Marten Oscar Duo loudspeaker Measurements

Sidebar 3: Measurements

I measured the Marten Oscar Duo's farfield behavior with DRA Labs' MLSSA system and a calibrated DPA 4006 microphone. I used an Earthworks QTC-40 mike for the speaker's nearfield and spatially averaged in-room responses. I didn't have the optional magnetically attached covers, so I didn't use them. The Oscar Duo's drive-units are protected with individual metal-mesh grilles.

My estimate of the Oscar Duo's sensitivity was 85.3dB/2.83V/m, which is within experimental error of the specified 86dB/2.83V/m. Marten specifies the Oscar Duo's impedance as 6 ohms, with a minimum magnitude of 3.1 ohms. My measurement indicated that the impedance magnitude (fig.1, solid trace) remains above 6 ohms for most of the audioband, with minima of 3.9 ohms between 35Hz and 40Hz, 3.8 ohms between 145Hz and 175Hz, and 3.9 ohms again above 12kHz. As the electrical phase angle (dashed trace) is high in several regions, I calculated what Keith Howard has called the "equivalent peak dissipation resistance" (footnote 1). The Oscar Duo has an EPDR of 2 ohms from 46Hz to 52Hz, 89Hz to 128Hz, and 3.7kHz to 8.6kHz, and the EPDR drops to 1.79 ohms at 100Hz and 1.82 ohms at 5.46kHz. The Oscar Duo should be partnered with an amplifier that doesn't have problems driving impedances below 4 ohms.


Fig.1 Marten Oscar Duo, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

The impedance traces are free from any discontinuities that would imply the presence of resonances of various kinds. When I investigated the vibrational behavior of the enclosure panels with a plastic-tape accelerometer, the only resonant mode I found on the sidewalls and top panel was at 652Hz (fig.2). This was very low in level, which, in combination with its high Q (Quality Factor) and high frequency, means it will not color the sound.


Fig.2 Marten Oscar Duo, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of side panel (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The saddle in the impedance magnitude trace at 39Hz suggests that this is the tuning frequency of the Oscar Duo's rear-panel port. This was confirmed by the fact that the nearfield response of the woofer (fig.3, blue trace) has its minimum-motion notch at the same frequency. (This is when the back pressure from the port resonance holds the cone stationary.) The port's nearfield output (red trace) peaks broadly between 25Hz and 75Hz, and while there are some peaks in its upper-frequency output, these are well down in level. The complex sum of the woofer and port outputs, taking into account acoustic phase and the different distance of each radiator from a nominal farfield microphone position (fig.3, black trace below 300Hz), suggests excellent low-frequency extension for this relatively small loudspeaker. The 3dB rise in the midbass response is an artifact of the nearfield measurement technique, which assumes that the radiators are mounted in a baffle that extends to infinity in the vertical and horizontal planes. The Marten's woofer alignment appears to be maximally flat, with a –6dB point at the port tuning frequency.


Fig.3 Marten Oscar Duo, anechoic response averaged across 30° horizontal window centered on the optimal axis at 50", corrected for microphone response, with the nearfield responses of the woofer (blue), and port (red), and their complex sum (black), respectively plotted below 300Hz, 1kHz, and 300Hz.

Marten's Leif Olofsson had explained that while the Oscar Duo's frequency response at 1m is optimized on an axis midway between the tweeter and woofer, this axis will also be representative at greater distances. I therefore performed the farfield measurements on this axis, which is 2" below the tweeter axis. The Marten's farfield response, averaged across a 30° horizontal window centered on the optimal axis, is shown as the black trace above 300Hz in fig.3. The response trend is respectably even overall, although a slight lack of energy can be seen at the bottom of the tweeter's passband. (The crossover frequency is specified as 2.5kHz.)

The plot of the Oscar Duo's dispersion in the horizontal plane, referenced to the response on the optimal axis (fig.4), indicates that this on-axis dip fills in to the speaker's sides, though there is a slight lack of energy to the speaker's sides at the top of the woofer's passband. The Oscar Duo's treble balance can be fine-tuned by experimenting with toe-in, as MF found. The contour lines in this graph are otherwise evenly spaced, which implies stable, well-defined stereo imaging. In the vertical plane (fig.5), a suckout in the crossover region develops immediately above the measurement axis and more than 15° below it. This loudspeaker needs to be used with stands that are sufficiently high to place the listener's ears on the optimal axis.


Fig.4 Marten Oscar Duo, lateral response family at 50", normalized to response on optimal axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.


Fig.5 Marten Oscar Duo, vertical response family at 50", normalized to response on optimal axis, from back to front: differences in response 45–5° above axis, reference response, differences in response 5–45° below axis.

Fig.6 shows the Marten Oscar Duos' spatially averaged response in Michael Fremer's listening room, driven by his darTZeel NHB-468 monoblock amplifiers. (This trace is generated by averaging 20 spectra, taken for the left and right speakers individually in a vertical rectangular grid 36" wide by 18" high and centered on the listening position.) I usually use a chirp signal with the FuzzMeasure app to examine a loudspeaker's in-room behavior. However, I tried something different for this review. I recorded the output of the speakers at the 20 individual microphone positions using Adobe Audition on my MacBook Pro and an Ayre QA-9 USB A/D converter while I played the pink noise track on the Editor's Choice CD (Stereophile STPH016-2) on Michael's dCS Vivaldi One. I used Audition's FFT frequency-analysis function to calculate the spectrum for each recording, averaged those spectra in Microsoft Excel, then subtracted the spectrum of the original pink-noise track to show the differences introduced by the loudspeakers and the room. Excel master Jim Austin then sent me an exponential smoothing algorithm so I could eliminate most of the high-frequency "fur" in the original data.


