Push-Push Bi-polar ML-TQWT Concepts with 2 radio Shack 40-1354 full-ranges
These concepts came about because of a discussion on the Full-Range Forum. Someone asked what could be done with 2 drivers per side and i suggested this. The discussion even lead to someone doing some experiments to see if the concepts work. His edited post is in the sidebar at the bottom. The drawings show 3 variations -- one of the other Full Rangers, Steven Brown, is donating a pair of 40-1354s so that I can build a pair -- I had already done a swap for my 1st pair. We are going to do the folded ones. This kind of configuration is something i have been thinking about for some time. This push-push toobz woofer is an earlier concept. Push-push cancels out a lot of newtonian load on the box for better micro-dynamics & inherently has no baffle-step. By mechanically coupling the two drivers we are actively canceling any motion that would be imparted on the enclosure largely removing driver induced resonances in the cabinet walls. A similar trick is the wedge between the back of the driver and the back of the enclosure. This passively loads the drivers newtownian motion (ie the cone moves in -- the enclosure -- or part of it -- moves the other way) more evenly thru-out the cabinet (putting less stress on the baffle). since both drivers go from 2pi to 4 pi radiation in the same place the loss below the bafflestep from one driver folds around the cabinet and perfectly compensates for the baffle-step loss of the opposite driver. Drivers need to be working in phase. These designs are all based on Bob Brines straight ML-TQWT for the 40-1354 which was developed using Martin King's TL software.
<clik images for larger drawings with dimensions and other details>
Steven Brown Experiments         I built two (very) quick pairs of cabs for a pair of 269-469's in each box. (total of 8 drivers) I used my own spreadsheet to calculate a ported enclosure for two drivers and used 2 pieces of 2" PVC firing out of the front. Vb=1.073 ft3 Fb=73.83 F3=59.004 Dv=2" Lv=1-7/16" Np=2 I made the first with the drivers front and rear with out putting anything in between them. I just wired them in phase. The second, I put a piece of oak dowel rod that fit inside the bucking magnet of the drivers glued in place with a little silicone. The volumes of the cabs were as close to identical as I could get them and there was no damping used for the sake of speed in building them. I ran the same pieces of music through both speakers several times and check for sound quality, cabinet vibrations and imaging. I will say this first: baffle step correctin is NOT needed IMO when using a driver in the back! Next for the comparison. Both cabinets sounded pretty decent, no pounding bass, but what was there was way clearer than my 4 speaker version. The pair with the dowel had less coloration from the cabinet and almost no vibration in the box at all. The imaging out of both pairs was excellent. The difference I heard from push-push is very detectable and no harder to setup than without (once you figure out the EXACT length of the dowel). The main difference is the lack of bass lost in the far field from baffle step. The conclusion: If you are going to use two drivers (or any even amount) face half the drivers to the rear and couple them together. YOU WILL HEAR A DIFFERENCE! If you do not, quit building speakers and go into oil painting or carving. (I would hope your eyes are not failing too!)             [ <-- Back to the Finlayson Arm Loudspeaker Lab | T-Line Speakers]