Wilson Audio Specialties Alexandria XLF loudspeaker Measurements

Sidebar 4: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Wilson Alexandria XLF's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield and spatially averaged room responses.

Performing measurements on such a large, heavy speaker as the Alexandria XLF poses two main problems. The first is practical: shipping the speakers to my test lab was out of the question, so I had to take my test gear to Michael Fremer's house. The second is that the assumption in any farfield acoustic measurement is that the distance from speaker to microphone is much greater than the speaker's largest dimension. There is also the fact that the speaker needs to be well away from any boundary so that reflections of its sound from that boundary don't corrupt the measurement. With a speaker as large as the Alexandria, neither of these conditions can be met without a very large (and very expensive) anechoic chamber.

For the impedance and in-room measurements, the speakers were in their usual positions. We then (carefully) fitted the supplied wheels to one Alexandria and (very carefully) wheeled it outside, to Michael's driveway, for the rest of the acoustic measurements. (It was a clear, windless day.) However, while this eliminated the wall and ceiling boundaries, it was impractical to raise the speaker's 655 lbs off the ground. The reflection of the woofers' output thus curtailed the anechoic time window I could use for the analysis, reducing the measurements' resolving power in the midrange.

My estimate of the XLF's voltage sensitivity was 92.6dB(B)/2.83V/m. While this is slightly below the specified 93.5dB, it is still much higher than normal. Despite the Alexandria's imposing bulk, it will play at high levels with only a few watts. (During the in-room measurements, performed at a reasonably loud level, the darTZeel amplifiers' meters never indicated more than 5W peak.)

Wilson specifies the Alexandria as having a nominal impedance of 4 ohms. Fig.1 confirms this specification, the impedance magnitude (solid trace) varying between 4 and 8 ohms over almost the entire audioband. Though there are minimum values of 3.7 ohms at 19Hz, 3.2 ohms at 510Hz, and 2.35 ohms at 35kHz, the electrical phase angle (dotted trace) is low at these frequencies and generally benign overall, meaning that the speaker will not be a difficult load for the partnering amplifier to drive.

Fig.1 Wilson Alexandria XLF, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

The traces in fig.1 are free from the wrinkles that would indicate the existence of enclosure panel resonances. I had neglected to take my accelerometer and its preamp to Michael's, so I'm unable to offer my usual cumulative spectral-decay plots of the walls' vibrational behavior. However, other than the vertical "wings" that flank the midrange-tweeter-midrange (MTM) array, all the enclosure walls were acoustically inert, to judge by the knuckle-rap test. This was confirmed by listening to the walls with a stethoscope while swept sinewave tones were playing.

The Alexandria's MTM array needs to be focused on the listening position, using the precision adjustments on the speaker's rear. I measured the height of MF's ears as he sat in his listening seat: 37". I then measured the height of the Wilson's front-firing tweeter—56.5"—and the distance from the tweeter to his ears: 94". Once we had the speaker outdoors, we placed the microphone at exactly this position and ran some response measurements. Unfortunately, the reflection of the upper frequencies from the ground followed the direct sound by just 3 milliseconds, meaning that the resolution of the measured response was 333Hz; ie, the datapoints lie at 333Hz and its multiples.

Fig.2 shows the Alexandria's response above 300Hz, with the speaker angled away from the microphone by 10°, which was the offset in Michael's listening room, and without the grilles, which Michael left off for his auditioning. Slight peaks in the upper midrange and mid-treble are balanced by a slight lack of energy in the presence region. Whether the peaks are audible as added detail and brightness or the presence-region dip is heard as "politeness" and a laid-back, forgiving nature will depend very much on the music being played, which in turn will determine which frequency band the ear latches on to as being its reference.

Fig.2 Wilson Alexandria XLF, anechoic response 10° to one side of listening axis at 94", corrected for microphone response, plotted above 300Hz.

