Eventually, we all want to take the jump into a "high-end" speaker. When you go to a retail store or search around the web, it becomes apparent that to take this jump, you either have to spend alot of money or you have to set your sights a little lower. Those of you who have been willing to put a little time and energy into building your own speakers know that for a mere fraction of the retail (or even deeply discounted) cost of commercial speakers, you can build a set of truly audiophile quality speakers yourself.

There are numerous excellent sounding speakers sold in "kit" form by various vendors. These kits will provide you a level of performance worthy of the term "audiophile". Many of these kits, however, are still beyond the reach of the average DIYer. Moreover, some of these high-end kits can cost over $1500 and still not have wrung every last bit of performance out of the drivers and crossover network -- to me, good engineering is worth alot more than expensive drivers, so a less expensive speaker that's better designed will sound better than a more expensive speaker that doesn't live up to its full potential. So, just as you all know that I firmly believe that speakers don't need to cost alot to sound great, I believed that I could make a top-quality speaker that compared well with anything else out there without breaking the bank. And this began the VSS Eros Project.

I. The Drivers

As with every speaker design, the first step is selecting the best drivers for the job. In this case, I selected the Vifa PL18 woofer because I had heard it produced the exceptional, highly regarded midrange clarity of the Vifa P17WJ but with the deep, highly resolved bass of the Scan Speak 8545k (without the high price tag of the Scan Speak woofer). From my experience with the Dayton III design, it became apparent to me that two woofers were going to be better than one for a more efficient and highly dynamic speaker.

For the tweeter, I thought about a wide range of units. My belief is that the more you have to attenuate the tweeter to match the level of the woofers, the more you will compress the sound coming out of the tweeter and the less dynamic it will sound. This lead me to look at tweeters with a sensitivity in the range of 89-91db. Second, I wanted a tweeter with excellent, open sound capable of very detailed reproduction but one that used ferrofluid in the air gap for a low resonant frequency and good power handling to accomodate a low crossover frequency without the need for an elaborate, expensive conjugate filter to reduce to the impedance peak at resonance. This narrowed the selection down to units from Scan Speak, Seas, and Morel. From among these manufacturers, I chose the Scan Speak 2905/9500 because it has a reputation from being one of the best sounding drivers that met these criteria. Also, I felt that this driver would have the best sound with a crossover frequency under 2khz that I wanted to target to maximize the off-axis performance of the woofers. Finally, my impression of Scan Speak drivers is that they have a lively, articulate quality without even a hint of harshness.

II. The Enclosure

My preference for this project was a floorstanding enclosure. With that being the only caveat, I then measured the thiele-small parameters for the woofers after a thorough break-in period. The PL18's tested almost identically (a good sign).

I then measured the frequency response of the woofers, splicing the ground-plane measurement together with the farfield response at about 200hz.

I then designed the enclosures. I selected an SBB4 alignment tuned to approximately 38 hz to give the best combination of low-end response coupled with a shallow (18db/octave) rolloff. This produces the best transient response in a ported design and lowest group delay for the cleanest, best resolved bass possible without using a sealed or transmission line enclosure.

The resulting enclosure has a net internal volume of 1.64 ft^3 and a vent port that is 3" (id) by 3 3/8". While this value is not exactly as predicted by the standard equations, the port was tuned through trial and error. After building the enclosures, I tested the impedance response and trimmed the vent tube until the exact resonant frequency was achieved. The bass response of the final enclosure is simply exceptional -- very deep and clear with wonder tonality. A very important factor for achieving this level of performance was the construction of an extremely solid enclosure. The front baffle is 1 1/2" thick mdf (made by gluing together two pieces of 3/4" mdf and clamping them overnight prior to cutting the piece to the appropriate size.) All of the internal surfaces were covered with 1/2" birch plywood for added ridgidity. The front baffle is 9.5" wide with an outer edge rounded with a 1 1/2" roundover router bit and the inner edge rounded with a 3/4" bit. This was done in combination with offsetting the woofers drivers 5/8" to the inside of the baffle's vertical centerline to improve imaging. The tweeter is offset 1 1/8" from the centerline toward the inner edge of the front baffle. The center to center distance between each woofer and the tweeter is 6.75" for reasons that will be more fully explained in the crossover design section. Don't be surprised that this number is somewhat larger than the center to center distance recommended by other designers, as my experience has found that this approach provides a taller, deeper soundstage with less compression in front of the speaker at the expensive of a slight amount of imaging that can be regained with a good quality amplifier and proper speaker placement in the listening room.

