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I was fortunate for my Amaroso design to win first place in the Dayton Audio category at last weekend's MWAF event. Following is a description of their design, followed by 4 photos (and I will provide several more posts with more photos and drawings:
Drivers used in the Amaroso are the Dayton Audio RS225-8 woofer, a Bohlender-Graebener Neo8 midrange and a Hiquphon OW2 tweeter. The woofer enclosure is a folded, mass-loaded transmission-line (ML-TL) modeled using Martin King’s ML-TQWT Worksheet (version 2/09/08) and with a predicted anechoic F3 of 33 Hz. The rather unique midrange enclosure uses a short, tapered TL, having a ¼-wavelength resonant frequency of ~400 Hz, to raise the falling lower-end response of the Neo8. The exit end of this tapered TL coincides with the apex of a triangular-shaped diffuser/deflector. Sound waves travel down the tapered TL, wrap around the diffuser/deflector into secondary tapered chambers to the sides of the box, then around the back of the diffuser and out the back of the cabinet through a vertical slot. All of the midrange enclosure contains fiber filling, mostly polyester and some fiberglass, with densities varying from 1.2 to 2.1 lb/ft3 depending on location and material. Fiberglass is used in the secondary side chambers; these chambers attenuate the lower frequency output from the rear slot, which results in a generally flat frequency output over its effective range, at about 5 dB below the front, on-axis output. The primary goals of the midrange enclosure design were to eliminate back-wave reflections through the driver and reduce standing waves, while providing a controlled rear output for a small enhancement of soundstage spaciousness and depth, yet allowing the cabinet’s back to be fairly close to the wall. Dan Neubecker conceptualized this midrange enclosure configuration. I built a midrange test box with an adjustable fore-and-aft location for the diffuser/deflector and shipped it to Dan. He used it to perform extensive testing of both front and rear outputs, using various stuffing densities and materials, various positions of the diffuser/deflector and a variety of rear slot sizes. Through this testing, the optimum geometry, stuffing densities and stuffing materials were determined.
The cabinet proper has external dimensions of 11-1/2 inches wide by 13-1/2 inches deep, with a height of 39-1/2 inches. The base adds 1-1/2 inches to the overall height and has a footprint of 12 inches by 14 inches. Internally the cabinet is 9 inches wide, 12 inches deep and 38-3/4 inches high. The woofer’s folded ML-TL resides in the bottom 26 inches of the cabinet with its 52.5-inch-long line having two turns, one of 90 degrees and the other of 180. Along its entire length, the line’s cross-section measures 9 inches wide and 5-3/4 inches deep. The first half of the line is stuffed with polyester fiber at a density of 0.75 lb/ft3. Above the ML-TL section is the sealed-off midrange section that has internal dimensions of 8 inches high, 9 inches wide and 12 inches deep. The tweeter resides in the top 3.5 inches of the cabinet. Baltic birch plywood, 18-mm thick, was used for the cabinet’s walls as well as for internal braces. Half-inch MDF was used for the ML-TL line divider, the top of the midrange enclosure and the angled dividers that form the tapered TL in the midrange section. The sides of the triangular diffuser/deflector are 9-mm Baltic birch plywood. Half-inch, solid Brazilian Cherry cladding on the cabinets’ sides increases their stiffness while improving aesthetics. The outside members of the base are constructed from 3/4-inch-thick pieces of this same Cherry hardwood. Countersunk magnets were secured with epoxy to the backs of the grille frames (9-mm Baltic birch plywood), aligning with heads of some of the drivers’ mounting screws. The crossover assembly is attached to the top of the base assembly, and the base assembly is attached to the bottom of the cabinet using ¼-20 bolts into T-nuts located in 4 gussets glued inside the bottom corners of the cabinet.
