The design process for the PeeCreek is a bit unlike
that of other designs. Normally, I choose a particular type of
speaker system with particular properties and then begin driver
selection and enclosure design. I then choose drivers and an
ultimate enclosure size that I think best mets the criteria for the
system I wish to build. Here, however, the enclosure dimensions
were part of the initial design-goal and, thus, the task became locating
a woofer that would provide optimal low-end response in the chosen
enclosure.
I first decided to make this a "budget" design, i.e.,
to keep the cost of parts and drivers around $150. That determined
which "class" of midbass woofers I would consider for the design.
After testing many, common midbass drivers and evaluating their
performance in a box having internal dimensions corresponding to the PE
0.5 cft enclosure, I narrowed the choices down to the venerable Vifa P17
and Peerless 850122. Since I have not worked with the Peerless
driver before, and it is been highly-regarded by others, I decided to
use it. Also, it seems to produce deeper, tighter bass than the
P17 (which some might argue is more of a midrange driver than a midbass
driver). The tweeter selection was actually quite easy.
Using a $40 woofer was eating up a good chunk of my budget, so I had to
think cheap. I had been sent a pair of the NCMS D25's for
evaluation and found them to be quite competent, even if they didn't
blow me away, but at $36 for a matched pair, how could I go wrong?
Since my initial evaluation of the woofer indicated a crossover point in
the 2khz region with 4th-order acoustic slopes (to suppress the woofer's
natural response peak at 4500hz), I felt confident that the D25 would be
working well-within its intended range in this design. Thus, the
Peerless- NorthCreek combo was born... the PeeCreek.
The
Enclosure
Parts Express #302-722 in
Cherry
Obviously, the easiest enclosure option, here, is to
purchase a pair of prefabricated enclosures. Quite frankly,
the new enclosures from Parts Express are among the most
well-constructed and finished "off-the-shelf" enclosures I've seen.
At about $75/each, this will cost you $150 plus shipping (which might
not be insubstantial, given their weight). Being the cheap guy
that I am, I chose to build exact replicas of the PE enclosures.
Instructions for those of you who wish to build your own enclosures, as
well, are shown below.
DIY-Version of finished PeeCreek Enclosure
The first step in building these enclosures is, of
course, to cut each piece to the desired size. All construction is
from 3/4" MDF, except the front baffle which is 1" mdf. You can
make your own 1" baffle by sandwiching together pieces of 1/2" MDF
(which is more easily available at major home-improvement stores and
lumber yards).
Cut Guide:
All pieces cut and ready for assembly
Top/Bottom: 10.75" x 7" x 3/4"
Left/Right: 14" x 12.5" x 3/4"
Front Baffle: 14" x 7" x 1"
Rear Baffle: 14" x 7" x 3/4"
Port: 2" I.D. (pvc) x 5" (total length)
Driver Cutouts:
Woofer -- 6 1/8" diameter +
1/2" radius x 1/8" deep rabbet
Tweeter: 3 3/8" diameter +
3/8" radius x 1/8" deep rabbet
Front baffle with hole and rabbeted recesses
(note that the rabbet radius will exceed the width of the piece)
Construction Schematics:
(click to enlarge)
You will notice from the schematics that the drivers
are centered on the front baffle with a center to center spacing of 6".
This would permit a maximum crossover frequency of about 2.25 khz.
I chose a frequency of 2khz for reasons explained below. Also,
while I have not provided a detailed drawing of the rear baffle, the
port should be mount 4" down from the top of the enclosure, centered on
the rear baffle. This places the port approximately directly
behind the tweeter. Shown below is the rear of the PeeCreek
Prototype. I used a 2" I.D. PVC port with a total 5" length, to
provide a tuning frequency (once the box is properly lined with 1
1/2" peak-to-peak acoustic eggcrate foam on the top and sides, leaving
the bottom open for crossover placement) of just under 50hz. Also,
you will want to place a wad of teased acoustic stuffing material (such
as AcoustaStuf) over the crossover, directly behind the woofer.
Just be cautious not to impede the airflow between the woofer and the
port.
This picture also shows the
"ultimate buyout" terminal cups I bought from PE for $0.63 each
(when you buy 10 or more). These are nice looking, gold plated
terminal cups for an amazingly cheap price. I removed the included
wires and replaced them with my own wires (16 awg Sound King). If
you are unable to obtain these terminals, figure about $3/each for
standard terminal cups.
Finishing these enclosures was interesting. I
had wanted to try the vinyl laminates being sold by Parts Express, so I
decided to finish the front, back, and bottom in the textured black
laminate, with the sides being done in the cherry. I'm quite
impressed with the look of the laminate, although I must caution that
it's not the most durable finish. If your speakers will see much
travel or handling, a painted or veneered finish might be more suitable.
