PSB Synchrony T600 loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the PSB Synchrony T600's frequency response in the farfield. My reference axis for the measurements was level with the center of the midrange unit, which is 38" from the floor, slightly above the height of my ears in my listening chair. I used an Earthworks QTC-40 mike for the nearfield and in-room responses and Dayton Audio's DATS V2 system to measure the impedance.

PSB specifies the Synchrony T600's anechoic sensitivity as 89dB, presumably for 2.83V at 1m. My B-weighted estimate was slightly lower, at 87dB(B)/2.83V/m. The Synchrony T600's nominal impedance is specified as 4 ohms—also the specified minmum impedance. The solid trace in fig.1 indicates that the impedance magnitude lies between 4 and 6 ohms over most of the audioband, with minimum values of 3.26 ohms at 39Hz and 2.95 ohms between 117Hz and 124Hz. The electrical phase angle (dashed trace) is mostly low. However, the effective resistance, or EPDR (footnote 1), drops to 1.8 ohms at 35Hz, and to 2 ohms between 74Hz and 85Hz, and between 2.3kHz and 3.1kHz. The Synchrony T600 must be used with amplifiers that don't have problems driving 4 ohms. Fig.1 was taken with the loudspeaker's three reflex ports open. With them closed, the impedance was the same above 70Hz but now there is a single peak in the bass, centered on 46Hz (fig.2).

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Fig.1 PSB Synchrony T600 with ports open, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

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Fig.2 PSB Synchrony T600 with ports blocked, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

The traces in figs.1 and 2 are free from the small discontinuities that would imply resonances of some kind. When I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer, I found sidewalls that were relatively inert but with a couple of resonant modes on the back panel (fig.3). The highest-frequency mode, at 504Hz, was also present on the top panel. However, because this mode has a high Q (Quality Factor), I doubt that it will result in audible coloration. (The lower the Q of a resonance, the greater the possibility that it will be excited.)

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Fig.3 PSB Synchrony T600, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of back panel level with the tweeter (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The three woofers are each loaded with their own internal chambers and ports and behave differently. The complicated set of traces in fig.4 shows the nearfield outputs of the top woofer and port (red traces), of the middle woofer and port (blue traces), and of the bottom woofer and port (green traces). All three woofers have a minimum-motion notch close to 40Hz, which coincides with the tuning frequencies of the three ports. (This is a little higher in frequency than the tuning of the Image T3's ports, footnote 2.) The bottom woofer has the narrowest passband, rolling off above 90Hz with a second-order, 12dB/ octave slope. The middle woofer peaks around 120Hz and rolls off just above that frequency, again with a second-order slope. The output of the top woofer extends higher in frequency, up to the frequency where it crosses over to the midrange unit. A peak is visible at 740Hz in all three port outputs; two other peaks are present in the port that loads the top woofer, at 595Hz and 306Hz. The latter is sufficiently strong that it gives rise to a discontinuity in the nearfield output of its woofer. (If you look closely at the red traces in fig.4, you can see that woofer's output is the Hilbert transform of the port's output, where the port's peak coincides with the fastest rate of change in the woofer's output.)

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Fig.4 PSB Synchrony T600, nearfield responses of top woofer and port (red), middle woofer and port (blue), and bottom woofer and port (green)

The sum of the three port outputs is shown as the blue trace in fig.5. It peaks at the tuning frequency in textbook fashion, but the upper-frequency rolloff is disturbed by the resonant peaks mentioned earlier. The red trace in fig.5 shows the sum of the woofer outputs with the ports open: It crosses over to the midrange unit's output (green trace) at the specified 450Hz with a clean high-frequency rolloff. The T600's farfield response on the midrange axis (green trace above 600Hz) is commendably even up to the top octave, where the tweeter's output starts to roll off below the ultrasonic metal-dome resonance at 22.7kHz.

