This is a
speaker I've wanted to do for a long time. A
3-way design from 10" bass drivers supplemented by
relatively small midrange drivers. I liked my 3W-Classic and I still use
the L26-3W from time to
time and I wanted to try this concept from the best
possible drivers, thus the SEAS W26 nextel bass drivers,
Crescendo tweeters and not least the 5 inch M15CH002
middriver. T29CF002 was chosen due to excellent
performance in the CNO. A second choice
will be the slightly cheaper T29CF001.
It's also an experimental
speaker and I never finalised the cabinet work as it evolved into other
speakers. So, I suggest you go with the Focal inspired design seen at
bottom of page allowing you to tilt all drivers for optimal listening
The construction was started in
February '08 and has been on hold for several months due
to other projects and despite not having made the final
cabinet design, I needed to get it off my chest because I
told a number of people about it and they keep asking how
it goes. So, here it is:
Commercial speakers I had in mind
for this construction were Spendor
SP100, Naim DBL and Harbeth
M40. All classic 3-way speakers being around
for many years and apparently still - I guess - holding a
small audience. The Naim DBL is a huge 65 cm wide
speaker, featuring a 15" bass driver surprisingly
married to a small 5" mid and a ScanSpeak 8513
tweeter, where Spendor and Naim feature 12 inch bass
WAF is low for classic 3-ways in rather large rectangular
boxes. High-WAF speakers these day have super-model
properties and I'm not sure only acoustics alone call for
this approach. So, this is a speakers for singles or
those blessed with a tolerant spouse.
What I also wanted to do
here was to deviate from all my other constructions in
using an either closed or aperiodic box for the bass
driver. If we want at least some bass from small
two-ways, the vented box comes in handy but with large
bass driver not having a too low Qt, other options are
available and may provide a more dry and firm bass
response with better transient response. As discussed
later, you may use this construction vented too. Taste
cannot be argued so in all three options are available
according to your taste or belief.
It's always exciting to set up a
new driver for test for the first time. I used
my 34 litres test cab for the W26. Frontpanel is 30 x 50
cm. Microphone is placed 50 cm from frontpanel and input
is normalised for 2.8V/1 metres distance. From the SEAS
data file my expectations were so-and-so. Some dip at 650
Hz and a bit peaky around 1600 Hz.
I have three emotional responses to the first time a feed
a new driver the CLIO MLS signal: 1) Bollocks!, 2)
Hmm.... and 3) YES!
Having made MLS measurements thousands of times you
know how you want the reproduced MLS signal to sound.
There are drivers that will shred your ears and you know
it's major trouble and there are drivers that will caress
your ears and you know it's a potential winner. And then
there are a lot of drivers in between....
The W26 is a YES!
Next I play some music without any crossover
attached. I play it fullrange and despite a sloped
response you may already enjoy what you're hearing. Some
drivers just sound awful due to serious cone break-up or
whatever. The W26 is so good I think it might even do in
a two-way system with a 1-1.5 kHz point of crossover. I'm
not saying this approach would make a great speaker, but
it seems possible. (I later tried and it didn't work).
Secondly I play some bass lines (Fender) from a test CD
and finally a kick-drum. The latter I compare to the good
12" Axiom 150 mkII driver, which is
the king in my speaker collection of making you feel the
impact of a kick-drum. Now, the W26 doesn't pull the
Goodmans off the throne, but it does deliver a punchy
kick and I was surprised to also hear speedy transient
attack from snare drums.
from SEAS data sheet measured at ½ metre
distance in 28 litres test box. Front panel
dimensions not given.
Right: My measurement of the
same driver in a 33.6 litres test box with 30 x
50 cm front panel dimensions. Measurement done at
½ metre distance normalised for 2.8V/1m and no
interesting to try a cross-calculation
of claimed data and see if they fit with the
math. To the left the most important TS data from
the SEAS data sheet. To the right I've inserted
selected data to the LspCAD box calculation
software and indeed we see a firm correllation
between the SEAS data and LspCAD prediction.
