Design of the Esquire
By Scott C. Blaier
10 Apr 1996
Bass Loading and Enclosure
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 equipment.
Vifa's Enclosure: Volume: 5 liters, Vent: 1 inch diameter 1.5 inches long (74 Hz), F3: 80 Hz, Alignment: QB3.
Esquire: 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 Fig. 1. Picture of The Esquire. 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 5.0 degree front baffle slope.
6.875 inches bottom
Conversion: 1.0 inch = 2.54 centimeters