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Fig.5 PSB Synchrony T600, acoustic crossover on midrange axis at 50", corrected for microphone response, with the nearfield response of the midrange unit (green), the summed nearfield responses of the woofers (red), and the ports (blue), respectively plotted below 600Hz, 3.1kHz, and 800Hz.

The black trace below 300Hz in fig.6 is the complex sum of the PSB's nearfield woofer and port responses, with the latter's acoustic phase compensated for the fact that the ports are on the loudspeaker's back panel. The peak in the upper bass is due to the nearfield measurement technique. The red trace below 300Hz in fig.6 is the sum of the woofer outputs with all three ports blocked. It starts to roll off earlier than the output with the ports open but does so with a 12dB/octave slope instead of the reflex alignment's 24dB/octave slope. Both nearfield traces have the slight discontinuity at 300Hz due to the resonance in the top port's output. As the port is blocked with the red trace, this behavior must be due to an internal air-space mode rather than one associated with the port itself.

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Fig.6 PSB Synchrony T600, anechoic response on midrange axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the sum of the nearfield responses with ports open (black) and with ports blocked (red), both plotted below 300Hz.

The Synchrony T600's farfield response, averaged across a 30° horizontal window centered on the midrange axis (fig.6, black trace above 300Hz), is even up to 15kHz with very slight dips balanced by equally small excesses of energy. Fig.6 was taken without the grille; repeating the measurement with the grille reduces the level between 6kHz and 9kHz by 2dB.

Fig.7 shows the Synchrony T600's horizontal dispersion normalized to the response on the midrange axis, which thus appears as a straight line. The contour lines in this graph are smooth and evenly spaced, behavior that correlates with the stable stereo imaging I noted in my auditioning. There is a slight off-axis flare at the bottom of the tweeter's passband, while a strong ridge of off-axis energy in the top audio octave reveals that the on-axis gulley in that region tends to fill in to the T600's sides. In the vertical plane (fig.8), the PSB's response doesn't change by much over a ±10° window centered on the midrange axis.

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Fig.7 PSB Synchrony T600, lateral response family at 50", normalized to response on midrange 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.8 PSB Synchrony T600, vertical response family at 50", normalized to response on midrange axis, from back to front: differences in response 15–5° above axis, reference response, differences in response 5–15° below axis.

Fig.9 shows the PSB Synchrony T600s' spatially averaged response in my room. (The spatial averaging (footnote 3) tends to average out the peaks and dips below 400Hz that are due to the room's resonant modes.) With the speakers' ports open (blue trace), the T600s maximally excite the lowest frequency mode just above 30Hz in my room, while with the ports blocked (green trace), the bass shelves down but is still relatively well-extended. With the speakers as I auditioned them—both top ports blocked and the right-hand speaker's bottom port blocked (red trace)—the peak at 32Hz is significantly reduced in level, but the octave above 50Hz is suppressed by a couple of dB. There is too much upper-bass energy in-room in all three conditions, but the balance at the listening position is generally even from 300Hz to 5kHz, though there is slightly too much energy between 500Hz and 800Hz. There is the usual gentle downward slope in the top two audio octaves. (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.)

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Fig.9 PSB Synchrony T600, spatially averaged, 1/6-octave response in JA's listening room with ports open (blue), ports blocked (green), and both top ports blocked and the right-hand bottom port blocked (red).

Fig.10 compares the Synchrony T600's spatially averaged response (red trace) with that of the similarly priced Canton Reference 7K that I reviewed in the September 2021 issue (blue trace, footnote 4). Both pairs of speakers have smooth, even in-room responses, though the PSBs have a little more upper-midrange energy than the Cantons. The Reference 7Ks have more top-octave output than the Synchrony T600s, as I discussed in my auditioning comments.

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Fig.10 PSB Synchrony T600, spatially averaged, 1/6-octave response in JA's listening room (red) and of the Canton Reference 7K (blue).

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Fig.11 PSB Synchrony T600, step response on midrange axis at 50" (5ms time window, 30kHz bandwidth).

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Fig.12 PSB Synchrony T600, cumulative spectral-decay plot on midrange axis at 50" (0.15ms risetime).

