AudioTechnology/ScanSpeak, ATS-4
Copyright 2022 © Troels Gravesen


The new drivers to the left in this construction:
AudioTechnology 23I52-15-08-SDKA, DCR = 10.3 Ohms, upper bass driver, and ScanSpeak D2908/714000 beryllium dome.


The Jenzen ATS is currently my preferred speaker system. With the GlowMaster running the mid-tweeter section and a 200 wpc Hypex digital amp running the bass drivers, I have a system with great dynamics, excellent transparency and good low-end extension.
So, how do we make good things even better? Hmm...One obvious thing is aiming at higher sensitivity and greater bass dynamics. The Jenzen ATS is some 6 dB below my DTQWT and it can be heard/felt on a few recordings.
The Jenzen ATS offers better transparency compared to the DTQWT, but the DTQWT can play a few tricks in terms of overall dynamics. If size was not an issue the answer would be simple. An AudioTechnology 12D77 + 10C77 bass drivers and a d'Appolito arrangement of two 18H52 middrivers. The ScanSpeak Be dome can cope with systems up to 95-96 dB sensitivity, no problem there. But size is an issue and if I settle with 91-92 dB system sensitivity, then what?
Rather than paralleling two 10C77 bass drivers, then how about mating a 10C77 and a 8-10 Ohms (DCR) 8C77 or 23I52*? We might get another couple of Decibels and still maintain a decent impedance for passive crossover solutions.

My thinking here is primarily to improve the 100-200 Hz range by a dedicated bass driver in an aperiodic or closed cabinet with a smooth roll-off towards lower frequencies delivering a fast and dry bass and then having the 10C77 dealing with the rough part of pumping low-end bass - because the 10C77 is good at it.
The 8C77/23I52 might perform as a kind of filler-driver in between the 10C77 and the 18H52. The 8" bass driver could be fitted with either a sandwich cone or a PP cone and somehow I felt more sympathetic towards a PP cone better mating the sonics of the excellent 18H52-06-13 SDKA middriver.
The question was if Per Skaaning could make me an 8" PP driver with a mechanical Q of not less than 5? The default 8I52 on AudioTechnology website is "only" 1.85 (alu voice coil former) but SDKA (kapton reinforced with alu) and appropriate suspensions should increase Qm. What we're talking about here is low-loss suspension and aiming at an aperiodic cabinet I might get along with a quite low Fs driver.
The ATS-4 is not really a true 4-way system despite having four crossover sections, rather a 3½-way system due to the upper bass not having a high-pass filter except for what the cabinet provides. It will have to be seen if the different transfer functions of the bass crossover sections may interfere with the transient response of the overall bass system. So, time was ripe to pay Audio Technology a visit.

* What can found in a range of larger speakers is the use of different size bass drivers. Why not 2 x 8 inch, 2 x 10 inch or 2 x 12"? The rationale is making a smoother transition from the bass to the midrange, in particular if we have large bass drivers. Radiation pattern differs from different cone sizes and if we have one bass driver close to the floor we have significant room-gain also making a transition to the mid even more problematic, hence a smaller upper bass driver better connecting the bigger bass and smaller midrange drivers. What is not so clear is why we may see these different size bass driver sharing the same cabinet volume as they inevitably have different properties like rise-time due to different cone weight, magnet strength, etc.

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Not much to say here. The ScanSpeak beryllium dome it must be. This 6640 does so well in the Jenzen ATS, thus I'm keen to learn what the new 7140 on it's Revelator magnet system can do. I pay notice to the new titanium voice coil former and higher impedance and an unusual high Qm. Higher impedance may save a few uF in the tweeter section.
Download spec

D2908/714000: Click images to view large

Midrange driver:
The Jenzen ATS 18H52 middriver is the best 6" driver I have ever had. In the Jenzen ATS it needs attenuation to balance the 10C77 bass driver and based on modeling capable of doing another 2-3 dB increase in sensitivity. No attenuation resistors would be nice but preliminary testing suggest 1 ohm i still needed.
The 18H52 has a rather flat cone geometry and combined with its domed 2" voice coil delivers an unusual upper mid presence considering its size (137 cm^2 membrane area). Some 6" drivers with a deep cone requires a rather low point of crossover to the tweeter not to sound a bit shut-in in upper mid.
Download TS data (text file).