Efficiency seems spot on at 89-90 dB/1W/1m. SEAS
says 89 dB. So far, so good.
- my measured TS data:
TS data on both drivers,
not fully burned-in, but they probably won't
change much from here. Good correlation, I think.
A driver well suited for vented, closed or
The mid box
BACK TO TOP
Why a section on
the midcab alone? The M15CH002 is a
tricky fellow with a potential
"problem" in the 1-2 kHz range, that is
when the baffle isn't right. We have a dip here
and it adds a significant fingerprint to vocal
presentation if you have flat upper midrange up
to 1 kHz followed by a ~3 dB dip in the 1-2 kHz
area. Using the M15CH on a wide baffle didn't
work - I've tried the PMS cabs and had to abandon
the PMS-NEXT project - it didn't sound right. Too
much presence - in the wrong way. Read below.
center mounted on a 400 x 1000 mm wide baffle,
340 mm from the top. I won't go into details with
the four graphs, only that these measurements
were made from flat to various degrees of curving
the driver in a 200 x 300 mm baffle (my 10 litre
test cabs) produces the red
graph. The driver center is 95 mm from top. Now,
this looks a lot better. Adding 130 mm to the
baffle height, makes the blue
graph. Less baffle step loss but also a dip at
~1.5 kHz. The beginning of the PMS trouble.
I had great hopes
for the smoothness of the M15CH driver
from Dickason's measurements in Voice Coil;
reading above. This almost looks as good as the
MCA15RCY on the PMS baffle. Vance Dickason uses a
203 x 430 mm (8" x 17") baffle and
unfortunately does not provide info on where on
the baffle the driver is mounted. So, let's see
how the M15 performs on a similar baffle in my
on a 200 x 430 mm baffle with driver placed in
the middle. Readings done at 0, 10, 20 and 30
deg. Not quite as smooth as the VD readings. VD
uses a gated sine wave technique, apparently at
little more gently on FR presentations compared
to the mercyless MLS readings.
on a 200 x 300 mm baffle with driver placed 95 mm
from top. Readings done at 0, 10, 20 and 30 deg.
Now we have an even better reponse in the 1-2 kHz
region. Nowhere near as bad compared to the PMS
Overall we have an even power
response up to 4000 Hz +/- 30 deg., allowing a
high point of crossover to the tweeter.
samples of M15CH002 on the 200 x 300 mm baffle. Right:
Impedance of four samples of M15CH002
impedance in free air. Fs = ~80 Hz. The minimum
spread in performance seen here is one reason we
pay more for these drivers.
Back to "the
mid box" intro picture. Leaving the
M15 in the test cab, various bits and pieces of
MDF and cardboard can be used to simulate the
upper part of this W26-Classic. The cab is 36 cm
wide and adding a 45 deg. chamfering to the sides
of the mid cab + minor chamfering of mid cab top
(the cardboard) makes the above seen frequency
response. This is clearly manageable in terms of
making an overall smooth response in the so
important upper midrange/lower treble (600-2400
Why this odd
interior for the middriver? Well, when
SEAS has done all that possibly can be done to
eliminate reflections from the driver's rear
structure, the least we can do is ensure that our
cabinet doesn't reflect any energy back through
the cone. So, I've tried to design a box where
the rear energy is absorbed as good as possible
and due to the slots in the rear, we have an
aperiodic system, reducing impedance peak at
resonance frequency. Same as for the bass, only
here managed by adding compressed damping
material to the cavity.
The Woofer Box
BACK TO TOP
Below 3 possible
scenarios for vented systems. Actually
it is my intention not to use a vented
box, rather two ScanSpeak Variovents in an
aperiodic system, but to get an idea of
performance I had LspCAD suggest QB3 and SBB4
Above the QB3 box
at 75 litres and a vent tuning of 32 Hz.
Here we get an almost flat response down to 40
Hz. Not bad at all, but 75 litres is quite a lot.
I was looking for something around 65 litres.
The SBB4 tuning
predicts a 60 litres cab and a vent
tuning of 32 Hz like the SBB4. The response at 40
Hz is down 1-2 dB compared to the SBB4.
