TQWT — Bigger is Better
by Terry Cain
After seeing this design on several Italian and Japanese web pages of course I had to try. Being a furniture maker for 25 years I have a simple way to establish designs that I like. I just build them and see how they sound. This pair took me 3 hours to construct start to finish including the finish (cat laq). This is primarily due to the fact I have a state of the art millwork facility by which I can utilize at my discretion ( I own it).
The cabinet shown is my simplest construction method I know of. All of the edges are mitred on a huge sliding table saw. Machine sanding is via a stroke sander with 365"x6" belts with 150 grit before assy. Cut to within + - 1/64" along the length, the panels are easily masking taped together and folded with glue in the corners. The entire structure is assembled this way in about 5 minutes. The baffle is lathe turned and the base just a slab of wood screwed to the bottom. This method of folding miters comes from the bank and office industry where I first apprenticed. With about a full 1-3/8" of diagonal glueline available, when panels are mitered this way they become the strongest element of a structure. The 15 psi required for carpenter glue to set firm is easily achieved by the masking tape folding method where you lay out the pieces flat and tape the joints "flat" and then flip this assembly and run glue down the "v's" and fold the box up. This is nearly impossible to do without a saw that can miter with the "good side up". Any left tilt saw such as the newer Delta's and of course the Powermatic 66 can do this cut. A right tilt saw can do it but you have to have the fence to the left of the blade so that the mitered edge of the panels touch the upper part of the fence without slipping under.
After my baptism into single driver theory a little over a year ago via this website I built Herbert Jeschke's TQWT. This system is still my all time classic "economy" all star. The original pair I made now reside in a wine bar here in town where I built the bar etc. and the speakers get constant daily use in a restaurant atmosphere.
This H. Jeschke design (left) proved a basic understanding to me about speakers that I had always suspected. The bigger the cabinet the better when it comes to horns and their variants. No amount of applied accepted engineering is enough to do the job sonically to make a system sing. The "art" aspect rules in my book. The design shown here tends to debunk a lot of currently accepted design methodology for TQWT in that the flare extends a full 140"" and is unobstructed at the top of the cabinet. Loading the ceiling opens the bass to propagate across the ceiling and onto the floor removing a little bit of mud that the H. Jeshcke pipe would sometimes display. This design after 2 hours of break in already showed far more bass propagation into the room than I could believe. The little 1354 now commutes full 40hz energy seemingly effortlessly. While still not "high efficiency" the sound was clean and detailed. I originally thought that this ceiling loading design would be bass-light against the other straight pipe but quite the opposite is true. The top of rooms are unobstructed and based on what I am hearing this maintains cleaner sound effectively making the speakers come alive.
Recently I have been using the 30ga. wire for my other horn systems with great success. The relative inefficiency of the 1354 became apparent at the volume knob. Requiring more current to drive, the 1354 do not work well with 30ga. and wire saturation/ constriction was obtained running the 1354's at high volumes. My David Berning ZH270 was well into the "green" on the bias led display where the horns barely crack them "on" (green represents approximately 1 watt). Giving "all she's got captain" at about the 1 o clock position the pipes were at ear splitting levels and just barely showing signs of distress. Bass was classic horn sound, deep powerful and very taught, far more than my other 1354 experiments by a magnitude I could not imagine by looking at the design. It easily sounded like 15" paper cone bass from something far more expensive. The thing I notice about 1354 based TQWT more than anything is that on paper, in listening the systems appearance causes severe brain ear eye dysfunction and chaos. The brain stuck between the eyes and ears cannot make the two correlate at all. Then comes the price and the brain has to run back to the era of $0.25 gas and $10,000 mortgages where this kind of value per item once existed.
A lot of really good information was found in these books:
Additional research is easily obtained by performing a google search using "tqwt jp" as keywords. In Japan, many build a tall transmission line TQWT variant for home theater. When searching Japanese pages I am continually amazed at creative and artistic design. Speaker building and all aspects of audio are elective courses in schools from the Jr. high school
stage and beyond.
The screen shot shows the cad drawing and the simplicity of the design. The exact numbers for all dimensions are not given as this design is presented here as just a starting point for your exploration. For the RS-1354 driver, the general dimensions are as follows:
- Outside box dimensions are 7"x14"x70"
- Driver height from base is 39"
- Baffle is centered at 5-1/2" between outer walls and floor of cabinet
Need more bass from TQWT? Here it is.
- Terry Cain