MartinLogan Dynamo 800X powered subwoofer

In the late 1980s, when I began reviewing high-end subwoofers, they were big and heavy, difficult to move or find space for in a room. Their controls were always on an inconveniently positioned rear panel, and there were no built-in automatic room-optimization options or parametric equalizers. Velodyne's 105-lb, downfiring ULD-18 ($2570), ca 1989, was typical: Two people were needed to unpack and move it; it was powered by an outboard 400W amplifier, connected inconveniently with a speaker cable and an RCA-terminated interconnect for its servo control; and its controls were on the bottom of the cabinet. Changing its crossover frequency involved soldering new resistors onto a printed circuit board inside the amp.

Since then, subwoofers have become more user friendly. Eight years ago, JL Audio's Fathom f113 offered built-in, automated room optimization activated from a panel on the sub's front. Three years ago, with the SB16-Ultra, SVS introduced its own smartphone app for wireless control of subwoofer settings from the listening-room chair, including room optimization and a parametric equalizer.3 And in 2018, MartinLogan introduced wireless signal connections to eliminate the need for long, costly runs of interconnect from preamp to sub. As I do with any such new technology, I wondered if wireless connectivity would be noise-free and reliable. When MartinLogan's Devin Zell offered a pair of their Dynamo wireless subwoofers for review, I selected the middle model, the 800X, which Zell recommended for my new, smaller listening room.

Wireless subwoofing
The Dynamo 800X weighs 30 lb and has a downward-firing 10" woofer with inverted surround, housed in a roughly cubical (13.7" high by 12.4" wide by 13.1" deep) enclosure, cross-braced to tame cabinet resonances. Its feet, attached by screws, can be moved to another surface to transform the 800X to a front-firing sub, the latter orientation useful for installation in a cabinet. Its built-in class-D amplifier (300W RMS, 600W peak) employs MOSFET transistors controlled by a proprietary inverse mathematical equalization (IME) filter to deliver more accurate low-frequency response.

The 800X receives its line-level signal from the preamplifier via MartinLogan's optional SWT-X wireless kit ($199.95), which includes a transmitter and a pre-paired receiver that plugs into a large port on the 800X's rear panel; its 50' range of operation doesn't require line-of-sight positioning.

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Setup is managed with ML's Subwoofer Control App, free from the online Apple and Google Play stores. Clicking on the appropriate icon opens a Discover page that detects any nearby ML Dynamo subwoofer, sets its output level, offers various listening modes (Movie, Music, Night), and sends to the sub's drive-unit a test tone that sweeps from 20 to 120Hz. The sweep can be stopped at a particular frequency to investigate and identify a source of unwanted vibration in the room.

Also available is the new Anthem Room Correction (ARC) Mobile app, which provides automatic room optimization for the 800X. This prompts the subwoofer to generate beep tones, records low-frequency room-response data, compares them to stored optimal response curves, and adjusts the sub's output to reduce room-specific anomalies. ARC can be run via a Bluetooth (smartphone) or USB (PC) connection. I used my iPhone's built-in mike.

Because those two apps include most of the 800X's controls, the sub's rear panel has only an IEC power inlet, two unbalanced input jacks (RCA), an LFE input (RCA), a power-on status LED, a 5–24V trigger jack, speaker-level inputs, a toggle for App or Local control, a Micro-USB port for firmware updates, and ARC, a large port for the SWT-X wireless receiver module, and a level control.

Setup
The Dynamo 800X's small size and 30-lb weight made it easy for me to carry the two of them, one at a time, up two flights of stairs to my listening room. And the rubber-tipped feet that cover the spikes meant that I didn't have to use Super Sliders to protect my listening room's hardwood floors.

