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Perlisten D215s Subwoofer Measurements and Analysis, Conclusion

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In order to secure the lowest noise floor for the most precise distortion measurements that we possibly could, we waited for a low-wind night for testing. Testing on the D215s was conducted at a 1-meter distance and then scaled back to 2-meters in our graphs by subtracting 6dB in output. The temperature was recorded at 45F degrees with 70% humidity. The subwoofers’ gain was set to maximum, phase was set to 0, and the low pass filters were left off.

D215s responses.jpg

The above graphs show the measured frequency responses for the Perlisten D215s subwoofer for each of its EQ modes. The “Large Room” mode yields the flattest response and is best used in larger rooms where not much room gain is likely to occur in low frequencies. The THX EQ response rolls off at a higher frequency but also at a more gradual slope, and this might be the best EQ mode for a medium-sized room. The “Small Room” mode is the most typical of a sealed subwoofer and is probably closest to that of the drivers’ native response in this enclosure. In a very large room, the lack of deep bass might be noticeable from this response, hence the need for a “Large Room” mode, but in a small room it should accrue a lot of gain and have a good deal of deep bass output. In all modes, the response stays flat to nearly 200Hz which is good news for those who want to use multi-sub systems to reduce room modes above the standard 80Hz crossover frequency.

D215s max bursts.jpg

CEA-2010 Data for Perlisten D215s (2 meter, RMS)

extremeThe 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 9 dB 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. The D215s’ puts out some massive numbers in this test, as would be expected from a sub of its spec set, but the full story of the sub is not told by raw output but by the measured distortion quantities. It is a sealed sub that can not be pushed past 10% distortion above 20Hz no matter how hard it is driven. It barely breaks 10% below 20Hz for that matter. All of these distortion quantities are well below anything audible, and no other sealed sub that we have tested can match this level of output with such low distortion. Except for the 10Hz measurement, all frequencies were only limited by the amp and not distortion, meaning the subwoofer simply could not touch the CEA-2010 distortion thresholds. Even our 10Hz measurement was limited by background noise rather than harmonics (it is always very difficult to get a passing 10Hz measurement due to environmental noise since the sub’s output at such a deep frequency is usually not very high with respect to the noise floor).

Of course, these numbers easily propel the D215s to our Bassaholics ‘Extreme’ Room Rating meaning it is sufficient to charge a room of over 5,000 cubic feet.

D215s lower level bursts.jpg

The D215s is overall the most powerful sealed subwoofer I've ever tested...

The above measurements show what happens when we turn down the gain a bit. This is a sampling from a few different gain levels. Distortion is phantasmically low. In upper frequencies, the noise floor is running up against what we can record from the sub itself, and the noise was relatively low for a subwoofer testing environment. These are still relatively loud levels, and from a perceptual standpoint, distortion is totally negligible. We posted these numbers to show just how low distortion falls merely by backing off the upper limits of the sub’s performance envelope. All subs have a dramatic decrease in distortion when not pushed to the maximum drive levels, and the D215s is no different, with distortion levels dropping next to nothing, even at these high levels of output.

D215s compression sweeps.jpg

Testing for long-term output compression was done by first conducting a 20-second sweep tone where 50 Hz hit 90 dB with the subwoofer 2 meters from the microphone. We then conduct further 20-second sweeps by raising the gain by 5 dB until no more output could be wrung out of the subwoofer. These tests show us the long-term continuous headroom that the subwoofer is capable of. The D215s is overall the most powerful sealed subwoofer I have tested. Above 40Hz, it can just about put out 120dB continuously. The compressed response shape is slightly altered from the nominal response but not by much for a sealed subwoofer. One thing to note is that the long-term output level does not differ that much from the maximum burst output, and that is very unusual. Most subs are able to produce a lot more output in a brief moment than over an extended period, but the D215s doesn’t vary its output a whole lot relative to the duration of the signal. This means it is more likely to stay true to the dynamic range of the input versus most other subs.

