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Klipsch Reference R-121SW Subwoofer Measurements & Conclusion

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R121SW outdoor testing

Testing on the Klipsch R-121SW was conducted with the microphone facing the woofer at a 1-meter distance with measurements scaled back to a 2-meter distance by subtracting 6dB. The temperature was recorded at 59F degrees with 70% humidity. The subwoofer’s gain was set to maximum, phase was set to zero, and the low pass filters were set to bypass.

R121SW Frequency Response 

The above graph shows the measured frequency responses for the R-121SW subwoofer. This response was produced by measuring the rear of the sub at 1 meter and the front of the sub at 1 meter and then averaging the two responses. A single measurement of either side doesn’t wholly capture the amplitude response of this unit. This is not quite the ruler-flat response that we see on more expensive subwoofers, but then this is not a tremendously expensive item. But those who are worried that it is not ruler-flat shouldn’t be; typical room acoustics pretty much make low-frequency ruler-flat responses a moot point since room modes will mangle the response anyway hence the need for equalization even for the most linear subwoofers. The response here centers around a broad peak at about 53Hz and has a gradual rolloff below that point down to the port tuning frequency. Below that point, the roll-off becomes steeper like we would expect to see from a traditional ported response. At about 16Hz and above, the response resembles that of a sealed sub. It looks to me like the port is more being used to reduce distortion and protect the woofer rather than giving the low-end of the response a big boost like in other ported subwoofers. The shallow low-end response should lend itself to pressure vessel gain which shores up the lower frequencies in an in-room response. Pressure vessel gain can give a very significant boost, especially in small to medium-sized rooms. This sub isn’t really made for large rooms, so this type of response is a good trade-off. This sub has a relatively low tuning for its size, but I guessed that we would see such a low tuning frequency by looking at the dimensions of the port. The upper-frequency extension is ok and we do get usable bass all the way up to 200Hz for those who want to use crossover frequencies higher than the standard 80Hz.

R121SW CEA2010 table

bassaaholicThe above CEA-2010 measurements are short-term bursts that show the subwoofer’s clean peak SPL before heavy distortion sets in. Our measurements have been referenced to 2-meter RMS, which is 9dB down from the standard requirement for the measurements to be shown at 1-meter peak. However most publicly available CEA-2010 measurements are shown at 2-meter RMS, so we followed that convention. What we see here is a healthy and respectable set of measurements for a small ported 12”. I was surprised the R-121SW could net a passing measurement at 16Hz, but it did, although just barely. The burst output trends generally follow the base frequency response with most output hovering between 50-80Hz with a gradual rolling off above and below that range. While the mid-bass region is about what I would expect, this sub has more lower frequency oomph than I would have expected with 93dB burst output at 20Hz and 95.4dB at 25. That does show that the deep bass that I heard when watching “MoonFall” was not just my imagination. The above measurement set technically would get this sub our Bassaholic’s ‘Small’ Size Room Rating, but since it only misses the 31.5dB threshold by 1dB, and since it is highly protected from being overdriven, I am going to give it a ‘Medium’ size rating, meaning it should be sufficient for a room of 1,500 to 3,000 cubic feet. While it’s not a THX Reference-level barn burner, I think most people would be pretty happy with its output in a medium-sized room. For information on how the room ratings are determined, please read our article “Bassaholic Subwoofer Room Size Rating Protocol”.

R121SW comp sweeps2 

Testing for long-term output compression was done by first conducting a 20-second sweep tone where 50Hz hit 90 dB with the subwoofer 1 meter from the microphone (graph has been scaled to 2 meters for easy comparison with our other review measurements). We then conduct further 20-second sweeps by raising the gain by 5dB until no more output could be wrung out of the subwoofer. These tests show us the long-term continuous headroom that the R-121SW is capable of. Eagle-eyed readers will note that the nominal response shapes in this graph do not match that of the base frequency response that we posted above, and that is because this is taken at 1 meter from the woofer only, and this does lose quite a bit of port contribution to the output. There is a bit more deep bass headroom from the R-121SW than what is shown here, and what is missing would mostly be between the range of 13hz to 28Hz. Pulling the microphone back from the sub further would have yielded a response with more port contribution, but it would also have raised the noise floor of the testing conditions, and since this sub doesn’t have a huge amount of headroom, we opted for a lower noise floor.

