The Amati Homage
Sonus Faber produce a range of beautifully finished speakers which produce a very listenable sound at the same time as excellent soundstaging and detail. The stunning-looking Amati Homage, with Scan Speak drivers and a complex and original cabinet construction, was for me the best speaker of the 1998 Hi-Fi Show at Heathrow. They gave me that rare and very satisfying of "rightness", at the same time as having a cavernous soundstage and great presence. Some people have found problems with room and amplifier sensitivity, suggesting that the Amatis are hard to build a system around, and I've heard that in the wrong system they can be a little fatiguing in the long term, so I suppose it's a case of each to their own tastes.
I've wondered on and off recently about building a pair of speakers based around the Amatis, trying to get them to look like the originals, but with a few minor - or major - changes to help an inexperienced constructor like me to get them working (and to iron out the odd wrinkle in the design!).
I have no immediate plans to start building, however - first of all, I'm actually very happy with my current DIY three-way speakers. Moreover, this would be a very expensive project (Wilmslow Audio quote over £1,000 for the drivers alone), and right now I haven't the time or the room to do all the woodwork. Finally, I don't have the space in the living room right now to do justice to speakers of this size and dynamic capabilities.
These speakers are named in homage to the Italian violin maker Andrea Amati (1525-1611) of Cremona, who is regarded as one of the greatest instrument makers, and who founded the Cremonese school of violin making. They are the second release in the Homage series, following three or four years after the Guarneri, which is built in a similar style, but on a smaller scale. The designer of the Homages, Franco Serblin, makes great claims to employ the traditional methods of violin construction in this series of speakers. I suspect that this may be partly a gimmick, but the Homages are certainly beautifully made, with a very classical appearance. The use of traditional varnishes and woodworking techniques is a very labour-intensive and costly way of solving the problems of speaker design and execution (constrast the Amati, for illustration, with the Wilson Benesch ACT, which uses similar shape and dimensions in its cabinet but very much more up-to-date materials and technology). However, there's no question that the result is an unusually elegant-looking speaker which doesn't provoke the usual problems with "spousal acceptance factor" encountered by the more usual monolithic loudspeakers.
The cabinets are designed to present the mid and bass drivers with a non-rectangular enclosure to spread the resonances, with the curve of the sides, the foam lining and the rear port presumably contributing a little transmission line effect for the backwave, though I haven't seen enough of the interior of the enclosure to be able to guess how much. The speakers are very heavy and seem rigid (I was happy with the "knuckle test" when I first encountered the speakers) - there is plenty of bracing, and the cabinet walls are thick and quite well damped.
I've estimated the cabinet dimensions and the positions of the drivers, ports and connections from pictures on the Web. The two JPEGs I've created here show to scale the approximate layout of the front and rear of the speakers.
All this, although it should improve the sound of the speakers, makes it an ambitious project for an amateur to build these speakers, even with a decently equipped woodworking shop. I haven't given much thought so far to how I would set about building the cabinets, although the structural parts, by which I mean the baffle and the internal bracing, ought to be fairly straightforward to put together from 18mm or 24mm MDF. The baffle of course will need careful work to get it into shape - without access to a computer machining shop I would expect to have to put a lot of effort in with the sandpaper. The two real time-consuming jobs are to put together a convincing copy of the side panels, and to get the furniture-grade finish on the cabinets as a whole.
As with all of Sonus Faber's top range of speakers, the baffle is covered in a soft black leather (see the closeup below left). This is partly to help dissipate surface modes on the baffle, but I would guess mostly for its looks - to me at any rate it gives a very attractive and expensive-looking finish, softening the hardness of even the most seductively curved wooden baffles. For the DIY-er leather is an expensive option (and perhaps an unacceptable one for the vegetarian/vegan too), but I notice that in the UK John Lewis stock a very realistic-looking synthetic alternative in their fabric department.
I am fairly sure that the drivers are as follows:
The responses of the drivers (the graph below right was interpreted by eye from the manufacturer's graphs and re-interpolated) look promising, although the unevenness at the top of the passband of the midrange driver (green trace) needs to be dealt with carefully. This seems to be the Achilles heel of designs using the ScanSpeak carbon paper drivers: despite their low coloration and distortion, more than a few listeners find them tiring to listen to in the long term, especially when used with a low-order filter. This makes me wonder if SF are being disingenuous in their boast of "first-order" crossover slopes, as if this were universally accepted as a Good Thing.
The relatively flat response of these drivers within their passbands suggests that simple crossovers might be possible without too much need to tailor the overall response, although the general upwards tilt might need to be addressed. All the same, this combination of drivers is definitely not for the faint-hearted designer. The Revelator tweeter is notoriously difficult to get to sound subjectively comfortable - Lynn Olsen, for instance, preferred the 9500 and 9700 for his Ariel design. It needs a notch filter at its resonant frequency to prevent over-driving (see, for example, this crossover by Lars Mytting), and also tends to sound "forward", no doubt not helped by the horn loading.
