DD Audio PM151 Powered Speakers and ABC10 Subwoofer Review

DD Audio PM151 Powered Bookshelf Speaker and ABC10 Subwoofer Introduction

The PM151 5-inch two-way powered desktop monitor speaker system and ABC-10 10-inch powered subwoofer represent a portion of Digital Designs (DD) Audio’s foray into the home audio market segment. DD Audio was established in 1986 and has been building various audio products with a consumer bias toward car audio. Their current product offerings include customizable loudspeaker drivers, amplifiers, signal processors, enclosures, headphones and home audio products. The word on the streets is that DD audio makes good sounding products. We will dig in and find out how their home audio powered monitor and subwoofer fare.

DD Audio PM15S1 Powered Monitors and ABC10 Subwoofer Review

DD Audio PM151 and ABC10 Design Overview

The PM151 system comes with a powered monitor and a passive monitor that connects to the powered monitor’s amplifier using standard speaker wire terminating to 5-way binding posts.  Both cabinets are made of ½-inch medium density fiberboard covered with a nice looking vinyl wrap fashioned after a dark grey brushed metal.  The four edges on the side of the cabinet have a ¾-inch round-over adding to the aesthetics.  There is no additional cabinet bracing but the vinyl wrap seems to dampen the cabinets sufficiently for the small cabinet size.  Acoustic damping material lines the perimeter of the cabinet.  The system is a bass reflex design utilizing a rear firing 1.5-inch port flared at both ends.  The speaker grilles are well secured using hidden magnets.  The drivers are properly flush-mounted and secured using wood screws requiring a hex key for removal.   

The powered monitor has a blue light on the baffle between the woofer and the tweeter that is active when the loudspeaker power switch is on.  Since the size of the amplifier electronics occupy significant volume relative to the cabinet size, I measured the tuning frequency of each monitor using a calibrated RTA system with the microphone placed at the face of the tuning port.  Both monitors had a tuning frequency of approximately 75Hz.  The fit and finish of the loudspeakers are on par with typical studio monitors below $500 per pair.

DD Audio PM151 Crossover and Amplifier

Each monitor has a 2^nd-order analog passive crossover with a crossover frequency of approximately 3 kHz.  The crossover uses polypropylene capacitors, an air core inductor, a solid core inductor and low inductance resistors.  The passive crossover is mounted to the amplifier board on the powered monitor and to the rear side of the cabinet on the passive monitor.

The two-channel 60 watt RMS plate amplifier has 3 switchable inputs including 2 stereo 1/8 inch inputs and 1 stereo RCA input.  There is also an RCA stereo line output that can be used to feed a subwoofer.  The plate amplifier also has a pair of gold 5-way binding posts used to connect the passive monitor to the system.  The amplifier simplifies connection to a subwoofer with an on-board switchable 80Hz high pass filter.  The plate amplifier has a few additional features not typically found on studio monitors including a USB charging port and a 2-prong auxiliary A/C outlet.  Clearly, the amplifier is designed with portable audio devices in mind. 

I have some experience in the pro audio arena and was surprised that the PM151 did not have any balanced inputs.  This is a mandatory feature for pro audio studio monitors.  I experienced substantial noise until I rerouted the cabling between a RME Babyface and the PM151 plate amplifier.  Usually, studio monitors also have low frequency and high frequency trim settings providing a way for end users to dial in the right sound for their room.  From a features and functionality standpoint, the PM151 is best suited for home users.

DD Audio PM151 Drivers

The PM151 is a 2-way design with a 5” woofer and 1” silk dome tweeter.  The 5” woofer has a surface area of approximately 87 square centimeters, which makes it a relatively large 5-inch woofer.  The cone is made out of aluminum with a butyl rubber surround.  The stamped metal basket design was well thought out and executed.  The vented motor system and suspension are typical for a well designed 5” woofer.

  

 PM151 Woofer and Tweeter

The 1” silk dome tweeter is relatively light with a fully enclosed plastic casing.  From looking at the outside of the tweeter housing, there is not much to say aside from the fact that the rear chamber is relatively deep as found on many tweeters with small cutout diameters.  Given the 3 kHz second order crossover point and 1-inch diameter, it should provide ample output throughout its frequency range.

