Test Bench: TB Speaker 25-2176S Dome Tweeter

May 10 2017, 05:00
The new TB Speaker 25-2176S 1” dome tweeter is one of the latest additions to the expanding company’s tweeter lineup (see Photo 1). Features for the TB Speaker 25-2176S tweeter include a 25 mm wide surround coated fabric diaphragm optimized for high-frequency cutoff above 20 kHz, a unique aluminum assembly that is both self-shielding and acts as a heatsink, a unique aluminum mounting ring for screw down mounting up to 0.5” mounting depth, ferrofluid voice coil cooling and resonance damping, plus gold-plated terminals.
 
Photo 1: The TB Speaker 25-2176S 1” dome tweeter.
Figure 1: TB Speaker 25-2176S free-air impedance plot.
Figure 2: TB Speaker 25-2176S on-axis response.
Figure 3: TB Speaker 25-2176S horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot).
Figure 4: TB Speaker 25-2176S normalized on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot).
Figure 5: TB Speaker 25-2176S 0° to 90° horizontal plane CLIO polar plot (in 10° increments).
Figure 6: TB Speaker 25-2176S two-sample SPL comparison.

Testing commenced using the LinearX LMS analyzer to produce the 300-point impedance sweep shown in Figure 1. The resonance for this 4 Ω device occurs at rather low (for a 1” soft dome) 763 Hz. The DCR for the 25-2176S was 2.63 Ω, while the minimum impedance above resonance of 3.02 Ω at 2.35 kHz.

I surface mounted the 25-2176S in an enclosure that had a baffle area of 14”× 7” 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 25-2176S’s on-axis response to be a smooth and a fairly flat ±2.4 dB from 1.96 kHz Hz to 23.2 kHz, a wide flat bandwidth for any tweeter.

Figure 3 depicts the 25-2176S’s on- and off-axis response, with the off-axis curves normalized to the on-axis response shown in Figure 4. The associated CLIO polar plot is shown in Figure 5. Figure 6 shows two-sample SPL comparison, indicating the samples were closely matched.

For the next test procedure, I again used the Listen SoundConnect and the SCM 0.25” microphone to measure the impulse response with the tweeters surface mounted on the test baffle. Importing this data into the Listen SoundMap software produced the CSD (waterfall) plot shown in Figure 7. Figure 8 depicts the STFT displayed as a surface plot.

For the final test procedure, I used a pink noise stimulus to set the 1 m SPL to 94 dB (4.48 V for the 25-2176S) and measured the second- and third harmonic distortion at 10 cm, which is shown in Figure 9 (on a log instead of linear scale).

Based on the data, TB Speaker has brought the industry another good performing soft dome, with possible applications in car audio OEM systems. For more information, visit www.tb-speaker.com
 
Figure 7: TB Speaker 25-2176S SoundCheck CSD waterfall plot.
Figure 8: TB Speaker 25-2176S SoundCheck STFT surface intensity plot.
Figure 9: TB Speaker 25-2176S SoundCheck distortion plots.

This article was originally published in Voice Coil, July 2016
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