1723 Center THX

SEALED BOX

All Arendal speakers start with an optimal, low Q sealed box designs. Low frequency performance is accurately damped delivering a tight impulse response – the time the driver takes to stop moving after the signal has passed is very short – and rolls off at the natural sealed box rate of 12dB/octave below the combined box and driver resonant frequency. This frequency (quoted as the -3dB point for the bass extension) is somewhat higher than a vented alignment, but the roll off below a vented speaker’s -3dB point happens at 24dB/octave. On paper the vented alignments -3dB point will look deeper, but the sealed speaker compensates with a more extension below roll-off.

It is worth bearing in mind that smaller rooms or speaker positions closer to a wall, tend to add 6-12dB of extra gain per octave with descending frequency below about 40Hz. This dovetails in nicely with the natural opposite delivered by the sealed alignment, to give a surprisingly extended and naturally flat, in-room response.

Thus, sealed boxes exhibit excellent, accurate sound reproduction, with a fast transient response and well damped impulse response. Their naturally flat in-room response and lack of ports, delivers minimal phase shifts, making them the easiest to integrate with a powered subwoofer.

VENTED BOX

The Monitor/Monitor S, Center/Center S and Tower/Tower S enclosures offer the ability to alternatively be used in a vented alignment. By removing the foam plugs inside the ports, low frequency -3dB point can be extended and given different bass characteristics. Damping and therefore impulse response are slightly less optimal than the sealed alignment, so the bass gains a slightly ‘fatter’ and warmer quality, with the extended response obviously delivering more bass output down to the ports tuning frequency. The other trade-off is that the port’s output adds a phase rotation at the bottom end, making addition of a subwoofer harder to integrate, but not impossible.

Larger rooms and/or speaker positions further from room boundaries, may value this extra natural output as they will be less supported than in a smaller room. Equally, some listeners may enjoy this extra output in smaller rooms to deliver truly earth shaking (if not entirely accurate!) bass.

Where Arendal Sound has been clever with the particularly bass proficient 1723 Tower, is the added flexibility of plugging combinations of the 3 ports and 2 ports for 1723 Tower S. With all ports open maximum bass output is guaranteed, but with a higher roll-off point. With one or two ports open you will get a middle way between extension and power. Obviously all ports plugged brings the Tower/Tower S back to a fully sealed alignment. The Tower/Tower S therefore delivers a choice of multiple roll-off, output and damping ‘tunes’ that will suit a wide variety of tastes, room acoustics and speaker placement.

In the case of the Monitor/Monitor S and Center/Center S, our recommendations are in line with the recommendations above with respect to port tuning, room type and positioning. Although remarkably bass proficient, it is envisaged that the Monitor/Monitor S and Center/Center S will typically be supported by a subwoofer for maximum bass extension and will therefore always perform at its optimum when run sealed in this situation.

CROSSOVER DESIGN

Crossover design is a culmination of model, measure, listen, remodel, remeasure, re-listen, all while refining performance in increasingly small steps. This is the single most time consuming task in loudspeaker design, as it is the glue without which, even the best components can be made to sound disjointed and poor.

As with the overall design goals for all Arendal Sound products, the crossover must be up to the task to deliver on the promise of hi-fidelity and robust construction, without compromise. All models within the 1723 series share common drive designs and this applies equally to the treble to mid-bass crossover designs across the range. The 1723 Tower and Tower S gains an extra low pass section for the additional bottom bass drivers.

Whilst all the attention and praise is shone on driver selection and design, the crossover plays the most critical role in delivering a smooth, seamless transitioning of the mid-woofer to the tweeter. Special attention must be paid to magnitude, phase and polar response so that the transition is contiguous on and off axis.

Components used are tight tolerance, audio grades, and where no suitable item was found, components were custom made for Arendal Sound. Selection was further refined through destructive testing with 24 hour cycles of pink noise, played at progressively higher levels, without a break, over a period of days. If it could break, we found out why, how soon and rejected it anyway.

