AT-SW
Copyright 2009 ® Troels Gravesen

AT-SW is Audio Technology and SWANS planar tweeters

The ambition of this project is to offer a high-end kit that even beginners in loudspeaker building can cope with. Thus a two-way loudspeaker with state-of-the-art drivers, a fairly simple crossover and a cabinet that is easy to construct. The cabinets must be rugged and well braced, but it doesn't have to look nice to sound good.
The kit is built around one of the best drivers Danish loudspeaker industry can offer, an 18H52 driver from the hands of Per Skaaning at AudioTechnology, the company that carries the fruit of all experiences gained by his father, Eivind Skaaning, from participating in the development of ScanSpeak and Dynaudio companies.

The 18H52 driver used here is made to my specifications and is proprietary to Jantzen Audio. Do not buy a standard 18H52-15-06 driver from AT. It is different with regard to materials used and voice coil impedance and the crossover shown below won't work properly. The 18H52's copper clad magnet polepiece provides an almost flat impedance profile and reduces non-linear distortion. The chosen voice coil impedance makes this construction well suited for valve amplification although not for 5-10 watt SET. 25-40 watts PSE or push-pull is recommended minimum. Obviously high-quality solid state amplifiers may perform well too.
Please do no ask what the difference to the standard units is, because I won't tell you (had the question numerous times already).

Like all planar tweeters the SWANS RT2H-A holds an extremely low moving mass, and the large diaphragm coupled to a well constructed die cast waveguide, makes excellent horizontal dispersion. Like all planars, vertical dispersion is limited and tilting the speaker a little leaves a comfortable listening window. The end result is speed, resolution and dynamic integrity that leaves conventional soft domes behind. Listening to cymbals and other instruments with high frequency content, makes you wonder whether you have ever heard something similarly natural from conventional domes.
Hand clapping (applause) from an audience on live recordings is a powerful tool for evaluating driver integration and treble quality, and this speaker excels over any other speaker I have made, and based on experience I know this is mostly due to the planar tweeter.

The RT2H-A planar tweeter used here is a standard unit, but it has been slightly modified (changing of damping materials behind diaphragm), the drivers are paired to +/- 1 dB SPL from 3-10 kHz and all units are tested in the final AT-SW speakers before release. I hope this will overcome the common sceptisism toward Chinese produced products. The diaphragm, by the way, is produced in Canada.

The basic characteristic of this construction is transparency above all and a surprisingly powerful bass considering the size of the bass driver. A seamless integration of drivers provides enhanced insight into the music and the bass reaching down to 40 Hz delivers a solid foundation for any source material. The AT-SW kit provides sensitivity of 86-87 dB/2.8 volts/1meter. Cabinet dimensions are 250 x 450 x 325 mm (W x H x D) if you want to build your own cabinets. US builders may use PartsExpress #302-730 cabinet, e.g. piano black finish as used for the prototypes here.
I do not suggest anything other than the very best capacitors for this speaker, thus Superior Z-caps used in this construction.

Amplifier requirements: I have run these speakers with different amplifiers, from class B solid state to NFB single ended triodes and feel sure that AT-SW will deliver more and more the better the amplifier and associated equipment. The best sound I had was from my 5687 line stage and modified Audio Mirror mono-blocks, but 20 watts is on the low side unless you never play at significant sound levels.

Further information on cost, shipping and payment at contact@jantzen-audio.com


Prototype cabs. Click image to view large.

The Crossover


AT-SW crossover.
L2011 and L1041: Jantzen Audio wax coils. L2031: Jantzen Audio baked air-cored coil.
All caps: Superior Z-caps. Resistors: 10 watt MOX.

Go to crossover layout and pics.


Crossover kit incl. AT 18H52 and paired RT2H-A drivers available from Jantzen Audio: contact@jantzen-audio.com
Damping materials available (egg crate foam and wool/acoustilux)

Cabinets


Use a port of 60 x 150 mm (D x L) or 65 x 175 mm or 70 x 205 mm to render a port tuning of ~38Hz.

Prototype made from PartsExpress #302-730 cabinet, black piano lacquer.


Routing for the vent.


Remember chamfering driver hole.


The RT2H-A tweeter doesn't need rebating. It might look nice, but having shart corners it's not easy to do.

Cabinet damping

Cabinet damping is very important for obtaining the best results, although different materials can be used. The prototype test cabs were damped with 30 mm egg crate foam on all sides plus a folded layer of acoustilux/MDM3 on top of the crossover - behind midbass driver.

Whether bitumen pads should be used on internal panels is up to the overall rigidity of the cabinet. If well braced, bitumen pads may be omitted. Please note that bitumen pads does not reduce sound reflections, it damps vibration of cabinet panels. I have seen some confusion over this.

Alternatively 10-12 mm felt pads may be placed on all in internal panels followed by acoustilux/MDM3 as suggested on drawing. In addition to this, a folded layer on top of the crossover placed behind the AT driver.


Finished wiring.


Left: Tweeter section placed in side wall toward rear panel.
Right: Bass section placed on side wall towards rear panel. Remove port when inserting bass section crossover.

Silver plated cobber wire in teflon sleve used.
Terminals to crossover boards: 2 x 25 cm black, 1 x 20 cm red, 1 x 30 cm black.
Crossover boards to drivers: 2 x 50 cm black, 2 x 50 cm red.
5 meters of each delivered with kit.

