AZ-2525 Shielded MTM
Dayton RS-125-8 & Audax TMF025
Last Update: 9 Feb 2007  

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I've gotten some pretty good mileage out of my Azurite MTM design. I've been using Azurites in the master bedroom with a 27" tube, and powered by a Sonic Impact T-AMP. They've been a great addition for my wife's deteriorating hearing. While I still have a few of those teal Vifa's in stock, I've been wanting to play with the RS-125 Daytons. A thin baffle, shielded MTM is a great addition for a medium size TV.

Our kitchen/dining/craft room has a 27" TV as well. I have a 2 channel system there but we'd like one on a wheel around cart with the TV. (Don't ask, it's all part of my wife's retirement). Over the holidays, I'll be building the cart, the AZ-2525 will be permanently attached to the cart and run by my Panasonic XR50. Hopefully, this will allow my wife to hear/see all those cooking/craft shows she is so fond of.

Those of you who've visited before, know I'm a fan of the Audax neo tweeters. The 1" TM025 is probably the most versatile, but requires a bit of fiddling to cope with rising response. The RS-125 has pretty substantial bass for it's size. Vented in 9 liters, they do a very nice job. In this design, there is a slight 1-2 db boost in the 70 hz range. I undersized the box a bit to control cone travel, and to add a bit of punch to the lower end as these will be run "sub-less" in a rather large room.

I tried to keep the costs down and the crossover simple. The rising response of the Audax and 8-12 KHz breakup modes for the RS-125 are clearly seen in the measurements  I thought the RS breakup was high enough to dispense with a notch filter -- if I could roll off the slope at a steep enough rate. I also wanted a benign impedance curve to facilitate low powered receivers (or T-amps).

I would up with a 3rd order design on both halves of the crossover. The dual 0.5 -18ga coils help smooth out, and raise, impedance a bit without breaking the budget too much. This sets up a 2500 Hz crossover point. The Audax also gets a 3rd order crossover. The 0.5 ohm resistor helps with smoothing out th upper midrange. The 2uF cap suppresses the rising response for the tweeter.

In a single speaker comparo of the AZ-2525 to the Ruby, the Ruby is more refined, smooth and warm and detailed. The AZ-2525 is more forward, crisp, and punchy and 1-2 db more efficient. I like the sizzle of the Audax, and the controlled vertical dispersion of an MTM for TV & home theater -- I find it enhances the intelligibility of dialog, and compensates for the typically crappy audio feed from TV internals.

Feb 9, 2007 - Minor Crossover Revision

After finishing the second box, I came to the conclusion this project is cosmetically cursed. I grabbed the wrong bearing for my rabbeting bit, screwed up the speaker mounting holes, and had some issues applying the Duratex finish. Some projects go that way. I got a chance to listen to the pair with the original crossover and thought it was a wee bit forward. I wound up changing the RC shunt leg in the woofer circuit just a bit. The revised crossover is shown below.

Mar 13, 2007 - MT Crossover

I had a request for a TM version of this speaker. I modeled it up in LspCad and came up with a workable crossover. (Shown at the bottom of the page) I have not built this version, so you are on your own for boxes & ports. If you keep the 6.5" baffle width, & driver spacing, it may work OK.