Dynaudio Special Forty loudspeaker Measurements

Sidebar 3: Measurements

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

The Special Forty's voltage sensitivity is specified as 86dB(B)/2.83V/m; my estimate was a little lower, at 84.4dB/2.83V/m. Specified as a nominal 6 ohm load, the Special Forty's impedance drops below 6 ohms between 125 and 320Hz, with a minimum magnitude of 4.9 ohms at 178Hz (fig.1). However, the impedance remains above 8 ohms for most of the treble and bass, and though the electrical phase angle reaches an extreme –54° at 94Hz, the magnitude is high at that frequency, ameliorating any drive difficulty. Fig.1 was taken with the rear-panel port open; blocking it with the supplied foam plug turned the Dynaudio into a sealed-box design with the woofer tuned to 69Hz (fig.2).


Fig.1 Dynaudio Special Forty with port open, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).


Fig.2 Dynaudio Special Forty with port blocked, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

The traces in fig.1 are free from the small wrinkles that would imply the presence of cabinet-wall resonances. However, the top panel had a low-level but sharply defined mode at 730Hz. More significant, I found a very strong mode at 512Hz on the sidewalls, with more, lower-level modes just below 300Hz and between 600 and 750Hz (fig.3). This behavior correlates with the problem I heard in my auditioning.


Fig.3 Dynaudio Special Forty, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of sidewall (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The impedance traces with the port open suggest that the reflex-loaded woofer is tuned to 51Hz, which is confirmed by the sharply defined null at this frequency in the woofer's nearfield response (fig.4, blue trace). The port's output (red trace) peaks in textbook fashion between 30 and 100Hz, but its upper-frequency rolloff has a severe resonance spike at 700Hz. Fortunately, the port faces to the speaker's rear, which should reduce the audibility of this mode.


Fig.4 Dynaudio Special Forty, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with nearfield responses of: woofer (blue) and port (red), respectively plotted below 350Hz and 1kHz, and complex sum of nearfield responses plotted below 300Hz (black).

Higher in frequency in fig.4, the black trace below 300Hz shows the complex sum of the nearfield drive-unit outputs, taking into account both amplitude and phase. The broad peak in the midbass will be mostly due to the nearfield measurement technique, which assumes that the drive-units are mounted in a baffle that extends to infinity in both planes. Above 300Hz, and averaged across a 30° horizontal window centered on the listening axis, the response is impressively flat, other than the gentle top-octave rolloff and a small peak just above 1kHz, followed by a narrow suckout. I have conjectured in the past that this latter behavior might be due to a cone-termination problem and, if severe, should result in a slight nasal coloration. As I heard no such problem, it would appear that in the Special Forty this measures worse than it sounds.

The plot of the Special Forty's lateral dispersion, normalized to the tweeter-axis response (fig.5), reveals that the tweeter starts to become directional above 7kHz, which might well make the speaker sound a bit lacking in top-octave air in large or overdamped rooms. Below the top octave, the Dynaudio's lateral dispersion is well controlled and even. In the vertical plane (fig.6), the use of a first-order crossover means that a suckout develops at the crossover frequency above the listening axis. This speaker will give its flattest balance on or just below the tweeter axis.


Fig.5 Dynaudio Special Forty, 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 Dynaudio Special Forty, 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.

The speaker that preceded the Dynaudio in my listening room was the 19-times-the-price Wilson Alexia Series 2. Fig.7 compares the spatially averaged response in my room of the Dynaudios (red trace) and Alexias (blue). (The traces were generated by averaging 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.) The two speakers appear to have broadly similar responses throughout the midrange and treble, but the Dynaudios have a little more energy in the presence region, a lot more energy in the upper midrange, and reduced output above 15kHz. The Wilsons, of course, have considerably more bass energy and low-frequency extension than the modest-size Special Fortys, but excited the lowest-frequency mode in my room a lot more.


