AudioTechnology 3-Way Classic
Copyright 2015 © Troels Gravesen

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The bass driver is the foundation of any speaker system and defines the overall sensitivity we can achieve. We have to take room-gain into account when voicing the speaker, but I still have to design a speaker specifically made for book-shelf or corner placement. When placing a speaker on a book-shelf we may well have an increase in the bass response by 3-5 dB below ~150 Hz, thus, from this point we would have to shelve the tuning up some 2-3 dB from what is lower-midrange (starting around 160 Hz). If we did so, we would still not overcome the loss of 3-dimensionality in the soundstage due to early reflections from the wall behind the speaker. Corner placement is even worse as we easily get 6-9 dB increase in the bass response, something that cannot be overcome in the crossover design. In that case we would have to use an extremely low-Qt driver with an intrinsically shelving response.
The speaker presented here is not designed for such application, rather meant to be placed on ~60 cm stands some 70-90 cm from the rear wall, providing optimal soundstage with regard to spatial information and an overall balanced sound of basic notes and overtones, but I have to admit that due to the character of the midrange, the speakers can be placed surprisingly close to the front wall.
Last year I very much enjoyed doing two classic 3-ways, the Discovery 3WC and SEAS 3WC mkII and they have been well received as was the SEAS 3WC mkI version.
The thing is that we can get an awful lot of good sound from a modest investment, cabinet work is as easy as can be, and crossovers are fairly simple too. All this mainly because making a good 3-4" driver really isn't that difficult, and fairly cheap too. The classic "6+1" is a compromise; adding a 2-4" driver handling upper mid and lower treble simply is better, but yes, adds cost and complexity to the overall construction.
The ambition here is to present a statement in modest sized 3-way classics, no less. I've had the opportunity to work with both 4 and 10 Ohms version of the 23I52 bass driver from AudioTechnology, and I've been impressed every time; in particular when the voice coil is made from aluminum reinforced kapton, improving transient response (high Qm). Forget about old time sloppy polyprop bass drivers. They were dull and lifeless due to the aluminum voice coil formers and sometimes also high-loss rubber surrounds, not due to cone material.
This speaker is not cheap, and it wasn't meant to be! The AT drivers alone are 1385 EUR incl. VAT and the tweeters are 238 EUR incl. VAT, a total of 1623 EUR incl. VAT. Non-EU builders you get away with 1298 EUR not paying VAT. On top of this comes crossover kit and cabinet material. For the money you get a seriously powerful speaker in a modest packing and you get a quite a sensitive speaker too, that can be driven from smaller amps, even tube amps.

3-way speaker from 8" bass driver, 5" midrange driver and 1" ring-radiator tweeter, all drivers time-aligned.
Bass reflex for bass and aperiodic tuning for midrange driver.
Points of crossover; 400 and 2600 Hz, 2nd order LR.
Impedance: 4-8 Ohms, minimum 3 Ohms above 5 kHz.
Sensitivity: 90 dB/2.8 volts, 1 meter.
Amplifier requirement: Minimum 20 watts.
Power handling: A lot! Read here.

Sorry, you cannot change front panel dimensions and drivers' placement without needing a new crossover. Nor can you use any other driver than those specified.
The values of the crossover components only come with the kit and they cannot be bought separately. Read here why.


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Download specs/data:     R3004/602010

23I52-2006-SDKA    15H52-0613-SDKAM TS data:

There are few things from the AudioTechnology drivers I could want better except for a perfectly flat frequency response, but no such driver exist to my experience, and what comes from the bass and mid here is easy to correct and leaves an almost as simple as possible crossover.
Highly ventilated magnet system, symmetric drive, kapton voice coil former reinforced with alu from the windings up to the spider, optimised cone geometry, low-loss suspensions, high mechanical Q, middriver with underhung voice coil and special rubber surround optimised for midrange drivers - and we could go on.
Now, cone material is a never ending story because the perfect cone material doesn't exist. Mineral filled polypropylene has been around for decades and I don't think the basic foil has been changed at all since we heard the first Dynaudio drivers back in the Seventies.
The thing about mineral filled PP is - besides its low cost - the ear-friendly break-up nodes. With all the things that have been added since then, the mineral filled PP can deliver an astonishing level of transparency and not least a dynamic headroom that beats most. This is not trivial, because we may experience cone materials that deliver a tad more transparency, but may display problems when pressed really hard - and in many cases require steep crossovers. The 18H52 used in my ATS-4 is to my ears the best 6" driver I've ever had with regard to dynamic headroom. You have to misuse it before it starts sounding bad.
I've become really fond of the small Illuminator tweeters from ScanSpeak. They feature the same domes as their more expensive siblings with the traditional face-plate. I like the protective grille and I like being able to getting it closer to the midrange driver reducing crossover lobing. And I like them being some 100 € cheaper!

