital mode mono (summed from both left and right channels) Simultaneous operation from one analog and one digital source is not possible. At any given time you may connect only one type of source to the pair.

1.6.5 Equalization 1.6.5.1 BASS Switch
The four-position rotary switch labeled BASS (see Figure 2, Equalization section) serves to alter the frequency response of the loudspeaker to compensate for the overemphasis of low frequencies that may result from the specific location at which the speaker is placed within the room: Position 0 = free standing Position 1 = placement a short distance before a wall Position 2 = placement flat against a wall Position 3 = placement in a corner of the room
1.6.2.3 Source 1x S/P-DIF or 1x AES 3id, connection using two t - connectors

1.6.5.2 MID Switch

If the loudspeakers are placed on the meter bridge, a certain overemphasis in the midrange will Active Studio Monitor O 110 D Page 5
typically result. Next to the four-position switch for room compensation which we just described, there is another four-way rotary switch labeled MID. The four switch settings are intended for the following kinds of placement: Position 0 Position A Position B Position C = free standing = placement on a table top = free standing on the meter bridge = on the meter bridge between other equipment directly on either side, or built into a wall.
Warning! The protective earth conductor must never be interrupted even for test purposes! This may be dangerous to life!

1.7 Display Functions

The illuminated K+H logo serves as a status display for the loudspeaker when the power switch is on and the fuse is intact: Continuous red:Normal operation, internal supply of power is in order Blinking red: Overload protection circuitry engaged If the light is blinking, this indicates that the overload protection circuitry has been triggered. Among the things that can trigger it are the scrubbing of analog tape in cue - mode, extremely bass - heavy signals or the sine - wave signals that are used in performing measurements. The protection circuitry limits the output power of the amplifier to a level that is safe for the speaker. If the output level should drop as in one of these cases, check for the cause and, if necessary, reduce the monitoring level.
Note: Since it is not possible to list all possible combinations of speaker placement and room acoustics, we strongly recommend checking the switch settings acoustically or by measurement. The frequency response curves of both equalizers are shown in Figure 12 in section 2, diagrams.

1.6.6 Ground Lift

Since the input is balanced, a ground loop hum will rarely occur. In special cases or if the source signal is unbalanced, it can become necessary to separate the signal ground from chassis ground. To do so, first unplug the mains cable from the mains socket, of course, then unscrew and remove the back panel, which has the amplifier electronics mounted directly to it. Figure 4 shows the amplifier circuit board below the XLR jack. The arrow is pointing to a jumper, which by default bridges the two pins. If you remove the jumper the signal ground is lifted from the chassis ground. Of course the chassis ground always remains connected to the protective earth conductor.

1.7.1 Overload Protection
As we just described above, the protection circuit limits the signal to safe levels. This occurs so gradually, that under certain circumstances you may not even notice that the protection circuitry has been triggered and the signal is being limited in dynamic range. But by moving an internal jumper you can change how this circuit responds, so that when it is activated, it will cause a clearly audible drop in level (hard position). To access this jumper, unplug the mains cable from the mains socket, unscrew and remove the rear panel,
Figure 4: Ground Lift Connection Figure 5: Jumper for Overload Protection Circuit Page 6 Active Studio Monitor O 110 D
on the other side of which you will find the amplifier electronics. In Figure 5, the arrow points to the spot on the input circuit board where the jumper is located, next to the XLR input jack.

1.8 Care of the Cabinet

The cabinet housing of the K+H O 110 D active studio monitor comes standard with a charcoal -
grey (RAL color 7021) or white (RAL color 9010) colored enamel finish. Handle the cabinet with care to avoid damaging the finish. To clean the cabinet, use a soft cloth with a mild cleaning agent only. Under no circumstances should you use chemical agents or any cleaners with abrasive action.