Fig.7 Dynaudio Special Forty, spatially averaged, 1/6-octave response in JA's listening room (red); and of Wilson Alexia 2 (blue).

A fairer comparison would be with Dynaudio's Contour 20, which I favorably reviewed in May 2017. The Contour 20's in-room response, measured in the identical manner, is shown in fig.8 (blue trace). Between 300 and 1200Hz it is very close to that of the Special Forty (red trace), though with slightly more energy in the midrange. The Contour 20 has greater bass extension, which excites the lowest-frequency room mode to a greater extent.


Fig.8 Dynaudio Special Forty, spatially averaged, 1/6-octave response in JA's listening room (red); and of Dynaudio Contour 20 (blue).

In the time domain, the Special Forty's step response on the tweeter axis is shown in fig.9; it reveals that both drive-units are connected in positive acoustic polarity, with the tweeter's output arriving at the microphone before that of the woofer. The slight undulation in the decay of the woofer's step is associated with a ridge of delayed energy at 1.11kHz in the Dynaudio's cumulative spectral-decay plot (fig.10). However, the decay in the treble is very clean, which suggests that the Esotar Forty is an excellent tweeter.


Fig.9 Dynaudio Special Forty, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).


Fig.10 Dynaudio Special Forty, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

Dynaudio's Special Forty offers generally excellent measured performance, but I was bothered by the woofer's behavior just above 1kHz, and even more so by that very strong vibrational resonance on the sidewalls.—John Atkinson

Dynaudio A/S
US distributor: Dynaudio North America
1852 Elmdale Avenue
Glenview, IL 60026
(847) 730-3280

Bogolu Haranath's picture

The new KEF LS-50 Nocturnes are powered wireless speakers, for $2500 ........ Everything we always wanted (and then some more) ........ May be JA could review them? ....... BTW, they won't obey voice commands or tell the outside weather or broadcast the latest news (or can they via you know who?) :-) .........

JimAustin's picture

I do like the graphics--are they any different INSIDE than the regular LS-50 wireless ?

Bogolu Haranath's picture

The only way we all will know is, if you review them ......... Don't wait for the boss .......... Get them and review them :-) ..........

JimAustin's picture

Hello, KEF? I'd like to review the LS-50W--the pretty ones please, with the android markings. :-)

Perhaps I shall. Any idea if they sound different from the non-wireless LS-50, which Stereophile has covered extensively?

Bogolu Haranath's picture

I know Stereophile has reviewed the passive version of the LS-50 ........ This new active wireless version can do many other things ........ It has USB input in addition to analog input ......... It has wi-fi and Bluetooth connectivity ....... It can connect to streaming services like Tidal ........ It is almost like a smart speaker (like HomePod) ...... The sound quality may be similar to the passive version :-) ..........

Bogolu Haranath's picture

It has built in DSP ....... So, it is possible it may sound better than the passive version ........ It also has sub-woofer output ....... It also has optical input in addition to USB input ......... All this "razzle-dazzle" for $2500 :-) ........

Bogolu Haranath's picture

Try them also with a powered sub-woofer, if you could ........... Go for the gold :-) ............

Indydan's picture

I think the LS50, whether active or passive has received more than enough reviews. The passive LS50 is one of the most overrated audio products ever.
I still cannot fathom how Stereophile has it in Class A (restricted lf) with the likes of Wilson and Magico.

Bogolu Haranath's picture

What about these new LS-50 Nocturnes? .......... They have built-in DSP along with other capabilities ....... The DSP may help with sound quality ..........

Indydan's picture

The LS50 Nocturne were recently reviewed by TAS. I find them ugly to look at!

Bogolu Haranath's picture

I know about the TAS review ......... I trust the ears of Jim Austin :-) .......... Beauty is in the eyes of the beholder :-) ...........

Jason P Jackson's picture

Compared to the Dynaudios reviewed here, LS-50's have less SD, meaning less cone area hence less ultimate loudness. If you have a small room or don't listen to music particularly loud, this won't matter so much. However, I believe, in a larger room the Dynaudio's will outperform them in the bass and power range.

