Satori WO24TX-8 9.5" TeXtreme cone woofer

  What and why am I testing?

Finally, my hands have reached the “father” of the TPCD diaphragm loudspeaker family of the top brand Satori from Indonesian company Sinar Baja Electric. When I say “father”, I don't mean the oldest, but the biggest, strongest, most powerful and authoritative speaker in the Satori TeXtreme family to date - the foundation on which the rest of the lineup stands and on which any loudspeaker is built. We're talking about the Satori WO24TX-8 TPCD diaphragm bass speaker, which the company positions in a 9.5“ size (9.5”=241mm, which corresponds to the outer size of the speaker basket).

The WO24TX-8 (-4) was introduced in early February 2023. It is built on the same chassis as the long-known and well-loved Satori WO24P-8 (WO24P-4) paper cone woofer. The unusual 9.5“ size fills the niche between 8” and 10“, and allows for a smaller loudspeaker cabinet than a 10” would normally require, and thanks to the large 8.55 mm linear excursion, delivers sound pressure on par with 10“-11” woofers.

At the time of today's review, the Satori TeXtreme lineup is already well grown and includes the following models:

• 1.2" tweeter TW29TXN (4 and 8 Ohm) (review)
• 5" midrange MR13TX-4 (review)
• 5" midwoofer MW13TX (4 and 8 Ohm)
• 6.5" midwoofer MW16TX (4 and 8 Ohm) (review)
• 6.5" midrange MR16TX-8 (review)
• 7.5" midwoofer MW19TX (4 and 8 Ohm) (review)
• 9.5" woofer WO24TX (4 and 8 Ohm)

Satori WO24TX woofer comes in 4-Ohm and 8-Ohm versions. Today we're taking an in-depth look at the 8-Ohm version WO24TX-8 as part of a series of reviews initiated by Sinar Baja Electric.

I would like to thank Mark Thomsen (Marketing and International Sales Manager at Sinard Baja Electric) and Frank Nielsen (CEO & Owner at Danesian Audio ApS) for kindly providing me with samples of Satori WO24TX-8 speakers for testing and helping me solve logistical problems.

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).

  The datasheet

Standard Satori datasheet. It is quite concise, but at the same time contains all the information necessary for the loudspeaker designer. It refers to a pre-production model, so it is quite likely that the production model may be slightly different.

The whole list of the main “features” given by the manufacturer unequivocally allows to classify WO24TX-8 to the highest caste of bass speakers. There are no clearly outstanding technical parameters, but they are all at a high level and very well balanced. I would like to note only a decent linear excursion - 8.55 mm per side.

  The package and construction

The WO24TX-8 comes in a sturdy package made of glossy corrugated cardboard. Inside, the speaker is protected by cardboard inserts with shaped cutouts.

The woofer is designed in the same way as the smaller cone speakers in the Satori line, only on a larger scale.

The acoustically very transparent basket is made of aluminum alloy and coated with black micro-textured powder coating. The flange thickness is 10.5 mm, the spokes are very strong. The magnetic system is equipped with a rubber ring with shaped elements that visually continue the spokes of the basket. It has no serious functionality, but it nicely complements the design of the basket. A foam gasket is glued to the back of the flange.

All elements of the magnetic system are not made by simple casting or stamping, but with subsequent turning, as evidenced by the cutter marks on the outer surfaces. This is one of the conditions for narrowing manufacturing tolerances and improving the consistancy of parameters, as well as an attribute of the highest class speakers. Inside the pole piece there is a vent ending in a 45 degree bevel at both ends. The double ferrite magnet is not visible as it is completely enclosed in a decorative rubber ring.

The regular convex half-roll surround is made of low-loss rubber.

The flat five-wave spider is attached to an aluminum ring that is about 15 mm away from the magnetic system. The middle part of the spider has eight 10 mm diameter holes around the circumference, a rather rare technique sometimes used to control the compliance of the spider.

The voice coil former is made of fiberglass and is wrapped along its entire length with a layer of damping paper. There are no ventilation holes in the former.

The flexible silver lead wires are quite stiff and attached to the voice coil former symmetrically at 180 degrees. This contributes to better balancing of the moving system.

The gold-plated terminals are pressed into the aluminum holder and sit very firmly in it. Thanks to the large amount of free space around them, connecting to them is very convenient and simple.

The TeXtreme diaphragm consists of two layers rotated 45 degrees relative to each other. Unlike regular carbon fiber diaphragms, it is perfectly smooth with a pleasant matte silky sheen and, thanks to the microfiber structure, shimmers very beautifully at different angles of incidence of light. The sound response of the diaphragm when tapped or stroked with a finger is very similar to the response of a ping-pong ball, there is no better association.

