Explorations in Audio

Karsten Hein

Are you ready to Explore?

In 'Explorations in Audio' I aim to share some practical insights on setting up and optimising an affordable HiFi system. Although one would think that, really, all has been said about HiFi, some surprisingly simple questions still remain, e.g.: 'Is digital superior to analogue?' 'Do cables matter?' 'Can digital cables pick up interference?' 'Should speakers be placed on spikes?' 'Has evolution in HiFi made older gear obsolete?' 'Where should I place my sub?' 'Which room correction works best?' - On the other hand: 'Are these really the right questions?' - We shall see.

What’s new in eiaudio?

While the entries in this blog are divided into the three distinct categories above, you will find a mixed listing of the most recent postings below. The most recent article is shown first. If this is not your first time visiting, the listing below is a good place to quickly check if anything is new.

Your input is more than welcome, as long as you follow the basic audiophile rule of ‘ear over mind’. This means that you do not comment based on what you think you know, but only on the basis of your own listening experience. Please feel free to suggest gear for testing as well as leave comments on the descriptions provided here.

  • Snell Acoustics Type C IV

    Snell Acoustics Type C IV


    Author: Karsten Hein

    Category: Gear & Review

    Tag: Loudspeakers

    I first heard Peter Snell’s C IV loudspeakers perform in the dining room of a Wiesbaden townhouse and was instantly taken in by the realism with which the club atmosphere of Christian McBride’s album “Live at the Village Vanguard” was recreated. The spacious room boasted a ceiling height of nearly 5 meters and was sparsely furnished, with a massive dining table and chairs dominating its centre. The speakers were positioned far away from the walls, approximately two meters from the front wall and 1.5 meters from each side. They were driven with a Dynaco ST70 tube amplifier. Everything in their sound—stage depth, width, resonances—suggested that we were were listening to the actual event, rather than a recording of it. I could literally smell the scent of stale beer and cold cigarettes.

    I learned two things that day: The ultimate goal of HiFi does not lie in deeper bass or higher treble, nor in clearer sound or greater dynamics, but rather in the sum of all parts to recreate the authentic event. And second: The room and positioning of the loudspeakers play a major role in making the illusion of a performance become reality. And once we have heard it, once that vision has been installed in our minds, it is very difficult to listen to anything less. Most newbies in HiFi have been taught to dissect music rather than achieve homogeneity. Data, rather than feeling, is the message conveyed by the audio press. Hence, new arrivals to the HiFi scene will look for the right specs on their gear rather than make sure to get the right sound. One can spend a lifetime in HiFi and still have very little clue of what it is actually about.

    It is probably fair to say that the Dynaco ST70 tube amplifier played a major role in the recreation of the authentic event. Neither the wattage of this amplifier nor its channel separation, damping factor, signal to noise ratio, etc. indicate the amount of realism this amplifier is capable of. Hence, it is no surprise that, in a world run on facts and figures, it took me close to 50 years and some repeated nudging from fellow audiophiles to finally be able to listen to and comprehend the merits of a performance that deserves the term ‘high fidelity’, i.e. as close to the original as possible. That day, “Live at the Village Vanguard” really felt live. It prompted me to purchase the vinyl record and write a review on it. And it also got me interested in the C IV speakers.

    Snell Acoustics was founded in Haverhill Massachusetts in 1976, and the company soon made a name for itself selling audiophile loudspeakers at reasonable prices. After sales service was exceptional, as Peter Snell was a perfectionist and made sure that each of his speakers measured to spec with deviations below 0.5dB per chassis. The same was true of all the replacement parts the company sent out, often many years after the original date of purchase. Audiophiles constitute a small and intimate circle, and especially bang for buck producers often benefit from word of mouth and manage to build up longstanding relations with their thankful customers.

    Launched in 1983, the Type C series was among the last loudspeakers actually designed by the company founder himself. Peter Snell died from a heart attack in his factory in the following year. Despite the absence of its original owner, the company continued to evolve and, in 1990, joined forces with Lucasfilm to design its first line of THX loudspeakers. In 2003, the by then renowned Joe D'Appolito joined Snell as chief engineer. In 2005, Snell and Boston Acoustics were purchased by D&M Holdings—which also owned Denon, Marantz, and McIntosh—and Snell would continue to build loudspeakers until 2010. Throughout its existence, the loudspeaker manufacturer stood for great customer service, tonally accurate acoustic designs, and great attention to technical detail.

