Today, I’ll be reviewing the AsciLab C5B, which features a 5.25-inch woofer along with two passive radiators.
For this review, I measured one official sample provided by the manufacturer and another pair owned by an individual who had purchased the product personally.
Impedance
The impedance drops as low as approximately **2.2 ohms** at its minimum.
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Frequency Response
Before delving into the frequency response graph, there’s an important matter to address.
As I reside in the same country (South Korea) as the manufacturer, I was able to obtain a reference sample directly from AsciLab to ensure an accurate comparison with their official performance data. Fortunately, the manufacturer was generous and promptly agreed to this request.
However, an issue arose during the measurement process: the frequency response curve I obtained showed significant discrepancies compared to the manufacturer’s official data, especially in the high-frequency range.
Given that the manufacturer uses Klippel’s NFS system, this discrepancy was concerning.
I immediately reached out to them, and they were incredibly cooperative. This collaboration allowed us to:
1. Compare the responses of my microphone against theirs.
2. Verify the NFS measurements using my microphone.
The results were enlightening:
I was able to overlay the curve measured with my microphone (red) onto the curve measured with the NFS system using my microphone (black). This reassured me of the validity of my measurement method.
It turns out my microphone exhibited a slight attenuation in the high frequencies, while their microphone showed a slight boost. Both microphones were within Earthworks' trusted tolerance range but were coincidentally skewed in opposite directions.
After compensating for the relative differences between the two microphones, the resulting curve closely aligns with the manufacturer’s performance specifications.
I’ve taken the time to explain this situation in detail, as it is crucial for understanding the context. Now, let’s return to the main discussion.
The overall balance is remarkably flat, with the bass slope gently tapering off around 40Hz. This suggests the speaker is capable of delivering substantial low-frequency extension in typical indoor settings.
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Nearfield Measurement
Each component performs its role cleanly, without any signs of resonance or unwanted artifacts. The crossover point is estimated to be around 1kHz, which is quite low. Achieving durability and sound quality at this frequency would require high-quality materials and advanced design expertise. It’s worth evaluating the distortion performance in this context.
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Directivity
The horizontal directivity is outstanding. The transition between the tweeter and the woofer is exceptionally smooth, with no noticeable crossover artifacts. Additionally, diffraction caused by the enclosure shape is well-managed. Truly impressive.
The vertical directivity is nothing short of stunning. Despite being a two-way design and not utilizing a coaxial structure, the drastically lowered crossover point has resulted in an exceptional vertical dispersion pattern.
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Beamwidth
Beamwidth remains consistent and smooth across both horizontal and vertical planes.
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Polar Plot
The polar plots reveal smooth and uniform attenuation across all directions, both horizontal and vertical. This naturally leads to a soft and even directivity index (DI).
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THD
No audible distortion or uncomfortable harmonic distortion (HD) artifacts were observed. The results are exceptionally clean.
In the lower midrange and below, the second harmonic predominates. For high SPL applications, pairing the speaker with a subwoofer would likely yield better results. Above approximately 600Hz, harmonic distortion becomes almost negligible, to the point of being virtually unobservable. Despite concerns about the tweeter’s behavior due to the low crossover point, it performed flawlessly, demonstrating incredible robustness.
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95dB SPL (@1m)
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Multitone Test
There is a noticeable rise in distortion just before the crossover frequency. Beyond that, the performance of the tweeter’s range is highly impressive.
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Compression Test
Compression performance is also exceptionally stable.
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Deviation Between Two Samples
The deviation measurements are based on the data from the pair provided by the individual owner.
Aside from minor sensitivity differences, the speakers demonstrate an exceptional level of pair matching, pushing the boundaries of what is achievable in passive speaker design.
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The most remarkable aspect of the C5B is its ability to maintain impressively low distortion levels despite lowering the crossover point between the woofer and tweeter to around 1.1kHz. This achievement is a testament to the thoughtful design. It’s a true triumph of engineering.
! Do we know price and date for worldwide availability yet, 
