Phase Technology PC60 CA loudspeaker Measurements

Sidebar 3: Measurements

I measured the Phase Technology PC60 CA's frequency response in the farfield with DRA Labs' MLSSA system and a calibrated DPA 4006 microphone. I used an Earthworks QTC-40 for the nearfield response. All measurements were performed with the grille removed.

My estimate of the PC60 CA's B-weighted voltage sensitivity was 85dB(B)/2.83V/m, which is significantly lower than the specified 87dB. The impedance is specified as 4 ohms, which I think appropriate, the PC60 CA's impedance magnitude varying between 3.3 and 6 ohms in the midrange (fig.1, solid trace), though it remains above 7 ohms in the mid–high treble. The electrical phase angle (fig.1, dotted line) is generally high, though its more extreme values never coincide with low magnitudes. A good 4 ohm–rated amplifier or receiver will have no difficulty driving this speaker.

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Fig.1 Phase Technology PC60 CA, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

The traces in fig.1 are free from the small discontinuities that would imply the existence of panel resonances. Nevertheless, when I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer (similar to a piezoelectric guitar pickup), I found a series of resonant modes on the top panel and both sidewalls (fig.2). Though some of these are relatively high in level, their frequencies are sufficiently high that I wouldn't expect them to add midrange coloration.

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Fig.2 Phase Technology PC60 CA, 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 single impedance peak in the bass, centered on 55Hz, suggests that this is the tuning frequency of the woofer's sealed-box alignment. This was confirmed by the PC60 CA's nearfield response (fig.3), which indicates that the low-frequency output is down by 6dB at that frequency. The apparent boost in the upper bass in this graph is entirely an artifact of the nearfield response technique; the PC60 CA is tuned to be maximally flat in the bass. Higher in frequency in this graph, the speaker's midrange output is impressively flat, though the tweeter appears to be balanced a couple of dB too high in level. (I note that Bob Reina did find the speaker unforgiving of recordings that had problems in the treble.) There is a suspicious-looking peak and dip in the presence region, though BJR didn't remark on any coloration in this area. The grille introduced some unevenness, the variations reaching ±2dB in the low and mid-treble.

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Fig.3 Phase Technology PC60 CA, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with nearfield woofer response plotted below 300Hz.

A speaker's on-axis response can't be examined in isolation; the dispersion will also affect the speaker's perceived balance. The PC60 CA's horizontal radiation pattern is shown in fig.4. Comparison with fig.3 indicates that the dip in the presence region fills in to the speaker's sides, while the limited dispersion in the top two audio octaves will work against the excess of energy in the same region on the tweeter axis. Fig.5 shows the vertical dispersion. The speaker maintains its response over a relatively narrow (±5°) window, suggesting that listeners should be sure to use stands that place their ears close to the tweeter axis. Though the crossover frequency is specified as 2kHz, a notch at 2.5kHz appears more than 15° above or below the tweeter axis, implying that that is the acoustic crossover frequency.

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Fig.4 Phase Technology PC60 CA, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

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Fig.5 Phase Technology PC60 CA, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45–5° above axis, reference response, differences in response 5–45° below axis.

Turning to the time domain, the step response on the tweeter axis (fig.6) reveals that both drive-units are connected with positive acoustic polarity, while the smooth blend of the decay of the tweeter's narrow step and the rise of the woofer's step implies optimal crossover design. Some suspicious-looking undulations follow the peak of the woofer's step; the cumulative spectral-decay, or waterfall, plot (fig.7) shows a significant ridge of delayed energy at 2750Hz. This might be due to a problem with the termination of the flat woofer diaphragm by the surround. This resonance might also contribute to the speaker's intolerance of bright recordings. But other than that, the decay of the PC60 CA's sound is impressively clean, especially in the midrange. I'm not surprised that BJR used the word transparency to describe the PC60 CA's sound quality.

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Fig.6 Phase Technology PC60 CA, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

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Fig.7 Phase Technology PC60 CA, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

Its measured performance indicates that, other than that resonant problem in the crossover region, this is a well-engineered little speaker.—John Atkinson

COMPANY INFO
Phase Technology
8005 W. 110th Street
Overland Park, KS 66210
(855) 663-5600
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COMMENTS
Hi-Reality's picture

Robert,

I wish all reviewers more frequently applied these kind of descriptions for great gears. (maybe someday a brainwave-based testing and reporting machine connected to reviewer's head will auto-generate these phrases).

..."ability to render hall sound"
..."air, hall sound, ambience, drama. I feel like I'm in the room with the musicians."
..."as realistic through the PC60 CAs as when I last saw Café Tacuba in concert."
..."gave well-recorded instrumental solos a high level of realism."

What was the room dimension when you tested these PC60 CA's? and what is the recommended font/side-wall distance for their optimum performance? (how close can they be placed to the front/side walls?)

Thanks for an enjoyable review!

Regards, Babak
Founder, www.Hi-Reality.com

Robert J Reina's picture

Thanks for your comments. I did most of my listening to this speakers in my larger room which is 35' x 18' along the long wall. My rule of thumb for all bookshelf speakers it to place them 4 feet from the real wall on good stands, and the Phase Tech are no exception. I'd say at least four feet for the side walls, but on the long wall of my large room, these spaakers were over 10 feet from each side wall

remlab's picture

..with the same type of hiccup seen here. Must be hard to eliminate.

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