Audio Technology 10C77-25-10 KAP. Mid: Audio
Technology 15H52-06-13-SDKAM. Tweeter: ScanSpeak
The middriver comes with new
rubber surround, optimised for better air-flow
and termination of cone energy, underhung voice
coil, 6 mm windings in a 13 mm gap.
Download driver specs: 10C77
The actual 15H52 varies from the one
shown on the PD in having an underhung voice
The correct type used here is 15H52-06-13-SDKAM,
Re = 5.5 ohms.
(SDKAM: SD = symmetric drive. KA = basic kapton
voice coil former reinforced with aluminium. M =
middriver (special rubber surround))
may be an odd place to start, but why
another speaker? The world is full of speakers
and don't we have enough? From mails coming in,
the appetite for new speakers in the diy
community is endless. Curiosity and the passion
for making something better than last time is the
main driver. This must have been going on ever
since we sat around the fire carving bows and
arrows. How do I make this arrow fly faster, with
more precision, with better penetration? If
only.... then I would only have to go hunting
half day and the afternoon could be spent sitting
in the shadow of the trees playing my bone flute
- until I get bored and start thinking:
"What if..?" Anyway, this isn't about
arrows or bone flutes, rather sophisticated
loudspeaker drivers that may enable us to get a
little closer to the music, reveal more detail
and provide an overall more truthful sonic image
of what was going on behind the microphones
capturing an acoustic event.
The construction shown
here will offer you an opportunity to
reach into serious high-end, that is: If you make
rock solid cabinets, if you damp them well, if
you offer serious money on drivers and crossover
components - and if you have a good amps and
source material, the latter not least important.
All of this doesn't come cheap and we're into the
area of diminishing return from our investment.
What we should get from expensive
drivers is the ability to play louder with less
distortion compared to el-cheapo drivers and here
you get it. Some people question the value of
expensive crossover components like super caps,
etc. My response to this is that if you can't
hear the difference between a standard cap and a
super cap, your amps, your CD player or turntable
cartridge simply isn't good enough.
During construction and
crossover optimisation, the Morel
CAT-308 was the tweeter in place
and did a damned good job. However, modelling a
large number of tweeters, it was found that the
venerable ScanSpeak D2905/9900 not only allowed
better phase integration, simpler crossover,
better sound, thus the 9900 it's going to be. The
slightly concave face plate adds distance to the
dome and impulse response could be further
improved. The low Fs allowed a simple 2nd order
LR to be established with as few components as
possible. I like that! Ideally the CAT-308 would
require a single cap and two notch filters to
shape the 2nd LR roll-off although a single LCR
circuit did well for the listening test. With SS
9900 in place a perfect 2nd order LR roll-off
could be had from a RL circuit to ground. The
9900's impedance peak at 500 Hz needs flattening
from a LCR circuit. Serious listening test were
performed w/wo this notch filter and it was
impossible to hear any difference, but for the
benefit of the doubt it stayed in place. View
schematics below and read comments on crossover
The PRELUDE will offer you
a rock solid bass playing high or low, a fully
integrated midrange and treble with some of the
best treble I've had due to driver quality and
the low-order filters employed. The PRELUDE will
handle anything from classical guitar, vocals and
trio-jazz to heavy metal. Give it some of the
best 100 watts you can afford and you may even
throw a Saturday evening party.
speakers. Very classic indeed and not to everyone's
taste. From visitors I know that some find oak veneer
just beautiful and others just plain ugly!
This speaker is so heavy I left out the spikes and
settled for some felt pads on the stools, which were made
from solid elm.
Click image to view large.
aim of this cabinet construction is to
make a rock solid enclosure for the AT drivers,
so be generous with bracing. Next I wanted the
midrange at ear height, thus a small stool to
lift the speaker to an overall height of 1 meter.
The stool is 16 cm high and some spikes or
whatever adds to the final 20 cm base height.
Finally I wanted a cabinet where most diy'ers can
follow in terms of overall complexity. No curved
panels or fancy forms that only CNC machines - or
talented diy'ers - can cope with. No, this is not
a skinny runt of 18 cm width, rather a 36 cm
(14") wide baffle providing acoustic support
for the drivers and enabling simplicity of
Regarding box size and
tuning: Please read here: http://www.troelsgravesen.dk/10C77.htm
Final box shown here is
around 55 liters net volume (for bass driver
alone) depending on use of bitumen pads, amount
of bracing, volume taken by crossover, etc. I
recommend a port tuning of 30-33 Hz. Use 2 x
vents @ 68 mm diameter and 220 mm length.
