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DD Audio PM151 and ABC10 Design Overview

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PM151 FrontThe 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

PM151 AmplifierEach monitor has a 2nd-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  PM151 Tweeter (small)

 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

ABC10 Cabinet InternalThe 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.  

 ABC10 Plate Amplifier

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.  

ABC10 Subwoofer Back 

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. 

ABC10 Subwoofer Driver

DD Audio ABC-10 Subwoofer Driver

 

 

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Recent Forum Posts:

shadyJ posts on July 14, 2014 22:17
Kudos for using a polar map. The more I learn about polar map charts, the more useful I think they actually are. Here is a informative presentation by Earl Geddes on the matter, who is, as far as I know, the chief proponent of Polar Maps as a measurement of loudspeakers, he gets into polar charts at around 13:00, but you will want to watch it from the beginning for context:
https://www.youtube.com/watch?v=fE2nWVwFT9k&feature=youtu.be
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