Jenzen Accu mkII
Copyright 2012-20 © Troels Gravesen
The Sound Crossover
Measurements Crossover Layout
The Jenzen Accu mkII
features the front panel from the Jenzen
D and a slightly modified tweeter crossover. Everything else is
the same as first launch.
Download mkI here
if you want to build the first version having an easier front panel
All loudspeaker drivers hold a sonic signature
depending on overall construction and components used, not least cone
materials. Making a blend of sounds from very different
cone materials may not always perform well regardless of how well we
implement the crossover. I
often had trouble
making a good blend of true alu ribbon tweeters and a midrange driver,
regardless of the latter's soft or hard cone. Lack of uniform
dispersion may be one problem, but the sonic signature of
ribbons is special.
In the crossover region we have a blend of sound coming from
diaphragms having an e.g. weight ratio of 1:1000, 10 mg to the ribbon
and 10,000 mg (10 grams) to the mid, sometimes even more. So, in this
range of overlap we have two drivers doing the same thing their
way; not always pleasing to the ear. I don't mind a tweeter having a
moving mass of e.g. 500 mg as the treble that counts is mostly in the
1500 Hz to - let's say - 7-8 kHz area. It may prove a lot more
pleasing to the ear - that is if the crossover is done well. The
crossover is the heart of the speaker and can turn anything into
misery if not executed properly.
As discussed before, soft domes may do well with paper and polyprop.
Sometime a good alu dome does well too. Planar tweeters, which I
like a lot, may do well with polyprop, but not always with paper pulp
based on my experiences. Obviously I haven't tried all
combinations and generally I don't exclude any combination of
drivers. It must all be tried before drawing conclusions, or prejudice
may exclude us from good times in front of our speakers.
The law of diminishing return goes
for high-end speakers as for economics in productivity of consumer
goods. We may throw in a diamond tweeter, but we can't be sure the
bottleneck is not somewhere else and further investments just doesn't pay off in terms of
All of the drivers shown here are pretty much SOTA, state of the art, in their
respective areas. This doesn't mean they're the best,
because best doesn't exist in speaker drivers. Nor does "world's
best speaker" exist although manufacturers love to claim so. Our
perception of sound is much too subjective for such statements and one
customer's aural nirvana is a another's nightmare.
are by all means serious compromises when it comes to reproduce the music we love. Not only can a driver only
reproduce a few octaves of the ten some of us can hear, thus we
need at least two, preferably three units to cover the entire range.
The inevitable overlap between drivers, the inevitable phase shifts
introduced by our crossovers, the lack of uniform dispersion due to
varying diameters, the lack of low-end extension, etc., all ads to a
particular sound of a system. We could
go on about all the imperfections associated with loudspeakers
based on dynamic drivers, but at the end of the day we can still
manage to put the best together and have an enjoyable hour in front of
our "boxes". The key issue before starting a DIY project is
that we make perfectly clear to ourselves what our objectives are.
What is the size (volume) of my room, how loud do I play, can my
amplifier handle the speaker's impedance and sensitivity, etc. Please read choices.
The Accuton C173 can't move more air than a Vifa P17, but it may be
able to do a couple of things the Vifa cannot.
The Accuton drivers fitted
with ceramic cones are considered some of the best transducers around. The
rigid cones display pistonic motion within their operating range, but
break up when we reach higher frequences, e.g. 4-5 kHz for a
6" driver. To dampen the ringing several options are available:
Do nothing and filter out the notches, add damping polymers to the
cones, punch holes or "ears" in the diaphragm (and seal them again), etc.
Whatever we do, the ringing of true hard cones will have an impact on
the sound that emanates from the speaker. The trick is to get the
resonances as far out of its operating range as possible and to get
them some 15-20 dB below output level.
The MLS signal coming from the C173-6-191E drivers during testing
suggests well-behaved break-up nodes compared to the ear-shredding
peaks from an e.g. pure alu driver. This is no comparison and
promise well for the Accutons.
