MartinLogan Perfect Bass Kit (PBK) Subwoofer Calibration System Review

There are three general methods used, in this order, to achieve improved bass response in a room: proper subwoofer placement, passive room treatments, and active room correction. MartinLogan’s Perfect Bass Kit, or PBK, tackles the last option, active room correction. In some cases, this is the only option because the best placement acoustically for the subwoofer is unacceptable aesthetically. The same goes for room treatments, not everyone wants bulky bass traps sitting in the corners of their room. Even if you do follow proper subwoofer placement and room treatment guidelines, bass response is still likely to need at least some active room correction. While nearly every new AV receiver and processor comes with some sort of automatic room correction system, the quality of said systems is usually severely lacking. For only $100, MartinLogan’s PBK offers an extremely affordable method of achieving high quality active room correction. That’s the idea anyway. Keep reading to see how, and how well, the system works.

Overview

The basic idea behind MartinLogan’s Perfect Bass Kit is to give consumers an accurate, inexpensive, and easy way to automatically EQ their subwoofer(s). For $100, you get a microphone, tri-pod, 2x12’ USB cables, and a software installation CD. If this kit sounds familiar to you, that’s because it’s virtually identical to the Perfect Bass Kit created by MartinLogan’s sister company, Paradigm. Paradigm, MartinLogan, and Anthem are all owned by ShoreView Industries.  Even though the Paradigm and MartinLogan kits perform the same (so, this could also be considered a review of the Paradigm PBK), they only work with the same brand of subwoofer. In other words, the MartinLogan PBK won’t work with any Paradigm subwoofer.

Operating PBK is straightforward, as everything is handled automatically. All you need to do is install the software, plug in the microphone and subwoofer to your computer via USB, and click “measure.” You move the microphone around the different positions in the room, and at each position the subwoofer will output a series of sweeps which the microphone captures. Your receiver and speakers are not even part of the equation. PBK is only concerned about getting a flat frequency response from the subwoofer. After it is completed, you then configure your subwoofer, speakers, and receiver to work in mechanical symbiosis.

In operation, PBK works very similarly to the auto setup systems that are built in to AV receivers, but there are a few key differences that make PBK a compelling purchase.

For example, some auto calibration systems do not actually apply equalization; they only set speaker level, distance, and size. If they do apply EQ, you might not be able to view the results. It’s entirely possible that it could EQ your system to sound worse, or apply too much gain at certain frequencies, causing audible distortion or damage to your gear. Without the ability to see what it is doing, you have no way to find out. Additionally, many auto setup mics that do apply EQ, don’t work with low frequencies.

Results from a very low quality auto setup mic. Blue = before. Red = after.

PBK, addresses all of these concerns. It provides calibration down to 20Hz, which is about the limit of human hearing. You can also view the averaged frequency response before and after calibration; however, you cannot make any manual adjustments. You can also feel safe that it won’t over EQ the subwoofer because it knows the characteristics of the connected subwoofer and limits gain to +6dB at any frequency.

The quality of microphone that comes with auto calibration systems is also cause for concern. A variance of +/- 3dB or more is to be expected. The mics are usually batch calibrated in order to save money, as opposed to individually calibrated to ensure accuracy. Many of them also lack a threaded insert for use with a tripod, making it very difficult to properly position the microphone when taking measurements. With PBK, each microphone comes with an individual calibration file, though we are unsure of the specific tolerance allowed. The mic does not have a threaded insert for use with a tripod, but it doesn’t need one because PBK comes with its own telescoping mic stand. The stand shrinks down to about 22” when collapsed and 47” when fully extended with boom pointing up.

MartinLogan PBK Microphone

The final major concern with auto room correction systems is how many measurement positions they work with. Most take measurements at three or more locations, but if it only takes measurements at a single position, chances are that the results will be very inaccurate.  PBK works with a minimum of 5 positions, and a maximum of 10.

As you can see, there are a plethora of reasons you might want to invest in PBK if you have a compatible subwoofer. If you do own a receiver/processor with a proven room correction system, like Audyssey Sub-EQ HT, MartinLogan recommends that you run PBK first and then run the other system. It’s unlikely that the EQ employed by the receiver/processor will apply much correction, as PBK should already have set the subwoofer as flat as possible. I wouldn’t be too worried about applying too much EQ and damaging the sub, as all MartinLogan subs we have tested are hard to break. That said, it’s certainly possible that any secondary EQ used would try to boost gain too much at certain frequencies, causing the sub to reach its limit early.

Software Installation

Installing the software should be simple for most people. Insert the included CD and wait for the installation wizard to pop up. Once it appears, click “next” a few times and wait for the software and drivers for the subwoofer and microphone to install. While installing the drivers, a “Windows Security” warning may pop up. Select “Install this driver software anyway” to finish up the setup.

