HiFiCompass

SB Acoustics SB21SDCN-C000-4, SB21RDCN-C000-4

What is on the test bench?

Young graduates of the Indonesian giant Sinar Baja Electric came to take the exam today. Two miniature tweeters with 21mm fabric diaphragms and neodymium magnet motors SB21SDCN-C000-4 and SB21RDCN-C000-4 extend the range of SB Acoustics 21mm tweeters. Until now this segment of tweeters of the brand was represented by only two models on ferrite magnet motors - SB21SDC-C000-4 and SB21RDC-C000-4 with a mounting flange diameter of 92 mm. This size allows the tweeters to be used in home systems, while the models tested today have a flange diameter of only 58 mm, which already opens the doors of the car audio system for them.

By its construction SB21SDCN-C000-4 and SB21RDCN-C000-4 are identical in absolutely everything, except for the sound radiating element. The first has a classic dome, and the second one has a ring radiator. Ring radiators have become widely known since 1999, after VIFA company released its XT25TG30-04 tweeter, which has gained a lot of popularity among both loudspeaker manufacturers and the DIY comunity. A few years later, ScanSpeak company, have already been acquired by VIFA and being already under the same roof with it, released a "high-end" version of XT25 - legendary R2904/7000 tweeter, which for several years became the company's flagship and took place in high-end loudspeakers of many well-known brands. Why am I saying this? Because the fact that the inventor of the very first ring-radiator XT25TG30-04 was Lars Goller, thanks to whom VIFA filed an application in 2000, and the next year received a patent for a "ring-radiator" tweeter. The essence of the patent was a phase plug in the center of the annular membrane. In 2006 Lars Goller became a member of the ScAR (Scandinavian Audio Research) group, which began to cooperate with Sinar Baja Electric. The result of that cooperation was in the emergence of the widest range of high-quality speakers under the SB Acoustics (budget segment) and Satori (high-end segment) brands. So, one of the first products were tweeters, ring radiators, SB Acoustics SB29RDC-C000-4 and Satori TW29R, which had great success. In order not to violate patent restrictions, Lars Goller applied a new way to neutralize the weak points of the ring membranes in these tweeters without using a phase plug. He changed the way of fixing the central part of the membrane, as well as the geometry of the membrane, making it flatter. Subsequently, he applied for a patent for a new membrane design.

It will be very interesting to compare advantages and disadvantages of the both technologies in this review.

Here you can learn about the history of the SB Acoustics and Satori brands, as well as one of the world's largest speaker drivers manufacturer - Sinar Baja Electric (www.sinarbajaelectric.com).

Why do we test this?

Sinar Baja Electric has kindly provided seven of its latest models for independent testing:

Tweeter SB Acoustics SB21SDCN-C000-4
Tweeter SB Acoustics SB21RDCN-C000-4
Tweeter Satori TW29TXN-B
Tweeter Satori TW29BNWG-4
Midrange Satori MD60N-6
Midwoofer Satori MW16TX-4
Midwoofer Satori MW19TX-4

Since all the models are just beginning to enter the market, it is impossible to find any additional information, except for meager numbers from the datasheets. Today's review opens a series of tests, the purpose of which will try to make up for the lack of information and to acquaint everyone with detailed technical characteristics and application features of the new speaker models

I would like to express my deep gratitude to Sinar Baja Electric company for the provided new products, as well as personally Mark Thomsen (International Sales & Marketing Manager SB Audience | SB Acoustics) and Melly Wulandari (SB Acoustics Project Manager) for their assistance in implementing the series of reviews.

What did the manufacturer state?

The datasheets are quite detailed and contain all the parameters a loudspeaker designer needs.

Since the review is comparative, first I will list the features common to all the models:

Copper cap for reduced voice coil inductance and minimum phase shift
Compact low distortion neodymium motor system
Non-resonant rear chamber with optimized damping for improved dynamics
CCAW voice coil for low moving mass
Long life silver lead wires
Low resonance frequency

Now, the individual features are:

for SB21SDCN-C000-4:

Large surround dome for increased acoustic output

for SB21RDCN-C000-4:

Non-resonant diaphragm design for minimum high frequency break-up

In terms of parameters, the models differ only in the effective radiating area of the membrane - 4.9 cm2 for the dome tweeter versus 4.6 cm2 for the ring radiator, and the sensitivity, which is 0.5 dB higher for the dome tweeter.

Visual inspection

SB21SDCN-C000-4

SB21RDCN-C000-4

The tweeters are delivered in a durable glossy corrugated cardboard box. Inside it there is an additional frame made of double-folded corrugated cardboard, in the grooves of which the speaker flange is rigidly fixed. To protect against dust, accidental scratches and scuffs, the front of the tweeter is wrapped in a soft, translucent cloth. Everything is simple and very reliable. The packaging is commendable.

The tweeter body, flange and rear chamber are made of plastic. The plastic is very durable, as trying to bend the flange even slightly with my fingers did not bring any success. With such rigidity, four mounting holes are quite enough. The rear camera barely responds to finger tapping. The flange has a small annular bead around the center hole. Most likely, this is how SB Acoustics engineers optimized the axial and off-axis frequency characteristics. A soft foam rubber seal is attached to the back surface of the flange.

