Summary

The PeeCreek is a simple, easy to build two-way design for those wanting great sound on a tight budget.  For PeeCreeks can be built for under $200 in parts.  Those who don't wish to build their own enclosures (or simply cannot, for whatever reasons) should be pleased to know that this project is designed specifically for use with the Parts Express 0.5 cft prefabricated enclosures.

Specifications

Response: 50hz-20khz
Impedance: 8 ohms (5 ohm min)
Sensitivity: 87.0 db

Designer Notes

This design is well-suited to small to moderately sized listening rooms where a clean, tight, neutral sound is desired.  In all but the smallest rooms, i.e., dorm rooms and bedrooms, most listeners will likely choose to use a subwoofer to fill-in the bottom octave.

Measurements


Fig. 1 -- Measured T/S parameters for the Peerless 850122


Fig. 2 -- On-axis, in-box woofer frequency response.


Fig. 3 -- Tweeter On-axis, in-box response.


Fig. 4 -- System Response


Fig. 5 -- Woofer in-box impedance.


Fig. 6 -- Overall system impedance.

 



Although there's no shortage of quality, budget 2-way DIY kits available, when I saw the new line of Parts Express prefabricated enclosures, I was a bit concerned that people would pay less attention to their enclosure tuning and would "shoe-horn" designs into the available sizes.  Although most of the better-known DIY designers provide good guidance on enclosure selection and modification, I'm (perhaps) a bit more of a believer in contribution of the enclosure to the overall sound of the system.  As such, I offer you the PeeCreek -- a combination of the Peerless 850122 6 1/2" midwoofer and North Creek Music System's D25 tweeter, a design optimized for a prefabricated 0.5 cubic foot enclosure.

Background

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.

All text and images copyright Wayne Jaeschke, 2003.
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