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Open Baffle - 15 inch, 3-way

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What is an Open Baffle?

Yes, Open Baffle speakers look like this - something quite different and unique! Most loudspeakers use some type of 'box/enclosure' made from wood, which enhances the reproduction of low frequencies generated by the woofer. There are different types of box/enclosure designs, mainly; bass reflex (ported/vented box or passive radiator), sealed box, bandpass, transmission line and backloaded/folded horn. Each of these designs have their pros and cons and as these designs use some type of enclosure to assists with increasing bass, they all, to different extents, introduce unwanted resonances which can be heard as a distortion/colouration of the original content.

The Open Baffle design does not make use of a box/enclosure, but rather one flat baffle only. The effect is that the sound waves travel freely from the drivers to your ears, unimpeded from any obstructions or interference.

Our Journey:

We had been aware of a few open baffle designs over the years and also heard some play (they were made in the USA). The sound was different in a good way - more open and more realistic sounding. We knew that this had potential and needed to be pursued. There were no open baffle speaker manufacturers in Australia and only a few worldwide, so we knew that this was a daunting challenge. And so, it was .... Although open baffle speakers appear to be 'simple' visually, acoustically, they are extremely difficult to 'get right' and reproduce good sound. As there is no enclosure, the drivers do not have a 'slug of air' behind them acting as a spring and this creates a whole lot of different challenges. Due to the complexity and desired outcome, we consulted with a great speaker driver manufacturer and a very talented sound engineer in the USA, who jointly assisted us with this work. This open baffle design requires extreme talent, design, equipment, materials and components!

 

Advantages of Open Baffle speakers:

  • Intriguing design

  • Huge sound stage presence

  • Sense of spaciousness

  • Larger listening sweet spot

  • Realistic and engaging

  • Controlled interaction with room

  • Less wall and floor reflections

  • Less inherent resonance compared to boxes/cabinets

Notes:

Open Baffle speakers benefit substantially from being positioned at about 1 meter from the rear and side walls - this open space allows the drivers to 'breathe', as a considerable amount of sound comes from the rear. A slight toe-in is also recommended and should be fine-tuned by experimentation. Speakers should preferably be placed against the shorter wall of a room (point down the longer length of a rectangular shaped room). The baffle includes a 2-degree rearward slant built into the design and this should be fine-tuned by adjusting the spikes so that the tweeter points to listening ear height.

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Baltic Birch Wood

We use 24mm thick Baltic Birch hardwood imported from Finland, which has 17 layers of 1.4mm laminated ply pressed and glued together in a cross-banded construction - guaranteed void free. This is the favourite wood to use for speaker baffles and cabinets due to its immense strength, resilience to harsh environmental factors and superior acoustic properties. When oiled with five coats of our proprietary organic oil mixture, this wood provides a beautiful natural satin look and provides decades of moisture protection. The unusual characteristics of this wood fibre and oil also gives the wood different caramel hues, contrasts and appearances under different lighting types (natural and artificial), brightness and angles.

Our wood is manufactured in Europe according to the strictest sustainability principles and obtained from legal sources that conform to the European Union Timber Regulation (EUTR).  UPM leads the integration of bio and forest industries into a sustainable future characterised by innovation, responsibility and resource efficiency.

Other speaker/cabinet manufacturers mostly use MDF (Medium-
Density Fibreboard which is just a 'finer wood chip' version of chipboard) because it also has favourable acoustic properties, is very cheap, readily available locally, easy to cut and not harsh on cutting tools, uniform shape, but is nowhere near as strong as Baltic Birch and it is also very susceptible to moisture ingression. MDF does not look good oiled, so it is usually painted or veneered. Most companies avoid using Baltic Birch due to its high cost, limited availability, heavy weight, extreme difficulty with machining neatly (tear-out), excessive wear rate on cutting bits and visual challenges with finishes/sealers.

