RS28F-4 Tweeter xo sim help?

[ODougbo]

My PE order of Dayton RS28F-4(ohm) tweeters showed up today; must say, they look very well made and nicely packed.

http://www.parts-express.com/pdf/275-140s.pdf

Need help with second order xo design. The plan is to cross them over 2,300 - 2,400hz. Checked some charts and on-line calculators; they were all over the place, but the general idea is:

C1 - 8.2uf
L1 - .5mh

I'll probably use twist type L pads for attenuation for now, but have section of resistor for l pad which I can slip in later.

Can anyone suggest a second order xo?

 

[Jay1111]

What woofer are you using? What are the baffle dimensions? What are the driver locations relative to the bottom of the cabinet?

A fairly accurate simulated crossover could be worked up for you with that information provided.

 

[ODougbo]

Thanks for taking a look Jay.

It's a MTM with 2 -6.5 (8ohm) in series - 16ohm. The front is small, only 1/2" on each side of woofer.

The bass is rock solid, with a very heavy sound. Listing to them now with ScanSpeak tweeters. The Madisound Speaker Store

The Dayton are for the prototypes which are the same box(s), etc.; can compare the two sets when done, side by side.

*both tweeters are in the $50 range, both have great reviews.

 

[Jay1111]

You didnt exactly give me the specifics for a completely accurate sim, this should get you very close to to good results. The nice thing about the RS28 is it can handle a low crossover.

 

[ODougbo]

Jay, Thanks for working on this, and apologies for beginner mix-up.
Although, before opening this post I was guessing that larger woofer coils may be needed, but never would have guessed 6.0mh.
I did try reversing tweeter leads the other day (Scanspeak tweeters) and not much sound loss when disconnecting them; so they must have been xo'ed way too high and acting like super tweeters.

In luck here, have parts, even a pair if 6.0 lam, 14gauge coils.

Thanks again!!

 

[fastbike1]

If you check the Parts Express Techtalk forum you will find a number of designs w/ the RS28F/A.

They are relatively interchangable and the various designs will give you a place to start.

 

[ODougbo]

Oh really, I did call the tech support number, no mention of that.

Any thoughts on MMT vs. MTM front baffle?

Might make another set if MMT is a better design. (or could fill holes and re-cut existing mock up boxes MMT)

 

[Jay1111]

A tmm would need a different 2.5 way crossover

 

[ODougbo]

TMM got it..no no don't want to try that again.

Have most of the parts; using 24R for the 20R.

Had to re-set the tweeters, which took a while since they were 1-2mm larger than existing recess.

 

[Jay1111]

That should still work pretty well. Looks like you're close to having these guys buttoned up.

 

[ODougbo]

Won't be long now, one cardboard "breadboard" finished.
Odougbo hopes 3rd times the charm

 

[ODougbo]

Success! Well for the most part, had to much high end - tried many combination of resistors and ever a smaller 8.2 cap. The smaller cap left a very noticeable "hole" in the middle, so put the 10uf back in.

As you can see I did install a L Pad and only it only needed a 1/3 of a twist (which may be typical).

So yes very nice, good imaging, solid bass, a wide range of sound.

Will have to find a way to remove L pad - maybe two amps or something; passive bi-amp, but still would need a way to attenuate the treble.

Jay thanks for helping out with this

Thumbs up on the tweeter!

 

[Jay1111]

Did you try the zobel?

 

[ODougbo]

Would like to try that also (although I thought that was more for the woofer).

 

[Jay1111]

Usually yes. A zobel drops the top end of a driver by controlling the impedance. The 5.1uf, 3 ohm zobel I pm'd you will give a very slight droop to the treble response. You can also pair that with a slightly higher value for r11 until you get the balance you're happy with.

 

[Jay1111]

Here's what you should get with the zobel added. The gray line shows what changing R11 to 5 ohm's would get you. An adjustment of R11 in 1 ohm increments will change the treble by that much, up or down. Notice how the top of the impedance response is tilted downward, and the filter transfer function shows a downward tilt. This is the effect of using a zobel on a tweeter.


The only questionable part of a pure simulation like this is getting the phase alignment right, but the driver levels are going to be correct based on what you are seeing.

 

[ODougbo]

Will add Zobel today - sorry I missed that, but the L pad gave me an idea what they can sound like (when finished). I did have to tweak it several times, but they sound wayyyyyy bigger than they are; with a sub-woofer like sound.

This xo is 10x better than the one I had (post #3), e.g. I started to realize that the sound stage would focus 6' to the right (very strange). All that craziness is gone now.

Again Jay, thanks!

 

[Jay1111]

Good to hear.

 

[ODougbo]

Oh yeah...much better just as shown.

Will try slightly larger resistor at R11, just for experiment.

 

[ODougbo]

This sounds better every day; there were a lot of new parts and new drivers, so a few days of break-in is expected.

Also...switched to a Luxman M-117; best sounding amp here.

used 6.8 at R11, which also sounds very nice, balanced.

I think I saw a build where the same tweeter does not have a zobel - I don't know about that, it has some sharpness to it (without one).