    The Type C IV series are said to have been heavily influenced by the methods and measuring philosophies of the National Research Council (NRC) based in Ottawa, Canada. Typical characteristics of speakers developed in conjunction with the NRC are steep crossover slopes, wide dispersion, smooth off-axis response, and special focus on a speaker’s interaction with natural listening rooms. The C IV has fourth-order crossover slopes, a very flat frequency response that varies very little off-axis. A rear tweeter was added to compensate for the front tweeter’s increasingly narrow beam at high frequencies. It can be turned off with a toggle switch to accommodate smaller listening rooms. The C IV boasts what the company called a “Zero Diffraction” grille. The idea was to wrap the removable grille’s wooden frame around the speaker front in order to minimise the distance between cloth and divers and decrease diffraction.

    The additional tweeter at the rear comes in at around 6kHz with a first-order slope. It contributes to the front tweeter’s energy and helps to create a stage impression that is both wide and deep. Depending on the distance to and material of the front wall, the additional tweeter can cause some harshness. To turn the speakers to the room, the C IV’s front tweeter can be regulated. Alternatively, a switch at the back allows us to turn the rear tweeter off completely. To make full use of the C IV’s abilities, it should be placed in a large room with approximately 1,20m distance to the front wall and some distance to the sides. Set up in this way, the rear tweeter supports the illusion of the music breaking free from the source with the speakers themselves becoming invisible. Toe-in helps to correct the stage impression. I must confess that, given the peculiar shape of our room, I did find it difficult to get the stage as perfect as I had heard the speakers capable of in the Wiesbaden townhouse, but I can say that I came quite close.

    With the rear tweeter switched on and the right distance to the walls, the C IV created a broad and open stage. And with the grille cloth in place, they produced a pleasantly soft treble, even at short range. For those sitting at a distance of 3 meters or more from the speakers, there is some treble fall-off, and listening without the cloth might be preferable. Despite Snell’s “Zero Diffraction” promise, the difference between open and closed operation is quite audible. In our listening room, the C IV produced an open and spacious top end and a natural and fully integrated bass. The speakers sounded tonally accurate and presented the music nice and full with great timbre on the lower piano keys. There was sufficient presence of the higher piano keys as well, however, in direct comparison they were missing some of the attack of our electrostatic speakers or even our more recent Tannoys. Male vocals sounded natural with a slight tendency of thinning when the rear tweeter was switched on (e.g. Nick Cave). Female vocals showed much of the same effect (Nora Jones, Come Away with Me), especially when playing music from digital sources.

    Also see: Snell Acoustics Type C IV Audio Demo

    The Snells showed convincing overall dynamics and, due to their large bass driver and ported design, they were capable of swelling in volume quickly. When set at 75dB volume, my wife reported that she felt quite overwhelmed by the music and that she would have preferred to sit farther away from the speakers. It was the first time that I had heard her comment on loudspeaker in this way. I would think that the effect was caused by a combination of the sonic impression and the speaker’s design. Standing far into the room, nearly 120cm tall and 40cm wide, with their black grille cloth in place, the physical image alone was quite intense, indeed.


    • Type: Four-driver dynamic loudspeaker
    • Drivers: 10" woofer; 5” midrange; 1” front tweeter; ¾” rear tweeter
    • Crossover frequencies: 275Hz; 2.7kHz (@24dB/octave)
    • Nominal impedance: 8 Ohms
    • Sensitivity: 88.5dB
    • Dimensions: 37cm (W); 117cm (H); 30cm (D)
    • Weight: 39kg
    • Year: 1983-1991

    Jörg Hegemann
  • Vinyl Singles Puck

    Vinyl Singles Puck


    Author: Karsten Hein

    Category: Gear & Review

    Tag: Accessories

    I remember vinyl singles mostly from my parents’ small vinyl collection in the seventies. The fact that singles have a lager centre hole than long-lay records was usually compensated by a thin plastic star that was clicked into position right after purchase. The centring star then remained in this position until the collection was stored in the basement and forgotten about. In this sense, singles were made to handle like LPs, and the advantage of them having a larger centre hole was lost.