Bogolu Haranath's picture

Agreed ....... Pairing the Nocturnes with a powered sub-woofer(s), would most likely increase the loudness capability. Also, that would provide more bass extension and loudness. We can still use all the other capabilities of the Nocturnes, which I mentioned. Of course that would increase the total cost. But, think about this ........ no need for amp, pre-amp ......... all the wires ........ may be not even any DAC. It has both optical and USB inputs ,,,,,,,, It has analog input ......... so, it is possible to hook-up even analog rig .........

Bogolu Haranath's picture

To add to the above ........... We can use the Nocturnes as a second system ....... We can hook-up lap-top/desk-top/phone/portable DAP directly to the Nocturnes ........ or, use the Bluetooth and Wi-Fi capabilities ............

Jason P Jackson's picture

I'm convinced. You'll end up with a great system. And the KEF's are better braced-less panel resonance.

Indydan's picture

You have researched the LS50 Nocturnes quite a bit. You sound sold on them. Are you going to buy them?

Bogolu Haranath's picture

I might ....... I am waiting for a review by Stereophile :-) ..........

Bogolu Haranath's picture

BTW ....... Stereophile Class-A rated SVS powered sub $2000 ....... Total cost of Nocturnes + SVS sub $4500 .........

Jason P Jackson's picture

...and the Nocturnes also happen to look gorgeous. To me anyway

Richard D. George's picture

I have several stand mounted Dynaudio's in out mountain home, including a pair of Focus 160's. Beautiful treble and surprisingly robust bass, given the speaker size.

It is unfortunate about the cabinet resonance. This is not something I would have expected from Dynaudio.

At a different price point, the Contour 20's sure look and sound wonderful.

Jason P Jackson's picture

I agree. The fact Dynaudio has a released a loudspeaker at this price with the degree of cabinet resonances revealed here has me absolutely baffled. Unless perhaps this is a means to compensate for the floor-bounce cancellation characteristic of all standmount designs (in most rooms). There are obviously other factors at play e.g. boundary and especially rear wall reinforcement which can ameliorate the suckout/ cancellation issue in the lower midrange. However, this is rarely a fix. Standmount boxes perched on 600mm stands in big rooms will nearly always have this colouration. If you believe that an acoustic guitar that sounds the size of a tennis ball is hifi, then you are in luck. But for me, I've spent my dollars on a well designed 3 way speaker system that has no such problem. And they were second hand too.

tonykaz's picture

Increasing the Mass and Dampening are the only ways to lower those Resonances.

These Speakers weigh in at only 10 lbs each yet they have rather largish panels.

JA is probably the only one able to notice details like this, I've seen Stethoscopes in pictures of his Work Area.

Tony in Michigan

Long-time listener's picture

Mr. Atkinson, you note that "not one other reviewer had noted an over-lively enclosure or any congestion in the midrange." I also note that you mention an overly-emphasized upper midrange in several different places in your review. I bought the 40s based on only one or two very early positive reviews, and on Dynaudio's reputation for quality speakers. I was pleased with the extra detail and bass extension (after my Excite X12s), but after listening a week or two, I wrote their customer service rep, assuming there must be a problem with my pair: they sounded consistently hard and forward in the upper midrange. No no no, they told me, Dynaudio speakers do not emphasize any part of the frequency spectrum. No no no, they said, there is no problem with the crossover or the tweeter at the bottom of its range. That cannot be--it must be your amp, they said. Today the unpleasant hardness still remains.

I'm trying to decide whether to upgrade may amp, as per their suggestions, or get a different speaker. My amp is and old NAD C272 -- 150 watts into both 8 or 4 ohms -- and I realize that price-wise it's not in the Special 40s' league. On the other hand, many people say amps is amps. What to do?

On another note, all the pictures on line, including here, show the Special 40 as straight-up red. My pair is a kind of pinkish-maroon, certainly not what I was hoping for or expecting.