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CNC Router cutting the wood

An industrial CNC router machine performing some high precision work on a beautiful piece of Baltic Birch wood. To avoid tear out, specific bit types, spindle speeds and feed rates are applied.

 

High quality tin coated carbide bits are necessary due to the thick hardwood and multiple layers (16) of tough weatherproof glue.

Flush mounted Speaker Drivers

All our drivers are flush mounted on the baffle to avoid diffraction. Sound waves from the drivers travel across the baffle and any obstacle in this path will result in diffraction, which will negatively impact the sound quality.

All drivers are also mounted on a thin layer of special 'closed cell' foam, to eliminate unwanted resonance and vibrations.

 

The mounting bolts are imported from the UK and are made from 7075 T6 Aluminium with a hard anodised surface to protect against corrosion. Aluminium is used as it is non-magnetic and does not interfere with the speaker driver's magnetic field. A special thread locker is applied to all bolts which are then torqued to specific values.

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Feet

The feet are made from 316 Marine Grade stainless steel which are laser cut and then drilled, tapped, TIG welded (stainless steel) and polished. No coating of any kind is required!

These are made from 10mm thick solid stainless steel plate to avoid resonance and vibrations.

Isolation Spikes and Pads

The M10 feet spikes and pads are manufactured in the UK from 303 Stainless Steel. A CNC machine is used to machine these parts for a good fit and flat finish. The purpose of the tapered point is to decouple (isolate) and reduce the surface contact area, so that no vibration is created and transferred. 

 

These spikes allow the baffle angle to be adjusted in order to achieve the perfect listening height at ear level (ideally the horn should be set to point directly to listening ear height). The baffle incorporates a default 2-degree rearward slant which assists in achieving a near perfect listening angle - adjusting the spikes will allow further fine tuning of the baffle angle to the correct ear listening height.

Bass can also be reduced (baffle lifted) or increased (baffle lowered) by adjusting all four spikes which alters low frequency coupling with the floor. 

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Mass Dampers (harmonic absorbers)

Mass dampers are used in many situations where mechanical vibrations need to be reduced. These include tall buildings, vehicles, power transmission lines, machinery, etc.

We have employed two proprietary mass dampers on each baffle which assist with reducing harmonic vibrations. They are made from laser cut 316 Marine Grade stainless steel plate and are attached to both sides of the baffle via fourteen (pair) 316 stainless steel M5 button cap bolts, nylon bushes and 'closed cell' foam gaskets.

These heavy mass dampers assist with absorbing the unwanted minuscule vibrations within the baffle, thereby reducing harmonic distortions. One of these mass dampers is highlighted in yellow on the left.

Bracing and Barrel Nut fasteners

Each baffle is fastened to a pair of rear wood braces and feet with eight 16mm outside diameter 316 Marine Grade stainless steel CNC machined barrel nuts and eight corresponding 316 Marine Grade stainless steel countersunk M6 socket head bolts. There is also an additional pair of M6 bolts that fasten the baffle directly to the 6mm stainless steel vertical uprights, for additional support and strength.

The clamping force created from this set-up is extreme and massively minimises unwanted vibration and resonance in the mechanical structure. 'Closed cell' foam is also applied between the baffle, wood braces and stainless steel feet. 

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Magnetic Covers - included

Some 'purists' prefer to listen with the speaker covers off, as most cover frames and cloth can inhibit some high frequency sounds from passing through. One still needs speaker covers as to avoid the all well too known 'finger in the cone accident', which can be expensive. To overcome many of these challenges, we have designed and manufactured an extremely transparent cover which is held in place with 10 (each speaker) very small nickel-plated neodymium magnets. This eliminates the use of plastic clips which wear over time, break and cause unwanted vibrations. The covers can now be removed and placed back on in one second! In addition, we have designed a low-profile frame which does not block the sound waves path and we use a retro looking, superior fibreglass reinforced vinyl cloth, that is extremely transparent - even to a highly sensitive calibrated microphone!