    From the 1950s until the middle of the 80s, vinyl records were the primary way of storing music in households, but also at public venues, such as nightclubs, bars, and radio stations. Due to their short running time, singles in many cases needed to be changed more often than long-play records. This could result in greater wear on the centre hole, especially, if the picking and placing was done by a juke box. The larger center hole distributed the forces along a larger surface and left greater margin for error, if the prong was conical in shape.

    I bought my first vinyl singles in the early 80s and simply adopted my parents’ method of clicking the star in place. Then there came a long time without records, from about 1995 to 2017, during this time I sold my collection and forgot all about vinyl. And although it has been a few years now that vinyl saw a comeback to our household, vinyl singles had not been among my prized possessions until my friend Charles handed me a stack of singles to keep. To my surprise none of them had the little star inside, and I no longer owned the typical plastic puck that came with every original player.

    When searching the web, I was actually surprised to find that one can still find the original plastic stars for centring vinyl singles, but I was not going to settle for this. I wanted to explore the benefit of singles having the larger hole and, frankly, I just wanted to own the best centring solution available on the market, one that makes best use of the possibilities that the design of a vinyl single provides.

    The puck I came up with is turned from a solid piece of metal with a smooth and polished surface. Singles effortlessly glide over the hemisphere and land in perfect position. Exact machining ensures that the fit is neither too loose nor too tight. Weighing a solid 150 grams, the massive puck can be used as record weight for LPs. Especially vintage players benefit from a less heavy record weight to reduce bearing and motor wear but also to keep the player position level.

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    I love the fact that the puck remains decorative and useful, even if it is not centring a single or pressing down on an LP. When placed next to the record plate, the puck helps to minimise chassis resonances and looks quite sophisticated at the same time. What more could we ask for in a puck?


    • Type: Vinyl singles puck
    • Material: Stainless steel
    • Dimensions: (D/o) 3.80cm, (H) 2.40cm, (D/i) 0.70cm
    • Weight: 150 grams

    CrossXculture Business Language Training
  • Speaker-Audio Demos

    Speaker-Audio Demos


    Author: Karsten Hein

    Category: Explorations

    Tag: Speakers

    What should a loudspeaker sound like? — Well, if there is a short answer to this question, it is probably this: Ideally, a loudspeaker should sound like the original audio material that is being played back on it. Meaning, the recording of a rocket-launch should sound like the rocket being launched. And the recording of a saxophonist inhaling before playing the next tune should sound exactly like a human being taking a deep breath. A loud sound requires sturdy build quality and lots of air to be moved quickly, whereas a human being inhaling deeply requires the speaker’s ability to present the tiniest nuance.

    Acoustic instruments should be tonally correct with wood sounding like real wood, metal sounding like metal, glass like glass, etc. Voices should be as sweet, captivating, or even as raw as the singer’s own voice demands. Tonal correctness requires the speaker’s material resonance frequencies to be minimal and the moving mass of its drivers to be low. Natural instruments and vocals usually have at least two components: the sound that is deliberately produced and the ambient sound caused by the dimensions of the venue on the day of the recording. Both components should be presented equally well.

    The speaker’s frequency band should ideally be extensive, ranging from 20 Hz to 25kHz and beyond without significantly dropping in dB volume per watt. The ability to do so assures that sounds occurring along the fringes of the spectrum are fully presented. Even if some of these frequencies fall outside of human hearing, they do affect the audible frequency band through layering and overlapping. Maximum realism can only be achieved, if no aspect of the original signal is omitted.

    Much has been written on the linearity of loudspeakers. This refers to the ability to play all frequencies at equal volume. When performing in a home or studio environment, however, the linearity measured and certified in a laboratory has very little to do with the acoustic reality of a private listening room. This is why loudspeaker manufacturers take an educated guess regarding your household or studio furnishings and will accentuate frequencies that they estimate will be absorbed by your furniture and dampen those that will be enforced by your walls and ceiling.

    The result of all this is that ‘speaker sound’ exists, even if loudspeakers are usually sold on the premises of being linear. But can this be shown, recorded, and archived for posterity? Well, at this point I am neither sure it is possible nor that the data produced in a recording of a loudspeaker has any value for the decision making process of which speaker to buy. But, since our project is called ‘Explorations in Audio’, I am willing to ‘explore’ the possibility. You see, explorers are naturally attracted to the unknown, especially, if they are greeted with lots of scepticism.