An unusual element is visible between the voice coil former and the diaphragm - a cone adapter made of TeXtreme. It serves to transfer and distribute force from the voice coil to the diaphragm in the most optimal point to reduce the excitation of parasitic vibrations of the diaphragm.

The production quality is exemplary, there is nothing to complain about. Perfectly fitted parts, complete absence of any cosmetic defects, no burrs, distortions, chips and traces of glue. The label is perfectly aligned.

Visual inspection revealed excellent modern construction, beautiful design and excellent workmanship.

  Impedance frequency response

Prior to all measurements, the WO24TX-8 was broken-in with a sinusoidal voltage of 12 Volts/23 Hz for 30 minutes. The diagrams below show the impedance frequency responses before (green) and after (purple) the break-in at different scales:

It is a rare case when the broken-ing had very little effect on the parameters. “Right out of the box” resonant frequency was Fs=26.92 Hz, and after broken-ing it was Fs=26.24 Hz. The measured values of the Thiel/Small parameters are slightly different from the datasheet. Even if the resonant frequency during of more intensive broken-ing drops to the datasheet value of 24.5 Hz, the Qts will become equal to 0.366, instead of the declared 0.34. It is not critical, but it can slightly affect the internal volume of the loudspeaker enclosure.

The impedance curve from 200 Hz to 1.3 kHz rises moderately and linearly (on a logarithmic scale), reflecting the low inductance of the voice coil achieved by the dual copper rings in the magnetic system, which help to reduce nonlinear distortion.

Over the entire frequency range, the impedance response is very clean, one could say almost perfect. Only at high magnification there is a barely noticeable ripple in the region of 4.2 kHz, caused by the main resonance of the diaphragm, as well as a small “pimple” at 430 Hz. A speaker with such a rigid diaphragm should be absolutely perfect and clean up to 1kHz, so I tried to find the cause of this “pimple”, and it turned out that the culprit is the Helmholtz resonance of the air mass in the magnetic system pole vent and the compliance of the air inside the voice coil former. This effect is seen in many speakers, and I am sure it could not have escaped the eyes of the designers of the WO24TX-8. It can be cured at the design stage, but every cure has side effects that can sometimes be more dangerous than the disease itself. Designing a good loudspeaker is always a wise choice of compromises, and it is quite possible that the designers thought that the target operating frequency range of the woofer would not reach the parasitic resonance at 430 Hz, and it is not worth putting out the fire with a grenade.

The impedance response tells us about the well balanced low loss moving system and the excellent motor.

  On-axis frequency response (at 315 mm)

Below are the axial smoothed SPL frequency responses for two WO24TX-8 samples measured in a test baffle at a distance of 315 mm to a microphone at 2.83 Volts:

The frequency responses of both samples perfectly coincide with each other in the whole frequency range and are very close to the datasheet. The measured sensitivity in the range of 150 - 900 Hz was 88 dB, which is in perfect agreement with the datasheet.

In the frequency range of 100 Hz - 3.2 kHz the total unevenness does not exceed +/- 2 dB, which is a very good indicator for a 9.5" woofer. The frequency response increases smoothly from 100 Hz to 1.3 kHz, except for the 300-450 Hz interval, where there is a small notch of about 1 dB depth, most likely caused by the previously mentioned Helmholtz resonance inside the magnetic system.

After 3 kHz, the diaphragm goes into a well-controlled break-up mode, accompanied by a pair of spikes at 4.2 and 7.8 kHz.

The engineers have coped with the inevitable resonance of the surround perfectly - in the 700 - 1500 Hz range everything is very smooth, without the usual dips.

In general, it can be said that the WO24TX-8 has a very extended and smooth frequency response.

  Off-axis frequency responses (at 315 mm)

Below are graphs of off-axis frerquency responses - conventional and normalized, in which the axial response is taken as a reference, and the off-axis ones reflect only the difference with it:

The off-axis frequency responses are in perfect order. No unpleasant surprises were detected. In the range up to 2 kHz they decrease monotonically with increasing deflection angle and frequency.

  Harmonic distortion (at 315 mm)

Above are the dependences of harmonic distortion at voltages of 2.83 and 22 Volts, which correspond to average sound pressure levels of 88 and 106 dB, respectively. The measurements were taken on axis at a distance of 315 mm to the microphone. To limit overloading of the speaker in terms of diaphragm displacement amplitude, a second-order digital high-pass filter with cutoff frequency of 50 Hz was used when measuring harmonic distortion. In these graphs, we analyze the frequency range only above 150 Hz.

