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CSS SDX12 Subwoofer Measurements and Analysis


Few reviewers have the technical capability of performing CEA-2010 testing of a subwoofer. The reason for this is clear, you need a lot of expensive equipment and a large quiet outdoor space to take measurements. In addition, you need to know how to process the final resulting data to accurately create the performance metrics. Sadly, because taking the measurements is not all that difficult (including that REW can do this for free), I have found that many have tried their hand at this measurement style and reported misleading or erroneous numbers. To help readers understand the difference between my measurements and those of others, I will provide a quick explanation of my testing procedure, location, and equipment. 

The equipment used for testing includes an earthworks M23 or MicW M215 measurement microphone, an SPL calibrator, a MOTO 828x, Room EQ Wizard on a laptop, numerous cables, the subwoofer under test, and a multi-acre field that is over 1000 feet from any road. In accordance with legacy reporting practices and that of most other official CEA-2010 measurements being published, I will report all values at 2 meters RMS. These values can simply be converted to the CEA standard of 1-meter peak by adding 9dB.

 CSS SDX12 CEA2010 measurements

The performance on this subwoofer is impressive when you consider its size, that it is a sealed box and its price point. Its midbass performance is slightly compromised as compared to its deep bass, but this tradeoff is minor when you consider the large difference in deep bass output and the small difference in midbass output as compared to its commercial competition. One thing to note is that the subwoofer largely fails the CEA burst tone intervals as a result of the more benign 2nd harmonic distortion. It switches to 3rd harmonic in the upper bass, outside its normal operating bandwidth, where the amplifier became an issue. The SDX12 was capable of absorbing a surprising amount of power we suspect a more powerful amplifier may have achieved higher output. 

 CSS SDX12 compression2

The compression test for this subwoofer was interesting. Basically, it didn’t compress. We ran out of amplifier power, and the subwoofer exceeded reasonable distortion thresholds before the subwoofer’s response shape ever changed. Part of this comes from the lack of limiters applied during testing. While I applied limiters to the subwoofer for my use, this is not a feature of the subwoofer, and so we turned them off for testing. 

Looking at the distortion data, it can be seen that THD rises at lower frequencies, as would be expected. Distortion is low in the upper bass range of the maximum output plot. At a maximum continuous output of 109 dB, the point at which we ran out of amplifier power for testing, however distortion below 30hz became unusably high. 

 CSS SDX12 Distortion

Group Delay was commendably low, falling below 1 cycle to well below 20hz. This subwoofer was tested without any EQ to flatten and extend the response, as would be seen in a commercial subwoofer. Adding a filter, as I used in my listening tests, would increase group delay slightly.    

 CSS SDX12 GD curve

One point that I would want to make about this driver is that, for a subwoofer, it has an unusually wide bandwidth. This driver has a smooth and flat response out to 1khz, if not beyond. That is not common. While that is not important for a subwoofer, it means the SDX12 could be used as part of a 3-way or possibly even a 2-way speaker (if the tweeter could be crossed low enough). The very linear motor with very low distortion makes this a good choice for a speaker with subwoofer performance. The biggest problem would be its relatively low sensitivity. 

The measured performance of the CSS SDX12 subwoofer is excellent when you consider its price and size. There are other 12” subwoofers that will outperform the SDX12 in pure output, they will typically be more expensive or ported. The deep bass output of this subwoofer is impressive when compared to the commercial competition. There are very few twelve-inch sealed subwoofers that can achieve this level. Further, moving up to the larger dual passive radiator kit is likely to gain 6-9 dB of additional output below 40hz. Hopefully we can test this in the future. 


CSX BuildIt has long been my dream to be able to directly compare a DIY subwoofer to a commercial offering and see which subwoofer would come out on top. Most of us who like to DIY would like to believe that our home-made custom subwoofers are untouchable for the money, that we would have to spend 2, 3, 4, maybe 10 times more to beat their performance. Recently, I've been lucky enough to test various DIY products against similar commercial offerings and gain a better perspective. In this review of the CSS SDX12, I can say that a DIY subwoofer will provide greater value than a commercial offering, accounting for size and alignment. However, as I noted, the final finished subwoofer is around $1000, and a similar commercial offering, like the SVS SB4000, is around $1500, so our value multiplier is only around 1.5 times. To be honest, that finding is unsurprising and even sobering. That is not a negative for the CSS SDX12 however. The output of this subwoofer allows it to earn the Audioholics Medium room size rating. It comes very close to meeting the large room size rating, falling slightly short at 30 to 40hz. This DIY subwoofer kit still provides immense value, allowing its owners the joy of having produced something great with their own two hands. Further, it provides deep bass performance that is without reproach. In fact, for not much more money than the SB4000, you could build two SDX12 subwoofers powered with a single NX6000D, which would provide as much as 6dB of additional output, clearly outperforming any commercial offering in its price class. Finally, I should note that a dual passive radiator version of this kit is also available for $750. That provides a an even better value. Taken as a whole, while requiring a bit more involved work by the buyer, a CSS SDX12 is a great value and something I would encourage all our readers to consider.

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

  • StarStarStarStarStar — Excellent
  • StarStarStarStar — Very Good
  • StarStarStar — Good
  • StarStar — Fair
  • Star — Poor
Bass ExtensionStarStarStarStar
Bass AccuracyStarStarStarStarStar
Build QualityStarStarStarStar
Fit and FinishStarStarStarStar
Ergonomics & UsabilityStarStarStar
Dynamic RangeStarStarStarStar
About the author:
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Matthew has spent the better part of the last two decades studying acoustics and good sound reproduction. He provides down to earth explanations of complex scientific topics related to audio reproduction.

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Recent Forum Posts:

lovinthehd posts on February 19, 2022 21:54
santodx5, post: 1540894, member: 97965
Please do a DIY NSW 21" devastator review.

Build one, set it up for AH to review, or maybe audiosciencereview or erin's audio corner….
santodx5 posts on February 19, 2022 21:37
Please do a DIY NSW 21" devastator review.

3db posts on February 04, 2022 16:46
Thank you for the write up. Does this kit come up with its own plate amp or do they have recommendations on one.
Verdinut posts on January 31, 2022 16:27
santodx5, post: 1535424, member: 97965
Yes HT and music. I am not confidence with Parts express component. I am looking at the best sub woofer driver!

Btw what app do u use to measure distortion? Any tutorial? I have never done it, I do have smaart for XO/alignment and EQ.

If you are looking for lower distortion, IMO you should build a ported box. Vented designs, as they are more efficient than the sealed type, don't require EQ boost to produce the lower frequencies which increases driver distortion.
lovinthehd posts on January 31, 2022 15:56
santodx5, post: 1535779, member: 97965
HST-18/HS-24 is doable if I use sealed enclosure.

Do you have freq response of above drivers in main listening position or near field?

Try these

Deep Sea Sound offers a finished product, too.
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