The measured low-frequency responses from the Sterophile review of the Amatis (left-hand figure) are interesting to compare with the raw driver responses (note the frequency scale on this graph only runs to 500Hz). In particular, the near-field amplitude from the individual drivers and the three ports shows that the woofers, the midrange and their ports are all contributing strongly below 200Hz, which will lead to a high potential sensitivity to room effects. This might explain the inconsistency in reviewers' opinions of the Amati's bass - it has been oddly described as "thin" by some, while elsewhere it is referred to as "powerful" or even "boomy".
This could also explain John Atkinson's puzzlement in the review concerning the bass performance, particularly the large peak at around 65Hz in the room-averaged response (right-hand figure). I would certainly be tempted to use higher-order crossovers to make life easier (my Neptunes used 4th-order Linkwitz-Riley), although this might lead to a sacrifice of the "naturalness" of the Amati. All the same, Siegfried Linkwitz doubts the audibility of phase distortion, at least in the bass-mid crossover and for slopes up to 24 dB/octave. This ought to reduce the spatial dependence of the bass reproduction, making the response more consistent. I'd also lower the mid-treble crossover point (2.5kHz) to reduce the prominence of the untidy top-end of the 8545, which can be seen in the farfield response plot (right) as well as in the raw driver responses - the peak at 2.5kHz in particular is likely to be associated with the midrange driver, and being in the middle of the presence band is likely to be audible.
The impedance of the Amati Homage (see figure to the left, again taken from the Stereophile review) shows that they are basically a four-ohm speaker. The low magnitude of the usual impedance peaks from the bass reflex system suggest either than there is very heavy damping in the box (unlikely) or that some impedance compensation has been used. The impedance drops almost to 2 ohms at 25Hz and 65Hz, which means it will need an amplifier with a good stiff output (in other words a solid state amp or a valve amp with a 4 ohm output tap). This is unavoidable with designs like the Amati which use parallel woofers; the 21W-8555-01 has a minimum impedance of around 6.5 ohms. However, the higher impedance above 100Hz opens up the possiblity of using a separate dedicated power amp for the midrange and treble (in other words a lower-powered valve amplifier, or a class-A solid state one). The stock Amati unfortunately only has a single pair of terminals and so doesn't allow bi-wiring or bi-amping. With a clone, by contrast, the opportunities are limitless - in particular, an active crossover between bass and midrange would offer large benefits here.
The little peak in the impedance curve at about 380Hz may well be a cavity resonance, corresponding to a wavelength of 90cm, or a half-wave length of 45cm. This could be a front-back dimension, but given the shape of the cabinet it's more likely to be the height of a midrange or bass enclosure. Anyway, this isn't obvious in the overall responses, so is unlikely to be a serious problem.
A serious conundrum for most loudspeaker designers is what to do with the front of the box. Even with the most beautifully finished cabinets, the fact remains that most driver cones look at best utilitarian, and don't fit easily with most living room environments. The standard solution is the mundane frame-and-cloth grille, which certainly hides the drivers and can look quite presentable, but this inescapably affects the sound, both through diffraction at the frame or high-frequency absorption by the fabric itself. Some manufacturers such as Wilson Audio use a sculpted foam cover instead, but I personally find these pretty flimsy and aesthetically out of keeping with the rest of the system.
The extraordinary creations on the Amati, which first made their appearance on the Guarneri Homage, are by contrast in a different world from what is routinely attached to even high-end loudspeakers. They are made from a black synthetic elastic substance, and seem to be pretty transparent to sound, while allowing just a glimpse of the drivers behind. The stringy material, incidentally, reminds me of the suspension on SME's Model 20 and 30 turntables. The Amatis will doubtless sound better without the grilles attached, of course, particularly since the substantial top fixing plate is just above the tweeter.
Technical Information (quoted directly from Sonus Faber's own pages)
System: Lute design 3 way reflex. Cabinet: Combination of sandwich construction, obtained by 21 sheets of maple wood and solid maple, special resonance control with tuning by copper lead devices. Tweeter: 28 mm soft dome ultra dynamic ultra linear driver, multicoated, high resolution, no ferrofluid. Midrange: 180 mm ultra dynamic ultra linear driver, paper carbonium cone multicoated, equalized with titanium phase plug. Woofer: 210 mm ultra dynamic ultra linear driver extra-rigid paper carbonium cone, multicoated with aluminium dust cap. Cross Over: 200 Hz low bass mid, 2.5 kHz mid treble, first order attenuated, very high musical value components. Sensitivity: 92 dB 1 W 1 mt 2.83 V. Impedance: 4 ohms nominal. Power Handling: 30 W-300 W without clipping. Frequency Response: 24-30.000 Hz, tuning port included. Dimensions: 265 x 580 x 1170 mm W D H, 11 x 23 x 47 in W D H. Weight: 140 Kg. (308 lbs.) net weight pair, 180 Kg. (397 lbs.) shipping weight. Finishes: Piano gloss.
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Alex Megann, June 2001