Woofer

The 15-inch woofer's function is to produce bass and as there is no box/cabinet to assist, it needs to have some special attributes. A high excursion limit and high QTS are the reasons we use this specific woofer in our open baffle.

 

The massive motor magnet has a vent hole for reduced compression and cooling. Long life silver lead wires are used to carry the power to the voice coil. 

The bass produced by this woofer is absolutely brutal and extremely responsive. Most open baffle systems lack bass - not this one. There is no replacement for displacement - you have been warned!

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Midrange

The-6 inch midrange incorporates a large neodymium magnet for improved response and is vented. The chassis is cast aluminium which improve stiffness and the cone material is made with graphite. 

A special shorting ring in the motor reduces distortion. The frequency range and clarity of this driver is very impressive.

Wave Guide (Horn)

The 90-degree by 90-degree nominal coverage wave guide has an excellent loading down to 600 Hz. This is bolted in front of the compression driver, which is a type of tweeter (produces medium to high frequencies).

 

Constant directivity is achieved with a smooth frequency response.

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Horn Compression Driver (Tweeter)

The huge 2.2kg compression driver with a 1-inch throat is bolted onto the rear of the wave guide (horn). Coupled to the crossover network, this compression driver is not stressed at all (most tweeters are the stress point) and delivers a very smooth and flat frequency response throughout its wide range. 

This driver provides a dynamic character to the overall sound which is complimented by the very high quality and well-designed crossover system it is attached to.

Passive Crossover Network

A crossover network 'filters and splits' certain frequencies to each type of speaker driver which are designed for a certain frequency range. Most speakers come with either passive or active crossover networks - we have chosen the passive type as these are preferred by the 'purists' and have many other benefits. As our speaker drivers are well designed and matched for this role, only a few key electronic components are required to perform the crossover function. The fewer components, the better!

There are mainly two types of crossovers:

  1. Active crossovers modify the audio signal before the amplifier and require a separate amplifier channel for each speaker driver, increasing the system equipment cost dramatically. They are very expensive, complex and extremely difficult to set - improper use could result in damage to the midrange and tweeter drivers. There may also be limitations to adjustments and additional specialised equipment and software may be required in combination and to correctly set them. The source signal can be significantly modified through all the complex component circuitry and many possible adjustments in the signal path, thus inadvertently decreasing the purity of the original signal. The tolerances on each of the many components in the signal path add up quickly, potentially resulting in noise.

  2. Passive crossover networks are mostly preferred by the 'purists' as they are specifically designed for each good quality speaker driver, optimising their maximum efficiency and sound quality. The sound source is not 'modified', but rather the frequencies filtered/split using only a few high-quality electronic components (capacitors, resistors and inductors). These passive crossovers still have some adjustments, but in a simpler and more controlled way using different resistor values (attenuation) - see "Adjustments and Tuning" below. 

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Design and Construction:​

A huge amount of work has gone into designing and building this outstanding crossover network, board and armoured enclosure. This is where a lot of the magic happens! The crossover networks have been designed using the most advanced sound equipment and software available worldwide, to achieve the best 'filtering' for each individual speaker driver at the highest efficiency and overall required sound image. Crossover designs are very complex and need to be specifically designed for each type of driver in conjunction with many other complex vital criteria. The high-quality electronic components are specially selected and imported from Germany, Denmark and the USA. The board and armoured enclosure are fabricated from Australian made 6mm polycarbonate (vastly superior to acrylic/Perspex) and has a special UV coating. Polycarbonate was chosen as it is extremely strong and tough (used in bullet proof applications), inherent sound dampening properties, high thermal ratings and are excellent electrical insulators due to their high dielectric strengths. It also looks very cool as it allows one to see the electronic components inside. Polycarbonate is frighteningly expensive, although worth it for this. This enclosure is not vented as to not allow easy ingress of liquids, dust, moisture, contaminants and insects. Electronic components with very high-power handling capabilities have been used to keep operating temperatures extremely low. 1.2mm tin plated, oxygen free pure copper solid wire is used to connect the components underneath the 6mm polycarbonate board. Safety was also a major decision factor when choosing the enclosure material type. The polycarbonate transparent lid is attached with six M6 button cap 316 Marine Grade stainless steel bolts (a 4mm hex screwdriver is provided to remove the lid for tuning). We are proud to show off our high-quality components and workmanship, hence the clear cover. You can show it off to all your friends as well, and is also a great talking point - you have been warned!