With some deep bass headroom missing from this graph, I don’t want to offer too much commentary in that region since it would be speculative. What I can say is that the R-121SW has a healthy amount of mid-bass, surpassing 105dB from 45Hz to nearly 80Hz. That isn’t bad at all, and this little ported 12” can throw a nice jab. Compression doesn’t really alter the response shape until the last few dB, so this sub should mostly retain the same tonality from low drive levels to high drive levels.

R121SW THD 

The above graphs show the corresponding total harmonic distortion to the long-term output graphs. Essentially, they depict how linear the subwoofer remains for the corresponding drive level seen in the long-term sweeps. The quantity being measured is how much of the subwoofer’s output is distortion and is shown here as a percentage. The results seen here are good for the class and pricing. Distortion stays below 10% above 45Hz even at the maximum drive level. In other words, this subwoofer has fairly clean mid-bass output even if you push it hard. At the highest drive level, meaning the last few dB that the R-121SW can produce, distortion does rise in the low end below 40Hz, but unless you push this sub to its absolute limit, it stays very well composed and largely keeps at or below 10% THD. The bass here is unexpectedly clean for a subwoofer of this size and pricing. In my outdoor testing for this sub, I noted that it was highly restricted from producing any kind of heavy distortion. It’s difficult to get this sub to make a bad noise; the rise below 40Hz is mostly comprised of the least audible distortion products and while they can be heard, they are not terribly jarring or dissonant. The driver doesn’t lose its composure, so the R-121SW is on a tight leash and cannot be over-driven.

R121SW 2nd order harm dist      R121SW 3rd order harm dist

The above graphs depict measurements of the constituent harmonics from the long-term output sweeps and are what the total harmonic distortion measurements are composed of for the 2nd and 3rd harmonics. These individual harmonics can give us a clue as to what might be the cause of some quirk or non-linearity. We are only showing the 2nd and 3rd here because they more or less reflect the higher even-order and odd-order behaviors, although higher-order harmonics tend to be much further down as a percentage of distortion compared to the second and third.

Here we can see that most of the distortion products of the R-121SW are even-order. The advantage to this is that even-order is less audible or objectionable than odd-order distortion products. The disadvantage is that it means that only one side of the driver’s motion or the signal waveform is being constricted or affected. And that means that there was probably an opportunity to iron out whatever was causing the distortion for more undistorted output. In the case of the R-121SW, I would guess that much of the even-order distortion is caused by induction effects. Induction occurs when the charged voice coil’s motion in the magnetic field creates a counter-current, but the problem is that the counter-current creates an opposing magnetic field that diminishes the initial, desired field. Induction tends to be a source of even-order distortion as well as a peakish frequency response as we see in the R-121SW. Many drivers use short-circuiting rings (often just called ‘shorting rings’) in the motor structure to address this, but it is more expensive to implement shorting rings, and I am not surprised that Klipsch decided to do without them in this lower-cost model. Shorting rings aren’t really needed for the distortion exhibited here since it is mostly at very low levels and also is of a more benign type. The rise in second-order distortion below 40Hz at the maximum drive level isn’t coming from induction but is more likely due to the moving assembly running into motor or suspension travel limits, so the inclusion of shorting rings wouldn’t help in that area. However, shorting rings would help to flatten the frequency response and increase upper-frequency sensitivity, so there are still real improvements that can be had by using them.

R121SW Group Delay2

Group delay is the measurement of how much time it takes for individual frequency bands of an input signal to be produced by the speaker. It can indicate that some frequency components are developing slower than others or are taking longer to decay. It is generally thought that 1.5 sound cycles are needed for group delay to be audible at bass frequencies, although there is an argument that group delay should remain under 20ms to be completely unnoticeable, but that is likely meant for mid and upper bass frequencies.

