Copyright 2014-20 © Troels Gravesen



20-01-2021: NEXT-4 updated with new SEAS W18NX003 driver.


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The ATS-4 concept of having a 8" bass driver in a closed box handling the 100-200 Hz range works so well it simply had to be tried with other brands of drivers. So, here's a SEAS version. Building cabs take time - a lot of time - and discussing future constructions with Jesper (Ekta Grande builder) I suggested making a NEXT-4 from some of his Cyclop drivers - and Jesper was positive.
Fortunately I still have my ATS-4 bass test cabs and Jesper had the 10" bass drivers and Crescendo tweeters - and I had the 18W middrivers. So, Jesper, after having heard the ATS-4, accepted the proposition of making the NEXT-4 speaker cabinets and buying a pair 22WNX001 drivers to complete the driver range needed. Jesper also made new test mid/tweeter cabs for the initial set-up. Se image below. These cabs front panels must be fine-tuned before making the very final cabs.
The layout is as close as possible to the ATS-4 with a single minor modification to the mid cabinet not being chamfered towards the bas cab. That's all. Everything else is similar to ATS4 - apart from the crossover, obviously.
The 8" upper bass driver used for the ATS-4 is quite sensitive, hence I had a 10 ohm version made for this application. Here the 22WNX001 fits perfectly into a similar set-up having the same sensitivity as the 26W bass driver - and fortunately we can maintain a minimum impedance of 3 ohms, not a problem for most good solid state amps. My Jungson amps (2 x 80 watts) runs these speakers without any trouble. For the final voicing and crossover fine-tuning I used my GlowMaster KT88 for mid/treble and Hypex amp for the bass drivers. Se "Gear" section.

There will NOT be a whole lot of writing on this speaker as it is so similar to the ATS-4, so before writing, please read the ATS-4 file. I do NOT have more drawings than those found below, so please do not ask. As always, stick to front panel design and drivers' layout, the rest is up to you. The drawing suggest bass section crossover to be placed at the bottom like the ATS-4. Jesper chose to place these on the rear panel. It's up to you. If you use the latter solution adjust bass cabinet volumes accordingly.
So, here we go on the SEAS NEXT-4 speakers:


Useful links:
Please read these files before e-mailing:

You cannot change cabinet front panel dimensions and drivers' placement without needing a new crossover - and I cannot help.
You cannot use any other drivers with the crossover shown here.
Please read these files before e-mailing:


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Download drivers' data files:
T29CF002   W18NX003   W22NY001    W26FX002


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Crossover components' values to come with the kit. You can buy the kit with or without the drivers - or some of the drivers if you already have some.
See options below.


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As always: Any change to the design and you're on your own. You need a new crossover, please read here.

Check out this file regarding construction tips:


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For optimal integration of tweeter and midrange tweeter cabinet should be some 18-20 mm behind the middriver front panel. Pull back tweeter cabinet a little more than seen on drawing. In my listening room I had a 9 mm block under the tweeter cabinet at the rear, but all depends on listening distance and listening height. Ideally mid and tweeter on-axis should cross at listening postion. Do spend some time finding the right tilt of mid and tweeter cabinets with regard to your listening postion.

Cabinet damping, view ATS-4 file.
The midrange port is cut to 100 mm total length and stuffed with a roll of 10 x 20 cm acoustilux to make an aperiodic tuning.

Test set-up for crossover fine-tuning.



Crossover components' values to come with the kit. You can buy the kit with or without the drivers - or some of the drivers if you already have some.
Please ask Jantzen Audio for options.

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

Download Kit Presentations here:

All technical questions to

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


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. The combination of drivers cannot be done from drivers' specs alone, it must be tried and different crossover must be tried too.

Left: Response of the two bass drivers in cabinet without crossover. Red = 22W, green = 26W. Both drivers display smooth response with no ripples around 600-1000 Hz where rubber surround resonances usually sets in. Both measurements merged with near-field response to fully display roll-off.
Right: Middriver response in cabinet without crossover attached. Again, smooth response making crossover work easy.

Left: Tweeter response in cabinet without crossover. No crossover trouble from this driver either. Right: Same thing, only 400-20000 Hz.

Left: Nearfield response from bass drivers with crossover connected. As can be seen the upper bass driver handles the important 100-200 Hz range.
Right: Nearfield response from lower bass driver with R4031 at different values: No LCR circuit, R4031 = 47 Ohm, 22 Ohm and 10 Ohm (green/orange/red/blue).

Left: To present an image of full frequency response from such a big speaker really takes a huge anechoic chamber - and I don't have one.
What I'm trying to illustrate here is the far-field response of mid-tweeter (red) and the near-field response of bass driver and port, giving you an idea of bass extension.
As can be seen point of crossover between bass and mid is around 250 Hz.
Right: Final system impedance. Despite the min. 3 ohm impedance, this is an unusual benign profile with no odd phase angles combined with low impedance.
My 60 wpc Einstein amplifier drives this speaker to thunderous levels without any problems.

Left: System sensitivity is around 89-90 dB/2.8V 1 meter distance. The bass-midrange level is what is important here.
Right: Horizontal dispersion from mid-tweeter at 0, 10, 20 and 30 deg.

Left: Point of crossover between mid and tweeter is around 2700 Hz with shallow slopes (LR2). Right: Inverting tweeter polarity produces this dip around point of crossover.


MT section crossover layout.
Full schematic comes with crossover kit.

Click images to view large, above and below.




Bass section crossover layout.


New MKT Z-caps takes up more space than seen here, but there is plenty of space.

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The trouble part! Obviously I cannot tell you how a loudspeaker sounds as little as I can tell you what the taste of cheese cake at NOMA restaurant will be like. One thing for sure is that the NEXT4 is the best SEAS speaker construction on these pages (until the CNO-4 came along :-)).
It's highly dynamic due to the closed box upper bass driver. The midrange is smooth when music is smooth and harsh when music is harsh. Treble blends with midrange as I never heard the Crescendo tweeter done before. It will cope with the best of source material.
Sorry to repeat some of the album covers from the ATS4 article. I actually listened to a whole range of records besides these once the NEXT4 was up and running. I often use the Stefan Grossman record to demonstrate the dynamic capability of speakers and in addition to the NEXT4 speakers, a new phono cartridge, the van den Hul, Canary, was on my turntable. The dynamics were scary! The Canary cartridge and the vdh Grail phonostage is simply a perfect match.
In addition to the upper bass dynamics, the lower bass delivers the grunt it takes to reproduce a live performance of Brothers in Arms by Mark Knopfler. In short: The NEXT4 is a big speaker. Give it the best of front gear and source material and it will throw a wide and open soundstage with gut felt dynamics. I used my GlowMaster for the midrange/tweeter and Hypex digi-amp for the bass drivers.