The Tower 6 is a slim tower mass loaded transmission line speaker, that uses the same drivers as our MLTL-6 - a 6” paper cone woofer, and either a 1” soft dome tweeter, or a dipole tweeter - both options are included. The bass extension is even deeper - the fundamental frequency is 25Hz vs 32Hz of the stand mount. The Linaeum dipole tweeter is great, but not always easy to find. The SB Acoustics dome tweeter is excellent, and has a smoother and more extended response. It is available retail - which is key!
This speaker has the best bass quality of any speaker I have heard in my nearly 4 decades of music listening. They are essentially flat in my room to about 25Hz, and also have wonderful “unboxy” midrange, and have a spacious soundstage; if it is there in the recording. The midrange of transmission line speakers is also much more open than conventional designs; and may rival open baffle designs.
The cabinet is 8”W x 39 3/8”H x 13”D / 203mm x 1000mm x 330mm and is made with 18mm thick material - either Baltic birch or MDF. Each finished speaker built with the Baltic birch flat pack weigh a bit less than 46 lbs / 21kg. The corners are designed to have a 12mm x 12mm chamfer; but the MDF can be left square, if you choose. See the images of the MLTL-6 flat pack, for how this will look. The chamfer also has an acoustic function of reducing edge diffraction. I can provide CAD files to make CNC cut files - the build manual includes drawings of the CNC version of the panels. It can be built with a table saw and plunge router, and/or with a CNC machine.
A strong benefit of a “folded” transmission line design is the internal baffles not only form the specific volumes and dimensions required for the correct tuning for the woofer - they also form asymmetrical bracing for the cabinet. I include a brace in the closed end, that greatly strengthens the front baffle - which is the most critical area, since the drivers are mounted there. Less obvious is the fact that the internal air pressure in a TL design is lower than an equivalent sealed, or even a ported design. This greatly reduces the panel resonances - and this is possibly why the midrange and bass are more open and clearer. The woofer has less of an “air spring” behind it, so it is more closely reproducing the music in the recording.
We are using 3rd order series crossover design for both the 1” soft dome, and the dipole tweeter. A parallel design is what we think of as “conventional” today, but the series type is what was commonly used in the past. A series crossover diverts the signal that is filtered out for one driver, and it goes to the other driver. A series crossover can be slightly more efficient, and they tend to have a smoother more even impedance; which can make them better for use with tube amplifiers.
A transmission line speaker cabinet is a tuned “column” of air behind the driver - it has lower distortion and greater bass extension that conventional sealed or ported designs. I used a program called Hornresp (short for Horn Response), and carefully matched the computer acoustic model to the cabinet design, using DataCAD.
The cost of the pair of woofers and a pair of the dome tweeters is about $150, from Madisound. They are both made by SB Acoustics. I have used all air core inductor coils, and the woofer inductor coil is 14 AWG or 12AWG for a low DCR. This is important for the best possible bass quality. The capacitors I have used on the tweeter are the best quality that I have ever heard - they are ClarityCap CSA. We include “good, better, best” crossover parts lists, with clickable links; for both tweeter options. The benefits of high quality crossover components cannot be overstated.
These speakers are fairly sensitive - the woofer is rated at 89.5dB @1W @1 meter. But the crossover lowers this somewhat, and the transmission line may increase it somewhat. I listen at a lower volume setting on my preamp than the other speakers I own. The Tower 6 speakers are 4-6 ohm nominal impedance - the dome tweeter version is a minimum of about 4.2 ohms. We use the amazing AkitikA GT-104 amp - it is rated at 60W/ch @ 4 ohms and ~30W/ch @ 8 ohms - it barely gets warm even after long listening sessions. Any amp that is rated for ~4 ohm speakers will probably work very well, with the Tower 6 speakers. If you have a tube amp, the series crossover means these speakers are relatively easy to drive.
The manual includes drawings in inches and in millimeters, Also included are CNC version of the panels. I can provide the CAD files for these, if you want to build it this way.
For folks who want to build the Tower 6 speakers - but do not have the tools to cut the panels, or do not want to cut them - we will have flat packs available in the near future! They will be 18mm Baltic birch, and you can select either the SB Acoustics dome tweeter, or the Linaeum dipole tweeter version - same price for either one.
The price is expected to be $450 per pair of flat packs, plus shipping via UPS.