The workmanship is excellent, there is nothing to complain about. Perfectly fitted parts, complete absence of any cosmetic defects, no burrs, chips and traces of glue. The terminals sit very firmly in the body and do not stagger at all.

The tweeters differ one from the other only in the shape of the membrane. The SB21SDCN has a fairly high profile, which gives it additional rigidity. The central part of the SB21RDCN annular membrane is absolutely stationary. One gets the impression that it was obtained from the SB21SDCN membrane simply by "pinning" the top of the dome to the magnetic system. In fact, this is not the case, the SB21RDCN ring membrane cannot be transformed from the SB21SDCN dome.

Visually and by touch the membrane material is exactly the same as in all other SB Acoustics and Satori fabric tweeters. It looks like this is the same fabric with damping impregnation. It seems not sticky, but from personal experience I would say this fabric attracts dust quite well, although not in the way that Morel (Israel) and Dynaudio (Denmark) tweeters do.

Impedance frequency response

SB21SDCN-C000-4

SB21RDCN-C000-4

The impedance curve of the SB21RDCN is just perfect. The SB21SDCN one exhibits a slight "swelling" in the 2.5 kHz region - an echo of the interaction of the moving system with the back chamber. Nothing critical, in my opinion. Throughout the rest frequency range everything is good. The both curves are absolutely smooth, without a slightest sign of any internal resonances. This is achieved thanks to the right damping of the interior cavity and the moving system. The increase in impedance with increasing frequency is very small - the result of using a copper cap on the pole piece of the magnetic system.

The measured resonance frequencies are:

For SB21SDCN-C000-4: Fs=834 Hz vs stated 850 Hz

for SB21RDCN-C000-4: Fs=867 Hz vs 850 Hz

The rest of the measured parameters are also in good agreement with the datasheet ones. The both tweeters have very well balanced moving systems and good motors.

On-axis frequency response

SB21SDCN-C000-4:

The measured sensitivity in the range from 2 to 20 kHz averaged 89 dB, which is 1 dB lower the manufacturer's declared value. The frequency response has a flat character with no tilt and extends from 800 Hz right up to 40 kHz. The total unevenness does not exceed 2 dB in the range 900 Hz - 18 kHz, which is very good for a fabric dome tweeter. At 21 kHz there is a low-Q resonance of the membrane with a height of about 3.5 dB. The parameters and location of the resonance are such that they can be considered practically not influencing on sound reproduction. Around 6 kHz there is a small shallow dip of about 1 dB. The responses of two samples differ no more than 0.5 dB up to 2 kHz. It is no matter because that is a non-target frequency range when using the tweeter in a real loudspeaker. In the range from 10 to 20 kHz the divirgence is 0.5 to 1 dB. Again, it is not so critical due to the lower ear sensitivity in that range. In the most important range from 2 to 10 kHz the frequency responses coincide perfectly. The measured tweeter's frequency response matches the datasheet very good.

SB21RDCN-C000-4:

The measured sensitivity in the range from 2 to 20 kHz averaged 88.5 dB, which is 1 dB lower the manufacturer's declared value. The frequency response has a flat character with no tilt and extends from 730 Hz right up to 40 kHz. The total unevenness in the 850 Hz - 33 kHz range does not exceed 2 dB (!!!) - very impressive figure for a fabric membrane tweeter. Around 6 kHz there is a small shallow dip of about 1 dB. The performance of the two samples in the ENTIRE frequency band does not differ at all. Yes, you heard right - at all. I even thought at first that I added the frequency response of the same tweeter twice during the preparation of the material for the publish. I checked myself - no, everything is correct. It's a fantastic, there are no other words. The measured tweeter's frequency response matches the datasheet very good.

A comparative analysis of the frequency responses of the dome and ring tweeters is already beginning to show the features of the two technologies. The annular membrane a priori does not have the piston mode of operation, so it does not have a transition from the piston to the modal mode and is less prone to resonances. This allowed to obtain a smoother frequency response, but not for free. The ring radiator had to pay off 1 dB of sensitivity.

Off-axis frequency responses

Above are the plots of the off-axis frequency responses. For each tweeter model there are two different plots - regular and normalized, on which the axial frequency response is taken as the reference and the off-axis ones reflect only the difference with it. All curves are smooth and fall off monotonically with angle and frequency. Due to the small dip in the axial frequency response at 6 kHz and its absence at off-axis frequencies, humps are observed in the normalized off-axis characteristics of about 6 kHz in both tweeters. The probable cause is diffraction phenomena at the interface between the membrane and the mounting flange.

Both tweeters radiate sound waves well on the sides up to 6 kHz, after which the radiation pattern begins to narrow. The dome tweeter has a wider dispersion than the ring radiator. This is a principal difference between dome and annular membranes.

Overall, I would not say the dispersion of the tweeters in the upper octave is very good. From such a small size I expected better behavior.