To get a more detailed look at the Wilson's behavior in the frequency domain, I moved the microphone forward, along the line connecting the height of MF's ears to the height of the tweeter, until it was at my usual distance of 50". The black trace in fig.3 shows the Alexandria's output averaged across a 30° horizontal window centered on the tweeter. The response is generally very flat—flatter than at the listening distance—but with the lack of energy between 2 and 4kHz still apparent. The output of the soft-dome Convergent Synergy tweeter smoothly extends at full level almost to the 30kHz limit of this graph, whereas the inverted titanium-dome tweeter used in earlier Alexandrias, as well as in the MAXX 3, peaked at the top of the audioband.

Fig.3 Wilson Alexandria XLF, anechoic response on listening axis at 50", averaged across 30° horizontal window and corrected for microphone response, with nearfield responses of midrange units (green), woofers (blue), port (red), and their complex sum (black), respectively plotted below 312Hz, 1kHz, 650Hz, 312Hz.

The green trace in fig.3 shows the output of the midrange drivers, taken in the nearfield. It rolls off smoothly below 150Hz, crossing over to the woofers just above 100Hz. The bottom woofer has a radiating diameter of 12.5", the upper woofer 10". However, their outputs, measured in the nearfield, were virtually identical, so fig.3 shows their summed output (blue trace). With a passband covering 40–120Hz, the excessive level of the woofers compared with that of the midrange units is entirely a function of the nearfield measurement technique, which assumes a 2pi or half-space environment extending to infinity in both the vertical and horizontal planes. There is a peak between 700 and 800Hz in the woofers' upper-frequency output, but this is suppressed by the crossover.

The saddle centered at 19Hz in the impedance-magnitude trace suggests that this is the tuning frequency of the large rectangular port, which, in MF's review samples, was open to the speakers' rear rather than to the front. However, the minimum-motion notch in the woofers' summed output actually occurs at 21Hz, while the port's output, again measured in the nearfield (red trace), peaks just below 20Hz but doesn't roll off until above 70Hz. The black trace in fig.3 is the summed output of all the lower-frequency radiators, taking into account acoustic phase and the different distances from a nominal farfield microphone position. Though it peaks between 45 and 125Hz, this again will be almost entirely a function of the nearfield measurement technique. The port doesn't fully reinforce the woofers' output at its tuning frequency, which is appropriate, given that when the speakers are in a room, the boundary effect will increase the port's output level to give a response that should extend down to 20Hz at full level.

Figs.4 and 5 show how the Alexandria XLF's response changes to the sides and above and below the listening axis. (Because the speaker is too bulky and heavy to position on my speaker turntable, I've shown the changes over a limited window.) Laterally, the speaker's output shows very little change in its output up to 15° to its side. In the vertical plane, the Alexandria XLF's response doesn't change significantly from 5° above to 15° below the listening axis. This speaker appears to be much less fussy regarding the exact listening axis than the Wilson MAXX 3s that previously enjoyed pride of place in MF's system (see figs.4 and 5 here).

Fig.4 Wilson Alexandria XLF, lateral response family at 50", normalized to response on listening axis, from back to front: differences in response 15–5° off axis, reference response, differences in response 5–15° off axis.

Fig.5 Wilson Alexandria XLF, vertical response family at 50", normalized to response on listening axis, from back to front: differences in response 10–5° above axis, reference response, differences in response 5–15° below axis.

In the past I have argued that perhaps the most meaningful measurement of a loudspeaker is of the pair's spatially averaged response at the listening position. Using SMUGSoftware's FuzzMeasure 3.0 program and a 96kHz sample rate, I average 20 1?6-octave–smoothed spectra, taken for the left and right speakers individually, in a vertical rectangular grid 36" wide by 18" high and centered on the positions of the listener's ears. This largely 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.

