Grill fabric ideas?

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I recently converted an oak liquor cabinet into a passive subwoofer as shown below. The dimensions are 41.5"h x 20.25"w x 14.25"d, giving an internal volume of approx. 233 liters. The sides of the cabinet are 0.75" oak except for the rear, which is 0.375" plywood. There are only two internal bracing structures:

1) A single board (the original shelf of the liquor cabinet) with an approx. 9" x 6" oval hole cut into it, located between the upper and lower drivers.

2) An approx. 6" piece of 2x4 connects the magnet of the upper driver with the rear of the cabinet directly behind it. The 2x4 brace is screwed and glued to the rear of the cabinet, and it connects with the driver magnet via a custom molded hard plastic cup studded with bits of plumbers putty and with free air circulation of the magnet's vent. The length of this brace was carefully measured to create a small amount of axial compression when the mounting woodscrews of the upper driver are firmly tightened down on the front of the cabinet.

All interior joints and seams were made airtight using polyurethane adhesive (hard-curing, not flexible). Then, 2 gallons of Soundcoat GP-1 were applied in multiple coats to all inner surfaces of the cabinet. Generous fiberglass stuffing was used.

The drivers are the VMPS New Larger Subwoofer model and were purchased as a kit. My custom cabinet has about 15% less internal volume than the standard cabinet sold by the manufacturer.

The upper driver is 12" woven carbon-fiber and the lower is 15" poly. A 15" mass-loaded passive radiator is located on the rear of the cabinet, directly behind the 15" active driver. Both active drivers are 8 ohm and are wired directly to separate pairs of binding posts with no crossover or other controls. All adjustments are made through the pre-pro. The amplifier is an Adcom GFA 555 at 200 watts per driver.

I have been using this subwoofer for about a week now, together with a new Sherwood P-965 pre-pro that I am still learning to use. This is my first DIY subwoofer. I would welcome any suggestions on how to test the performance of the sub. What test discs do you recommend? I have a Radio Shack analog SPL meter. Do I use fast or slow response, C or A weighting? Do I need to add any correction to the measured SPL at low frequencies? According to the RS instructions, the meter's response is -50 dB at 20 Hz compared to 1000 Hz. I am sure this question has been asked many times in this forum; thank you for your patience.

Subjectively, the sub sounds very good to my untrained ear. When I place my hand on the sides of the cabinet during loud bass passages, I only feel slight vibration, and not any more than I feel on the walls, floor, and furniture elsewhere in the room.

As you can see, the cabinet and the heavy bronze sculpture sitting on it suggest a rustic, Old American West style. I would welcome any suggestions for a suitable grill fabric other than plain boring black. I am considering burlap for its texture, color, and breathability. Also, are there any pre-made or made-to-order rectangular frames for a grill mount?

Thanks in advance.
 

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Yes. That is the design of the VMPS New Larger sub. Their website has more information if you are interested. Their standard cabinet has about 15% more internal volume than my converted liquor cabinet. The huge size of the cabinet is the chief complaint with this subwoofer, which is why I thought it might be fun to take an existing piece of furniture, turn it into a sub, and continue to use it as a pedestal for the bronze sculpture.
 

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