Turning to the time domain, the Synchrony T600's step response on the midrange axis (fig.8) reveals that the tweeter, midrange unit, and woofers are all connected in positive acoustic polarity. The decay of the tweeter's step blends smoothly with the positive-going start of the midrange unit's step, and the decay of the midrange unit's step smoothly blends with the positive-going start of the woofers' step. This implies optimal crossover design. The Synchrony T600's cumulative spectral-decay plot (fig.10) is commendably clean.

Although I was puzzled by the presence of those port resonances, as I have come to expect from PSB, the Synchrony T600 offers 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: See fig.3 here.

Footnote 3: 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.

Footnote 4: The Canton Reference 7K costs $6995/pair.

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COMMENTS
TomS's picture

JA, no preamp, really? where was volume control happening? I would think your listening notes might be different if there was an active preamp in the chain. which brings me to the second point, the treble response of these speakers seems to be deliberately shelved down above 10khz, though with a large peak over 20khz. You commented at length about getting the bass right, but you said little about treble detail in the listening section (except to note the Cantons sounded more detailed). Is the fact the the crossover to the treble is relatively low (1.8khz) somehow related to the fact that the FR is so tipped 'down'? Again, I would have thought that using an active preamp in the chain (the parasounds are presumably designed to be used with a preamp) would have changed the total sonic signature. Of course, I am well aware that a truly transparent active preamp is hard to find and expensive. Etc.

John Atkinson's picture
TomS wrote:
JA, no preamp, really? where was volume control happening?

I controlled volume with Roon.

TomS wrote:
I am well aware that a truly transparent active preamp is hard to find and expensive.

Yes indeed. The excellent but expensive MBL, Audio Research, and Pass Labs preamps I have used in the last year or so have all gone back to the manufacturer or to other reviewers.

John Atkinson
Technical Editor, Stereophile

Duck851's picture
Quote:

I controlled volume with Roon.

Digitally, or "analogly" ?

John Atkinson's picture
Duck851 wrote:
Digitally, or "analogly" ?

Control in the digital domain.

John Atkinson
Technical Editor, Stereophile

Ortofan's picture

... is "the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered."

According to KR, the Benchmark LA4 preamp is "probably the most transparent and revealing audio component I've ever used. It does not seem to leave any fingerprints on the sound."

The price of the Benchmark LA4 preamp is (only) $2,499.

https://www.stereophile.com/content/benchmark-la4-line-preamplifier

JRT's picture

Benchmark also offers their HPA4, which includes a very good headphone amplifier, but is otherwise similar to the LA4 preamplifier that you mentioned.

These seem to be a good choice for use with a pair of loudspeakers using conventional passive crossovers, and include an additional summed mono output which might be useful for connecting a subwoofer system, but without any facility to reshape the satellites' high pass response for better integration with a separate subwoofer system.

Sadly, while either of those preamplifiers might be a good choice for use with a pair of conventional loudspeakers with passive crossovers, these are not very useful with more advanced systems using DSP active crossovers in multi-way loudspeakers, or in other playback setups requiring use of more than two channels of audio, because they lack any facility for slaving more channels to the one master volume control.

Kal Rubinson's picture

Sadly, while either of those preamplifiers might be a good choice for use with a pair of conventional loudspeakers with passive crossovers, these are not very useful with more advanced systems using DSP active crossovers in multi-way loudspeakers, or in other playback setups requiring use of more than two channels of audio, because they lack any facility for slaving more channels to the one master volume control.

See:
https://www.stereophile.com/content/benchmark-la4-line-preamplifier-multichannel-application

https://www.audiosciencereview.com/forum/index.php?attachments/la4x3small-jpg.55706/

JRT's picture

Yours was a creative solution. Thank you for posting that.

John Atkinson's picture
Ortofan wrote:
According to KR, the Benchmark LA4 preamp is "probably the most transparent and revealing audio component I've ever used. It does not seem to leave any fingerprints on the sound."

