Jenzen SEAS ER
Copyright 2011-20 Troels Gravesen

Crossover     Cabinet     Measurements    Speaker Kit    Crossover Layout     6" drivers on the Jenzen baffle

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Download driver specs for CA26RFX    ER18RNX    T25C003 / T25CF001

Also check out Jenzen NEXT

5th Oct 2020: As nobody builds the version with the CA18RNX middriver, this version has been discontinued.

The first speaker
in the Jenzen series comes with modest priced drivers, yet delivers a significant soundstage. Size matters and using drivers with a decent membrane area means they don't have to move much. In particular for the midrange this is important and releasing it of the tedious task of pumping bass, things start developing. Drivers we may have found having a harsh upper mid in the common two-way set-up may all of a sudden deliver crystal clear sound in all of the midrange.

The Jenzen series of speakers are meant to offer high-end sound for low-end price, even for the constructions to come with expensive drivers. As discussed in Speakers' Corner; what diy people can do speaker manufacturers cannot, is this: Spoil our drivers with the best of cabinet work. MDF is cheap and it's no problem making 30-50 mm panels and adding solid bracing to produce low-resonance enclosure that is often a significant part of high-priced speakers. I recall Eggleston speakers, and the knuckle tap test suggests a solid log of wood. No problem. Laminate 2 x 22 MDF; add bracing and we have the same thing. And it pays off. Cabinet resonances add more to the sound than we may think.
We may think commercial speakers are overprized - and some are - but making a living from manufacturing speakers is not an easy task despite having drivers and crossover components at less than half price compared to what we pay retail. As diy'ers we only have ourselves on the payroll, no packing and shipping, no dealers' profit, no advertising, etc. If production price is 10-20% of retail price we may have a viable business, hence the price of a single cap or added bracing may prove pivotal for competitiveness. 

The drivers for SEAS ER come for less than 700 USD ( @ Madisound; we in Europe have to face some ~20% value added tax) and if you have the time and skills to make cabinets, you're in for a treat for a fraction of what a similar commercial speaker will cost. Without blushing I dare say the finished speakers will compare to commercial speakers in the 10-20 kUSD range. But you have to be prepared for quite some woodwork. These four cabs won't emerge from a couple of weekends' late night hours.

With the ER18RNX, SEAS is back into hard pressed paper cones, not seen since the Excel W21EX001. This ER18RNX cone is or has been added some reed pulp, usually used for water reed roofs.
The sound from this hard pressed reed/paper pulp cone midrange driver is good, really good. It has the clarity of magnesium, only comes with better sensitivity and frequency response, which makes crossover work easy. This driver appears to be a serious contender to the Peerless Nomex (830875) drivers when it comes to uncolored midrange presentation. Generally, if you think a 50-80 USD driver cannot deliver detail, try one of these two drivers.

Bass driver CA26RFX features a standard coated paper cone, rubber surround, huge magnet and healthy 90 dB sensitivity. As always from SEAS: Well built.

For tweeter I could have chosen one from the PRESTIGE range, but finally decided on the EXCEL T25C003/T25CF001. This tweeter comes with excellent build quality and it doesn't add much in overall building cost. Due to low slope crossovers it may prove beneficial to use the T25CF001 having ferrofluid in magnetic gap. 

The crossover features the simplest possible LR2 filter and for proper integration of amplitude and phase the middriver is 19 mm in front of the tweeter. The significance of this is noticeable, in particular on vocal performances and e.g. acoustic instruments like flute, oboe and piano. Furthermore the edgy snappiness of high-frequency transients is reduced for a more ear-friendly presentation with enhanced sense of depth and spaciousness. 
Quality of crossover components is a vital part of any multi-speaker design. Unfortunately super caps are expensive and we need a lot of microfarad for the midrange to make the high-pass section. The 3 x 33 uF STANDARD Z-CAPs chosen here for the midrange deliver most of it, but Superior Z are better although comes at a price. I had really good results from STANDARD Z-caps for mid and a Silver Z-cap for the tweeter.
It's my experience that a parallel of many smaller caps of same value makes better sound compared to a single 100 uF cap, but the choice is yours. By-passing a large lesser quality cap with a small one of better quality is not my cup of tea. It makes a blend of two transfer characteristics and not always for the better, but opinions on this vary considerably. 
The present construction is designed to deliver with later up-grades. The mid's reed paper cone can deliver the goods should you at a later stage decide to up-grade e.g. midrange series capacitors. You can also use the W18NX001 driver for mid without changing the crossover. 
You may choose to immediately replace the tweeter 4.7 uF STANDARD Z-CAP capacitor with Superior Z-cap or Silver Z-cap, the latter I found had a really good synergy with the STANDARD Z-caps. I can't help pointing to a 3-Way Classic builder here, who chose modest priced drivers and the best of crossover components. Well done to my thinking. Too often we see people buying expensive drivers and modest crossover components. The caps are of more importance than the coils and a 10 mH air-cored coil for the bass is a waste of money - if you can find one with suitable low resistance. If you want to up-grade here, use e.g. Jantzen C-Coils.