At all sound pressure levels in the range up to 300 Hz, the exclusively euphonious second harmonic dominates. We see very low level of the second and fourth harmonics in the entire frequency range and a monotonous increase in the 3rd and 5th harmonics, starting from 200 Hz.

At a frequency of 420 Hz, small bursts of the 3rd and 5th harmonics are noticeable, as a very small reminder of the parasitic Helmholtz resonance.

Overall, I would characterize the harmonic distortion as "very low" in the range up to 400 Hz.

  Harmonic distortion in the near field (at 20 mm)

Due to the specifics of my test setup, to analyze the nonlinear distortion of woofers in the frequency range up to 200 Hz it is more correct to use the results obtained by measurements in the near field at a distance of 20 mm from the cone. The diagrams below show harmonic distortion at voltages of 2.83 and 16 Volts. To limit the speaker overload in terms of the diaphragm displacement at a voltage of 16 volts, a second-order digital high-pass filter with a cutoff frequency of 20 Hz was used:

We observe the typical for all woofers increase in distortion with decreasing frequency. The overall level of harmonics can be described as "very low".

Above 40 - 50 Hz at any sound pressure level, the exclusively euphonious second harmonic dominates.

  Voice coil current harmonic distortion

This type of measurement, despite its simplicity, is a good tool for assessing the linearity of the speaker motor. The diagram above show the frequency responses of the 2nd, 3rd, 4th and 5th harmonics of the voice coil current at a voltage of 2.83 Volts.

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. The level of current distortion largely determines the minimum level of distortion that can be obtained from a speaker.

Nothing unusual in the behavior of harmonics is observed. Everything is fine, everything is smooth, without unexpected resonance spikes. The usual growth of all components with decreasing frequency at the bottom of the operating range. Above 200 Hz there is a monotonic increase in odd harmonics.

I would rate the overall level of current harmonics as “very low” up to 300 Hz.

  Intermodulation distortion

The intermodulation distortion measurement is one of way of to analyze the device non-linearity. It is not an alternative, but an additional method and allows you to identify the spectral components of the inharmonious structure, which are much more harmful for high-quality sound reproduction and to which our hearing is more sensitive.

For testing I chose the frequencies of 30 Hz and 255 Hz. With this ratio (1:8.5) the contribution of the Doppler distortion is not yet dominant and the contribution of amplitude modulation can still be observed. In addition, this is a very realistic situation that occurs in both two-way and three-way systems. The measurements were performed for different 30 Hz cone excursions and their conditions are indicated in the lower left corner of each plot. By various colors are indicated:

• test frequencies (30 and 255 Hz)
• 2nd order harmonic distortion components for the test frequencies (2nd HD)
• 3rd order harmonic distortion components for the test frequencies (3rd HD)
• 2nd order intermodulation distortion components (IMA2)
• 3rd order intermodulation distortion components (IMA3)

The graphs above show the IMD spectrum for 3 mm and 8 mm cone excursion with a 30 Hz modulating signal.

However, in these plots products of the motor nonlinearity are mixed with products of inevitable frequency modulation of the Doppler effect. How do you define who is who? We can analytically estimate the level of the first pair of the side Doppler components using the following formula [http://www.linkwitzlab.com/frontiers.htm#J]:

As(dB) = 20*log10(pi*A1*f2/c), where pi=3.14, A1- the modulating signal amplitude in meters, c=343 m/s, f2 - carrier frequency. In our case f1 = 30 Hz, f2 = 255 Hz.

Aplying the last formula we get the maximum level of spectral components corresponding to Doppler distortion is approximately as follows:

For A1=3 mm, IMA2Doppler=-43.12 dB
For A1=8 mm, IMA2Doppler=-34.57 dB

It can be seen from the graphs that the levels of the measured spectral components for WO24TX-8 at different amplitudes of the modulating signal are:

For A1=3 mm, IMA2= -40.53 dB
For A1=8 mm, IMA3= -30.68 dB

At an amplitude of 3 mm, the level of second-order intermodulation distortion was 2.59 dB higher than Doppler distortion threshold, and at an amplitude of 8 mm, it was 3.89 dB higher. This means that at any volume, amplitude modulation slightly dominates frequency modulation.

Overall, I would rate the level of intermodulation distortion as "very low".

  Step response

The step response rises very quickly and returns aperiodically to the resting state. In the falling part it is slightly spoiled by the oscillation process from the diaphragm's main resonance - for a woofer, this is of no significant importance.

