Gaida is a project that combines Thrax's experience in acoustics, electronics, digital signal processing, and manufacturing technology to provide our vision for the high-end audio industry's future.
Most audiophile companies' innovation focuses on improving a single piece of the puzzle, which is a well-designed audio system. Thrax has been looking at the essential pieces that make up the picture of this jigsaw for years, optimising the fit and interaction to make the picture clearer. Gaida represents the complete picture, assembled as envisioned. A speaker system capable of reproducing the full audio frequency spectrum with realistic sound levels. Gaida uses custom designed drivers for each band and a separate amplifier for each driver optimised for the particular driver’s intended use. Each amplifier is fed by a dedicated DAC, which is in turn fed by a digital processor implementing the crossover and time/phase alignment. This has been done before, some might say, but not at this level, we might add. Gaida's basic features are: 1. Two independent motion controlled 15” woofers with built in sensors for velocity and acceleration feedback, each with its own 1000W amplifier. 2. A custom-designed horn profile for controlled directivity and loading of a dual diaphragm midrange compression driver with its own current output amplifier. 3. Custom bi-radial horn profile for matching directivity for our custom compression tweeter, again with its own current drive amplifier. 4. DSP with 24bit AD/DA processing the crossovers, timing, and levels of the different drivers 5. Monocoque construction from Dupont Corian with stainless steel reinforcements, blending all the curves into a single body. Here are the underlying design objectives:
1. Increasing the directivity uniformly to increase the direct/reflected sound ratio is one of them. Working on another project called Spherovox (https://secure.aes.org/forum/pubs/conventions/?elib=16761 (https://secure.aes.org/forum/pubs/conventions/?elib=16761)) and listening to the sonic signature of different acoustic spaces, one recognises the need to minimise the influence of the listening environment and to push its contribution as much as possible in time (reduced early reflections). So for me, the obvious first step was a wider baffle for the new design, and horns were the natural choice for the job.
2. The next step was to design a midrange horn that can cover the all important range of 300–3000 Hz with minimal internal reflections and HOM (high order modes). While working on the Spherovox, a mid-range driver now known as BMS4599 was used. It has more surface area than most and is capable of the highest sound pressure level in the industry, so for our application, we force it to go into the uncomfortable low range. Having proven that this is the case with the blasting performance of the Spherovox. Using computer modelling tools, we designed a horn with the desired directivity and loading for the chosen compression driver down to the desired cutoff frequency. Of course, it did not work as expected, as all the modelling and simulation was done in free space, and our speaker will be for sure on the floor, and the horn will interact with the front baffle of the bass units as well. It meant we had to optimise for a particular listening distance, so the sum of the reflected energy from the floor will be taken into account in the desired band. Large horns don’t do well with high frequencies, so the shape of the throat of the horn had to be further optimised to reach the 3K region without any reflections or other artefacts. Higher frequencies are handled by a different driver or horn. 3.Time alignment. In this layout, the mid-range driver is 50cm behind the tweeter and 45cm behind the bass drivers. The general layout was taken from a vintage Lansing monitor. Modern DSP crossovers allow for the introduction of independent processing chains for each driver, so one can linearize the driver and model its frequency, phase, and level, making it possible to truly time align. However, each driver has its own unique resonances and phase challenges. Therefore, the adjustment of the driver's phase and level needed thorough analysis around the crossover frequencies, considering their impact on level and timing. 4. Current amplifiers are driving the compression drivers. One of the rarely mentioned facts is that moving coil speakers are actually linear motors and nothing else. As such, the force moving the voice coil is dependent only on the current it passes through. Rarely understood and barely used, current drive solves many of the problems related to phase shifts and adjacent driver-induced artefacts as it linearizes the phase response of the driver and prevents the flow of stray current induced in the system. 5. Experimenting with the sonic characteristics of various crossover types showed that they all introduced unwanted phase shifts, altering the impulse response, which was quite audible. At low slopes, the phase shift was reasonable, but you could not make the drivers shut up in the frequency range they should, so the overlap was too great. Increasing the slopes makes the system fall apart, or particular frequencies stick around or become too prominent due to timing, phase shifts, or stored energy. Linear phase filters can fix that at the expense of another artefact called pre-ringing. This phenomenon is particularly bothersome. It took months of research to figure out what is audible and annoying and what is masked by the operating principle of the human auditory system. The end result is a crossover that uses mixed phase, where each driver is “linearized” and faded at the desired rate or level, making the transition between the different drivers completely unnoticeable and unique to the Gaida geometry and drivers used. 6. Resonance free enclosure. The curved surfaces needed a material that was formable and inert. Corian by DuPont can be thermoformed to the desired shape, and once curved, it is rather rigid and well-dampened, but it can easily break, so we reinforced key surfaces with stainless steel plates, improving the damping and rigidity of the enclosure. Gaida is made entirely of corian and stainless steel reinforcements as a monolithic sculpture, with the only drawback being its weight and cost. Gaida is a practical implementation of what you need to take into account when designing your sound system, all in a single package. A short cut with nothing cut short.