The red trace in fig.6 shows the spatially averaged response of the Alexandria XLFs in MF's listening room, driven by darTZeel NHB-458 monoblocks via TARA Labs speaker cables. It is even between 300Hz and 6kHz, with small peaks balanced by similarly small dips. Above 6kHz the response smoothly slopes down, due to the increasing absorptivity of the room furnishings in the high treble. At low frequencies, the Alexandria's in-room response is basically identical to that of the MAXX 3 (blue trace)—hardly surprising, given the similar woofer configuration and positioning in the room. A lack of energy in the upper bass is followed by small peaks at 80 and 50Hz, the frequencies of the lowest resonant modes in MF's room. However, the Alexandria has a little more low-bass energy, and the upper-bass dip is less extreme. Perhaps of more importance, the new speaker shows a little more energy in-room in the upper midrange and low and high treble, giving a more evenly balanced response overall.

Fig.6 Wilson Alexandria XLF, spatially averaged, 1?6-octave response in MF's listening room (red); and of Wilson MAXX 3 (blue).

A couple of weeks before driving to Michael's place I had auditioned another pair of Alexandria XLFs, at Manhattan dealer Innovative Audio, where they were driven by Dan D'Agostino Momentum monoblocks and a preproduction sample of D'Agostino's Momentum Ultra-Analog preamplifier, wired with Transparent Reference XL speaker cables and balanced interconnects. The ports were open to the rear, as they had been in MF's room. With a Meridian MediaSource 600 feeding data to a dCS Scarlatti D/A converter, this system gave the best sound I have heard at Innovative. I therefore asked Innovative's Scott Haggart if I could measure the Alexandria XLFs' spatially averaged response in the big room where I had auditioned them. Innovative's owner, Elliot Fishkin, was amenable; the result is the green trace in fig.7. (The red trace is, again, the speakers' spatially averaged response in MF's room.)

Fig.7 Wilson Alexandria XLF, spatially averaged, 1?6-octave response in: MF's listening room (red), Innovative Audio (green).

Above 250Hz, the XLFs' response in the Innovative listening room meets very tight limits: ±1.5dB. Again, small response peaks are balanced by small dips, but the response trend between 250Hz and 6kHz is a little flatter than in Michael's room. This may well be due to the greater distance to the listening position at Innovative: 128" vs 94".

The slight slope down above 6kHz will be due to the increased absorption of the room furnishings in this region, but I suspect that the plateauing of what would otherwise be a smooth rolloff between 10 and 18kHz in the Innovative room will be due to the effects of the XLF's rear-firing tweeter. The sharp rolloff above 18kHz in both rooms will be due to the 1" front tweeter's inevitable increasing directivity at frequencies at which it is larger than the wavelength of the sound it is emitting.

The spatial averaging has not entirely eliminated the effect of the low-frequency modes in the Innovative room, but the buildup of bass energy due to the proximity of the room boundaries will be mitigated by the overdamped woofer alignment. The effect will be to add some bass weight without obscuring clarity. The low-frequency extension is excellent, the level at 20Hz being the same as at 1kHz.

The lower-midrange dip at Innovative is both narrower and higher in frequency than the corresponding dip in MF's room. I suspect this is due to interference between the direct sound from the midrange units and the reflection from the sidewalls. (The floor-bounce cancellation of the woofers' output will be above their passband and is thus inconsequential.) The 200Hz dip is inevitable given the room dimensions, and I suspect that much of the fine-tuning of the speakers' positions is to arrange for this cancellation notch to have the least effect on music.

In the time domain, the Alexandria XLF's step response at the listening position (fig.8) indicates that the tweeter and woofers are connected in positive acoustic polarity, the midrange units in inverted polarity. However, the decay of the tweeter's step smoothly blends into the start of the midrange units' step, and the decay of the midrange units' step smoothly blends into the start of the woofers' step. This indicates optimal crossover design, which, in combination with the adjustable geometry of the upper-frequency drivers, will give the smooth blending of the drive-unit outputs in the frequency domain claimed for the Aspherical Group Delay technology.

