A520G2 Axisymmetric R-OSSE
⌀520 x 174 mm A520G2 (main body)	1.4" / 36 mm
	T520-36-STD-1	T520-36-EXT-1
	1" / 25 mm
	T520-25-STD-1	T520-25-STD-2
	T520-25-EXT-1
	Special
	T520-ROSSO-STD

This set of waveguide kits offers a unique solution to the DIY audio hobbyists, especially to those who like to experiment in a long run. The main, big and the most demanding "mouth" parts needs to be made only once, while the adapters for different throat sizes, extensions and shapes are easily replaceable. If, for example, a driver calls for a special throat plug, or a different exit angle, a new adapter can be easily adopted. The kits are provided as STL files for 3D printing.

A520G2 Waveguide

The first set available, the ATH A520G2, is a relatively large waveguide (520 mm / 20.5" outer diameter), usable with a wide range of compression drivers. The usual approach in the past was to start with some smaller devices and later add the bigger ones. Not this time. Size is still one of the most important factors for the best possible results, so let's go right with a big one.

Although the waveguide profile is specified as R-OSSE [1] (which it is for the common part), the individual throat adapters are of more general shapes, each smoothly connected to the common profile. Those throat parts marked as 'STD' are the standard, non-resonant types. The parts marked as 'EXT' are extended-throat versions, improving on the low-frequency capabilities [2]. Each combination is optimized to provide an exceptionally low-diffraction, i.e. a very smooth, frequency response and a balanced, well-controlled directivity with a mildly rising directivity index through the whole operating range. Figure 1 shows a (BEM-calculated) benchmark of the performance (T520-25-STD-1).

A corresponding ANSI/CEA-2034-A [3] report for the waveguide alone is shown in Figure 2. The data for these reports has been normalized for 5° off axis, meaning that they represent the performace of the waveguide with the frequency response at 5° equalized to being perfectly flat.

It is to be noted that the directivity (and all the curves in Fig.2) stays virtually the same for all the throat adapters, irrespective of a compression driver used or its exit size. There may be small differences above ~15 kHz but overall the performance is very similar. This is possible because the A520G2 waveguide has been designed mainly with 1.4" drivers in mind, with a usable crossover frequency around 500 Hz and with the directivity adjusted accordingly. Smaller drivers with 1" exit can also be used however, with the possible advantage that the top octave may be a bit cleaner. The extended 1" throat still allows even some of the 1" drivers (if not most of them) to be used down to perhaps 600 Hz.

References