This was supposed to be the last speaker of my lifetime, and I thought it would be a good choice. I'm disappointed.

Thank you for your review, more honest than most, and more honest than the impression the Dynaudio customer service reps gave me.

Long-time listener

ken mac's picture

You try another amp. I've heard the Special 40s and the rest of the Dynaudio line here at a local NYC store with a variety of amps from inexpensive Marantz integrateds to expensive LIne Magnetics. They've never sounded harsh or forward, but neutral in the best sense of the word. And spatially beautiful. Why not check out the Heed Elixir or Rega Brio? Not crazy bucks and great sound.

Ortofan's picture

... if you want to try changing power amplifiers, consider the Schiit Vidar, or possibly the Parasound A23.
Otherwise, perhaps you'd be better served by some sort of tube amp.

Axiom05's picture

A good dealer should help you work through these issues. Your dealer should be able to loan you a different amp to try. The dealer should also provide an avenue to replace the speakers for something you are more happy with either through exchange or trade-in. Don't start throwing more money into the system until you have determined where the problem lies.

Richard D. George's picture

Try Contour 20’s, in addition to getting a better amp. I think you will really like the Contours. Maybe your dealer could make the swap less painful.

Richard D. George's picture

Another thought if budget is an issue is to find a used pair of Focus 160’s and buy a better amp. Down the road you could then consider more expensive stand-mounts like Contour 20’s. I have the Focus 160’s and will probably hang on to them when I get a pair of Contour 20’s (or maybe Contour 30 floor standers).

Ortofan's picture

... ELAC Adante AS-61.

ken mac's picture

Died with Mr Hirsch.

Ortofan's picture

... Harman-Kardon Citation II.

Long-time listener's picture

Given where I'm at and what's available here, I'm considering an ATC P1 (driven directly from an NAD M51), or a Simaudio Neo 340i integrated.

I note that both with pink-noise and on the in-room response, JA pointed out emphases in the upper midrange. Measurements on Soundstage also show off-axis flares between 2 and 5 kHz. How much can I expect a better amp to really cure my problem? Thanks

Ortofan's picture

... is troubling you, then you might want to try the Marantz PM8006 integrated amp, which has a midrange tone control whose action is centered around 900Hz.

Bogolu Haranath's picture

Another suggestion is Pass XA-25 ........ Stereophile Class-A ..... Under $5k ........ XA-25 may be the amp to beat under $5k ...........

Bogolu Haranath's picture

Another possible pairing is with the new Rogue Audio tube/transistor hybrid integrated, Sphinx-V2 for $1395 (that is not a typo, $1395) ...........

jaiello's picture

I have owned a pair of the Special 40 for about 10 days now. I have about 50 hours of break in on them. I understand that they need closer to 200 hours to really begin to sound their best. That said I think they sound wonderful. I don't hear that congestion that JA hears but maybe we don't listen at the same levels or same type of music. I prefer 50s and 60s jazz. I listen a moderate volume levels. Before I bought these I tried both the KEF LS50 and the Buchardt S300 MKII SE. The KEF have awesome mid range but couldn't satisfy me in the lower bass regions. The Buchardt had loads of bass but the mid range magic I was seeking was lacking. The Special 40 seem to me like the best of both those speakers. I am 65. This is probably my last speaker purchase. I bought the Red Birch. I just love to sit there and look at them. Beautiful speakers.

Long-time listener's picture

(As of May 2019)(And updated again, July 2019): I've sold the Dynaudios and kept the Buchardt S300 MKII. The Buchardt Audio S300 MKIISE is a very interesting speaker. To me it sounds more evenly balanced than the Special 40, without that unpleasant upper-midrange emphasis, and it sounds "open" rather than "congested." It has a deeper soundstage as well. Bass is equally good. The drivers of the Special 40 do exhibit better control in certain respects; the Buchardts tend to slightly soften detail. One reviewer found them to sound slightly "glassy" at times, but with my NAD M32 and the right cabling, I don't have that problem. To me, the Dynaudio Special 40 seems very clearly to be less than the sum of its parts. The Buchardt, by contrast, is "well-sorted," and any small compromises in its design lead to result that, overall, very much belie its $1000 price. Pretty amazing.