The sound

Yes, I'm going to write a little about the sound, something I really hate, because what I hear is not what you will hear. Nevertheless: This speaker delivers tonnes of detail. I can't help putting this first, because the mid-tweeter integration works so good that it will provide a rare insight to your recordings and it also tells good from bad, albeit not in any aggressive way.
Due to the stepped baffle and simple low-order crossover it handles vocals really well and Siri's Killer Note is no problem. Female opera singers? No problem. As my JungSon was occupied elsewhere I connected the speakers (in my workshop) to my 8 wpc 300B amp and I was surprised to hear loud it could actually play. Louder than my wife usually plays, but this flea-powered amp is not what I'll recommend despite the magnificent midrange. Feed it 30-50 watts PP if it has to be valves, or 50-100 watts solid state; really good solid state that is. My JungSon does well here, but....

It's a never ending topic how much power is needed for a given speaker. The short answer is that it depends on how loud you play. The CD above is Ulf Wakenius: "Forever you". This is an analog recording (2007) and you can even hear a faint tape hizz from the recording. Very little compression is used - if any. Apart from liking the music, I use this CD to test my speakers for loose wires or whatever. It comes with tremendous dynamics and will make anything capable of rattling - rattle. It also makes a litmus test on your amp's capability of handling severe transients and playing this CD really loud it could make even the Jungson start clipping! And this not at a level where the drivers would suffer serious risk of damage. Two things: This speaker can handle a lot of power and if you're a head banger, prepare for some 100 watts minimum solid state amp.

Bass is tight and surprisingly dynamic and kick drum comes through really well, much better than anticipated I have to say, and speaking of drums, the whole drum kit comes through with all the speed and agility I could ask for.
The Jenzen speakers are fairly big, not only physically, but also in the overall soundstage it provides. When dealing with large speakers, take care of your hearing, because it can play loud with low distortion and we tend to crank up volume when possible.

Evaluation was done with STANDARD-Z-caps to the midrange and a Silver-Z to the tweeter. With STANDARD-Z to the tweeter some details are gone and upper mid and treble appears a bit more compressed, all in accordance with standard polyprop performance. Good caps make listening easier and we can better sort out details, room reverberation seems more clear and e.g. applause from an audience all of a sudden sounds like clapping rather than just noise. Hand clapping is a terribly good test on capacitor's ability to transmit complex information without smearing detail.

FAQs having the answer NO:
Can I make the cabs with a plane front panel? Can I use a cheaper tweeter, like 27TFFC or 27TDC? Can I use any other than the specified drivers? Can I change the cab dimensions without impairing performance? Do you have more detailed drawings? Do you have a suggestion for an active version? Can I tilt the cabs? Do you know when the NEXT and further versions will be ready? Do you know how the vented version sounds compared to TL? Will Jenzen ER replace your DTQWTs? Will there be any clean 1st order filter Jenzens*? Will there be a version with magnesium drivers?

*1st order filters may be nice but don't handle power very well. To my mind we need a 4-way speakers to realise true 1st order filters and we need driver being linear some two octaves below and above point of crossover. True 1st order filters a prone to become extremely complex as we need to linearise drivers' response and this speaker was made to be simple with as few crossover components as possible without sacrificing performance. 1st order filters are not just a coil and a cap! I've tried modelling a 1st order filter and the mid has to be some 5-6 dB below system sensitivity (8 ohms series resistor!) and the bass and tweeter cross only 12 dB down at 1 kHz! We need a middriver with really low efficiency to make this work - technically. Or we should use a dedicated subwoofer and let the middriver go below 80-100 Hz. No wonder Vandersteen speakers are seriously inefficient (~85 dB).

FAQs having the answer YES:
Can I use 22 or 25 mm MDF? (Keep outer dimensions, front panel layout and 19 mm for the mid's outer panel). Can I use the W18NX001 nextel driver for mid without changing the crossover? Can I use a single rectangular vent for the midrange transmission line, like 20 x 150 mm in replacement of the 4 x 30 mm holes?

Useful links (Please read before writing!):

FAQ (Please read before writing!):
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-maling:


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Just in case you may be wondering what R2042 and C2041 do across middriver's series coil.
This RC circuit is of vital importance for making a smooth rool-off. So don't leave it out.

The Cabinets
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Click image to go to cabinet construction website.

