NuCau

The Audiopoli NuCau is Kinopoli's main speaker pair: active three-way loudspeakers that Audiopoli members designed and built in 2011–2012. They replaced Kinopoli's legendary cow-patterned main speakers, the "Cows", which moved to a well-earned place in the student museum. The same speaker series was continued by Kinopoli's centre speaker (2015), and the speakers' crossover filtering was redone in 2023 (NuCau 2.0).

The speakers were designed to be placed in the corners of Kinopoli, and the corner placement clearly adds space to the room. Every driver has its own amplifier channel, and the sound processing is handled by a digital signal processor (DSP). The speakers' sound quality is finished off by an aluminium waveguide designed with FEM modelling.

The NuCau speakers in Kinopoli on either side of the screen

The NuCaus in Kinopoli

Specifications

The NuCau information sheet

The speaker's information sheet (in Finnish)

Waveguides from aluminium

Design began in spring 2011: the drivers were chosen to suit the purpose, and it was decided to make a separate waveguide for the tweeter and midrange. Commercial machining would have been very expensive, so a keen doctoral student from the mechanical engineering department was brought into the project, and the waveguides were machined with their help. About 40 kilograms of raw aluminium were needed. The freshly machined, unfinished waveguides were presented at HifiExpo 2011.

The curved front panel

From the start the speakers were meant to have a distinctive look, and the idea of a curved front panel was born. The challenge was to design the speaker so that it could be manufactured with equipment the association had access to. UPM supported the project by donating Grada plywood, which bends with heat, and a lot of bending was tried during spring 2012. In the end it had to be concluded that the bending isn't possible without industrial tools and expensive moulds. The curved front panel was therefore made by sawing grooves into the plywood (kerfing), which lets it bend into the desired shape.

Departing from the original concept, all the electronics were moved out of the enclosures into a separate rack. The plans were finished by autumn 2012.

Kerfing: plywood with closely spaced grooves, used to make the curved front panel

Kerfing: dense grooves are sawn into the plywood so that it can bend into a curve

Assembling the enclosure and shaping the curved front panel

Assembling an enclosure and shaping the curved front panel

Building and finishing

The enclosures were built over three weekends in October 2012 in the HOAS SK6 workshop, with a lot of Audiopoli regulars and keen newcomers taking part. The enclosures were painted: the groundwork was done in-house, and the actual painting was handled by a car paint shop to get the best possible result. The waveguides were bead-blasted and anodised. The finished components were assembled over a single weekend at the turn of October and November, just before HifiExpo. Basic measurements and adjustments were done before the fair, and a couple more weekends at Kinopoli were spent tuning afterwards.

Noretron supported the association with the amplifier purchases.

Painted and unfinished NuCau enclosures in the workshop

Painted enclosures and a curved plywood blank in the workshop

Plan of the signal chain: AV receiver, DSP, three amplifiers and speakers

Signal chain plan: from the AV receiver to the DSP, to three amplifiers and on to the speaker's three drivers (diagram in Finnish)

Result

The finished speakers were presented at HifiExpo 2012, and Kinopoli's new main speakers in particular received a very positive reception. At the fair the volume was controlled directly from the DSP over WLAN. The Finnish hi-fi publications Hifimaailma and AudioVideo.fi mentioned the speakers in their fair reports. The speakers have been a joy to Kinopoli's customers ever since.

Dolby Atmos and the centre speaker (2015)

In 2015 Kinopoli's sound system was upgraded to be compatible with Dolby Atmos. The new centre speaker was built on the NuCau principle: a robust three-way speaker with PA-class sound pressure but studio-monitor sound quality, with a separate amplifier and DSP channel for every driver. The aluminium waveguides had been expensive and heavy on the NuCau, so the centre speaker's waveguide was machined from plastic this time.

The renovation was carried out over the weekend of 17–18 October 2015. Four speakers were installed in the ceiling so that they are completely hidden inside it, Genelec speakers were installed on the walls and ceiling (Genelec supported the project), acoustics were improved with damping panels added on the side walls, and dozens of metres of cables were run under the structures. After installation the system was measured and tuned. AudioVideo.fi published an extensive article about Kinopoli.

A 3D model of Kinopoli with the Atmos speakers

A 3D model of Kinopoli, used to plan the placement of the Atmos speakers

The centre speaker enclosure and the machined plastic waveguide

The centre speaker enclosure with its damping wool, and the machined plastic waveguide

NuCau 2.0 (2023)

The NuCau had sounded "a bit strange" for a long time. First it was suspected that the cause was the acoustically transparent fabric in front of the speakers, whose mounting frame causes its own diffraction. When the fabric was taken down in Kinopoli's 2023 renovation and the NuCaus were listened to directly, they still didn't sound right.

The speakers were taken outside to Kinopoli's yard so their raw responses could be measured without the influence of the room, and it turned out that the crossover filtering had clear room for improvement. The new crossover was designed by simulating the measurements in the VituixCAD software. As a result the NuCau now sounds better than ever.