I joined this forum in early December 2008 in an effort to reconnect with an early fascination with JBL. At the same time, I wanted to build a DIY system to rival the audiophile systems I’ve collected over the years – without spending a fortune.
In 1973, I built a pair of large bookshelf speakers (out of ash wood!), using a D123, an LE20 tweeter and an LX2 crossover. A year or so later, I built a respectable PA using JBL pro drivers that I later turned into large home speakers not unlike the S7R system. My so-called audiophile years began in the late 1970s and I don’t need to cover that here.
My first instinct was to buy and upgrade an older JBL studio monitor cabinet. But I had my heart set on using a large format compression driver, specifically the 2441. (My uncle once owned a Paragon and I just loved the speed and presence of the large drivers.) However, I did not want to surrender my living room to a 4350-sized box. I decided to build my own boxes and incorporate more recent thinking with respect to cabinet construction.
Nearly all of today’s high-end speakers are exercises in extreme cabinet design. Thin or resonant cabinets absorb sound energy and add distortion. The more inert and solid (read heavy) the enclosure, the better the sound. Ideally, rapping a knuckle should elicit the experience of rapping a rock. I know this is old news around here, but I thought I would mention it anyway.
An early pioneer in this school of speaker design is David Wilson. A few months ago, I had the opportunity to listen critically to one of his flagship models and more recently to the Focal-JMLab Grande Utopia EM with the field coil woofer (Wilson uses the “regular” Focal woofers in his big cabinets). In each case, I was struck by the “tightness” of the bass and the complete lack of boom. I know it is a cliché, but the speakers all but disappeared, as one might expect from such ultra-expensive systems. Wilson’s liberal use of a special wall material (and lots of epoxy) contributes to extremely solid speakers that weigh more than 600 lb per side. In any event, I felt I could give these a good run with a JBL based system.
My DIY system starts with a collection of drivers I assembled last fall. I bought a pair of freshly re-coned 2235H 15-inch speakers and a pair of E-110s that were freshly re-coned with 2122H cones – so they are essentially 2122Hs. As mentioned, I have a pair of 2441 drivers with original (and clean) diaphragms. These attach to a pair of 2397 “Smith horns” I found on Ebay. Lastly, I wanted to use a pair of 2405 alnico slot radiators for the ultra-highs.
David Brink sold me the parts for the upper section of a Giskard-designed charge-coupled 3145 crossover network. I assembled this myself, using the schematic and pictures of other completed units.
Now on to the cabinet build. First, I owe a great debt to LH member “macaroonie” whose step-by-step posting, Backyard Box Building – The Build, provided me with the courage and guidance to build my system. My second debt is to this forum for carrying posts such as his.
While macaroonie used a combination of 1 inch and ¾ inch plywood, I decided to combine plywood and MDF. As noted in a March 2006 post by Mr. Widget:
“As many DIYers know MDF is an excellent speaker box material as it is self damping (non-resonant). The only thing wrong with it is that it is about as structural as a wet noodle. This becomes more of an issue as the box grows in size...”
By combining MDF and plywood, I could do two things: 1) provide the required density and 2) create nearly indestructible joints.
My plan called for the most flexible system possible. That meant one cabinet per side housing the 15” and 10” speakers. The horns and tweeter would sit on these. Also, if I decide down the road to switch to a different upper-mid/tweeter arrangement (such as a small cone and dome setup), the bass section would not have to change. This also meant that the crossovers would be outside the boxes and each cone driver would have a dedicated binding post.
Like macaroonie, I used only a portable circular saw, a power drill, a plunge router and a small electric sander. Plus lots of clamps and glue. I also relied on a Jasper Jig for cutting circles. If I had to do it all over again – which I might – I would get myself a nice table saw.
The bass cabinets are 18” wide, 38” tall and 21” deep, yielding a somewhat similar size and shape to the bass sections of the large Wilson and Focal speakers. There is a ½ cubic foot (internal volume) “doghouse” built into the cabinet for the 2122H. The side panels of the main cabinet form the interior sides of the doghouse. This leaves roughly 5 cubic feet for the 2235H. As discussed below, I glued the ¾ inch MDF to the ¾ inch oak-faced plywood to create a sandwich. So each wall is 1.5 inches thick. An extra ½ inch sheet of plywood was glued to the inside of the front baffle, bringing that surface up to 2 inches thick. This also yields a more secure material for the driver mounting screws to bite into.
By cutting the MDF ¾ of an inch smaller than the outside plywood on all sides, I created a rabbet joint as well as a “cabinet inside a cabinet” effect. I first pre-assembled five sides of the plywood box and then fit the MDF inside of it, all without gluing. With the panels lined up, I drilled and installed between two and four wood screws per panel to temporarily secure the MDF panels to their plywood counterparts. I then disassembled each cabinet, backed the screws out and, using a six-inch plastic spackling blade, spread Titebond glue on one surface and used the wood screws to align the panels before clamping together. Multiple, clamped two-by-fours were used to press the panels together while the glue dried. (Best to remove the wood screws at this point.)
When reassembling, all joints were glued liberally and clamped without screws or nails. Dado-type grooves were cut into the front baffle, both sides and the top, in order to secure the bottom and back MDF walls of the mid-bass doghouse. An extra ½ inch plywood section was glued to the back wall of the doghouse to further dampen this structure.
Internal bracing consists of a plywood cross support for the two 4 inch diameter rear-mounted ports, a plywood brace along the bottom and 1 inch dowels securely glued into place – one connecting the back of the doghouse to the rear panel and one connecting the sides just below the woofer. Although it is not cheap and difficult to cut, I used heavy, ¾ inch wool-based felt for sound dampening, mainly because I just hate working with fiberglass. The two, four-inch diameter ports are 11 inches long, yielding a tuning frequency of around 33Hz. I am guessing that each box weighs in north of 250 lbs.
I fashioned a terminal plate from a ¼ inch thick phenolic sheet. Each cabinet has a pair of Vampire Wire BP-3 binding posts, one each for the 2122 and the 2235, mounted to the plate. Oxygen-free 12-gauge wire connects the drivers to the posts.
After touching up minor overhangs using the router’s trimming bit, I applied ¾ inch wide oak trim to all exposed plywood edges. I sanded and then applied a stain and varnish to the cabinets. T-nuts hold four screw-in “glider” feet per side. Plastic press-in mounts hold the grills in place. Zilch provided the grill cloth. I plan to build some nice supports for the horns and the slot tweeters.
Now on to the sound. For the time being, I am using a mid-level Rotel AV receiver to power the mid-bass, horn and tweeters. I connect the sub outputs of the Rotel to a Krell KSA 300s amplifier (300 watts per channel of pure, class A power and 180 lbs), which, in turn, connects directly to the 2235s. The Rotel’s crossover frequency is set at its maximum of 120Hz.
The first thing I noticed is how incredibly dynamic and efficient this system is. The resolution blows away anything I have yet heard. The bass is very deep and tight, with no boom or overhang. I no longer need my twin 18” Bag End Elf-based cabinets and will be selling these. The mids and highs are smooth and extended. If you were blindfolded, I doubt you could tell there were horns in this system. No “honk” or coloration to speak of. But they are forward and are definitely not shy. Perhaps they are too forward for some tastes. And they can easily overwhelm anything less than a large room. So I’m working on dialing them in and will continue to experiment. I’ll keep you posted!
Here are some photos of the finished speakers. Construction shots are available upon request.
All the best,
Jerry
