Test Bench: ETON 29HD2 Magnesium/Ceramic 28mm Dome Tweeter

November 11 2017, 05:00
This month’s Test Bench samples came from a respected home audio OEM transducer manufacturer from Germany. From Eton I received the 29HD2, its 28 mm magnesium ceramic diaphragm neodymium motor tweeter (see Photo 1). ETON is a well-known name in high-end home/car hi-fi. ETON Electro Acoustic GmbH was founded in 1983 with the goal of developing loudspeakers and loudspeaker systems to provide the highest degree of customer sound enjoyment, which is pretty much the goal of all OEM transducer manufacturers that aspire to the rarefied atmosphere of high-end audio.
Photo 1: The ETON 29HD2 magnesium ceramic dome neodymium motor tweeter.

The ETON Hexacone sandwich cone, patented by ETON became known worldwide for its high degree of stiffness and its light weight. This results in a unique sonic timbre that is proprietary to ETON loudspeakers. ETON’s 29HD2 neodymium motor tweeter has, as you would expect, a fairly rich feature set that includes an aluminum faceplate, a 28 mm diameter magnesium diaphragm with a ceramic coating on both sides protected by a cosmetically attractive grill/phase plug, and driven by an aluminum former wound with round copper-clad aluminum wire (CCAW). Other features include an injection-molded surround, an underhung neodymium magnet motor design with a cast-aluminum cavity/heatsink, a 0.6 mm Xmax, and gold-plated terminals. There is no ferrofluid (magnetic fluids are great for lowering warranty replacement, but even very low viscosity magnetic fluids can cause audible damping to musical transients). Specs also state a 120 W power handling and a frequency range of 2 kHz to 20 kHz, suggesting a low crossover at 2 kHz—especially if you include a LCR (inductance, capacitance, and resistance)—conjugate in the
crossover design. 
Figure 1: ETON 29HD2 impedance plot.
Figure 2: ETON 29HD2 on-axis response.
Figure 3: ETON 29HD2 horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot).
Figure 4: ETON 29HD2 normalized on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot).
Figure 5: ETON 29HD2 180° horizontal plane CLIO polar plot (in 10° increments).

To begin, I used the LinearX LMS analyzer to produce the 300-point impedance sweep shown in Figure 1. The 29HD2’s impedance resonance occurs at 619 Hz (factory spec is 590 Hz at 1 W). With a 6.77 Ω DCR (factory spec is 6.80 Ω), with the minimum impedance for this tweeter measuring 7.28 Ω at 3.42 kHz. Next, I recess-mounted the ETON tweeter in an enclosure with a baffle area of 17” × 8” and measured the on- and off-axis frequency response with a 100-point gated sine wave sweep at 2.83 V/1 m. Figure 2 shows the on-axis response to be a flat ±2.6 dB from 2 kHz to 10 kHz, with the diaphragm breakup mode centered on 22 kHz.

Figure 3 gives the on- and off-axis response, with the off-axis curves normalized to the on-axis response shown in Figure 4, plus the CLIO 180° polar plot (measured in 10° increments) shown in Figure 5. Figure 6 shows the two-sample SPL comparison, indicating the two samples were closely matched to within 0.25 dB throughout most of its operating range, with some minor 1 dB variation at 2 kHz and 7.5 kHz. Next, I used the Listen SoundConnect analyzer along with the Listen SCM 0.25” microphone to measure the impulse response with the tweeter recess-mounted on the test baffle. Importing the windows impulse response into the Listen SoundMap software resulted in the CSD waterfall plot shown in Figure 7. The same data was used to produce the STFT displayed as a surface plot (see Figure 8).

For the last objective test, I used a noise stimulus to set the 1 m SPL to 94 dB (3.20 V) and measured the second (red curve) and third (green curve) harmonic distortion at 10 cm (see Figure 9). All the ETON drivers I have either reviewed or worked with over the years have exhibited outstanding performance and build quality and the ETON 29HD2 obviously delivers the same “je ne sais quoi.” For more information, visit www.eton-gmbh.com. VC
Figure 6: ETON 29HD2 two-sample SPL comparison.
Figure 7: ETON 29HD2 SoundCheck CSD waterfall plot.
Figure 8: ETON 29HD2 SoundCheck STFT surface intensity plot.
Figure 9: ETON 29HD2 SoundCheck distortion plots.
This article was originally published in Voice Coil, April 2017
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