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Bass Reflex System - 8 inch, 2-way (Seas Exotic)

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What is a Bass Reflex system?

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 assist with increasing bass, they all, to different extents, introduce unwanted resonances which can be heard as a distortion/colouration of the original content.

 

Our Journey:

When choosing a box design, we looked at all the advantages and disadvantages of each type and identified the many challenges that we felt we could overcome and/or mitigate. With high precision and extreme engineering backgrounds, and many previous years of experience in speaker enclosure designs and manufacturing, we chose the bass reflex system (ported box). The challenges with this type of system are that of eliminating unwanted box resonances in the audible frequency range, maximising the efficiency of the woofer-midrange driver by calculating the optimal internal enclosure volume and finding the most favourable port dimensions in order to maximise bass without creating noise. After the ideal internal volume was calculated, our challenge was to then design a highly efficient, but quiet port tube, which would be tuned to the optimal resonance frequency for effective bass reproduction. Designing this port turned out to be very challenging and frustrating, although the outcome is amazing and worth every tear shed. For the box design and construction, we consulted an 'old school' cabinet maker who had many, many years of experience with different wood, complex wood joints, long term fibre expansion and contraction, gluing, assembly and oiling. This was very interesting and we enjoyed this part of the design - wood being remarkably complex. We decided to use 24mm Baltic Birch wood for reasons discussed below. The weak point of any box are the joints and to overcome this, we were advised to use complex box joints on all four side corners and tongue & groove joints all around the front and rear panels, for ultimate joint strength. In addition, seven 19mm thick Tasmanian Oak dial rods are incorporated into each box, maximising bracing and overall rigidity. This added substantial complexity to the overall box design and assembly, but was an absolute necessity in sharply reducing decay and unwanted resonance to a point of inaudibility. Wood expands and contracts with humidity, dryness, heat and cold, so this also had to be taken into account when deciding on joint types, glue types and wood sealers.

Industrial grade waterproof glue from the USA and an industrial strength polyurethane glue are used in specific areas. 4.5 tons of clamping force is used on each box when gluing together and is left for 24 hours to dry. The result is a very rigid box, which is the foundation of our design. 

Notes:

A slight toe-in is recommended and should be fine-tuned by experimentation. The port faces forwards, so these speakers can be placed very near to the rear wall. The closer they are to the rear and side walls, the more bass coupling. Speakers should preferably be placed against the shorter wall of a room (point down the longer length of a rectangular shaped room). The stand height has been chosen to meet the average listening ear height (tweeter height) - a taller or shorter stand can be manufactured.

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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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Internal Cross Bracing Rods

Although the speaker boxes are constructed from very thick and strong 24mm multi-layered hardwood ply, sound generated resonances are very powerful and can even vibrate/excite such rigid enclosures, causing unwanted colourations in the sound. 

Damping materials are usually employed to address this, although with limited effectiveness. We incorporated many cross-bracing 19mm Tasmanian Oak beams throughout the enclosure to enhance its rigidity, which significantly minimises unwanted resonance - within a human's hearing frequency range of 30 Hz to 20 KHz.

Tongue & Groove Joints - Front and Rear Panels

The front and rear wood panels need to be securely fastened to both sides, top and bottom panels to prevent vibrations due to gaps within the joints and air leaks, which would both impact the sound quality. 

Our wood consultant suggested using the 'old school' tongue and groove joint, as it was extremely strong and also acts as an 'O-ring gasket'. This is yet another one of the most complex wood joints to manufacture, although we had no choice but to use the best. High precision matching grooves are cut in both the outer and inner panels, which receive a special plywood insert upon gluing and assembling. These joints are extremely strong, as the front and back panels are 'keyed' in place. 

The picture to the side displays the 16 plywood 'keys' used to make a pair of cabinets.

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Tuned Port - Double Flare

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This is probably the most complex and difficult component to get right in any bass reflex system. This specialised area shares many similarities with fluid dynamics, which gets very complex. Contrary to common belief, speaker ports do not relieve the pressure created by the woofer at all. Its sole purpose is to enhance the bass with a moving 'slug of air'.

There is an optimum ratio between the tubes inside diameter, length and shape. We initially experimented with many already-manufactured premium port tubes of different sizes and shapes from Europe and the USA, but did not achieve the desired results. After much research and experimentation (real world), we decided to use a double-flared port which has the advantage of providing the outgoing and incoming 'slug of air' with a smoother transition, thus increasing efficiency and eliminating chuffing (sound caused from turbulence when the air's path is disturbed).

We therefore had to make our own proprietary flared ports and after much trial and error, discovered the one which delivered. Each pre-made port is pressed and sized over a hard anodized CNC machined aluminium mould under extreme pressure and heat, in order to achieve exact tolerences. The radius dimentions of the inner flare match that of the outer wood baffle flare exactly.

The port is tuned to a specific Hertz which meets our end goal sound performance.

Damping Materials

As mentioned earlier on, damping materials assist with reducing unwanted resonance and so we also incorporate this trick - actually we use two different kinds of damping materials....