D215s THD 3D View.jpg

D215s THD 2D View.jpg

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. We can see here that the D215s can be made to produce some significant distortion quantities at high drive levels below 20Hz, so the D215s can’t really sustain the ultra-low distortion seen in the burst measurements for long periods of time, however, its distortion output above 20Hz is the cleanest I have seen on any sealed subwoofer and pretty much any subwoofer I have yet measured. At 100dB and lower drive levels, the D215s can’t surpass 5% THD at any frequency. While we have seen examples of subs that can maintain lower distortion below 20hz, the D215s puts up a remarkably good performance level, and it is pretty much untouchable for undistorted sound above infrasonic bass regions.

D215s 2nd Harmonic.jpg  D215s 3rd Harmonic.jpg

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.

The 2nd harmonic is vanishingly low, and we can see that the vast bulk of THD is comprised of the third harmonic. This is strong evidence of the push-pull design’s efficacy which theoretically would greatly reduce even-order harmonics. While odd-order harmonics are more audible in musical content, it is the mark of a balanced design to have primarily odd-order over even-order harmonics, and the reason is that even-order harmonics stem from non-linear motion that only occurs in one-half of the cone’s travel, whereas odd-order harmonics are from non-linear motion that occurs in both directions. When pushed hard enough, a moving assembly will inevitably run into non-linear motion as it reaches the full swing allowed by the motor or suspension. Having very little even-order distortion indicates that measures were taken to keep linear travel as great as possible before the driver inevitably runs into the end of its available excursion.

D215s Group Delay.jpg 

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 20 ms to be completely unnoticeable, but that is likely meant for mid and upper bass frequencies. Regardless, the D215s doesn’t surpass 20ms until below 30Hz where it will be inconsequential. We can see that the response shaping filters do hike up group delay a bit at lower frequencies, but it never comes close to 1 cycle, and the group delay in mid and upper bass frequencies are among the lowest I have ever seen. The time-domain behavior exhibited here is overall excellent.

Editorial Note on Measurements & Further Product Refinements:

Since the time that these measurements were conducted, Perlisten has made further refinements to the DSP control of the subwoofer’s behavior, and, through a firmware update that can easily be performed from their app, have reduced nonlinear distortion even more without sacrificing much output. Additional improvements can be expected throughout the lifetime of Perlisten’s subwoofers as firmware updates continue to fine-tune performance parameters and add features.

Conclusion

D215s angle side 3.jpgTaking stock of the overall performance seen here, I have to ask myself is the D215s one of the most accurate subwoofers that can be had at any price? I would need to test a lot more subs to answer that definitively, but I am leaning towards yes, especially above 20Hz. A subwoofer can only err in two ways with respect to audio performance: linear and nonlinear distortion. Linear distortion is a distortion that occurs independent of amplitude, and in our measurements, that is the frequency response and group delay. The D215s’ frequency response is perfect, and the group delay is terrific, although we have seen some subs with lower group delay below 30Hz and comparably low above that range. Still, for much of the audible bass frequency range, the D215s group delay is as good as it gets.

With respect to non-linear distortion, the D215s offers some of the best performance I have seen in a sealed sub above 20Hz. The only sealed subs that can challenge its distortion levels below 20Hz that Audioholics has dealt with is the JTR Captivator RS1, and even then only in long-term output. Above infrasonic ranges, however, the D215s keeps total harmonic distortion below 10% which is impeccable performance for a sealed sub. We should mention that there are low-tuned ported subs that offer more deep bass output with extremely low distortion levels that pretty much no sealed subwoofer can match, but they tend to be huge, and, as a consequence of their design, group delay will always surpass 1 cycle at the port tuning frequency, although the audibility of that extra group delay is very much debatable (Perlisten feels that having low group delay and time-domain performance is important to ensure fidelity, and this was a serious consideration in their design).

