RS125s / TB 25-302SH bookshelf / surround MT

[patrickm]

I've had these for a while, and am just getting around to writing it up, because i thought it'd be a good project for people stocking up on RS125s, especially since the Sinar Baja SB TWD25NH05 tweeter, which based on T/S data and visual comparison appears to be identical to the TB 25-302SH, is on sale at madisound for $6, so these are currently a really good deal.

The original design was inspired by RJB's Microbe, so I wanted to give credit where it's due. But I'd already bought a few of the 302SH tweeters to fix up some commercial speakers, I wanted to try and work that in. These make great rear surrounds or desktop monitors. The phase tracking is ok in the crossover region, but not as good as my RS150S MT or MTM's, but the modeled on-axis FR is +/- 2dB.

The cabinet is .22 ft^3, mine is 11.5"x6.5"x9", vented to about 55hz tuning. Modeled F3 is 58 Hz, F10 is 45 Hz. Crossover is ~2500 Hz, 3rd order electrical w/ L-pad on the tweeter, 2nd order electrical with a bottomless notch (small cap across inductor) near the breakup frequency. Schematic is below. The main inductor can run from 1.3mH to 1.5mH depending on baffle step needs (more BSC=higher inductor). Parallel resistor can be tweaked from 4-8 ohms to taste on the tweeter.

If you use dayton poly caps on the tweeter high-pass, the cost is about $60 each, or $55 for 4+. With electrolytics, you could build 5 for $200.

and, as you can see in the pictures, with some of the leftover wood and some MDF scraps, you can make some stands pretty easily too.

[pypes]

Nice work! Wish I had some 125's laying around, I'd give it a go. But, alas, all I have are the 100's :o

[patrickm]

Nice work! Wish I had some 125's laying around, I'd give it a go. But, alas, all I have are the 100's :o

thanks. are you sure there still aren't a couple left? this is probably also a good candidate for the new RS125-8... the F3 / F10 are a couple hz lower in the same box.

[patrickm]

built another pair with the sinar baja tweeter from madisound -- just as good as the tang band, i couldnt' tell the difference.

finish is rustoleum granite stone.

[james_e5]

I'm a big fan of that little SB tweeter. Sounds better than the ND20 series and the Vifa BC25 to me and for less money!

Nice work on those little guys!

-j

[martyh]

I'm sitting on about 10 of the RS125's. If you're interested in building these and want a great deal on the 125's, PM me.

[steveschenkel]

What gauge is the 1.5mh inductor?

[patrickm]

What gauge is the 1.5mh inductor?

to maximize sensitivity, i've used p-core 15ga or laminated steel core. if you go air core, 18ga is probably ok.

[steveschenkel]

That's perfect I have some laminated I Core inductor's I can just unwind a bit.

[steveschenkel]

Do you have any idea how much of a change you would have to make in the schematic to use the RS125-8 since the S is not longer available?

[patrickm]

crossover-wise, i think there's a thread and some measurements suggesting it's virtually a drop-in replacement... i don't have any, but you might want to get some slightly smaller or larger resistors and a couple tiny (like .47 or 1 uF) cheap mylar caps, so you can adjust the values just a little bit from stock. i'd venture a guess that it won't be more than about +/- 1db difference, so it might be just a tweeter level adjustment.

the box can be a little smaller with the 125-8 than the shielded, or you can just run a winisd model and aim for a little more extension.

[patrickm]

i should also mention, if you haven't bought the parts and have the space, check the vifa / RS150 MT in my signature... overall i'd give that one the nod, and it's only marginally more expensive, especially if these are going to be main speakers vs surrounds with a sub, where extension isn't so much of a concern

[steveschenkel]

Thanks for the info. I was given 6 of the TB 25-302SH tweeters a few years back and was hoping to find a project to use them for. I will probably build them for friends. I am currently using a pair of TMM towers using the Cabasse Dom 4 and a pair of Focal Access 6A midbass units. These are hard to beat. I didn't design them, Joe D'Appolito did and they are really wonderful.