Measurements Page

A400G2 ⌀400 x 130 mm (⌀15.75 x 5.12")

A460G2 / E460G2 ⌀460 x 160 mm (⌀18.11 x 6.30")

A520G2 ⌀520 x 174 mm (⌀20.47 x 6.85")

E520G2 ⌀520 x 174 mm (⌀20.47 x 6.85")

ATH Gen2 Waveguides

The "Gen2" set of devices offers a unique solution to the DIY audio hobbyists and audiophiles. The main, big and the most demanding parts of the horns need to be made only once, while the throat adapters for different driver sizes, exit angles, extensions and shapes are easily replaceable.

Although being "versatile" in the sense just described, these waveguides also offer excellent acoustic performance in any absolute terms, basically free of diffractions and reflections. The frequency responses within the whole listening window are virtually identical - a truly remarkable feature and an evidence of the absence of any strong diffraction effects.

The A520G2 is a kind of "no-compromise", moderately large waveguide, while the A400G2 is basically just a smaller version, still performing extremely well though. A460G2 is the latest iteration, maintaining virtually the same overall performace of the large A520G2 down to around 600 Hz, but in a noticeably smaller format. It can be recommended for 1" drivers in general, where a bigger device offers typically only a negligible advantage. E520G2 is a segmented version (see [3]) of the A520G2. Performance wise, it is on par with the axisymmetric version, with possible practical advantages. (If in doubts which one to choose, pick the A460G2 - it doesn't lack anything of its bigger siblings, yet being smaller.)

The horn profile used is a R-OSSE [1] variant for the common part, while the individual throat adapters are of more general, smoothly connected shapes. Those throat parts marked as 'STD' are the standard, short, 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 smooth, well-controlled directivity with a mildly rising directivity index through the whole operating range. Figure 1 shows a (BEM-calculated [5]) benchmark of the performance (T520-25-STD-1 adapter shown).

Although this stems obviously from its axisymmetric nature, it's worthwhile to note that the data presented here describe the behaviour of the horn everywhere in the far field. In other words, a complete picture is shown. Don't get fooled by the so often presented cherry-picked data, where only a single selected plane is considered, even if the device itself is highly asymmetrical (and so is inevitably its acoustic performance). It's very rare that a complete picture is shown when there is good and not-so-good data to be choosed from :)

Moreover, these devices are round not because it's just easier (it is to a degree), but mainly because it actually turns out that the round shape simply provides the best acoustic results. They can be virtually perfect when optimized, and here's the evidence.

The whole range of the adapters can be used with all the Gen2 waveguide bodies. The corresponding ANSI/CEA-2034-A [4] reports for some chosen combinations are shown in Figure 2. For convenience, the data for these reports has been normalized to 5° off axis, meaning that they represent the performace of the device 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 waveguides were designed mainly with 1.4" drivers in mind, with a usable crossover frequency around 500 Hz and with the overall directivity adjusted accordingly. Smaller drivers with 1-inch exit can also be used, with the possible advantage that the top octave may be cleaner. The extended-throat ("EXT") adapters still allow even some of the 1" drivers, if not most of them, to be used down to perhaps 600 Hz. The latest addition to this approach is the long adapter for the BMS 4554 compression driver.

Figure 3 shows normalized throat acoustic impedance for both A520G2 and A400G2, simulated in free air, using the standard 1.4" adapter. Maybe not anticipated by common intuition, the throat impedances are basically the same - they are simply not dependent on mouth size in these kinds of waveguides. In fact, no matter how irrelevant, the low-frequency point⁽¹⁾ of the smaller waveguide is a tiny bit lower in this case.

Acoustic measurements with various drivers are available on the measurements page.

As a "spin off", the A460 horn has been designed, based on the A460G2, but already including a throat section and with the optimization boundaries loosen to not be limited by the existing Gen2 bodies. The result is a waveguide designed and optimized from throat to mouth as a single R-OSSE curve^[1]. The opening angle of the 1" throat was set to 21.7°, matching Peerless DFM-2535R00-08, but of course other similar drivers can be used.

Gen2 Throat Adapters

References