Open baffle: how speakers can fill an entire room

The DIY kit KATANA-M1 shows what the open baffle design can deliver

The open baffle was little accepted for decades. Apparently unfairly, because in recent years the so-called 'open baffle' speaker - i.e. a speaker without a rear panel - has been making a comeback. You can find out why the legendary acoustic tinkerer Frank Kuhl likes the open baffle so much, why he has just now developed a corresponding DIY kit and what a Swiss artist collective - BRAINFART - has to do with it right here.

What is an open-baffle speaker?

Speakers with an open baffle used to be quite common: take a wooden board, cut a hole, put the speaker in, a bit of soldering and it works. Audio enthusiasts also call this construction affectionately 'the sounding board'. Speaker cabinets were not added until later, thus designing speaker systems that are closed on all sides. These still dominate the market and the living rooms today, for there is a challenge with the open baffle: there is no sound pressure generated in the low bass range. But it is particularly the bass that has become increasingly important in electronically dominated popular music since the late 1990s: the bass has to pump.


What is an open-baffle speaker?

Speakers with an open baffle used to be quite common: take a wooden board, cut a hole, put the speaker in, a bit of soldering and it works. Audio enthusiasts also call this construction affectionately 'the sounding board'. Speaker cabinets were not added until later, thus designing speaker systems that are closed on all sides. These still dominate the market and the living rooms today, for there is a challenge with the open baffle: there is no sound pressure generated in the low bass range. But it is particularly the bass that has become increasingly important in electronically dominated popular music since the late 1990s: the bass has to pump.

Prejudice has it that the bass is weaker in speakers with an open baffle. Why is the open-baffle design coming back anyway? Spoiler: open baffles can do bass too, just differently.

The character of an open baffle: unmatched width and powerful sound provide a special listening experience

An open-baffle speaker builds an acoustic stage. The directivity is not simply a forward-radiating cone, but a 'figure of eight' in two directions, to the front and to the back. To the sides (in the drawing: 270° and 90°) you hear almost nothing. With an open baffle, the sound is distributed differently throughout the room due to this figure of eight, the so-called 'dipole characteristic'. Many people who hear a speaker with an open baffle for the first time are first irritated, then thrilled. For comparison, imagine you are wearing a gargantuan pair of headphones.

Copyright Galak76 / CC BY-SA 

The character of an open baffle: unmatched width and powerful sound provide a special listening experience

An open-baffle speaker builds an acoustic stage. The directivity is not simply a forward-radiating cone, but a 'figure of eight' in two directions, to the front and to the back. To the sides (in the drawing: 270° and 90°) you hear almost nothing. With an open baffle, the sound is distributed differently throughout the room due to this figure of eight, the so-called 'dipole characteristic'. Many people who hear a speaker with an open baffle for the first time are first irritated, then thrilled. For comparison, imagine you are wearing a gargantuan pair of headphones.

Copyright Galak76 / CC BY-SA 

“An open baffle sounds very spatial, with a wide stage presentation. You can compare it to a choir, an orchestra or generally a concert in an enclosed space. You have to experience that.”

— Frank Kuhl

Often it is also described this way: the open baffle sounds much less like a single sound source emitting sound from one direction. “In comparison, a normal speaker has a clearly directional radiation pattern,” says Frank Kuhl. Additionally, many traditional speaker systems also have resonances in the speaker cabinet. These resonances are sometimes audible as 'box sound': unwanted vibrations through the speaker cabinet, e.g. due to wrong material or poor workmanship. With the open baffle, on the other hand, there are no such resonances because there is no traditional cabinet.

 
Frank Kuhl

“With an Open Baffle, you should play around with the positioning. Move around the room a bit and test different angles. Once you have found the perfect set-up, you will be rewarded with a tremendously powerful sound.”

Or as the colleagues from the online magazine HiFi Selbstbau put it so nicely in their review: “Speakers like the KATANA do not work unless you really mean business.”

Why speakers with an open baffle sound different and why they have been little accepted for many years

The human ear works like a pressure sensor. It converts pressure differences of sound waves into sound. A sound wave is a so-called longitudinal wave that oscillates in the direction of propagation, as opposed to a transverse wave.