Having a low point of
crossover between bass and mid (~200Hz) I wasn't too concerned about
compatibility between bass and mid. These are both hard cone drivers
and should mate well, and so they did.
Exploring the new Accuton S280-6-282 was an option but 1200+ EUR/ea is
a lot of money - and I have the Audio Technology drivers; an argument
hard to ignore. The AudioTechonology drivers are 525 EUR/ea. Also the
Accutons (11") are a bit too large for the Jenzen cabs, thus
10C77 it is.
Should the Jenzen Accu catch
your attention and should you want to replace any of the specified
drivers, please DO NOT ask if this or that driver is suitable. I can't
tell and I won't speculate on replacements based on driver specs.
Accuton C30-6-024. 6 Ohms. Click images to view large. Download specs
Buying Accuton C30-6-024
tweeters I had other projects in mind, but while working on Jenzen SEAS
speakers, I couldn't help wonder what would become of a Jenzen Accuton
set-up. Having received the Accuton tweeters I quickly
did some measurements and based on modelling this tweeter appeared an easy
implementation in a range of 2- and 3-ways. Thus, the search for an
Accuton* midbass driver started.
For the time being (2011) Accuton faces
the problem of neodymium prices reaching the skies and their neo drivers have to be redesigned to fully utilise smaller neo
magnets - or using ceramic magnets. I don't fancy any particular magnet
material over another and I don't think anyone ever compared exactly
identical drivers with either alnico, ceramic or neodym magnets.
Preferences are most likely due to other design features.
was also looking at the Morel SCM634
having heard from Eggleston speakers what they can do, but the more I
looked at the C173-6-191E, the more convinced I was that this was the
driver to look for in this project. The SCM634 is even more expensive
(320 €/ea) than the Accuton.
Click images to view large. Download specs
hope the Accuton C173-6-191E midbass driver will stay consistent in
the Accuton program for years to come.
Developing a speaker based on drivers that are out of stock next
year is no fun! The present C173-6-191E is a development of C173-6-195E. Comparing the two drivers we find Mms to be reduced by
1.7 grams, Qms slightly increased, hence Qt increased from 0.27
to 0.32. Cms has decreased from 1.35 to 1.20 and Sd increased from 130
to 132 cm2. Efficiency
appears slightly improved as expected from lower mass. That's all.
This mostly sounds like a new rubber surround, but there may be
changes to rear coating as well, because this cone does have a
coating on the rear side.
"E" means it has "anti-resonant cutout fills" to dampen inherent resonances and
crossover work easier and the hope is that a simple 2nd order low-pass filter
will do. Based on modelling it appears we
can get away with a 1st order low-pass filter supplemented by a
filter smoothing the minor 4 kHz bump. This provides the target 2nd
Listening to music from the
C173-6-191E without any crossover doesn't suggest serious cone
break-ups or high-Q'd peaks. Quite remarkable from a hard-cone
10C77-25-10-KAP sandwich cone. Click images to view large. Go to AT website
Audio Technology 10C77-25-10-KAP
bass driver has been reported in detail here.
Not much to add except that in its category*,
this is the best 10" bass driver I've had: Fairly efficient, easy on crossovers, a punchy performer with
low-level detail (high Qm) and only bad thing I can think of is
weight... In a well constructed enclosure it breaks my back from moving speakers
around from its 10 kg added weight.
* I reckon this driver in the
family of mid-efficiency bass drivers. A 10 inch
high-efficiency bass driver like the Eminence Deltalite II 2510 in a
well-constructed horn will - to my ears - outperform the 10C77 with
regard to transient response, and low-end extension is only a matter
of horn properties. The price to pay is size. If it has to be small
the 10C77 is the driver to look for and the price to pay is decent power
amps that can handle the current needed.
Jenzen Accu mkII
Click images to view large. Tweeter
baffle still needs final finish.