I have included both port side and cone side measurements since I think that just posting the cone side measurements doesn’t fairly account for all of the group delay that the R-121SW is producing. In general, group delay here is fairly low, so there isn’t enough to worry about either way. With the exception of a pipe resonance at around 150Hz (which is unlikely to manifest into anything audible when using the standard 80Hz crossover frequency), group delay doesn’t surpass 1 cycle at any frequency. Normally, ported subs have a 1 cycle spike at the port tuning frequency where the port resonance lags behind the woofer output, but that isn’t seen here. One reason might be that the port seems underdamped compared to the rest of the response meaning that its output simply is not on the same level as that of the cone output, and likewise its contribution to group delay would also not be as great. Also, Klipsch could have implemented some kind of phase compensation in the DSP to keep group delay in line with that of the woofer’s output- we have seen that strategy employed by some other ported subwoofers such as Monoprice’s Monolith subs. The group delay from the R-121SW is above average, and its time-domain behavior is quite good.

Conclusion

Before bringing this review to a close, we will briefly go over the strengths and weaknesses of the product under evaluation, and, as usual, we will start with weaknesses. In my opinion, the Klipsch R-121SW doesn’t have any particular weaknesses. That isn’t to say it is perfect, but rather it doesn’t fall way short in any particular respect. It is a well-rounded and competent sub. I might complain about the lack of features, but buyers probably shouldn’t expect anything too fancy at its price point. If it did sport any advanced feature, that would come at the expense of some other aspect of the sub to maintain the same price point, and that isn’t a worthwhile trade-off for what it is trying to be. The chief weakness of this product doesn’t really lie in the product itself but rather in its MSRP. We will get back to that after we address its strengths.

 Klipsch badge

the R-121SW is that it does dig a bit deeper in frequency than what would be expected of a sub of its size and pricing.

While the R-121SW doesn’t have any real weaknesses, it doesn’t have any aspect that makes it outstanding either. It does have a few attributes that are above average, however. First of all, the electronic limiter does a great job of keeping the driver out of trouble. This sub is bulletproof and cannot be over-driven. If you like to blast your equipment hard or if you want it protected from those who will blast it hard, the R-121SW will survive that kind of abuse, at least for a little while. Of course, it’s not a good idea to blast it hard all the time, and that kind of use surely would lead to a premature failure, but if you have a moment of lapsed judgment and decide to see how loud it can get, the R-121SW will not self-destruct

Another strength of the R-121SW is that it does dig a bit deeper in frequency than what would be expected of a sub of its size and pricing. The trade-off is that it doesn’t get tremendously loud, but that can be compensated for by purchasing multiple units. You can always increase dynamic range by buying more subwoofers, but you cannot increase low-frequency extension by adding more of the same sub. I am guessing that most people will be purchasing this subwoofer for home theater applications, and in that respect, the exchange of dynamic range for deep bass was a wise one.

In addition to its better-than-normal extension, the R-121SW also has very good time domain performance. This sub isn’t slow or sloppy. Many ‘big box’ store brands such as Klipsch take flack for somehow not having ‘tight’ bass, but that just isn’t the case with the R-121SW. This can be seen in the group delay measurements, and it was what I heard in my own listening. This sub can sound good if any care is taken in its calibration. I would love to see what would happen in a blind test between this ‘big box’ store brand sub and any of the pricey hi-fi brands. I think the outcome of that comparison would be surprising. 

Another strength of the R-121SW is its size. This is the smallest ported 12” subwoofer that I can recall seeing. There is a sacrifice that must be made to achieve its size, and that is dynamic range. This goes back to an axiom in loudspeaker design, ‘Hoffman’s Iron Law’ which roughly states that there will always be a trade-off between small size, wide dynamic range, and low-frequency extension. Physics dictates that an increase in one of those elements necessitates a reduction in one or both of the others. The R-121SW balances all three aspects pretty well, but it does go in more for small size and low extension than it does for dynamic range. It’s not a tiny sub, but I think many household members will not be too bothered by its size. 

 R121SW hero2     R121SW grille

The R-121SW doesn’t do anything wrong, but it is up against some stiff competition at its MSRP. Its problem is that there are subs that we recently reviewed that can match or exceed its performance for under $500, namely the RSL Speedwoofer 10S MKII and the BIC Acoustech PL-300. What complicates this is that the R-121SW frequently goes on sale for much less than $500, and when it does, that makes it a serious option in that price range. At the time of this writing, the R-121SW was on sale for $359, and that pricing has to make it the best bang for the buck in subwoofage at the moment. But at its $599 MSRP, it is a tough sell. If you happen to need a sub that isn’t large and has respectable deep bass extension with very good time-domain performance as well as bullet-proof protection from large signal abuse, it would still be extremely competitive, but if you prioritize deeper bass or wider dynamic range, you can get a sub with most of the R-121SW’s strengths for significantly less than its MSRP.  Of course if you're a Klipsch fan building an entire modestly priced Klipsch speaker system, the R-121SW would compliment it nicely.

