18 SOUND
NTLS-12
Copyright 2026 © Troels Gravesen
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DRIVERS
CROSSOVER
CABINET
WORKSHOP PICS
MEASUREMENTS
SPEAKER-KIT
CROSSOVER LAYOUT
For the time being my reference speaker is the
The-Loudspeaker-4. For the size, I just don't think I can do better.
It gives me all I want in our 24 sqm living room. Like the TL-4 was my
take on giving me the TL-5 from a smaller footprint, this NTLS-12 is my
attempt to give me most of the
Revelator-44 from an easier build. The Revelator-44 is basically
simple, but technically difficult due to cabinet design.
No, you do not get the same deep bass from the TL-4, but the
12NTLS3500-8 bass driver does go deep and does so well with the
6NTLW2000-16 midrange driver, that a coherent upper-bass/lower mid gives
an extraordinary fullness to vocals, piano and upright bass. This partly
done by moving the point of crossover between bass and mid up some
80-100
Hz compared to the
Revelator-44.
The 12NTLS can handle a lot of midrange. This had the
consequence that the bass driver had to be tilted some 5 deg. for proper
integration with the midrange. Sorry,
doesn't make cabinet work easier, but still, much easier than the
Revelator-44.
This 12" bass driver makes F3 = 40 Hz from the given volume. Not bad at
all. And not a lot of break-in needed.
12NTLS3500-8.
This driver has a rubber surround rather than the fabric surround of
the 12NTLS2500-8, which was tried but didn't do as well as the LTLS. Fs
specified to 41 Hz.
Crossover for mid and tweeter wasn't that difficult having done a lot on
these two drivers in my Rev-44.
My first-to-hear friend couldn't believe the bass when he first heard
it. What?? The bass doesn't use to be like this! The precision
and articulation took his breath. Even at moderate levels you feel chest
punch you didn't notice before.
What the TL-4 also taught me was that the midrange, being 8NTLW2000-16
or 6NTLW2000-16, is highly sensitive to the series capacitors! More than
I have ever experienced before. Here the 6NTLW2000 was initially fed
through Superior-Z caps and it worked well in most cases but on some
recordings and slight edginess appeared and by chance I added about 20%
of the capacitance from Alumen-Z - and this made a significant change
for the better. Really? I switched back and forth, but the change was
significant. Thus, C2 is a mix of Superior-Z and Alumen-Z. I may have to
revise my Revelator-44 to see if this is consistent.
Basics:
3-driver speaker.
Dimensions: 37.5 x 30 x 104 cm, WxDxH.
System sensitivity: 90 dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
Power requirement: 30+ watts/channel.
Useful links (Please
follow all links before e-mailing!):
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/LCR-RC.htm
http://www.troelsgravesen.dk/Inverted-Polarity.htm
http://www.troelsgravesen.dk/choices.htm
http://www.troelsgravesen.dk/Placement-of-ports.htm
ScanSpeak D2904/710003 tweeter
18 SOUND 6NTLW2000-16 midrange driver
12NTLS3500-8, 88 mm voice coil and rubber
surround. I gave them 2 hours at 30 Hz to soften. I'm not sure this was
needed, but doesn't hurt.
Massive motor structure from its 88 mm diameter tetracoil.
Download specs here:
D2904/710003 6NTLW2000-16 12NTLS3500-8
Download white paper on tetracoil/dual-gap drivers here.
Crossover features an LR2 topology throughout with inverted midrange polarity. Upper bass hump is smoothed by R10/C6/L5.
Click image to view large.
I used 20 mm Baltic birch/HDF (rear) for the basic cabinet and 25 mm HDF for the front panels.Bottom compartment is for the crossover and make bottom panel removable - or leave it open, I did. A base frame was made from 25 mm solid oak with my usual adjustable feet.
As always, a mockup! Does this have any future?
60 liter cabs for the bass was made and some
12 liter for the midrange and tweeter.
Lots of crossovers were hardwired and taken through a wide range of
recordings. I used a pair of Hypex FA501s as power amps for the bass
drivers through the passive crossover. I could use the Hypex DSP to
shape the low-pass section of the bass drivers but this is for all and
people generally favour fully passive speakers.
A faceted upper front panel was tried -
not much change to sound - if any, thus optional.