Download excel file to calc. vent length here. Note
excel file is set for one port. When you use two
ports, double vent length.
Work on this
crossover has been ongoing for 4-5
months, much longer than any other speaker I've
made and eventually produced "Siri's
Killer Note". The
reason for this is not that the drivers are
particularly difficult, and going the standard
route of 2nd/3rd order filters, the crossover was
in place in a few hours. But these drivers are
not any drivers and upper mid and treble
presentation suggested more work to be done, thus
a whole range of crossovers were simulated and
tested for the mid-tweeter section going from 3rd
LR to 2nd LR to 1st order filters and eventually
a combination of LR2 and 1st order Butterworth
did what I was after. In reality true 1st order
filters for all drivers cannot be realised and
the acoustic roll-off is indeed often something
between a true 1st order Butterworth and 2nd
order LR and depends on how far above or below
point of crossover we want the slope to follow
What often happens
during crossover development is that you reach a
certain point where the sound is very good, but
measurements suggest more to be done and slowly
you improve measured performance - and decrease
sonics. Reaching crossover version 7 mkII,
everything looked great - but magic had gone. Now
bass and mid integration was pretty much in place
but what happens here will also have an impact on
upper registers and in reality I had reached a
rather perfect LR2 topology for both mid and
tweeter. The close-to-first-order mid-tweeter
filter of previous versions was gone - and so was
the magic. Hmm... Back to LspCAD and some more
late night hours' simulation and crossover
soldering. When the final middrivers were at
hand, another round of crossover fine-tuning had
too be done, but nothing serious compared to the
temporary 15H52-15-06 SD I had used for initial
LR2 between bass and mid
was run for a long time, but having the mid on
top, driver integration wasn't perfect, thus the
1st order high-pass to the mid was tried and an
LCR circuit takes care of the mid's impedance
bump at 80 Hz. The mid cabinet has a 40 mm vent
and Fb = 47 Hz, but eventually the vent was
stuffed lightly with damping material and the
impedance flattening circuit introduced. This
works. Actually the LCR circuit also works very
well with the vent not stuffed, so take your
pick. The sound is slightly different and I
strongly recommend adding the vent for
experimentation with closed, aperiodic and vented
With a second order low-pass section to the bass
driver and true 1st order high-pass to the mid,
good driver integration could be achieved with
regard to amplitude and phase. This step also
included lowering point of crossover between bass
and mid some 100 Hz, now close to 320 Hz. Not
only did it measure well, it also sounded great.
The final crossover
is asymmetric, providing LR2 slopes to bass and
tweeter and 1st order to the middriver. Thus
proper phase integration is achieved with
enhanced impulse response. In a commercial add
this would account for perfect transient
response, time-aligned, zero time and phase
distortion and bla bla bla.... But let's be
honest and agree only e.g. QUAD ESL speakers come
close to these virtues. Dynamic drivers can do a
lot of things electrostatics can't, and as always
there is room for improvements.
Looking at the step
response below, we're close to a perfect
time alignment between mid and tweeter and this
truly pays off in terms of transient response and
enhanced overall transparency. Adding an all-pass
section to the tweeter to render same polarity
for mid and tweeter was tried and didn't pay off.
Serious listening tests were performed but I'm
really not sure that same polarity pays off as
long as proper phase integration is accomplished.
It may be a give-and-take situation where the
added series components detract from any possible
benefits of same driver polarity.
The crossover seen below may
seem a bit complex to some people and here are my
comments, click here.
I've already had the
question on the differences between the
middrivers tested and I had three identical pairs
except for voice coil former material, alu,
kapton and kapton/alu. The voice coil former
material has a significant impact on performance,
particularly on upper mid and treble range and
what works the best may depend on choice of
tweeter and crossover topology. The impact on
sound is very subtle and the choice was hard. The
mids with alu formers had the best (smoothest)
frequency response but eventually the kapton/alu
was chosen based on sonics and please do not ask
how they differ, because if I put in onto paper
it would be black and white - and it isn't. The
choice of voice coil former material will depend
on the actual application, and we can't simply
conclude one material is better than the other.
Read here at Audio Technology website about voice
coil former materials: What
is the difference between Kapton and aluminum,
kit excl. drivers available from Jantzen Audio: email@example.com
Additional resistors for fine-tuning
tweeter attenuation and bass LCR circuit are included in
The layout here is rather compact to fit the
bottom panel of my cabs. My basic cabs were made for the
JBL L100 set-up and use fillets to hold rear and front
thus only 2 times 140 x 240 mm "floor" space
available. If you make the cabs like seen above, you have
some 140 x 290 mm space available. Much better!
