Many call it nostalgia, or more recently even vintage, but Seas was definitely not thinking about the good old days when it designed what nowadays is a very unconventional box. Pairing a 26 cm bass with a 35-mm tweeter has always failed because of the available chassis elements, or rather, the unavailable chassis elements. A 17 cm and a one-inch calotte have been the usual combination for years when it comes to large compact speakers. Even as pure bass speakers, it is rare to find anything over eight inches. A two-way box requires mid-range capabilities, too, and only people over the age of sixty really remember the matching drivers. They probably also clearly remember the days when speakers were only built into radios at best, or into their parents’ music cabinets. Building separate speakers was something best left to professional sound engineers at festivals and dance halls, the predecessors of the disco.
The triumph of home sound transformers only began in the 1960s, thanks to people like Villchurch, who used a clever technology called acoustical suspension to reduce the format from the size of a washing machine to something much more manageable. Small, flat, closed boxes could be hidden behind the curtains, with 30-cm basses that had previously required wardrobes to house them and hardly left any room for a listener. Since two-channel recording technology was also able to create a virtual stage in the living room, people started enjoying concerts on a daily basis, even in their slippers. It was the Gold Rush of the entertainment industry. The need for boxes was constantly growing, given that amplifier technology was keeping up thanks to transistors and almost unlimited outputlt.
In 1969, Seas Norway, which was originally a radio-speaker factory, created the first Dynaco A 25. It was no longer satisfied with a hidden corner of the room. Because of its dimensions, it needed to be placed on a stand in the middle of the room so that it could bring pleasure to the eyes as well as the ears. In the following decade, it became a top-seller, and no fewer than a million of this now-unusual sound transformer were sold. The work of Australian Albert Neville Thiele and American Richard H. Small, which today is used as a basis for calculating the volume of almost every bass reflex box, came too late for planning the A 25. However, it had long been known that damped ventilation openings can be used to amplify the bass range. We still vividly recall the recommendation from a book author to drill holes in the rear wall with a 10-mm drill until you were happy with the bass reproduction. After that, you were supposed to smooth out the exaggerations in the deep notes using cotton or sheep’s wool, with the famous trial and error method. The Dynaco A 25 was developed using this simple but effective method, although the holes were replaced by a damped slit.
It would have been really nostalgic if Seas had brought the old chassis elements back to life in order to rebuild the A 25. But since they are an innovative company, the Norwegians preferred to rely on brain waves, and they gave birth to new constructions using the old patterns but the latest technology. The W 260 Classic uses uncoated paperboard, which is still rightly known as impeccable membrane material, in front of a very soft rubber surround in a well-ventilated basket; a 39-mm coil bracket holding a four-ply voice coil with an even 3.8 mH; and what seems at first glance to be a very small magnet with a 90-mm diameter. The development goal was to give the bass mid-range speaker a very well-tempered roll-off so that it would take itself out of the running at about 2 kHz, without any additional measures. That used to be a fairly common trick.
Seas W 260 Classic
Item No.: 1381080
|Membrane:||paperboard||Air gap height:||6 mm|
|Surround material:||rubber||Coil winding height:||14 mm|
|Pole piece hole:||yes||Mounting holes:||6|
|Zentrierung:||Raised flat spider||Ouside diameter:||270 mm|
|Magnetic shielding:||no||Installation opening:||234mm|
|Voice coil:||39 mm||Milling depth:||6 mm|
|Voice coil former:||Aluminium||Installation depth:||107 mm|
|Frequency under 0/ 30/ 60°|
|Distortion for 90 dB||Step reponse||Waterfall|
The tweeter was also redeveloped on the basis of the old H 087. Its 35-mm voice coil leaves room for the giant 28-mm-diameter pole-piece hole. The connected volume of lightweight cast metal, made of 6-mm-thick aluminum, was screwed onto the reverse of the front panel. Ferrofluid is nowhere to be found in the air gap. At 546 Hz, the resonant frequency is very low. Theoretically, the T 35 C 002 could even be used starting at 1200 Hz.
Excel T 35 C 002
Item No.: 1381729
|Membrane:||Textile||Effective membrane surface:||12 mm²|
|Voice coil:||35 mm||Pole piece hole:||yes|
|Winding height:||2 mm||Mounting holes:||4|
|Poleplate thickness:||3 mm||Magnet:||Neodymium|
|Qts||0,41||SPL 2,83V/ 1m||95||dB|
|Frequency under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
Now the loudspeakers needed a cabinet, for which we naturally also provide an assembly plan.
It is made of 19-mm MDF or veneered plywood. For aesthetic reasons, we mitered the edges. We did not use any reinforcements. They would have made the gluing easier, but with 28 liters of interior space, the Moss engineers didn’t think they were relevant for the sound. The original version does not have any additional boards in the belly of the A 25 either, so the design was based on that. Of course it is in the blood of every assembly-kit enthusiast to find things that are technically okay, but that he would have done differently. We consciously avoided that. We probably would have ended up with better results later, though without ever hearing the original. But this way we saved ourselves the trouble of reinventing the Seas product ourselves just for the sake of claiming credit. Sometimes you have to give the laurels to the ones who have truly earned them. So in the following, we will just restrict ourselves to describing and photographing the work steps involved in creating the boxes, and to the mirror-image design of the tweeter, which was not part of the original.
Once all of the boards were mitered and the cutouts for the installation parts were finished in the front and rear walls, they could be laid out on a workbench without the lid and base, and tied together tightly with packing tape. A little caution is advised when turning the box over; we placed a ratcheting strap under the boards for later. Then we put some joint glue – what else? – in the joints.
Before finally folding the boards together, don't forget to apply glue to the last joint, too. The right-hand picture shows how to use the tension belt.