DD Audio ABC-10 Cabinet Design

The Active Bass Circuit 10 inch subwoofer from DD Audio is a perfect visual complement to the PM151 monitors.  The cabinet also uses the metallic looking vinyl finish and rounded edges along the side, like the monitors.  While the subwoofer is not large at 16.93”(H) x 12.64”(W) x 17.72”(D), it is not small sitting next to the relatively small PM151 monitors.  The bass reflex subwoofer design uses two 2.75” diameter ports with a tuning frequency close to 36Hz.  The cardboard port tubes are not flared, however. I was not able to detect any issues related to turbulence.  The cabinet is made of 5/8-inch medium density fiberboard on all sides except the bottom which is 13/16 inch medium density fiber board.  

Internally, there are two window braces used to stiffen the subwoofer cabinet.  However, a knock on the cabinet yields a pretty hollow sound.  The front face of the subwoofer does not make contact with a window brace and it is obvious.  In my opinion, I would have shaved cost somewhere else and used ¾” MDF all around as well as a brace making contact with the front of the subwoofer.  As a nice touch, the subwoofer is secured to the cabinet using 8 hex key screws threaded into hurricane nuts.  The speaker sits on 4 well built spikes that are both attractive and functional.

DD Audio ABC-10 Crossover and Amplifier

I was a little surprised to pull out the subwoofer amplifier and find a massive toroid audio transformer.  I did not dissect the amplifier design but the transformer clearly provides enough of a voltage swing to create the rated amplifier power into a 4 ohm load.  The four 4700uF capacitors, large toroid and bridge rectifier are evidence of a linear power supply.  Compared to the switch mode power supply I expected to find, a linear power supply typically has less output noise at the cost of efficiency.  The amplifier transistors have a large heat sink attached from the back side of the amplifier board.  

 

DD Audio ABC10 Subwoofer Amplifier

The plate amplifier accepts signal from stereo RCA inputs only.  There is no separate LFE channel or any type of balanced input.  The subwoofer has a built in crossover with a selectable frequency range from 30Hz to 90Hz.  The ABC-10 has a 35Hz bass extension switch that increases the output centered around 35Hz.  The subwoofer also has a 2-position phase selection switch and supports signal sensing automatic turn on.  The IEC A/C power socket is fused and the subwoofer accepts selectable 100-120V/60Hz AC or 220-240V/50Hz AC power.  

 

DD Audio ABC-10 Amplifier

DD Audio ABC-10 Subwoofer Driver

The subwoofer driver is a very rigid treated fiber cone with a rubber surround.  The subwoofer motor is vented and allows a relatively long stroke before bottoming out.  The basket is stamped metal but appears to be strong due to the curved under lips and sufficient metal thickness.  Although there is no mention of it in any literature, the subwoofer appears to have a bucking magnet, which is typically used for magnetic shielding.  The woofer resembles some of the woofers in DD Audio’s Redline series but there are definitely some differences in the fit and finish.  However, the primary cone, basket and motor look very similar in terms of material and design. 

DD Audio ABC-10 Subwoofer Driver

 

DD Audio PM151 and ABC10 Setup and Sound Quality Tests

The DD Audio PM151 and ABC-10 were unboxed and set up where they belong, in my small 12’ X 14’ home office.  I spend quite a bit of time in the home office; it is great when I can evaluate a product while getting other things done at the same time.  Since it seemed fitting for studio monitors, I used a RME Babyface as a DAC for all listening evaluations with both a MacBook Pro and Windows PC as sources.  All music tests were run through the MacBook Pro using Audirvana as the source program.  The DD Audio PM151 monitors took the place of a pair of do-it-yourself studio monitors that I have thoroughly enjoyed over the past year.  To contrast, I also have a KRK Rokit 6 G2 limited edition loudspeaker on-hand from a good friend.  

As far as setup goes, the PM151s were placed near the back of my desk approximately 9 inches from the back wall.  They were toed in so that they were directly facing me at my comfortable typing position.  In this configuration, the speakers are approximately 3 feet from my ears.  The PM151s 80Hz high pass filter is engaged and the ABC-10 subwoofer crossover is set to 80Hz with the 35Hz bass boost setting engaged.  A calibrated RTA was used to level match the subwoofer and PM151s.  The volume was set to 100% on the PM151s and the ABC-10 was level matched with the volume control set to approximately 70%.  

DD Audio PM151 Setup

Sound Quality Tests

Evaluating a powered monitor is a little different than evaluating a loudspeaker meant for the living room.  First of all, when I think of the word “monitor,” I think of something a performer uses to hear themselves as they perform.  The term studio monitor describes something designed for engineers to use as they mix music down for broadcast, movies or audio recordings.  The engineer is looking for a studio monitor that allows him to create a single mix that sounds good on car stereos, portable audio devices, boom boxes, over the radio, on televisions and even on hi-fidelity playback systems.  Unfortunately, a good purpose-built studio monitor is not necessarily a good sounding speaker to the average listener.  