18H52-06-13-SDKA: Click images to view large

Upper bass:
The common practice of mating bass drivers of different size is to mount them in the same cabinet sharing the same volume and run them in parallel. Very simple - and apparently quite effective. But if we want to do better in the 100-200 Hz range we might get an improvement from separating the drivers and relieve the upper bass from pumping deep bass, not by applying a high-pass filter but from designing a cabinet providing a smooth roll-off towards lower frequencies. The aperiodic or closed cabinet is well suited for this, basically delivering 3rd order roll-off and if we apply an LCR circuit to smooth the impedance peak it may look/sound even better.
After some discussions Per Skaaning suggested we made a 10.3 ohm (!) 23I52-15-08 SDKA and used the standard 10C77, DCR = 5.6 Ohm. An 8 Ohms upper bass driver might be too loud working as a filler-driver, and this turned out to be correct. The 23I52-15-08 SDKA is quite an efficient driver.
Download TS data (text file).

click images to view large

23I52-15-08-SDKA: Click images to view large

Lower bass:
Here we need a high-Qm bass driver delivering pistonic movement. The 10C77 does this and from modeling it was decided to stay with the 10C77-25-10-KAP 8 ohms version despite a somewhat lower impedance than I initially wanted, but to reach a healthy 92 dB system sensitivity the added sensitivity of the 8 ohms version might come handy and the worry was that two 12 ohms bass drivers might leave the upper bass too sensitive and make the 100-150 Hz range too boomy. Thus, DCR = 5.6 ohm for the lower bass and DCR = 10.3 ohm for the upper bass.


From a 55 litre vented cabinet with a port tuning of 32 Hz we make some -5dB at 30 Hz and with bass driver some 45 cm above floor level, 1 meter to front wall and 1.8 meter to side walls we have a flat response down to 30 Hz. Room gain is an inevitable parametre to consider when setting up bass drivers. No need to tune flat under anechoic conditions and then place speakers too close to corners or wide out on the floor.
Now, finding an average of room conditions is nearly impossible and too many people are forced to place their speakers under less than ideal conditions. Too much bass or too little bass is the too often response I have from builders - and not much I can do about it except urge to try out different placements to at least give an idea of what the speakers are capable of.
In this construction I will use a rectangular port on the front made from Baltic birch. Better than plastic - and cost is zero as it can be made from leftovers. I admit this is not exactly a low-budget project....
Download TS data (text file).

10C77-25-10-KAP: Click images to view large


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To make the bass section crossovers work properly we need some control of impedance in the 50-200 Hz range. As always, we have some huge impedance peaks, and to make the low-pass sections work correctly, we need to linearise impedance, thus LCR impedance linearising circuits in both bass driver sections. Besides this, we find traditional LR2 filters for both drivers. You may notice both drivers use a 10 mH C-coil despite different points of crossover. This is due to the 23I52 having double impedance.
For the mid-driver we again find LR2 filters and both R2051/C2051 and R2061/L2061/C2051 circuits help making a perfect LR2 low-pass filter for the middriver. C2021 is a key capacitor in delivering the transparency the 18H52 is capable of. Anything less than super-caps is a Porsche with a VW engine.
As mentioned above, the 7140 dome took quite a few rounds of crossover optimisation. Rather than using an LCR circuit to tame the impedance peak, a 15 Ohm shunt resistor is used. Next, shunting C1041 with a 10 ohms resistor alters the phase and smooth the 4-8 kHz range making proper integration with the mid-driver thanks to the tweeter cabinet being some 16-18 mm behind the mid-driver.
Improving linearity could easily be accomplished by using a LR4 crossover at 2.3 kHz between mid and tweeter. It was tried but didn't sound as good as the one above - and it would also add to the overall complexity of the crossover. The ear can more easily accept linear distortion when not accompanied by large phase shifts at the same time. I fully agree with Richard Vandersteen on this issue, only that using 1st order filters takes a whole new line of compromises.


Describing sound is an exercise in writing a story on something that really cannot be put into words. Please read here. My main point is that "what I hear is not what you will hear". Your references in speaker performance may be anything from 8 litre 5+1 two-ways to large 15" + compression driver systems. The ATS-4 is none of these things.

