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DRIVERS
CROSSOVER
CABINET
WORKSHOP PICS
MEASUREMENTS
SPEAKER-KIT
CROSSOVER LAYOUT
Since introduction in 2021 the GRT-145W-8 has been replaced by
GRT-145W-4, the 4 Ohm version. This facilitated a simplified crossover,
thus some of the images may not be correct.
Due to unavailability of the Viawave ribbon
tweeters, Jantzen Audio can no longer supply the
complete kit.
The kit is there for officially discontinued.
However,
if you can source the Viawave tweeters elsewhere,
Jantzen Audio can offer both the 4-ohm and 8-ohm tweeter versions
of the DIY kit, with or without the Purifi mid-woofers included.
It's been quite some time since I tested the Purifi PTT6.5-W04-01B driver,
now PTT6.5X04-NFA-01.
Read
here.
So, time to set up a 2-way stand-mount and hear what this quite special driver can do.
In-depth here: https://purifi-audio.com/blog/
- and here:
https://purifi-audio.com/wp-content/uploads/2019/12/PURIFI-AES-9607.pdf
Another driver that has been on the shelf for too long is the Viawave
GRT-145W-8 ribbon tweeter. Tested
here.
All the time I had these two drivers in mind for a small stand-mount and
I started making a mockup in some test cabinets to make final
measurements for simulation and determination of
dZ. Even with the ribbon's waveguide and retracted
ribbon, the Purifi driver turned out to be acoustically some ~15 mm behind the ribbon
on a flat baffle at point of crossover as dZ is frequency dependent. Not a lot, but something to consider when
we start
simulation.
Based on these new measurements, I made two basic simulations for
testing, one LR4 crossover and one LR2 crossover. From the LR4 crossover
the difference in acoustic depth was easily overcome and produced at
flat response measuring somewhere between the ribbon and the midwoofer.
For the 2nd order filter the optimum listening height was closer to the
midwoofer axis and could handled by tilting the speaker a little, some
3-4 deg. Rather than making a stepped baffle I chose the tilt, but
eventually not a big deal. One thing is what we measure with the
microphone at a given point, another what we actually hear.
Initially I made the 4th and 2nd order crossover for comparison.
I finally decided on the 2nd order, maybe because I have used it
extensively, but also because the 4th order, although very straight
forward, had the familiar upper-mid projection, not too strong, but
noticeable. In the end a matter of taste, but I favour shallow sloped
crossover as I find more tonal fidelity here. 1st order is no-go here as
we have to protect the tweeter and the Purifi, although well behaved,
doesn't have the most smooth roll-off around.
Playing this rare Musica Nude vinyl recording, which I played hundreds of times, immediately made it clear this mid-woofer is special.
Resolution was the first superlative that came to mind. I also know that
whenever we introduce a new driver, we'll always hear something we
didn't hear before. But having a ruler flat mid- to lower-treble
response made it clear it wasn't just a peak or whatever that might have
brought some details to life, rather a genuine ability not to smear the
signal it is fed.
Clarity and resolution all indicates low
distortion. Accuton C173 also came to mind, but without its distinctive
character to the sound. Now, the Purifi doesn't work alone, the clarity
of the Viawave ribbon defines the timbre of any basic note. Without
overtones we don't have the tonal characteristics of any instrument. So,
what counts the most? We can't tell, but only conclude these two drivers make a great
couple crossing over around 2.2 kHz thanks the wave-guided ribbon.
Links:
Test Purifi PTT6.5X04-NFA-01:
http://www.troelsgravesen.dk/Purifi.htm
Test Viawave GRT-145W-8:
http://www.troelsgravesen.dk/GRT-145W-8.htm
Purifi website:
https://purifi-audio.com/
Basics:
2-driver speaker.
Dimensions: 24 x 24 x 45 cm, WxDxH.
System sensitivity: ~87 dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
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
http://www.troelsgravesen.dk/choices.htm
http://www.troelsgravesen.dk/power-handling.htm
DRIVERS
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Purifi PTT6.5X04-NFA-01 midbass driver. (The name was changed from
PTT6.5-W04-01B to PTT6.5X04-NFA-01)
Read test here:
http://www.troelsgravesen.dk/Purifi.htm
Viawave GRT-145W-4
Read test here of 8 Ohms version:
http://www.troelsgravesen.dk/GRT-145W-8.htm
Download specs here:
PTT6.5X04-NFA-01
GRT-145W-4
CROSSOVER
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The crossover features a standard LR2, 2nd order, crossover around 2.2
kHz.
This ribbon has a
phenomenal sensitivity, up to around 102-104 dB compared to the Purifi
having some 88 dB intrinsic sensitivity, hence a few resistors to bring
it down to that level, R1/R4/R5.
The PTT6.5 low-pass section is pretty straight forward and R7/C3 helps
shaping the low-pass roll-off.