Setting up loudspeakers can
become boring! Regardless of how the paper pulp or polyprop is used, we may have an idea of how this or that speaker is going to
perform - and so they mostly do. Not quite so with these Accuton drivers.
After crossover simulation and a couple of hours' fine-tuning,
the first test crossover was up and running - and well, finally
something happened that usually doesn't happen: You hear something
that sounds radically different from all other speakers. Depending on
how the crossover is put together, these drivers will throw a
different soundstage. Most noticeable is the reduction of the noise
floor, and by this I mean that most other drivers will smear detail to
some extent and leave a thin curtain of "noise" that we
really don't notice until it's gone. Next we may go through acoustic instrument
recordings and every single time start wondering if
this is how it should sound. Is this driver right and all other
drivers wrong? We only have the concert hall for reference so it's
hard to compare, but for sure it seems like most instruments have
reached a timbre quality few drivers can match.
midrange and tweeter level right took much longer than anticipated and
of crossover from 1.8-3.0 kHz were tried. Taking the point of
crossover really low first of all confirmed the C30 can go
really low, but on-axis response had to be recessed in the 2-5 kHz
range to balance the wide dispersion. This was bit like the Chario speaker
crossing over at 1.5 kHz and voiced to have a recessed on-axis
response in the 2-5 kHz range. On paper this may look bad, but in
reality provides a good balance between basic notes and overtones. If
dispersion in this frequency range is wide we have a lot of energy projected
into the room and we may have to attenuate a decibel or two to render
a perceived "flat" response. In reality this also depends on
room conditions and why some speakers may sound good in an
acoustically lively room and in other rooms not. As a speaker designer
this is an inevitable compromise to be considered. Most living rooms
are less than ideal for sound reproduction and how do we voice a
speaker to suit an average of living room acoustics? Not easy.
Eventually 2.3 kHz proved beneficial in not having a too strong
upper-mid projection a fairly flat on-axis response. The
mid crossover turned out more simple than anticipated and basically we
have a 1st order filter on the electrical side with a single notch
filter handling the 4 kHz bump. Acoustically this makes a close to
perfect LR2 roll-off. The tweeter needed equalisation around 6-7 kHz
in order to reduce some tendency to sibilance and an impedance
correction circuit is also applied to smooth the high-pass slope and
improve power handling.
What pleased me the most in this setup was the lack of attenuation
resistors to the midrange. During some of the stages of development I
had to attenuate middriver and every time this reduced midrange vitality. These Accutons should be handled with care!
What was also noticed during crossover development was the quality of
crossover components. Initially I had a 3 x 33 uF Obbligatos for the mid
high-pass section and they're good but changing these for super caps
revealed their shortcomings in delivering micro detail.
The soundstage depth these drivers can
astonishing. I couldn't help thinking of the Mangers
I did in between the Jenzen NEXT and Jenzen Accu. We could make a
2-way from these two Accuton drivers that would forever put the
Mangers on the shelf. And by the way: Running the C173 fullrange
without high-pass filter suggested a strong and solid bass
response even from the progressively stuffed TL mid cab. Material for
a small vented two-way monitor some day....
Initially I ran the SEAS 26WFX002 for bass as I had to make new front
panels for the 10C77s. The SEAS nextel drivers did well, but 10C77
further improved bass response and made an excellent match to the C173
mids. Over and over again the 10C77 proved a deep and articulate bass
response from whatever material I fed them. They do very well with the
TL design, firm, "short" and solid.
Getting the point of crossover between bass and mid proved a
challenge and speakers had to be set up in different environments to
get the best possible compromise, because this will always be a
compromise as the acoustic environments these speakers may have to
endure will vary greatly. Most people have to place their speakers too
close to the front wall and too close to corners and the inevitable
room gain starts playing its thing. The bass driver's notch filter is
the trick to pull if things turn out too boomy. Leaving it out will
increase response around 100 Hz and different resistors can be tried
to make the best possible balance.
