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ATELL-3
Copyright 2022 © Troels Gravesen
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DRIVERS
CROSSOVER
CABINET
MEASUREMENTS
SPEAKER-KIT
CROSSOVER LAYOUT
AudioTechnology - Ellipticor: ATELL. I could have included the Viawave
contribution, but VIATELL would sound like a telephone company. ATELL it
is.
The
Ellipticor-3 project was the spin-off of a client project. Sometimes
a client asks for things you wouldn't have considered, because you have
your ways and routines. Except for the 2½-way concept,
the client asked for quite a different speaker, but it forced me to take
another view on the Ellipticor drivers and what we can do with them. I
had not anticipated a 1st order filter being possible, but it is and it
has given ideas to a whole range of new constructions, and here's one of
them. Like the Ellipticor-3, this will be a pyramid cabinet and my guess
is there will be more pyramids. Being fairly easy to construct and
allowing larger bass drivers to be implemented, the pyramid is less
obtrusive in a domestic environment, yet delivering substantial volume
and subsequent deep bass. Having the bass driver close to the floor has
the extra advantage of significant room-gain - and the mid-tweeter
section can be tuned to higher sensitivity.
Initially this project was thought as an up-scale of the ATiRi speaker by adding the magnificent AudioTechnology 10C77 bass driver, which can go deep from modest volume. This would allow the drivers from the ATiRi speaker to be tuned higher, but turned not as easy as anticipated. In fact, the 18H52 midrange crossover would be rather complex to get where I wanted. After a couple of weeks' fine-tuning I couldn't help thinking I had a driver on the shelf that could do just what I wanted - from just one single coil. Thus the Ellipticor 18WE driver entered the scene. In fact this would not be a whole lot more expensive compared to the 18H52 + complex crossover. Next the question was if it should be the 4 Ohm or the 8 Ohm version. Both drivers were tried and for bi-amping the 4 Ohm driver would add to overall system sensitivity, but the 8 Ohm version just turned out better for a fully passive version, where the 4 Ohm version would produce an final system impedance that might be a challenge to some amplifiers.
Like the Ellipticor-3, the midrange driver here doesn't have a high-pass filter, which has unquestionable benefits, but also reduce power handling and you have to consider this before you start cutting wood. However, the dynamic headroom of the 18WE driver is significant, and to help out delivering in the lower octaves, we have an 8" passive radiator mounted on the rear of the cabinet, the same way as the ATiRi. ScanSpeak doesn't have a passive radiator suitable for this, although it can be easily made. The AudioTechnology PR23 can be used here. Should you have an old pair of ScanSpeak Classic 21W/8555 drivers, remove the magnet (hacksaw) and voice coil - and you have a perfect passive radiator. I used the 21W driver here. Not a bad choice having a very rigid paper/carbon cone. I guess the SEAS SP22R is also suitable, but haven't tried. I strongly advice not to leave out the passive radiator. We need all the low-end weight we can get from a single 6" midbass driver - and the passive radiator does it.
What has survived from the ATiRi project is the GRT-145 ribbon tweeter and it's a superb match for the 18WE driver. This only 18 milligram ribbon and its powerful neodym magnets delivers some treble quality only matched by seriously good compression drivers, and what even more remarkable is that it can handle a 1st order crossover giving it an initial 1st order roll-off gradually transcending to a 2nd order and finally a 4th order roll-off below 1 kHz.
As for the Ellipticor-3, not having a high-pass filter on the midrange
pays off. The coherence in upper-bass/lower-middle is hard to ignore,
although is does not have quite the same fullness and bottom weight of
the Ell-3. It can't - and it shouldn't. We have a significant smaller
cabinet and we have saved 2.5 k€ on drivers. Yet, the ATELL-3 has
qualities that made me go through record after record to hear yet
another way of telling me what I may have overlooked before. Any new speaker
will do things differently and hopefully give you new insight into your
record collection. The ATELL, like the Ell-3, has a naturalness to the
overall presentation, a transparency only limited by the source material
and for the size, surprisingly dynamic. On top of this, deep dynamic bass
from the 10C77 sandwich cone driver. I don't know of any 10" bass driver
that comes even close to the 10C77. Not cheap, but I can't find
alternatives unless we go to 12" bass drivers, but then we need a bigger
sized cabinet and here the objective was to make the best of a smaller
cabinet with higher WAF. And BTW, my wife loves it!
