Vandersteen Audio Treo loudspeaker Measurements

Sidebar 3: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Vandersteen Treo's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield and spatially averaged room responses. As I suspected from my auditioning, the Treo is relatively insensitive. My estimate of the Treo's voltage sensitivity was a low 82.5dB(B)/2.83V/m, the same as the BBC LS3/5a. However, the impedance remains between 6 and 10 ohms for almost the entire audioband (fig.1), with a benign electrical phase angle. The minimum magnitude is 5.5 ohms, at 26 and 75Hz; the Treo will be relatively easy for the partnering amplifier to drive.


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

The slight discontinuity just below 200Hz in the impedance traces implies that there is some kind of resonant mode in this region. Investigating the panels' vibrational behavior with a simple piezoelectric plastic accelerometer, I did find a low-level mode at 195Hz on the side panel level with the subwoofer (fig.2), as well as some slight flexing in the midbass. There was also a mild resonant mode present just below 600Hz on the rear panel (not shown). Overall, the Treo's enclosure seems well damped and relatively resonance free.


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

The saddle centered on 26Hz in the impedance-magnitude trace suggests that this is the tuning frequency of the downward-facing port. Its output, measured in the nearfield and scaled in respect to the outputs of the other radiators in the ratio of its radiating diameter, is shown as the red trace in fig.3 and peaks between 20 and 50Hz, with a smooth rolloff above that range broken by a slight plateau at 150Hz. While the port is tuned to 26Hz, the two low-frequency drive-units have slightly different minimum-motion notches in the nearfield responses: the subwoofer's (green trace) lies at 22Hz, the woofer's (blue trace) at 25Hz. These figures imply excellent low-frequency response for the Treo, which was indeed what I heard. The subwoofer's output effectively fills in the gap between the woofer and port outputs.

Fig.3 reveals that the Treo's woofer covers a wide range, not handing off to the midrange unit until 1kHz, which means that it is actually responsible for most of the Treo's midrange output. Both the woofer and the midrange unit (black trace below 5kHz) roll off very gently outside their specified passbands. Both, however, are well behaved outside those bands. I have shown the Treo's upper-frequency response measured on the midrange axis, as that is what I had understood from Richard Vandersteen's own measurements to be the optimal listening axis. The grille was left on for all the farfield measurements, as it provides a smooth acoustic environment for the drive-units. The treble output on this axis is generally flat, though with a slight lack of energy in the region of handoff to the tweeter. That same lack of energy can be seen in the Treo's farfield response averaged across a 30° horizontal window centered on the midrange axis (fig.4). Other than slight excesses of between 400 and 600Hz and between 9 and 14kHz, the response is very flat, falling within a ±2dB limit across the entire audioband. The 3dB rise in output in the midbass is an artifact of the nearfield technique used to assess the response below 300Hz in this graph. The Treo's woofer alignment is actually maximally flat, and reaches its –6dB point at the port tuning frequency of 26Hz.


Fig.3 Vandersteen Treo, acoustic crossover with grille on MF axis at 50", corrected for microphone response, with nearfield responses of woofer (blue), subwoofer (green), port (red), and midrange unit (black), respectively plotted below 312Hz, 1kHz, 600Hz, 355Hz.


Fig.4 Vandersteen Treo, anechoic response with grille on MF axis at 50", averaged across 30° horizontal window and corrected for microphone response, with complex sum of nearfield responses plotted below 312Hz.

The Treo's lateral dispersion, referenced to the midrange-axis response, is shown in fig.5. The apparent off-axis peak at the cursor position just below 5kHz is actually due to the suckout in the upper crossover region filling in to the speaker's sides. The speaker's lateral radiation pattern is otherwise well behaved. In the vertical plane, the dispersion, again referenced to the Treo's output on the midrange axis, which is 36" from the floor with the speaker supported by its cones, is shown in fig.6. (Work by Home Theater's Tom Norton when he was with Stereophile showed that the average seated listener's ears are the same 36" from the floor.) The response is maintained 5° below the midrange axis, but as you move above the tweeter axis, the region covered by the tweeter is boosted and the suckout in the crossover region deepens.


Fig.5 Vandersteen Treo, lateral response family at 50", normalized to response with grille on MF axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.


Fig.6 Vandersteen Treo, vertical response family at 50", normalized to response with grille on MF axis, from back to front: differences in response 15–5° above axis, reference response, differences in response 5–10° below axis.

Fig.7 shows how this quasi-anechoic behavior sums in my listening room. To generate this trace, 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 vertical rectangular grid 36" wide by 18" high and centered on the positions of my ears. This eliminates the room acoustic's effects, and integrates the direct sound of the speakers with the in-room energy to give a curve that I have found correlates reasonably well with a speaker's perceived tonal balance. With the boundary reinforcement offered to the port's output by the floor, the Vandersteen's low frequencies extend at full level to 25Hz. The Treo's spatially averaged response is impressively flat in the decade of 400Hz–4kHz, above which it smoothly rolls off as a result of the increasing absorptivity of the room's furnishings. However, there is a lack of energy in the lower midrange that I couldn't eliminate by experimenting with the speaker positions. I suspect that it results from the woofer and midrange being similar distances from the floor and sidewalls in my room.


Fig.7 Vandersteen Treo, spatially averaged, 1/6-octave response in JA's listening room.