I can't help pointing to the
distortion measurements shown below. This is the lowest distortion
levels I have ever measured from a loudspeaker. At 5.6 volts input
equivalent to ~94-95 dB at 1 meter, the total harmonic distortion is
below 0.5% from 1000-20000 Hz and below 1% down to 400 Hz. Amazing! No
wonder these drivers deliver an unprecedented level of transparency
Every evening during development I
went to the workshop to hear another CD from my collection. One day
the Getz/Gilberto CD. Although it had been a long time since last
hearing, I didn't recall it sounding like this before.
It sounded ruthlessly
naked, not as lush and colourful as I remember it. The shortcomings of
the recording is clearly audible in terms of inadequate microphone
placement and the semi-stereo recording and mixing. Getz' handling of
his mouthpiece is clear as ever and the Accutons put you closer to the
event than most other speakers will do.
I won't call the Accutons discriminating, nor sterile or
"clean", rather neutral and "if this is what you feed me,
this is what you'll get". This doesn't mean they're not influenced by the
baffle geometry, crossover topology, crossover
components' quality, points of crossover chosen and overall
dispersion into the room; obviously they are and they appear to be an
everlasting challenge in terms of overall voicing in making the best
I brought CDs that I was sure would fall apart and they didn't. I
brought CDs I was sure would sound great and they didn't. These Accutons
are a diy'ers dream as you will learn new stuff about all the things going into speaker building. You won't be bored!
So, what are the limitations of
the Jenzen Accu? Considering the overall cost there shouldn't be any
shortcomings at all. Well, there are and the bottleneck is size if we
play really loud. Playing the
Stan Getz Cafe Montmartre track two, "I thought about
you", at loud level - like sitting 3rd row, the sax solos may
become compressed as we approach a sound level exceeding the capability
of the midrange driver. Hmm...I took the CD to
our living room and played the same track on the DTQWTs with their
8" middrivers and despite a slightly reduced sense of soundstage
depth, they reproduce these solos at ear-shredding levels without problems.
Size matters. I'm reluctant to put this "on paper" as it may
turn off someone who would otherwise be highly satisfied with the
The problem is that when we buy a loudspeaker - or build one -
we'd rather not hear about its shortcomings. But every speaker has its
shortcomings, let's face it. I had a mail from a guy badly wanting the
PRELUDE and considering the cost I asked him if he was aware of its
shortcomings, like how loud a 5" middriver goes? I never heard from
him again. We look at gorgeous drivers and fantasize it may be aural
nirvana and forget thinking of how much air they can move. I rush
to say that the Jenzen Accus were played at levels where most people
will leave the room.
You may argue I didn't get the crossover right - or my front gear wasn't
up to its task. Maybe so, but so far I have to conclude that the
Accutons have their strengths, actually a lot of them - and they have
their weaknesses like all other drivers. They can deliver an amazing
level of transparency, but they may fall for the "insufficient
linear volume displacement capability" like all other drivers. I
could take the point of crossover between bass and mid up to 400 Hz and
relieve the middriver from some of its duties in upper bass/lower mid,
but this takes away the magic of the midrange.
28-04-2012: What was my fear
of writing the above has already come true. People are reading
reservations like the Devil read the Bible. Again, face it, every
speaker has a maximum SPL mostly determined by the size of the
I often play John
Campbell's Down in the Hole as a start for first time DTQWT visitors. Then
we're kind of clear on bass performance and ability to play a rough
vocal presentation at loud level. From here we can go on exploring more
subtle features. So, can the Jenzen Accu do this track at loud level? It
can. I'm only adding this example to emphasize that every speaker has
its strengths and weaknesses - and to balance the statements made above.
drivers will time after time make you wonder if what you've heard before
is really what it should sound like. Not that the Accutons are right,
only a possible reference of neutrality. They will be my
reference speakers for evaluating transparency and low distortion.
I know some people
are fed up with references to this recording, but it's still an
excellent example of spatial information. I can assure the C173/C30
more than ever will make you want to reach out for the beer glass on the bar.
