1961 Bookshelf

For our 1961 series speakers and subwoofers we did not cheap out on looks. We felt using typical pin inserts in the cabinet and grills, as most manufacturers will in the price range, just did not feel right. We custom designed and tooled our own grills in ABS plastic material including neodymium magnets in both the cabinets and grills, with a protective rubber surface to avoid scratches.

The grills are perforated and free flowing, wrapped with a thin fabric cloth, ensuring they do not affect sound quality. And get that right Arendal Sound look to them.

There is something enjoyable about the nice “thud” when you let the grills seat, be it on one of the speakers or a subwoofer. You can rest assured that the sub-surface neodymium magnet will hold the grills tight in place to avoid any rattling sound during playback.

5.5″ woofers

Our 1961 series utilize 5.5″ woofers that are built around the same core fundamentals as their bigger brothers from the 1723 series. The cone body is the same, using long fibre pulp paper with our proprietary coating that ensures covering a wide frequency range from the deepest bass to well above 1500Hz without any hint of cone resonance. The cone material also makes it inherently self-damped which results in a natural sound without coloration throughout the frequency band.The entire surround of the driver is designed to follow the same curvature as our waveguide, so the entire baffle of the speaker has a sleek appearance. No screws or cheap plastic to hide them. The looks are just like on our 1961 Subwoofers and 1723 Subwoofers, except here it is a single integrated piece in the woofer design.

Modelling

While many brands may advertise FEA design and modelling, usually this only refers to the basic magnetic circuit. Arendal Sound has taken the science of transducer modelling to another level. The motor topology is designed first to meet flux density and excursion requirements. Fine-tuning the materials and geometry to minimize flux modulation and stabilize the inductance vs both position and current comes next. Lastly, the voice coil stroke or BL(x) shape is optimized for zero-point centring and symmetry which are the final points for maximizing motor control over excursion and minimizing distortions.

Extensive analysis

To analyse the compliance of both the spider and surround to achieve excursion requirements and optimize Cms(x) to compliment the motor we use non-linear FEA modelling which works on a much deeper level compared to linear FEA modelling analysis. This translates to increased excursion and lower distortions which equals maximum sound quality.We utilize Klippel Laser based diagnostics. It’s a tool often misunderstood, but when used properly in conjunction with component design, a woofer’s design can be dialled in. Klippel testing basically serves to confirm the initial FEA modelling and accuracy of part tooling and offers the diagnostic abilities to allow our engineers to refine the initial designs until final goals for excursion, linearity, stability and distortion are met.

Materials selection and design

Distortion is closely related to how far the cone and motor have to move at a given volume level. Size presents its own engineering challenges, so the motor, suspension and diaphragm all must be delicately balanced to be able to cover the critical midrange frequencies without coloration.We utilize low carbon steel specifically chosen for its ability to carry more flux in the magnetic circuit.

Vented motor structure

The vented T-yoke is CNC milled to final dimensions to ensure tight tolerances, correct fit and to prevent flux robbing losses often found in typical motor assemblies. Vents in the aluminium bobbin as well as the T-yoke, vents in the basket under the spider and in the cone body all together reduce physical and thermal compression, maintaining a hugely dynamic response. 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 (i.e., 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.Aluminium voice coil wire is chosen for its weight and conductivity properties and its lower sensitivity to temperature changes compared to copper. This results in higher efficiency and lower thermal compression. The driver also has a large linear excursion of 13mm peak to peak and a very low inductance design to maximize sound quality, bass response and extension.We use copper shorting rings to reduce inductance, increase frequency bandwidth and lower distortion.Symmetrical suspension consists of critical components such as the NBR surround, polycotton spider material with progressive roll geometry, and integrated tinsel leads. All combined to create very high excursion capabilities with exceptionally linear suspension. Again, this contributes to high output and low distortion at all operating frequencies.

Our 1961 speakers are built around a 28mm synthetic soft dome with a custom designed, matching waveguide. This tweeter was designed for the 1723 series, and most of its design principles are transferred to the 1961 series. The soft dome itself is very lightweight, completely pistonic up to ultra-high frequencies, optimally damped, produced to exceedingly tight tolerances and specifically chosen for its sweet sound character and consistent frequency response. We basically utilize the same tweeter as in the 1723 series, but instead of a neodymium magnet assembly we opted for a less expensive ferrite magnet assembly that still makes the tweeter sound exquisite.The role of the waveguide is to take an already excellent tweeter and further refine its performance. The size and shape, although appearing to be rather simple, is in fact the result of painstaking modelling, testing and refinement. By precisely controlling the directivity over the entire frequency range of the tweeter, we are able to broaden top end dispersion that the tweeter naturally wants to beam straight ahead, and focus the frequencies at the lower end of the tweeter range that naturally want to spread out in all directions. This provides a more consistent polar response across the tweeter’s entire frequency range and a close match to the dispersion pattern of the mid-bass driver it is working with, simplifying the crossover design.

Design

Everything about this tweeter except for the diaphragm has been completely modelled, designed and tooled from scratch. The motor of this tweeter is a powerhouse, all bespoke designs by Arendal Sound and extensive FEA modelling and optimization through Comsol. As usual we use Klippel analysis to review all driver designs.The end result is a high performance, high power handling tweeter with very good bandwidth, low distortion and high efficiency.

• High temp polyimide CCAW wire.
• Underhung voice coil design.
• Ultra-low viscosity ferrofluid contributes to voice coil cooling and ensures the best possible transient response.
• Large aluminium heatsink/shorting ring reduces distortion and prevents thermal compression.
• Multiple vents for increased airflow and balanced compliance.

Waveguide assembly

The waveguide was designed specifically for the new 1961 tweeter and its new speaker applications. It’s a constant directivity, custom designed and tooled waveguide in ABS plastic material, thick and sturdy to avoid any resonance.To give the waveguide assembly that final touch in feel and look, we designed and tooled an NBR rubber ring that fits smoothly to the end of the waveguide shape, covering screw holes and showing off a subtly integrated Arendal Sound logo.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 lower end efficiency.
• Precise polar response control (constant directivity).
• 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 with no secondary resonance peaks, which typically cause electrical phase shifts that present an awkward load for amplifiers and further smear the sound, adding a harsh character.

Sealed

All Arendal Sound 1961 speaker enclosures are designed for optimal sound quality and are based on sealed low-Q designs that provide excellent transient response. A low-Q design means that the low frequency performance is accurately damped, which delivers a tight sound without any boominess. The roll-off occurs at a natural sealed box rate of 12dB/octave below the resonance frequency of the speaker. This frequency (quoted as the -3dB point for the bass extension) is somewhat higher than that of a vented alignment. So, although sealed alignments may look less impressive on paper compared to vented alignments, you may be surprised at how deep they actually still go in-room.

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 nicely with the natural opposite delivered by the sealed alignment and results in a surprisingly extended and naturally flat in-room response.

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 deliver minimal phase shifts, making them the easiest to integrate with a powered subwoofer.

Vented

1961 Tower offer the possibility of being used in alternatively in a vented or sealed alignment. By removing the foam plug inside the slot port, the low frequency -3dB point (at a slope of 24dB/octave) can be extended and given different bass characteristics. The damping and therefore the impulse response are slightly less optimal than with 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 tuning frequency of the port.

Larger rooms and/or speaker positions further from room boundaries may appreciate this extra natural output because they are less supported than in a smaller room. Similarly, some listeners may enjoy this extra output in smaller rooms to deliver truly earth-shattering (though not entirely accurate!) bass.