This was originally posted at PETT, but I thought I'd add it here as well.
I'd like to introduce my latest project. This is my most ambitious and
expensive project to date. I had obtained several high end drivers on
sale, and always wanted to build a dipole, and this is the result.
I always wanted to try and build a full dipole system, similar to what
John K has done, but the cost of a fully active system and needing 4
large woofers (pair per side) had me at a disadvantage. After some
research I decided to build a dipole system that utilized a monopole
woofer, needing only a pair of woofers (1 per side) to make the desired
SPL. I also decided to use a DSP plate amp, utilizing 1 channel for the
mid and tweeter, and 1 channel for the bass range. A basic passive
crossover is utilized between the midrange and tweeter, with response
shaping applied by the DSP.
The woofers are Peerless XXLS 830847 10" subwoofer. These were chosen as
I purchased the last few available at Solen, which were on a
significant discount when the driver model was discontinued. They offer
low distortion, relatively high sensitivity considering the xmax, and a
healthy xmax and power handling.
The midrange are Peerless HDS Exclusive 6.5" 830883. These were
purchased from the swap meet forum at DIYAudio several years back. I had
used them in a centre channel for a few years, which was later
dismantled. They are a excellent driver and found a very nice home in
The tweeter is the Dayton AMTPRO-4. These were purchased from a forum
member via the classifieds here. They are the model with a removable
face plate, different that the faceplates currently sold. I originally
had the thought to remove the face plate and mount the tweeter directly
to the baffle, but eventually decided against it. These came with an
ugly "veil" over the tweeter which was removed. These are a truly high
end product, and are a fully dipole capable tweeter, the rear wave can
be easily damped as well by adding felt (included with the tweeter).
The baffle is a 1.5" thick bamboo counter top from Lowes. Originally I
was going to use baltic birch plywood, but I liked the look of these
boards more and the price was right so here we are. The baffle shape is
optimized for dipole operation, and the shape was cut by CNC. I was
fairly disappointed with these boards after cutting them, as there were
significant gaps inside that needed to be filled. The gaps were filled
with sawdust, then epoxied over top and sanded down. The round-overs
were completed by hand.
Finish is Circa 1850 Tung oil. As far as I know this is straight tung
oil with only thinner added (no varnish). I really liked using it for
another project, and I am not disappointed here either. 4 Coats were
applied, with a rub down using super fine steel wool in between coats.
What is left is the natural wood lustre with a nice sheen. Some
scratches and dings are visible up close, but I am real happy with how
these turned out.
If I was doing this again, I would add a small brace in the middle of
the port, as the bottom of the baffle does have some flex to it.
The baffle is 14" wide by 42" tall, which puts the tweeter at face
height when sitting down. The baffle will not be glued to the cabinet,
it is held on by steel angle brackets (standard hardware store
materials) and a foam gasket prevents air leaks. The brackets are
screwed in from the inside of the cabinet, it is awkward but they are
all accessible through the woofer hole to remove the baffle if needed,
or reaching my arm through the back by removing the plate amp.
The cabinet is simple 3/4" MDF with 1/2" round-overs. The finish here is
White Duratex, applied with a foam finishing roller. This created a
very fine texture, much finer than when using the standard Duratex
rollers. It was tougher than the normal application to get the roller
marks to not show, but I settled after 4 coats. It looks great next to
the natural Bamboo colour.
The cabinet if I recall is 60 Litres, tuned to 30Hz.
The crossover is a hybrid design, utilizing both DSP and a passive
crossover. I got this idea after looking at another project doing just
the same, using a Seas Subwoofer and a Seas Excel coax (Seas KingRO4Y
A simple passive crossover is used between the midrange and tweeter,
that provides the necessary transfer function to cross over as well as
attenuation of the tweeter. The passive crossover does not apply any
other response shaping such as BSC or dealing with the rising response
of the tweeter. This was tamed using the DSP as well as any other
response shaping to suit the room and listener. The passive crossover is
electrically a 2nd order on the midrange, a 3rd order on the tweeter,
and a single 3 Ohm resistor in series with the tweeter provides
attenuation. Crossover frequency is 1500Hz.
The DSP crossover is used between the midrange and woofer drivers. This
arrangement makes the best use of the available amplifier power, and the
crossover here is 300Hz. The availability of the DSP allows any further
system tweaking to by applied on the fly.
The DSP amp is a Hypex AS2.100D purchased from another forum member in the classifieds here.
So far I am absolutely amazed with the sound. The clariy through the
entire midrange up to the trebel is astounding, and I felt the impact of
the bass was very nice, it should need only small adjustments with the
EQ. There is something special about the dipole arrangement I think, the
stereo separation and spaciousness is like no other speaker I've built.
Photo album is available on Google Photos below. There is a description
available in most photos, just press the little "i" button.