Sidebar 3: Measurements
I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Marten Parker Trio Diamond Edition's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield and in-room responses. I measured the speaker's impedance with Dayton Audio's DATS v2 system.
Usually, I measure loudspeakers in our backyard, weather permitting, or in our living room with the furniture pushed to the sides. This eliminates or moves back in time the reflections of the speaker's output. However, as this loudspeaker was too heavy for me to move outside or upstairs to the living room, I performed the quasi-anechoic measurements in my basement listening room. I managed to maneuver one of the speakers, standing on its IsoPuck bases, onto a small, wheeled dolly and rolled it forward so that it was aimed across the room's diagonal and was as distant as possible from the nearest sidewall. However, the proximity of room boundaries, the floor in particular, meant that I had to window the time-domain data a little more aggressively than I usually do. This reduces the measurements' resolution in the midrange. The geometry of my listening room also meant that I could only measure the horizontal dispersion over a ±45° angle rather than my usual ±90°.
While Marten specifies the Trio Diamond's sensitivity as a high 91dB/2.83V/m, my estimate was significantly lower, at 86dB(B)/2.83V/m. (I noticed I had to set the volume control about 3dB lower than when I listened to the 83dB-sensitive Falcon Gold Badge LS3/5a's Herb Reichert reviewed in the April issue for the same perceived volume, which subjectively corroborates the measurement.) The Trio Diamond's impedance is specified as 6 ohms with a minimum magnitude of 3.1 ohms. According to my measurements, the impedance magnitude (fig.1, solid trace) remains above 4 ohms over most of the audioband, with minimum values of 3.3 ohms between 110Hz and 120Hz and at 2.9kHz. The electrical phase angle (dashed trace) is occasionally high, which means that the EPDR (footnote 1) drops to 2 ohms between 64 and 111Hz and between 1.7kHz and 2.8kHz, with a minimum value of 1.5 ohms at 83Hz and 2.2kHz. The Trio Diamond Edition should be used with amplifiers that don't have problems driving 4 ohms.
Footnote 1: EPDR is the resistive load that gives rise to the same peak dissipation in an amplifier's output devices as the loudspeaker. See "Audio Power Amplifiers for Loudspeaker Loads," JAES, Vol.42 No.9, September 1994, and stereophile.com/reference/707heavy/index.html. Footnote 2: Using the FuzzMeasure 3.0 program, a Metric Halo MIO2882 FireWire-connected audio interface, and a 96kHz sample rate, I average 20 1/6-octave–smoothed spectra, individually taken for the left and right speakers, in a rectangular grid 36" wide by 18" high and centered on the positions of my ears.
Fig.1 Marten Parker Trio Diamond, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
Other than a small bump centered on 140Hz, the traces in fig.1 are free from the small discontinuities that would imply resonances of some kind, but when I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer, I did find some resonant modes. The strongest of these was at 855Hz on the sidewalls level with the upper woofer (fig.2). There was also a lower-level mode lower down on the sidewall and on the top and back panels. But because all these modes have both a relatively high frequency and a high Q (Quality Factor), it is unlikely they will color the Trio's sound. The metallic ringing sound I heard when I rapped my knuckles on the enclosure's sidewalls turned out to be due to the metal grilles that cover the woofers and passive radiators, the latter in particular. However, because the radiating area of these grilles is minuscule, this ringing will be innocuous.
Fig.2 Marten Parker Trio Diamond, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of side panel level with upper woofer (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).
The saddle centered on 29Hz in the impedance magnitude trace suggests that this is the tuning frequency of the passive radiators. The minimum-motion notch in the woofers' summed output (fig.3, red trace), which is when the back pressure from the reflex resonance holds the woofer cone still, lies at the same frequency. There is a small suckout in the woofer's output at the frequency of the impedance magnitude bump, which implies some kind of internal antiresonance in this region. The passive radiators' summed output (fig.3, green trace; both behave identically) has one peak centered on the tuning frequency of 29Hz and another an octave higher. The upper-frequency rolloff is initially clean, though some low-level hash can be seen between 200Hz and 500Hz. As the radiators fire to the rear of the loudspeaker, I doubt this behavior will have audible consequences.
Fig.3 Marten Parker Trio Diamond, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the summed nearfield responses of the woofers (red) and passive radiators (green), and the complex sum of their nearfield responses (blue), respectively plotted below 300Hz, 500Hz, and 300Hz.
