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Hifi Review JAMO Concert 8 Loudspeaker System The Concert 8 Series main front speakers are beautifully made and give outstanding performance for their size. Designing loudspeakers has tended to be more of an art than a science. However, this review of the Jamo Concert 8 home theatre speakers demonstrates that the Dolby Digital system encompasses a lot of science and this is incorporated into the Jamo design. Review by LOUIS CHALLIS 6  Silicon Chip J AMO HAS BUILT its reputation as Denmark’s preeminent manufacturer of loudspeakers. Having tested many of its more innovative products, I have been consistently impressed by the manner in which they have been prepared to break new ground in the “quest for the Holy Grail”. To create a good loudspeaker, you have to start with appro­priate drivers and then the cabinet also plays a significant role in the resultant sound quality. The underlying reason for this interaction between the cabinet and its drivers relates to cabinet resonances which degrade the purity and integrity of the reproduced sound. That interaction is frequently extended beyond the initial transient when the walls of the speaker cabinet exhibit resonanc­es with minimal damping characteristics. When that occurs, an initial transient excitation can be extended for periods of as much as 50 milliseconds or more. The net result is a pronounced coloration of the sound. There are many ways through which such problems can be minimised. B&W in England have developed their modular foam-filled honeycomb structure, which has proved very effec­tive. A simpler (and less expensive) way is to add mass combined with an efficient damping mechanism. Jamo have adopted this strategy and applied it to the design of some of their latest loudspeaker cabinets. The Jamo approach involves the use of a double-plastic layer wall structure, whose internal cavity is filled with a special mixture of high density mineral sands and what Jamo describes as “a resonance deadening binding agent”. This structure results in an extremely heavy cabinet which then displays very good control of cabinet ‘coloration’ and other less obvious anti-resonant characteristics. Why am I bothering to tell you all this? Well, the Jamo Concert 8 and the Jamo Concert Center are the centrepieces as it were of the 5.1 channel loudspeaker system that I have just been reviewing. Those three speakers were supported by a pair of small Jamo Concert Surrounds for the rear speakers of the system, with a Jamo SW3015 Subwoofer providing the low bass content. Home entertainment is currently undergoing a dramatic change as more and more homes install a DVD player with that ubiquitous 5.1 channel audio capability. The aim of the game is to replicate your local cinema’s Dolby Digital Sound System in your living room. While that sounds like a tall order, it is now far easier to achieve than one might think. The basic elements that the latest generation of home thea­tres have are: a reasonable size screen, a good DVD player, five channels of sound amplification and the five speakers that go with it. Lastly, a self-powered or externally powered subwoofer is desirable. The Jamo Concert series are among the most visually attrac­tive home theatre loudspeaker systems currently being marketed in Australia. Each of the cabinets has been carefully designed to neatly fit on bookshelves, attach to the wall or to sit on stands. The rear of the Concert Center features foam backing, whilst the tops and bottoms of the Concert Surrounds have a soft rubber surface which allows them to be slid or moved without damaging them or the supporting surface. The Concert 8 Series left and right main front speakers are beautifully veneered, conforming to the highest Danish furniture standards. At just a modest 380mm high, they achieve an outstanding level of performance for their size. They employ a 165mm combined woofer and midrange driver that covers the frequency range from 40Hz to 2.5kHz. A 25mm diameter fabric dome tweeter then covers the top end and provides an unusually flat output response. The cabinet has a neatly contoured rear port. A rear ported vented enclosure can be an asset or liability, depending on how close the cabinet is placed to the rear wall or bookshelf; too close and the low frequency response will suffer. The Concert 8s have four sets of speaker terminals on the rear panel and they are designed for bi-wiring when required. With 4Ω impedance and a claimed 180W peak power rating, they are particularly potent, delivering sound level peaks that frequently exceed 110dB at your intended listening position. The front centre speaker, or Concert Center, as it is de­scribed, is a 3-way system with a cabinet construction very similar to the Concert 8. It utilises a pair of 165mm diameter woofers to cover the frequency range of 65Hz to 1100Hz. A sepa­rate 38mm diameter mid-range driver then covers the frequency range of 1100Hz to 3.5kHz and a 25mm diameter tweeter serves the top end of the spectrum. The Concert Center also has a 4Ω im­pedance and is similarly designed for bi-wiring where adopted or preferred. The rear of the cabinet features an impact absorbent foam lining while the rest of the cabinet is veneered. The Concert Surround speakers are based on design princi­ples laid down by THX. They provide a diffuse sound field by virtue of their V-front configuration, with two sets of speakers on each of the angled speaker faces. The speaker line-up compris­es a pair of 130mm diameter woofer/midrange speakers together with a pair of 25mm diameter soft dome tweeters. This composite speaker configuration provides a wide later­al sound field over the frequency range from 100Hz to 20kHz. The adoption of a rubber top and bottom surface enables the speakers to be inverted without fear of damage and provided the most convenient cable feed to the internally recessed angle speaker terminals. The acoustical outputs of the five speakers in the Jamo Concert series line-up are precisely matched, as you would ex­pect. They only require the addition of a good The Jamo SW3015 subwoofer uses a 15-inch driver and has a 300W amplifier. It has no difficulty in providing wall-shaking sound level over the frequency range from 30Hz to 150Hz subwoofer to fulfil the more demanding requirements of a “fully fledged” Dolby Digital or the alternative DTS Sound Decoding System. 