Applying glue to the base and lid rounds out the gluing work; the rest is done with two additional straps. The boxes can dry overnight and then be sanded; fill in any gaps with wood putty in a matching color. To make the surface look nicer, we finished it with two rolled-on coats of Douglas-fir stain. Walnut would have been more historically accurate, but we didn’t have any. That wasn’t the last step for the box, though – we also had to attach the nifty grate (a 25 x 50 cm piece purchased at the hardware store for €10.95, and two sections cut off with an old pair of poultry scissors – yes, really!) over the reflex opening.
We made some adjustments, applied Uhu metal adhesive all the way around and pressed it on using a board and some pliers. That was that!
Seas calls for 12 grams of filler for non-resonant damping, and one Sonofil mat weighs 62 grams. We cut off one-fifth of a mat and pressed it evenly into the slit, which was covered by the grate.
The crossover consists of two parts for the tweeter, which we glued onto the terminal. It is screwed into the back of the box, with the wires coming out of the chassis openings. We don’t know if it’s a coincidence or not, but Seas calls for 50 grams to fill the boxes – exactly the amount we had left over after cutting up the Sonofil mat. Once it was positioned along the rear wall, the chassis elements could take their places. The positive poles are indicated by a red marking.
Once the speakers were screwed in, the A 26 was carried into the measurement room, where we had it sing into a microphone placed at 1.5 meters (the middle of the tweeter).
|Frequency under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
Naturally we also took a couple of measurements to test the effects of the crossover; these can be admired in the diagram as branch curves and overall curves.
Once again we hear that quiet muttering, wondering whether there wasn’t some other way to design it, since with today’s measurement technology we could have gotten an even better-looking diagram in terms of the craftsmanship. The minimal cancellations between 500 and 1000 Hz as well as 4 to 6 kHz, and a certain waviness from 1 to 4 kHz, will bother the measurement faithful who can judge boxes by their diagrams; young engineers will find plenty of room for smoothing suction circuits and anti-resonant circuits. But what is interesting is comparing the frequency curve with the Norwegian curve. Despite the different measurement systems and above all the different measurement spaces (reduced sound against the measurement chamber), there is hardly any deviation. That’s what we expect from Seas – our Nordic colleagues don’t produce measurements that are prettied up for a catalogue.
Still, we were much more interested in how the unusual two-way box would sound in the listening room. That’s the only place to tell whether the Seas concept of breathing new life into a time-tested construction, for research purposes, could still provide useful results for today’s applications. So we set up our manageable large-bass cabinet in the middle of the room on a solid base. This time we hooked it up to the Destiny-Hybrid DS 222, which combines a tube in the preamplifier with a downstream transistor amp. The tweeters were inside, and the boxes were angled slightly toward the middle of the sofa.
40 years ago, the reviews of the sound quality of the Dynaco 25 were unanimous; every relevant gazette praised its natural musicality. So that’s what awaited us in the listening test. Naturally we started by putting a vocalist in the CD player, with minimal accompaniment. Nina Simone, the legendary pianist and blues singer from the 1950s to ’90s – which clearly made her the right partner for the A 26 test – was in fact very convincing. The voice reproduction was amazingly relaxed, something we never would have expected from such a large bass mid-range speaker. She sat right there, played the piano and sang a couple of stirring songs from “Porgy and Bess,” accompanied by some fairly subtle percussion that could also kick it up a notch on occasion. The live atmosphere in Ronny Scott’s jazz club was captured wonderfully – a truly great show to enjoy with your eyes closed.
As another witness to the A 26 era, the red and black Beatles record 1962-1966 was essential. “Norwegian Wood,” recorded in ping-pong stereo; two acoustic guitars on the left and the right; the bass in the middle; voices and tambourine from the left, too. No, there was no stage, but there were clean notes without any distortion. Well, all right, every trade-fair demonstration in the world likes to use a woman with a guitar or a man with a piano to show off the tonal superiority of the super high-end boxes. When they really want to impress people, they put a movie soundtrack in the player and let it rattle the windows, which means all of the listeners are deaf for the next three days. That’s not our style, and we’ll openly admit that it’s not the A 26’s specialty; its bass won’t bowl anyone over. The bass drum in “Hotel California” is fairly streamlined, but somehow it fits much better with the rest of the music. What was a whole lot of fun was when Dollar Brand performed live in Montreux, and his outstanding fellow musicians played “Ishmael” without any special effects. Rarely have we heard so much detail as with this combination – with a bass that was actually much too big, and a tweeter calotte that never shoved its way to the front, but didn’t leave anything out. Unlike many other tweeters, this one stayed back politely with the instrument it was creating. The Seas concept was a success in part thanks to the absolute harmony of the A 26, which assured its place as the rightful heir of a great legend.
This time it was a little hard for us to assign it to a class; the A 26’s domain is not exactly the very deep or fat bass that is expected of a large bass today. Those who are looking for something really rocking will probably not find what they want in this DIY Dynaco model. But lovers of delicate sounds that also need definition and dynamics will agree with us immediately: this belongs to the Blues Class.
|Chassis||Seas W 260 classic||Wood list in 19 mm|
|Excel T 35 C 002||per box:|
|Sales||Intertechnik||31,0 x 51,0 (2x) front/ rear wall|
|26,0 x 51,0 (2x) sides|
|26,0 x 31,0 (2x) lid/ floor|
|Function principle||Box with damped opening||All boards mitered|
|Nominal impedance||8 Ohm|
|Terminal||T 105 MSAU||Milling depth:|
|Damping / insulation||1 bag Sonofil|
|Woofer: 5,8 mm|
|Approx. cost per box:||330,-||Tweeter: 6,0 mm|
The complete assembling kit includes all loudspeakers, crossover parts, connecting terminal, Sonofil insulation, screws as well as cable and can be ordered here.