My intended 65
litres cab suggest an F3 around 35 Hz and
this volume is what I'll be going for. We can
tune the port a little higher and gain a decibel
or two in the 50-100 Hz range. But hardly
necessary here. F3 = 35 Hz is deeeeep if you want
to go this route.
W26FX002 in a 65 litres closed box would
produce the above seen response. We are some 8 dB
down at 35 Hz compared to the vented system.
How the performance from
W26FX002 in a 65 litres aperiodic box
will be is to be seen. The rear panel will have a
small separate section for either vents or
- why vented boxes (for
small speakers) ?
I've often had
the question why I always use vented
boxes and the answer is simple: To get more bass
from small designs. An additional 3-4 dB at 40 Hz
is clearly audible and the bass may be more
precise from a closed box, but who cares if you
can't hear it. My speakers are always 3/4-1
metres from the rear wall and some 1½-2 metres
from side walls, so I can't rely much on room
gain. If you don't like the sound from the vented
systems, stuff the vent with a pair of socks!
Dynaudio sometimes supply a polyester foam plug
for those who suffer excessive roomgain.
I cannot simulate the
response from the driver in the same 65
litres enclosure fitted with acoustic vents.
We'll have to wait for the measurements to see
how it performs.
The Variovent is device sometimes causing much
debate. What is an acoustic vent? An acoustic
vent allows some ventilation at low
frequences and virtually none at higher
frequences. What's that supposed to be good for?
Neville Thiele studied the Variovent in detail
and concluded it didn't offer any advantage over
a properly designed vented systems. I don't
subscribe to that statement. It depends a lot on
the actual driver used.
The general advice on the use of acoustic vents
is simple: Try it! Which doesn't offer much
comfort to those addicted to math. But box
calculation based on Thiele/Small data really
only apply for speakers with a Qt = 0.35, which
only very few drivers have. Based on experience
we use speakers with high Qt in cabs too small
and drivers with low Qt in cabs too large
compared to what math may suggest.
Comparing the impedance
peaks of a driver in free air and a
perfectly closed and empty box should reveal the
same peak height, so we have no loss in the
closed box. Obviously the resonance frequency
is higher. Adding damping material to the closed
box we see a decline in peak height; now we have
some loss. Adding an acoustic vent may produce a
significant reduction in peak height depending on
how open the vent is. So, the system Q-value is
lowered (= more loss) from applying an acoustic
vent although we really can't speak of a Q-value
of an aperiodic system.
Basically a closed box has 2nd order roll-off, a
vented system a 4th order roll-off and the
aperiodic system a 3rd order roll-off.
In this system I'll try all 3 options and see how
my 20 wpc SET amp responds to the various
impedance profiles generated - and obviously try
to evaluate the quality of the bass performance.
It'll be interesting to A-B test the various
For the final set-up the bass cabs must be tilted some
6-7 deg. and the mid cab placed vertically.
Pics from cab construction
(Identical to JBL L100
Making the mid cabs
Cut the following sheets of felt material: 4 pcs
32 x 21 cm (top and bottom), 4 pcs 24 x 13 cm (sides) and
2 pcs 30 x 13 cm (rear reflector).
The slots to the rear must be damped with some folded
acoustilux/MDM3. More details to come.
LspCAD Predicted Response:
Final measurements of drivers, no
Left: impedance and phase
of all drivers in final cab. Red/black = bass,
green/yellow = mid, red/purple = tweeter.
Right: SPL of bass driver i final cab. SPL bass
driver merged at 250 Hz. Blue = minimum phase. An
overall system sensitivity of 91 dB/2.8V seems
Left: SPL and minimum
phase of mid-driver in final cab. What really
pleased me here was an even response from
500-4500 Hz making overall crossover construction
Right: SPL from tweeter in final cab. No problems
Mid cab and test crossover on top.
fine-tuning, version 2 = final crossover.
BACK TO TOP
Crossover version 2. As can be seen, a lot of
small changes to version 1.
