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1NT can easily be improved

216.78.101.80

Posted by layman on October 14, 2001 at 07:43:45

In Reply to: REVIEW: B&W CDM 1NT Speakers posted by Arnel on October 14, 2001 at 00:54:53:

The CDM1NT's performance can be improved with a few benign tweaks. Firstly, I would tame the treble performance by using felting around the dome. Specifically, there is an edge beneath the tweeter that leads to audible diffraction effects, that treble roughening (visible on a graph) that tends to irritate the ear. Covering that edge (and adjacent edges) with an absorptive (in this case felt applied with rubber cement) greatly smoothes treble response. I would cover that bottom edge (and the B&W logo right below the tweeter-another cause of roughening) with a wide piece of felt, as well as placing felt strips along the entire left and right edges of the baffle (keeping in mind that the baffle is 3-dimensional in this model). After felting, the treble sounds much cleaner, and sweeter and has much less of a tendency to irritate.

Furthermore, I have noticed that treble response is greatest, directly on axis with this model. Coincidentally the upper mid-band peak characteristic of the stiff kevlar woofer is also greatest directly on axis. What this means is that these speakers sound much calmer and more relaxed (laid-back) with less toe-in, so try experimenting with toe-in until you achieve the right blend of detail and smoothness.

I would also recommend covering the back and side-walls adjacent to the speakers with cotton, either plain cotton batting or a decorative wall hanging. You want something that is at least 1-cm thick and that completely covers the wall surface. This tweak results in a sweeter sound as well. The CDM 1NTs are wide-dispersion monitors, which means that you hear a lot of first reflections from the back and side-walls at the same time (or mili-seconds after) as you hear the speaker's direct radiation. These reflections can cause the sound, especially in the upper mid-range (800 Hz - 5 kHz) to take on a "hard" quality. Treating the area around the speakers removes this effect.

Lower mid-range and bass frequencies pass straight through the felting and if the speakers are within half a meter from the wall, help to boost these frequencies (as does toe-in, the more toe-in, the more bass boost). Measuring strictly on a (+ or -) 2 dB scale the CDM1 NTs do reach down to about 60 Hz, but the bass roll-off is very slow, almost like a sealed-box speaker (indicating a "dry" or well-damped bass response) and since B&W have not resorted to artificially boosting the upper bass with a high-Q port resonance, these speakers can greatly benefit from proximity to a wall (especially if the upper mid-range reflections have been dealt with as outlined above).

Also keep in mind that this speaker's bass potential is maximized by harnessing the physics of boundary effects. Measure carefully the distance between the center of two speaker's woofers divided by two. Call this value measurement n. Then compare n to the distance from the center of the woofer(s) to the back-wall, side-walls, and floor. The trick is to make sure that none of these values are the same or multiples of each other (which would result in an ever-deepening floor bounce suckout). Positioned advantageously, the CDM1NTs (and any speakers) can maximize their bass potential.

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