Jamo Concert 8 and Concert Center Speakers (a review from early 1997)

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[Review by D. B. KEELE, JR., orig. from Audio magazine 100th anniv. issue, May 1997]

Jamo (pronounced yah-mo), a 30-year-old Danish company, is currently the largest loudspeaker manufacturer in Europe. The company offers more than 61 different speakers in the United States, including models for high-end audio, home theater, and architectural acoustics. Jamo’s products are distinguished by sleek and sometimes unusual Danish design. Two of its most arresting speakers, the Atmosphere (for wall- mounting) and the Converta (which can be wall-mounted or suspended from a cable) have built-in halogen lights, This review is primarily of Jamo’s new, high-end Concert 8 speakers, together with the Concert Center speaker designed for use with them in home theater systems. But Jamo also supplied a pair of Surround One dipoles from its Home THX line, to flesh out the system. (I used a subwoofer I had on hand, although Jamo has a line of those, too.) The Concert 8 is a compact, two-way model with a 6½-inch vented woofer and a 1-inch dome tweeter. Designed for horizontal placement on top of a TV set, the Con cert Center is a three- way system with two 6½-inch woofers, a 1½-inch dome midrange, and a 1-inch dome tweeter. The Surround One ($998 per pair) has a 4-inch woofer and a 1-inch dome tweeter on its front and an identical array on its back, plus a third 4-inch woofer (which operates only below 200 Hz) on the side that faces the listening area.


The speakers in Jamo’s Concert series boast many high-end features. These include voice coils wound from pure silver wire, Jamo-manufactured internal cabling of premium oxygen-free copper, 24-karat gold-plated terminals, individually matched components, solid-copper phase plugs, neodymium magnets, die-cast magnesium frames, and exotic wood veneers. The Concert 8 is the smaller and less expensive of the two main speakers in the Con cert line. The Concert 11 ($3,600 per pair) differs only in having a large, floor-standing cabinet and a second 6½-inch driver (a different design optimized for low-bass reproduction) that crosses over at 150 Hz.

The Concert 8 and Concert Center have several unusual construction features in common. The most important is the com position of their front baffles, which are made from quartz sand mixed with a resonance-deadening binding agent and covered front and rear by cast shells of a synthetic material. Jamo says this patented Non-Coloration Compound structure is extremely rigid and inert. The speakers’ medium-density fiberboard grille frames are thin, to keep the drivers close to the grille cloth. And their cabinets are manufactured from 1-inch-thick medium-density fiberboard, reinforced with braces and lined with honeycomb-patterned acoustic foam to maximize damping.

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CONCERT 8

Rated Frequency Range: 38 Hz to 22 kHz.

Rated Sensitivity: 90 dB at 1 meter, 2.83 V rms applied.

Rated Impedance: 4 ohms, nominal. Rated Power Handling: Long-term, 120 watts; short-term, 170 watts.

Dimensions: 15 in. H x 9 in. W x 12¼ in. D (38 cm x 24.5 cm x 31 cm).

Weight: 24.9 lbs. (11.3kg) each.

Price: $2,400 per pair; available in swietinia mahogany or cherry wood.

CONCERT CENTER


Rated Frequency Range: 65 Hz to 20 kHz.

Rated Sensitivity: 91 dB at 1 meter, 2.83 V rms applied.

Rated Impedance: 4 ohms, nominal. Rated Power Handling: Long-term, 110 watts; short-term, 150 watts. Dimensions: 8¼ in. H x 22 in. W x 11¼ in. D (21 cm x 56cm x 28.7 cm). Weight: 23.8 lbs. (10.8 kg) each. Price: $800 each; available in swietinia mahogany or cherry wood.

Company Address: 1177 Corporate Grove Dr., Buffalo Grove, III. 60089; 847/465-0005;

jamospeakers.com

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To minimize diffraction, the drivers of the Concert 8 and Concert Center are recessed into their front panels and the corners of the baffles and enclosures are rounded. The recess surrounding the Con cert Center’s midrange driver is especially deep, forming a horn-like sound director. One effect of this structure is to improve the driver’s response at the low end of its range. Others are to restrict its coverage to the listening area and minimize wall reflections (both standard design goals for center speakers).