         

      Setup Wizard                                       Windows Security Warning

Once the software and drivers are installed from the CD, you need to go to www.martinlogan.com/PBK and check if a newer version of the software is available. If you aren’t running the newest version (the manual included with PBK tells you how to check the current software version), you will need to download and install the most recent version. Why the software doesn’t automatically check to see if you are running the most recent version before installation is beyond me.

Because the laptop I installed PBK on doesn’t have a CD drive, I skipped using the CD altogether and went straight to the website. I downloaded the software, and installation went perfectly, but as soon as I tried to run the program I ran into an issue. The CD contains a mic calibration file that is specific to the microphone that comes with each individual PBK. Without that file, the software will not let you take any measurements.

Oops! That would be my fault

Thankfully, there’s a quick fix to this problem, though it’s not outlined anywhere in the manual. The calibration file can be copied off of the CD and pasted into the PBK program folder (C:\Program Files (x86)\Martin Logan\PerfectBassKit). The next time you try to take a measurement, the software will automatically find the calibration file. This entire rigmarole could be avoided if the missing file warning actually included a hyperlink where the file could be downloaded. OmniMic follows a process similar to my recommendation. By doing everything online, MartinLogan could also save some cost by not including a CD.

Taking Measurements with PBK

Measuring the frequency response of the sub and applying equalization is easier than it is on any other standalone system I have ever used. When the software starts, you can either select “Start a new measurement” or “Open a previous session”. Opening a previous session allows you to load up past measurements to either re-upload to the sub or for reference. After you select to start a new measurement, the software asks how many positions will be used. Next, the software checks for a valid subwoofer, mic, and calibration file. You have to re-select the same calibration file every time you start a measurement. I suppose this is done for users with more than one PBK (or to make testing different mic easy during R&D), but I don’t know why anyone would ever own more than one kit.

Selecting the number of measurement positions

At this point, PBK is ready to rock n’ roll. All you need to do is move the mic to the first measurement location and hit “OK”. The actual measurement process is lightning quick. PBK only takes a few seconds to measure each position and about 20 seconds to calculate the results and upload them to the subwoofer. Once PBK is finished, you still need to set the level, crossover, and phase adjustments so the subwoofer meshes well with your speakers.

After you are familiar with the system, it only takes a couple seconds to launch the software and start taking measurements.

Results

You are nearly 1500 words into the review and have yet to read a single word about how well the system actually works. Wait no longer.

I tested PBK with a MartinLogan Dynamo 1500X placed in the optimal position for a subwoofer in the room. I used my OmniMic system to measure frequency response before and after running PBK.

The image below shows the frequency response averaged across seating locations before running PBK (red), after calibration using the minimum 5 locations (purple), and after using the maximum 10 locations (green). In all of my tests the differences between 5 and 10 measurement locations were subtle. PBK did a great job of getting rid of a huge peak centered at 45Hz, and a smaller dip at about 70Hz. It employed a nice balance of adding and cutting gain to achieve a remarkable +/- 3dB response from about 23Hz to 150Hz. Keep in mind that this is averaged. Some of the individual seating locations do fall within +/-3dB up to about 100Hz, but others are still negatively affected by room modes and nodes that create variances of over 15dB. Adding a second subwoofer would help ensure a more uniform frequency response across multiple seating locations. Note that the before/after EQ curves are offset by several dB, even in the frequency regions where the response shape is identical. I did not adjust the level of the subwoofer or receiver between tests, the difference is from the EQ applied by PBK.

Red - Before PBK; Purple - PBK at 5 location; Green – PBK at 10 locations. 

After testing out PBK under normal circumstances, I wanted to see what would happen if the system was used improperly. I wanted to know if it could be broken. I tried taking a series of measurements at various problem spots in the room (corners + back wall + center of room). I took all of the measurements in the exact same location, so see if it would over correct. Much to my delight, I could not force PBK to make any major mistakes. The graph below is the result of sticking the microphone right in a corner in the room and taking 5 measurements without moving the mic. Sure enough, it made a huge improvement in the frequency response. It didn’t get rid of a node around 23Hz, but I’m not surprised. Adding a few extra dB that low would cause undue strain on the Dynamo 1500X’s amplifier, which, during our review, we found was already heavily equalized to allow the sub to reach down to 20Hz.

Red – Before PBK; Purple – PBK results from 5 measurements at a single location

After I had taken a series of before and after measurements, I compared the results shown in the software versus what I measured. After calibration, PBK shows the measured response before calibration (red), the target curve (blue), and the actual calculated response after EQ has been applied (purple).