Fig.8 Wilson Alexandria XLF, step response on listening axis at 94" (5ms time window, 30kHz bandwidth).

The cumulative spectral-decay plot (fig.9), taken at the closer 50" microphone distance in order to push back boundary reflections, shows a very clean initial decay, but with then some low-level hash in the mid-treble. A small ridge of what appears to be delayed energy is visible at the computer monitor's line-scan frequency just below 17kHz. This is spurious and should be ignored. However, there is a notch in the on-axis response, and a more powerfully defined ridge of delayed energy at a lower frequency, 14,875Hz, both of which appear to be real.

Fig.9 Wilson Alexandria XLF, cumulative spectral-decay plot on listening axis at 50" (0.15ms risetime).

As I said at the beginning of this section, there are practical limitations when measuring so large a loudspeaker. While I am confident that my measurements regime fully characterizes the performance of a small speaker (such as KEF's LS50, which I reviewed last month), with a speaker as large as Wilson's Alexandria XLF, the measurements offer suggestions rather than certainties. Note, also, that I don't measure distortion, which in this high-sensitivity speaker is likely to be very low. But overall, this is an impressively well-engineered design. As well as auditioning the Alexandria XLF at Innovative and in Michael's room, last January I had the opportunity to perform extended comparisons between the XLF and the earlier Alexandria X-2 Series 2 at Wilson Audio's headquarters. There is no doubt in my mind that this is the best speaker yet to come from the Utah company, which makes it a very fine speaker indeed.—John Atkinson

Wilson Audio Specialties
2233 Mountain Vista Lane
Provo, UT 84606
(801) 377-2233

Mike Lomond's picture

Have you heard it Pauly.  Or are you another critic that, depite being in the "Hi Fi Industry for 30 years" ( Who with, what doing?), can judge a product without listening to it.

I have no idea what it sounds like.  It may sound awful or it could transport me to realms untravelled.

What gets me about the Stereophile comments section are the naysayers, the armchair critics, experts on products they've never seen, let alone heard.

"David Wilson, amateur!  That guy just throws a few drivers in a box and wants 200 grand.  I could do better than that".

Give me a fucking break.

Many posters here try to suck the joy out of all that's fun and positive about this marginal, slightly bizarre, yet wonderful hobby.

Thanks JA.  Enjoy the mag.





Paul Luscusk's picture

Mike among the companies I worked  for as a rep where Mc Intosh, Dynaco, Hafler, and Hafler Pro, Sherwood,Rockford  Fosgate Jim Fosgate,AR, NHT, ADS, NAD, PSB,  Ixos, and Esoteric Audio. I also worked as a Buyer for 8 years,and did  two of the LA Stereophile shows. SO you give me a break. I have heard many Wilson speakers(Not this one) and I'm not impresed by them. I have never judged a audio product without a listen.If you had read my post I was defending Micky's choice  to by the Wilsons. I just said they don't do anything for me as a audiophile.

BillK's picture

I ask this simply because I'd never heard anything I liked from earlier Wilsons, including generation of W/Ps and the Maxx 2s, and even some newer models like the Sophia 3, but to me the Sasha and Alexia have been truly special sonically, finally not suffering from the "cones in a box" disease of most dynamic designs.

billyjul's picture


it is not difficult to do excelolent speaker for good DIYER

they no mistake 

if you use corectly a driver, you can't go wrong, on internet there a quantity of utilitise to simulate parametters, listenig for learn how make a speaker

but construct a driver is far difficult, it is a crutial point, a good speaker bigin whith good drivers, and goods drivers choice to have a good intégration

whith a good reflexion you can make not a good, but a very good speaker in 2voice, a three voice is more complicate

i think, 


"David Wilson, amateur!  That guy just throws a few drivers in a box and wants 200 grand.  I could do better than that"

yes, i agree his speaker have problem, the integration of the drivers, in the cabinet and the design of this are the problem i think

