Testing on the BIC Acoustech PL-300 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 PL-300 subwoofer per its operating modes. While these responses are not the perfectly flat ones that we often see with DSP subs with a finely EQ’d response, there is still a lot to like here considering the price of this sub. Plugging the port maintains a strong response to below 20Hz, especially in the “Max Output” setting. In fact, the “Max Output” with a plugged port is probably the setting that makes the most sense for this sub and is the one I would recommend. The main advantage of this sub is its deep bass extension, and that is what I would try to exploit as much as possible. The PL-300 does have a somewhat peakish response centered at 50Hz, and that combined with a downward slope above that point indicates that the driver is running into induction effects. Induction occurs when the 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. Many drivers use short-circuiting rings (often just called ‘shorting rings’) in the motor structure to address this, but that does add a significant cost increase to the driver, and given the cost of the PL-300, it probably doesn’t have a shorting ring. The addition of a shorting ring would have brought down the 50Hz peak and brought up the reduced mid-bass output above 60hz.

While the sub could have had a tidier response with a shorting ring, the reality is that typical room acoustics will mangle the response much more than induction effects, so it’s not a big deal in practice. Plus, many users will just use an auto-EQ system like Audyssey, which will fit the response to its target curve anyway, so the natural response of the sub is almost a moot point. That being said, those who don’t EQ their subs might be left with softer mid-bass with a traditional 80Hz or higher crossover frequency. As I mentioned in the ‘listening sessions’ part of this review, I initially thought I had a slight phase mismatch due to this response when I measured the room response. What is more, induction effects do reduce overall headroom by making the system less sensitive in mid-bass frequencies, so the PL-300 will run out of steam in mid-bass earlier than if shorting rings had been employed. This can be negated if the user has the option of using a lower crossover frequency like 60Hz as I did.

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. For $450, the PL-300 is putting out some pretty good numbers. Since this is the sub being pushed to its maximum limits, plugging the port is making a much larger difference than the ‘Bass Boost/Max Output’ switch. Plugging the port delivers more headroom at 25Hz and below, but leaving it open delivers more headroom at 31.5Hz and above. With the ports open, the PL-300 struggled at 20Hz and would not post a passing result at 16Hz. If this sub is being used for music, I would run it with the ports open, but for movies with very deep bass, plugging a port would be my choice. We can see that bass above 80Hz is really getting hammered by induction effects, so I would not use a crossover frequency above 80Hz. If the user has speakers with very capable mid-bass headroom then 60Hz might be even better so that the PL-300 is pouring power into ranges where it is most effective rather than dumping power into ranges where it is less efficient. Altogether, these numbers illustrate the trade-offs that are being made with the variable tuning system, and the user can decide where the sub’s strengths should lay.

These burst test numbers make the PL-300 a peculiar sub to assign our Audioholic’s Bassaholic Room Rating. With a port plugged and set to “Max Output” mode, this subwoofer clears our ‘Large’ room rating for deep bass at 25Hz but barely clears the bar for 31.5Hz to 63Hz for the ‘Medium’ room size. That nets this sub a ‘Medium’ room size rating indicating it should be sufficient for strong bass in a room of up to 3,000 cubic feet, although this particular sub will have more deep bass than most subs that achieve the ‘Medium’ room rating. 

We normally post long-term output graphs at this point in our subwoofer review, but the PL-300 wasn’t very happy with being fed with a large signal at very low frequencies. The filters it used were not enough to keep it from bottoming out, so we decided to cease long-term output tests instead of beating the sub to death. The PL-300 isn’t bulletproof from being overdriven like many subs with DSP filters. However, it should be kept in mind that the signals that we send to it come from pro-audio interfaces so they are very high and don’t really occur in normal use. A consumer audio AVR would be hard-pressed to replicate these testing conditions; in fact, I was not able to overdrive it in my listening sessions, and I felt like I throttled it pretty hard in those circumstances. It’s possible that if you played the handful of movies with known high infrasonic signals at full blast, you might be able to get the voice coil former to chatter with the backplate, but if you want totally clean monster deep bass from a subwoofer, you will need to multiply your budget many times over what the PL-300 cost.

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 results shown here are very good. The PL-300 doesn’t even cross below lowest threshold of concern, 20ms, until well below 30Hz, and it doesn’t reach 1 cycle of delay until 20Hz, the lower edge of what is commonly considered humanly audible frequencies. The time-domain performance exhibited much better than what I was expecting given that this is a low-cost subwoofer that is more geared for home theater. I believe a reason for that is the simplicity of the system as a whole; there just aren’t a lot of filters interfering with the individual frequency timings of this sub. We do see a hump that centers around 50Hz, and I think that is at least partly due to inductions effects again. Past research has shown that induction can take a toll on transient performance, and here we see a rise in group delay where the inductance-related peak is. However, it is still so low that this is an academic matter and not one that is humanly audible, so it isn’t anything to be concerned about. Nonetheless, technical improvement in group delay is another argument for the addition of a shorting ring. Port tuning seems to be maybe 18Hz in this tested mode with a port plugged, and that is extremely deep for such a low-cost sub.

