Testing on the Polk Audio HTS 12 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.

The above graph shows the measured frequency responses for the HTS 12 subwoofer. This response isn’t ruler flat like we normally see in pricier subs, but it is in line with other subs we have looked at in its price class. Getting a totally flat response is nice, but it does all get ruined once the subwoofer is placed in any normal-sized domestic room since room modes will completely mangle the response. That being the case, the response shape shown here is just fine for practical purposes. The room will take its toll, and many users will EQ it after that. In this response, we can see that the port-tuning frequency is a bit under 30Hz, and below that the response sharply falls off. I think that for most users, room gain will shore that response up to at least the mid-20s. This is not the deepest digging sub that we have seen, but this bandwidth will capture the bass in the vast majority of music and most bass in movies. If we assume that room gain shores up a steady response down to 25Hz, that should net a very satisfying bass sound for most people. The HTS 12 doesn’t have a whole lot of usable upper bass extension, and I wouldn’t bother with a crossover frequency higher than 100Hz, although a 120Hz crossover would probably work ok with some equalization if it was needed.

The 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. While the HTS 12 doesn’t really try too hard in deep bass, it makes up for that in mid-bass power. The burst output shown here is well above average for this segment. From 50Hz to 100Hz, the HTS 12 averages 111dB, and that is an impressive amount of punch. 103dB at 31.5Hz and 107dB at 40Hz are also quite competitive for this segment. One notable attribute is that even though THD plus noise is significant at 21.5% at 31.5Hz, it tops out at that point, and it cannot produce any more distortion than that. From 31Hz and above, the HTS 12 does not surpass the CEA-2010 distortion thresholds. At 40Hz and above, it can barely be pushed above 10% THD which is very clean for a maximum drive level. You can push this sub hard and it does not lose control. The DSP is likely tightly regulating the type of signal that the amp is sending to the driver. The goal here is not just to have a clean, undistorted sound; since Polk makes so many of these things, they are keeping the driver on a short leash, because it would be very bad news for them if they were experiencing widespread failures when they are manufacturing thousands of these.

This burst test data places the Polk HTS 12 solidly in Audioholics’ Bassaholic ‘Medium’ Room Rating, meaning it should be able to handle a room of 3,000 cubic feet. For information on how the room ratings are determined, please read our article “Bassaholic Subwoofer Room Size Rating Protocol”.

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 HTS 12 is capable of. This is a respectable showing, with the HTS 12 maintaining a long-term 105dB from just above 40Hz to 100Hz. At the highest drive level, the response does become rather peakish as output below 40Hz compresses, but that only happens in the last 5dB of output. The HTS 12 holds its response shape very steady until that point.

The response shape has indications of induction affecting the response. 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. It is usually characterized by a peak in the response somewhere from 50 to 70Hz, lowered upper-frequency sensitivity, as well as a steady rise in even-order harmonic distortion products with increasing amplitude. Higher-end subs employ short-circuiting rings (frequently called ‘shorting rings’) in the motor to short out the induced current, but we don’t see shorting rings used often in subs of the HTS 12’s price range due to the increased cost. If Polk had used a shorting ring in the HTS 12 driver, we might have had a flatter response overall with more upper-bass sensitivity albeit with reduced output at the ~50Hz peak seen on this graph.

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 shown here are mostly good and are what would be expected based on the previous performance date shown for the HTS 12. At nominal drive levels, the distortion is extremely low for the HTS 12. In fact, much of the increase in deep bass at the lowest level sweep shown here, the 95dB sweep, is mostly environmental noise rather than distortion from the sub itself. At this level, we are looking at 1% THD from 40Hz and above. Even if you blast the sub to its absolute maximum drive level, THD cannot be pushed past 10% above 40Hz in long-term signals. One thing we can see from this graph is that the port tuning frequency seems to be 25Hz; the dip in distortion at 25Hz shows where the port is restricting the driver’s motion most effectively. At higher drive levels, distortion skyrockets below 25Hz. However, it should be kept in mind that output is also plummeting fast, so the overall distorted sound being produced by the sub is also at a much lower level and is thus less audible. In my testing, this sub was well-controlled and refused to be pushed into making a nasty sound. The HTS 12 is really only concerned with 25hz and above, which is a very reasonable compromise to make for a sub of this class and price range.

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.