I recently bid on mint condition Pawnshop LPs from the Eighties and they
went up to 300 USD. I got them and they were worth the price. They clearly
tell what happens to LPs when they've been played several hundred times,
they loose micro detail and the soundstage depth is reduced.
Above my most likely
two desert island LPs. I have a reserve copy of Still Live when
current pressing gets too warn. Every
time I put these LPs on the spinner I discover something new. These
are excellent live recordings on par with the Köln concert.
Better bring that one too... I enjoyed all LPs thoroughly played on the
Jenzen Accu and maybe this is what the (Köln) Bösendorfer piano is
supposed to sound like? Usually Keith plays Steinways.
Accu has a unique ability to put your power amp on the spot. My power
amp stock is limited and I can only refer to the 300B, 6C33 PSE and
Jungson JA88D-09 (8, 45 and 80 watts respectively) and the sonic
differences are significant. OK, the 8 watt 300B amp really isn't up to
the task of driving any of the Jenzen speakers, but it strongly suggests
not driving the speakers with even the slightest harsh sounding amps. I
tried my old Rotel RB981 power amp and even without any input capacitor
this amp sounds really bad. The 6C33 PSE had better grip, but heavy bass
transients on a ~89 dB speaker is not its favourite dish and it misses
the punch of the Jungson. The Jungson
drives it very well, only has a slight emphasis on the midband at loud levels despite excellent
I wish I had a pair of really good high-powered valve power amps, maybe
the Conrad Johnson LP125M being reviewed in the Dec 2011 Stereophile
magazine. Or the BAT REX Power to stay with the 6C33 tubes.
And by the way: Hifi can easily become an exercise in beautification of
reality and the speakers are often the usual suspects if things go
wrong. The Accutons may force you to critically review your whole system
and try out different cables, coupling caps, etc. But be careful, maybe
a piece of harsh sounding music is really supposed to be harsh, only you
never heard it before before because you've chosen "smooth"
sounding caps, "smooth" sounding cables, soft-cone drivers,
etc. Go to the nearest symphony hall and listen carefully to the whole
string section when all are a doing a crescendo. It mostly doesn't sound
particularly good - regarded as sound itself. The music may be great,
but the sound of a string section is often massive and harsh. I mean,
this is what it should sound like in your living room too and not be
beatified by a whole range of precautions.
Knud Jörgensen Jazz
Trio on OPUS3 label. Another example of the magnificent
recording from this record label. Intro track Satin Doll has some
heavy piano chords I often use to test speakers' ability to not smear detail and sound congested. The ceramics are absolutely
cool on this material, no problem at all.
Above a few of the
classical vinyls enjoyed during Jenzen Accu development. I often
play Heinz Holliger to demonstrate speakers' ability to play oboe at
realistic levels without distress to the ear. The Decca Benjamin Britton
LPs of Brandenburg Concertos were picked up at a local 2nd hand market
for nothing. Mint condition vinyls and not CD as shown here. The
Sibelius 5th is a reissue and an excellent pressing. Mahler's 5th,
Chicago Symph. Orch. is a classic and probably the best recording ever
made of this symphony - and it was done in 1958! I have this recording
on both LP and CD (JVC srcd). The original vinyls are worn; never
managed to find a mint pressing. By the way: Check out this youtube
video of Leonard Bernstein directing the Vienna Philharmonics (4th
Maybe an even better vocal presentation by Edith Mathis. Magnificent!
Also listen to the 3rd movement; soothing for the soul: http://www.youtube.com/watch?v=X0uxQmnBhxk&feature=related
- quite different from the Chicago recording, which I like the most.
- blue(s) -
OK, I'll stop with
these two before
it turns into a review of all my music; the remastered Joni
Michell recording Blue. Hearing the track Case of You is
something on the Accus. I've listened to this tune many times from the
Diana Krall Live in Paris recording. Here we have the raw,
stripped to the bones, version by the artist herself. It sounds like
recorded on a two-track tape deck without any editing, added reverb,
etc. Blue really doesn't sound particularly good - because it
shouldn't. Like old Miles Davis recordings, Blue has an
authenticity, which may be hard to find these days. The Accutons can help
you getting there.