Make your boards like this and expand the layout for both
crossovers. This is in particular welcome for the
The reason for 2 x plus and 2 x minus input to the
bass/tweeter board is that I want to run different cables
for these drivers. For the bass I use 2.5 mm^2 Supra
cable, where the mid and tweeter will have silver plated
copper in teflon. This is what I currently use for
speaker cables, although a heavier gauge compared to
internal wiring used here. For internal wiring of mid and
tweeter I use 1.3 mm^2 (16 AWG).
The finished crossover ready for installing. 270 uF PP is
HUGE! When doing the cabinet rear panel, make a hatch for
installing the crossovers as suggested on cab drawing.
Make sure you can actually get the filter into the
cabinet. Making the crossover before the cabs is actually
a good idea. I also suggest adding another 2 liters to
your cab volume
to compensate for the crossover volume. No big deal, but
some people are very picky on this I know from mails
Click images to view large. Right: Mid section.
Getting the final crossover in
place is always an exiting moment. The crossover
prototype is always a mix of bundled caps, electrolytics
in a few places, long wires, etc., and although working
perfect technically, there's usually a minor change in
overall sound - and usually for the better when the final
crossovers are in place. The PRELUDE didn't deviate from
this practice. Treble and mid appeared smoother and
tighter, but the biggest surprise came from the woofer.
This 3.9 mH C-Coil with an all time low DCR of 0.08 ohms,
just had a significant impact on bass performance being
tighter and more precise. Not the last time I'll be using
these C-Coils. Fortunately the final crossover didn't
suggest further work on balancing mid and tweeter level.
Left: SPL/1meter/2.8V merged at 300 Hz with bass
nearfield measurement. Port nearfield inserted. Right:
Impedance of final system. Minimum = 3.6 ohms at 100 Hz.
Left: The most troublesome part: Middriver low-pas
section. Right: Mid and tweeter with same polarity
display a wide and deep suck-out.
Middriver response vs. target. 1st order Butterworth is
Left: Response from drivers driven from crossover. Points
of crossover is ~380 Hz (BM) and 3.8 kHz (MT).
Right: Bass and mid with same (blue) and inverted (red)
Left: ETC plot. Right: Step response. Note mid with
Left: CSD 20 dB scaling. Right: CSD, 40 dB scaling.
Graphs above display impedance of middriver with added
bass notch filter. Left is for closed box, right for
vented box. Works for both.
Left: Horizontal dispersion at 0, 10, 20 and 30 deg.
Right: Vertical dispersion measured at 1 meter distance
with measurement evenly distributed from below tweeter
faceplate to above mid driver.
Frankly, I was afraid vertical dispersion would be worse.
Left: Impact of mid
high-pass section LCR circuit (10 mH + 270 uF +
6R8). The reason for showing this is that in a
commercial speaker this circuit would definitely
left out due to added cost, but as diy'ers, we
don't necessarily have to be that fixed on cost
although 270 uF PP doesn't exactly come cheap.
You may use an electrolytic...
Although deep in frequency, the LCR circuit does
add to proper phase integration between bass and
mid. Measurements not shown.
Right: Distortion measurement done at 1 meter
distance and ~95 dB sound level (high!). I was
pleased to see this; no spooky dips or peaks in
upper mid and treble range.
I think this is enough. Basically
measurements tell very little - if anything -
about how a speaker actually sounds.
FIRST AND FOREMOST:
DO NOT forget some serious chamfering for the middriver.
No compression allowed here! Chamfer 45 deg down to 6-8
mm from edge of rebate.
Left: Modifying existing cabs took serious
measures! Right: Inserting panel for mid cab. 30 mm MDF
Left: Gluing part of old front panel. Right: Checking out
driver rebates. A fresh router bit can handle the brittle
oak veneer and leave sharp edges
Left: New tweeter calls for experiments
before routing the final cab front panels. Would the
simulated crossover fit real life? It did.
Right: Covered dome ready for routing.
Routing for the 9900
tweeter may discomfort some people, but it's
easy. Your router bit (use an old one) will
easily cut through the aluminium face plate, but
it has to be done slowly. Lower router bit some
0.2-0.3 mm at a time and move the router slowly
over the 9900 face plate. The 9900 tweeter comes
with a fixed gasket and from my experience, some
5.3-5.4 mm depth is required to make the face
plate flush mounted. Tightening the screws a bit
further will take the face plate ~0.1 mm below
surface plane and you won't scratch the face
plate's anodisation when moving the router.