This animated picture shows the difference between a longitudinal wave and a transverse wave very well. You can see that the sound wave moves back and forth. During the movement, the speed (sound particle velocity) and the pressure ratios (sound pressure level) of the propagating sound wave change constantly.

Specialist literature often claims that an open baffle cannot generate any sound pressure, especially in the bass range. Therefore, a deep bass reproduction is said to be impossible and the 'acoustic short circuit' is mentioned. This is what it is called when an (undesired) pressure equalisation occurs between the sound which the bass speaker radiates to the front and the sound simultaneously extracted from the rear of the baffle. However, this only applies to the sound pressure, not to the sound particle velocity. A sound wave can also be generated by the sound particle velocity, not only by the sound pressure (which is lost through pressure equalisation). This is the reason why a narrow open baffle also allows for bass reproduction.

How to set up an open baffle speaker

To benefit from the extraordinary effect of an open baffle, you must not place speakers without rear panel directly in front of a wall. The open baffle needs a distance of about 1 metre from the wall. The bass reproduction is most effective if you place the speaker at approximately ⅓ of the room length.

With the KATANA-M1, a full-range speaker radiates the sound in the mid-high range to the front and back. Due to the concentrated radiation, the sound pressure to the sides is reduced. This in turn leads to a reduction of reflections from the side walls. The sound radiated to the rear is reflected at the side walls and the rear wall of the room.

The human auditory system localises sound - for example, where a singer or guitarist is standing on the stage - on the basis of the first wave front of the sound waves arriving at their ear. These come from the speaker baffle radiating to the front. The sound waves emitted to the rear and to the sides arrive at the ear with a time delay due to reflection. This leads to the large spatial sound impression described above. When setting up the speakers, you should experiment with the angle and different positions in the room to achieve the best possible sound impression.

A DIY kit like from the 80s and 90s, the golden years of DIY speaker kits

Frank Kuhl says: “If I would have asked any of my colleagues 15 years ago whether we should design another speaker with an open baffle, most of them would have laughed.” The acoustic short circuit had become too deeply rooted in the minds of sound engineers. For a long time, even experts considered the acoustic short circuit too serious an obstacle to develop marketable speakers with an open baffle. With the KATANA-M1, Frank Kuhl has debunked this.

“A speaker without a cabinet cannot work properly,” they said. And then someone did it (again)

The background story of the KATANA-M1 is quickly told: Frank Kuhl came across an open-baffle kit by chance. And because he has always liked designs with an open baffle and was rather disappointed that open baffles have gone a little out of fashion, he decided to order the kit for testing purposes. He entrusted its assembly to two interns at MONACOR. The result was, though both were skilled and assembled the speaker correctly, a speaker sounding like a telephone receiver. To give the two interns a sense of achievement and to defend the honour of open baffles, Kuhl built a new crossover network and decided to develop a DIY speaker kit with an open baffle again himself using better chassis speakers.

Open-baffle speakers can be particularly suitable for DIY construction

“[...] not just another box, it is a DIY kit with character,” wrote one commentator in a review. And it is true: open-baffle DIY kits are often well suited for DIY beginners who want to build their first do-it-yourself speaker and yet already have high demands on the sound. They are also a good solution for hi-fi enthusiasts who would like to have an 'open baffle' in their living room without too much effort as well as for those who are interested in getting to know the individual components of a speaker.


A DIY kit like from the 80s and 90s, the golden years of DIY speaker kits

Frank Kuhl says: “If I would have asked any of my colleagues 15 years ago whether we should design another speaker with an open baffle, most of them would have laughed.” The acoustic short circuit had become too deeply rooted in the minds of sound engineers. For a long time, even experts considered the acoustic short circuit too serious an obstacle to develop marketable speakers with an open baffle. With the KATANA-M1, Frank Kuhl has debunked this.

“A speaker without a cabinet cannot work properly,” they said. And then someone did it (again)

The background story of the KATANA-M1 is quickly told: Frank Kuhl came across an open-baffle kit by chance. And because he has always liked designs with an open baffle and was rather disappointed that open baffles have gone a little out of fashion, he decided to order the kit for testing purposes. He entrusted its assembly to two interns at MONACOR. The result was, though both were skilled and assembled the speaker correctly, a speaker sounding like a telephone receiver. To give the two interns a sense of achievement and to defend the honour of open baffles, Kuhl built a new crossover network and decided to develop a DIY speaker kit with an open baffle again himself using better chassis speakers.