Obviously you can use 22 mm MDF in replacement of the Baltic birch used here and if you think all this transmission line stuff is just a bit too weird - and it does admittedly add to the overall volume - you can make a vented version instead. 
If you remove the bass cab transmission line panels you have a net volume of 78 litres. This makes a nice F3 of 35 Hz. Port tuning = 32 Hz. Port = 100 mm  (ID) x 155 mm length. 
If you cut depth to 360 mm (depth without front panel) you get 65 litres and F3 = 38 Hz. Maintain port tuning of 32 Hz and port is now 100 x 197 mm. 
With this new cabinet depth for midrange - and by removing internal panels - we have around 25 litres minus volume of tweeter cab and bracings. This fits the ER18 well and I suggest adding a port to the rear of 50 mm (ID) x 75 mm. Stuff the port lightly with damping material to make an aperiodic tuning. The port leaves you the options of vented, aperiodic and closed box (the latter by stuffing the port hard).

Jantzen Audio ports: For bass cab: 2 pcs 100 mm (ID) x 200 mm, item #900029. For mid cab: 2 pcs 50 mm (ID) x 145 mm, item #900023. Cut to required length for mid and for bass if you choose the large vented option.

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If you do so, add two braces to the bass cabinet and one brace to the mid cab. Please check other files for how this can be made, e.g QUATTRO cabs.
Regardless of your choice, maintain front panel dimensions, driver layout and front panel chamfering. This is of vital importance of how the crossover performs. The middriver front panel provides an unusual flat response from the 4 drivers tested so far. View at bottom of page how CA18RLY, CA18RNX, ER18RNX and W18NX001 perform. There will not be a version with the CA18RLY.
For the vented version damp bass cabinet with 8 mm felt internal panels plus 30 mm acoustilux on top and 2 layers on bottom and right behind bass driver.
For mid use 8 mm grey felt on all panels and 30 mm acoustilux in lower cavity (25 x 50 cm folded) and behind midbass driver, same dimensions. Check damping materials here.

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Generally measurements tell close to nothing about the sound of a speaker system, thus only a few will be shown. From 300-3000 Hz we have a fairly flat response providing lots of presence and detail.
I think my future presentations will start with minimum attenuation as I've already had the question if this speaker isn't fairly tilted towards higher frequences. What cannot be seen from these measurements is the overall power response of the speaker and not even a horizontal plot fully reveals how the overall sound is perceived in our listening rooms. Should you be a sucker for treble, check tweeter attenuation below and use 1R5 to the tweeter. As always: Your gear and your room play an important role in how the tonal balance will be. Unfortunately we don't have tone controls on our pre-amps anymore.
The bass response of a speaker is serious trouble in terms of presentation. Usually our gated measurements are valid down to ~250-300 Hz with a room height of 2.4 meters (standard on these shores). What we can do is merging the far-field response with near-field measurements of the bass driver. This provides a reasonable suggestion of bass extension, albeit does not include port response. The port response can be added the near-field response also, but when all this is done we have to take into account room gain as well and here we may choose all kinds of environments providing everything from 1-2 dB to almost 9 dB (corner placement). Bottom line: This speaker does well down to 35 Hz and depending on placement even lower.

As always: You MUST try out the various resistors for tweeter attenuation. It's a key element in fine-tuning your speakers to your system, your room and your taste. I use 2R7 for R1011 but, I know many younger people prefer excessive treble. Your ears may be more tolerant.  

Left: SPL @ 0.5 meter between M and T, normalised for 2.8V, 1 meter. Overall system sensitivity = 88-89 dB/2.8V.
Right: Response merged @ 250 Hz with bass nearfield response. Port response not included.

Left: Tweeter attenuation from R1011 being 1R5, 2R2, 2R8 and 3R3 respectively. 1R5 is too little to my ears.
Right: Step response displaying positive polarity of tweeter & bass and negative polarity of middriver.

Left: Left and right speaker. Right: Final system impedance. Minimum around 6 ohms.

Left: Just to show two points of crossover between bass and mid. I wanted the midrange to go as low as possible,
because the ER18RNX can go low here and ended up with just below 200 Hz (red/blue). Nearfield response of drivers shown.
Right: Point of crossover between mid and tweeter is around 2.7 kHz. Pay notice to smooth roll-off from both tweeter and mid.
Disregard shown bass level at 60-300 Hz. This very much depends on where we merge nearfield and farfield readings.
we do this at 250-300 Hz where the farfield reading is highly unreliable.

The Complete Jenzen SEAS ER Kit
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 For price quotation incl. shipping, please contact Jantzen Audio at:

All technical questions at:

Download SEAS Jenzen ER Kit Sales Presentations.

I strongly suggest including the damping materials as this is of vital importance for making the bass TL work properly.