Cover the dome with a piece of gaffa tape (70 x
70 mm) and don't forget to add a piece of paper
(50 x 50 mm) where it covers the dome!! After
routing, clean the 9900 cut-out edge with fine
grade sanding paper and run a black marker over
I'm sure I'll have the question if this is really
necessary, and why can't I just mount the 9900
tweeter below the middriver? Well, vertical
dispersion is not a nice view when dealing with
low order filters and having the drivers as close
as possible helps, so... just do it!
Front panels modified for 9900 tweeters.
I use two materials: 10
mm (green) felt and MDM3 (Monacor). Check
materials here: http://www.troelsgravesen.dk/cabinet-damping.htm
1. Before adding damping material,
4 mm bitumen pads were added to all internal
panels except front panel.
2. 10 mm felt was added - again to all panels
except bottom panel (where crossover is placed)
and front panel.
3. ½ roll MDM3 is folded and placed right behind
bass driver on rear panel.
4. ½ roll MDM3 is placed on top of crossover at
5. ½ roll MDM3 is used in mid cab placed on side
panels and double layer on rear panel. Nothing
(except felt material) on top and bottom.
That's all. 3 rolls of MDM3 - and please
calculate yourself how much felt material is
suggested an interesting option (read
S.D.Batti, , book 3). The common double
impedance peak from placing the woofer in a
vented cabinet may alter the working conditions
for the woofer's low pass filter creating an
increase in response around 100 Hz, thus it may
be advantageous to flatten the second impedance
peak with a notch filter, in this case 220 uF +
22 mH + 6R8 (DCR of coil is 0.96 ohm). Based on
modelling it looks like this:
As can be seen we have some 2-3 dB difference at
100 Hz and the notch filter produces and overall
Lower: What happens to the
system impedance looks like this: Have added red
to the +LCR lines (thick = impedance, thin =
phase. Disregard > 1 kHz red.).
All in all this makes
better impedance in the 100-200
Hz area but ~2 ohms lower around 30 Hz. The huge
phase shift at 50 Hz is gone, but still remains
around 25-30 Hz. Jantzen Audio does have a 18 mH
coil, DCR = 5.7 ohm (coil # 1699), which seems
perfect for the application. Only thing is that
we may have to use a 330 uF electrolytic
capacitor. The CrossCap range does include a 330
uF value, but it is huge: 68 x 110 mm and I
hardly have room for more. And it's around 70 USD
Without having tested this addition, I render it
an interesting option for adjusting the speaker
to various room positions. A lot of people have
major trouble in placing their speakers optimally
with regard to room acoustics (WAF!) and having a
elevated response around 100 Hz may render your
Left: Measured impedance of final system with
(red/and without bass LCR circuit (22 mH + 220 uF + 8R2
"Total" means combined resistance of coil and
resistor. Resistance of coil is 0.96 ohm, thus 6R8 in
series to make 7.76 ohm.
Included in parts list is 15R and 33 R to finetune bass
level to your taste.
Right: Nearfield measurement of bass driver w/wo LCR
curcuit. All very well as predicted by simulation.
Above predicted bass response and final system impedance
from total DCR = 15, 8.2 and infinite (no LCR) of LCR
The final LCR circuit,
here temporarily set-up for test. The board will
be placed on rear panel behind bass driver.
If you want to be able to adjust resistor value
frequently, place an additional set of binding
post on rear panel and use these for holding the
sonic impact from adding the bass LCR circuit is
a more balanced and subjectively pricise bass.
Strangely enough, bass extension appear enhanced
too. Conclusion: The LCR circuit has come
Last but not least: Tweeter attenuation
This is one thing you
must do. Tune tweeter level to suit your taste,
your room and not least speaker position.
I find the PRELUDE to sound the best only
slightly toed in, that is not listening directly
on-axis. Due to the constant
directivity face plate of the 9900 tweeter
dispersion is somewhat different from
conventional domes and needs attention.
Above can be seen tweeter levels from R2021 = 2.2
ohm, 3.3 ohm and 4.7 ohm. Try it out on a range
of different music before deciding.
My final value for R2021 has changed from 3.3 ohm
to 4.7 ohm. I guess most will settle on 3R3, possibly
3R9. 4R7 may be too laid back for some people, but to ears makes
the best balance of basic notes and uppertones.
Extra 3R3 resistors have been added to parts
list. If you want additional 3R9 and 4R7, specify
BTW: Tweaking tweeter balance I used graphite
resitors for R2021 and R2051. Better sound? Maybe
BACK TO INTRO PAGE