 

Mundorf Angel Hair Sound Damping:

TWARON Angel Hair is a speaker box filler for acoustic damping which is produced by the Thüringische Institut für Textilund Kunststoff-Forschung (TITK), Germany, exclusively for MUNDORF. In contrast to fibreglass and other plastic fibres, TWARON conducts heat generated vibrations away very well and absorbs acoustic motion energy. Result - improvement in the sound quality (fine dynamics in the midrange, “more airy” reproduction of voices and instruments, better 3D properties).

Thick wool and cotton padding:

The full rear panel, both sides, top and bottom are covered in 14.5mm heavy commercial underlay. This works extremely well where resonance reduction is a requirement. The pre-cut pads are attached to the already internally sealed panels (painted on the inside with polyurethane) with an industrial glue and barrage of stainless steel staples (for just in case).

 

The padding is made from wool and cotton, and is asthma and allergy friendly. This product is made in Australia by a well-known brand company. We do NOT use any hazardous materials (eg. fibreglass, stone/rock wool, etc).

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Polycarbonate inspection window

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Now this is something neat..... I know that a lot of you, like me, love to look inside things and see how they work. Well, now you can look inside this speaker box through a 14.8mm thick polycarbonate inspection window, allowing you to see almost everything inside the cabinet (crossover electronic components, wires, rear of both speaker drivers, padding, Angel Hair, 7 dial rods and port tube). You need to place your thumb or finger on the two gold pins on top of the box (indicated in the picture to the side with a red circle) and this activates two 10mm LEDs via a capacitive sensor and switch which we designed inhouse (proprietary design). The capacitive sensor and switch are on standby all the time and only draws a miniscule amount of power from the 9-volt battery, which is placed in an external nylon draw in the rear panel. The estimated life of a battery used for 30 seconds per week is at least 2 years. It takes 10 seconds to replace the standard 9-volt battery. This allows you and your friends to see all the good stuff used inside our speakers!

Note: Please only use good quality batteries. The nylon battery draw is installed inside its own wooden box and has a stainless steel spring and two stainless steel terminals. The battery draw also has a special fuse attached to it on the inside, as a good practice.

Isolation Spikes and Pads

The feet spikes and pads are manufactured in the UK from solid brass. A CNC machine is used to machine these parts for a good fit and flat finish.

Both the box and the stand have spiked feet which decouple (isolate) the two structures, so that vibrations can't pass between each other and the floor, and affect the sound quality.

 

The purpose of the tapered point is to reduce the surface contact area, so that no vibration is created and transferred. 

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Stands - included

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The stands are an essential part of the speaker system and as such, are included as a set. The top of the stand's dimensions matches the base of the speaker box exactly and is made to a specific length which brings the tweeter to listening ear height.

 

The same 24mm Baltic Birch wood is also used to make the stands. The top plate and base are fastened to the vertical pillar via four 16mm outside diameter 316 Marine Grade stainless steel CNC machined barrel nuts and four 316 Marine Grade stainless steel countersunk M6 socket head bolts. The clamping force created from this set-up is extreme and again eliminates any possible resonance or vibration in the system. 'Closed cell' foam is applied between the connecting pieces. There is also a large hole down the middle allowing for the speaker cable to be threaded through so that it does not hang from the rear of the speaker and create a 'pull down' hazard for little children. It also looks neater hidden inside.

The base is 48mm thick and has a large foot print for additional stability. Picture taken from the side, showing the special barrel nuts.

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 8 (each speaker) very small nickel-plated neodymium magnets in the corners. 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!

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Woofer

The well-known Seas Exotic W8 is an 8-inch woofer-midrange driver is designed for smooth, wide frequency response, high sensitivity and low distortion.

The paper cone is embedded with papyrus fibres to optimise stiffness and damping. The surround is made from a special foam rubber which reduces mass by 40%, resulting in higher sensitivity and excellent damping properties. This part is made to last for decades.

The spider employs an extremely 'open weave' and is held together with a special resin formulation. This creates a highly acoustically transparent design which minimises reflections and resonances.

An Alinco V ring magnet was chosen to enhance the high sensitivity and excellent stability. Copper rings on each side of the magnet gap lower distortion due to eddy currents and flux. An Ash wood phase plug provides optimal radiation for the critical mid frequency band.

Dome Tweeter

The well known Seas Exotic T35 classic dome midrange tweeter is designed to provide high sensitivity and a smooth extended frequency response.

A specially coated fabric dome forms an integral piece of this driver. An Alinco V ring magnet provides high sensitivity and low distortion. 

The large 35mm voice coil is made from copper-clad aluminium wire which further enhances the sensitivity. Venting holes in the aluminium coil former and flexible lead-out wires assist with minimising noise.

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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!

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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). 

Design and Construction:​

A huge amount of work has gone into designing and building this outstanding crossover network, board and fastening system. 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. The crossover component board is fabricated from Australian made 6mm polycarbonate (vastly superior to other types of PC boards, for this use) and has a special UV coating. Polycarbonate was chosen as it is extremely strong and tough (used in bullet proof applications), inherent sound damping properties, high thermal ratings and are excellent electrical insulators due to their high dielectric strengths. Polycarbonate is frighteningly expensive, although worth it for this. 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 board. The polycarbonate board is fastened with 6 dampened M4 button cap 316 Marine Grade stainless steel bolts. We are proud to show off our high-quality components and workmanship, hence the clear polycarbonate inspection window at the top of the box. You can show it off to all your friends as well, and is also a great talking point - you have been warned!

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 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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