The 800X was designed to be used with an audio system's main speakers running full range, which explains its lack of a built-in high-pass filter. However, I used Quad ESL-989 electrostatic loudspeakers for this review because their limited deep-bass response and dynamic range can be augmented by subwoofers. In addition, sustained pedal chords from pipe organs and bass-drum whacks can overload the Quads' electrostatic panels and trigger their protection circuits. To avoid this problem, I limited their bass excursion by using the high-pass filter in JL Audio's CR-1 external electronic crossover.

Setup was aided by the 800X's instruction manual and by ML's excellent video tutorial, "Subwoofer Setup & Optimization." I recommend this video, though my own setup differed: I used the JLA CR-1, and measured SPLs and the room's frequency response. (See sidebar, "Using the MartinLogan Dynamo 800X with an External Crossover.")

The next step was to pair the Dynamos' wireless transmitters with the corresponding receiver modules, to establish the subs' wireless signal connections. LEDs on the transmitter and receiver modules slowly flashed red while linking, then a steady green when paired. The right-channel transmitter and receiver paired immediately; the left-channel kept blinking red, refusing to pair, though I tried all possible configurations. Devin Zell sent me a replacement wireless kit, and that paired instantly. I was very glad that the wireless receiver wasn't hardwired to the 800X, as it is in some other subwoofers.

It was time to check the wireless connections. Try as I might, there was no sound. Re-reading the manual revealed a switch on the rear panel that selects between App and Local control. Toggling the switch to App woke up the Dynamos, after which the Subwoofer Control app quickly detected both 800Xes.

I moved the two 800Xes into my room's front corners, one next to each Quad speaker, and played through both "Cosmo . . . Old Friend," from James Horner's film score for Sneakers (CD, Columbia CK 53146). I used this track's endlessly repeating bass-drum beat to optimally set the phase and the physical distance of each sub from its corner, one sub at a time, listening for the drum beat while adjusting the app's phase control between 0° and 180°—the latter position produced the loudest bass. To determine the subs' optimal positions, I moved each a short distance out of its corner on the diagonal, equidistant from the front and sidewalls, listened, then pulled them out a bit more and listened again. About 2' from the room's corner to the sub's rear panel, the drum beat became solid, heavy, and loud. That's where I left them.

I then ran the Anthem ARC app's wireless, semiautomatic room-analysis and -correction routine, beginning by pointing my iPhone's mike at the sub to be optimized and tapping the Continue button on the phone's screen. This caused the sub to generate five two-second beeps. This was then repeated at four other positions. The app then averaged the five room measurements, calculated corrections to the sub's output, and transmitted them wirelessly, one sub at a time.

The ARC Mobile app now run and shut off, I restarted the Subwoofer Control app, to match the output levels of the subs and Quads. Playing a digital file of uncorrelated pink noise, I adjusted the preamplifier's volume control until each Quad delivered a sound-pressure level of 75dB at my listening chair. I switched off the Quads, then turned on the subs and used Subwoofer Control to adjust the sub's output to deliver an SPL of 75dB. For all measurements, I used the SPL Meter module of Studio Six Digital's AudioTools (v.10.5.6) in conjunction with their iTestMic, a professional-grade test and measurement microphone for iPhones.

COMPANY INFO
MartinLogan
2101 Delaware Street
KS 66046
(785) 749-0133
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COMMENTS
gcvanwinkle's picture

I found this information from Harman interesting:

https://www.harman.com/sites/default/files/multsubs_0.pdf

I'm planning on implementing a two subwoofer setup with subs on opposites sides of the room as shown in the document

GC Van Winkle

Bogolu Haranath's picture

Stereophile 2008 article 'The science of subwoofing' by DO is also helpful ....... Everything you always wanted to know, but were afraid to ask :-) ..........

Bogolu Haranath's picture

If the loudspeaker manufactures incorporate powered subwoofers like the GoldenEar Triton Reference (Stereophile Class-A full range), it would be a good idea :-) ........

larrylgreenhill's picture

Thanks to GC Van Winkle for alerting me to the excellent slide lecture from the Harman engineer.

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