There was a significant amount of variance between what I measured and what PBK showed. As you can see in the image below (on the right), the red “Measured” line makes it look like the average frequency response was horrible before EQ. In reality, that is not the averaged response. The program seems to choose the single worst response at any individual location and show that as the before EQ curve.  I sifted through the measurements I had taken before running PBK and found the curve that most closely matched what PBK showed, and used that for the red line in the image below (on the left). The calculated response after EQ also did not quite match my measurements; however, that is partially because I used 1/12^th octave smoothing and PBK displays results using 1/6^th. In nearly every test I performed, PBK claimed to have calculated an almost perfect frequency response. The results below are the worst that I was able to get the software to show me.

I’m not sure exactly what is going on when PBK generates its results, but they do seem to be rather optimistic. Thankfully, my measurements showed that PBK was always effective, even if the calculated line didn’t quite match what I measured.

         

Left – Results window in PBK; Right – Actual measured response in OmniMic

Beyond automatically “perfecting” the bass in your room, PBK has another trick up its programmed sleeve. It has a “Quick Measure” option that allows you to test the frequency response at individual locations. I see this feature being useful in determining the proper location for your subwoofer. There is no way to save the curve for future reference, but you can always do screen capture and save it as an image.

I noticed two anomalies when using Quick Measure. First, it always showed a giant rise in frequency response above the actual response of the subwoofer (see the sudden rise above about 140Hz in the image on the right). Second, it showed the frequency response before calibration, even if equalization was currently being used on the subwoofer.

        

Left – PBK Quick Measure results; Right - OmniMic

Recommendations

The results PBK produced were rock solid, but that doesn’t mean I don’t have some suggestions for future improvements. I had a number of issues trying to get my computer and microphone to play nice. The drivers had trouble installing and the mic kept disconnecting. This is a known issue and something I assume MartinLogan is working on.

Taking measurements and applying correction is very easy, but reading the results was difficult. The Frequency response graph is very small and difficult to read with much accuracy. You can zoom in/out and set the dB and frequency range shown, but doing so is unpredictable as it is controlled via the scroll wheel on your mouse. You can also hold down the left mouse button and drag a box around the area you want to show. Neither method works very well. I would prefer a larger graph and buttons to adjust the response window with precision and in a repeatable fashion. I’m also unsure as to why the Quick Measure results only show pre-PBK results and why the both PBK main and Quick Measure graphs show high output above the 150Hz LPF on the sub.

PBK Screenshot. I think the term “utilitarian” fits well.

I think that those gripes need to be addressed, but the rest of my recommendations would just be bonus. The ability to manually adjust the PEQ (Parametric EQ) using the software, save Quick Measure results, toggle Quick Measure between EQed/non-EQed sweeps, overlay results, and calibrate multiple subwoofers simultaneously, would take the functionality of PBK to another level. You can daisy chain subwoofers together using the RCA or XLR output of the subwoofer (if it has either), but what I am asking for is the ability for the software to manage multiple subwoofers connected via USB and measure each sub separately, then simultaneous, and set the best curve. Besides the software, it would be nice if the actual subwoofers incorporated the ability to choose among multiple PBK results (The BalancedForce subs do have an on/off toggle for PBK) or manually adjusted PEQ. This could allow consumers to easily switch the operation mode of the subwoofer from a preferred Movie mode to a Music mode, or from an EQ for even bass response across multiple seats to one targeted at achieving the best results at a single location. Again, these are not complaints about PBK as it is, these are the cherry on top features that would take it from great to unbelievable.

Conclusion

PBK is, without a doubt, the most accurate and well-behaved room correction system I have used. Quirks aside, like an overly optimistic calculated curve and overly pessimistic measured curve, PBK does exactly what it is supposed to. It will apply an appropriate amount of EQ at the proper frequencies in order to achieve a flat frequency response, without over-equalizing the subwoofer and risking damage. The only reason I could think of to not buy PBK would be if you had a receiver with Audyssey Sub-EQ HT, but even then, I have had better results with PBK. Plus, you can use PBK then Audyssey if you wish. The bottom line is, as of writing this, the least expensive subwoofer that PBK works with is the Dynamo 1500X for $1599. If you are spending nearly two grand on a subwoofer (with tax), you have no excuse not to spend an extra $100 on a product that will almost guarantee noticeably better sound quality from your sub. If you have a compatible MartinLogan sub, go buy PBK. If you are looking for a subwoofer with PEQ/EQ capabilities, but don’t want to try to figure out the best settings yourself, then I would recommend that you consider a PBK compatible subwoofer from MartinLogan, or Paradigm for that matter.