Dan also authored the crossover design using an otherwise completed speaker I built for in-box measurements, crossover simulation, mockup, testing and voicing. Using Dan’s completed crossover design to finish assembly of both speakers, I set them up for listening tests and potential tweaking in my home to accommodate my needs and preferences. In the end, the only change I made was to use 3 ohms for the resistor in series with the Neo8 (R4) instead of 4 ohms, which raised the midrange output by ~1 dB over its operating range. Crossover corners are nominally 610 Hz and 2.7 kHz, and there are 19 components in the crossover. The crossover design was targeted for a listening height of 37-38 inches at a horizontal offset of 15 degrees and utilizes mixed-order roll-offs. For the woofer low-pass and the midrange high-pass, 2nd-orders were used, while the midrange low-pass and the tweeter high-pass are 4th-orders. Split series resistors, one before the crossover and one before the driver, were utilized in the midrange leg to contour the response and improve phase tracking. A similar split-resistor configuration, one before the crossover and an Lpad before the tweeter, was used in the tweeter leg, again to shape tweeter response and improve phase tracking. As a result, there are 7 resistors in this crossover. Two notch filters were used, one for the woofer and one for the midrange. The woofer’s notch suppresses its initial cone breakup by 35 dB and its higher-frequency breakup by 45-50 dB. Similarly, the 12-kHz peak in the Neo8’s response is attenuated by at least 50 dB. The resulting phase tracking is excellent and the overall response is very flat, mostly exhibiting SPL variations of +/- ½ dB or less from 500 Hz to ~17 kHz. Impedance magnitude dips just below 4 ohms around 2 kHz, but the concurrent impedance phase is only slightly negative. Up to 1 kHz and above 6 kHz the impedance magnitude is 7-8 ohms or higher, including when the impedance phase is at its two most-negative points. Most amplifiers should be happy with the Amaroso. All crossover capacitors are polypropylene from Jantzen, Audyn, Solen and ClarityCap. All of the resistors are 12-watt Mills. The woofer’s inductor is an Erse 16-gauge steel laminate, while the other inductors are air-cores from Jantzen and Madisound. The final system sensitivity is 84-85 dB (re: 2.83v/1m). An input of 25 watts will generate 102 dB SPL above 45 Hz with the woofer reaching its rated Xmax at 22 Hz and a peak port air velocity of 17 m/s at 27 Hz.
Paul
Drivers used in the Amaroso are the Dayton Audio RS225-8 woofer, a Bohlender-Graebener Neo8 midrange and a Hiquphon OW2 tweeter. The woofer enclosure is a folded, mass-loaded transmission-line (ML-TL) modeled using Martin King’s ML-TQWT Worksheet (version 2/09/08) and with a predicted anechoic F3 of 33 Hz. The rather unique midrange enclosure uses a short, tapered TL, having a ¼-wavelength resonant frequency of ~400 Hz, to raise the falling lower-end response of the Neo8. The exit end of this tapered TL coincides with the apex of a triangular-shaped diffuser/deflector. Sound waves travel down the tapered TL, wrap around the diffuser/deflector into secondary tapered chambers to the sides of the box, then around the back of the diffuser and out the back of the cabinet through a vertical slot. All of the midrange enclosure contains fiber filling, mostly polyester and some fiberglass, with densities varying from 1.2 to 2.1 lb/ft3 depending on location and material. Fiberglass is used in the secondary side chambers; these chambers attenuate the lower frequency output from the rear slot, which results in a generally flat frequency output over its effective range, at about 5 dB below the front, on-axis output. The primary goals of the midrange enclosure design were to eliminate back-wave reflections through the driver and reduce standing waves, while providing a controlled rear output for a small enhancement of soundstage spaciousness and depth, yet allowing the cabinet’s back to be fairly close to the wall. Dan Neubecker conceptualized this midrange enclosure configuration. I built a midrange test box with an adjustable fore-and-aft location for the diffuser/deflector and shipped it to Dan. He used it to perform extensive testing of both front and rear outputs, using various stuffing densities and materials, various positions of the diffuser/deflector and a variety of rear slot sizes. Through this testing, the optimum geometry, stuffing densities and stuffing materials were determined.
