Stereo Amplifier

Review: Jamo Concert 11 Speakers

This is a good loudspeaker. No, I'll amend that: this Concert 11 is a very good loudspeaker; one of a handful that have visited Hornsville over the years which I have been truly reluctant to move on. Not that it is perfect - none of them are - but its departures from the ideal are scarcely worth detailing. However, that is part of my job so in due course they will get a brief mention. In the meantime, let us deal with its merits.

The cabinet is about four times the volume of the Concert 8 and an insight into its quality can be gained from its weight which is a hefty 32.5kg (72 lb). However, despite its bulk the presence of a pair in my listening room was far from visually overpowering; this is a tribute to the skill of the design stylists - not at all obvious on first acquaintance. The width is a shade less than 280mm (11 in) and is broken up vertically by the inset baffle which, as in the Concert 8, consists of two cast plastics shells with the 30mm-plus space between them filled with quartz sand bonded with a resin to form a heavy, solid mass. Into it the three drive units are recessed and the thin grille frame plugged; the latter is narrower than the baffle which curves back to meet the projecting cabinet sides, also curved to minimize diffraction. The frontal area is also broken up horizontally by a projecting arc of the baffle carrying the company logo and a cross-banded veneered section between it and the thick plinth. This plinth is also a black plastics moldings which incorporates four deep button feet which are centrally threaded to accept a set of supplied spikes if required.

A view from the side reveals the fact that the composite baffle, which Jamo calls NCC (Non Coloration Compound), is in fact sloping backward, being considerably thicker (50mm) at the lower end; this tends to put the seated listener near to the axis of the central bass/midrange unit. The main cabinet carcass is made from double-skinned MDF of 25mm nominal thickness. My samples were veneered on all visible surfaces in mahogany and lightly finished with a satin lacquer. The cherry finish seen on my earlier Concert 8 samples is also available. All the major corners are rounded and the veneer carried seamlessly around them. This is a process which seems to defeat the majority of cabinet makers who resort to painted infills or solid wood inserts.

The overall appearance has met with almost universal favour from those visitors I have asked, which is unusual for a fairly large loudspeaker; significantly none has commented until asked. Internally there are two sculpted internal MDF braces roughly opposite the two cone units and a bracing shelf below the heavy front baffle assembly. Near the bottom of the rear face is a labelled connection plate carrying six robust goldplated but uninsulated terminals with 4mm socket centres. Although these loudspeakers carry the CE endorsement I had thought both these details caused severe indigestion in Brussels.

Crossover networks for the bass/midrange driver and tweeter are mounted on a stout board held in place by the extended threaded portion of these terminals. There is a separate board for the woofer which carries two heavy iron dust core inductors, and this is screwed to the rear wall opposite its drive unit. The Concert 11 is a reflex design with a larger than usual tunnel port at the bottom of the baffle, 70mm in diameter and approximately 150mm long; it is formed of a plastics tube flared at both ends and with a deep lip sealed to the front face so that it can pass through the slightly oversize hole in the baffle. All the internal walls have sheets of thick and deeply sculpted acoustic foam wedged over them.

As mentioned earlier, the upper two units are identical to those used in the Concert 8; to recapitulate briefly, the tweeter is a 25mm fabric dome with multiple coatings on a 6 ohms silver wire voice-coil immersed in magnetic fluid. Its rear face ventilates to a damped chamber to keep the self-resonance frequency low. The main driver carries the full range up to about 2.5kHz and has a mildly flared 25mm diecast magnesium cone on a 38mm 3.3 ohms coil with a convex rubber roll surround; there is no dust cap but a tapered copper phase plug is fixed to the centre pole which works in conjunction with interior copper rings to soak up eddy currents. Both of these units come from SEAS in Norway and are part of its 'Excel' range.

The bass driver also appears to originate with SEAS and is described as having "a die-cast PP membrane". I translate this as having a moulded (as opposed to vacuum formed from sheet) polypropylene diaphragm - at any rate that is what it looks like. It appears to share the same cast magnesium chassis and magnet assembly as the bass/midrange unit but has a conventional dust cap. The one I checked had a freeair resonance at 35Hz, rather higher than it s fellow at 28Hz. Both will probably drop a couple of Hz after a few months of use. The DC resistance of the voice-coil was over twice that of its mate at 7.8 ohms. Very often the feed to the lower unit of these 2-1/2-way systems - so called because both cone drivers are handling the low frequencies – is just a single series inductor. This exists here in the form of a large iron dust cored thick copper winding of about 11mH inductance, although it is supplemented in this case by a second slightly less imposing cored coil in series with 450μF worth of reversible electrolytic capacitors and 10 ohms of resistor together shunted across the voice-coil. I'm no t sure what little anomaly this exists to counter but it is nice to know that someone thought it worthwhile.