Beryllium option, read below. Click image to view large.


What strikes the most is the amount of detail from the 15H52 midrange. It's .... whauuu! The power handling, the dynamic headroom, its dispersion, its presence quality, etc. In one way it's a demanding midrange, in another it's not. No matter what you do to it, it sounds great. The problem is in the voicing of the speaker. It's one of those speakers where you can go on and on adjusting midrange and treble level, because it always sounds great, but the trick is to get it sounding natural, to give the drivers the best possible balance, providing the correct timbre. It took a lot of records of all sorts of music to find the best balance - and the best compromise, because it's always a compromise. And it took a long time before I ordered the final crossover components from Jantzen Audio.

I had to get used to the speaker not delivering the bass of the ATS-4 and Illuminator-5 - because it can't. In that way it's no different from Discovery 3WC and SEAS 3WC mkII although its dynamic headroom is significantly bigger than any of said speakers. One 8" driver will not deliver the same bass as 10 inch + 8 inch. The bass is tight and firm and I was torn between a quite low port tuning of 30 Hz and 38 Hz, the former delivering a very tight bass. Eventually I ended up with 38 Hz delivering a bit more warmth to the low end. From its 30 litre volume we have a -3 dB @ 40 Hz. If you want the sound of a truly full-bodied system, add a subwoofer to get the lower octave.

Yes, you can place this speaker up against the wall (I never thought I'd write this...), even fairly close to corners, but do not have the same distance to front wall and side wall. I've been playing the speakers with some 15 cm from the back side to the front wall and some 75 cm from the side walls. The speakers will, like all speakers, suffer lack of midrange depth from such placement, but the 15H52 midrange has an unusual presence and level of detail that will still project the soundstage into the room.

It's my desert island 3-way classic! (There will be quite a few speakers following me to that island, but this is for sure one of them).

What you get here from a serious investment compared to the three other classic 3-ways is a certain smoothness of sound, ease if listening, a refinement in overall presentation and not least, an unprecedented dynamic headroom. The large voice coils, the thorough symmetric drive, the proper ventilated magnet systems, etc., all make this speaker deliver more from its size than any other similar equipped system.


Values come with the Kit Instruction

The crossover is a straight forward LR2 filter with inverted midrange polarity. RCL-2051 shapes the middriver upper roll-off and takes care of a minor peak at 5 kHz. The LCR 2031 shapes the middriver's lower roll-off together with the driver's intrinsic roll-off by smoothing the impedance peak at around 110 Hz.
Tweeter RCL-1041 helps shaping the roll-off towards lower frequences. It doesn't get much simpler. C1021 is made from two identical capacitors to make target value.


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The cabs are 30 x 30 x 60 cm, some 2 cubic feet for you over there. From 20 mm Baltic birch this makes a net volume of 40.8 litre. From this we deduct bracing, fillets, port, driver, crossover and mid cab and end up with some 30 litre, and this is what we want for the 23I52 driver.
The fillets holding the front panel is 20 x 20 mm cuts from BB. Bracings are made from 15 mm BB and the lower one has 4 holes of ~115 mm diameter, the upper two braces being part of the mid-cab have 3 holes of 128, 60 and 50 mm.
The mid brutto volume is ~6.9  litre, net volume 4.9 liter. The mid-cab has a damped slot to the rear to make an aperiodic tuning. This is optional and you can leave it closed if you want to. The slot is 10 mm wide and 158 mm in height, the internal height of the mid-cab. See damping instruction below.
The stepped baffle between mid and tweeter is mandatory, the stepped baffle between bass and mid is optional. The bass and mid have an acoustic depth almost identical, but as the speaker most likely will end up on stands, the bass will be a little further away from point of listening, hence the 12 mm extra baffle for the bass driver. Ideally the bass driver should be on a slightly tilted baffle, some 3-4°, but it's not an easy thing to do, so I left it out.
Place is rather limited on the front panel, so before routing for drivers, cut all panels +2 mm and mark drivers and port and see if it all fit in. In particular the space for the port is limited, so find its position with equal distances to edges and bass driver before marking the center for routing.

