Here’s a measurement comparison between the TD15M Apollo and the TD15X, with 1/12th-octave filtering. The TDM is driven by a 2W SET amp with a couple of series caps tuned to give the -6dB @ 60hz (and which also includes the low damping-factor of the SET output). The TDX is driven by an 8W SET amp. So, apples and oranges, to a certain degree, but both measurements showed very low distortion (from the amps) and coincided with other measurements, so I think they’re worth something. Elsewhere here, the TD15M impedance plot shows that its pretty flat in the midbass, so thats probably coming into play with its frequency plot being flatter in the 100-200hz octave, wrt the TDX. I’ll be using both because 1) I have them on hand and 2) I sense that the TDM sounds smoother in the midbass than the TDX. Without going into too much boring detail: 1) the TDX will have a 60hz marchand XM46 LR4 lowpass imbedded in its amp and 2) the TDM will have a 220hz lowpass imbedded in its amp. The mids on the original Unity Horns reach a -6dB at about that 220hz. I’ve taken lots of measurements and decided to give these values a shot. I should pick up the XM46 units in August and then be able to post new measurements and impressions.
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I’m working on a tri-amped system with the Unity Horns and Lambda woofers. If you go to this site http://www.cowanaudio.com/index-2.html and look for “Unity the Finale” you’ll find a schematic for the mids and compression drivers, including some interesting deciphering notes for the same. If you have an active crossover, I think it would also be feasible to use a first-order 300-1200hz bandpass on the mids, instead of the passive speaker-level circuit.
Cool, I’ll look into that, for posting pics.
Hey Simon, thanks for the design of the monster enclosure advice for the TD15Xs. It turns out that the over-damped design complements the under damped SET output to a “T”. I’ll probably end up with 20W of PP300B, but for the moment 8W of SE 300B sounds great.
Here’s the pertinent formula, for adjusting the speaker’s Qe to include the low-damping SET output….
I forgot to mention that after the active LR4 lowpass, the TDX’s will be driven by solid state amps, so there’s no problem with the speaker’s impedance effecting that part of the filter. I’ve modeled the 20hz, 14 cu ft box with other AE drivers and it looks like the TDS would do even better than the TDX. Which of the HT drivers would also excel in such an enclosure? Is there one that would be even better than the TDS? Might there be a TD+ 15″ driver in the future that would particularly want to reside in such a large, low-tuned enclosure?
Luckily I have the stock, JBL 4320 monitors to listen to, in the meantime. I have pretty much resolved my path forward on the Lambda system. It looks like it will involve an active 4-way near-unity-gain crossover, with effectively LR4 filters at around 105hz (LR4/TDX in big box to TDM/LR2 Q=1 in Q=0.5 box) and 300hz (TDM to unity mids). Within the unity horn itself, I’ll use the time-alligned passive filters at first, with dedicated amps for mids and highs, and morph towards doing more and more of the filtering in the active realm, with the BMS 4550 in mind for the highs, eventually. But, before all that, I’ll do a sort of proof of concept on the 4320, doing and effective, active LR4 crossover at 750hz, to replace the stock 2nd order + reversed polarity, stock passive crossover.
Looks like I’ve got 3 good options for the TDM15’s, then. A 6ft3 box tuned to 40hz, a 3ft3 sealed box (looking here for both a smooth 1st order, acoustic high pass and maximum LF extension), and a horn modeled with the “horn response” program thats about 36″ long and has a 30×30″ mouth (the horns model pretty smoothly from 70-300hz, but for the moment I’m hoping to resolve the system as also sounding good in the nearfield). First step though is to wait for the 16ft3 boxes to arrive for the TDX15’s, and hear what they and the TDM15’s sound like with a LR-4 lowpass at 300hz. If the TDM15’s sound a lot better, then I’ll put them in the 3ft3 sealed boxes and add a first order low pass around 80hz for the TDX’s in their new bass bins. Should be interesting, however it works out. Yeah, I now see that the TDM15 is not an open baffle speaker, that’s what the Dipole 15 is for, right? Congrats on the new TD6’s. If using just the TDX15’s works out in the main system, I’ll build a second one around the TDM15 in the 6ft3 40hz vented enclosure and the TD6M — as a sealed midrange, it looks like from the curves you posted that its a12dB/octave, 2nd order roll-off at 150hz. Nice. Thanks for the input.
The response of the TDM15 in a 6 ft3 enclosure tuned to 40hz looks really good. Does “tuned” mean a port or passive radiator? Could a similarly flat response be achieved in a sealed enclosure (sealed so as to combine better with a vented sub)? Mine are in 2 ft3 enclosures and looking for a new home 🙂
Hey, thanks for all the info. I’ve just ordered the enclosures, with lots of window bracing added to the design, and about 5 and a half sheets of 3/4″ material (ply outside and mdf inside) in each one. Luckily they will be delivered! Really looking forward to hearing the TDX15’s in their new habitat!
I’ve designed a 16 cu ft box for the TDX15, inside dimensions of 29″ x 37″ x 26″ and walls will be 1.5″ thick, so OD will be 32 x 40 x 29. I’m thinking of a 3/4″ layer of MDF on the inside and a 3/4″ layer of good ply on the outside. Any advantages to going with all-MDF or all-ply? And, what would be a good port(s) dimension to use, for a 16-20hz tuning? The port(s) would be on the back and so would have to be less than about 22″. Also, my first inclination for damping is to try 2″ and 4″ layers of fiberglass insulation, since its available here. I figure the 1.5″-thick walls would be rigid enough, but would there be an advantage to sub-dividing the interior space? Thanks for any suggestions!
This is now morphing away from the TD18+ and focusing exclusively on LF extension.
I’m now ready to have built a pair of good, 10 cu ft BR boxes tuned to around 20hz, for use, intially, with TDX15’s.
My first question is, assuming I stick with the TDX15 indefinitely: would going for 12, 15 or 20 cu ft BR enclosures improve LF extension?
Second, once the final enclosure size of 10 to 20 cu ft is determined, would swapping in other TD15 or AV15 drivers make an improvement in LF extension? It seems like a really good idea to make the project upgrade-able, to achieve the greatest possible results, using single 15″ AE drivers in such BR enclosures.
And third — and ignoring higher efficiency, since I do have two 300W plate amps — would it make sense to put IB15’s in such large BR enclosures, but ones tuned to a lower FB? It looks like 300W feeding an IB15 would still get me theoretically to 110dB peaks, which would be PLENTY of headroom for my system.