an exemple, the focal berylium tweeter have to be flush mounted on the cabinet, is you don't do this , the response curve is awfull, not flat, flush mounted it is excellent, and the sound is realy better


whtih air motion transformer you can do to directive driver, i think one of the best design is the adam adio x-ART but the model whith the most powerfull magnet, for the high-end speaker

and they have an high medium whitch is a very interesting driver, he goes lower than most other, and they are no to long and vertical directive

they make reference direct radiation drivers for 800hz to 20000hz 


sommovigo's picture

As I said at the beginning of this section, there are practical limitations when measuring so large a loudspeaker. While I am confident that my measurements regime fully characterizes the performance of a small speaker (such as KEF's LS50, which I reviewed last month), with a speaker as large as Wilson's Alexandria XLF, the measurements offer suggestions rather than certainties.

I'm not sure I understand what the implication is here - because it would seem that, by this statement, you could be confident in the response of the speaker above a certain frequency (let's say somewhere above the high pass moving from the bass drivers to the mid/tweet module) - and that those measurements, per the assumptions you derive from your methods ordinarily, would be more of the "certainty" variety and less of the "suggestion" variety.

Would you say that you are cnfident in the response of the speaker above ca: 150Hz?

Michael Fremer's picture

I tend to stay away from the comment section following reviews, mine and those of other reviewers, and this thread is a good reason why. 

The arrogance, stupidity and ignorance is simply appalling and depressing.

I have had many of the world's greatest speakers in my room and I've heard others in other settings: homes, stores and shows around the world.

There are MANY different sounds that are valid and designed for different tastes. The inability of some here to understand that, not to mention understanding how to interpret measurements, is just plain pathetic.

Were I to be led around by measurements, all of which are CRUDE compared to the ear/brain, I'd be listening to CDs... 

This hobby combines science, art and human perception. 

Some of the comments here are sub-human, I'm afraid...

MVBC's picture

Beyond the finished product measurements, drivers parameters can help figure out the style of sound, especially in bass.

For instance, the difference of sound between 18" pro bass drivers JBL 2241 and 2242 can be traced to certain parameters such as BL and moving mass:

JBL 2241  BL 19,  mm 145g, 98dB/w/m versus JBL 2242 BL 24, mm 158g, 99 dB/w/m

Despite a slightly heavier moving mass, but thanks to a more powerful motor, bass from 2242 are much tighter offering better transient response and allowing more freedom in upper frequency cut off while bass through 2241 are more of the rolling type.

Similarly one can compare the same parameters in JBL pro offering versus the Focal drivers used in the Wilson family design:

In 15"

Audiom 15 BL 18, mm 137g, 92 dB/w/m versus JBL 2226 BL 19, mm 98g, 97 dB/w/m

In 12"

Audiom 13 BL 18, mm 108g, 90 dB/w/m versus JBL 2206 BL 18, mm 65g, 95 dB/w/m

Clearly, with a low BL and heavy moving mass, the Focal drivers exhibit quite a low output for such large drivers - a serious problem when trying to recreate live dynamics-, and won't physically deliver faster transients than their JBL pro counterparts, that is clean, lean bass. Other factors such as cone rigidity might help compensate but from the start, I would expect the Focal sound to be plump. Conversely, the 2226 won't go as deep as the Audiom 15, yet its bass will be tighter, punchier. My recent audition of the Focal Grand Utopia confirmed that feeling versus the quickness and tone of the JBL. And here we keep the comparison to bass/upper bass, as cone midranges versus compression would add another level of challenge for the expensive speaker as it did with the Utopia.

So the Wilsons or Focal are of course beautifully crafted, well designed speakers destined to plush interiors and lovers of a certain kind of sound, just as Cadillacs can deliver a certain style of ride. Fine. Yet at $200,000 there is plenty of space for DIY audiophiles to challenge them at more reasonable costs, especially when using active networking designs. Notwithstanding the choice of pro monitoring speakers that are much more affordable than these luxury items. Therefore, some DYI can proudly defend the quality of their bespoke work; however, others could tone down their arguments of authority, checkbook arrogance and quick tongue.

