Design for $13 MTM buyout plate at PE

Starting out with some individual driver information, just to get an idea of some capabilities of the drivers. The in-box measurement is in the one detailed in a post above. Not too many problems with the drivers. Workable enough for something in this price range. Smooth, with no major issues in the non-linear distortion. I had to use a non-standard semi near field measurement technique for the HD sweeps, since I did not have an enclosure yet. The woofers are slightly insensitive but somewhat higher impedance. The impedance when paralleled shouldn't toast many cheap receivers, and the sensitivity in that case will be merely low instead of bad.

This design is meant for a freestanding stand mount setup. In other words, the L and R but not the C. It's a relatively simple 3rd order at around 3kHz that offers controlled vertical dispersion. For those trying to figure out which components to buy, don't sweat the details. Just get close, and DCR is not important. R11 above is a real 1 ohm resistor, and the only sensitive value is the .08 inductor. (.10 will miss the notch center frequency a bit) Getting some actual measurements correlates well with the model. Diffraction ripple smooths out a bit off the horizontal axis.

While there is only a few dB baffle step compensation in this design, when run full range in a freestanding setup they still sound a bit bass heavy and warm due to sub-100Hz distortion. These speakers really need a sub with a proper active crossover to handle everything below 100Hz. That effectively removes the mud and turns it into a pretty good sounding system.

This design is specifically for horizontal center channel use. It maintains a taller vertical listening window which becomes the horizontal window when laid sideways. There is very little BSC in this design as it will typically be placed on top of a TV, and a mild rise up to 2Khz should preserve dialog in typical installations.

If the speakers will be wall mounted, this is probably the crossover to use for that also. Be aware that all the standard wall mounting disclaimers apply - if it doesn't sound good, blame your crappy placement rather than the design. I'm less inclined to care for the rear channels, but for the front left and right you really should not mount these on the walls. Use the other crossover and a set of stands for that. Or if you want, build the design into a floor standing tower. Put a couple of actively crossed over subs in the bottom chamber.

This is about all I intend to do for this design. I won't be pouring detail into it like I typically do for my other posted designs. (doesn't seem worth it for a discontinued buyout) I can say that those of you who managed to get some of these before they sold out won't be disappointed with your $13 purchase.

Here's a quick comparison with the nearest cost level system I have in the house right now, the ZBM4: The ZBM4 performs better in the bass even though it's only one 4" woofer. There's a little less mud there and I have no problems listening full range at low levels. This MTM plate really needs a sub to shine. Not surprisingly, the $13 plate beats the ZBM4 in output capability however. Otherwise, they sound similar with the differences probably a result of the power responses of the MTM and TM designs.

Mine will be dismantled to be painted. I'll post a picture later when they are finished. Paint takes a long time to dry in this cool weather. (basement) I actually tried the stick-on vinyl and peeled it off because I didn't like the way it looked.

Note that I only built the sealed and I didn't try the vented. Vented would require a somewhat high tuning, leaving the woofer to unload anytime there's any content at all in the bottom octave. Still, vented may lower distortion in the 60-120 Hz range by nature of lowering excursion, so it may make running full range more tolerable. If anyone tries it, let me know how it works.

(PDF) - Enclosure design

Finally, just to summarize everything in a single post, there's the cabinet design. The plate drops into it and bolts into some gussets nicely.