The Subwoofer DIY Page v1.1 - Projects
Enclosures for the NHT 1259
last updated: 16 August 2010
Author: William Eckle

Introduction
I've had several (well 5) requests for details on the cabinets I built for the NHT 1259 driver. Lets start with the driver specs:

Factory Specs: Actual specs.
(Driver #1)
Actual specs.
(Driver #2)
Re 3.4 ohms 3.56 3.69
Fs 19 Hz 20 Hz 20.5 Hz
SPL 90 dB/1W/1M* 85.8 dB/1W/1M 86.4 dB/1W/1M
Qms 2.6 2.87 2.87
Qes 0.56 0.61 0.66
Qts 0.46 0.50 0.54
Vas 190 liters 186 liters 217 liters

* with room gain

Enclosures:
Built a box from 1" MDF that measures (OD), 26" h X 16" w X 22" d. or, (ID) 24" h X 14" w X 20" d. Installed two dividers in this box that resulted in three compartments each 24" X 14" X 6". These two dividers (braces) have 6" diameter holes in the center. The net interior volume of the box is 6048 in^3 or approx. 99 liters. not counting the 6" holes in the dividers or the volume of the rear of the 1259 driver. Each "compartment" is 2016 in.^3 net. Between the front and the first divider, between the two dividers, and between the second divider and the rear, are five (in each section) 6" oak 1 1/4" round "closet poles" spaced in a circular pattern around the 6" holes in the dividers, to brace the assembly front to rear. These 1" MDF boxes are assembled using "carpenter's yellow glue", counter sunk dry wall screws, and clamps. The material list for the 1" MDF: (one cabinet)

    2 Top/bottom            22" X 16" 
    2 Sides                 24" X 22" 
    4 Backs/fronts/dividers 24" X 14" 
    15 Oak "closet poles"    6" X 1 1/4" 

Box contruction

Construction:
Now we get ready for the cool edges (since I can't/won't miter). Install over the above assembled cabinet 1/2" MDF on the two sides and the back and front, to the vertical edges, of the above cabinet, _BUT NOT_ overlaping each other, and 1/2" from the top edge, hanging over the bottom the amount you would like the bottom recessed for the later installation of casters (this puppy will weigh more than 120 lbs. so you or the WAF _will_ want casters). In other words, you will end up with a 1/2" X 1/2" VEE shaped groove on all edges (except the bottom). The material list for 1/2" MDF (for one cabinet), with 1" overhang on bottom (adjust the overhang on the bottom for the casters you use and the height you want the cabinet from the floor/carpet):

    2 Front/backs     26 1/2" X 16" 
    2 Sides           26 1/2" X 22" 

These 1/2" MDF panels are glued, countersunk screwed, clamped to the box, as instructed above. Is the box getting heavy yet ?

1259 enclosure #2

Finishing:
Now cut from 1/4" furniture grade plywood, taking care to have the grain go the direction and match adjacent panels as you desire. Cut these panels from the un-finished side and mark on this side which panel goes where ie. left side, top etc. Also cut them oversize, at least a 1/4" on all sides. Now glue these panels to the top, sides, and back/front. I used to use contact cement here, but found "yellow glue" works better, although you can remove these panels with lacquer thinner at a later time if you use contact cement. Once these panels are set, use a router to trim all the panels to the 1/2" X 1/2" Vee grove you left on all the edges. With the addition of these 1/4" panels, you now have a Vee groove of 3/4" X 3/4" on all edges (except the bottom). Obtain needed lengths of "quarter round", 3/4" X 3/4" at your lumber/woodworking store in the wood to match your choice of furniture grade plywood and glue the mitered pieces all around the top in the 3/4" X 3/4" VEE groove, now glue the pieces on the four corners of the sides.