The Concert 8’s port tube, 6 inches long and 2½ inches in diameter, is flared at each end and exits near the top of the rear panel. The woofer has a very rigid but light die- cast magnesium diaphragm with a rubber surround. Its most interesting feature is the solid-copper phase plug in the center of the cone. The plug takes the place of a dustcap but is attached to the driver’s center pole so that, unlike a dustcap, it does not move with the cone. It is said to reduce distortion caused by cone breakup and eddy currents and to improve cooling by increasing heat transfer from the voice coil. The phase plug is also said to smooth the driver’s upper- midrange response. The Concert 8’s tweeter has a coated cloth diaphragm and is ferrofluid-cooled.

The Concert Center is an aperiodic design—essentially, a box with a highly resistive vent formed by narrow rear-panel slots whose total area is roughly 20% that of the woofers’ diaphragms. This enables the use of relatively large drivers in a small cabinet. The woofer diaphragms are of glass fiber, and the magnets are shielded to allow placement directly on or below a TV. Al though the Concert Center’s tweeter is different from the Concert 8’s, it also has a coated cloth diaphragm and ferrofluid cooling; both it and the dome midrange have high-energy neodymium magnets.

The crossovers for the Concert series speakers were designed to smooth their power response and to ensure that the drivers are essentially in phase through the cross over range, which improves vertical coverage and minimizes lobing error. The Concert 8’s crossover contains three air-core inductors, four capacitors, and three resistors, hooked up as a second-order low- pass filter (with impedance compensation) and a third-order high- pass. The crossover is mounted to the input-connection panel, directly behind the woofer. Bi-wiring and bi-amping are supported via large, heavy-duty, gold-plated binding posts on about 1” centers. Straps are provided for normal, single-wire operation.

The Concert Center’s crossover has a third-order low-pass filter for the woofer, a second-order band- pass for the midrange, and a third- order high-pass for the tweeter. These filters are implemented with four inductors (one iron-core, the rest air-core), four capacitors, and two resistors. The Concert Center’s input connections are identical to the Concert 8’s.

Measurements:

Figure 1 shows the on-axis anechoic frequency response of the Concert 8, with and without its grille, and of the Concert Center (lowered 10 dB for clarity). The measurements were taken in a large anechoic chamber at a height halfway between the Concert 8’s woofer and tweeter and halfway between the Concert Center’s mid range and tweeter. The response below 200 Hz has been corrected according to near- field measurements.


Fig. 1—On-axis frequency response of Concert Center (lowered 10 dB for clarity) and Concert 8.

Fig. 2—On-axis phase response, group delay, and waveform phase of Concert 8.

Fig. 3—Horizontal off-axis frequency responses of Concert Center.

Fig. 4—Vertical off-axis frequency responses of Concert Center.


Fig. 5—Impedance magnitude of Concert 8.

Fig. 6—Impedance magnitude of Concert Center.

Fig. 7—Three-meter room response of Concert 8.

Without the grille, the Concert 8’s response is commendably smooth and ex tended but shelves down about 3 dB below 600 Hz. The overall curve fits a moderately tight, 4.8-dB, window between 54 Hz and 20 kHz. The low-frequency response is flat and extended, about 3 dB lower at 48 Hz than at 200 Hz and down another 3 dB at 43 Hz; that’s very good for a speaker of the

Concert 8’s size. The grille has only minimal effect on the response; the major deviations are only about ±2.5 dB in the narrow range be tween 6 and 8 kHz. The right and left speakers matched reasonably well, within ±0.5 dB of each other below 4 kHz and within ±1.5 dB at higher frequencies. Averaged from .250 Hz to 4 kHz, the Concert 8’s sensitivity measured 86 dB, 4 dB below Jamo’s rating.

The Concert Center’s on-axis response is not as smooth and flat as the Concert 8’s, occupying a wider, 6.5-dB, window between 82 Hz and 20 kHz. Averaged from 250 Hz to 4 kHz, the Concert Center’s sensitivity measured 88.8 dB, 2.2 dB below Jamo’s spec.