Indydan's picture

It's a shame about the cabinet resonances. I thought that for the price, these speakers were too good to be true. Dynaudio put in some very good drivers, as well as a beautiful cabinet finish. Expecting a bullet proof cabinet for this price was asking too much.

woodford's picture

i've had a pair for about a year, and have used them with amps from Musical Fidelity, Peachtree, Icon, Lyngdorf, and a classic marantz receiver. i've owned "bookshelf" speakers from Focal (1007), B&W (Matrix 805), KEF (LS50w) and others, and these are by far the most satisfyingly musical standmounts i've heard in my system.

i don't hear the congestion JA mentions.

and as he and others have said, the finish is spectacular, particularly in red.

Indydan's picture

It's good that your pair of 40s doesn't sound congested. I am happy you like them.

jaykay3's picture

Bummed about this review.
I have focus 160s - which are incredible with Naim equipment, btw...
I was planning on the Specials being my next pair but now maybe no...

Indydan's picture

Duplicate post.

Indydan's picture

I was also somewhat considering the 40s, along with the ATC SCM19. I'll probably still listen to the 40s before making any purchase. I am not too thrilled about this resonance problem though.

Long-time listener's picture

I have auditioned at home the Aerial 5T, which has shown me how much better resolution is possible in the midrange of a speaker this size. But the Aerials, to my ears, were seriously lacking in bass weight.

What I have ended up doing is this: I use three hardwood footers that raise the Dynaudios about an inch above the surface, two in the front corners and one in the middle at the back, and at the same time, I place a stone on top of each speaker, in the middle but a little toward the front. This helps hold the cabinet still and improves the resolution. Previously it was a little like looking at tri-color printing in which the three shades were not aligned, but now things are in better focus. And I find it helps to toe-in the speakers until they face almost directly at you. If you listen too much off-axis, it emphasizes the upper-midrange hardness that I found so unpleasant. Still not a perfect speaker, but better.

Jason Victor Serinus's picture

Every speaker has a different sound. Ditto for every amplifier / integrated amplifier / preamplifier / DAC / turntable / cartridge. In addition because of differences in cable geometry and materials which, in turn, affect capacitance and inductance as well as the ability to convey signals effectively, different cables sound different with different components.

One approach is to strive to purchase components that sound as full, balanced, and neutral as you can afford, and match them synergistically with other neutral-sounding components. Another is to strive for a sound that pleases you, regardless of whether its balanced or neutral. (Tube warmth and bloom are examples of same.)

A third approach is to acknowledge the deficiencies of a particular product you already own and choose not to replace, and find other components that can help compensate for and balance out the deficiencies. That's another way of saying that you can search for components that counter-balance imbalances in other components. In all three scenarios, I consider cables (speaker / interconnects /power) as components.

None of these approaches can be implemented effectively solely by looking at measurements. You need to put everything together and listen.

Long-time listener's picture


Jason Victor Serinus's picture

Shall I list the number of component choices I made years ago that I came to regret? No point shoulding ourselves to death. We learn and move on... unless we want to stop learning. They who are not busy being born are busy dying.

Bogolu Haranath's picture

"He not busy being born, is busy dying" ............. Bob Dylan :-) ..........

"There is nothing so stable as change" ............... Bob Dylan :-) ...........