I did write about the sound of the Benchmark LA4, along with that of the MBL N11, in my review of the Pass Labs XP-32: www.stereophile.com/content/pass-laboratories-xp-32-line-preamplifier-page-2.

John Atkinson
Technical Editor, Stereophile

Ortofan's picture

... "a truly transparent active preamp is ... expensive".
The Benchmark was intended to be an example of a truly transparent active preamp that was not particularly expensive.

One would then have to audition the preamp to see if it does indeed offer improved sound quality over no preamp at all.

Also, if you already had these ($8K) speakers as part of a preamp-less system, and have about $17K (which is the price of the Pass XP-32) in the budget for a system upgrade, would you be likely spend that entire sum on a preamp, or might a greater improvement be realized by spending part of it on a preamp and the balance on upgrades to other system components?

Jonti's picture

...for "Student Demonstration Time"! Surf's Up is a near-perfect album without that track. I always have to remind myself to lift the tonearm as soon as "Disney Girls" (the penultimate track on side one) ends.

Incidentally, do you approve of the modern remasters of Surf's Up? I've never heard a version anywhere near as lush as the original vinyl pressing.

Oh and on the subject of the extraordinary closer, the title track, I would urge you to search out David Thomas & Two Pale Boys' fascinating elongated reinterpretation from 2001. It's on their album of the same name. Not so much a cover as an homage. Enjoy!

dcolak's picture

Are we looking at the same graphs? There is nothing excellent in that frequency response. Twitter dropping like a stone at 15Khz? Uneven all over the place? What's excellent?

Axiom05's picture

But at least the tweeter response goes higher in frequency than the Magico M2's. Haha

What I find interesting is that for the longest time designers tried to push the tweeter resonance higher and higher in frequency, getting further away from the audio band. However, recent trends seem to be the use of tweeters that have their resonance just about 20KHz resulting in "poor" performance in the last octave.

John Atkinson's picture
dcolak wrote:
Are we looking at the same graphs? There is nothing excellent in that frequency response. [Tweeter[ dropping like a stone at 15Khz? Uneven all over the place?

It appears that you are looking different graphs. Mine show that the T600's farfield output is impressively even from the midrange through to 15kHz, with small dips balanced by equally small peaks. (The ear is insensitive to this behavior, as long as the departures from flat are small.)

The drop in the tweeter's output above 15kHz is, I believe, relatively inconsequential given the ear's relative insensitivity to energy in this region, even for those with hearing that extends above 15kHz.

John Atkinson
Technical Editor, Stereophile

krahbeknudsen's picture

I often wonder how such a sharp upper resonance/ringing of a metal dome tweeter affects the rest of the response. I would be interesting to excite the peak while measuring response and distortion in the rest of the tweeter's spectrum if that is possible? Think a NOS dac throwing an alias of a cymbal up there for instance.

tonykaz's picture

Dear John,

I wonder if a proper piece on living without a PreAmp would be helpful to we readership at large ?

I would love to read the opinions of our Leading Authorities ( like you and even Mr.HR ) on this significant concept.

I've been without a Pre for some time now while feeling rather liberated.

Your clarity is refreshing.

Tony in Florida

Jazzlistener's picture

…is a real let-down. Could you have been any less enthusiastic? Were you late for an appointment?

TomS's picture

I found some discussion on the Roon user's group about where the digital volume control occurs in the signal chain inside the unit (as DSP?); I am actually somewhat surprised that JA considers this a better solution all around, especially if one is losing resolution by attenuating in the digital domain. Correct me if I'm wrong but I read the earlier review of the Roon and there's no analong volume control there. Be that as it may, there are advantages and disadvantages as always. Still think using an active preamp might benefit the overall result with a speaker that is somewhat reticent in the treble.

Kal Rubinson's picture

"I am actually somewhat surprised that JA considers this a better solution all around, especially if one is losing resolution by attenuating in the digital domain."
It depends on how it is done. The better ones work at 64bit resolution.

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