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
MetricRating
Bass ExtensionStarStarStarStar
Bass AccuracyStarStarStarStar
Build QualityStarStarStar
Fit and FinishStarStarStarStar
Ergonomics & UsabilityStarStarStarStar
FeaturesStarStarStar
Dynamic RangeStarStarStar
PerformanceStarStarStarhalf-star
ValueStarStarStarhalf-star
gimpy posts on January 21, 2023 12:57
FYI, for anyone interested in this sub, Crutchfield has it on sale right now.
Teetertotter? posts on January 19, 2023 15:45
I have had their R-100SW{10"] for 3 years, in my 10 X 12 room. It has been a stellar subwoofer and have the gain turned down, as do not like a whole lot of base, but just enough. At low AVR volume, the base still comes through loud and clear for all movies. Thank you for your review.
shadyJ posts on January 17, 2023 04:07
gimpy, post: 1587369, member: 99846
shadyJ, thx for this review. I just bought this sub on Black Friday (Thanksgiving) at my local BB store at a very good price. It replaced an older DIY sub that I built several years ago (a Dayton 15 inch woofer in a sealed 20" square box) with a 250 watt (I think) amplifier. Any way, I don't think my sub had been working the last couple of years (this was confirmed when I hooked the Klipsch up and it started rattling the house).

I have a mixture of a 5.1 speaker setup and was wondering what you had your gain set on the back of the sub? I initially set it halfway. That is when it really rattled the house making the wife complain about it. I have run audessey a few times since and have gotten the gain at —7.5 readout on my Denon avr. So, just curious what your gain was set at.

When I ran an spl meter, I was getting quite a bit lower dB readings than the 75.(in the 60's). Would you suggest using the audessey settings, or running the test tones using my spl meter and raising the gain/dB levels?
I would appreciate any answers you could/would give me.
Thx.
Markers on the sub's volume dial are almost arbitrary and don't usually mean anything specific, unless you have a sub that has a gain tied to some reference point like THX. I don't remember what I had the gain set at. If I were you, I would just use Audyssey to set the levels initially, and then adjust the gain from there to where ever you think it sounds the best. The bass level is a matter of personal preference, so there is no right answer here unless you are just going after a level-matched setting with your speakers for the most accurate sound.
gimpy posts on January 16, 2023 23:44
shadyJ, thx for this review. I just bought this sub on Black Friday (Thanksgiving) at my local BB store at a very good price. It replaced an older DIY sub that I built several years ago (a Dayton 15 inch woofer in a sealed 20" square box) with a 250 watt (I think) amplifier. Any way, I don't think my sub had been working the last couple of years (this was confirmed when I hooked the Klipsch up and it started rattling the house).

I have a mixture of a 5.1 speaker setup and was wondering what you had your gain set on the back of the sub? I initially set it halfway. That is when it really rattled the house making the wife complain about it. I have run audessey a few times since and have gotten the gain at —7.5 readout on my Denon avr. So, just curious what your gain was set at.

When I ran an spl meter, I was getting quite a bit lower dB readings than the 75.(in the 60's). Would you suggest using the audessey settings, or running the test tones using my spl meter and raising the gain/dB levels?
I would appreciate any answers you could/would give me.
Thx.
XaVierDK posts on January 14, 2023 01:37
It's always great to see more budget-oriented options under review. Both because they're what most of us will end up buying anyway, but especially because it's a great eye-opener for people that good sound isn't necessarily prohibitively expensive, and it's a category where more interesting compromises are made to ensure value and performance targets match.
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About the author:

James Larson is Audioholics' primary loudspeaker and subwoofer reviewer on account of his deep knowledge of loudspeaker functioning and performance and also his overall enthusiasm toward moving the state of audio science forward.

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