For the 1723 Monitor/Monitor S, 1723 Center/Center S the crossover is a 2-way design, with a crossover point of 1500Hz, 1400Hz for 1723 Surround and 1500Hz for 1723 Surround S. Slopes are all 4th order (24dB/octave) which serves to further protect the tweeter at high SPLs and limits out of band interactions between the drivers.

Both tower designs starts as a 2-way design very similar to the monitors, using the upper two woofer with the tweeter. This insures consistent voicing throughout the 1723 family. What sets the towers apart is the addition of the lower two woofers. These operate in tandem in below 120Hz for 1723 Tower and 100Hz for 1723 Tower S with the upper mid/bass drivers to further extend low frequency capabilities and increase headroom across the entire frequency range.

To summarize, all Arendal Sound crossovers have the same characteristics:

• 24dB/octave slopes.
• Heavy gauge, low DCR air-core coils.
• Metalized Polypropylene capacitors.
• High power, low inductance wire wound resistors.
• Wide, 1oz copper traces on 1.6mm thick FR4 PCBs.
• Low inductance, low insertion loss, twisted-pair wiring.

We are especially proud of our new exclusive and fully custom made grills. For all Arendal Sound speakers we have made a free flowing, perforated metal grill which does not affect sound quality. We have then wrapped it with a clean black cloth to tone down the visually hard look, whilst simultaneously damping out any residual vibrations.

In addition, we did not want plastic pins to add the grill, which will degrade the clean look of the cabinet with pin cups. Neodymium sub-surface magnets grip the metal grill with great force, preventing unwanted movement and vibration during high level playback. The grills have a rubber protection to ensure the cabinet is not damaged when you attach the grill and you will hear a nice ‘thump’ when you let them seat. Grilles on or off, our speakers look and sound great either way.

The 6.5” (for 1723 S THX Series) and 8” (for 1723 THX Series) woofers are built upon the same core fundamentals as the the 13.8” subwoofer, but with application specific details changed. The woofer cones does not have the glass fibre reinforcement of the 13.8” as it is already stiff enough and the bass material’s inherent self-damping with its proprietary cone treatment is chief quality. An entirely bespoke design, the mid-woofers are optimised to cover a very wide frequency range from 1500Hz, down to the lowest bass notes without a hint of cone resonance. Distortion is closely related to how far the cone and motor has to move and for a given volume level. Size presents it’s own engineering challenges and the motor, suspension and diaphragm all must be delicately balanced to be able to cover the critical midrange frequencies without coloration.

WE USE:

1. CCAW (Copper Clad Aluminium Wire) in the voice coil, balancing the lightness of aluminium, with the conductivity of copper.

2. An aluminum shorting ring to reduce inductance, increase frequency bandwidth and lower distortion, whilst benefiting from the greater heat dissipation of a larger voice coil.

3. Suspension FEA analysed to deliver symmetrical travel, lowering non-linear distortion

4. Klippel analysed, lightweight, long fiber pulp cones, treated with a custom formulation for inherent self damping, that remains pistonic through its operating range and beyond.

5. Voice coil venting to reduce physical and thermal compression, maintaining a hugely dynamic response.

MULTIPLE DRIVERS

Multiple drive units are combined to further reduce Doppler distortions and augment bass output and power handling. The result is clean, dynamic, high output capability, maintaining composure and subtle details.

After thorough optimization and testing (using FEA, Klippel and other methods) of aluminum shorting rings with a focused field design, the result is a linear magnetic field over a wide range of input levels, ultra-low distortion, low inductance, and very dynamic bass.

Symmetrical suspension consists of critical components such as the NBR surround, Connex spider, and integrated tinsel leads. All combined to create very high excursion capability with an exceptionally linear suspension. Again, this contributes to high output and low distortion at all operating frequencies.