Figure 2 shows the Concert 8’s phase and group-delay responses, referenced to its tweeter’s arrival time. The phase curve is well behaved but rotates 240° between 1 and 10 kHz. When averaged be tween 700 Hz and 2 kHz, the group-delay curve indicates that middle frequencies are delayed about 0.25 millisecond relative to the tweeter range. The curve for waveform phase is not at or near 0° or ± 180° over any frequency band, which indicates that waveshapes will not be preserved. But this is normal behavior for all but the very few speakers designed specifically to maintain waveform phase.

The Concert 8’s horizontal and vertical on- and off-axis responses were very well behaved. Horizontally, the response was quite broad and even, with ex tended off-axis coverage to above 16 kHz. Vertically, the response was very uniform from on-axis to 15° above and was essentially flat through the crossover region. At 15° below axis, a moderate, octave-wide dip developed between 2 and 4 kHz.

The Concert Center’s horizontal off-axis response is shown in Fig. 3. (The bold curve at the rear of the graph is the on-axis response.) Like most center-channel designs, this speaker has significantly greater directivity (narrower coverage) than speakers designed for stereo music listening, primarily because of the wide spacing between the woofers, which operate together below 1.1 kHz. The most significant anomaly is an abrupt widening of the response just above the lower, 1.l-kHz, crossover, where the wavelengths are too great for the horn recess to control their directivity. The high- frequency coverage, on the other hand, is quite even and extended.

The Concert Center’s vertical off-axis response is shown in Fig. 4. (The bold curve in the center of the graph is the on-axis response.) Note that the coverage is quite broad below 3 kHz, as compared to the horizontal off-axis radiation seen in Fig. 3. At higher frequencies, in the tweeter’s range, the vertical and horizontal coverages are essentially the same and quite well behaved.

Figure 5 shows the Concert 8’s impedance magnitude versus frequency. There are no surprises here. The two peaks below 100 Hz are the hallmarks of a vented enclosure; the 5.8-ohm dip between them indicates the speaker’s tuning frequency, 50 Hz. Be cause the Concert 8’s minimum impedance is 4.4 ohms and its maximum is 23.6 ohms, the overall impedance variation is a moderately high 5.4 to 1 (23.6 divided by 4.4). So, for example, if you want to keep cable-drop effects from causing response variations greater than 0.1 dB, cable series resistance should be limited to about 0.063 ohm or less. For a typical run of about 10 feet, 12- gauge (or larger), low-inductance cable would suffice.

The Concert Center’s impedance magnitude is shown in Fig. 6. The variation is significantly less than for the Concert 8—a relatively low 2.6 to 1 (10.8 ohms divided by 4.2 ohms). The impedance is also uncharacteristically flat below 100 Hz, varying only from 5 to 6.3 ohms, because of the speaker’s aperiodic enclosure design.

The Concert 8’s raw and smoothed 3- meter room responses (Fig. 7) were taken in my listening room, rather than my home theater, for comparison with the room responses I’ve measured for other speakers. The Jamo was in the right-channel stereo position; the test microphone was at ear height (36 inches), at my listening position on the sofa. If you exclude the peak at 1.6 kHz, the smoothed curved fits a tight, 6.5- dB, window from 650 Hz to 20 kHz. Overall, the smoothed curve fits a looser, 13-dB, window, including all peaks and dips.

Figure 8 shows the Concert 8’s G (49- Hz) harmonic distortion, with input power ranging from 0.05 to 50 watts. The second harmonic reaches only a low 71%, while the third rises to just 2%. Higher harmonics are 0.8% or lower. Interestingly, the third harmonic did not decrease at lower levels but remained in the 1% to 2% range. The low distortion at G is because its frequency, 49 Hz, coincides almost exactly with the Concert 8’s tuning frequency of 50 Hz.

The E (41.2-Hz) tone I usually use for this test is significantly below the Concert 8’s tuning frequency and thus caused excessive distortion. With 50 watts input, the second-harmonic distortion at this frequency reached nearly 100%; the third harmonic was 17%.