CABINET
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Cabinets were made from 20 mm Baltic birch. Use 19-22 mm depending on
local availability and adjust dimensions to keep specified volume (16.4
litres). Stick to front panel dimensions and drivers' placement!!
The port is Ø68 x 160 mm and lined with felt material. See images below.
This lowers the Fb (port tuning) from 50 Hz to 42 Hz and we have F3 = 37
Hz, quite impressive.
I wouldn't hesitate to recommend the Purifi 6R for studio monitoring if placed
horizontally.
Turn the ribbons 90o and listen on mid-woofer
axis.
Workshop pics
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Every speaker construction must start with a mockup to measure what the
drivers do on the intended baffle and I had some ~15 liter test boxes
and made a preliminary front panel, heavily chamfered to make 22 cm
effective baffle width. Fortunately the frequency response of both
ribbon and mid-woofer were so good, this turned out to be ideal for my
final cabinets.
Fine-tuning of crossover in workshop set-up.
The final cabinets:
Left: All pieces for one cabinet. Right: Test assembly with tape. Note
slots for the brace.
Rear panel made 5 pieces to minimise loss. Front panels have oak
fillets.
Making the bracing.
And BTW: NO! You do not see a laminate of side panels. Just the rebate
for the rear panel. Sorry, have this question all the time :-)
http://www.troelsgravesen.dk/tips.htm#MAKING_REBATES
Left: Rear panel in place.
Routing for the drivers and port. The Purifi driver is NOT
flush-mounted. Route a 145 mm hole.
Chamfer the front panels to make 22 cm effective width.
To make the port fit without using glue, the hole must be 96.5 mm
diameter :-)
Make sure to
chamfer for the midbass to allow free ventilation.
Finally! Gluing cabs.
Left:
I decided to add 4 mm bitumen pads and increased depth to 25 cm to
compensate for loss of volume.
If you want to do this, add 2 pcs 50 x 50 cm 4 mm bituman pads to
your order.
Glue to panels with floor tile adhesive:
http://www.troelsgravesen.dk/tips.htm#Glue_for_Bitumen_Pads
Right: Adding felt damping. Cut two sheets 20 x 54 cm to cover sides and
top. No felt on rear panel. Here we place the crossovers and cover
with acoustilux.
Left: Gluing the front panel.
Right: First coat of lacquer.
Cut two pcs like seen on drawing for the port. Slide it nicely into the
port and fasten with dots of Superfix - or similar. See image below.
Port seen from rear. Secure felt in port with a strip of Superfix.
Port seen from front.
People have complained about the look of the felt in the port tube. If
this troubles your sense of aesthetics, use 10 mm polyester foam.
Unfortunately I couldn't get it in black...
MEASUREMENTS
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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.
Response of drivers on actual baffle with no crossover. PTT6.5X04-NFA-01 driver
merged with near-field response at 250 Hz.
As can be seen, the ribbon requires quite some attenuation.
Impedance of PTT6.5X04-NFA-01 driver in free air (red), in cabinet with
un-lined port (green) and felt lined port (orange).
With the felt lined port we have a port tuning of ~40 Hz.
SPL of Viawave ribbon w/wo crossover. As can
be seen, a lot of attenuation is needed.
SPL of Purifi driver w/wo crossover, merged at 200 Hz with nearfield
response.
Final system impedance. Minimum 3.8 Ohm @ 187 Hz.
Vertical dispersion. Quite good. Optimum flat response at a listening
height somewhere between the two drivers.
Horizontal dispersion at 0, 10, 20, 30 and 40 deg. off-axis.
SPEAKER-KIT
BACK TO INDEX
All kit and component prices may be subject to
change and are always to be confirmed by Jantzen Audio Denmark.
Download Complete Kit Sale Presentations:
All technical questions to
troels.gravesen@hotmail.com
All questions regarding purchase of
kits, please mail Jantzen Audio at
contact@jantzen-audio.com
CROSSOVER-LAYOUT
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Layout for tweeter. Place tweeter crossover
on rear panel in upper part of cabinet.
Connect input to either R1a or R1b depending on preferred tweeter level.
Check this out:
http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS
Layout for bass. Place board on rear panel
above speaker binding posts.
SPEAKER WIRING
Tweeter crossover. Pay notice the tweeter
layout has been changed to GRT-145W-4.
Bass crossover.
Details about R7 and C3.
Right: Soldering input wires to the crossover board.
Left: Mount the bass crossover on rear panel
up against the brace.
Right: Mount the tweeter crossover in upper section with coils upwards.
Connecting the drivers. The ribbon inverted
polarity is done on the crossover board. See wiring.
Take one piece 50 x 50 cm acoustilux and cut in 20 and 30 cm width.
Fold the 30 cm cut, fold and place above tweeter crossover and up
against top panel.
Fold the 20 cm cut, fold and place above bass crossover.
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