The lines are a little blurred in today’s market place because many of the studio monitors found at your local music store are sold to people that are not true recording engineers, but individuals that have a computer, microphone and an acoustically inadequate room.  Most of these individuals would not buy a studio monitor that didn’t sound good to them.  Therefore, the term studio monitor is becoming increasingly ambiguous.  Given this ambiguity, I will gauge this powered monitor system as something that a consumer would purchase primarily for music playback and secondarily for computer activities like video games.

 John Legend – Redemption Song

This song is a great place to start because the bass and electric guitar recordings are excellent while the vocals typically sound a little harsh on systems that have a flat frequency response.  On the DD Audio PM151, the bass guitar sounded pretty right to me in the subwoofer region.  However, above that I felt like the chest thump was missing.  So at this point I turned the subwoofer off and fiddled with the 80Hz high pass switch and found that the bypassing the high pass filter seemed to significantly improve the bass response in a region I would guess is above 80 Hz.  Using the RTA again, I changed the subwoofer crossover to 70Hz which evened out the bass pretty well in-room.

This combination provided that expected chest thump at pretty decent power levels.  I continued to crank the volume and reached a C-weighted slow SPL of 101dB before noticing any obvious distortion.  Enabling the 80Hz high pass filter allowed the system to play a little louder but it is not worth it unless you are hosting a party.  This compact system outputs plenty of power for near field listening for most people that still have normal hearing.  

The bass and lower midrange of this speaker are clear.  However, I sensed a little bit of muddiness in the midrange and treble.  An issue with any studio monitor sitting on a desk is reflections off of surfaces such as the desk, back wall, computer monitor and anything else that clutters your desk.  I placed a four inch stack of CDs under each speaker and felt like this improved the speaker’s response and imaging at my listening position.

While the song now sounded much better, I was not missing the harshness of the vocals in this recording.  This means that the treble region is definitely laid back compared speakers with a flatter frequency response.  To validate this theory, I sampled a few tracks with known annoying high frequency content and was not annoyed at all.  Just to get an idea of how the PM151 sounded compared to a standard monitor, I ran the same test with the KRK Rokit 6 and noticed the same phenomenon when the tweeter level was set to flat.  However, the KRK Rokit 6 has an adjustable high frequency driver so it was easy to make annoying songs sound annoying.  Using the RME Babyface, I added a 2dB shelf filter at 2kHz that clearly added the sibilance I was used to hearing in this track.

Youth Group – Skeleton Jar

While this is a pretty obscure title, I am very familiar with it.  Youth Group released this song in 2003 and it features a pretty real sounding drum kit, clean electric guitar, bass and vocals.  This track is great for testing the midrange and treble balance of a system.  This recording has the propensity to get harsh on many systems.  This harshness comes primarily from a great amount of energy in the midrange and lower treble from the cymbals in this drum kit.  The cymbals have a tendency to just smear into a constant clash that is extremely fatiguing.  

On the PM151 and ABC-10, the kick drum stands out as sounding very real.  The vocals, electric guitar and bass were on point too!  The cymbals and snare, while a little fatiguing, were manageable on the PM151s.  This means, to me, that this system will let you enjoy your music collection without extreme bias toward favorable recordings.  I think this is what the majority of listeners are looking for.  I am admittedly spoiled when it comes to imaging and I cannot say that this system produced much of an acoustic image in this setup.  I didn’t really expect it considering the price point or convenient desktop placement though.

Youth Group - Skeleton Jar

Video Game: Bioshock Infinite

I am not much of a gamer but with a little time on my hands I figured I would give Bioshock Infinite a run and see how gaming sounded on the DD audio system.  One thing is for sure, the audio in video games has come a long way!  This game is set in a fictional floating city in 1912.  The game’s score is original and the sound effects are awesome.  While the imaging of the PM151s was not extraordinary for music, it was easy to locate where enemy gunfire was coming from using stereo imaging cues alone.  The dialog, music and gunplay were extraordinarily immersive and realistic.  It is fun playing video games with a subwoofer capable of reproducing explosions that can scare you when you are not expecting them.  

Overall, game sound translated to feelings as the designers intended.  Much of this is due to the game’s use of and DD Audio’s ability to create a large dynamic range.