I really like these speakers and they will be in my permanent
collection as reference and I wish I could convey a precise description
of what it sounds like, but like Caspian caviar or French truffles, you
won't know until you've had it your mouth. There's a naturalness and
honesty to the sound - the best way I can describe it. The magnificent
properties of all drivers, the superb integration of mid and treble and the simplicity of the crossover let as
much come through as possible. A true speaker for testing your
interconnects and cables.
Click image to view large
Basics:
Three-driver speaker from 10" bass driver, 6" mid-bass +
Viawave ribbon tweeter.
Dimensions: 34 x 40 x 105 cm, WxDxH.
System sensitivity: 88 dB/2.8V/1 meter.
Impedance: 4-8 Ohms for MT section. Depending on crossover version and
bi-amping/not-bi-amping, there are four impedance scenarios, see below.
Point of crossover: 80 and 3000 Hz, 1st order. 2nd order for bass.
Power requirement: 20+ watts/channel.
Power handling: 100 watts. Please
also read:
http://www.troelsgravesen.dk/power-handling.htm,
and remember any burned driver is a misused driver.
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
And please also read this:
http://www.troelsgravesen.dk/choices.htm
Click images to view large
Download specs here: GRT-145-4 18WE/8542-T00 10C77-25-10-KAP
Click images to view large
The passive radiator:
Click images to view large
Left:
AudioTechnology PR23 passive radiator. Right: ScanSpeak 21W-8555 cone (no magnet and voice coil):
Remove the magnet and cut off voice coil. No further treatment
needed.
Crossover as shown on this page. The bass features a 2nd order filter where the mid-bass/tweeter section is 1st order.
The crossover below is dedicated for bi-amping as impedance will be pretty low if sections are combined (2.6 Ohms). Alone the MT section stays above 5 Ohms, so no problem. The crossovers are tuned to the same frequency response and to my ears - and with the Alumen-Z cap used above - do not produce any noticeable differences, which may be disappointing to some, but good caps really aren't that bad, but if you're in the mood for "sine-cap" and bi-amping, try it out. Both versions are shown in the Kit Instruction, so you may later try the two options and compare.
The actual front tilt is 4.9 deg, but stick to the 310 cm depth at top.
Sides are tilted 3.8 deg. to make 200 mm width at top from 340 mm at
bottom.
Cabinets were made from 20 mm Baltic birch and damped with extra MDF
sheets and 4 mm bitumen
pads.
Front panels were made from 25 mm black HDF. Laminate if you cannot get
25 mm. Thicker is fine, but remember to chamfer 18WE driver hole:
http://www.troelsgravesen.dk/chamfer.htm
The 10C77 bass driver does extraordinary well from small volumes, here
some 35 litres.
Given the 20 mm panel dimensions we have 44 litre net volume at hand for
the bass driver; too much. Cladding all interior panels with 12-19 mm
MDF/HDF
make a net volume of 35.4 litre.
This makes all bass cabinet panels 32-39 mm thick. A rock solid enclosure! See below.
It has to be said the damping
materials will add to the virtual volume of the cabinet, maybe even 10%,
but the ports, bracing and driver will take up some of that volume. My
test cabinets were 34 litre and the bass is as deep and powerful as I
could want.
Click image to view large
Workshop pics
First time setup of side and top panels.
Mark all interior panels on side panels
before assembly!
(not shown here - should have done)
3.8 deg. side tilt works as intended. Nice top joints.
The the right: Have a plane rectangular surface and mark up the front of
the speaker.
With 1050 mm height and 5 deg. tilt, the front length
is 1054 mm, 4 mm more.
The side panel length is 1052 mm with a 3.8 deg. tilt.
Now you can position the cabinet correctly when gluing sides, top and
bottom. I suggest doing this first in one operation.
My table saw doesn't allow me to cut such long length. Same technique is used for the front of the side panels.
Do around 1 mm at a time from left to right as the rotation of the router is clock-wise.
To the left the finished rear panel. I suggest gluing the bottom panels
first. Add blocks of wood by screws to prevent the panel being squeezed
out when applying pressure. Make sure cabinet is in line with the
drawing on the board. Having the rear panel loosely in place helps
aligning the cabinet properly.
Left:
Time for some rear panel routing. Right: Checking out driver rebates and
port holes.
Warning: Take care when you glue the rear panel. Be careful when
applying pressure around driver holes or you may easily squeeze these by 0.5 mm in
diameter and the drivers won't fit the rebate. I did and had to sand the
10C77 routing by
hand for ½ hour to enlarge the rebate.
Left: The basic cabinets sanded and ready.