In the time domain, the use of a sloped-back baffle and first-order crossover filters gives a step response on the midrange axis that generally resembles the right-triangle shape of a true time-coincident design (fig.8). The sharp leading-edge spike suggests that the tweeter is a little too hot, while the double arrival after the spike implies that the optimal axis is actually just below the midrange unit (fig.9). The cumulative spectral-decay plot (fig.10) is clean in the midrange and top octaves, but is dominated by a hashy-looking region in the upper crossover region. I am not sure where this behavior stems from; it's fair to note that it is absent from the cumulative spectral-decay plot taken on the same axis and sent me by Richard Vandersteen.


Fig.8 Vandersteen Treo, step response on MF axis at 50" (5ms time window, 30kHz bandwidth).


Fig.9 Vandersteen Treo, step response 5° below MF axis at 50" (5ms time window, 30kHz bandwidth).


Fig.10 Vandersteen Treo, cumulative spectral-decay plot on MF axis at 50" (0.15ms risetime).

With a time-coincident first-arrival sound and a basically flat response, the Vandersteen Treo offers respectable measured performance.—John Atkinson

Vandersteen Audio, Inc.
116 W. Fourth Street
Hanford, CA 93230
(559) 582-0324

MVBC's picture

I noticed more details about the brand of cables used than the brand of drivers used in this "highly recommended" 85dB/w/m shhhpeaker.

VandyMan's picture

That information is a few clicks away on the Vandersteen website. I applaud reviewers who don't waste space recounting spec sheets and marketing literature. Providing a link is more than enough.

I have not heard the Treo yet, but the Model 2 Sig turned me into an audiophile. I still clearly remember the day I demoed it 15 years ago. I had no idea that there was such a big difference between speakers or that "inexpensive" speakers could sound that good. It literally brought tears to my eyes when I listened to A Tribute to Jack Johnson in the show room.

(My username is because I'm a fan. I have no link to the company.)

MVBC's picture

The type, yes, BUT not the brand of drivers.

Bill B's picture

At least some of the drivers are custom or semi-custom and I believe Vandersteen works with Scanspeak (and perhaps others) to create and modify drivers.

attilahun's picture

When I first saw the picture I assumed it was a reprint of an old Thiel review from 20 years ago. These really remind me of the old Thiels.

commsysman's picture

I have been looking for the perfect loudspeaker for over 30 years.

I started with some Polk RTA 12 Monitor speakers, then went to Vandersteen 2Ci speakers, then Vandersteen 3 and 3A speakers.

I have gone to hi-fi stores and the CES in Las Vegas untold times looking for something that cost under $10,000 and would be the holy grail; the one that really could come close to flawless reproduction of the live sound, but never could find it. 

I heard many excellent speakers, but for me there was always one major flaw of some sort that made them imperfect and overall not equal to my Vandersteen 3A speakers.

I finally became convinced that the Vandersteen Treo would be, if not perfect, an improvement over my 3A speakers that was worthwhile, so I bought a pair.

When I actually hooked them up in my home, I was awe-struck. These are not only much much better than my 3A speakers, they come as close as anything I have ever experienced to being a flawless perfect reproducer of the live musical experience. 

I have never heard a speaker that comes so close to perfection, without one single sonic flaw that I can identify in playing classical, jazz, vocal, name it and it makes it come to life.

My NHT subwoofer adds some bass power and bass extension to the extreme low end, but the Treo is quite capable of very good bass performance on its own. For 80% of my music, the subwoofer is really not needed.

But as far as audible sonic flaws, I can find NONE!! That is a totally new experience for me.

My wife, who was not real convinced that any speaker could be worth $6000, and was more than ready to find some flaws she could criticize, listened for a couple of minutes and got a silly smile on her face and said not a word. She is in love with them. Wife approval factor; off the chart.

These speakers have totally redefined my concept of what ANY speaker is capable of, especially for less than $10,000.

commsysman's picture

Vandersteen, in his owner's manual and product literature, makes a BIG point of his assertion that these speakers WILL NOT perform at their full potential unless they are bi-wired.

John clearly did not bi-wire the speakers when he tested them.

That seems odd to me and I wonder why he did not go with the manufacturer's recommendation. Surely he has access to some high-quality bi-wire cable sets.

With my Vandersteen 3A speakers and now with my Treo speakers I use eight lengths of Belden #10 102-strand wire with Audioquest gold-plated spade lugs to bi-wire them, and the result is superior sound quality.

pulsetsar's picture

I don't quite understand JA's statement in the review about the grills being mandatory due to baffle reflections:

"Each of the three upper drive-units stands proud of the baffle on a small subchassis; the grille's frame surrounds each of the diaphragms with a smooth surface to optimize diffraction and minimize reflections of the high frequencies from the baffle edges. Use of the grille is mandatory, therefore"

Is he saying that he listened with and without and determined this (because it doesn't sound like it). If not, has anyone heard them with/without the grills and reached their own conclusions? A lot of manufacturers claim their speakers sound great with the grills on, but it's rare for them to be right in all respects. There are bound to be trade offs with either scenario, rather than across-the-board improvements.

John Atkinson's picture

pulsetsar wrote:
A lot of manufacturers claim their speakers sound great with the grills on, but it's rare for them to be right in all respects. There are bound to be trade offs with either scenario, rather than across-the-board improvements.

I thought the text of mine that you quoted self-explanatory. Unlike most speakers but like some of the Paradigms, the Treo's grille is an extension of the baffle and provides an essential part of the acoustic loading of the upper-frequency drive-units. The speaker sounds and measures worse without the grille.

John Atkinson

Editor, Stereophile

pulsetsar's picture

Ah, thanks! That was, indeed, more explanatory! I also looked more closely at some pictures and the baffle-extending aspect makes sense.