Introduction
Here is the design for what I call the Vx2T. Vx2T simply stands for "Vifa times two Tower".
As the name implies, its a 2-way slim tower design. The short story is that this is basically
John K's P17/D25 Design in a different box.
Why a different box? I wanted to build a system capable of producing a decent amount of bass
without the use of a sub-woofer. Additionally, I wanted a small footprint cabinet that didn't require
stands - as my kids or cat would surely knock them over.
These speakers would serve as the front L & R in a Home Theatre system in the future, so the fact that
the drivers were available shielded for the center channel, and the fact that they are very reasonably
priced, made a lot of sense to me.
The Design
The drivers are the Vifa P17WJ-00-08 mid-bass, and the Vifa D25AG-35-06 tweeter.
These drivers have earned a good reputation, and there are many designs out there built around these
drivers.
Click on the driver for specs.
I once read a review of the
PMC FB1 speakers. The styling of this speaker quickly caught my eye as it met my requirements
for a small footprint, no stand design. They are large but do not require any more floor space than a
typical stand mounted bookshelf speaker would. This design appears to be very popular these days, I
liked the FB1 cabinet so much that I designed a ported box for my project of roughly the same
demensions.
I soon came across a problem as the internal volume was
larger than recommended for the P17. Hummm... I split the cabinet (internally of course), into two
seperate compartments. The top serves as the enclosure for the driver, and the bottom halve is
just stuffed with carpet underpad and acts like a stand. I was planning to put sand in the bottom
compartment, but after constructing them, I found the were heavy and steady enough that I just put
carpet underpad to kill any resonances.
I wanted as much bass extension as I could possibley get, so I made the internal volume of the top
enclosure 28 Litres, the largest size recommended for the P17.
I lined one side wall with 1.5" eggcrate foam. The top and bottom of the enclosure is lined with
carpet underpad.
Click on the plans for a larger printable image.
I don't have the required tools for measuring speaker response, nor do I have any speaker design software.
As such, I wasn't about try and design my own crossover. Nor was I willing to waste my time trying text book formulas.
I did some looking around and found a few crossovers for this driver popular combo on the net.
I first tried the series xo, as there was lots of series xo talk going on at the time, and besides - it only
required a small investment. While very easy to implement, I wasn't comfortable listening to what I consisdered
a very forward sound. The mids were very much out there, a far departure from what I was used to with the Energy 22s.
The sound was very open, but I'm not sure that it wasn't a direct result of the fact this xo didn't account for
baffle step compensation.
Next, I decided to try John K's crossover (pictured at right) which was designed for these drivers but in a
different enclosure. I knew using a different encloser would yield different results, but I placed my bet that
those differences would be small. I played around with this xo for months to see if I could make the system
sound any better, but in the end only changed R9 from 2 ohms to 6 ohms. This adds just a bit more on top.
Note that R1 and R3 represent the resistance of the coils L0 and L2 respectively, R6 represents resistance
of the coil and an additional resistor.
Port tuning was interesting. I started out with a port tuned to 42Hz (green line - 3.25" port length) which
according to winISD produces and F3 of 40Hz. I found the extension to be good, but the amount of bass output
was just not enough for my liking.
I then changed the tuning a few times untill I ended up with a 1.75" long port which yielded a tunning of 50Hz.
This tuning (blue line) apparently produces a 2db bump at 60Hz, but I found this much more suitable for my taste.
I would highly suggest you start with a port length of 3.25" (tuned to 42hz) and shorten from there.
Don't make the port shorter than 1.75". Click the winISD graph to enlarge it.
The Costs
The cost of this system is only about $200 usd per pair without cabinets.
The Vifa P17WJ-00-08 mid-bass is about $40
The Vifa D25AG-35-06 tweeter is about $30
The xo, port and terminals for one speaker are about $30
There you have it, $100 per speaker plus wood. I was able to build two Vx2T and a Vx2C from one sheet of MDF
which costs about $20usd. The veneer was about twice the cost of the mdf, but this still keeps the cost about
$125usd for each speaker complete.
The Product
It took me a long time to finish this project as I worked on it an hour here, an hour there, type thing.
I'm not a woodworker by any stretch of the imagination and was very surprised at my ability to create such
a professional looking cabinet. I guess the phase "take the time, do it right" hit home here. Below are some
pictures of the finished Vx2T... tada!
The Reveiw
In a word, excellent! I know that means different things to different people, so I'll
try to explain.
The bass response is good for a 6.5" woofer. While not with the level of
authority that can be expected from a larger woofer, the bass extension is adequate enough
that you don't need a sub-woofer. There is a bit of tubbyness and lack of definition in the
lower bass region - probably caused from the large internal volume of the cabinet and my
port tuning. I do plan to play around with the treatment of the enclosure to see if I can
tighten the bass response up a bit. I'll update this page if I succeed.
The midrange is very smooth. I'm actually very impressed in this regard and would
say that this is the strongest point of this system. Detail is very good, and I have
heard nothing offensive from this driver.
The treble is about as good as can be expected from a metal dome in this price range, and
probably better. I like the level of detail provided, and don't really notice that metalic
sound that seems to plaque so many metal domes. This tweeter has been used in some pretty
expensive systems. You can get better, but it fit the bill for this project perfectly.
As for the crossover, the integration of the two drivers is excellent.
They really sound tightly knitted, you don't have to be a certain distance
away from the speaker before the sound comes together, which makes these
speakers excellent for close monitoring in small rooms.
So, how does the Vx2T compare to the Energy 22? The Vx2T has a thinner sound than the
Energy 22. The Energy has better bass response and this probably accounts for its warmer,
fuller sound. The Vx2T does have a much clearer mid-band that never sounds muddy, which is
the only complaint I've ever had about the Energy. The top end of the Energy 22's is a bit
softer than the Vifa, but this is to be expected from a tweeter costing twice as much.
I have a really difficult time remembering that the Vx2T is a $250 system, listening to it
for a few moments soon makes me forget. Keeping that in mind however, I shouldn't be so damn picky as
this system really does shine.
Wrap-up
Feel free to e-mail me any questions you may have about this design. I don't check this e-mail account that
frequently so it may be easier to reach me at the MAD board. If you decide to build this design, I hope you
will send me a review and some pictures so I can post it here to others to see.
E-mail me!
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