Bioshock Infinite Title

DD Audio PM151 and ABC10 Measurements & Analysis

A full suite of measurements were conducted on the PM151 and ABC-10.  The PM151 measurements closely followed the Audioholics Loudspeaker Measurement standard except the amplifier in the PM151 powered monitor was used for all tests.  Loudspeaker sensitivity and impedance were not measured, as they are not relevant for powered monitors.  However, a max sweep test was run to provide the reader with an indication of how loud the system plays.  All tests were conducted with the 80Hz high pass filter turned off and the volume knob set to 100%.  

PM151 Powered Monitor Measurements

DD Audio PM151 On-Axis Frequency Response

The on-axis frequency response above 300Hz was measured with an input signal required to produce approximately 90dB at 1 meter.  The microphone was placed on-axis 1 meter from the loudspeaker at a height that was half of the distance between the tweeter and the woofer.  The low frequency response was spliced into the high frequency response at approximately 300Hz.  The low frequency response was measured using the ground plane measurement technique at 2 meters.

The PM151 on-axis frequency response slopes downward as frequency increases.  The difference between the bass and the 2 kHz to 10 kHz range is nearly 6dB.  This creates a warm sounding speaker.  Since there is nearly a 5dB reduction between 1kHz and 2kHz, this explains my desire to add a few decibels back above 2kHz.  A loudspeaker with a downward slope can still sound great but I believe the magnitude of change between the critical 1kHz to 2kHz is drastic over a short change in frequency.  After analyzing the frequency response I added a -3dB parametric equalizer centered at 700Hz with a Q of 0.7.  This created a more agreeable response for vocals.  That said, this is knit picking an already good sounding powered monitor loudspeaker system that costs a mere $279.  Given the response, the PM151 is definitely geared toward the home user, since this is not a typical response for true studio monitors but rather a pleasing response that does not offend or take too much away from recordings.  

DD Audio PM151 Max SPL Sine Sweep

I ran a max SPL sweep test in-room to get an idea of what this speaker is capable of.  This test was run on-axis at 1 meter with only the powered PM151 monitor.  I increased input signal until the PM151 stopped producing an appreciable increase in decibels.  This response is in-room and includes the effects of room modes and reflections so the roughness in the low frequencies should be ignored.  The output above represents a single speaker.  Mutual coupling of a pair will produce close to 100dB at 1 meter throughout the entire usable audio range of the PM151.

DD Audio PM151 Listening Window

The top listening window measurement is a composite of all of the frequency response at the angles listed on the graph.  The additional responses give you an idea of how the loudspeaker will sound when a listener moves out of the sweet spot.  This includes 15 degrees above and below the loudspeaker.  This can be very useful in helping with desk placement.  For example, you might prefer the -15 degree vertical response meaning you can increase the listening height of the PM151s on your desk and alter the frequency response at the listening position significantly.

DD Audio PM151 Polar Response

Polar response measurements are obtained by measuring the frequency response of a loudspeaker at various points around a circle with the loudspeaker baffle in the center.  This measurement shows the response from -90 degrees to +90 degrees on the circle where 0 degrees is directly in front of the loudspeaker baffle.  Measurements were taken every 7.5 degrees and put together to form the above graph.  The DD PM151 polar response is pretty even out to 30 degrees.  Beyond 30 degrees, the polar response varies significantly with frequency.  Uneven polar response in a reflective room can lead to issues with imaging.  Due to the 500Hz to 1kHz dispersion characteristic of the PM151, I would recommend sitting closer to the speaker and move them as far away from walls and surfaces as practical.  The polar response graph is saying that the 500Hz to 1kHz range is only down approximately 5dB at 90 degrees off-axis, which means a slew of midrange sound is available at the side of the speaker.

DD Audio PM151 Harmonic Distortion

The harmonic distortion graph was generated using a 90dB stepped sinusoid sweep measured at 1 meter.  This test was run from 30Hz to 20kHz.  The PM151 performed well considering the speaker size and price.  The higher distortion numbers in the low frequencies are of little consequence because this speaker is primarily responsible for 70Hz to 20kHz.  The peak in the 3^rd harmonic at 3kHz is notable but not likely noticeable.