2. Diagrams

The outstanding acoustic impression made by the O 110 is confirmed by measurements using todays most critical test methods. The test plots shown here and on the next several pages are but a small sampling of these measurements.
Figure 6: Horizontal Directivity
Figure 7: Vertical Directivity
Using the new material LRIM (Low Resonance Integral Molding) allowed us to seamlessly integrate a waveguide into the baffle that is ideal for optimal dispersion. So an elliptical horn for the tweeter was Active Studio Monitor O 110 D
added. Thus came to be the dispersion pattern we mentioned earlier which is narrower vertically and broader horizontally, as is clearly evident in the test plots presented in Figures 6 and 7. Page 7
Figure 8: Frequency Response (free field)

Figure 9: THD, 2 nd and 3 rd order distortion @ 95 dB/SPL and 1 m distance

Figure 10: Group Delay

Figure 11: Cumulative Spectral Decay Plot The loudspeakers cumulative spectral decay plot indicates a very clean decay without any major resonances or standing waves being evident.
Figure 12: Equalization BASS (upper set of curves) and MID (lower set of curves) Page 8 Active Studio Monitor O 110 D

3. Warranty Information

All K+H products undergo an extensive procedure of quality control testing before leaving the factory. Before semiconductors are mounted on the circuit board, they are subject to rigorous tests. Every single unit is guaranteed to match its technical specifications within strict predetermined tolerances. Please store the original carton in a safe, dry place. If you should ever need warranty service, put the unit in its original packing material and carton together with a detailed description of the problem, and ship it (freight prepaid) to our distributor or directly to: KLEIN + HUMMEL GmbH Customer service Zeppelinstrasse Ostfildern / Germany K+H warrants, that the product is free from any defects in both material and manufacturing and that it meets the specifications. A warranty case can only be acknowledged under condition that the complaint is filed to our distributor or to us in writing within 8 days after delivery or detection of the fault. Not covered under this warranty are damages due to inexpert packing and shipment, wear and tear, improper handling, installation, operation and maintenance. The limitation period for warranty claims is described in the terms and conditions of K+H GmbH. Its our choice to repair, to supply a new product or to withdraw from the contract. In the event warranty service is required, presentation of a warranty card will not be necessary. Proof of purchase date can be made by filing copies of appropriate documents (invoice, delivery note).
4. Technical Specifications
Maximum SPL in half space, 3% THD at 1 m distance averaged between Free field frequency response Self generated noise level at 10 cm Total Harmonic Distortion 150 Hz and above @ 1 m Directivity Horizontal Vertical
107.7 dB/SPL 100 Hz and 6 kHz 58 Hz - 20 kHz 2 dB < 20 dB(A)
< 0.5 % @ 90 dB/SPL 40 (-6 dB) 30 (-6 dB)
Electronics Power amplifiers Bass amplifier Treble amplifier Crossover section Crossover frequency Crossover slopes Protection circuit Input analog Impedance Sensitivity Volume control Common mode rejection ratio Digital inputs and outputs XLR: AES/EBU BNC: S/P-DIF, AES 3id Terminator Sensivity Volume control Switch Input Select Active Studio Monitor O 110 D

50 W at 6 Ohm (THD < 0.1 %) 50 W at 6 Ohm (THD < 0.1 %) 2.5 kHz 24 dB / octave against overload of both drivers 14 kOhm (electronically balanced) + 6 dBu continuously variable from 0.-24 dB > 50 dB @ 15 kHz impedance 110 Ohms, transformer balanced, floating 75 Ohms, unbalanced 75 Ohms for BNC jack (external, not included) 12,5 dBFs continuously variable from 0.-24 dB analog / digital left / digital mono / digital right Page 9
Digital converter Resolution, type Sampling rate
24 bit DA, Delta - Sigma 32 - 96 kHz
Equalization 4 position switch positioning on mixing console 0; -1.5; -3; -5 dB 4 position switch positioning on rear/side walls 0; -2.5; -5; -7.5 dB Drivers Bass Treble Connectors Mains Analog / digital inputs Digital inputs / outputs magneticallay shielded 5.5 , Composite - Sandwich - Diaphragm 1 , Titanium Fabric Dome Tweeter 3 - terminal Euro connector XLR connector 3-pin female BNC 18 VA 70 VA 230 V AC, 50/60 Hz, other voltages on request 170 x 267 x 190 mm 8.6 liters 5.0 kg enamel charcoal-grey RAL 7021 or white RAL 9010 LH 31 mounting bracket LH 28 tripod bushing (LH 31 mounting bracket required) LH 29 TV - spigot (LH 31 mounting bracket required) LH 27 ball clamp mount (LH 31 mounting bracket required) LH 7 or LH 8 adaptor (LH 31 mounting bracket required) LH 32 wall bracket C 15 eyebolt KG 30 ball clamp mount
Power consumtion Idle Full power Mains Dimensions (W x H x D) Volume Weight Cabinet finish Accessories

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