    In this new series of explorations I am sharing with you how a given loudspeaker performed on the day of the recording in one of our listening rooms, using the recording equipment available to me at the time. The material is then uploaded to a streaming platform to be played back on any random equipment that you might have at hand: anything ranging from the built-in speaker of your mobile phone to your own High-End stereo system. The listening result is then up to you to interpret. I would be interested in reading about your findings during playback in the comments section below or under the YouTube file. — Enjoy :-)

    Standard Audio Source (Type 1):

    • CD-Player: Marantz CD-17
    • DAC: Cambridge DacMagic 100
    • Preamp: Dynaco PAS-4
    • Amplifier: Hafler XL-280

    Standard Recording Equipment:

    • Microphones: the t.bone SC1100 (x2)
    • Recorder: Zoom H4n Pro
    • Mastering: Apple iMovie

    Standard Measuring distances:

    • Microphone to speakers: 200cm
    • Music volume: 75dB (peak average at 200cm)
    • Between microphones: 40cm
    • Distance from ground: 100cm
    • Recorder input sensitivity: 80

    Dahlquist DQ10

    Tannoy XT8t

    Snell Type C IV

    Original CD Audio

    80s night
  • Dahlquist DQ10

    Dahlquist DQ10


    Author: Karsten Hein

    Category: Gear & Review

    Tag: Loudspeakers

    Married audiophiles will confirm that you can tell you are onto something special, when your wife comes home and—without prior talk on the subject—leaves you baffled with a congratulatory comment regarding your new loudspeakers. I cannot remember the exact words, but they were something along the lines of: “By the way, I saw the new speakers. They look absolutely fabulous! Are they here to stay?” With us, the latter is a valid question. Because, more often than not, the speakers are only with us for testing, before they are given back to their owners.

    The loudspeakers on display were a pair of Dahlquist DQ10, and they were given to me for sampling by my friend and fellow audiophile Luigi. This is nothing unusual, and those who have followed my reviews will know that I have tested much of Luigi's HiFi equipment over recent months. And—to my surprise—my wife was not the only female showing instant affection regarding the Dahlquists. My sister in law, someone who is aware of my hobby but does not stop by our house on a regular basis, marvelled at the new speakers when she noticed them in the room. I think you will agree that this is not something that women usually do, regardless of how much money you have spent. It is pretty much the equivalent of a guy commenting on the beauty of a girl’s makeup or shoes. Normally that doesn’t happen, right? And yet, with the Dahlquists, it happened twice within a very short timeframe.

    The Dahlquist DQ10 was the first loudspeaker manufactured by the Dahlquist company, then based in Hauppauge New York. Among the company’s founders were some famous names in audio, such as Jon Dahlquist and Saul Marantz, Irving M. Fried and Werner Eymann. The DQ10's design was first exhibited at a New York audio show in 1972. It was revolutionary, because it parted with the traditional boxy shape of conventional speakers. Dahlquist had instead constructed a cabinet that suspended its drivers freely in an open array and in correct phase alignment. From the DQ10 onwards, the term 'Phased Array' became the Dahlquist trademark.

    The design idea was loosely based on the popular Quad electrostatic speakers of the 60s and, among Dahlquist enthusiasts, is said to have successfully achieved a marriage between the powerful bass slam of conventional cone drivers with the low refraction, high transparency, and phase accuracy to be expected from electrostatic speakers. The resulting loudspeaker had a square and convex frontal face that was covered in dark cloth and flanked by slim sides of natural wood. To play at ear level, the speakers were then positioned on slender stands that, at their base, matched the wood colour of the speaker sides and held each unit suspended on three black columns or pillars.

    In combination with the speaker stands, the DQ10 looked light and non-technical from the front and slim from the side. It arguably held greater resemblance to a radiator than a loudspeaker, an aspect that made it both stand out as a design element and an understatement in terms of technology. Strangely enough, its appearance fits into a modern household just as well as it did back in the seventies. It is not surprising, therefore, that close to 60,000 pairs of Dahlquist DG10s were sold between 1973 and the end of its production in 1988. And the Dahlquist remains popular among audio enthusiasts until this day, reaching 4.8 out of 5.0 stars on audio-review. With more and more units going out of service due to their advanced age, used prices of this speaker have been on the rise over the past 15 years.