But I think it will make the final cabinets look nicer.
What turned out to be important was the tilt of the bas cabinet by 5 deg. Due to the relative high point of crossover between bass and mid, for full integration the bass section must be tilted. Not something that makes cabinet construction easier, but no way around it.
Next step was moving the mockups to the living room. Basement is almost
100% concrete, living room 100% wood. It makes a difference. Not least
to the bass.
Well, this 12NTLS3500-8 is phenomenal. It goes deep, it's dry and highly
articulate. This is probably going to be my favourite 12" bass driver.
It could be use in all my pyramid constructions where I have a 12" at
the bottom.
Honestly: Dave Holland's upright bass never sounded better!
So, time to cut some BB sheets and some 25 mm HDF...
Start gluing the mid-tweeter cabinets to have some firm building
section.
And remember to add felt to the cavity below midrange panel - much
easier to do before gluing it all together. Also add felt to the rear
panel behind tweeter.
Routing for drivers.
If you use 25 mm front panels, chamfer around midrange driver hole! It
needs breathing.
Right: Wire hole to midrange driver. Do not forget to make cutouts in
the felt!
As the front panels are attached with glue, I added 20x20 mm fillets all around to increase contact surface. Also the bass panel must have a fillet at top to seal of the bass cabinet.
Left: Cabinets fully damped with felt material. Time for sanding and
lacquer before attaching the front panels.
Acoustilux damping
2.2 sqm supplied:
Cut 12 pcs 30 x 50 cm
Cut 2 pcs 40 x 50 cm
Left: Add 1 pcs 30 x 50 cm as seen on photo.
Add 1 pcs 30 x 50 cm loosely behind midrange driver.
Behind bass driver.
Left: Add 1 pcs 30x50 cm at bottom and up one side.
Right: Add 1 pcs 30x50 cm on bottom and up the other side. I used 10 mm
staples to keep in place.
Left: Add 1 pcs 40 x 50 cm behind tweeter/midrange.
Right: Fold 2 pcs 30 x 50 cm at bottom, fold pieces.
Gluing front panels.
The finished speakers.
A few comments on
MEASUREMENTS before you start interpreting 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.
Measurements may give us an idea of tonal balance of a system, i.e. too
much or too little energy in certain areas, although dispersion
characteristics play a vital role here. A two-way 7+1 and a three-way
7+4+1 may display similar horizontal dispersion, yet sound very
different. 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 we 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
maybe 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
speaker, because speaker cones made from polypropylene, aluminum,
Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even
diamonds all have their way of adding spices to the stew. Nor do
measurements tell what impact the quality of the crossover components
add to the sound, from state of the art components to the cheapest of
coils and caps, they all measure the same if values are correct, yet
sound very different.
SPL merged with bass response. System sensitivity around 90 dB/2.8V
The most interesting measurement, impedance of the MT-section. Truly an
8 Ohm load with very modest phase shift. Any tube amp will love this.
Final system impedance with bass and MT-section in parallel. Minimum 3.7
Ohm.
To configure a DIY kit and get a
written offer including shipping cost, please use the DIY kit
configurator in the Jantzen Audio website:
https://jantzen-audio.com/diy-kits/
Remember to add terminals when ordering at
Jantzen website. No longer included in kit.
I suggest 4 pairs of #012-0190, binding posts M6, satin nickel.
All technical questions to troels.gravesen@hotmail.com
CROSSOVER-LAYOUT
BACK TO INDEX
Check this out before start making crossovers:
http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS
Also please read this:
http://www.troelsgravesen.dk/LCR-RC.htm
MT-section.
Treble level was later fine-tuned and a parallel resistor was added to
R1, thus not in all pictures.
Now treble level was just right!
Bass section.
Placement of crossovers at bottom of cabinet.
Speaker wiring.
Here placed at bottom of cabinet.
First time setup in workshop. Now only base frames are needed.
Making the base frames from solid oak. Glued with epoxy - with Teflon
sheets below and above clamps!
Frames cured and holes made for bolts for the
adjustable feet. The finished base support.
I'm not sponsored by 18 SOUND, but this helped me keeping warm during
the winter months :-)
Living room setup.
With the bass driven from my UcD400 amps - solid bass!
Front grills finished.