Looking at the nearfield outputs of the individual woofers reveals that the lower woofer starts to roll off above 300Hz, its output at 1kHz lying 10dB below that of the upper woofer. The blue trace below 300Hz in fig.3 is the complex sum of the nearfield woofer and passive radiator responses, with the latter's acoustic phase compensating for the fact that they are on the Parker Trio's rear. There is the usual peak in the upper bass due to the nearfield measurement technique, but the Trio definitely offers extended low frequencies. The Marten's farfield response, averaged across a 30° horizontal window centered on the tweeter axis (fig.3, blue trace above 300Hz), is even but with a slight lack of energy at the bottom of the tweeter's passband. This suckout was a little deeper with S/N 20103001B than it was with 'A. The tweeter's on-axis response starts to rise above the audioband, reaching a peak near 35kHz.
Fig.4 shows the Trio Diamond's horizontal dispersion, normalized to the response on the tweeter axis, which thus appears as a straight line. This graph reveals that the small dip in the lower treble in the on-axis response fills in to the speaker's sides, though the tweeter's output falls off rapidly off-axis. In the vertical plane (fig.5), a suckout in the crossover region develops more 5° above the tweeter axis, but the top-octave response doesn't drop off below the tweeter axis as much as I was expecting from my auditioning.
Fig.4 Marten Parker Trio Diamond, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45–5° off axis, reference response, differences in response 5–45° off axis.
Fig.5 Marten Parker Trio Diamond, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15–5° above axis, reference response, differences in response 5–15° below axis.
Fig.6 shows the Marten Parker Trio Diamond Edition's spatially averaged response in my room. (The spatial averaging, footnote 2, tends to average out the peaks and dips below 400Hz that are due to the room's resonant modes.) With its extended low frequencies, the Trio Diamonds maximally excite the lowest frequency mode in my room, but other than some small peaks in the upper bass and midrange, the balance at the listening position is impressively even, especially in the low and mid-treble. The Trios' output in the top two octaves slopes smoothly down; as I have written before, a loudspeaker that offers a flat on-axis response and well-controlled lateral dispersion gives a gently sloped-down treble in the spatially averaged room response due to the increased absorption of the room's furnishings and the narrowing of the tweeter's radiation pattern at high frequencies.
Fig.6 Marten Parker Trio Diamond, spatially averaged, 1/6-octave response in JA's listening room.
The standard Trios gave a very similar spatially averaged response from 40Hz to 12kHz in my room (not shown) but with a little more energy above 16kHz, and they didn't excite the lowest mode to the same extent as the Diamond Edition. Fig.7 compares the Parker Trio Diamond's spatially averaged response (red trace) with that of the Marten Oscar Duo (blue trace). The two loudspeakers behave similarly in the midrange. The Oscar Duos' top-octave output is a little higher in level than the Parker Trio Diamonds'. The Trio Diamonds have a smoother in-room response throughout the treble.
Fig.7 Marten Parker Trio Diamond, spatially averaged, 1/6-octave response in JA's listening room (red) and of the Marten Oscar Duo (blue).
In the time domain, the Trio Diamond's step response on the tweeter axis (fig.8) reveals that the tweeter is connected in inverted acoustic polarity, the woofers in positive polarity. (I confirmed this by looking at the step responses of the individual drive-units.) The decay of the tweeter's step smoothly blends with the positive-going start of the upper woofer's step, suggesting optimal crossover design. There is a second low-frequency arrival around 0.5ms after the first, which may be due to the lower woofer. The Trio Diamond's cumulative spectral-decay plot (fig.9) is generally clean, though there are some decays of resonant energy visible in the lower treble. The decay is also slightly hashy-looking between 7kHz and 11kHz; I suspect that this is due to early reflections from the grille that covers the tweeter rather than to actual resonances.
Fig.8 Marten Parker Trio Diamond, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.9 Marten Parker Trio Diamond, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).
The Marten Parker Trio Diamond Edition offers generally excellent measured performance.—John Atkinson
Footnote 1: EPDR is the resistive load that gives rise to the same peak dissipation in an amplifier's output devices as the loudspeaker. See "Audio Power Amplifiers for Loudspeaker Loads," JAES, Vol.42 No.9, September 1994, and stereophile.com/reference/707heavy/index.html. Footnote 2: Using the FuzzMeasure 3.0 program, a Metric Halo MIO2882 FireWire-connected audio interface, and a 96kHz sample rate, I average 20 1/6-octave–smoothed spectra, individually taken for the left and right speakers, in a rectangular grid 36" wide by 18" high and centered on the positions of my ears.