Jason P Jackson's picture

Now for me, that saying is one slap in the face.

dalethorn's picture

But he who is born again - not of flesh, but of the spirit - shall never die.

johnnythunder's picture

We live and learn by our mistakes and some of the best audio decisions I've made have been based on reviews and some of the worst too. I know it can be somewhat disappointing to read a negative review of something you've already purchased and hear that an expert find's it somewhat "flawed." But ultimately, just trust your ears. If you like the equipment, nothing any reviewer says should really matter (within reason of course, like if someone points out a safety risk.) I never spend that much on equipment that a bad decision will derail me forever. I just take it as a learning experience and sell the equipment (or give it to my daughter which I did with a pair of (to me) ultimately horrible speakers!) And if I had the disposable income to shrug off a 5 or 6 figure mistake, I could correct it just as easily.

rlo's picture

I own both the Special Fortys and the ATC SCM19 v2 currently. I’ve had the ATCs going on a year now, and the S 40s for about 4 months. I’m thinking of selling the ATCs...the Dynaudios are just eminently wonderful music makers. Definitely more relaxed in the treble region than the ATCs. And voices are just sublimely smooth with perfect body, compared to the ATCs which are leaner and slightly grainier though the mids (in comparison). The ATCs sounds like they have lower distortion overall (I’ve never heard a cleaner, clearer speaker than the latest gen ATCs) but that doesn’t automatically make them better music makers. Are the Dynaudios less accurate and have slightly more distortion? Maybe. But they are simply more fun to listen to and they give me a more “real” experience that I can listen to for longer with less fatigue. I love these speakers.

EDIT: Oh and I forgot the big wide open soundstage on the Dynaudios, which is not a strongsuit of the ATCs at all. There is very precise imaging on the ATCs but mainly within a space that is confined between the speakers. The Dynaudios fill my entire room with sound that extends outside, above, below and behind the speakers.

johnnythunder's picture

Smooth and musical vs. incisive and dynamic and to me, somewhat aggressive. ATCs speakers, like Proacs, are a speaker for a lover of fast, clean, dynamic music. Linn and Naim lovers should love them. If I listened to Led Zeppelin all day with perfect source components I'd like ATCs for a while. I'd also like a big tube amp with JBLs too. Dynaudio 40s strike me as a perfect small system speaker to listen to singer songwriter, classical solo and chamber music etc....A generalization perhaps but this is based on my own auditions of all three brands at shows etc.

Indydan's picture

I have a Naim amp and source. I admit that your written description of the ATCs appeals to me (except for the agressive part).
Your description of the Dynaudio Special 40 sounds like Harbeth!

avanti1960's picture

and found no trace of ill effects from enclosure resonances. They may very well have been voiced in the crossover to compensate as many other speaker manufacturers do.
However the treble was overly extended and slightly edgy for my tastes. They did not sound natural as is often a Dynaudio signature characteristic. This should have been mentioned in the review.

rlo's picture

The review specifically mentioned “The Special Forty's top octave was a touch on the mellow side” and “This recording's rich, warm balance was complemented by the Dynaudio's clean, fatigue-free high frequencies.”.

If you don’t like these speaker’s extended treble and find them “edgy”, you will hate most ATC, Focal, B&W, KEF and many more speakers. These speakers are not edgy in the treble IMO and I would not judge them by a Hi-Fi show listening session - I’m sure the room and the other equipment used would have had a significant impact on what you heard and what you typically hear at home.

avanti1960's picture

yes, i do not care for the speakers you mentioned either. i prefer a speaker that sounds natural like the ones i own and love. many speakers have an exaggerated sense of air and sparkle and many people like that. i'm just not one of them. i believe this is an important distinction to make when reviewing speakers.

rlo's picture

Did you ever think that maybe your preference is for rolled off highs? Nothing wrong with that, but this may not exactly be neutral from a measurement standpoint. If that’s the case, then of course they are not going to call this out in the review because it’s simply not objectively true, and not true to the majority of other listeners who like those other speakers just fine and don’t find them “exaggerated”.

Archguy's picture

Tested a full eight feet out into the listening space.

donnrut's picture

Is the discussion over? Did Dynaudio ever comment about this? Any more up to date 1st hand exper?