Replace 4.7 uF Standard Z cap for the tweeter with a Silver Z-cap if money allows. The difference is only ~35 EUR. Worth every hard earned Euro cent.

The price for 3 x 33 uF is the same as for 1 x 100 uF STANDARD Z-CAP. Usually we pay by the microfarad when it comes to caps.

Should you fancy loud playing, include 4 x 5.6 ohm resistors for replacing R2031 with two 10 watts in parallel.
I also suggest extra tweeter attenuation resistors: 2 x 2.7 ohm and 2 x 3.3 ohm, all 10 watt. My preferred R1011 is 2R7.

SEAS W18NX001 nextel coated driver can be used without changes to the crossover.

For ported version, order the following:
For bass cab: 2 pcs 100 mm (ID) x 200 mm, item #900029. For mid cab: 2 pcs 50 mm (ID) x 145 mm, item #900023. Cut to required length for mid and for bass if you choose the large vented option.

Crossover Layout
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Click image to view large.
Pics of finished crossovers to come asap.

As the crossover is going to be placed at the bottom of the bass cab, we have lots of space and you may increase board size to later accommodate Superior Z-caps, wax coils or whatever. 
If you choose e.g. Superior Z-caps for mid you have to increase height of the speaker base by e.g 15 mm. These caps come with quite a diameter. Use an e.g. 8-10 mm slant of plywood for the crossover. Also consider height of base if wax-coils are used.
You can obviously separate the bass and mid/tweeter sections and run bi-wiring/bi-amping as I have done.

Connecting drivers, click image to view large.

Kit crossover parts, here with added Silver Z-caps and silver plated copper/teflon cables. 
Click image to view large.

Click images to view large, 1200 pixel width.

As can be seen from photos, bass and mid/tweeter sections are separated for the sake of bi-wiring.
I also used 2 x 5R6 in parallel in replacement of R2021 (2R7) as I intend to play loud from time to time. These resistors take some heat.

Click image to view large, 2000 pixel width.

For connecting crossovers to mid cab I use these excellent terminals found on eBay from Taiwan. Search for "terminal block". The best terminal is no terminal
and these minimalistic terminals will beat any WBT at a fraction of the cost. These are actually the same used by Vandersteen loudspeakers. Been looking for 
these for years and finally someone on eBay started stocking. They take 7 mm fork connecters. 
For internal wiring I use silver plated cobber in teflon. Order separately.

Terminals blocks mounted with connections from bass cab to mid-tweeter cab.

For once: Lots of space for crossover. The crossover board is 23 x 27 cm leaving space for super caps as can be seen below.
These cabs are going to see multiple speaker drivers and flexibility is important.

Left: Trying out space for super caps. These 4 x 22 uF are huge! 
Right: Fully mounted crossover. I made a loop from mid/tweeter wires to allow future experiments.

The Jenzen MT baffle
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Below the response of 6" drivers I have at hand over the last year. I'm pleased with the performance of the Jenzen baffle as all of these response profiles allow simple crossovers to be made. In particular the W18NX001 is smooth as ever and even the ScanSpeak 18WU performs very well.
Reason for showing these files is to demonstrate it pays off spending time on proper front panels in order to provide the best possible acoustic support for the driver. As can be seen, this makes crossover construction easy - and cheaper! You may have specific ideas on how your speakers are going to look and I have a lot of suggestions on fancy cabinet designs and if I think it will work OK. I can't tell. Only measurements can tell although experience tells me some of these people building their dream speaker will have a hell of a time making the crossover, simply because design came first and acoustics second.

Left: CA18RLY. Right: CA18RNX.

Left: ER18RNX. Also semi-hardcones have some break-up nodes at 5-7 kHz.  Right: W18NX001, it doesn't get much better than this!

Left: Accuton C173-6-191E. Right: Same on mkII baffle; smooth as can be.

This Accuton driver doesn't do much above 4.5 kHz where the others make 6-7 kHz. The question is if this driver has a bump at 4.2 kHz or a dip at 3.5 kHz. Hmm... hard to tell. Whatever, this driver does well on the Jenzen baffle too. Listening to the MLS signal is always a good indicator of serious cone break-ups. This Accuton has a smooth response and sounds pleasing to the ear - even without any crossover attached. I recall the MLS signal from pure alu and magnesium drivers - ear-shredding! Modelling the Accuton looks promising with basically second order filters for all slopes. Due to the C173's steep upper roll-off we are facing an asymmetrical crossover with 2nd order to the tweeter and 4th order for the mid (acoustically).

Left: Accuton CSD plot. 
Right: And here's finally the ScanSpeak 18WU/8747-T00 on the Jenzen baffle. This does look much better than the infinite baffle response at ScanSpeak facility
Again, it pays off spending time on baffle geometry.

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