    The DQ10 featured a closed bass cabinet with angled sides and an asymmetrically positioned 10” cone driver. It had a dedicated 5” mid-bass driver to support the woofer and provide the Dahlquist’s legendary mid-bass punch. The midrange was produced by a 1.75" soft dome driver, much like the tweeter, which was of 0.75" dome design. A super tweeter served to extend the upper frequency band using piezo technology. With the exception of the woofer, all drivers were held freely suspended by metal brackets and radiated both towards the front and the speaker's open back. A 5-way crossover made sure that each driver only played a limited frequency band and cut off from mid-bass to super tweeter at 400, 1000, 6000, 12000Hz, respectively. The crossover components played such an important part in the Dahlquist’s overall performance that there were many specialists in the market offering upgrades.

    The Dahlquist was rated at 8 Ohms and appeared to be easy to drive, and yet, the phased array design required lots of clean power from the amplifier to sound at its best. 150-200 watts paired with high-current ability went down well with the DQ10. In many ways, its demand for power and its overall performance were similar to Martin Logan, Magnepan, etc. speakers that were of electrostatic or magnetostatic design. The positive aspect was that the DQ10 was also able to compete in this range and that the investment into a decent amp was poised to be rewarding. I hooked the Dahlquist up to our Hafler XL-280 power amplifier to satisfactory result, however, Luigi was quick to assure me that the large Audio Research D-115 tube amplifier (which I had already returned to him) would have been able to bring out even greater effortlessness and transparency in the DQ10. This was well possible, as the Dahlquist liked to be driven a little harder to achieve greater musical coherence.

    Although the speaker was positioned relatively low for many seating arrangements, its height became less of an issue when sitting further away from the speakers. Generous distance to the speakers was essential to minimise phase differences resulting from the spacious array design. In our less than perfect listening room under the roof, I was sitting just two meters from the speakers with a huge space opening behind me. I was positively surprised by how full and consistently lush they sounded, both in my listening position and when walking across the room. The DQ10 produced a spacious, intense, and full soundstage that was in many ways similar to a live-event. The thumping of the mid-bass, the space between instruments, and its timbre when playing Jazz and Vocal Jazz resembled the sensation of being at a dingy small-club concert. The speakers produced the most realistic audience clapping that I had ever heard coming from a two-way system. The highs were detailed and spread out as you would expect from an electrostatic speaker and they were non-aggressive at all times. Voices were affectionate and full with a slight leaning towards throaty.

    Also see: Dahlquist DQ10 Audio Demo

    If you like your music to sound lush with rich harmonics, and if you enjoy full-bodied vocals and a live-feel when playing music from acoustic instruments to be found in Jazz, Folk, Singer-Songwriter, etc., and if you own a beefy high-current amp to pair them with, the Dahlquist DQ10s just might be the right speakers for you. Give them a bit of time to settle in and some space to breathe on all sides, and they will make music for you like few other loudspeakers today. And let's not forget the wife acceptance factor, of course.


    • Type: 5-way phased array, open baffle
    • Frequency response: 35 Hz — 27,000 Hz
    • Recommended amplification: 150 to 200 Watts
    • Crossover frequencies: 400, 1000, 6000, 12000 Hz
    • Nominal impedance: 8 Ohms
    • Bass: 1 x 25,4cm (cone)
    • Mid-bass: 1 x 12,7cm (cone)
    • Midrange: 1 x 4,45cm (soft dome)
    • Tweeter: 1 x 1,9cm dome
    • Super Tweeter: 1 x piezoelectric
    • Dimensions: (h) 99cm x (w) 77cm x (d) 33cm
    • Weight: 22,7 kg
    • Years: 1973-1988

    Digitising Records
  • 25. Audiophile Cooling

    25. Audiophile Cooling


    Author: Karsten Hein

    Category: High Fidelity

    When outside temperatures are rising during the summer months, many audiophiles are beginning to dread the increase in noise floor that results from various methods of keeping cool indoors. For many of us, our listening hours fall into the evenings, a time when the streets and buildings are still hot from the day. This is when the electrical noise on power grid and the physical noise from outside slowly subside, normally giving way to endless hours of listening pleasure. However, this pleasure is relatively short lived, when the listening room becomes too hot for comfort.