We can see from the above graphs that the distortion seen on the THD plots is largely composed of even-order products. Some of the even-order products stem from induction effects, but the lower frequency rise is much more likely due to excursion strain in the magnetic field and/or tension in the suspension. The good news is that even-order products are less audible and less objectionable than odd-order harmonics, and the HTS shows very little odd-order distortion products above 25hz. One reason why I didn’t really notice any nasty noise from the HTS 12 in outdoor testing is because even-order distortion is just less obvious and dissonant sounding than odd-order distortion. Unfortunately, having the total distortion being dominated by even-order products also means that there might have been a chance to increase total clean output a bit more since even-order distortion indicates that something was only hindering one side of the cone’s travel. It’s possible that Polk decided to give up a little bit of Xmax in favor of having even-order distortion being the dominant type on account of its less offensive nature.

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.

The HTS 12 puts up a good showing here and never even crosses over the 1 cycle mark until well under its port tuning frequency. There is a pipe resonance spike at about 180Hz, but that would be totally filtered out using any normal crossover frequency to the main speakers. The stricter 20ms threshold isn’t crossed until just above 30Hz, a fairly deep frequency and unlikely to lead to any audible artifacts, even in the most critical listening environments. In short, anyone worried about any problems in the time-domain shouldn’t be concerned. I didn’t hear any problems in my listening sessions, and, seeing this graph, I wouldn’t have expected to.

Conclusion

if you are looking for a clean undistorted sound in music range frequencies, the HTS 12 has your ticket.

Before bringing this review to a close, I will briefly go over the strengths and weaknesses of the product under evaluation, and, as usual, I will start with the weaknesses. When taking the pricing into consideration, I don’t see many weaknesses with the HTS 12, and it does a lot of things right. However, if you are looking for a subwoofer that digs down into extremely deep frequencies, this one doesn’t do that. It does dip into the mid-20Hz region with some power, but it is completely out of steam below that point. That isn’t a bad trade-off though, since to even break into the 20s is fairly deep bass, and it does capitalize on its lack of infrasonic bass extension by providing more dynamic range in regions that are a lot more audible, i.e., 30Hz and above. Nonetheless, buyers who are looking for a sub that has serious output in extremely deep bass for a dedicated theater room should probably be looking at other models. Most of the other subs that we have looked at in this price range had a bit more low-frequency extension than the HTS 12. There is no doubt that it digs deep enough for most people’s tastes, but home theater enthusiasts will want something with more potency below 30hz. On the other hand, they would probably be looking to spend a lot more than $550 on a subwoofer anyway, so the HTS 12 wouldn’t even enter into consideration for them.

Some potential buyers might criticize the HT2 12 for having a lack of amplifier features such as app control or EQ functions, but much of that stuff is better done on the AVR or whatever device is controlling the sub rather than the sub itself, so I don’t regard its sparse feature set as a con but rather just not a pro. That sort of stuff is nice to have but not at all necessary.

There isn’t much else that I can think of that the HTS 12 could be faulted for, so let’s now go over its strengths. In my view, its foremost strength is its overall performance. Above 30Hz, it packs a punch, maybe as much as can be had at its pricing for a home audio subwoofer. 110dB at 50Hz and above in burst testing is excellent for this segment. It proved to pack a major punch for music and had some real muscle for movie content as well. What is more is that it produces very clean bass too. The HTS 12 did not produce much distortion above 40Hz, so if you are looking for a clean undistorted sound in music range frequencies, the HTS 12 has your ticket. At the highest drive levels, it could generate some distortion at 25Hz to 35hz, but even then, it was fairly well controlled and is comprised of less audible even-order distortion products. So even when this sub is pushed hard, it manages to keep its cool. It cannot be pushed to a level that would endanger it, and its self-protection is rock solid. Its time-domain behavior is good for a ported sub, and the HTS 12 won’t sound laggy or sloppy at all.

Outside of its performance, this is one of the nicest-looking subs within its price range. It is stylish without being garish, which is a real feat for a low-cost subwoofer. Polk’s industrial design is usually pretty good, and the HTS 12 is no exception to that trend. It is unlikely to garner complaints about its appearance from anyone but the pickiest aesthetes. Its build quality is well above the norm for this price segment as well; it has multiple internal windowpane braces, a very serious port, heaps of acoustic stuffing, and a substantial base for the enclosure. That mass can be felt in its 50lbs., which makes it one of the heavier subs in this class. 

In the end, I would say that the HTS 12 is a solid choice for the money. It has been out for a little while now, and much of the customer feedback for it has been very positive. I can see why people like it so much. It’s a well-rounded and well-executed sub from Polk that doesn’t really cut any corners which is surprising given its pricing. It’s good for movie watching and terrific for music. I think that a lot of people looking for a simple, nice-looking sub for their family room are going to be surprised at the performance it offers. I also think that those audio aficionados who would dismiss a subwoofer from a major manufacturer like Polk don’t really have any ground to stand on with the HTS 12. Its overall performance is too good, and it doesn’t have any significant shortcomings for its cost.