This is what happens during actual measurements and
R2021 is the actual resistance of 4.00 mH coil, so no
true resistor here.
Complete kit only available from Jantzen
Kit can be bought with/without drivers.
Please state where you live for full quotation
All kit and component prices may
be subject to change and are always to be confirmed by Jantzen Audio
Download Kit Sales presentations
here (zip file)
All technical questions to me at
Please specify tweeter option on order.
BACK TO TOP
Left: Actual response at tweeter height, 1 meter
distance, 2.8V input.
Right: Point of crossover between mid and tweeter is 3
Left: Horizontal dispersion at 0, 10, 20, 30 and
40 deg. (tweeter height)
Right: Vertical dispersion from bass height (middle) to
10 cm above tweeter height. Red and purple are the
Left: SPL 1m/2.8V, merged at 300 Hz with woofer
Right: Impedance of final system, an easy load. Blue =
Left: CSD, 40 dB. Right: CSD, 20 dB.
Left: 8 wpc 300B SET. Middle: 20 wpc Audio Mirror 6AS7
PSE. Right: 100+ wpc, modded Rotel RB-981.
First of all:
Do not use any capacitors (for mid and treble) of
lesser quality than the Superior Z-caps used
here. I'm not saying these are the worlds best,
but you will never get the best from these
magnificent drivers if not driven from a
high-quality crossover. I do not recommend
spending mega bucks on foil coils and the like,
use your money on the caps. Buy perfectly wound
and baked coils made from round copper - now
available from a number of suppliers.
Next: If you
think this speaker sounds bad, take a look at
your CD-player, your phono cartridge and phono
stage, your line-amp and your power amp and see
if there are bottlenecks causing sonic
degradation. Or your room may be totally
inadequate for hifi systems, i.e. forget about
modern homes with concrete walls, tile floors and
no bookshelves or curtains! Sell the leather sofa
and buy one with some heavy fabrics, and bring in
some floor carpets, etc.
If you still think it
sounds bad: Well, we have very different
taste in loudspeaker performance....and I suggest
you read these comments from Art
point in referring to this again is that we're
into the best of traditional high-end hifi here.
I won't even try to describe the sound in detail
because it's meaningless.
I will however
comment on the bass performance because of the
use of Variovents. If you want deeper and a more
voluminous bass, add vents (find dimensions
above). As can be seen from the impedance plot,
this is an overall very easy load on your
amplifier and due to the Variovents we have a dry
and "short" bass performance, free of
any bass boom overhang on transients.
And one more thing: I am particularly surprised
by these speakers ability to reveal depth and
space around the performers. Three-dimensionality
is some of the best I've ever had and this
follows up to even very high listening levels, a
clear sign of very good drivers displaying very
low distortion. The M15CH002 is indeed an
extraordinary fine driver.
The 300B amp was on the
stand when I brought the speakers to our
living room. I didn't expect 8 watts to do much
here, but it could actually drive the speakers
well beyond my wife's usual listening level. And
the mid and treble sounded really good.
The Audio Mirror brought some more punch to the
bass and overall suitable for most situations,
that is if we never throw a party or want to
impress out hifi friends with some butt-kicking
Give these speakers some 35 wpc PP minimum - or
one of the very best 50+ wpc solid state amps you
can find and it will deliver. With the modded
Rotel RB981 on the stand I'd not even consider a
vented version. The 10" bass driver in its
aperiodic 65 litre cabinet is doing just great;
solid, tight bass - but you will get more and -
subjectively - deeper bass from a vented design.
This speaker did
not turn out to be a classic design as
it was planned. Sloping the cabs is a must due to
size and due to the bass driver handling a good
part of the midrange. The construction shown
above will work excellent with a 5-7 deg. tilt of
bass cabinet and vertical mid cab.
Thinking of possible cab designs, the Focal
approach seems the best way to make the best of
the current construction. Something like this:
Thanks, Rodolphe, for the pics!
This will allow the drivers to be
individually positioned to suit any listening
Suggested cabinet design à la
from Cyclop builders