The performance is outstanding, but at $9k for a subwoofer, the user has a right to expect this level of performance. Perlisten delivers, and I suspect that a lot of other subs from high-end manufacturers can not touch this level of performance even for equally priced subs. The D215s enters the strata of audio products where performance is immaculate, much like their S7t loudspeakers, or ultra-low distortion amps such as the Purifi modules or the Benchmark AHB2 or ultra-low distortion DACs with a greater than 130dB range of clean signal output. These are all state-of-the-art products- the very best performance that money can buy for the purpose of sonic accuracy. A system where price is not an object and audio performance is not negotiable could certainly include Perlisten D215s subwoofers. The best of the best is not inexpensive, but the good news is that there are certainly subwoofers that are more expensive than the D215s that would not match its performance. If you want one of the most advanced and accurate subwoofers on the planet per decibel of output as well as per cubic foot of space, the D215s has to be my first suggestion. 

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 ExtensionStarStarStarStarStar
Bass AccuracyStarStarStarStarStar
Build QualityStarStarStarStarStar
Fit and FinishStarStarStarStarStar
Ergonomics & UsabilityStarStarStar
FeaturesStarStarStarStarStar
Dynamic RangeStarStarStarStarStar
PerformanceStarStarStarStarStar
ValueStarStarStarStar
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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Recent Forum Posts:

cutedaddy posts on August 22, 2021 20:08
Tx. Shady
ski2xblack posts on August 22, 2021 19:08
Can't argue against the cold, hard data (thanks for the links, guys!). It apparently works. I have enjoyed what it does in my old M&K sub for years.
shadyJ posts on August 22, 2021 18:43
cutedaddy, post: 1500500, member: 66436
The question that remains object of study in my mind is:

Why, how, and how much, would the ‘RMS’ of non linearities resulting from one forward and one backward movement (w/respect to motor assembly) of two cones, by two drivers simultaneously (and all this twice), be an improvement over the ‘RMS’ of non linearities of one backward and one forward movement of one cone of one single driver (and all that times two)?

Which is what you get when you just put two drivers facing outward, in phase, but sharing the sealed cabinet. So they still moderate each other through their common air spring, just not in push pull.

Do we know a researcher that did AB measurements for both alignments? In an otherwise identical cabinet? Or in two cabinets, where the one with push-pull has a smaller air chamber, as is mentioned in this thread somewhere? (Why would that be, btw?!). Did Perlisten publish anything on that? Any white papers anywhere?
Wayne Parham is the only one that published an actual comparison in this area. One thing Perlisten could do to compare is publish distortion measurements for their single 15" driver sub. If distortion is disproportionately low at -6dB max output versus the D215s, that should be good evidence of the push-pull advantage.
cutedaddy posts on August 22, 2021 17:56
The question that remains object of study in my mind is:

Why, how, and how much, would the ‘RMS’ of non linearities resulting from one forward and one backward movement (w/respect to motor assembly) of two cones, by two drivers simultaneously (and all this twice), be an improvement over the ‘RMS’ of non linearities of one backward and one forward movement of one cone of one single driver (and all that times two)?

Which is what you get when you just put two drivers facing outward, in phase, but sharing the sealed cabinet. So they still moderate each other through their common air spring, just not in push pull.

Do we know a researcher that did AB measurements for both alignments? In an otherwise identical cabinet? Or in two cabinets, where the one with push-pull has a smaller air chamber, as is mentioned in this thread somewhere? (Why would that be, btw?!). Did Perlisten publish anything on that? Any white papers anywhere?
cutedaddy posts on August 22, 2021 17:31
ryanosaur, post: 1500353, member: 86393
I'm gonna take a stab at this in hopes I can be corrected and learn something from my mistake.

If I understand what is happening correctly with this design, one woofer is excusing outwards away from the motor while the second is excursing outwards towards the motor, and it would be in that action which the distortions of the drivers are minimized.

Anybody? Am I getting this?

So actually, in hindsight, that IS right. I just didn't read that correctly. Yes, one is moving outward away from the motor while the other is also moving outward, towards the motor. So moving in phase (with respect to the cabinet, the signal, the soundwave they produce) and out of phase with respect to the direction in which they're facing.

As Watne Parham explains, the assymmetry of the cone movement (different non-linearities on the inward excursion than on the outward excursion) are more or less evened out by making one's backward travel coincide with the other's forward travel and vice versa, with respect to the motor assembly.

So excuse me for interpreting your accurate comment incorrectly.
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