Distortion for A (110 Hz), well above the Concert 8’s tuning frequency, rose to only 8.6% second harmonic and 4.5% third, with higher harmonics below 1.4%. The A (440-Hz) harmonic distortion was very low, 0.4% or less.

The Concert Center’s 50-watt harmonic distortion at G (49 Hz) rose to 6.3% second, a high 46% third, and 8.2% fourth, with higher harmonics less than 1%. Raising the test frequency one-third octave, to 63 Hz, reduced the harmonic distortion readings to the more reasonable levels of 3.4% second, 12.6% third, and 2% fourth.

The Concert 8’s cabinet is quite solid: A high-level sine-wave sweep caused minimal vibration except at about 340 Hz, where the side walls vibrated noticeably. The woofer overloaded quite gracefully and exhibited a maximum excursion of about 0.5 inch, peak to peak. Significant dynamic distortion was evident just below the 50-Hz box resonance and above 80 Hz, where the cone displaced outward. A healthy reduction in excursion occurred at the speaker’s resonance. Some chuffing was evident from the ports.

The Concert Center also has a very solid cabinet, although I noticed some side-wall vibration at about 230 Hz. I heard significant buzzing and chuffing from the ports between 60 and 80 Hz at high input levels with test signals. The woofers’ maximum excursion was about 0.3 inch, peak to peak.

I measured only the Concert 8’s short- term peak power input and output (Fig. 9). The peak input power starts low, 8 watts at 20 Hz, and then rises very rapidly to 400 watts at 50 Hz, the speaker’s tuning frequency. After a slight fall to 230 watts at 70 Hz, the power handling rises quickly to the speaker’s maximum of 7.2 kilowatts above 600 Hz. Between 80 and 160 Hz, the woofer exhibited significant dynamic offset, with the cone moving outward.


Fig. 8—Harmonic distortion for G (49 Hz) of Concert 8.

Fig. 9—Maximum peak input power and sound output, Concert 8.

With room gain included, the Concert 8’s peak acoustic output starts at an unusably low 78 dB at 20 Hz, rises very rapidly (passing through 100 dB at 42 Hz and 110 dB at 46 Hz), and reaches a healthy peak of 113 dB at 55 Hz. After a slight decrease to 110.5 dB (at 100 Hz), the output sound pressure level rises rapidly up to about 125 dB above 600 Hz, passing through 120 dB at 250 Hz.

Use and Listening Tests

The Concert 8s, which came to me in the mahogany finish, looked gorgeous and seemed very substantial and well built. They looked even more distinctive without their grilles, thanks to the shiny machined- copper phase plug in the center of each woofer’s light-colored cone. Every detail, from the screws in the tweeter flanges to the terminals on the rear, contributed to their elegance.

Naturally, I was quite curious to find out if the Concert 8s sounded as good as they looked. I was not disappointed. Played as stereo music speakers, they stood out from the pack of other small bookshelf systems, possessing a smooth, extended response that competed very well with the output from much larger systems. I was particularly impressed with the quality and quantity of the bass, which was exceptional considering the Concert 8’s size. They weren’t bass- shy, as many small speakers are.

The Concert Center clearly is cut from the same cloth as the Concert 8, though it did not look quite as distinctive, particularly without its grille. Both use the same gold- plated terminals, whose large, ¼-inch holes can take wires of jumper-cable size. The terminals are not spaced on the standard ¾- inch centers that would enable them to accept double-banana plugs, but I discovered that you can wedge such plugs securely be tween the terminals’ shafts. (European safety rules forbid ¾-inch terminal spacing, as that’s too close to the spacing of many European AC power plugs and sockets.)

At 122 pages, Jamo’s instruction manual for the Concert series speakers looks impressively thick—until you realize its information is repeated in eight different languages (English, Danish, Dutch, German, French, Swedish, Spanish, and Chinese!); it would make a good Rosetta Stone for language reference. The 18-page English section is well written, informative, and very thorough—one of the best manuals I’ve seen. (The Surround Ones’ 64-page multilingual manual—of which 10 pages are in English—was also quite detailed and helpful.)