What you get is state of the art drivers from Audio Technology and Scan-Speak, state of the art crossover components from Jantzen Audio, LR2 filters crossing at 200 and 2800 Hz, and depending on your tweeter attenuation setting, a fairly flat response. System sensitivity is around 90 dB/2.8V and it's a 4-ohm speaker to get the basics in place. And it goes down to some 35 Hz not to forget. If you want the 20-30 Hz range flat, add a decent 12 inch subwoofer with a plate amp and equaliser. You don't get 20 - or even 30 Hz from a 60 litre cabinet without sacrificing efficiency seriously. And this wasn't my intention. Bear in mind that my "35 Hz" would mean 25 Hz if this was a commercial speaker because most manufacturers can be quite optimistic about low-end extension. Actual F3 = 33 Hz for this construction based on modeling the 10C77 driver. Not bad at all.
It's takes a decent ~80 watt min. amplifier and I suggest bi-amping as 200 watts for the bass drivers are cheap - and you can save your money for the very best you can afford for the midrange and tweeter, because the mid and tweeter will follow whatever you put in front of them; that's how good they are. I use a 200 wpc Hypex digital amp for the bass delivering some 400 watts in 4 ohm - and I use my GlowMaster KT88 for mid and tweeter. Make sure your two amps have the same gain if using bi-amping.
You can use the ATS-4 in rooms ranging from 12-40 square metres. I've had quite a few mails on the Jenzen speakers in terms of adequate room size and generally people have fears of using big speakers in small rooms. The bigger the speaker, the easier it can load a room and we have reduced distortion. Look around on the web and you will find people using humongous JBL speakers in fairly small rooms, in particular Japan. Here people are not afraid of using what in the West would be considered oversized speakers.

I have praised the 18H52 middriver in the Jenzen ATS file and you can find the details here. This is one of the best mid-drivers I've ever had. Ultra dynamic, transparent - and fairly easy on crossovers.

The new 7140 beryllium dome is an easy tweeter - and it is not. The 7140 Revelator dome has a special frequency response with lot of energy in the 4-8 kHz range, actually declining some 5 dB from 4 kHz to 20 kHz, thus takes some equalisation to reduce upper treble (5000-10000 Hz) and to reduce sibilance. No less than ten different tweeter crossovers were tested before deciding on the one seen below, which is as simple as possible and yet delivers a reasonably flat response, some +/- 2 dB from 3-20 kHz. The easy part was that whatever I tried it almost always sounded good, only different depending on actual frequency response. The 7140 is clean and transparent like few and belongs to the family of top-notch tweeter like ceramics and diamonds and I would say it supersedes ceramics. It also clearly demands the best of amplification and the best of crossover capacitors to deliver what it can do, thus I used Jantzen Audio Silver-Gold caps for this section.

Bass performance: This is the main area of difference to the Jenzen ATS and what I initially set out to achieve was an even better bass performance in terms of dynamics and low-level detail. And I got what I was after and even more than expected. Dynamics and low-level detail is not alone dependent on hard-cones and high mechanical Q, but also on the cabinet used. I can see closed-box aficionados nodding: Finally he got it! The 8" polyprop in its 16 litre closed cabinet does the trick in making you feel even low-level transients traditional vented cabinets just don't do, regardless of bass driver quality. Modern bass drivers usually have low Qt, making them unsuitable for closed box application and I think this combination of a vented sub and closed box upper bass delivers the best of both worlds from a fairly small footprint. The ATS-4 is a smaller speaker compared to the other Jenzen speakers, mainly due to the smaller mid-tweeter cabinets. And every speaker has to be heard - and valued - in context of its size.

Dynamic contrast has become a buzzword lately and one of many attempts to bring in words and phrases to describe sonic qualities and impress people to think we've got something special for you. Many may have experienced extreme dynamic contrasts from huge horn speakers due to their inherent ability to respond instantaneously to impulses. Once we've heard what a well integrated horn loaded 4" compression driver can do, we realise how far away small speakers are from the dynamic contrast in live music.
Now, over the last decade we're seen manufacturers respond to the demand for better dynamics by introducing low loss suspensions, better voice coil former materials (away from aluminium), better cone materials, etc., in the pursuit of enhanced dynamics - and it has paid off. We no longer necessarily have to source vintage bass and mid-drivers with their paper voice coil formers to get dynamic drivers. The long and the short of it is that the combination of bass drivers in this construction delivers the bass punch I've so far only experienced from my OBL-11 speaker. A 15" bass driver on an open baffle can do things few other speakers can do. The price to pay for getting this from small footprint is efficiency. The OBL-11 can be driven from modest valve amps, the ATS-4 requires a decent solid state/digital amp to get the cones swinging, but watts are cheap these days and no obstacle to having the 200 watts needed.

