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To the right of fig.3 are shown the crossover's complementary high-pass responses for the drive to the Beethoven panel, with the woofers turned on and off. A small degree of tonal shaping can be seen between 200Hz and 1kHz. Without the subwoofers, the crossover adds a modest amount of boost below 150Hz to flatten and extend the panel's output, with then a steep rolloff below 40Hz. When the subwoofers are used, the crossover gently rolls out the panel woofers below 100Hz. The crossover's input impedance was a high 86k ohms (balanced), while its output impedance was a low 450 ohms. The…
In the time domain, the Beethoven's step response (fig.9) is not coherent. The tweeter and midrange units appear to be connected with inverted acoustic polarity, the woofer with positive polarity. Fig.10 shows the cumulative spectral decay plot calculated from the Beethoven's impulse response. It is superbly clean throughout the treble, but there is some hash present in the low treble, which I suspect is due to early reflections from the speaker's structure. However, as SD had nothing but praise for the Beethoven's sound, I assume this is benign.
Fig.9 Audio Artistry Beethoven,…
I've long been a fan of Naim electronic gear, and have used it for many years. I also have admiration and respect for the company's uncompromisingly consistent and determinedly individualistic approach to the various tasks and problems of loudspeaker design. But my enthusiasm for Naim speakers has long been tempered by a feeling that mechanical aspects of the design are given priority over acoustics and styling.
Naim's new NBL loudspeaker has been wowing plenty of hi-fi show visitors recently, and is unquestionably the most attractive-looking speaker the company has yet produced. The…
While the bass drivers will normally be acoustically coupled to wall and floor, the cabinet's depth not only ensures excellent stability (to some extent unnecessary in view of the mechanical decoupling and horizontally opposed bass drivers), but also places the mid and treble drivers sufficiently far from the wall to avoid the most serious effects of reflection coloration. The main enclosure and its substantial, neatly styled, cast-alloy plinth is the "virtual mechanical earth" for this speaker system. Its lower 23" act as the main, 2.1ft3 (60-liter) bass cavity, but above that the cabinet…
The first time I heard the NBLs in my room, I was reminded of the wall-mounted drive-units by Tannoy (15" alnico-magnet dual-concentrics) I sometimes use. These drivers, flush-mounted in a structural wall and left unobstructed to their rears operate as true boxless infinite baffles, and are regular reminders of the limitations of normal loudspeaker enclosures. While the NBL doesn't share the same tonal balance of these wall-mounted Tannoys by any means, it does have something of the same "boxless" sound quality. This would seem to confirm the efficacy of that complex enclosure decoupling.…
I discussed the NBL's tonal balance with Phil Ward, who said that the speaker had existed in active form for some months before the passive version was finalized, and that the control settings arrived at under active drive provided a "target function" for the speaker's passive balance. It's my suspicion that an active system can get away with being more "forward" than its passive equivalent, simply because the absence of passive crossover components invariably makes the sound inherently cleaner. A slightly more restrained balance might be more acceptable in the marketplace.
Stereo…
Sidebar 1: Specifications
Description: Three-way, floorstanding, sealed-box loudspeaker. Drive-units: 0.7" cloth-dome tweeter, 5" paper-cone midrange unit with phase plug, two 8" paper-cone woofers. Frequency response: 25Hz-20kHz ±3dB in-room. Nominal impedance: 4 ohms minimum. Sensitivity: 92dB/W/m. Power handling: 150W (music).
Dimensions: 44.9" (1140mm) H by 11" (290mm) W by 19" (430mm) D. Weight: 90 lbs.
Finishes available: Black Ash, Walnut, American Cherry, Ebony, Beech, Santos Rosewood.
Serial number of units reviewed: Not noted, auditioning samples; 160627 (speaker),…
Sidebar 2: Associated Equipment
Because I normally use Naim electronics, I already had access to and was familiar and comfortable with the "manufacturer-approved" driving system for the NBLs. But because I still haven't managed to get my mitts on a Naim NAP500, I did most of my listening using a Naim NAC52 preamplifier and Naim NAP135 monoblock power amplifiers. Other amplification included Mana Stealth MA-1 monoblocks and a Bryston BP25/2X7B pre-/power combination.
Prime sources were Naim CDS II and Audio Note CDT-Zero/DAC 5 CD players. Vinyl replay was mostly via a Linn LP12…
Sidebar 3: Measurements
The Naim NBL's specified sensitivity is very high at 92dB/W/m, though this will be boosted 3dB by the speaker's 4 ohm nominal impedance. (That "W" in the specification is therefore actually equivalent to 2W). I measured approximately 89.8dB(B)/2.83V/m, which is still high. Fig.1 plots the Naim's impedance magnitude and phase against frequency. The former varies little, staying within 4 and 6 ohms over most of the audioband, with only a moderate phase angle. A good 4 ohm-rated amplifier will have no problems driving this speaker. A couple of small wrinkles can be…
Fig.4 shows the NBL's response on the tweeter axis, averaged across a 30 degree horizontal window to minimize the effect of position-dependent, and hence irrelevant, interference effects. Though it is very even, the entire treble is shelved-up compared with the lower midrange and bass, which is why PM commented on the speaker's bright, forward balance. As I've said, the NBL's low bass will be boosted by the Allison Effect, but this will leave the region between 300Hz and 600Hz depressed in comparison with the regions above and below. In addition, as PM found in his in-room measurements, the…