For general use, however, these laminates will perform extremely well at
a very low price. I used about 1/4" a roll of each laminate to
finish both speakers, so if I pro-rate the cost of the whole rolls I
purchased, that comes to about $6 in vinyl. That's cheaper than
even my "old stand-by", which is Duplicolor Truck Bed Liner (which is
great when you want a very, very durable finish that looks ok).
One suggestion I have regarding the application of the vinyl is to use a
veneer trimming knife,
such as this one. It allows you to make very precise, sharp
edges that look quite professional.
Overall, I figured the cost of the enclosures
(finished) to be approximately $35, with all hardware included.
Your overall cost will depend on the type of finish you choose.
Designing the
Crossover
The PeeCreek crossover mounted on a 5" x 9"
board (so it fits through the woofer hole). Notice that it is all
point-to-point wired and uses electrolytic capacitors in the lowpass.
The crossover for the PeeCreek is relatively simple,
using only 9 elements. Do not be alarmed at the use of a series
notch filter, as this was employed to avoid a common problem in 2-way
DIY designs -- the dreaded "midbass dip". This dip tends to occur
at the frequencies where the baffle-step rise begins to occur (i.e., the
frequencies where the speaker's radiation is transitioning from
half-space to full space -- if you don't fully understand this concept,
don't worry, you don't need to understand the theories behind baffle
spreading loss to build this speaker!). The end result of the
PeeCreek crossover is to provide very flat response in the 200hz to 1khz
region, to provide a well-constructed soundstage and proper imaging.
Overall, these speakers image extremely well and produce a wide, deep
soundstage that is indicative of a well-designed 2-way speaker.
The crossover employs filters that result in 4th
order (acoustic) Linkwitz-Riley rolloffs for both the woofer and the
tweeter. These slopes were chosen to avoid over-excursion of the
tweeter at high power and to suppress the woofer's natural response peak
at 4500hz. Further the crossover frequency of 2000hz was chosen to
ensure that the 4500hz peak was attenuated at least 18db, thus avoid any
negative interaction of the woofer with the system response above the
crossover frequency. Many folks are touting the sonic advantages
of 2nd order slopes, in recent designs. They are absolutely
correct in that such slopes tend to produce a fuller, richer sound
without coloration or distortion.... but that's only true when the
drivers permit such slopes to be used. This was not the case with
these relatively inexpensive drivers. Moreover, attaining 2nd
order slopes for these drivers requires a much more complicated
crossover network than the final topology chosen for this project, as
much greater equalization is required to maintain the rolloff rates
without obtrusive peaking in the response.
The final crossover network schematics is shown
below:
Please note the reverse polarity of the tweeter.
Also, all caps are polypropylene, although electrolytics can be used in
the lowpass without any noticeable degredation in sound quality.
The purists among you will still use poly caps in the lowpass, which is
fine.
Listening Tests
and Final Thoughts
These little 2-way speakers produce excellent, clean
sound and are a very good value for the money. Although a sub is
truly needed to fill in the bottom octave, most users in small listening
rooms will find their sound full, uncolored, and smooth throughout the
spectrum, even without a sub.
Invariably, people will ask me to compare this system
with other budget-priced systems. I'm not going down that road and
will allow those who build and listen to such systems in side-by-side
comparisons to determine where the best bang-for-the-buck lies. As
well, people like different "flavors", so I doubt a "best" will emerge
-- just more great options for the DIY'ers out there.
Finally, I am not providing a detailed parts list for
this project. The tweeter is available from
North Creek
Music Systems for approximately $36 for a matched pair (that's a
great deal!). The remaining parts are available from a wide
variety of distributors, such as
Meniscus Audio,
Parts Express,
Madisound, and
others. Who you choose to give your business to is up to you and
may depend on whether you choose to build your own enclosures or buy
prefabricated ones. I strongly recommend, however, purchasing your
woofers from a company that will provide you with matched pairs, such as
Meniscus (for a small fee). Unlike commercial speaker
manufacturers, we don't have the benefit of buying large lots of drivers
and rejecting those that don't meet "spec". Buying matched, tested
drivers from a reputable company that will take the time to service the
needs of the average DIYer, therefore, becomes a paramount consideration
for us, when we want to get the best possible results.
Acknowledgements
Anyone who builds
this project and enjoys the result should send a special thanks to
Jason Panek, who sent me the North Creek drivers that were used in
this project. Without Jason's generosity, I may never have
considered evaluating yet another tweeter in this price-class.
I'm sure glad I did. It was Jason's hope that these drivers
could be used for the benefit of the budget-minded DIYer, so I hope his confidence in my design
abilities was well-placed. Thanks Jay! P.S. Sorry
about the project name :-) But it gives me a good chuckle.
This design may be freely used for
non-commercial purposes. Any other use is prohibited, as is
any unauthorized reproduction, retransmission, or other public or
private distribution of the images, text, or accounts herein
provided.