Setting up the speakers

Placement of speakers is something I usually leave to the builder to decide, but a few comments here on my own experience on setting up the AT-SW speakers.
Setting up a 2-way speaker is in many ways trickier than most 3-ways, where the bass driver usually finds its place some 35-45 cm above floor level. This often provides a suitable room gain allowing a bass driver to gain a little extra weight in the lower octaves. For a 2-way we can't have the floor augmenting bass level as early floor reflections would compromise the midrange. Thus, a pair of stands is a must for the AT-SW speakers - as for any other 2-way in this category.
Before making the final stands, make a pair of mockup stands from some MDF leftovers. Make them approx. 50 cm high, allowing additional height to be gained from adding books or whatever below the speakers or stands. Move the speakers around in your listening room and try to avoid having the same distance to floor and rear wall - not to forget side walls!
In my listening room I always have speakers on the long side allowing some 160-180 cm to side walls. This may a bit of a luxury, but it solves a lot of problems. The worst placement we can have is the exact same distance to all three nearby boundaries. If we place the AT-SW midbase driver e.g. 65 cm to floor, rear and side walls, we will have some 4-5 dB extra at 50 Hz - but a 10-11 dB dip at 160 Hz and it sounds awful.
Next to building your speakers properly, placement is second most important thing to consider. The sound from any good speaker can be totally ruined by misplacement.

Also try tilting your speakers while sitting in your favourite listening chair. The tilt will depend on your height, your chair and the distance to the speaker.

I find the best sound from the AT-SW by toeing in the speakers to listen almost on-axis while still being able to see inner side panels from my listening position.

If you want to thoroughly evaluate the many hours going into your project, move the whole set to another room and hear what happens. Next, try various amplifiers and source material, CDs and vinyl set-up if available. I've recently compared the AT-SW driven from an "average" power amp (Rotel) and a 2 x 80 watts class A solid state amp (Jungson) and the test was devastating for the Rotel. Feel sure the AT-SW will deliver the details from the very best equipment available.

Measurements


Left: SPL @ 1 meter, 2.8 volts for drivers. Right: Impedance and phase of drivers mounted in cabinet.


Left: SPL for 2.8 volts/1 meter for final crossover. Right: Horizontal dispersion at 0, 5, 10 20 and 30 deg. (red, blue, green, purple).


Left: Vertical dispersion starting at tweeter height (mid). Red = 0 deg., blue = + 5 deg., green = -5 deg., purple = -10 deg.
Right: Cumulative spectral decay from finished speaker.


Left: Final system impedance. Minimum 5 ohms at 500 Hz. Right: SPL of drivers driven from crossover and summed response (blue).
Point of crossover = 3 kHz.

The Sound

Basically it doesn't make much sense trying to describe the sound of a loudspeaker. What I hear is not what you or anyone else will hear. The way we perceive sound varies enormously and every well constructed loudspeaker may have something to offer that will please the ear - for some people. "The best loudspeaker in the world" is quite often read in loudspeaker ads. Obviously this is nonsense. The people who build it may think so, but other people may disagree. In the end it's a matter of taste.

What is immediately apparent once you sit in front of the ATR is the lack of distortion, the smooth electrostatic treble and the surprisingly deep bass considering the size of midbass and cabinet volume. Despite the modest cabinet, this driver goes all the way down to 40 Hz, significantly adding to the perceived scale of the acoustic scenario.

If you think polypropylene drivers may not be able to provide the same level of transparency compared to magnesium or ceramic drivers, try this AT midbass. The old ScanSpeak 18W/8543 driver was probably the best polyprop driver in the world in the early Nineties, but from personal experience this new AT driver is simply a lot better. The mineral filled polypropylene material used in AT drivers easily outperforms the old and softer ancestors. Where hard-cones need careful filtering to eliminate break-up nodes in the upper registers, we can get away with simple low-order filtering from this AT driver.

The treble quality from this construction is where this speaker most noticeable differ from most other brands. If you know the sound of electrostatic loudspeakers, this is where you should seek brands for comparison, because "electrostatic" is what it is, and dispersion - although not as good as the best domes - is much better compared to what is usually experienced from fullrange electrostatics.

Magnesium drivers will sound like magnesium drivers; ceramic drivers will sound like ceramic drivers and polyprop drivers will sound like - - polyprop drivers. Don't be mistaken here. Whatever material is used for speaker cones, they will all have their own distinctive way of reproducing sound. Hard-cones may sound slightly "clean and sterile" (Read: I miss the colouration of my old paper cones) and polyprop usually have been characterised by having a smoother and more forgiving sound (Read: It allows me to hear all my old and poorly recorded records). Due to the exceptional build quality of the AT midbass combined with the electrostatic quality of the planar tweeter, I think an exceptional good compromise is at hand. We can't have it all, but we can choose carefully to combine some of the best qualities of all technologies available.

Crossover layout


AT-SW crossover is devided into two sections to fit into PE cabs, if necessary.
Using wax coils and Superior Z-caps means a bulky crossover and putting it all
on one board wasn't possible.


Bass section. Board = 11 x 24 cm.


Tweeter section. Board = 11 x 13 cm.