The outer shape of the cabinet is a result of many considerations:
Optimal front panel (frequency response), minimum baffle, optimal
vertical placement of front drivers at presumed listening height,
aesthetic consideration with regard to width, height and depth, etc. As
a result of this we have some surplus volume. Yes, we could decrease
depth, but I didn't like it for aesthetic - and acoustic - reasons.
I also wanted a rock solid cabinet with considerable weight. The 10C77
bass driver weight is some 10 kgs, thus for the bass cabinet the 20 mm
Baltic birch is cladded with 19/12 mm MDF/HDF glued with vinyl tile glue (check
here). This makes a flexible bond and adds to the overall damping
properties of the panels. Also a traverse brace is added.
The MT section is added slanted panels to reduce volume to some 16-17
litres and make an overall irregular shaped enclosure minimising
reflections. Below we go step by step in shaping the interior:
Left:
Start gluing the panel between bass and MT section. Use stop blocks to
prevent panel from sliding when applying pressure. Make sure the middle
panel fits exactly not to squeeze the cabinet on the middle.
Right: Insert tweeter panel and glue in place.
Left: Reinforce bass panel with 19 mm MDF as seen on photo.
Right: Reinforce bottom panel with 19 mm MDF
Left: Make brace in middle of bass cabinet. Make cut-out for bass driver
and make two holes as seen on image ~Ø13 cm.
Right: Double panel thickness between bass and MT section with 19 mm
MDF.
Apply 12 mm MDF/HDF to side panels of bass cabinet.
So much for the bass cab. We now have ~35 litre net volume and a panel
thickness of 32-38 mm.
Midrange cabinet slanted panels:
Mark upper slanted panel on side panels as to the drawing.
First of all, mark up the two slanted panels (red lines) before
assembling the cabinet - ex. front panel.
Cut out pieces of thin hard cardboard to fit in. Use these as templates
for cutting the final panels.
The sides of the slanted panels were cut approx. 4 deg. to fit the
side panels as tight as possible.
The slanted panels are the only tricky parts of the cabinets - and they
don't have to be nice - only air-tight!
Same procedure for the bottom panel, but take your measurements and
adjust dimensions to actual cabinet.
Bitumen pads on midrange panels.
The bitumen pads are optional and must be added to your order.
Faceting the front panel. Can as well de done manually:
http://www.troelsgravesen.dk/tips.htm#Faceting
Table saw setting: 30 deg.
Table saw side table: 3.1 deg. This must be tried as it depends on your
table saw calibration.
Try reaching the final faceting some 35-39 cm from top. No big deal.
Click images to view large.
Testing front panel with drivers. Now time for final sanding, lacquer
and paint (right).
Felt damping of bass and mid cabinets.
Use
vinyl glue to fasten felt sheets.
Dampen the unused cavities with felt sheets as seen on images. No need
for potential resonant cavities next to the drivers.
I placed the bass crossover close to the front panel - as far away from
the magnet as possible.
Front panel is added felt and a double layer of acoustilux. This is the
only acoustilux used in the construction.
The last and vital part of the damping procedure is placing a piece of
folded 22 x 50 cm acoustilux between the 18WE and passive radiator. Like
the ATiRi we need to make an acoustic low-pass filter to the passive radiator.
Otherwise we have some spurious impedance disturbances around 400 Hz.
Secure the acoustilux in corners with dots of sealing agent or similar.
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
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.
Above the frequency response merged with near-field response @ 200 Hz.
Low-end response from merged near-field response of 18WE and passive
radiator.
Contribution from bass driver not shown here.
Now, the above graph may all look nice and smooth, but let me remind you the graph tells nothing about what the speaker sounds like. Sound quality cannot be pinned down a some nice looking graphs.
Impedance of MT section (red) and bass (green). Both driven from
crossover (capacitor version).
Minimum impedance for the MT section is 7.3 Ohm, love a first sight for
any decent tube amp.
Above the combined system impedance for bass and MT section (capacitor
version).
Minimum impedance 3.5 Ohm, nothing that should bother any amplifier,
being solid state or tube, although not for faint-hearted SET amps of 6-10
watts or similar.
Above the standard version with tweeter
capacitor.
The bitumen pads are optional and must be added to your order.
Above the sine-cap version for
bi-amping
The bitumen pads are optional and must be
added to your order.
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/
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
Bass layout
MT layout - capacitor version
MT layout - sine-cap version
Wiring:
Note double pair of binding posts for either bi-wiring or bi-amping.
Wiring MT section, sine-cap version
Click images to view large
Above the bass section, left, and MT section, right. This for the
capacitor version.
In an updated version the Premium Electrolytic is replaced by Cross Cap,
PP capacitor.
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