The cabinet proper has external dimensions of 11-1/2 inches wide by 13-1/2 inches deep, with a height of 39-1/2 inches. The base adds 1-1/2 inches to the overall height and has a footprint of 12 inches by 14 inches. Internally the cabinet is 9 inches wide, 12 inches deep and 38-3/4 inches high. The woofer’s folded ML-TL resides in the bottom 26 inches of the cabinet with its 52.5-inch-long line having two turns, one of 90 degrees and the other of 180. Along its entire length, the line’s cross-section measures 9 inches wide and 5-3/4 inches deep. The first half of the line is stuffed with polyester fiber at a density of 0.75 lb/ft3. Above the ML-TL section is the sealed-off midrange section that has internal dimensions of 8 inches high, 9 inches wide and 12 inches deep. The tweeter resides in the top 3.5 inches of the cabinet. Baltic birch plywood, 18-mm thick, was used for the cabinet’s walls as well as for internal braces. Half-inch MDF was used for the ML-TL line divider, the top of the midrange enclosure and the angled dividers that form the tapered TL in the midrange section. The sides of the triangular diffuser/deflector are 9-mm Baltic birch plywood. Half-inch, solid Brazilian Cherry cladding on the cabinets’ sides increases their stiffness while improving aesthetics. The outside members of the base are constructed from 3/4-inch-thick pieces of this same Cherry hardwood. Countersunk magnets were secured with epoxy to the backs of the grille frames (9-mm Baltic birch plywood), aligning with heads of some of the drivers’ mounting screws. The crossover assembly is attached to the top of the base assembly, and the base assembly is attached to the bottom of the cabinet using ¼-20 bolts into T-nuts located in 4 gussets glued inside the bottom corners of the cabinet.
Dan also authored the crossover design using an otherwise completed speaker I built for in-box measurements, crossover simulation, mockup, testing and voicing. Using Dan’s completed crossover design to finish assembly of both speakers, I set them up for listening tests and potential tweaking in my home to accommodate my needs and preferences. In the end, the only change I made was to use 3 ohms for the resistor in series with the Neo8 (R4) instead of 4 ohms, which raised the midrange output by ~1 dB over its operating range. Crossover corners are nominally 610 Hz and 2.7 kHz, and there are 19 components in the crossover. The crossover design was targeted for a listening height of 37-38 inches at a horizontal offset of 15 degrees and utilizes mixed-order roll-offs. For the woofer low-pass and the midrange high-pass, 2nd-orders were used, while the midrange low-pass and the tweeter high-pass are 4th-orders. Split series resistors, one before the crossover and one before the driver, were utilized in the midrange leg to contour the response and improve phase tracking. A similar split-resistor configuration, one before the crossover and an Lpad before the tweeter, was used in the tweeter leg, again to shape tweeter response and improve phase tracking. As a result, there are 7 resistors in this crossover. Two notch filters were used, one for the woofer and one for the midrange. The woofer’s notch suppresses its initial cone breakup by 35 dB and its higher-frequency breakup by 45-50 dB. Similarly, the 12-kHz peak in the Neo8’s response is attenuated by at least 50 dB. The resulting phase tracking is excellent and the overall response is very flat, mostly exhibiting SPL variations of +/- ½ dB or less from 500 Hz to ~17 kHz. Impedance magnitude dips just below 4 ohms around 2 kHz, but the concurrent impedance phase is only slightly negative. Up to 1 kHz and above 6 kHz the impedance magnitude is 7-8 ohms or higher, including when the impedance phase is at its two most-negative points. Most amplifiers should be happy with the Amaroso. All crossover capacitors are polypropylene from Jantzen, Audyn, Solen and ClarityCap. All of the resistors are 12-watt Mills. The woofer’s inductor is an Erse 16-gauge steel laminate, while the other inductors are air-cores from Jantzen and Madisound. The final system sensitivity is 84-85 dB (re: 2.83v/1m). An input of 25 watts will generate 102 dB SPL above 45 Hz with the woofer reaching its rated Xmax at 22 Hz and a peak port air velocity of 17 m/s at 27 Hz.
Paul
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