Design of the Esquire
The Esquire is a two-way loudspeaker system
incorporating the Vifa P13WH-00-08 woofer/midrange and the Vifa D27TG-45-06 one inch fabric dome tweeter. The impetus
for the project was a need for a pair of extension loudspeakers of high quality but low cost. Because I did not need
bass performance below 80 Hz., I decided to build a pair small of "mini-monitors" to fit on a bookshelf. I set a budget
of $ 140.00 per pair. The basic design presented allows room for individual tweaking and upgrading, and depending on how
many carats your golden ears are, and how deep your pockets are, you may pursue them. I did not pursue them, citing the
law of diminishing returns.
I believe the first and most important step
in designing any loudspeaker system is selecting good drivers. If a designer successfully chooses good drivers,
designing the loudspeaker system becomes much easier than trying to correct deficiencies intrinsic to the drivers
themselves with crossover manipulation. After considering many drivers I chose the Vifa P13WH-00-08 5.25 inch
midrange/woofer. My ears are convinced that it is one of the best 5.25 inch midrange/woofers in existence, especially
considering its price to performance ratio. It comes highly recommended by many designers, and has found a home in some
very high-end, high dollar loudspeakers. I chose as its mate, the Vifa D27TG-45-06 silk dome tweeter. The D27TG's
specifications showed it to be an excellent match for the P13WH woofer. It incorporates all the best features of the
more expensive silk domes currently available, such as aperiodic resonance damping, smooth and extended frequency
response, treated and doped silk dome, etc., but at a fraction of their cost. I have seen what looks to be the D27TG in
at least one high end loudspeaker costing $ 1500.00 dollars per pair.
The enclosure volume and port dimensions are
based on the Thiele/Small parameters for my individual drivers, optimized using Perfect Box and CALSOD. The drivers you
receive will probably have different parameters than Vifa's specified parameters and my measured parameters. Therefore,
the volume and tuning frequency of the enclosure I describe here may not provide the best performance for the woofers
you purchase. Although my parameters differed from the manufacture's, they varied proportionally, and the enclosure
volume and port frequency I calculated were similar to those recommended in Vifa's literature. Coincidence, no doubt. Be
sure to add extra enclosure volume (10 % over volume is often used) to compensate for the space that will be occupied by
the drivers, bracing, vent, and crossover. Also consider the effect of series resistance on the woofers Qtc (Qtc'). I
calculated the initial vent length using a formula, but the final vent tuning was determined empirically using test
||Volume: 5 liters, Vent: 1 inch
diameter 1.5 inches long (74 Hz.), F3: 80 Hz, Alignment: QB3.
Volume: 5.3 liters, Vent: 1.25 inch diameter
1.625 inches long (75 Hz.), F3: 75 Hz., Alignment: SC4 (better transient stability than QB3).
The final enclosure is rectangular and made
from 0.625 inch particle board I purchased from a Hechinger's scrap bin for one dollar. Initially I designed a
complicated enclosure of PVC tube inside a rectangular enclosure with the annular space filled with sand or lead. But
the final enclosure became too large to be considered a "minimonitor". Fortunately, the length of the panels are short
compared to their thickness, and the final enclosure is very rigid. An internal diagonal brace has been placed to
breakup standing waves due to the parallel walls of the enclosure, and to raise panel resonance. Corner braces are used
extensively. The enclosure easily passes the "knuckle rap" test with flying colors, and a high pitched "ping" is heard
if you rap on any of the panels. A tweak would certainly be to use 0.75 inch MDF or the construct the aforementioned
PVC/lead enclosure, but I am not sure how significant the audible benefit would be. The enclosure is filled with virgin
polyester batting to attenuate the P13WH's rear cone output and optimize the subjective bass quality.
The front baffle is sloped approximately 5.0
degrees (the rim of the drivers separated by 3/8 inches) to better align the drivers acoustic centers. This technique is
an admittedly poor solution to align the drivers' acoustic centers since one can not easily determine a driver's
acoustic center by visual inspection. But I had to at least improve the drivers' alignment to some extent because CALSOD
modeling showed a slight trough in response around crossover frequency and increased phase disturbance if the acoustic
centers were significantly out of alignment. I flushed mounted the drivers on the baffle by routing, but did not find it
necessary to round the baffle's edges or use a "felt tweeter ring" to further suppress edge diffraction.
I chose to veneer my enclosures with Pau
Farro (Brazilian Rosewood), an absolutely beautiful wood. The cost was $10.00 per enclosure, but if properly applied and
finished, the Pau Farro will give you a gorgeous cabinet on par with the most expensive loudspeakers available. The
choice of finish for the enclosure is a personal choice, and less exotic, politically correct, domestic wood veneers
such as walnut, oak, and cherry are available and less expensive. A photograph of the loudspeakers is included with the
article. Please note that the wood veneer has not been finished at this stage.
Width 7.50 inches
Height 11.25 inches
Depth 5.875 inches top to produce the required
6.875 inches bottom 5.0 degree front baffle slope.
Conversion: 1.0 inch = 2.54 centimeters
The crossover described here is not a
cookbook design whose values were determined by plugging a nominal driver impedance value into a formula. All of the
component values were optimized using the CALSOD computer program and later "tweaked" after listening tests. I choose
these two drivers specifically for their smooth amplitude response, rolloff characteristics (especially the P13WH which
is ruler flat with an almost perfect 2nd order rolloff), resonance control, off-axis dispersion, etc. to ease in
crossover design; the effort paid off handsomely. Although the final crossover is complicated, I feel it is justified,
and exploits the best features of the drivers in this system. I designed and experimented with many other types (Bessel,
Chebychev, Butterworth) of filters of different orders (1st, 2nd, and 3rd) at many frequencies. But in the end, I found
that a fourth order Linkwitz-Riley network at 3.0 kHz. looked the best on paper, and more importantly, sounded the best.