Above some LPs I pulled down from the shelved for trying out the ATS-4's ability to deliver dynamic contrast. EMI/Karajan/Finlandia: Lots of dynamic contrast. I have a Japan cutting of Stefan Grossman/John Renbourn making a direct-cut recording in the Eighties. This record has phenomenal dynamic contrast. OPUS4 is always a good source of minimum manipulated recordings, no reverb, no (or very low) compression, no overdubs, just the thing that came from the microphones. Mahler 2nd/Solti/Decca; Doesn't get much better than this! I've experienced many times John Scofield on-stage and this recording captures everything Scofield can do live. Greensleeves/Göran Söllscher is a fine recording made in a not too acoustically dead environment, bringing in lot of background noises adding to the authenticity of the event. I enjoyed them all and had the best sound ever in my living room.
The ATS-4 allows me to fully enjoy the bass/cello sections of a full symphony orchestra in my 25 sqm listening environment. And it's still weird that improving the bass section has such a profound positive impact on mid and tweeter performance... 

MEASUREMENTS, bass section


The upper 8" bass has a peak at ~70 Hz and above to the left you can see impedance with and without the LCR circuit consisting of R3031, L3031 and C3031. Above to the right you can see the lower 10" bass driver impedance from a port tuning of ~36 Hz with and without impedance correction circuit, consisting of R4031, L4031 and C4031. When these corrections are made we can start applying the actual low-pass filters, L4011/C4021 and L3011/C3021.

Above to the left we read nearfield measurements of bass drivers. Green is 8" driver and red and light green is 10" bass driver from two port tunings, 35 Hz and 25 Hz. In the test cabs I used two ports of Ø 72 x 200 mm and the orange graph shows response from port from 25 Hz tuning by stuffing one port. Actually this leaves the option of some bass tuning depending on room placement. If speakers are close to wall/corner, try out the low port tuning to reduce the impact of room gain.
To the right we have the combined impedance of the bass section driven from the complete crossover. Lowest value is 3 ohms at 33 Hz, nothing that makes my JungSon sweat.

MEASUREMENTS, mid-tweeter section 

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.  
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 way 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.

Left: This is the MT sections (no bass drivers attached) displaying a system tuning around 89 dB/2.8V with a ~2dB decline from around 91 dB at 100 Hz to 20 kHz providing a proper balance of basic notes and upper tones. Right: Tweeter response with R1011 = 0, 1, 2.2 and 3.3 Ohm. My default is 2.2 Ohm.

Left: Response of mid (red) and tweeter (yellow) and summed response (green) driven from crossover.
Right: Step response of MT section showing the tweeter well integrated in the mid response.

Two graphs on overall system impedance. Left we can see a system impedance of 4 ohms with a minimum at 3.0 ohm at 32 Hz.
Right: Same graph showing a phase angle of -32 deg @ 27 Hz.
This is indeed a very easy load and my workshop Duro amp feels better than ever and can drive this speaker to thunderous levels delivering some 2 x 180 watts.

Finally horizontal dispersion @ 0, 10, 20, 30 and 40 deg.

The Cabinets




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Crossover Kit

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Buy Audio Technology 10C77, 23I52 and 18H52 directly from factory:

The drivers alone for this speaker is around 3600 EUR. Find prices for AT drivers at AT website:

Crossover Layout

Check this out before start making crossovers:




Images of MT section:

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1800 pixel width

Here with Alumen Z-Cap for tweeter

MT-crossover fully mounted. Click image to view large




Wiring is the same despite new layout with Alumen-Z caps for tweeter.

Wiring the same despite new layout with MKT caps.


Bass section

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Mozart/Clarinet Concerto on a Sunday afternoon.
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