And finally the Café Blue by Patricia Barber. I recently had
this one on vinyl and I'm afraid this will be a desert island LP too.
The level of transparency and the dynamics put into the grooves here is
remarkable. An outstanding recording and the Jenzen Accu will nail you
to your listening chair.
The Accutons may
give you another view of your source material, and there's a logic to
this. If you have a highly revealing system with low distortion, lesser quality program material will be presented as such,
where more "forgiving" speakers may never truly tell you the
quality of your recordings. There are bad CDs and there are bad LPs,
either due to poor recording* or poor post-processing of master file -
and quite often both. By nature vinyl displays higher distortion than
CDs and poor LP pressings or poorly mixed recordings may stay on the shelf with
The "thing" about these Accuton drivers is that you pretty
much get what you feed them.
So, can your system - and your ears - "handle the truth?"
*: I always felt the
microphones Diana Krall uses for her vocal are really crappy, or she
sings too close - or some producer thinks he/she should spice up the
sound a bit. Mostly sibilant regardless of speakers I've tried - and
System sensitivity is around 89
dB/2.8 volts and minimum impedance is 3.7 ohms and generally an easy
load on the amplifier.
The crossover design is as close as
possible to a 2nd order Linkwitz-Riley
topology. The tweeter is off-set by 19 mm to render flat amplitude and
proper phase integration between mid and tweeter.
For bass the LCR circuit (R3031, L3031 and C3031) is optional. Due to
the low point of crossover the rise in impedance towards lower
frequences alters the behaviour of the low-pass section and by
smoothing the bass driver's impedance we get a smoother frequency
response. Leaving out the LCR circuit creates a bump in the ~80-120 Hz
range. Some may find this adding warmth to the low end response and
indeed we have some equalisation options here by altering R3031 and to
some extent adjust to room conditions. Placed close to corners the LCR
circuit may come handy. Try out 10, 15 and 22 ohms to hear what
With the Flex unit bass driver, the mid could fortunately do without any
series attenuation resistor. Every time I tried reducing mid level
with a series resistor as low as 1 ohm, it had a slightly negative impact on
For tweeter high-pass sections is derived fromC1011 and L1021. LCR circuit 1051 flattens
impedance peak and shapes roll-off. LCR 1061 removes a little too much
energy around 6-7 kHz (sibilance). Tweeter attenuation is provided by
R1031. View response graphs below from various R1031 values. My defalt
is 3R9, but try 3R3 and 4R7 to find what suits your the best.
Jenzen-D site to find all details on cabinet construction
Jenzen cabinet construction websit for bass cabinet details
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
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 anything 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.
- to come -
Extra tweeter attenuation resistors included
For price quotation
incl. shipping, please contact Jantzen Audio at: firstname.lastname@example.org
Accu Kit Presentation:
All kit and component
prices may be subject to change and are always to be confirmed by
Jantzen Audio Denmark.
I strongly suggest including the damping materials in your purchase as this
is of vital importance for making the transmission lines work properly.
Builders send me images of damping materials and based on
photos I cannot tell if these materials work properly.
Include 2 pcs 100 mm (ID) x 200 mm, item
#900029 and 2 pcs
50 mm (ID) x 145 mm, item #900023 if you go for a vented solution.
I bought my Accuton drivers
There a quite a few dealers on Accuton so take a look around.
For US citizens, Madisound seems the place to go: http://www.madisound.com/
Audio Technology drivers
available directly from the factory: http://www.audiotechnology.dk
Asia from where I live is
"Far East" and I honestly don't know where you guys
buy your speaker parts. I know Korea has diy shops like SOUNDFORUM,
but that's about it. They trade both Accuton and Audio
questions at: email@example.com
Click image to view large.
Click image to view large.