    In very few cases, the ideal listening room will be located in the basement of your own house, on which high outside temperatures have little effect. Basements tend to have low ceilings and concrete walls that will pound back bass frequencies in an unbecoming way. No, most proper listening rooms will rather be situated above ground with wooden or masonry walls. And in such an environment, temperatures can become quite high, especially in an apartment or under the roof of a building. While perhaps also not ideal in terms of bass performance, a listening room under the roof can be advantageous to sound, because of the relative absence of parallel walls.

    To make matter worse, many audiophiles will be running HiFi gear that produces more heat than regular consumer products. Tube gear, for instance, radiates far more heat than solid state devices. But even when operating solid state equipment, audiophile amps tend to be oversized MOSFET beasts running in class A, rather than being more power efficient class B or D designs. Actually, audiophile gear often only sounds at its best, once it has reached full operating temperature. And, in many cases, this means you could literally fry an egg on them.

    The most economic and ecologically friendly way to cool down a room is to simply open the windows, but in many urban locations, this will raise the noise floor in an unpredictable way, bringing in sounds from cars, planes, trains, and from people walking by. In rural areas, the noise might come from the wind in the trees, from birds, etc. but also from the local traffic. I think most audiophiles will agree that a closed window is an effective way to drown out sound coming from outside and will be preferred.

    If the windows cannot be left open, cooling must ultimately come from some apparatus that is placed or installed in the room. Some buildings have air conditioning installed into the walls, and, in most cases, this will be the best option to address cooling, because this method also extracts excess moisture, a fact that makes any temperature more bearable. However, air conditioning is also the most expensive solution and, from an environmental perspective, not without concern. A simple cooling fan would present a cheaper and more sensible choice, when no air conditioning has yet been installed.

    If you have ever listened to music in a room where a cooling fan with open propeller is running, you will already know that this will quickly make chop suey of our musical experience. There are few audiophiles able to tolerate the presence of a running fan in the room, perhaps with the exception of an ultra-slow and silent ceiling fan. No, there must be a better solution to keep the listening room cool in summer, one that does not interfere with the music so much. At least this is what I was thinking, when I set out to purchase a cooling device that would not spoil the fun of listening.

    At the time of writing this, air movers without open blades have not yet been popular for a long time, and yet, they help to solve the problem of rotating blades interfering with our music. While they are mostly referred to as bladeless fans, this definition is not strictly accurate. Their rotors are rather smaller and encapsulated by the housing, with the air being moved through one or more ducts for speed and direction. Rather than producing a frequency of air-compression and expansion, the resulting air flow is seamless and calm. This non-pulsating quality is preferable in audiophile settings, even if the fan itself should have a similar dB-noise rating as a fan with exposed blades.

    The model shown here stands representative of a whole range of bladeless fans from various manufacturers. It was bought at the German DIY store and REWE subsidiary ‘Toom Baumarkt’ and offers a host of features that make it a decent companion for extended music listening sessions. There are 9 air speeds to choose from, ranging from relatively silent to more noisy in operation. The good news is that levels 3-5 will offer sufficient airflow for most applications, while still being reasonably silent. All levels offer decent reach into the room, so that the fan does not need to be positioned close to the listening position. Although the fan does not cast its breeze all too broadly, the angle should still be wide enough for an individual listening spot and can be increased by engaging the 90 degrees rotation function.

    The tower fan comes with a remote control that can be fixed to the shaft via magnet, e.g. for storing or for strictly local operation. The remote turns the fan on and off, sets the air speed via plus and minus keys, engages the rotation and sleep function. It can also set a sleep-timer and has a button to jump to maximum airflow and back to the previous setting. With all these functions available from a seated position, wind speed and noise can be adjusted to suit the listening moment. Rock & Pop music will probably be more forgiving of noise than classical or Jazz music that are often more nuanced with lots of quiet passages. The fan’s hight is just under one meter and therefore very convenient for a seated position. The air is conveniently drawn up from the colder floor and then ejected into the room. The tower fan is Smart Life compatible and works with Alexa. This means it can be integrated with other Smart Life machines in the households and operated from the smartphone. Have a look online. Similar products are available from other brands and stores.


    • Maximum airflow:  22 cubic meters per minute
    • Power consumption:  26 watts, 240 V, 50 Hz
    • Standby consumption:  0.8 watts
    • Noise level:  56 dB, maximum
    • Air speed:  4,6 meters per second
    • Remote battery: CR2025, 3 V
    • Year:  2020