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Adjustments and Tuning:

Each crossover box has two pairs of removable resistors (see above picture), held in place with gold plated terminals. These resistors can be easily removed with the supplied magnetic tip Phillips screwdriver and swapped out with other values, to change the tonal sounds. A large selection of resistors with different colour coded values are supplied with the speakers and these will give you a huge range of adjustment. This is a simple, yet effective and enjoyable way to tune your speakers to your room and preferred tonal sound. The amplifier must be switched off , it's AC power plug must be unplugged and the speaker cables removed from the crossover box, when opening the crossover box - no high voltage present in the crossover box, but just a good safety precaution. Also, do not let the speaker wires, or terminal spades ,or banana plugs touch/short, as this can and will probably damage the amplifier. The 4mm quality hex screwdriver is also included for removing the crossover box polycarbonate lid when swapping out the resistors.

Bi-Wiring and Bi-Amping capable

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Bi-Wiring and Bi-Amping can be incorporated to further improve sound quality. As a standard set-up, each crossover has bridging wires/links installed and only one speaker wire (2-core) is required for each speaker and only a 2-channel output amplifier is then needed.

Bi-Wiring can be used if your amplifier has only 2 output channels (right and left), although you want to improve the sound quality. Two identical speaker wires (pair of 2-core, or one 4-core) can be run from the amp's ONE Right output channel and each speaker wire attached to the two pairs of terminal posts on the crossover - one pair of terminal posts on the crossover supplies only the woofer and the other pair of terminal posts supplies the midrange and horn. Same can be done for the Left channel. The bridging wires/links on the crossover terminal posts would need to be removed for this application. The power from the amp is then carried through different wires to the speakers (crossover networks), resulting in a cleaner power transmission. See Bi-Wired diagram on left.

Bi-Amping is the preferred option if your amplifier has 4 output channels and designed to perform Bi-Amping (please check your amplifier's instruction manual for function availability and set-up). Two identical speaker wires (pair of 2-core, or one 4-core) can be run from the amp's TWO Right output channels and each speaker wire attached to the two pairs of terminal posts on the crossover - one pair of terminal posts on the crossover supplies only the woofer and the other pair of terminal posts supplies the midrange and horn. Same can be done for the Left channels. Again, the bridging wires/links on the crossover terminal posts would need to be removed for this application. The amplifier can now share its power output over four different output channels, placing less strain on the amp and thus improving the sound quality considerably. See Bi-Amped diagram on left.

 

Care must be taken when connecting wires and cables to speakers, amplifiers and other sound equipment - the equipment AND AC power should be turned off and unplugged when connecting anything! 

Terminal posts, wire and solder

Our Terminal Posts are made in the USA from Tellurium Copper (99.5% Copper and 0.5% Tellurium) with a gold plating. These posts can accept speaker cables from the amp with a bare wire (2.9mm x 3.9mm opening), spade terminal (6.5mm) or standard banana plug. These terminals offer a superior connection and conductor for amplification power.

To further ensure that we achieve the best sound quality, we use special speaker wire which is made in Denmark. Each wire connecting the crossover network to the speaker driver terminal (gold plated spade) is a massive 13 AWG gauge (2.5mm square), silver plated, oxygen free copper (99.99% pure) wire. The wire is coated with Teflon (PFTE), which is extremely durable and the preferred choice for audio power cables. 

Every soldered joint is made using solder made in Denmark which contains 4% pure silver and 96% tin. This enhances conductivity and power transmission, thus retaining superior sound quality.

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