1259 Enclosure #1

Preparing for driver installation:
Using a router with a circle attachment, cut a "shelf" the diameter of the driver, the depth you want the driver to set in the front panel. keep reducing the diameter of the cut till you then have the desired width of the mounting flange in the box. Then cut the cut the hole all the way through by gradually increasing the depth of the cut. Temporarily set the driver in the front panel cutout and mark the eight mounting holes. Drill the mounting holes the size appropriate for the bolts you plan to use. I used round Allen head 1/4-20 cap screws threaded into T-nuts on the inside of the cabinet. I also made a ring of soft wood (pine or scrap 1/2" or thicker plywood) and glued this ring on the _inside_ of the cabinet to hold the T-nuts, as the points on the T-nuts tend to bend and not grip in MDF. Sand and finish the cabinets to your taste. I sand the cabinets with 280 paper, then 400 paper, then two coats of sealer, sand between coats with 400 paper, than apply two coats of satin polyurthane. This results in a very professional looking cabinet in _real_ wood, that with the rounded edges, appears smaller than 28 1/4" high, 17 1/2" wide and 23 1/2" deep in final outside dimensions.

I use 1/4" red oak plywood @ $19 per 4' X 8' sheet, red oak quarter round 3/4" X 3/4" moldings @ .50 per ft. 1" MDF @ $30 per 4' X 8' sheet, 1/2" MDF @ $15 per 4' X 8' sheet. and miscel. screws, input terminals, driver mounting bolts & nuts and casters. Note: Many builders like to veneer the MDF, but I prefer 1/4" furniture grade plywood as it covers many mistakes in the MDF and the counter- sunk screw holes, allows sanding etc. The edges on the 1" MDF do not have to perfect, where as with veneer _all_ will show through, and locally, at least a sheet of 1/4" oak plywood is one third the cost as the same amount of oak veneer ???

Tools:
The only tools I have are: A router w/circle attachment, reversible elec. drill/screwdriver, assortment of bits and countersink bits, router bits (including a 3 1/2" long 1/4" bit to reach the thick panels), a hand miter box & saw, a elec. circular saw and an elec. sander. Am lucky to have a neighbor who cuts all my MDF to my order on his professional table saw at his employment (and since I _gave_ him the drivers and Xovers for his home made Altec A7s, he won't let me pay for any MDF I need). I also have several clamps borrowed (long term) from my neighbor. As you can see, am using minimum equipment, and could probably use less for a one time project, I usually build 3 to 5 pairs of loudspeaker systems a year.

Results:
Measurements in a 100 liter sealed box, with no stuffing.

           Unit #1   Unit #2
    Fc     32.3 Hz   32.1 Hz
    Qtc    0.78       .89 

Measurements in the same box w/a "curtain" of 12" X 10" X 4" fiberglass covering the 6" hole in the divider in back of the driver.

    Fc     34.0 Hz   34.0 Hz
    Qtc    0.62      0.75

This is where I stopped, although can play with more/less stuffing in the future. Note: the only access to the interior of the cabinet is by removing the driver as all other joints are screwed and glued. I put a bead of clear RTV between the outer edge of the driver and the cabinet, which can be broken by a razor blade if I need access to the inside of the box.

To build one cabinet as above, requires a 4' X 8' sheet of 1" MDF, a 4' X 8' sheet of 1/2" MDF, and a 4' X 8' sheet of 1/4" finish plywood. You will have plenty of wood left over to build a pair of medium size satellites plus a pair of puter speaker cabinets.

Grill cloth, terminals etc. are up to the constructor, although I never use grills as I'm not ashamed of seeing the driver cones (especially the pretty yellow Kelvars). Form follows function or is it the other way ?

Hope _all_ this helps and answers questions that have been asked re. the NHT 1259 cabinets. Whew, am NOT a typist. Of course this is my personal preference as to constructing this unit, your milage may very, so feel free to make changes (and share them). You may want to make a smaller and lighter cabinet, but I'm from the old school, instead of engineering for the minimum material usage, I prefer to "add more meat", when it is easy and reasonable.

William Eckle