Left: All Baltic birch (BB) panels. Right: I hate seeing good BB going to waste and having 4 pcs 15x61 cm leftovers, rear panels were made from gluing together two panels with a fillet turned 90 deg for decorative purpose.

Cutting all Baltic birch panels in the raw:
4 pcs 310 x 610 mm, 20 mm BB, side panels
4 pcs 310 x 310 mm, 20 mm BB, top and bottom panels
2 pcs 290 x 600 mm, 20 mm BB, rear panels
6 pcs 270 x 290 mm, 15 mm BB, for bracings
2 pcs 170 x 400 mm, 20 mm BB, for mid cabinet
4 meters of 20 x 20 mm BB for fillets supporting the front panels.
Before starting cutting the panels to exact size, I added one coat of lacquer, which helps preventing edge ripping.

Front panels, raw:
2 pcs 300 x 600, 15 mm black MDF, inner panel (tweeter level)
2 pcs 300 x 510, 20 mm black MDF, middle panel (midrange level)
2 pcs 300 x 350, 10 mm black MDF, outer panel (bass driver level) This layer is really optional and you can mount mid and bass on the same level.

Left: Panels with lacquer drying before final cutting. The first coating always takes 48 hours before fully dry.
Right: Sides and top/bottom cut 45 deg + rebate for rear panel. Take one side + top/bottom and join with painter's tape.

Start folding cabinet and add the other side panel.

Left: Cutting rear panel to exact width. Right: Cut rear panel to exact height.

Making the traverse rear panel of the mid cabinet.  Cutting odd angles sometimes requires a minor rig to get the right angle.
The 39 deg cut needs to be cut 90 deg to fit the slot.

If you don't care to the elaborate solution above, just let the
mid panel go to the bottom and drill some holes having the same area as the slot, ~15 cm^2.
A third option is to leave the mid cab closed. Aperiodic tuning is not the holy grail when we're talking point of crossover @ 400 Hz.

Add felt to all internal panels of mid cab and press it firmly towards the slot.
Make sure the slot is fully covered by felt and seal with some filler.
Place a piece of 16 x 30 cm acoustilux towards the rear of the mid cab.

Plenty of room for the middriver magnet.

Right: The lower brace standing up here has been changed in the drawing as we don't need such large cut-out for bass driver.

Test assembly of all parts.

Start gluing the traverse mid-cab panel. This helps a lot when gluing the cabinets giving a rigid structure.

Left: Gluing fillets for baffle support. Right: Cabs almost finished.

Routing the slot for the middriver, 10 x 150 mm.

Right: Always make test routing for drivers. Here the small tweeter.

Right: Mark braces not to chamfer outside mid-cab enclosure. Make sure you have lots of ventilation for the middriver.

Left: Mid-driver seen from behind. Free air-flow is secured. Right: Testing all drivers.

Left: Can't get enough of first full appearance. Right. Tweeter cut-out.

Left: Port cut-out. Right: 2nd coat of lacquor. 


"Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted". Albert Einstein.

A few comments on MEASUREMENTS before you start interpreting all the readings below.
First of all, if we think measurements will tell us how a speaker sounds, we're wrong. The perception of sound is way too subjective to be reflected in any measurements we can perform. A loudspeaker system is meant to give us a satisfying idea of an acoustic event and for some people a pair of 5 USD ear-plugs are enough, others spend 200 kUSD on a truly full-range pair of speakers - and the latter may not be happier than the former.

Above you see the same graph presented in different width. Now, we may think the graph to the right looks rather rugged, but if we stretch out the presentation (left) it suddenly look rather smooth. The left presentation is often used by Chinese manufacturers to make their frequency response graphs look better. No smoothing was used on the above measurements, but if we apply e.g. 1/6 or 1/3 octave smoothing things look even better. Just this to display how easily measurements can be manipulated to look nice.

Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas. Measurements may tell us about bass extension if far-field measurements are merged with near-field measurements. In addition to this, ports may contribute to bass extension. Most of us diy'ers do not have access to an anechoic room for full-range measurements from 20-20000 Hz, nor do manufacturers for that matter.
What cannot be seen is what kind of bass performance we get in a given room. Bass performance is highly dependent on in-room placement of your speaker and the same speaker can be boomy in one place and lean in another.
Actual SPL level at 1 meter distance and 2.8V input is useful for en estimate of system sensitivity and combined with the impedance profile may give an idea of how powerful an amplifier is needed to drive the speaker to adequate levels.
What measurements do not tell is the very sound of the speaker unless displaying serious linear distortion. The level of transparency, the ability to resolve micro-details, the "speed" of the bass, etc., cannot be derived from these data. Distortion measurements rarely tell much unless seriously bad, and most modern drivers display low distortion within their specified operating range. 
Many people put way too much into these graphs and my comments here are only meant as warning against over-interpretation. There are more to good sound than what can be extracted from a few graphs. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.
What measurements certainly do not tell is the sonic signature of the drivers, because cones made from polyprop, alu, Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of colouring the sound.
The choice of crossover topology has a huge impact on the sound we get. We may produce the same frequency response from 1st, 2nd or 4th order filters and they may be Butterworth, Linkwitz-Riley, Bessel and others and they all sound different, very different indeed, so take care!


AT-3WC measurements:

Left:Impedance measurements of the 23I52 driver during TS data determination from stepped and sweep sinusoidal measurements . Both added mass and added volume were used. As can be seen we have an Fs around 25 Hz (green/red) and the huge peak indicates high mechanical Q - and so it is. Right: 15H52 impedance in cabinet.

A few comments on tweeters. You may think these tiny tweeters cannot be as good as their larger siblings with their bigger (?) rear chamber and large face-plates. I have found no reason to believe so. Above to the left a set-up for measuring distortion. To the right the R3004/602010 impedance plot showing an unusual low point of resonance. This is as good as any of the standard tweeters. Below distortion tests:

Above distortion measurements done at 2.8 V input, hence the high SPL from measuring at 0.25 meter distance.
Green is 2nd harmonics, blue is 3rd.
To the left the R3004/602010, to the right the R3004/662000. The 662000 has slightly higher sensitivity, but otherwise these tweeters have nothing to tell one another. 

Left: The most interesting initial measurement is frequency response on the intended baffle and with the intended driver placement. Here frequency response merged with near-field response at 200 Hz on actual baffle. Nice flat response up to 1 kHz. This will make crossover work easy. Right: Midrange frequency response.

Left: Tweeter response on actual baffle, smooth and easy. Right: Bass driver response w/wo crossover.

Left: Response of B and MT driven from crossover plus summed response. Right: Tweeter roll-off included.

Here's a screen shot of the mid-tweeter section with R1011 = 1R0. Quite a flat response.
I prefer R1011 = 1R5-1R8, minus 1-1½ dB.


Left: Mid-tweeter response and summed response driven from x-over. Point of crossover ~2600 Hz.
Right: Final system impdance.


Again: Please read intro to measurements. These graphs tell nothing about how the speakers sounds!



Crossover components' values to come with the kit.

All questions regarding purchase of kits, please mail Jantzen Audio at

All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.

Download Sales Presentations here. (pdf file)

Kit will be available from Jantzen Audio including all drivers to save shipping costs.

All technical questions to






Bass section:


Mid-tweeter section:

L2041 was changed to litze-wire coil after the drawings ere made.
I didn't find any sonic difference between wax-coil here and the litze-wire, but the litze wire coil had the advantage of being slightly smaller and a little more space here doesn't hurt.




Mounting crossovers

Mount the bass crossover next to the port and connect to binding posts and driver. Cover x-over with 3 layers of acoustilux.

Mount the mid-tweeter section on rear panel and connect to binding posts and drivers. Cover with two layers of acoustilux.
Make sure the mid-driver is connected with inverted polarity!

Using ScanSpeak D3004/604010 Be-dome

Using ScanSpeak D3004/604010 requires no changes to the crossover, only a little tweeter attenuation. R1011 can be either 1R0 or 1R8 for the 602010 tweeter depending on your preferred tweeter level, where the D3004/604010 requires 2R7 - to my ears. 1R8 makes a rather flat tuning but does emphasise treble on certain recordings. If you want to use the Be dome, ask Jantzen Audio to substitute the 602010 ring-radiators with the D3004/604010 Be domes - and ask for 2 x 2.7 Ohm resistors as well.