Test Bench: Morel TSCT 1044 High-End Tweeter

January 26 2017, 02:00
For this Test Bench I received from Morel a new addition to the Supreme tweeter line, the 28 mm Titanium Supreme Copper sleeve Tweeter (TSCT) 1044 (see Photo 1). As part of the Supreme line, the TSCT 1044 and the similar TSCT 1144 (which is the same tweeter with a larger faceplate) are both an entirely new design for Morel and incorporates the company’s Improved Dispersion Recess (IDR) faceplate design, which is a shaped inset in the round metal faceplate. The shape is intended to increase the high-frequency output in the tweeters off-axis response.
 
Photo 1: The 28-mm TSCT 1044 is Morel’s new soft dome tweeter from its Supreme product line.

Additional features for the TSCT 1044 include a 28 mm Acuflex hand-coated fabric dome, a 104 mm IDR metal faceplate, a vented “flat pancake” ring-type neodymium magnet structure, a Hexatech hexagonal shaped aluminum voice coil wire (originally licensed from Dynaudio) wound on a titanium former, an underhung 1.125” diameter voice coil (4 mm gap and 2 mm coil height), a replaceable voice coil assembly, a damped die cast aluminum rear cavity, magnetic fluid in the gap for enhanced cooling, and gold-plated terminals. Because of the motor configuration, the top of the magnetic return path (pole piece) is about 60% open, providing a relatively small reflective surface beneath the dome. The remaining surface is damped with a round “donut” shaped felt ring. Last, the Din power handling specification for this tweeter is a robust 200 W.
 
Figure 1: Morel TSCT 1044 free-air impedance plot.
Figure 2: Morel TSCT 1044 on-axis response.
Figure 3: Morel TSCT 1044 horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot).
Figure 4: Morel TSCT 1044 normalized on and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot).
Figure 5: Morel TSCT 1044 two-sample SPL comparison.

To begin, I created an impedance plot using a LMS 300-point impedance sine wave sweep (see Figure 1). The tweeter resonance occurs at 594 Hz, with the obvious damping from the large rear cavity and magnetic fluid. With a REVC =4.04 Ω, the minimum impedance for this tweeter is 4.56 Ω at 5.2 kHz.

I recess mounted the TSCT 1044 in an enclosure that had a baffle area of about 17” × 8” and measured the on- and off-axis frequency response at 2.83 V/1 m with a 100-point gated sine wave sweep from 40 kHz to 300 Hz. Figure 2 shows the on-axis response. The TSCT 1044’s frequency response is a gently rising slope and a smooth ±2.2 dB from 1.5 kHz to 10 kHz, with the low-pass rolloff beginning at about 20 kHz. Figure 3 depicts the TSCT 1044’s on- and off-axis response.

You can easily see the effect of the Morel-shaped IDR faceplate. Off-axis, the device is only –3 dB down at 13 kHz from the on-axis response with respect to the 30° off-axis curve and –4 dB at 45° off-axis (also at 13 kHz), again with respect to the 30° off-axis response. This is a nice improvement over the typical 1” soft dome type tweeter off-axis response above 10 kHz. Figure 4 shows another view of the off-axis response in the normalized on- and off-axis plot. Figure 5 gives the two-sample SPL comparison, indicating the two samples were well matched. Of course this is the kind of consistency you expect from a company such as Morel.

Next, I used the Listen, Inc., SoundCheck analyzer to measure the impulse response with the tweeter recess mounted on the same baffle that I used to measure the TSCT 1044’s frequency response. Importing this data in the Listen SoundMap software produced the cumulative spectral decay plot (waterfall) shown in Figure 6. Figure 7 shows the Short Time Fourier Transform (STFT) displayed as a multi-color surface plot. Last, I set the 1 m sound pressure level (SPL) to 94 dB (3.03 V), and the analyzer range to 1 kHz to 20 kHz. Then, I measured the second and third harmonic distortion at 10 cm (see Figure 8). The new TSCT 1044 is another well-conceived tweeter from Morel engineering. For more information on the TSCT 1044 tweeter and other Morel OEM drivers, visit www.morelhifi.com.
 
Figure 6: Morel TSCT 1044 SoundCheck CSD waterfall plot.
Figure 7: Morel TSCT 1044 SoundCheck STFT surface intensity plot.
Figure 8: Morel TSCT 1044 SoundCheck distortion plots.

This article was originally published in Voice Coil, February 2016.
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