Test Bench: The New TW 104.28 N/Ag 1.1" Soft Dome Tweeter from RS Speakers

RS Speakers is a new Italian brand recently introduced by SICA Altoparlanti, to enter the high-end home transducer market. The brand is named from the initials of Raimondo Sbarbati, SICA’s founder and head designer. The driver on this Test Bench is a 28mm soft dome tweeter that features a treated silk dome directly bonded to the voice coil, with a wide roll surround and an unusual wire screen to keep the damping in place beneath the dome.
  Based in Trecastelli Ancona, Italy, SICA was founded in 1979 manufacturing primarily musical instrument speakers for organs and keyboards. In the late 1990s, under a licensing agreement, SICA commenced production of the legendary Jensen brand of musical instrument speakers. These Jensen “reissues,” after intensive research and analysis, are made to the same specifications as the original Jensen speakers used by Leo Fender and others. SICA introduced the new Jensen D series in 2019 and recently decided to enter the high-end home transducer market with its RS line of speakers.

SICA sent its new 28mm RS TW 104.28 N/Ag soft dome tweeter (Photo 1) to this Test Bench. The feature set for the TW 104.28 N/Ag begins with a treated silk dome that undergoes two different treatments, one internal and one external, to create a mini-sandwich structure, intended to prevent any possible dynamic deformation, especially when the tweeter operates in the frequency band just above its resonance frequency. The dome is then directly bonded to the voice coil, before other treatments, to ensure optimal energy transfer. The rubber-based treatment of the wide roll surround increases stability and elasticity.

Looking at Photo 2, the dome has a fairly high profile, and in Photo 3 you can see the unusual wire screen used to keep the damping in place beneath the dome, which is a nice touch. Remaining features include a copper-clad aluminum wire (CCAW) voice coil winding on an aluminum former, driven by a neodymium ring magnet motor structure that has a vented top plate and silver shorting ring (Faraday shield). The vented top plate opens into a damped rear cavity that yields a 520Hz resonance. The TW 104.28 N/Ag has 2.7mm winding height with a 3mm gap for a underhung format 0.3mm Xmax, a Qts=0.39, an IEC 60268-5 rated noise power of 120W with a rated 91.5dB 1W/1m sensitivity. Last, the TW 104.28 N/Ag has a flared 104mm diameter 4.6mm thick aluminum faceplate and gold-plated terminals.
  I began characterizing the TW 104.28 N/Ag with the legacy LinearX LMS analyzer and generated the 300-point impedance sweep illustrated in Figure 1. The impedance resonance occurs at 550Hz (factory spec is 520Hz). DCR for the RS TW 104.28 N/Ag is 6.04Ω, while the minimum impedance is 6.59Ω at 3.46 kHz. The impedance resonance almost looks like it has been damped somewhat with magnetic fluid in the gap, however, no magnetic fluid was used so this is just some well applied mechanical damping.
  Following the impedance testing, I recess mounted the RS tweeter in an enclosure with a baffle area that is 15”×8” and measured the on- and off-axis frequency response using the Loudsoft FINE R+D analyzer (provided to Voice Coil courtesy of Loudsoft) and the GRAS 46BE ¼” microphone (courtesy of GRAS Sound & Vibration). The analyzer was set up to measure the frequency response from 200Hz to 40kHz (using a 192kHz sampling rate) at 2V/0.5m and normalized to 2.83V/1m. Sweeps were performed at 0°, 15°, 30°, and 45°. Figure 2 shows the on-axis response of the TW 104.28 N/Ag tweeter, which measured ±2dB from 800Hz to 10kHz, followed by 4dB peak centered on 16kHz, where the dome begins following the typical second-order asymptotic low-pass slope.
  Figure 3 gives the on- and off-axis response of the TW 104.28 N/Ag silk dome tweeter, with the off-axis curves normalized to the on-axis response shown in Figure 4. Figure 5 shows the CLIO 180° polar plot (measured in 10° increments with 1/3 octave smoothing). Figure 6 shows the two-sample SPL comparison, indicating the two samples were closely matched to within 0.5dB to 1dB throughout its operating range from 1.5kHz to 20kHz.
  For the remaining group of tests, I initialized the Listen SoundCheck AudioConnect analyzer along with the Listen SCM 2 ¼” microphone (provided courtesy of Listen, Inc.) and measured the impulse response with the tweeter recess mounted on the same 15”×8” test baffle used for the SPL test.

Importing this data into the Listen SoundMap software produced the cumulative spectral decay (CSD) waterfall plot given in Figure 7. Figure 8 depicts the Short Time Fourier Transform (STFT) displayed as a multi-colored surface plot.
  For the final test procedure, I set the 1m SPL to 94dB (3.8V), using a pink noise stimulus, and measured the second and third harmonic distortion at 10cm, illustrated in Figure 9. Distortion is dominated by the second harmonic with a very low third harmonic distortion, however even the second harmonic content is below 1.3% above 2kHz.
 
The build quality of the SICA RS Speakers TW 104.28 N/Ag is definitely appropriate for the high-end two-channel and studio monitor market for which it is designed, not to mention the very nice red/black packaging. So, given all the above data collected for the TW 104.28 N/Ag, I would say that this new RS Speakers high-end OEM tweeter line-up (there are two other soft dome ferrite magnet RS tweeters) is definitely a strong competitor for other high-end home audio transducer companies. For more information, visit www.rsspeakers.it. VC

This article was originally published in Voice Coil, May 2025