Conclusion

Before wrapping up this review, I will briefly go over the strengths and weaknesses of the product under review, and, as always, I will start with the weaknesses, since I am the kind of person who prefers the bad news first. In my view, the PL-300’s most significant disadvantage is its lowered mid-bass sensitivity. Without equalization, the sag in the response above 60Hz could soften up mid-bass content, and that is a very important range for music bass. Even with equalization, there isn’t as much headroom in that range as there is below it, so if you like to blast your system hard, that range will compress before deeper frequencies would. The simplest solution is to just use a 60Hz crossover frequency to the subwoofer. Some people might ask about situations where the smaller main speakers cannot reach down to 60Hz, but in those circumstances, a higher crossover can be used since the PL-300 will still have more mid-bass headroom than a small bookshelf speaker or satellite speaker out below 200Hz.

The PL-300 has other flaws, but I don’t consider them a big deal. The response shape has some peaking at 50Hz, but, as I said previously, your room’s acoustics will mangle the response much more badly than that, so if you care about the response shape, you will end up EQing it anyway. The sub can be over-driven, but that would be difficult to do in normal use. If you played the opening credits of “Edge of Tomorrow” on a loop and set the gain to maximum, you would probably destroy the driver after a while, but short of that kind of use, users need not worry.

There are opportunities for improvement in future editions of the PL-300. As I harped on in the measurements section, the inclusion of a well-placed shorting ring would do wonders for the overall performance of the sub. It would increase mid-bass sensitivity and shore up the response above 60Hz. That would make the PL-300 more neutral as well as give it some more mid-bass punch. It would also improve group delay around the inductance peak, although, as mentioned before, that is more of a technical exercise since group delay is already reasonably good. Something else I would like to see changed is to just remove a port and delete the unnecessary complexity of the variable tuning system, and so eliminate the “Bass Boost/Max Output” switch as well. Optimize the system for a single response, and just play to the PL-300’s strength of lower frequency extension. 

By that same token, moving onto the PL-300’s strengths, I think that its chief advantage is its low-frequency extension. The PL-300 maintains a strong response below 20Hz, and it is almost certainly the only sub that costs less than $500 to do so. The RSL Speedwoofer 10S II manages to get down to 20Hz as a -6dB point, so room gain would likely shore up the low up to have usable output down to 20Hz, but, if you don’t factor in the PL-300’s 50Hz peak, its -6dB point is around 17Hz, at least with a port plugged in “Max Output” mode. That response will catch more deep bass in movies and music that actually have content that digs that low. That makes this a great choice for those who are building a home theater on a tight budget and want to get the deepest bass extension possible for their money.

In addition to its extension, the PL-300 has good output for its size and cost. In burst testing, it was capable of 90dB at 16Hz, 100dB at 25Hz, and 110dB at 40Hz; those numbers are nothing to sneeze at, especially for the pricing. That would be sufficient for most people especially if they are not trying to fill a large room with bass. As I said before, I was running the sub with a pair of powerful $10k/pair tower speakers that were fed with 300 watts of amplification per channel, and at the levels I was listening to, the PL-300 managed to make a positive contribution to the system. While the speakers could probably have left the subwoofer in the dust at higher loudness levels, that didn’t happen in my own listening at medium-to-loud levels. The system as a whole sounded legitimately good, and the PL-300 played a part in that.

On top of the output and extension, the time-domain performance of the PL-300 is good. For the music ranges of 30Hz and above, it does not rise above 20ms, and it only surpasses 20ms below 30Hz which is too deep in frequency to matter for human hearing acuity. In other words, the PL-300 is not a ‘slow’ subwoofer, especially for most music bass which seldom dives below 40Hz.

One application that the PL-300 is uniquely suited for is adding low-frequency extension to a system with tower speakers. Many lower-cost tower speakers only dig down to 40Hz before their low-end rolloff, and even quite a few higher-end towers don’t extend a whole lot deeper. That is enough extension for bass in most acoustic music so the manufacturers are happy with that. For those speakers to chase after even deeper bass requires that they either become a lot less efficient or they grow a lot larger in size, which aren’t trade-offs that the manufacturers are willing to make. Such a system is well suited for the 60Hz crossover frequency that plays to the PL-300’s strengths instead of its weaknesses since those speakers are often very capable in mid-bass ranges. It allows the PL-300 to cover for those speakers’ deep bass shortcomings which it can do very well. The irony is that a lot of loudspeaker manufacturers’ budget subs don’t have much more extension than the tower speakers. The PL-300 is a lot like the kind of subwoofer they should be making to compliment a tower speaker but they so often do not (case in point).

In the end, I liked the PL-300. It isn’t perfect, but its particular strengths make it a strong choice for some very common situations. If you are trying to add some real low-frequency extension to a system that already has good mid-bass performance without spending a fortune, these are a great choice. The PL-300 has ok mid-bass so it can be used with smaller speakers, but its performance from 20Hz to 60Hz is where it shines. With sub-20Hz extension, it can make a sound system be legitimately full-range, and it does so for less than $500. That makes it a very useful tool for a lot of people.  The 5-year amplifier warranty is an unusual, but welcome feature that just sweetens the deal.