Power 200 Speakers
E&MM's 200W high power loudspeakers bring down the price and cabinet size of quality sound. Suitable for home, studio or gig
Here's the ideal stereo speaker system for the budget-conscious electromusician - small enough for the home studio yet with plenty of power for the gig, and designed in conjunction with Fane Acoustics Ltd., to give top quality sound.
Parts cost GUIDE £216 STEREO PAIR (excluding wood)
There's been quite a big swing in the music industry away from the traditional 4x12 cabinet stacks that have dominated the PA market in past years towards smaller cabinets that are easier to carry around. Today, it is more usual to hire the extra high power stacks for large halls so that the musicians cab for the small gig can be of the best quality relating to size, price, power and suitable response. With the increasing use of synthesisers and sound effects that utilise virtually the whole audio frequency range, it is also becoming more important to use a speaker system with a sufficiently wide response.
When E&MM visited the large factories of Fane Acoustics Ltd, last year (see March 1981 issue), we were privileged to see Fane speakers in production and soon after, the company kindly agreed to co-operate in the design of this speaker system. The speakers recommended for the project were the new 12" and bullet units, suitable for professional monitoring. The requirements for the cabinet were to make it as small as possible for the best frequency response over the speakers' range up to 200 watts.
The resulting design has proved to be one of the smallest high power systems for its price, with a considerable cost saving if you build the cabinet yourself. However, so that even the busiest electro-musician can take advantage of this superb system, E&MM can supply ready-made cabinets that simply require speakers and crossover to be fastened in place.
Fane Acoustics Limited was founded in 1958 as a manufacturer of hi-fi cabinet speakers. In the early sixties the company specialised in high power loudspeaker manufacture and now more than 75% of all speakers used by U.K. manufacturers are supplied by Fane. One of the reasons for their success has been due to the development of the glass fibre voice coil which enabled them to more than double the power output of their speakers.
Each Power 200 Speaker cabinet contains a Studio 12L, 12 inch speaker, an HF250 Bullet Tweeter and an HPX4 crossover unit.
The Studio 12L has a power rating of 200W before distortion begins to appear, a frequency response of 45Hz to 7kHz and an average sensitivity of 101dB (1W@1m). The sensitivity parameter is a measure of loudness level of which the speaker is capable of at a distance of 1m from the speaker with a power input of 1W.
The HF250 tweeter has a power rating of 250W, a frequency range of 5kHz to 20kHz and sensitivity of 105dB (1W@1m). To protect this unit from the low frequencies a crossover must be employed. The one recommended by Fane is the HPX4 which is an 18dB/octave high pass filter operating a 5kHz, i.e. frequencies lower than 5kHz attenuated before being applied to the tweeter.
The cabinet construction is of the reflex type, i.e. a tuned port or duct is cut into the woodwork to relieve the internal air pressure in the otherwise closed box, and to separate the forward and rearward movements of the cone. The waves produced by these movements are arranged to be in phase, thus boosting the efficiency of the speaker at low frequencies. It also means that the speaker enclosure can be smaller than otherwise required, as illustrated by our cabinet which measures approximately 22 x 16 x 12½ inches. The only drawback with this type of enclosure is that the size and design of the duct is fairly critical. Consequently the measurements given should be adhered to as closely as possible.
The response curve of the speaker units is shown in Figure 1. The curve was obtained from measurements made in an anechoic chamber, which is an acoustically 'dead' room. The curve is reasonably uniform over the complete audible range, i.e. 50Hz to 15kHz.
The material used for the cabinets is 18mm chipboard and for both cabinets one 8' x 4' sheet (2438 x 1219mm) will be required. Cut the pieces to size according to the plan on Figure 2. (If you are not particularly adept at sawing ask your local carpenter since the measurements should be adhered to as closely as possible. The wood for our 2 cabinets cost £7). Cut the holes for the handles in the side panel and the speakers-in the front panels using a jig saw. (Drill a hole to insert the saw blade to begin.) Drill a 27mm diameter hole in the centre of the back panels to accommodate the jack socket recess plate. Drill the screw holes for the speaker units in the front panel.
Using one of the impact adhesives or Evostick Resin W, glue the upright pieces to the side panels. Use clamps to hold these in the correct position and leave to dry.
When these are firmly fixed glue the top, bottom, side and back panels of each cabinet together. Remember that airtight seals should be formed at each join so apply liberal amounts of glue along the edge. Also glue the bottom piece of the front panel which forms the duct to each of the front panels and set aside to dry.
When firmly fixed, round off all the outside edges of the cabinet. Cut two strips of cabinet cloth 380mm wide, 1880mm long. Glue these around the top, sides and bottom panels arranging so that the join is on the bottom panel and that approximately 45mm overlaps the front edges. This should leave approximately 16mm overlapping the rear edges. By making cuts at the corners bend the material round the edges. At the front, the cloth should cover the inside faces of these panels by approximately 25mm. Cut two pieces of cloth for the back panels measuring 550 by 400mm and glue these in place. Finally cut two further pieces for the front panel; 530 by 390mm. When positioning these pieces over the front panel allow approximately 5mm overlap at the top and side edges and bend the excess cloth at the bottom around the duct panel.
With a modelling knife remove all the material covering the holes previously made. Fix the metal corner protectors using chrome nails or self tapping screws (no. 6 ½inch). Also mount the handles, recess plate and rubber feet using the following screws: two no. 6 ½ inch for the recess plate; six no. 4 ½ inch for the handles and one no. 4 ½ inch for each foot. Mount the crossover PCB just below the jack socket plate using two no. 6 ½ inch self tapping screws with ¼ inch 4BA spacers as stand-offs. Fix the speaker units in place using four 2BA nuts, bolts and washers per speaker.
Wire the cabinets according to Figure 3 using heavy duty loudspeaker cable. Note the jack socket must be left floating until the connections are made.
Finally glue the front panels in place, making a neat finish with the excess cloth, turn them on their backs and allow to dry.