I will not be providing a detailed mechanical construction guide to this enclosure. I strongly encourage those of you wishing to build this speaker to carefully design your own enclosure to meet your aesthetic requirements. I will, of course, answer questions and will give suggested dimensions if requested.

The photos below illustrated the enclosures in various states of construction. If you have questions regarding the construction of the enclosures, feel free to email me.  If you wish to build the Eros speakers, please download these high-resolution mechanical drawings of the enclosures. (2.0 mb)

III. The Crossover

The heart and soul of any multi-way speaker is in the crossover design. To develop the crossover, I used the Clio measurement system to obtain the frequency response and impedance of the drivers while mounted in the actual enclosures. I then imported the measurements in Calsod Pro 3.10g to model and simulate the crossover. Many different crossover topologies were tried, including some that produced exceptionally flat measured response, as that seen below.

Flat didn't necessarily translate into the level of performance I was looking for and also resulted, in some instances, in complicated crossover networks with many components. I believe strongly that the number of components in the signal path must be kept to a minimum to allow the drivers to reach their maximum dynamic potential and to sound as open and natural as possible. This eventually lead me to the following crossover network in which only a signal component is in the signal path to each driver. In fact, even the attenuating resistor for the tweeter was moved in parallel to the driver (thanks for computer optimization) and final tweaking was done by ear to provide a pristinely accurate, yet very open and natural sound. The final result is what I think is an outstanding speaker with high efficiency and very lifelike dynamics and sound quality. I'm currently using these speakers with my monoblock 300B amplifiers that produce 8 watts/channel and they are capable of incredible output.


ignore the box around the .22mH inductor, that's just an artifact of the design program

Please note that the woofers are connected in parallel and all drivers are connected with normal polarity. The crossover frequency of the final version is around 1750hz and the woofers are rolled off with a 2nd order acoustic slope. The tweeters also use a 4th order acoustic slope. The relatively low crossover frequency permits a wide center to center driver spacing to improve the quality of the soundstage without succumbing to the traditional compression of the soundstage that many MTM designs are plagued with. The mixed-order slopes provide better phase tracking of the drivers to compensate for the offset of their acoustic centers. As a result of the excellent phase tracking, the drivers sound exceptionally well integrated, as is evidenced by a 38db reverse phase null (not shown).


Frequency response of finished speaker

While there may be some concern that the top octave is rolled off a bit too much, the truth is that my testing mic's preamp has been causing a bit of premature rolloff. The response is actually down only 1db at 20khz and the overall response is flat to +/-<3db from about 40hz to 20khz. The peak from about 600hz to about 1khz is inherent in the woofers used and suppressing the peak did not improve the sonic quality of the speakers. The impedance is a nominal 4 ohms with a minimum of 2.5ohms at 4000hz. While the impedance minimum may be a slight problem for low-quality amplifiers, no audible distortion is heard with my 300b amps, nor with various solid state receivers. Due to the very benign impedance phase angle (less than +/- 20 degrees), even moderately powered amps can produce very dynamic sound with these speakers.

IV. Listening Impressions and Final Thoughts

Without hearing these speakers, it's almost impossible to describe why I feel so strongly about them. I've heard many speakers ranging in price from $20 to $20,000 and these speakers have an overall magic to their sound quality that would let them sit proudly among even the most highly acclaimed commercial speakers. The imaging and openness of these speakers is stunning at times, and the dynamics are truly sensations. The drivers are capable of excellent resolution with low distortion to cleanly resolve complicated musical passages while retaining delicate timbres. Ultimately, these speakers drove me to my next project -- the 300b's.

View the Parts Express Parts List for this project