8 inch woofer test, SB Acoustics vs STX
The 8/9.5" Mid-woofer
We will test several 8/9.5" Mid-woofer in this article:
- Wavecor WF223
- SbAcoustics SB23NBAC
- SbAcoustics WO24P
- ScanSpeak 22W4534G00
- Tymphany Peerless HDS-P830869
- Sica 8H2CP
- Visaton TIW 200 XS
- STX W22.200.8.MCX_V2
- STX W22.200.8.MCX_V3
- PURIFI PTT 8.0X 4 NAB 2
We will measure distortion with and without a 1.2mH air core inductor, to reduce the driver breakup impact on distortions when possible, as seen in speaker breakup article.
In essence: We use Back Electromotive Force principle with an air core inductor that will increase gradually the impedance, affecting the voice coil, and replace some EQ to linearize the woofer in the same time, it works very well if the woofer is already rising up in his final box.
It will reduce a lot H3 and H5 distortion related to breakup.
Distortion measurements are done at 25cm 98dB, all drivers are EQ flat to be compared : The SPL is the same on all the bandwidth, for all drivers, with and without air core inductor, the difference with and without air core inductor is not due to SPL but to Back Electromotive Force principle, as explained in our dedicated article.
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ScanSpeak 22W4534G00: A huge H3 rise up, very audible, badly placed as the generated harmonic will be for H3 200/300Hz an unwanted (and impossible to avoid) sound produced at 600/900hz.
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Sica 8H2CP: not very bad but the rise up between 100/200 hz some does it better, it was an excellent Q/P driver before, now his price has risen so he lost his interest.
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Tymphany Peerless HDS-P830869: It’s the better of the four but the next 4 others will do it better.
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Visaton TIW 200 XS: hard to use.
H2
H3
H5
H3 with air core inductor at the same EQ SPL
H5 with air core inductor at the same EQ SPL
All performs extremely well, the WO24P is the better when the STX is extremely good and costs literally 10 times less.
The Wavecore WF223 is good for a high crossover.
It’s not shown here as all are EQ but the SB23 is naturally flat, an advantage in passive filtering but not mandatory in active one when we use the air core inductor, as we will see it after.
We see here that with the air core inductor there is a top 2 almost ex-aequo between two drivers, the WO24P and the STX W22.200.8.MCX.
The SB23NBAC remain on inductor charts even if he don’t have and cannot have an air coil (has it not rise up in box)
A new process, for new tests, is used and allows us to better differentiate the best options, including new top-of-the-line 8" drivers with the PURIFI.
On this graph, we will select all the best solutions, both with and without air-core inductors.
These drivers are so good that only the H2 and H3 stands out from the noise and offers a noticeable difference.
H2
H3
H2 with air coil inductor at the same EQ SPL
H3 with air coil inductor at the same EQ SPL
The H5 of these excellent drivers is below 0.05% and not very significant.
The STX W22 is surprising, as the back electromotive force applied by the air-core inductor reduces distortion at 200 Hz. Even the H2 is reduced, indicating that the distortion increase at 200 Hz was, in fact, related to the breakup.
Time-domain measurement
As always, there’s nothing to see in the time domain if we stay away from breakup:
WO-24P
PURIFI PTT8.0
STX W22.200.8.MCX_V3
Conclusion
Without the little rise up on H3 at 200/300hz the STX V2 and V3 will be ex-aequo on distortion with the WO24P.
The self transform both WO24P and STX in low-medium woofer for a 2 way usage cut at 1250/1300 hz with an X-Shape 25.
With a Back Electromotive Force system, such as a notch filter or an air-core inductor, the STX matches the best-in-class woofers in terms of distortio, at a fraction of the price.
The Purifi is an expensive killer and doesn’t need an air-core inductor to perform extremely well compared to the WO24P. The last advantage of the WO24P is its 1.5" more larger size (more emissive surface), which will make a difference in the very low end (not visible on charts) and also in directivity control when we want to control directivity as low as possible with the HF horn at crossover.
The best compression drivers usable with them are tested here: 1" compression driver test.
There is a huge difference in chassis between the WO24P and this STX that is an stamped sheet metal making the STX harder to integrate, but well, we have seen that it doesn’t impact performances.