15-inch subwoofer I already had a Jamo SW3015 subwoofer and this will team up with the Jamo Concert system. The SW3015 uses a 15-inch motional feedback controlled subwoofer capable of working without any sign of cone break-up to a frequency four times its upper intended operating limit. The voice coil is designed to accommodate a 20mm movement and is driven by a 300 watt amplifier. The amplifier has an outstanding 85% efficiency (presumably it is switchmode design) so that the heatsink and the size of the cabinet may be appropriately reduced. When producing a 100dB sound pressure (at 1m) the total April 2000  7 The Concert Center (front, centre) loudspeaker system matches the styling of the Concert 8. The cabinet houses four drivers: a pair of 165mm diameter woofers, a 38mm diameter mid-range driver and a 25mm diameter tweeter. harmonic distortion is claimed to be less than 1%. With that sort of performance, the SW3015 has no difficulty in providing wall-shaking sound level over the frequency range from 30Hz to 150Hz. A particularly nice feature is its “Auto On/Off” function that shuts the unit down automati­cally after 10 minutes with no input signal. each of the side walls and approximately 500mm from the rear wall of my listening room. The Concert Center was located directly between the two main speakers and all with a common height of 1.2 metres above the floor and 3.5m from the central listening posi­tion. Initial tests The two Concert Surround Speakers were located at matching positions at the rear of my listening room, separated by 5m and approximately 1.6m above the floor and 2m to the rear of my listening position. The first test disc I used was “DVD Spectacular” Delos DV7001 issued by Dolby Laboratories, who worked with Delos on its development. It makes it possible to test the swept frequency response of each of the five main channels, as well as the sub­woofer. With all six channels connected correctly in phase and with inputs correctly balanced, the measured frequency responses appeared to be exceptionally good; in fact, almost too good to be true. What surprised me was that each of the five separate Jamo speakers appeared to have a uniformly flat response all the way down to 30Hz. How could this be? It turned out that the subwoofer was the critical source of all the low frequency energy. I then realised that Dolby Laboratories had been more inno­vative than I had thought. By deactivating the sub­ woofer chan­ nel, I confirmed that Dolby Laboratories had designed a system that did not rely on any of the five primary channel speakers being flat below 100Hz. All the output below 100Hz is supposed to come from the subwoofer. So if you don’t own a subwoofer, you are forced to rely on the output from your two main (front, left and right) speakers to provide an extended low frequency response. Whilst the Concert 8s are adequate in that regard, they simply cannot match the perfor­mance of the SW3015. Obviously, Dolby Laboratories haven’t publicised this fea­ture, as they saw no need. Their licensees however, are well aware of this critical design characteristic. When designing their loudspeakers for an integrated 5.1 channel Dolby Digital compatible system, the five main speakers only need to cover the nominal frequency range 100Hz through to 20kHz. As it happens, the Jamo Concert main speakers offer a rela­tively wide frequency response that extends well below the 100Hz criterion. The Concert 8s provide a remarkably smooth response down to below 40Hz. That response was measured with the subwoofer inactive, to ensure that I didn’t fool myself. For my initial assessment of the Jamo Concert system, I connected the five loudspeakers to a Yamaha model DSP-E492 3-channel amplifier coupled to a Yamaha M80 amplifier which served the two front channels. The Yamaha audio-visual processor/amplifier has a neat sequential reference tone to make it easy to adjust the five channels for equal output. Subsequent checking with a sound level meter confirmed that my subjective adjustment was accurate to within 2dB. I placed each of the Concert 8 loudspeakers on stands at one metre from The Concert Surround speakers provide a diffuse sound field by virtue of their V-front configuration, with two sets of speakers on each of the angled speaker faces. The driver line-up includes a pair of 130mm diameter woofer/ midrange speakers plus a pair of 25mm diameter softdome tweeters. 8  Silicon Chip Too good to be true Fig.1: this graph shows the frequency response of the Concert 8 left and right speakers, with the sub-woofer active (red). The green line shows the response of the subwoofer by itself at two metres. Fig.2: this graph shows the frequency response from the right front at 1.4 metres with the sub-woofer active (red) and the right front at 1.4 metres with the sub-woofer active. The subwoofer’s high frequency cut-off was set to 100Hz for my testing. However, the SW3015 can cover a significantly wider frequency range, up to 180Hz. The Concert series do not incorporate protection circuitry. Instead, each is designed to withstand short-term transient power inputs exceeding 150W. I used a 300W per channel stereo amplifier to drive the Concert 8s and a five-channel amplifier (5 x 150W) and although I subjected the speakers to some pretty nasty input signals, they never missed a beat. With peak inputs of 130W there were no problems at all, although at that input level, harmonic distortion is readily detectable. With unweighted peak and pressure levels exceeding 110dB, I was able to replicate the sound levels currently heard in cinemas. There is a surprisingly large amount of Dolby Digital soft­ware available in Australia. By contrast, there is relatively little DTS material around, although the first ‘dribs and drabs’ are now trickling into Australia. Fortunately I was offered a sample of the latest DTS audio material produced by Telarc, a 5.1 DTS Surround Sampler with which I evaluated a Kenwood model D 1888 DE 5-channel amplifier. This provided the opportunity to make a comparison with comparable Dolby Digital material. My assessment is that well recorded DTS encoded material is every bit as good as equivalent Dolby Digital encoded software. Irrespective of which source input you choose, the Jamo Concert 8, Concert Center and Concert Surrounds supplemented by the SW3015 subwoofer provide an audible performance that has to be heard to be appreciated. Irrespective of the software, the frequency response is impeccable. With a choir singing and organ playing, a bass drum being struck, a cannon firing or an orchestra playing, I had no difficulty in replicating the subjective feelings that I fre­quently experience when sitting in a concert hall at the Sydney Opera House. In short, the Jamo Concert series look impeccable and sound very impressive. For more information, contact SC Jamo Australia on (03) 9543 1522. DON’T MISS THE ’BUS Do you feel left behind by the latest advances in com­puter technology? Don’t miss the bus: get the ’bus! 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