BillK's picture

I have no doubt that a good DIYer could build a speaker with better frequency response, but I'd still like to see the plots and hear what a reviewer had to say about the sound (I've heard any number of components with impeccable response graphs but that sounded simply horrible.)

That of course ignores what price you'd have to sell it for to afford a full-blown factory with staff to produce it in the US, but let's just start with that.

There are any number of "hot rodders" who can build a Porsche-beater for less than the price of a new 911, but they too tend to be one-offs rather than something you can walk into a showroom and purchase.

MVBC's picture

Check the price differential between some Watt/Puppy and a 4348 JBL pro studio monitor and compare the sound... Your answer is there. At the price of this professional gear, even DIY are almost getting not economical.

billyjul's picture

plat frequency response for a driver used in a speaker is just the beginning, but with active crossover witch contain an equalizer, you can correct the response of a speaker, to make better, butt, good driver hame flat frequency response there are other parameters, you have to look, when you make a speaker, parameters, that most audiophile , don't know and a speaker tha measure good on overall parameter can't be a bad speaker, it is not the case for this wilson audio and the jbl mansionned is better than this for much lower price, beaucause jbl know what to do and have developed all the excellent driver to achieve their desgn

NMMark1962's picture

WOW, what a load of TROLL CRAP here.....some people here need to get a life and if you hate Wilson so, then get the hell out of here....you will NOT convince one person with the anti-Wilson spew.....I agree with others....build us your own XLF and prove that Wilson is building garbage or perpetrating a fraud....

When your fabulous speaker is built, let me know so I can buy your wonderful effort and save myself tens of thousands....

To some of you.....quit feeding the idiotic trolls who shit all over these and other forums....i guess that these trolls were run out of the asylums for audio elsewhere...

By the way, for you Wilson haters....I am planing an ultra high end system for late this year...the XLF's are on the list...for the turd here who claims to be able to build an XLF for way less, let me know and I will add it to MY list....hehehehehe...and I bet it will sound oh so sexy.....




ABCDEFG's picture

Perhaps it would be enlightening for some here to consider the genuine economics of this situation.

Mr. Fremer did not pay $200,000 for his XLFs, whatever their cost of construction or subjective worth. In fact, it is very likely that he received a discount considerably greater than Wilson’s 40-45% retail margin.

Considering the dealer cost, it is likely that Mr. Fremer paid less than $100,000 for his pair.

Add a payment plan directly financed by Wilson Audio and a future resale value greater than the accommodation price and the picture of Mr. Fremer’s purchase snaps into focus with remarkable clarity.

Michael Fremer's picture

Is your obtuseness. Guess what? I can buy just about any loudspeaker known to man at an accommodation price. In fact, were I like some reviewers I could get a "long term loan" for just about any speaker known to man and just have them here for as long as I like.

However your libelous comment that there was a "payment plan directly financed by Wilson Audio" is where I tell you with no due respect to go f...k yourself.

The money came from Bank of America, not Dave Wilson or Wilson Audio.

SNI's picture

I would not pay too much attention to the speakers frequency response.
It is a very large speaker, and FR is always measured on the tweeter axis.
Low frequency measurements in smaller rooms are also questionable.
What I do find interesting is the speakers time domain behavior.
This is not very good, and I cannot imagine, that this will not ad a lot of collouration to the sound of this speaker.
It simply emits sound long time after the input signal has stopped.
In my experience this will mask the sound in a way, so that a lot of low level signal is lost.
Also the impedance of this speaker would make me worry.
Anyways I do not think this is a speaker for life, I´d believe that one would get fed up with this "Sound Of Its Own" as time goes by.

If one would like to see a clean time domain behavior, then look at the newly tested Dali Rubicon, that´s how things should behave
, if you want transparancy.


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