I first listened to the Concert 8s as standard stereo speakers. I placed them as Jamo’s manual suggests, allowing a minimum of 12 inches to the wall behind them and at least 30 to 40 inches to the side walls, and toeing them in toward my listening position. I was immediately impressed with the Concert 8’s smooth and balanced sound, extended broad-coverage high-frequency response, and even bass response, which made it sound like a significantly larger system. Small speakers often make you want to turn up the bass because the speaker sounds rather anemic on its own. This was not the case with the Concert 8s, which sounded well balanced.

The Concert 8s sounded as smooth as the B&W 801 Matrix Series 3 speakers I use for comparisons but had a slightly elevated high end that made them sound crisper and more open. Only on program material with high levels of low bass did the B&Ws beat the Jamos. The Concert 8s and the B&Ws had essentially equal sensitivity. The Concert 8s reproduced female vocals quite faithfully, with no harshness and only a slight emphasis on sibilants when com pared to the B&Ws. Their imaging and soundstaging could not be faulted.

On pink noise, the Concert 8’s upper- midrange balance did not change significantly when I stood up, which is very good. On third-octave, band-limited pink noise, the Concert 8s exhibited strong output from 50 Hz up, with quite usable output down to 40 Hz. When the speakers were driven hard, dynamic offset caused significant outward cone displacement in the 40-, 80-, and 100-Hz bands, accompanied by a sudden increase in second-harmonic distortion. And at levels that caused large cone excursions, I heard some chuffing sounds from air moving around the copper phase plugs.

After my initial stereo music listening, I transferred the Concert 8s to my home theater and set them up with the Concert Center and the Surround Ones. The Concert 8s were placed 20 inches to either side of a 52- inch rear-projection TV, and the Concert Center was centered on top of it. The Sur round Ones were mounted to the sides of my chair, somewhat above ear level. The subwoofer was the Boston Acoustics VR 2000 that I reviewed in the January issue. Aside from the speakers and a Sony VCR, all the audio/video equipment in this system was Pioneer Elite.

The Jamo speakers were installed in my home theater long enough for me to be come familiar with their capabilities on a wide variety of material. The Concert Center performed flawlessly on most, reproducing both male and female voices intelligibly and realistically. Compared with the KEF Model 200C center-channel speaker I normally use, the Concert Center did exhibit some slight upper-midrange tonal differences, primarily when I listened to net work anchorwomen. On male voices, it sounded fairly dry and analytical, with no chestiness or tubbiness; Jamo’s aperiodic design seems to have paid off well here.

The Concert 8s also performed strongly in their home theater role. On soundtracks with dynamic sound effects (such as Top Gun’s jet fighters), the Concert 8s, Concert Center, and Surround Ones rose to the occasion, reproducing them loudly and cleanly. The Surround Ones did everything they were supposed to do, creating a properly dif fuse surround sound field that contributed greatly to the realism of soundtracks.

Music CDs also sounded very good through the Jamo home theater setup. I am still surprised at the large increase in real ism often provided by playing music recordings through a Dolby Pro Logic decoder in a good home theater system. Live concert recordings, especially those with audience sounds and clapping are tremendously enhanced. Having soloists actually come out of the center also improves the presentation greatly.

I am very satisfied with these Jamo speakers, both for stereo music and home theater use. I was particularly impressed with the Concert 8s’ wide, smooth response and well-balanced sound, coupled with impressive bass output for their size. The bass was solid and strong when called for, with out boominess, and the Jamos competed very well with my reference systems over the rest of the audio range. The Concert Center and Surround Ones were equally adept at bringing out all the best qualities of movie soundtracks. The Concert speakers also boast first-rate looks and construction, suitable for display in any home entertainment system. If you desire speakers with a true high-end pedigree and features suited for both stereo and home theater reproduction, you need look no farther than the Jamo Concert 8 and Concert Center.

Adapted from Audio magazine (1947-2000). Classic Audio and Audio Engineering magazine issues are available for free download at the Internet Archive (archive.org, aka The Wayback Machine)






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