Fig.6 Marten Oscar Duo, smoothed, spatially averaged response in MF's listening room.

You can see from fig.6 that the Oscar Duos produced a respectably flat in-room response from 400Hz to 8kHz, with the sloped-down output above that range due to the increased absorption of the room's furnishings. Below 400Hz, the spatial averaging has not eliminated the effect of the room's acoustics. There is a lack of energy apparent in the lower midrange and a significant boost in the midbass region, below which the output drops rapidly. With its excellent low-frequency extension (for a standmounted design) and maximally flat woofer tuning, the Oscar Duos should be used farther away from the room boundaries than was possible in Michael's room. (The Marten speakers had to be placed in similar positions to his usual Wilson Alexxes.)


Fig.7 Marten Oscar Duo, 1/6-octave smoothed, spatially averaged response in JA's listening room.

I could hear the excessive and rather "lumpy" low frequencies with the pink noise signal when I was performing the measurements; I therefore measured the Oscar Duos' spatially averaged response in my own room with them placed where stand-mounted speakers work best in my room. The amplifiers used were Parasound Halo JC 1+ monoblocks. The result is shown in fig.7. There are still some peaks and dips in the bass that have not been eliminated by the spatial averaging, but, aided by the lowest-frequency mode in my room, the Oscar Duo had impressively extended low frequencies. Higher in frequency, there is a slight excess of energy in the upper midrange and an equally slight lack in the presence region. However, the in-room response is otherwise respectably even and very similar in the midrange and treble to that in MF's room, before the usual downward slope in the top two audio octaves.

Turning to the time domain, the Marten Oscar Duo's step response on the optimal axis (fig.8) reveals that the drive-units are connected in opposite acoustic polarity. This is usually the case with a second-order crossover like the Oscar Duo's, to avoid the drive-units' outputs canceling in the crossover region. The tweeter's negative-going output arrives first at the microphone, and the decay of its step then smoothly blends with the beginning of the woofer's positive-going step, implying optimal integration of their outputs on this axis in the frequency domain. The Oscar Duo's cumulative spectral-decay plot (fig.9) is extraordinarily clean overall.


Fig.8 Marten Oscar Duo, step response on optimal axis at 50" (5ms time window, 30kHz bandwidth).


Fig.9 Marten Oscar Duo, cumulative spectral-decay plot on optimal axis at 50" (0.15ms risetime).

The Marten Oscar Duo's excellent measured performance is indicative of some equally impressive engineering.—John Atkinson

Footnote 1: EPDR is the purely resistive load that gives rise to the same peak dissipation in an amplifier's output devices as the loudspeaker's complex load. See "Audio Power Amplifiers for Loudspeaker Loads," JAES, Vol.42 No.9, September 1994, and Keith Howard's article here.
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Anton's picture

So, you are the guy who blew up the Coltranes!

I have a trip down memory lane for you:

The last Stereophile Show in NYC, I think it was, and whatever new company Mark Levinson had invented was in a big room with windows demonstrating a big big big black box speaker.....with chrome accents. (It looked like it should have been called "The Nagel.")

I was sitting in the room as you had him play a piece that I was familiar with, but now forget then name of, and I don't think he knew the piece. He cued it up at a rather healthy level and I recall thinking, "Well, this is is certainly going to be something!"

When the huge bass transient hit, it really was something, but something bad. The woofer gave the biggest painful clunk of despair I have ever heard from a woofer and I honestly thought you broke his speakers.

An awkward silence followed. (I can still picture his frown.)

Thanks for prying loose that old memory.

Perhaps 2004?

I think it was the Daniel Hertz M1 speaker?

To bring it all back home, the Daniel Hertz looks a lot (!) like the recently reviewed Göbel High End Divin Marquis.

End of ramble.

Ortofan's picture

... the 24" Hartley woofers, in massive cabinets, that were part of the HQD system.

MhtLion's picture

My title (subject) tells all. It will be truly impressive to see a head-to-head with speakers like LS 50 Meta. So, please don't return these tiny Martens yet.

Charles E Flynn's picture

It would also be interesting to see how these speakers and the KEF LS50 Metas compare with the B&W 805 D3. In my view, these three speakers are among the best-looking small standmounts.

MhtLion's picture

Definitely B&W 803 D3 is one of the best looking bookshelves. LS 50 and Marten Oscar Duo are great looking too.

John Atkinson's picture
MhtLion wrote:
My title (subject) tells all. It will be truly impressive to see a head-to-head with speakers like LS 50 Meta.

My review of the LS50 Meta in the January 2021 issue will include a comparison with the Marten Oscar Duo.

John Atkinson
Technical Editor, Stereophile

MhtLion's picture

Awesome! You are the man, sir!


Ortofan's picture

... at the bottom of the 'measurements' page should be
rather than
" index.html"
as it is presently posted.'s picture

Maybe you would like to check out the NEW Marten Parker Duo monitor, apparently $11,000 plus, depending on ceramic or diamond tweeter, etc. One of three models in Parker series. As a longtime user of the Marten Miles speakers, I predict Duo is superb. And it's gorgeous.

remlab's picture

Even in the big guns? Wow! That's pretty high praise!

John Werner's picture

I'd guess there's others like me who read about the stuff I'd never rationally spend for. Usually it leaves me mostly empty not adding to my audiophile pursuits. This one was different as it actually delivered a surprise. A small stand mount box that could be called a full-range loudspeaker with few caveats. It already appears to be a kind of benchmark type of speaker proving what can be achieved in a fairly compact format. I do get quiet tired of super expensive stuff and I get the analogy of car rags that cover exotics. Still I find more interest in modestly priced gear that far over-achieves. At $5K with stands this misses price-wise but the excellent review found me genuinely engaged with interest. Great review on a relatively affordable piece of the true high-end.