I found a noticeable discrepancy between the measured off-axis responses and the those published in the datasheets. It seems the 60-degree response from the datasheet is more consistent in reality to the measured one at 45-degree, and 30-degree response to the one at 20-degree.

Harmonic distortion (315 mm)

Above are the frequency responses of harmonic distortion for each tweeter at average sound pressure levels of 89 and 98 dB for the dome version (at voltages of 2.83 and 8 Volts respectively) and 88.5 and 97.5 dB for the ring radiator. In these diagrams we analyze the potential operating range of the tweeter - from 3 kHz and above.

The harmonic distortion pattern is practically the same for both tweeters and, taking into account the small radiating area, can be assessed as low. This indicates a good magnetic system.

The second harmonic clear dominates in the both tweeters. Its level is 15 to 25 dB above the nearest third harmonic. Such a behavior is usually typical for membranes with a relatively wide convex surround. The fifth harmonic is above the fourth, it's not the best scenario.

On average, the second harmonic level of the dome version is 3-4 dB lower through the entire range compared to the ring radiator. This is one more difference between dome and annular membranes. In the context of tweeters of this size, I would rate the distortion level as low.

Voice coil current harmonic distortion

This type of measurement, despite its simplicity, is an excellent tool for assessing the linearity of a speaker motor. The above plots show the frequency dependences of the 2nd, 3rd, 4th and 5th harmonics of the voice coil current at 2.83 Volt.

Voice coil current nonlinearity is the direct nonlinearity of the mechanical force driving the speaker cone, since this force is related to the current by a simple relationship F=B*L*I, where B is the magnetic field strength, L is the length of the voice coil wire inside the magnetic gap and I is the current. So, in principle, it is practically impossible to obtain sound pressure distortion lower than current distortion in the frequency range where the contribution of the motional nonlinearity becomes insignificant.

The distortion behavior is the same for both tweeters. This is no coincidence, because they have the same motor.

The fact that the level of the 2nd harmonic of the current is 25 dB lower than the level of the 2nd harmonic of sound pressure suggests that the main source of 2nd harmonic distortion in the tweeters is the nonlinearity of the moving system.

Step response

The step responses demonstrate excellent slew rate and fast decay. The responses calm down completely rather quickly, though not aperiodically, but cross the zero line twice. This is due to the fact that the Q-factor of the main resonance is more than optimal. If used in a real loudspeaker with a cutoff frequency of 3 kHz or more, this can be ignored. Very good.

Waterfall

SB21SDCN-C000-4 водопад

SB21RDCN-C000-4 водопад

The waterfall shows the same effects as a step response, in addition exposing hidden resonances that are difficult to see in other types of measurements. Both versions demonstrate a great waterfall. As you can see, the dome resonanse at 21 kHz in the SB21SDCN is well damped and does not leave any traces behind. Excellent!

The ridges in the 2 - 5 kHz region are not related to tweeters, but are caused by reflections from the test baffle edges. They appear in most of my measurements.

Listening impressions

Due to the low resonance frequency and very flat frequency response both tweeters sound full with good reproduction of the space and the room atmosphere. The tonal balance is absolutely neutral. The dominance of the second harmonic gives the sound some thickness and relief. Unlike their larger counterparts, small fabric tweeters convey the sound of percussion more detailed and sharper, and this is their undoubted advantage. The SB21SDCN-C000-4 sound seemed more airy and emotional to me, while the SB21RDCN-C000-4 sounds more neutral and restrained. The differences are most likely caused by the different sound dispersion.

"How to use" recomendations

Thanks to the low distortion, low resonance frequency and extended low frequency response, both tweeters can be used down to 3 kHz in high-quality two and more way loudspeakers of moderate size. The compact size of tweeters removes all barriers before using them in car audio. The small diameter of the voice coil, low sensitivity, low maximum power and the plastic housing, which makes heat dissipation difficult, impose restrictions on the maximum sound pressure and this must be taken into account when designing loudspeakers.

What is the price and where to purchase it?

The tweeters are already ready to order and can be purchased, for example, in the following online stores:

SB21SDCN-C000-4, the retail price is in the range of €23-27/piece excluding VAT

SB21RDCN-C000-4, the retail price is in the range of €28-36/piece excluding VAT

Summary

Overall, these compact budget tweeters made a good impression on me by their measurements and sound. Many years of personal experience with SB Acoustics speakers confirm that all datasheet data can be trusted with confidence. This testing once again confirmed that the measured axial frequency characteristics, impedance characteristics and resonance frequencies are in good agreement with the stated ones. The measured sensitivity values turned out to be 1 dB lower than the nominal ones. I was a little surprised by the discrepancy between the measured and declared off-axis frequency characteristics.

Comparison of tweeters SB21SDCN-C000-4 and SB21RDCN-C000-4 made it possible to identify the advantages and disadvantages of two types of sound radiators - fabric dome and ring. The advantages of dome radiators are a slightly hihger sensitivity, wider sound dispersion, a couple dB lower the 2nd harmonic distortion. The advantage of ring radiators is that their membranes are less prone to resonances, resulting in a smoother and more extended frequency response.

I would highlight the following features of the tweeters: