Trenner & Friedl Sun loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Trenner & Friedl Sun's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield responses. My estimate of the Sun's voltage sensitivity was 82dB/2.83V/m, which confirms the specified figure but is well below average. This is hardly surprising considering that the woofer cone has an effective diameter of just 3.5" (footnote 1). The Sun's specified impedance is 4 ohms; the graph of its impedance magnitude and electrical phase angle against frequency (fig.1) reveals that while the impedance drops slightly below 4 ohms between 200 and 400Hz, reaching a minimum value of 3.7 ohms at 270Hz, it remains above 6 ohms for the bass and treble regions. Even considering the combination of 5 ohms and a phase angle of –42° at 150Hz, this speaker won't give any 4 ohm–rated amplifier drive problems.


Fig.1 Trenner & Friedl Sun, electrical impedance (solid) and phase (dashed) (5 ohms/vertical div.).

The traces in fig.1 are free from the wrinkles that would indicate the presence of cabinet resonances. Nevertheless, I found a strong mode at 605Hz that was present on all cabinet panels, but strongest on the top (fig.2). A couple of lower-level modes are present close to 605Hz, but as Ken Micallef didn't comment on any midrange congestion that might have resulted from this behavior, it's possible that all these modes are too high in frequency and of too high a Quality factor (Q) to be maximally excited by music.


Fig.2 Trenner & Friedl Sun, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of top panel (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The black trace in fig.3 shows the Sun's farfield response on its tweeter axis, spliced at 300Hz to the complex sum of the nearfield outputs of the woofer and the four tiny ports at the corners of the rear panel. The response is superbly even between 300Hz and 10kHz, and the slight rise below 300Hz will be entirely a result of the nearfield measurement technique. The sharply defined notch just above 10kHz in this graph will be due to destructive interference between the tweeter's output and the reflections of that output from the edges of the woofer cone. This is a common problem with coaxial drive-units; of the speakers I've measured that use coaxial drivers, only the KEFs and TADs have been free from it.


Fig.3 Trenner & Friedl Sun, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with nearfield responses of woofer (blue) and ports (red), plotted in the ratios of their radiating diameters, and complex sum of nearfield woofer and port responses plotted below 300Hz (black).

In fig.3, the nearfield output of the woofer (blue trace) has the expected minimum-motion notch at the port tuning frequency of 56Hz, and the summed output of the ports (red) peaks between 40 and 100Hz. Although KM comments that the Suns "cleanly produced bass notes of substance when present on the recording," the measured response doesn't really support that. I did at first wonder if KM's impression of "ample bass reproduction" was due to an underdamped woofer alignment, but the nearfield woofer and port responses in fig.3 and the shape of the impedance-magnitude trace in fig.1 suggest that the Sun has been tuned for clarity and definition rather than for apparent low-frequency extension. However, KM's placement of the speakers just over a foot away from the wall behind them will add some low-frequency reinforcement, as he found when he played the warble tones from my Editor's Choice CD.

As is to be expected with such a small enclosure, the Sun's lateral dispersion, normalized to the tweeter-axis response, is wide and even (fig.4), which corresponds with the excellent stereo imaging noted by KM. The apparent off-axis peak just above 10kHz in this graph is due to the interference notch in the on-axis output filling in to the speaker's sides, which will minimize the audibility of this suckout. The vertical dispersion is similar (fig.5), which is to be expected, given the symmetrical placement of the SEAS drive-unit on the front baffle.


Fig.4 Trenner & Friedl Sun, 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.5 Trenner & Friedl Sun, 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.

Fig.6 indicates that the tweeter section of the coaxial drive-unit is connected in positive polarity, the woofer section in negative polarity. The tweeter's output arrives at the microphone slightly before that of the woofer, but as the decay of the tweeter's step blends smoothly with the start of the woofer's step, this will not be a problem: The Sun is time-coherent if not time-coincident. The waterfall plot on the tweeter axis (fig.7) features a superbly clean initial decay, with just a small degree of delayed energy apparent in the crossover region.


Fig.6 Trenner & Friedl Sun, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).


Fig.7 Trenner & Friedl Sun, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

Other than that single cabinet resonance in the upper midrange and the misleading use of the Golden Ratio in its promotional materials, the Trenner & Friedl Sun offers excellent measured performance.—John Atkinson

Footnote 1: The SEAS driver is specified as being 4.7" in diameter, not 3.5", but this is because it is usual to specify the diameter of the drive-unit's chassis, not that of the actual cone.
Trenner & Friedl GmbH
US distributor: Profundo
2051 Gattis School Road, Suite 540/123
Round Rock, TX 78664
(510) 375-8651

fetuso's picture

When i saw the picture of these speakers I thought they were my Vandersteen VLR Wood bookshelf speakers. They look remarkably similar. The VLR'S also have coaxial drivers and are about 12 inches tall. Vandersteen also states in the manual that spades are required, but i have mine connected with bananas while i shop for new wire. I'm gonna look into those Cardas adapters. The VLR'S also have wood cabinets, but the face of the speakers are not wood. One other difference is the vlr have a sealed cabinet.

popluhv's picture

how these compare to Harbeth P3ESRs. I see one of these in my future!

Kal Rubinson's picture

This is a fascinating report and, between the subjective report and the bench measurements, I am motivated to hear them. The only piece of info I do not see is some objective measure of what the dynamic capabilities are. How can those little cones play loud enough (for me)?

IgAK's picture

There was also the RCA MI-11411 series "coaxial" driver in the 40's to mention another. (Actually "coincident" is more appropriate where coaxial actually may involve a bridge such auto speaker drivers often have.)

But as to the "Golden Ratio" it possible the internal dimensions conform more closely to that than the external ones? Those would be the ones that matter more.

RelaxWithPep's picture

These are very good looking speakers whose design has clearly been given a great deal of thought. I would be delighted to own them. I'm sure they produce excellent sound. However, the review doesn't seem to support the conclusion. "The finest stand mount speaker I've ever heard," with no qualifiers? Really? Not "at its price" or "for its size" or "for those listening in small spaces"? Could the reviewer comment on the differences between these and the KEF LS-50, another small, highly touted, bookshelf speaker with a coaxial design?

jmsent's picture

it's pretty easy to compare them. Leaving aside the subjective comments, the KEF certainly has more bass extension and somewhat higher sensitivity. I believe the cone area on the KEF is larger as well, which accounts for the bass response. I have heard the LS-50 more than once and I own a set of speakers based on the coaxial unit that is one size up from the one used in the T & F speaker. These coaxial drivers all have a unique coherence to their sound, which is reminiscent of what you get in a full range driver. Done right they're very smooth with no obvious handover between drivers. Their vertical and lateral responses are virtually identical and as you can see in John's dispersion graphs there are no major holes or peaks off axis. All of this points to a good sounding speaker. Where I see the problem is in dynamic ability and ultimate SPL capability, which has to limited by the small cone size. Also, at high levels you run into intermodulation problems because the cone acts as a waveguide for the tweeter's radiation. As the woofer cone moves, you then modulate the energy coming from the tweeter as well. I'd think these would be good candidates for a subwoofer, but getting a seamless match might not be that easy.

Anon2's picture

Thank you for this review and taking the time to review this product. I'm sure that its makers put thought and workmanship into the speaker under review.

I don't have the access to listen to as many products as the Stereophile staff. Forgive me for asking if $3,450 is a sum that we should spend on a speaker with 82dB sensitivity (requiring a new amplifier in many cases), and that weighs in comparably to speakers that cost less than $500 in many cases.

A major kit retailer sells a DIY product whose driver is probably the same as the one we see on this product. I'll let the curious investigate this product, and its cost.

Before we declare this product "the finest stand-mount ever," we might benefit from a few more reviews of similarly priced products that are available. For about $345 more per pair, and for a tank-like product weighing in at 16 lbs. more per unit, Stereophile could provide some more perspective, for all, by testing this recently released product:

And for some unique engineering and solid manufacturing, we are still awaiting the SP test for this product. It has just been enhanced with a passive radiator, it has good sensitivity, deep bass, its own waveguide technology, and has an impedance curve that can accommodate virtually any amplification. It's also about $600 less than the product we read about in this review. A European sound engineer called it "the best nearfield monitor he had ever used in his studio."

Let's have a few more tests, in some cases long overdue, before we make such sweeping declarations about a single product.

John Atkinson's picture
low2midhifi wrote:
Stereophile could provide some more perspective, for all, by testing this recently released product:

My review of the Aerial 5T will appear in our March 2017 issue. However, it won't include comparisons with the Trenner & Friedl Sun, as that speaker was returned to the distributor after the review.

John Atkinson
Editor, Stereophile

Anon2's picture

Fair enough. I know you guys can't test everything, and do a lot as things stand. I look forward to the 5T review, and your listening and test-bench results. I'd also enjoy, if circumstances permit, a test of the new Dynaudio Excite X18. I heard this product in a dealer open house, and was impressed, though I had to turn the volume knob up quite a ways on the Arcam FMJ A19 integrated to get a serviceable level of sound. Still, the sound was great. Any thoughts as to when the B&W 805 D3 might be making it's way towards a test? Keep up the good work.

John Atkinson's picture
low2midhifi wrote:
I'd also enjoy, if circumstances permit, a test of the new Dynaudio Excite X18.

Herb Reichert was going to to review the Excite X18 but decided instead to review the smallest in Dynaudio's new Contour series. That review is scheduled for our April issue.

low2midhifi wrote:
Any thoughts as to when the B&W 805 D3 might be making its way towards a test?

My review of the 805 D3 will be in March, the same issue as the Aerial 5T.

John Atkinson
Editor, Stereophile

JohnG's picture

Footnote 2: As the Golden Ratio is either 1.618 or its reciprocal, 0.618, as the ratio of the Sun's height to its width is 1.3125, that of its height to its depth 1.5, and that of the width to the depth, 1.1, Trenner & Friedl's use of the Golden Ratio in its promotional literature is both incorrect and misleading.—John Atkinson

Could it be that the interior dimensions of the enclosure match the golden-section proportions? After all, if there is some magical audio property to that ratio, it would presumably have its effect inside the box rather than outside.

John Atkinson's picture
JohnG wrote:
Could it be that the interior dimensions of the enclosure match the golden-section proportions?

Although I didn't dismantle the Sun speaker, I very much doubt it. That would mean some of the interior walls being inches thick.

John Atkinson
Editor, Stereophile

homebrew's picture

They may sound wonderful, but I fail to understand how a pair of $150 drivers and $75 for crossover parts and cabinets can add up to a $3500/pr. speakers.

HansRamon's picture

Could be interesting with a test of the large Trenner&Friedl Ra's, since it appears to be DeVores Orangotangs, which are Your's uncrowned king. (probably mine too..)

dronepunkFPV's picture

God this makes me laugh at all the disposable income.
If you people buying these are business owners you are not paying your employees enough.
Status seeking chumps.