Air flow venting underneath the dust cap (vents in cone body) and spider (vents in the basket) is added for two very important reasons. First, air heat from the voice coil is forced away with each stroke of the cone diaphragm. This continuous exchange of air mitigates thermal compression and increases the woofer’s overall power handling capability. Second, the airflow relieves asymmetric compliancy and noises (ie, distortion) due to non-linear compression and rarefaction of air typically trapped under the dust cap and spider. Typical vented pole designs will be limited in effectiveness due to the lack of airflow volume. Meaning, at the highest power and excursion where the airflow is needed most, the pole vent alone will not be sufficient.

Shielding is added to all drivers except for 1723 S models.

The heart of all Arendal speakers, our Tweeter utilizes a 28mm synthetic soft dome with the custom-designed, matching waveguide. The soft dome itself is sourced from the high-end stable of Dr. Kurt Mueller. It is very lightweight, totally pistonic to ultra-high frequencies, optimally damped, produced to exceedingly tight tolerances, and specifically chosen for its sweet sound character and consistent frequency response.

The role of the waveguide is to take an already excellent tweeter and provide refinements to the tweeter’s performance. The size and shape, although appearing rather simple is in fact the result of painstaking modeling, testing, and refinement. In precisely controlling directivity across the tweeter’s frequency range, we are able to broaden top-end dispersion, which the tweeter naturally wants to beam straight ahead and focus frequencies at the bottom end of the tweeter’s range, which naturally wants to spread out in all directions. This provides a more consistent polar response across the tweeter’s entire range and provided a close match to the dispersion pattern of the mid-bass driver it works with, simplifying the crossover design.

HIGH EFFICIENCY, HIGH POWER MOTOR

The motor of this tweeter is a Tour de Force. All components are bespoke designs for Arendal Sound, extensively FEA optimized. The result is a very wide bandwidth, high efficiency, low distortion tweeter capable of being crossed over at very low 1500Hz, even at very high powers. This is truly a rare combination of such low crossover point, high output capability, and clean sound.

•  Large, high-grade neodymium ring magnet
•  High temp polyimide CCAW wire
•  Underhung voice coil design
•  Copper and aluminum shorting rings
•  Ultra-low viscosity Ferrofluid contributes to voice coil cooling and ensures the best possible transient response
•  Large aluminum heatsink/shorting ring lowers distortion and prevents thermal compression.

HYBRID ALUMINUM & HDF WAVEGUIDE ASSEMBLY

The final piece to Arendal’s tweeter performance is mating the dome with the custom-matched, proprietary waveguide, entirely optimized in-house. The waveguide serves several purposes, augmenting tweeter performance to a level that no flat baffle mounted single dome solution could reproduce:

•  Increased efficiency by controlling lower frequency dispersion – Typically a 6dB gain
•  Very low distortion due to increase in bottom end efficiency
•  Precise Polar Response control (sometimes referred to as directivity response control)
•  Low crossover frequency (approx. 1 octave lower than without the waveguide)
•  Excellent directivity transition from mid/woofer to tweeter

AIR FLOW VENTING

The air chambers, venting and damping materials found behind the dome and surround are optimized to create a very well controlled impedance, void of secondary resonance spikes that typically result in electrical phase shifts that present an awkward load for amplifiers and further smear the sound, adding a harsh character.

Not to be forgotten, the connection point of each speaker offers potential pitfalls for installation woes and signal degradations.

Each binding post is made from copper (not brass or other lower conductivity metals), then CNC machined into shape. After the machining process is completed, each component is polished to insure burr free, smooth function and clean cosmetics. The final step is Rhodium plating. Chosen for its excellent conductivity, corrosion resistance and hardness; all serve to protect the copper material and music signal carried within. Each post accepts commonly used wire terminations – banana, spade, pin and bare wire. Input jumpers, made from the same materials as the binding posts, create a simple bridge between inputs without any compromise in quality for use when Bi-wiring is not employed.

The exclusive terminal plate in brushed and anodized aluminum does not only have a beefy look but it also offers a, rigid resonance free performance. The reason for its size is the massive crossovers which are mounted on the back and they need all the space they can get. Mounting the crossovers directly on the plate gives the option for easy future upgrades…