Spending more than a
year on Jenzen speakers, handling a small 8 liter speaker is quite a
relief. Only real challenge is placing the crossover in the small rear
compartment, but more on this later. Ever since the launch of the CURV
cone material, reviewed in Voice Coil, October 2006, I'd wanted to try
out a drivers made with this cone material. I always liked the sound
of the SEAS TPX cone drivers, unfortunately discontinued. I still have
four T17RE drivers on the shelf with this cone material.
Polypropylene, PP, has excellent properties for speaker cones, in particular mineral filled
PP used by e.g. Dynaudio and AudioTechnology for decades. A fairly new
variant of PP is the CURV® material being a "woven,
self-reinforced polypropylene material with excellent internal damping"
to quote SEAS'
introduction allowing low-loss rubber surrounds. CURV is more rigid
compared to mineral filled PP, yet provides an exemplary roll-off
profile as can be seen from measurements below.
And finally we have a
95 cm2 cm cone area from a SEAS 5" unit. Size matters and going from 75
cm2 to 95 cm2 does make a difference in
mini-monitors. To my mind the U16RCY/P could well be placed in the EXCEL
range of drivers - maybe with a copper phase plug and magnet rubber
boot to fit the general appearance, although these features have
nothing to do with sound quality.
The 29TFF/W tweeter provides an unusual flat frequency response and is
an excellent partner for the CURV driver. Overall the performance of these
drivers allow high quality reproduction from modest priced drivers.
The construction here features simplest possible cabinet work,
something that should enable the first-timer to engage and build a
pair of high-quality minis for a modest investment.
I can't help thinking of
the old Vifa P13WH driver, which must have been produced in the tens
of thousands, cherished by the DIY community and professionals. The
P13WH was an easy driver allowing simple crossovers and should I point
to a possible substitute, this SEAS driver is one of the candidates.
Do not read this as a "replacement" candidate. Every new
driver will require it's own fine-tuned crossover to render proper
amplitude and phase. What this CURV driver can deliver compared to the
old P13 is enhanced resolution, more micro-detail, a modern
well-ventilated basket, higher mechanical Q and a light-weight foamed
rubber surround - just to name a few features.
Useful links (Please read before writing!):
FAQ (Please read before writing!):
You cannot change cabinet front panel dimensions and drivers' placement
without needing a new crossover - and I cannot help.
You cannot use any other drivers with the crossover shown here.
Please read these files before e-maling:
SEAS drivers H1520-08, U16RCY/P
and H1318-06, 29TFF/W.
Click links to view SEAS data files. Click images to view large.
THE TOO OFTEN SEEN CROSSOVER
Above the quick'n dirty crossover.
What is seen much too
often is the crossover depicted above. Any driver mounted on a baffle
will have an f3 = 11,600/width of baffle in cm, here 11,600/19 = 610
Hz, in short, we have a rising frequency response towards higher
frequences and this is usually dealt with by adding a large series
inductor for the midbass in order to tame too much energy around 1
kHz. Problem is that by doing so we tilt the response so much we have
a dip right in the middle of the midrange around 500 Hz, see figure
below (green hraph). Depending on the intrinsic response of the actual
driver this may be more or less severe and a few times we can get away
with the simple "v1" crossover. In this case we can't. With
the Jenzen D
as reference, it was immediately clear that there was something wrong with male vocals becoming thin and anemic. Thus,
crossover v2 was produced with a smaller coil in series with the
midbass and a very narrow working equalising circuit consisting of
R2031, L2031 and C2031. Orange and beige colour below. Now things
started working out right and the speaker had a smooth presence and
singers no longer sounded as had they gone half a meter back from the
SEAS CURV FINAL
Final SEAS CURV crossover. Please note the orientation
of components in parallel LCR or CR circuit does not matter. My layout
below may be different from what's seen here.
Rather unexpectedly a
simple 2nd order filter (4th order acoustically) could be realised with the drivers both
connected with positive polarity. Not too often this happens but it
tells we can never predict the outcome of a crossover design before
you have the drivers on the actual baffle and have done the
measurements. The 29TFF/W does indeed have an unusual flat response
making crossover work easy. Point of crossover is 2.2 kHz. As we only
have a single capacitor in the tweeter circuit, I've picked a Superior
Z-cap here not adding significantly to the overall cost. If budget is
low you may replace this by a STANDARD Z-cap. Also the 500 grams
air-cored coil for the midbass can be replaced by a cheaper cored
inductor. If money allows, I wouldn't hesitate to use Superior Z-caps in
all places, these drivers will deliver further detail if we use the
7-9 liter net volume is adequate for the U16RCY/P
driver, here modeled for 8.5 liter providing F3 = 58 Hz.
With Fb = 48 Hz we get a little extra level below 100 Hz to compensate
limited bass extension.
Cabinet volume = 9 litres minus bracing, port and
crossover, approx. 8.5 litres.
Place port on rear panel behind tweeter.
I didn't make the bracing exactly like seen on drawings but do make
the lower hole in the vertical brace some 110 mm diameter to allow
mounting of crossover.
I think this is the first time I used tape
only for assembly. Works well if everything is cut to exact
Add 10-13 mm felt to
sides, top and bottom. Fold 170 x 200 mm 30 mm acoustilux and place
behing bass driver in rear compartment.
Speaker Kit incl. drivers
Click images to view large. Damping
material not shown.
For full quotation
incl. shipping, please contact Jantzen Audio at firstname.lastname@example.org
Remember to state where you live to calculate shipping cost.
All kit and component prices may
be subject to change and are always to be confirmed by Jantzen Audio
Download kit sales presentations:
All technical question
Left: Intrinsic response of drivers on
baffle. Pay notice to the smooth roll-off of midbass driver. This
drivers just dies out towards higher frequences, most likely due to
not having a dust cap. Dust caps add to the radiating area, but much
too often also creates spurious peaks in the high-frequency domain.
Right: Response of drives driven from v2 crossover. The tweeter
produces an almost text-book LR2 roll-off towards lower frequences.
Left: Again, the response from v1 and v2
displaying the impact of the notch-filter.
Right: Point of crossover is 2.2 kHz as can be seen by reversing
tweeter polarity, blue graph.
Left: Speaker response
with R1011 = 4R7.
3R3, 3R9 and 4R7 delivered with the kit. System sensitivity is
~85 dB/2.8V/1 meter, midband range.
Right: Final system impedance.
Green = electrical phase.
Click right image to view large.
Click images to view large.
Crossover board made as compact as
possible to be inserted through bass driver hole.
Place vertical in lower compartment to allow access to terminals.
If all STANDARD Z-caps are used, the board can be made even smaller.
Getting the crossover
in place proved more difficult than first anticipated. Take these
1. Assemble the crossover before gluing the cabinet.
2. Assemble the cabinet with tape and try placing the crossover
through the hole in the bracing.
3. Round corners of crossover board as seen here.
4. Mount the crossover before the terminals and damping material.
This way you should be safe.
Click images to view large.