DD Audio PM151 Cumulative Spectral Decay

The cumulative spectral decay graph shows how various frequencies die out as a function of time.  A transient perfect speaker would stop playing a frequency the instant the input frequency changed.  Since that defies the laws of physics, we have to give the speaker time to stop moving at a given frequency.  This graph is useful in finding issues with cabinet resonance, etc.  There is a bit more energy in the 500Hz to 1kHz range than expected.  Given the polar response graph in conjunction with this graph, I suspect that the ½ inch MDF cabinet is radiating sound in this range.

DD Audio PM151 Group Delay

The group delay graph shows the rate of change of the slope of a loudspeaker’s phase.  As a rule of thumb, values below 1.6ms in the mid to high frequencies will likely not affect perception of sound quality.  Increasing group delay in the low frequencies is not as objectionable as it is in the mid to high frequency ranges.

 

ABC10 Powered Subwoofer Measurements

DD Audio ABC-10 Crossover Settings Effects

All measurements were conducted at 2 meters using ground plane technique.  The above graph shows the effects of the 30Hz to 90Hz adjustable low pass filter.  The graph shows that the crossover frequency does not really line up with the setting on the back.  A setting of 50% yields a response that should integrate well with the PM151 monitors according to this measurement.

DD Audio ABC-10 32Hz Boost Setting Effect

The ABC-10 subwoofer has a 32Hz bass boost setting.  This setting makes the subwoofers -3dB point below 30Hz and yields a pretty flat response throughout the subwoofers usable range.  Depending on content and room gain, some users may opt to turn off the 32Hz boost.

DD Audio ABC-10 Power Compression

The ABC-10 was subjected to a long-term compression test where long sinusoid sweeps at increasing power are run through the subwoofer in quick succession.  Immediately following this test, the output is measured again at a nominal output of 90dB.  The ABC-10 performed well and did not show any signs of thermal compression at 90dB.  The thermal compression test shows how the output response varies as a function of sound pressure level.  The ABC-10 was able to output just over 105dB at 50Hz.  Adding input that should result in 110dB generated additional output below 30Hz but was unable to increase the acoustic output above 30Hz.  Therefore, the maximum power sweep generated nearly 100dB at 30Hz and over 105dB at 50Hz.

DD Audio ABC-10 Harmonic Distortion at 90dB

The ABC-10 subwoofer harmonic distortion at 90dB is low remaining below 4% across the entire audio range.  The ABC-10 performance related to harmonic distortion is excellent.

DD Audio ABC-10 Group Delay

The group delay measurement for the ABC-10 was very well behaved. The subwoofer never approached the 1 cycle of delay threshold throughout its usable bandwidth.

 

 

DD Audio PM151 and ABC10 Conclusion

At $279 a pair, the DD Audio Powered Monitor 151 represents a very good value.  They get many things right including good sound, attractive finish and sufficient sound pressure levels for most near field listeners.  The PM151 adds some consumer features including a USB charging port, A/C outlet and easy connectivity to portable devices.  The PM151 does not have balanced connections and I had a hard time with noise where it has not been an issue before.  I was able to solve it but it is just something to keep in mind.  

On the sound quality front, the PM151s sound good with a nice downward sloping frequency response giving them a laid-back sound.  In my opinion, the 500Hz to 1kHz range was a little excessive but nothing offensive.  I preferred the speakers slightly above my ears, which improved things for me.  Ultimately, the sound seems to vary quite a bit based on placement so it should be possible to adjust these speakers to taste.  For the given price tag, they are well constructed and attractive.

The ABC-10 subwoofer plate amplifier and driver are both nice for the $429 price point.  The subwoofer easily keeps up with the PM151s in most rooms so they complement each other well. The ABC-10 cabinet uses 5/8 inch MDF on the front, back, sides and top, which makes it pretty light.  The subwoofer sounds good for music and is a good sound quality match for the PM151.  I never had issues with the subwoofer bottoming out or sounding bad.   

Acoustically integrating the ABC-10 with the PM151 was not as intuitive as the switches would indicate.  I got the best results by turning off the high pass filter on the PM151s and using a RTA to adjust the ABC-10.  Once they are dialed in, they sound good on just about any recording.  The stereo imaging for music was nothing special but I do not know of a $279/pair desktop monitor that has amazing imaging.

DD Audio PM151 (left) and ABC10 (right)

DD Audio PM15S1 Powered Monitors and ABC10 Subwoofer Review

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

• — Excellent
• — Very Good
• — Good
• — Fair
• — Poor

Metric	Rating
Build Quality
Appearance
Treble Extension
Treble Smoothness
Midrange Accuracy
Bass Extension
Bass Accuracy
Dynamic Range
Performance
Value