Performance Both the weight and the weather I'm writing this at the end of our wettest June - have put me off attempting to move one of these Concert 11 is into my anechoic chamber, otherwise known as the open air in the garden. Therefore what measurements I have been able to make have been in my usual listening room. A preliminary check on the in-box bandpass resonances turned up the figures of 17 and 52Hz which suggested that an extended bass response was to be anticipated. This proved to be the case and organ pedals well below 30Hz could be felt with ea se and with no trace of the knocking noises which many loudspeakers exhibit when asked to perform in this area at any substantial volume.

In a fascinating introduction to subwoofers, "The lowdown on the low down", Alvin Gold painted an admirable picture of the very real advances to realistic listening which well reproduced bottom octaves can generate. I read it with great joy because I had begun to think that I had been treading a lonely path all these years in stressing that building your audio house on anything less than the firmest foundations is a permanent denial of musical satisfaction. However, such satisfaction is not dependent on the acquisition of a good subwoofer loudspeakers such as these and a few others I have met up with can manage it very well on their own. I like to think - in fact I know - that quite a few visitors have left to seek such a benefit for their own equipment; even our Audio Editor has contrived a clever augmentation of his ESL-63s.

The other great failure of loudspeakers in general is transient response, a discrepancy between their attack and decay and the electrical signals responsible. Poor attack sets limits to vividness and life; poor decay introduces audible frequency dependent errors, bloat in the upper bass, muddle and incoherence in the midrange and sibilance and sting in the treble. Recent computer technology has permitted ready examination of this aspect in the form of three-dimensional 'waterfall' plots which display frequency versus amplitude as a repeating series against time. Interestingly, some 40 years ago, D. E. L. Shorter of the BBC was laboriously accomplishing this by hand plots made in the form of cardboard cut-outs and placed one in front of the other in a slotted board! These were described as a fade spectrum which I think is a better term. It was because of their feather-light diaphragms, unable by their nature to store significant energy, that early electrostatic loudspeakers scored such high marks, completely overshadowing their other very considerable limitations. Since their arrival on the scene 40 years ago, this aspect of loudspeaker performance has been under attack by every significant drive unit designer.

Recent work has concentrated on diaphragm materials and these two Concert models show a promising advance in the metal cone faction which has been rapidly developing of late, following pioneer work by Brittain and Jordan in the 1950s and '60s. This improvement is demonstrated by Specification the remarkably clean and eloquent response to the whole important midrange area; the definition achieved is quite outstanding, particularly on voices which can be startlingly real at times. Using excellent pianoforte recordings I thought I could detect a slight edge to the upper response of this unit which is used up to 2.5kHz but has only a 12dB/octave roll-off. Others have reported a slightly metallic accent to the Concert 8 but I feel this comes from visual expectation rather than audible evidence - I certainly did not experience it. That said, I thought this Concert 11 was slightly sharper than my recollection of the smaller model and I preferred with the very minor filtering provided by the grille. It is possible to vary the relative level of the tweeter either at the crossover frequency or in the extreme treble by moving links on the terminal block but I came back to the level position every time.

The only other area which I initially questioned was the bloom imparted to plucked double-bass on some of my jazz discs and this caused me to try other room placements, but nowhere was an improvement on my usual position just over a metre from the rear wall and around half that from the sides, with slight toeing-in to reduce early reflections from the side. I also tried introducing a little resistance in the port with acoustic foam which overdid it and then a loose plug of long haired wool which seemed to do the trick. However, after having the loudspeakers in use for a few weeks I was playing a friend's organ recording and experimentally removed the wool to discover that the original problem had almost disappeared - so too had the piano ping: these loudspeakers obviously benefit from a prolonged run in. This won't take too long because once installed the main difficulty is finding enough time to go on listening to them. Granted they are not cheap, but at a couple of grand they are remarkable value for money - probably more so than any others that have flattened my living/listening room carpet over the years.

Thoroughly recommended without question. Music at home was intended to be like this.