Although the tweeter's excellent damping and low resonance suggest a lower crossover frequency could be used with a
shallower rolloff, I found that such an approach often unbalanced the driver's bottom to top frequency response and
resulted in audible distortion. The choice of a Linkwitz-Riley fourth order filter, with a crossover frequency located
more than 2 octaves above the tweeter's resonance may seem a bit conservative. But listening tests indicate that this is
a solution that allows the tweeter operate at its best. Fortunately, the relatively high crossover frequency poses no
problem for the P13WH, because its off-axis performance is down only -1.0 dB 30 degrees off-axis below 3.0 kHz.
The graph show a near theoretically perfect
fourth order Linkwitz-Riley response centered around 3.0 kHz. The power response dips - 3.0 dB around the crossover
frequency, as it should, and total amplitude response is flat through the crossover region. Also note the near perfect
symmetry and smoothness of the each driver's rolloff curve around the crossover. The electrical filters' response
exactly compliment each driver's acoustic rolloff to strictly maintain a 4th order Linkwitz-Riley transfer function well
above and below the crossover point. Please note that the drivers are operating in phase, and reversing the polarity of
the tweeter will produce a severe response null of - 25.0 dB centered around the crossover frequency of 3.0 kHz.
Both drivers have outstanding off axis
response, and coupled with Linkwitz-Riley's absence of frequency dependent polar tilt, superior damping, and minimum
driver interaction, provide excellent stereo imaging.
The cost of the complicated 4th order
Linkwitz-Riley network is somewhat compromised phase and transient response. These design compromises are unacceptable
to some listeners; however, my ears are less sensitive to these shortcomings then to the many problems solved by using a
high order crossover. Loudspeaker design is an exercise in comprise, and it is these compromises that determine the
overall "sound" of any loudspeaker system. The nice part about building your own loudspeaker is that you can choose what
to compromise on, based on personal listening preferences. I did not use the crossover to compensate for the response
step because these loudspeakers are to be used on a bookshelf against the wall, which will reinforce bass response.
A diagram of the
crossover schematic is included with the article. I used quality Mylar capacitors in the tweeter circuit and quality
electrolytics in the woofer circuit. Both circuits use quality air core inductors whose parasitic d.c. resistance is
considered throughout the design. Certainly tweaks such as buying expensive polypropylene capacitors and exotic
inductors are possible. But these tweaks can double the overall project budget for perhaps a modest overall increase in
performance per dollar spent. I purchased a surplus of Mylar capacitors and precision matched each capacitor to 1% of
the theoretical CALSOD value. Finally, if you wish to improve inductor quality, please note that it will effect each
driver's Qts by changing its Qes, and overall crossover performance. Replacing the inductors in series with the woofer
with lower d.c. resistance "exotic" inductors may improve overall sound. But the d.c. resistance in the tweeter circuit
inductors contribute to each legs total damping resistance, and should not be changed; if you insist on using low
resistance "exotic" inductors, you must make up the lost resistance by using a larger value series resistors.
I will not begin with the usual cliche "
this loudspeaker sounds as good as loudspeakers costing five to ten times as much". I never know exactly what that
means, other than too many loudspeakers are overpriced. However, I seriously doubt you could find a commercial
loudspeaker this good for $70.00.
In my opinion, the greatest strength of the
system is its neutrality. It is exceptionally clean, resonance and peak free, with no emphasis on any frequency. It can
play surprisingly loud for its size, without losing any its sonic composure. It likes all types of music. Cloth domes
are back! The Vifa tweeters are silky and airy, and the fourth order crossover allows the tweeter to perform without
"harshness" or "raspiness". The crossover transition between the drivers is seamless and smooth, while dispersion
off-axis response is excellent, providing a very stable and credible stereo image. The P13WH exceeded all of my
expectations reproducing midrange, but as you would expect, a 5.25 inch woofer can not reproduce the bottom octaves with
authority. However, perceived bass is robust and taught, and quite satisfying. A quality subwoofer and crossover would
remove bass from the Vifa woofer and further improve midrange performance, as well as provide the missing bass
extension. I have already began design work on a large three-way floor monitor loudspeaker system for a friend using
these two drivers and crossover teamed with the widely acclaimed NHT 1259 12 inch woofer/subwoofer. Stay tuned.
In addition to high fidelity, you will have
a aesthetically pleasing loudspeaker, in contrast to the many wood- grained "vinyl siding" clad commercial loudspeaker
in this price class.
Each loudspeaker costs approximately $ 70.00
to build. The Vifa drivers and their shipping make-up about 90 percent of that cost. Surplus items you have on hand will
lower cost even more, while tweaks and "goldplating" will certainly add to the cost. I must say however, the basic
loudspeaker described here yields unsurpassed "sonic" value when compared to available commercial models in its price
class. Remember, this is a price class where one cheap electrolytic capacitor passes for a crossover, cheap cone
tweeters are the status quo, and 1/8 or 1/4 inch unbraced undamped plastic or wood boxes pass for an enclosure.
The cabinet and crossover are easy to
construct for any competent hobbyist, and I found the whole project quite enjoyable. In conclusion, if you need a set of
very high quality loudspeakers, but your on a budget, these loudspeakers are an excellent choice. In addition, the basic
design certainly leaves room for you to give it a personal touch by upgrading items such as the crossover components, to
further refine overall performance. A word of caution though, the Vifa drivers and crossover design are fatally linked
in this design, and they can not be changed or altered without penalty. Good luck.
Scott C. Blaier