Open-baffle speakers can be particularly suitable for DIY construction

“[...] not just another box, it is a DIY kit with character,” wrote one commentator in a review. And it is true: open-baffle DIY kits are often well suited for DIY beginners who want to build their first do-it-yourself speaker and yet already have high demands on the sound. They are also a good solution for hi-fi enthusiasts who would like to have an 'open baffle' in their living room without too much effort as well as for those who are interested in getting to know the individual components of a speaker.

The goal was to create a DIY kit that anyone with a soldering iron and a desire for music could build. For professionals, DIY kits are also a good basis for further optimisation.

The KATANA-M1 as a canvas - the artist collective BRAINFART runs wild

Designs like that of the KATANA leave a lot of room for experimentation and optimisation, and not only in terms of audio technology. The drivers are screwed into a 'standing board' that leaves the customer the choice: keep it minimalistic, paint it, wallpaper it, have it signed by Frank Kuhl. The colleagues from the online magazine HiFi-Selbstbau recommend “a little clear varnish, wood oil or furniture wax to give the Katana a elegant look.”

The artist collective BRAINFART from Zurich has pimped the KATANA-M1 in urban art style:

More info and much more from BRAINFART

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Dear BRAINFARTs, please introduce yourselves.

Time and place of BRAINFART's creation was the lower Letten, a quarter in Zurich, on a warm summer evening in 2011. We, at that time only Bex and Nahuel, actually just wanted to draw, to show the world from a simpler, funnier and more colourful perspective. From this evolved what is now called BRAINFART. Since then, we were able to present our urban art to the general public at various events. You can find us not only at exhibitions, but also at live painting events. We organise urban art workshops in our studio and do commissioned work.


Dear BRAINFARTs, please introduce yourselves.

BRAINFART in a short interview: Urban Art from Zurich

Time and place of BRAINFART's creation was the lower Letten, a quarter in Zurich, on a warm summer evening in 2011. We, at that time only Bex and Nahuel, actually just wanted to draw, to show the world from a simpler, funnier and more colourful perspective. From this evolved what is now called BRAINFART. Since then, we were able to present our urban art to the general public at various events. You can find us not only at exhibitions, but also at live painting events. We organise urban art workshops in our studio and do commissioned work.

How did you get into contact with MONACOR Schweiz AG? After all, when you think of urban art, you do not immediately think of speaker styling.

The cooperation with MONACOR goes back a few years. We could already design smaller illustrations for MONACOR. But even then it was clear that MONACOR and Brainfart wanted to go one step further in the field of art. Now the time had come.

And why the KATANA-M1 of all things?

In 2020, MONACOR knew immediately which product would be perfect for a BRAINFART project, namely the KATANA speakers. They showed us the speakers and we were also blown away by the product. The design was a perfect fit for this art project. The KATANA-M1 speakers have the advantage that there is enough space in the lower part to place our BRAINFART characters. Of course, we could have painted the entire speakers, but together we decided that the speaker had to have a certain wit and yet fit elegantly into a living room.


Last but not least: KATANA-M1 thoroughly tested by the Speakershocker

The YouTuber Speakershocker talks about his first encounter with an open baffle on his channel Speakershocker, Hi-fi mehr als nur Technik (Hi-fi more than just technology).

 

“I am really surprised how a speaker can suddenly sound very different and much, much more spatial. [...] and you hear stereo effects in the music, no matter what kind of music it is, much, much more intensely. And you also hear how the music moves from the right speaker to the left speaker and back and forth, you hear that much more intensely - as if you had a completely different amplifier standing there or as if there was a much better channel separation all of a sudden. I once saw a YouTube video about an open baffle, the builder had tears in his eyes when he heard it for the first time and yes, I can understand that now. It is really brilliant.
After the speakers were broken in, I sat down for an hour and took notes to explain what an acoustic spectacle was going on here and I still cannot explain it properly - it is just brilliant!”


Did this whet your appetite for DIY? Just look in at our Components Store, learn more about the KATANA-M1 or read about what else Frank Kuhl is up to in his workshop.

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