SpeakerBuilding.com - A gift from the Gods? Seas presents mythological speakers

A gift from the Gods? Seas presents mythological speakers

By Lars Mytting
05 Mar 1996

Printed from SpeakerBuilding.com, 21 Nov 2008 03:40
URL: http:///content/kits/1038/

Introduction

Ok folks, here they are; fresh from the oven, the new Seas kits. Five of them uses Seas' top-of-the-line drivers, the Excel series. These five are designed by Murray Zeligman from USA, an independent consultant with over 25 years experience in design of speakers and amplifiers. The two other kits are designed "in house" at Seas; the Embla by Bjørn Børja, the Njord by Jon Paulsen. Four of the kits has been baptized with names from the old Norse mythology, three of them has not got any name yet. For these three, we have so far no information on how they will be marketed, or if there will come changes to them. The drawings and crossover schematics on these should therefore be regarded just as suggestions.

Who are these gods?

For those interested, the mythology department at The Speaker Building page presents a short introduction to relevant Norse:

Odin - The master of the gods, also god of poetry, sorcery and wisdom.
Embla - The first woman, the Norse equivalent to Eve.
Njord - God of the sea and of wealth, Frøy's father.
Froy - God of fertility and good crops. (A note: We assume that Seas has meant "Frøy", which is the real Norwegian name, but that they have omitted the "ø" for better anglo-computer-compatibility)

The Excel drivers

The Excel kits are based on three different woofers, in single and D'Appolito configurations. The T25-001 tweeter is used in Excel kits. Drivers used are:

T25-001 1" tweeter, double magnet, silver wire voice coil.
W14 CY-001 5" driver, magnesium cone, solid copper phase plug.
W17 E-001 6.5" driver, glass fibre cone, solid copper phase plug.
W17 E-002 6.5" driver, magnesium cone, solid copper phase plug.

The most remarkable with the woofers are the cone materials, which gives low distortion figures. Especially the magnesium drivers has remarkable low distortion compared to paper and polypropylene. The tweeter has very good off-axis response, at 30 degrees it is only 2db down at 13.000 hz.

The main challenge for the amateur speaker builder using Seas Excel drivers has been to get the crossover right. The problem for the glass fibre cone has been to attenuate the midrange correct, because the driver's rising sensitivity with increasing frequency. It has also a more uneven midrange response than the magnesium cone. The magnesium drivers has a extremely steep and narrow cone resonance peak at 5000 or 10.000 hz. This is easily attenuated with a LC circuit. The T25-001 tweeter has a slight rolloff from 4000 hz, which may be corrected by parallelling a capacitor over a series resistor.

The Excel series includes several other drivers. The 6.5" drivers are available with three magnet sizes, the W17E 001 and 002 being of medium size. Unfortunately (and unavoidable) the different W17 drivers has different frequency response, so the present crossovers is not fully compatible with the other Excel drivers. But, using the same crossover topology as presented here, and adjusting the values with computer simulation like Leap or Calsod, it should be easy to get optimal results using the other drivers.

The Excel kits

The magnesium drivers in the Odin and Froy kits rolls off steeply at the end of their frequency range. Thereby it is possible to achieve steep acoustical rolloff with just a few crossover components. Mr. Zeligman has designed elegant (and hopefully, good sounding) crossover solutions, and has used only one or two inductors in series, and the rest of the correction components in parallell. Different crossover topology is used in the D'Appolito designs with glass fibre and magnesium drivers, probably because the latter driver's steeper rolloff. The Odin is crossed at 2.200 hz, the Frøy at 2.500 Hz. According to Seas, both has Linkwitz-Riley response.

One smart trick used in the Excel kits is the shape of the bass reflex port. The port is made by two MDF boards, forming a open path into the cabinet, a solution wich also gives additional bracing. An idea which comes close when looking at the Odin drawings is to extend the cabinet to a height of ca. 100 cm., use sand fill in the extra volume, and create a slim, heavy floorstander.

The Njord and Embla

Both the Njord and the Embla use standard units, all well-known oldtimers from the Seas range. The Njord is a floor-standing speaker with the CA21REX 8" (H373) and the 25TFFC (H519) 1" tweeter. The CA21REX has a coated paper cone, and has many similarities to the Seas woofers used in the old Snell E and J. The 25TFFC is a very versatile fabric dome.

The Embla is a bookshelf-speaker with the 6,5" P17REX and the 25TAFC/D (H537) 1" aluminium tweeter. The P17 has a polyproplylene cone with smooth response. The 25TAFC/D has been used in expensive German high-end speakers.

Njord and Embla are bass-reflex designs with simple crossovers. They will probably fit the needs for those wanting a system that is cheaper and easier to build than those in the Excel range.

Why the old drivers?

Seas has released many interesting new drivers the last year, among them woofers with aluminium and TPX cones. Because of this, I personally find it somewhat strange that Seas in the new Njord and Embla kits have decided to use "old" drivers that has been around for several years. Of course, a good driver never turns bad as time passes. But from a "technical" view, I believe many people would be more interested in kits or building hints for the new, more "exciting" Seas drivers, like the small woofers with aluminium cones and the stunning 8" drivers with 2" voice coils. None of these are more expensive than the drivers used in Njord and Embla.

But we are in good hope that Seas are hammering together more kits, hopefully also some migthy three-way floorstanders. So go on; there are several interesting gods left in the Norse mythology. Odin of course needs his wife "Frigg" - the goddess of love and fertility. And we certainly hope there will be a "Tor" - the god of thunder...

Where to get parts

In Norway, kits and parts are sold by

Eltek
Boks 6244 Etterstad
0603 Oslo
Phone: 22 65 80 70
Fax: 22 64 58 08

The rest of the world should be able to get hold of the drivers at their local Seas dealer.

Lars Mytting