MartinLogan Dynamo 800X powered subwoofer External Crossover

Sidebar 3: Using the MartinLogan Dynamo 800X with an External Crossover

I used a JL Audio CR-1 external electronic crossover because its high-pass filter could be used to protect the electrostatic panels of my Quad ESL-989 speakers from deep-bass pulses. To do this, I connected the line-level output of my Bryston BP-173 preamplifier to the input of a JLA CR-1 with balanced interconnects. Additional balanced interconnects were run from the CR-1's high-pass outputs to the Mark Levinson No.534 power amplifier I used to drive the Quads.

The CR-1's high-pass filter was set to 70Hz/24dB/octave, and its low-pass filter to 150Hz/24dB/octave so it wouldn't interfere with the sub. Then the 800X's built-in low-pass filter was set to 35Hz/24dB/octave.

I played Lyle Lovett singing "Friend of the Devil," from Deadicated: A Tribute to the Grateful Dead (CD, Arista DCD-8669). The bass seemed overblown, with weak pitch definition, and the sounds of the ML subs and the Quads didn't blend well.

I used the Fast Fourier Transform (FFT) module of Studio Six's AudioTools to measure the in-room response with uncorrelated pink noise. I averaged five room responses across a 2' horizontal window at the level of my ears when I'm sitting in my listening chair. The in-room response revealed a stubborn –10dB null centered at around 60Hz. Changing the subs' phase or modifying their built-in "subsonic" filter between 20 and 30Hz didn't fix the problem. I then set both the 800Xes' low-pass filter and the Quads' high-pass filter to 80Hz, based on a recommendation for a starting crossover frequency for subwoofers given me by Revel's Kevin Voecks when he and I set up Revel's Ultima Rhythm2 subwoofer in my old room ($10,000).

VoilÖ! The midbass suckout disappeared, bass extension and soundstage depth increased, and the blend of subs and Quads was smoother. (To protect my Quads, I used this setting for any listening session involving bass-drum passages.) Fig.1 shows the in-room response of the Quad ESL-989s run full-range with the high-pass filter bypassed, fig.2 that of the 800Xes with their low-pass filter bypassed. Then I turned on the subwoofers crossover filters to measure the system's in-room response (fig.3).—Larry Greenhill


Fig.1 MartinLogan Dynamo 800X, full-range in-room response, 8Hz–2kHz (5dB/vertical div.).


Fig.2 Quad ESL-989, full-range in-room response, 8Hz–2kHz (5dB/vertical div).


Fig.3 In-room response of Quad ESL-989 and MartinLogan Dynamo 800X (using JLA CR-1 high-pass and 800X low-pass filters), 8Hz–2kHz (5dB/vertical div.).

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gcvanwinkle's picture

I found this information from Harman interesting:

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.

avanti1960's picture

the feet attach to "another" surface? How about they attach to the rear surface- you know the ones with the power connections, wired audio connections and manual adjustments?
So then with a front firing setup, the controls and connections will be facing down, under the subwoofer. Are the feet tall enough to fit the power cable, banana plugs, etc? All the cables need to feed downward and exit under the feet to the rear of the unit?
What an absolutely horrible design. I sure hope it sounds good down firing.
If I were reviewing this subwoofer this aspect of the design would have certainly been mentioned and admonished.

avanti1960's picture

I just purchased a pair of these subwoofers based on this review and so far they have integrated really well and sound excellent. A little "dry" sounding but hopefully they will bloom just a little as they wear in. MartinLogan recommends at least 50 hours before any critical listening is done.
With respect to the front firing setup requiring the connection and control panel to face the floor- it turns out that there really aren't any issues with doing this.
The controls are app based and the power cable has a 90-degree connector which gives plenty of room for the cable to exit under the unit and out the back. Same with the banana plugs for high level connections.
It would have been nice to have this outlined in the review at least to calm any concerns but all is well with this particular design application.
Thank you for the review which was a key factor in purchasing them and I am very happy with the results.
Tony, Suburban Chicago area.