Joseph Audio Perspective loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Joseph Audio Perspective's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield and spatially averaged room responses. All measurements were performed with the ports lined with the foam tubes, which is how I preferred the speaker in my auditioning.

My estimate of the Perspective's voltage sensitivity was 84dB(B)/2.83V/m, which is on the low side. However, as indicated by its plot of impedance magnitude and electrical phase against frequency (fig.1), the Joseph is a very easy load for the partnering amplifier to drive. Not only is the phase angle relatively low, the impedance remains above 8 ohms at almost frequencies, with a minimum magnitude of 6.27 ohms at 135Hz.


Fig.1 Joseph Perspective, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

There are no discontinuities in the impedance traces that would imply the existence of resonant modes. Investigating the enclosure panels' vibrational behavior with a plastic-tape accelerometer, I found very little problematic behavior. There were a couple of low-level modes present around 450Hz on the sidewalls level with the lower woofer (fig.2), but the affected area was small. The rest of the sidewalls and the top and rear panels were effectively inert.


Fig.2 Joseph Perspective, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of side panel level with lower woofer (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The saddle in the impedance magnitude centered on 27Hz (fig.1, solid trace) suggests that this is the tuning frequency of the port, and both woofers did indeed have a notch in their nearfield outputs at that frequency (fig.3, blue trace). (This is because the back pressure from the port resonance holds the woofer cones stationary.) The port's output (red trace) covers a slightly wider passband than is usual, but its upper-frequency rolloff is clean, with no resonant modes apparent. The blue trace in this graph shows the combined outputs of the woofers, but examining the drive-units separately revealed that the lower woofer rolls off earlier in the midrange than the upper, the former's output being down by 14dB at 1kHz.


Fig.3 Joseph Perspective, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield responses of woofers (blue) and port (red), respectively plotted below 350Hz, 220Hz.

Higher in frequency in fig.3, the upper woofer crosses over to the tweeter at a slightly lower frequency than the specified 2kHz, with a steep rolloff broken by resonant modes at 6.2 and 9kHz. These are well suppressed by the crossover, however. Comparing this graph with fig.3 in the Pulsar review, the Perspective's tweeter is balanced a little hotter than the Pulsar's, though its response is even overall.

Fig.4 shows the Perspective's farfield response, averaged across a 30° horizontal window centered on the tweeter axis and spliced to the complex sum of the nearfield woofer and port responses at 300Hz. The rise in output in the upper bass is mostly an artifact of the nearfield measurement technique; the low-frequency response is down by 6dB at the port tuning frequency, as expected. At the other end of the spectrum, the tweeter's output rises slightly in the top two octaves.


Fig.4 Joseph Perspective, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield responses plotted below 300Hz.

To some extent, this will be compensated for by the speaker's narrowing dispersion in the same region (fig.5), while the apparent excess of energy between 3 and 5kHz to the speaker's sides in this graph is actually due to the slight depression in fig.4 filling in off axis. But note in fig.5 the evenness of the contour lines, something that always correlates with stable, precise stereo imaging. In the vertical plane (fig.6), the high-order crossover results in a tonal balance that doesn't change significantly over a wide (±10°) window.


Fig.5 Joseph Perspective, 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.


Fig.6 Joseph Perspective, 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 5–10° below axis.

So far, so good with these quasi-anechoic measurements. But how did the Joseph Perspectives fare in the listening room? As usual, I measured the pair's spatially averaged response at the listening position. (I average 20 1/6-octave–smoothed spectra, taken for the left and right speakers individually using SMUGSoftware's FuzzMeasure 3.0 program and a 96kHz sample rate, in a rectangular grid 36" wide by 18" high and centered on the positions of my ears.) The result is shown as the red trace in fig.7; also shown, for reference, are the responses of: the Vivid Giya G3, which I reviewed in April (blue); and my 1978 pair of Rogers BBC LS3/5As (green). All three pairs of speakers were measured with the identical technique, with all responses normalized to the level at 1kHz.


Fig.7 Joseph Perspective, spatially averaged, 1/6-octave response in JA's listening room (red); and of Vivid Giya G3 (blue), Rogers BBC LS3/5A (green).

As expected, the Joseph and Vivid speaker responses produce considerably greater amounts of low-frequency energy in-room, though even with their ports partially plugged, the Perspectives excite my room's lowest-frequency diagonal mode, at around 30Hz, to almost as great an extent as the larger Vivids. The Josephs and Rogerses have more top-octave energy apparent than the sweeter-toned Vivids, though the G3s and Perspectives have similar midrange outputs. But note how the Perspectives output 2–3dB more presence-region energy than either of the other two speakers, which are virtually identical between 2 and 10kHz. Here, I believe, is why Erick Lichte found the Perspectives not to work optimally in his room, which is smaller than mine, and why I found the Josephs to be unforgiving of poor-quality recordings and fussy about choice of amplifier. The presence region is where the ear is most sensitive—even a slight emphasis in this region can significantly affect the listening experience.

In the time domain, the Perspective's step response on the tweeter axis (fig.8) indicates that all three drive-units are connected in positive acoustic polarity. The very small discontinuity, where the decay of the tweeter's sharply defined step would otherwise blend smoothly with the start of the woofers' step, suggests that the optimal axis is actually just below the tweeter axis. Jeff Joseph's use of a taller support for the front of the speaker than the rear therefore appears to be justified. The Perspective's cumulative spectral-decay plot (fig.9) is superbly clean, with the first breakup mode of the woofers' cones, indicated by the cursor position, well suppressed.


Fig.8 Joseph Perspective, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).


Fig.9 Joseph Perspective, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

Its measured performance indicates that the Perspective is a well-engineered design, but also suggests that careful system matching will be necessary to get the best sound quality from it.—John Atkinson

Joseph Audio Inc.
PO Box 1529
Melville, NY 11747
(800) 474-4434

Naimdude's picture

Does the 13 000$ big ones get you the speakers, and that giant violin?

otaku's picture

Yes, it adds lots of "bass"!

JRT's picture

JA wrote, " fig.3, the upper woofer crosses over to the tweeter at a slightly lower frequency than the specified 2kHz, with a steep rolloff broken by resonant modes at 6.2 and 9kHz. These are well suppressed by the crossover..."

What I think we are seeing at 6.2kHz in your measurement is not a modal breakup resonance of the diaphram, but rather is the low pass crossover response above the notch at ~3.8kHz. The peak you measured at ~9kHz is more characteristic of the modal breakup resonance of Seas' Excel W15 family of woofer diaphrams.

The low pass crossover displays characteristic effects of an elliptical filter that combines a notch and low pass, with the notch steepening the intial rolloff of the low pass. For a description of this take a look at Albert Neville Thiele's US patent 6854005.

Jeff Joseph's picture

The magnesium woofer without a filter has resonances as JA correctly noted at 6.2 and 9kHz, but the woofer's highest peak is actually at 4.9kHz! (about 5dB above the 6.2kHz resonance). JA's measurements confirm that the resonances are well-supressed.

Anon2's picture

I have not heard this particular JA speaker. I have heard the JA Pulsar at an audio exhibition. JA speakers are out of my price range, but it was a privilege to hear the Pulsar.

The diminutive Pulsar projects an enormous soundstage that simply belies its size, and exceeds that of some larger, dare I say floorstanding, speakers. The build quality of these speakers is something that you have to see in person to appreciate fully, though they look great in this article, too.

The top-end Seas drivers used in these speakers are heartily capable, and maintain their composure, even at the highest volumes. They ably handle powerful amplification (I heard them with Hegel integrated amplification).

JA Speakers are fine products. I hope those interested get a chance to hear these speakers.