  Waterfall

A waterfall shows the same effects as the step or frequency responses, in addition to exposing hidden resonances that are difficult to see on other types of measurements:

No new resonances were detected. We see a very clean, flawless waterfall up to 3 kHz. In the break-up mode, there are only two "tails" - a very short one at 4.2 kHz and a moderately long one at 7.5 kHz. A fairly decent waterfall for a 9.5" woofer with a rigid diaphragm is achieved thanks to good internal damping of the TeXtreme diaphragm.

  Listening impressions

After the objective testing stage was over, as usual, I moved on to subjective evaluation of the sound. The speaker was listened to, being installed in the test baffle, in the following sound reproduction chain: Laptop→EMU 0404 USB→ DSP Xilica XM2040→Purifi 1ET400A. Listening was performed both in the full frequency range and with second-order low-pass filtering with a cutoff frequency of 300 Hz.

This is not my first experience of listening to speakers with TPCD diaphragms (see Satori MW16TX-4, Satori MW19TX-4, Satori MR13TX-4, Satori MR16TX-8, Satori TW29TXN-B, BlieSMa M74T-6, BlieSMa M142T-6) and from the WO24TX-8 I heard the same familiar signature. The following are the main distinctive, so to speak, “generic” features of the sound of speakers with diaphragms from TeXtreme (this is how I hear it personally):

• Natural, neutral or closer to warm timbre. Less colorful than paper diaphragms, less ringing and bright than metal or ceramic diaphragms
• “Solid”, dense and dynamic sound with excellent reproduction of sound attack. The sound is closer to, but inferior to, metal or ceramic diaphragms, but superior to paper diaphragms
• High resolution and transparency, without a veil and any turbidity of soft diaphragms (paper, polypropylene). In these parameters, it is a little inferior to metals and ceramics, but superior to paper and polypropylene
• Characteristic velvety sound, especially noticeable on wind and string bowed instruments, as well as vocals
• A slightly lower sense of body, tactility of sound images and “blackness” of the musical canvas than than that of paper diaphragms
• No audible distortion or shoutness even at high volumes

 

The sound signature of the WO24TX-8 is very similar to that of the Satori MR13TX-4 and Satori MR16TX-8 midranges with TeXtreme diaphragms, except that it has an emphasis on bass, a lower timbre and more of a “body” feeling in the sound. Aerodynamic noise in the motor is practically absent, no whistling and grunting even at maximum diaphragm excursions.

In general, the bass driver made a very pleasant impression.

  "How to use" recommendations

With its very low nonlinear distortion, long linear excursion and low resonant frequency, the WO24TX-8 will find excellent use in the bass section of a high-end multi-way loudspeakers. The speaker seems to have been optimized for use as a woofer up to 400Hz, although its extended and smooth response allows it to be used even in a two-way loudspeaker up to 2kHz.

The T/S parameters of the WO24TX-8 are optimized for use in a bass reflex design in the enclosure volume of 30 to 60 liters.

Below are the results of modeling the woofer in the VituixCAD software in 40 and 60 liter bass reflex enclosures:

Excellent results. In 40 liters the lower limit frequency was 33.2 Hz, and in 60 liters 26.2 Hz. The larger volume of the enclosure allows for a deeper bass at the cost of an additional 20 liters and a reduction in maximum sound pressure by 1.8 dB.

The "Passive radiator" design is also possible, but for the WO24TX-8 I don't see any special bonuses compared to the "Bass reflex" design, except for a significant increase in the cost of the design.

  What is the price and where to purchase it?

The retail price of WO24TX-8 is on average from €314/piece to $406/piece excluding VAT. You can buy it in the following online stores:

• madisound.com
• audiohobby.eu
• toutlehautparleur.com
• soundimports.eu

​

  Summary

The WO24TX-8 woofer is a great addition to the Satori brand of TPCD diaphragm speakers. The measured parameters and characteristics, although not perfectly matching the datasheet, were very close to it and at the same time confirmed that the speaker belongs to the highest class. The consistency of parameters from sample to sample is excellent. I really liked the sound signature and bass potential of the woofer. The design of the speaker is optimized to work as a woofer in the frequency range up to 400 Hz. I can safely classify it as one of the best woofers available on the market today, regardless of the price.

What I liked:

• Very low harmonic distortion until 400 Hz
• Very low intermodulation distortion
• Low mechanical losses
• Smooth frequency response up to 3.2 kHz
• Neutral timbre, high detail and sound transparency
• Excellent consistency of parameters from sample to sample
• Excellent workmanship

 

What I don't liked: if we consider the WO24TX-8 from the point of view of using it as a woofer in the range up to 400 Hz, then I do not see any flaws in it

More detailed measurement results can be found here:

Yevgeniy Kozhushko/04.03.2025