B&W DM70 Instruction manual test certificate and guarantee
DM70 B&W D M .
Contents Page 1. General Description 2 2. The Listening Room 3 3. Installation — unpacking and connection 5 4. Installation — Siting 10 5. Ancillary equipment 12 6.
General description and introduction The DM70 is a precision monitor loudspeaker for domestic and professional use, built to very high standards. This loudspeaker, employing the combination of dynamic bass drive unit in conjunction with an electrostatic transducer for the mid-range and upper frequencies, is capable of most realistic reproduction of both speech and music programme material.
The listening room M o s t people have relatively little control over their listening room in terms of size or shape, but as the environment in which the loudspeaker is used plays such a big part in the quality of sound we hear, some comments on room characteristics may be helpful before we proceed in section 3.
The ideal is a solidly built ground floor room with a concrete floor. In rooms where there is a board and joist floor this will play a part in both adding to bass gain and room colouration. The suspended floor acts as a supplementary bass radiator operating at the main resonance of the room. If your listening room has other than a solid floor and you are troubled by excessive or resonant bass response as a result, positioning your loudspeaker away from the corners will assist.
Installation unpacking and connection For safety in transport t h e D M 7 0 Improved system is packaged in three cartons, f o r each loudspeaker:— Carton 1 Main cabinet with fitted power supply unit. Carton 2 T w o metal stands for the pair of loudspeakers. Carton 3 The " 7 0 2 " electrostatic unit complete. WARNING IT IS ESSENTIAL THAT THE ASSEMBLY A N D INSTALLATION INSTRUCTIONS BE CAREFULLY READ BEFORE CONNECTING THIS SYSTEM TO THE MAINS OR AUDIO SUPPLY. Unpacking.
Fig. 1 Rear view of Continental power supply, showing label indicating the power supply voltage. The power supply for the Standard version is similar but rotated through 90 degrees. The regulation of the power supply is such that, normally, no adjustment will be necessary and the unit is set for the country of destination, e.g. European or America, etc.
. To remove the power supply unit from the cabinet, unscrew the four screws at the side of the rear panel of the unit and withdraw it, unplugging the audio output to the bass unit. (If the 701 electrostatic unit has already been fitted to the cabinet, it will be necessary first to remove this, by reversing the assembling instructions which follow.) The various adjustments to the mains voltage selector are selfexplanatory.
It is advisable to keep the series resistance of connecting cables as low as possible by using reasonably heavy gauge cables. Our recommendations are.— Loudspeakers under 10 metres away from amplifier: use 16/0.2mm. Loudspeakers over 10 metres away from amplifier: use 24/0.2mm. Phasing.
J I desired to operate the DM70 at very high sound levels, or where high powered continuous sine wave inputs are applied, the rear absorbent pad should be placed in position. It will be observed that on the rear panel of the Power Unit there is a neon indicator. This shows that the mains supply is functioning. If the neon does not light when the mains is connected, the fuse should be checked.
Although in the case of the DM70 (due to its remarkable dispersion characteristic) positioning is not as critical as w i t h many conventional loudspeaker systems, this system is quite a substantial piece of furniture in its o w n right, and it is worthwhile taking care in siting the loudspeakers in the most acceptable positions, both visually and acoustically.
3. Due to the wide and balanced horizontal dispersion of the DM70, their horizontal position will not be critical. We would normally suggest that in domestic rooms of normal size they be not closer than eight feet (2.5 metres) apart, or separated by more than fifteen feet (4.5 metres) to give an even and solid stereo image. 4. The final point for consideration is whether to place the loudspeakers parallel with the wall or surface or to angle them towards the listening area.
Ancillary equipment Because of its exceptionally good frequency linearity and relative freedom from colouration and distortion, the DM70 is capable of extremely faithful reproduction, provided that the signal fed to it is of the very highest quality. A monitor loudspeaker — and the DM70 is such a high-quality system — is therefore analytical and will reveal faults in ancillary equipment and programme material which could well be masked by an inferior loudspeaker.
Specification General Description B. & W. D M 7 0 is a h y b r i d design employing exclusive Model 701 11-element wide dispersion doublet electrostatic unit (patent no. 1239658), DW 13/70 high power low distortion moving coil bass unit w i t h complex crossover and filter unit and dividing network. Relative sensitivities between the dynamic and electrostatic units are accurately equalised by a massive auto transformer.
Electrostatic Unit model A prime design point of the 701 is that it is free-standing. This makes it possible easily to remove the unit in the event of damage etc., and service being required, thus avoiding the transportation of entire heavy and bulky system. Crossover and Filter Unit The 500 Hz. crossover frequency between the DW13/5 bass unit and the 701 electrostatic unit ensures that both these transducer elements operate over their o p t i m u m frequency ranges.
STANDARD Dimensions. Weight: Weight w i t h stand: 4 5 . 4 k g .
Frequency Response. On-Axis ± 5 dB. 60 Hz. to 15kHz. On axis response of a production sample DM70 taken in Ft & D Anechoic Chamber. B & K equipment used throughout, w i t h type 4133 microphone at 1 metre. Crossover and Filter Unit. Individual Acoustic o u t p u t f r o m each Drive U n i t , showing Crossover frequency. Polar Distribution. + 3 dB envelope to on-axis f r o m 20 Hz to 20 kHz over 60 degree arc. DM70 response for 30 degree arc and 60 degree arcs.
Impedance. Nominal impedance 8 ohms. Not greater than 30 ohms or less than 4 ohms 20 Hz to 9 k.Hz., the impedance m i n i m u m occurring in a frequency region of very low music energy. Plot of impedance of production sample of DM70. Distortion. Harmonic analysis plotted against frequency Content of 2nd. and 4th. Harmonics. Content of 3rd. and 5 t h : Harmonics.
Transient Response. Tone Burst oscillograms taken at one-third octave intervals in ou Research Anechoic Chamber. Microphone type B & K 4133. 31.5 Hz 40 Hz 50 Hz 63 Hz 80 Hz 100 Hz 125 Hz 160 Hz 200 Hz 250 Hz 315 Hz 400 Hz 500 Hz 630 Hz 800 Hz 1kHz 1.25 kHz 1.6 kHz 2.0 kHz 2.5 kHz 3.15 kHz 4 kHz 5 kHz 6.3 kHz 8 kHz 10 kHz 18 12.
Polar response 100 Hz Polar response 1 k.Hz. Polar response Polar response 10 k.Hz.
