Photon-8 Design and Construction
My big subwoofer adventure continues this time with a little one. That is big adventure, little subwoofer. The little subwoofer is the Chrysalis Acoustics Photon-8, a diminutive sub that claims a kilowatt of juice, RMS, a full 3 dB of headroom dynamic power, and a 26 Hz roll off point. That’s quite an impressive claim for a sealed sub design not much bigger than its 8 inch driver is.
Chrysalis Acoustics is a subsidiary of well known and
well regarded subwoofer manufacturer Velodyne. The Chrysalis Acoustics product literature cites 25 years
of experience designing and building subwoofers. That experience is rooted in parent company
Velodyne’s history as a subwoofer manufacture that was founded in 1983. It is not entirely clear how intertwined the
actual engineering and manufacturing of the two companies actually is, but only
one of the two companies has been around long enough to claim 25 years
experience so the other would have to draw off of the first heavily to
substantiate that claim. Rest assured if you're buying this product, you're getting Velodyne engineering know how and technology.
Design and Construction
The Photon-8 is a very modestly sized powered subwoofer with a front firing 8 inch driver. The cabinet is a rectangular sealed design that is little more than 10 inches squared by over 12 inches deep that weighs in at 35 pounds. Actually, the Photon-8 is about the size of the subwoofers that come with computer speaker systems with some extra depth, kind of a computer speaker sub on steroids. The only subs that come with cabinets smaller than this usually also come with a smaller driver.
They also rarely have a frequency response of 26 Hz at the -3 dB point.
The cabinet itself features radiused edges and corners and the top panel is slightly recessed below the side panels providing reveal lines. The driver is internally mounted with no visible mounting screws and recessed into the baffle with radiused edges around the circumference of the opening. The black cloth grille is also inset to be flush with the extended side panels at the front and wraps over the top with the Chrysalis badge top and center. At the bottom, the unit sits atop rubber feet as the only support option with no apparent accommodation for carpet spikes.
The single finish option is a textured black vinyl. While the finish is competently applied, the sub will not win any interior design awards or fool anyone into believing it is fine furniture, or even that it is made of wood for that matter. The good news is that a subwoofer this small should be easy to hide just about anywhere if it violates the décor of the surrounding room in any way.
The rear of the unit is home to the typical mounting plate for the amplifier and ontrols. To the left side is a large rocker styled master power switch and a non-detachable power cord while to the right side are all the controls and inputs. These controls include two knobs allowing continuously variable settings for volume and the low pass crossover frequency. There are toggle switches for activating the auto on/off feature, the internal crossover, and setting the subwoofer phase between 0 and 180 degrees. Below the controls are two pairs of gold plated RCA connections for line level input and output as well as two pairs of five way binding posts for speaker level input that also have gold plated leads.
The internal crossover system for signal input is adjustable from 40 to 120 Hz and uses staged for low pass filtering that varies between –12 dB/octave at the crossover frequency to –24 dB/octave above the crossover frequency. The line level output is said to have a high pass crossover that can be set for either 80 or 100 Hz that filters at –6 dB/octave below this frequency but there is no control apparent on the subwoofer to adjust this setting.
The driver used in the Photon-8 has an 8 inch outside diameter that Chrysalis states provides a 6.5 inch effective piston diameter. The cone itself is a composite resin that is reinforced with Kevlar fibers and is mounted to the frame with an oversized EPDM rubber surround while the internal suspension is said to use an oversized spider, both to accommodate high excursion but retain linearity.
The motor structure on the back of that cone is also appreciably oversized. The magnet structure weighs in at 204 oz (12.7 lbs) that effectively constitutes fully 1/3 of the entire subwoofer systems weight and weighs more than some comparably sized subwoofer systems. In between the cone and that magnet is a high temperature, 2.5” diameter, dual wound coil. Coupled with a cast aluminum basket frame and we have the makings of what should prove to be a very potent little driver.
The Photon-8 is not video shielded but this is an ever diminishing problem in this era of post CRT display technologies. If video shielding is an important consideration the Photon-10 is shielded, which provides an accommodating option in the product line.
The Photon-8 also boasts a digitally controlled class D amplifier section that is said to deliver 1000 watts rms power and 2000 watts dynamic power. Chrysalis jumps on the green bandwagon by pointing out its class D amplifier is 95% efficient, producing minimal heat. This can be said to be true of all class D amplifiers, and not specifically the Chrysalis amplifier, which are considerably more efficient that traditional audiophile class A and AB amplifiers. Based on the power consumption rating of 8 amperes listed on the back of the unit at the standard 120 volts we get a power rating of P = 0.95(8A * 120V) = 912 watts which is close enough to the 1000 watt rating that with a slo-blo fuse leaves little to suspect the rated power of the amplifier.
Both the amplifier and driver feature overload protection circuitry. The driver is digitally controlled with a current limiting driver servo to limit distortion by prevent clipping and over excursion. The amplifier section has thermal protection as well as protection against excessive voltage drops.
Disassembly of the Photon-8 to reveal the internals can only occur through the rear amplifier plate, which is secured with 10 wood screws around the perimeter. Inside the cabinet, fiber batting is wrapped around the outside faces of the cube and a second piece separates the driver from the electronics mounted to the back. The cabinet itself is constructed of ½” MDF with glued joints and triangular wedges used to reinforce the outside corners.
The amplifier, which is separated into two sections, occupies the entire back plate. One board dedicated to the power supply supporting the transformer and main fuses. The second tiered board supports the preamp functions and six 470 microFarad, 200 V power supply capacitors. There is a small heat sink to the side of the capacitors while the majority of the circuitry lives under a grilled metal housing.
The majority of the interior volume is dominated by the driver, which fills about half of the space. The magnet itself, stamped with Velodyne and 6 ohms, is about 6 inches in diameter and about 2¾ inches thick. The powder coated cast aluminum basket, mounted to the inside of a two layer baffle with aluminum brackets and machine screws, appears quite sturdy.
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