Upcoming Khanspire build and questions

[paint guy]

Hey guys, I know this is a little older, but proven design and since I already had all the parts for the InKhaneatos (surrounds), I pulled the trigger and ordered all the parts. Of course, the older shielded drivers are NLA and that shouldn't prove to be an issue using the non shielded drivers as they are basically drop in replacements.

However, the tweeter is a different matter. The original design called for the RS28A-4, which is also NLA. PE automatically recommended the RST28A-4 as the "replacement" when I ordered all the parts. Unwittingly, I just assumed it was also a non shielded version of the original, but apparently that is not the case. So, a couple of questions:

First, has anybody used the RST28A-4 as a direct replacement for the RS28A-4 yet, and was it a drop in or did the x-over need tweaking?
Second, if I do need to tweak the x-over, where do I start? Crossover design software? Or just listen to it and see?

Because I do have a couple of the older RS28A-4's I thought about going ahead and building the cabinets and using one of each in each cabinet and do a side by side comparison to listen and quickly switch them back and forth. Does anybody have any suggestions for some sort of device like this? I wouldn't think it would be too hard, but haven't really put much thought into it just yet.

I am definitely open to all suggestions and direction that ya'll could provide, especially you crossover guru's!

Thanks,
Brad

[Jonasz]

I remember reading a long time ago the Vifa XT25 was a drop in replacement for the rs28a as long as the crossover wasn't too low, maybe Jon can chime in here?

[paint guy]

I've heard good things about the Vifa tweeter, but I already have the RST28A-4's.

[chrisn]

I heard they aren't a drop in replacement,but haven't seen any comparisons. Using the FRD/ZMA files from PE I simmed them on the Khans baffle (educated guess on the acoustic offsets) using the crossover listed. I wasn't able to replicate the 1uf notch across the smaller mid inductor in PCD 7, but it's missing for both, so the only variable is the tweeter. Assuming the new tweeters distortion profile is good with this XO, then it looks like you could try a little resistance on the tweeter to match levels/taste. First pic is the RS28a, second one is the current production RST28a:

[chrisn]

Just for fun here's the XT25, with an LCR on the tweeter:

[paint guy]

I heard they aren't a drop in replacement,but haven't seen any comparisons. Using the FRD/ZMA files from PE I simmed them on the Khans baffle (educated guess on the acoustic offsets) using the crossover listed. I wasn't able to replicate the 1uf notch across the smaller mid inductor in PCD 7, but it's missing for both, so the only variable is the tweeter. Assuming the new tweeters distortion profile is good with this XO, then it looks like you could try a little resistance on the tweeter to match levels/taste. First pic is the RS28a, second one is the current production RST28a:

[ATTACH=CONFIG]30248[/ATTACH][ATTACH=CONFIG]30249[/ATTACH]

The overall response doesn't actually look too bad. If I wanted to pad it down a bit, what resistor values might I want to get to try? I came up with a 1.17 series and 9.7 parallel for a 3 dB attenuation just using a quick down and dirty online calculator. Should these be the last components in the circuit before the tweeter? And exactly how close to the values need to be?

Maybe it just doesn't look too bad to me because I don't have a concept of how much brighter it will actually be? Would the curve be more "correct" with more attenuation?

[paint guy]

And thank you for working those up, BTW! I so wish I understood crossover design better.

[paint guy]

Just for fun here's the XT25, with an LCR on the tweeter:

[ATTACH=CONFIG]30250[/ATTACH]

Do you think I would be better off with this tweeter, instead? And if so, exactly which one did you model here? I guess I could check with PE and see if I could exchange the RST's for the XT25's. The response on it does look pretty nice.

[chrisn]

I would stick with the RST28a you already have. The Vifa file is probably taken from Zaph audio, back when the tweeter was made in Europe. Keep in mind these sims are using the factory data with revised drivers, vs the originals were done with in box measurements, in a real room. I would build the crossover as designed, and try adding a resistor in line with the tweeter between the "amp" and the tweeter xo. I'd try 1-4 ohms and see what sounds right. If you can do measurements/RTA even better

[paint guy]

I would stick with the RST28a you already have. The Vifa file is probably taken from Zaph audio, back when the tweeter was made in Europe. Keep in mind these sims are using the factory data with revised drivers, vs the originals were done with in box measurements, in a real room. I would build the crossover as designed, and try adding a resistor in line with the tweeter between the "amp" and the tweeter xo. I'd try 1-4 ohms and see what sounds right. If you can do measurements/RTA even better

Thanks so much! I was wondering if I needed to do a true Lpad or just a series resistor. Sounds like just the resistor should work and also much easier. I'll just order a bunch of resistors and play around with it. Should I just use a basic 10W or 12W resistor or do I need to parallel some higher values to drop the resistance and increase the wattage?

I'm also planning on throwing together a switching circuit of some kind and putting one of each tweeter in two enclosures so I can switch back and forth and do an A to B comparison. I generally prefer a little brighter sound, but I may find out that they way CJD designed them sounds just right to me.

And if I were to start getting some measurement equipment for this and future use, what would you recommend? It would be cool to take measurements after I get them souding right to my ears to find out how "good" (or "bad") my ears are.

At least I'm in the position of having to figure out how to cut down the highs instead of wishing I had more!

Thanks again,

Brad

[chrisn]

Series resistor is fine, especially for minor adjustments. 10-12 watt resistors are fine in that position. I'll double them up in that spot just because the leads are stronger when braided together. It also allows fine tuning of the value. Use a multimeter/whatever to verify the value of the resistors. Generally they are very close, but it's nice to match them close, and there is the occasional 7.3 ohm resistor in a bag of 8's

I believe PE has some measurement systems so you don't have to piece things together. I use a Cross Spectrum Labs calibrated mic, the Dayton version of the ECM8000. I formerly used a Blue Icicle usb preamp for the mic, which eventually was replaced with a Behringer UMC202HD. A Behringer UCA202 DAC sends the output to an Onkyo A-9050. This was all stuff that people at the time had found to work, and it has There are many other solutions worth looking into now

[paint guy]

Series resistor is fine, especially for minor adjustments. 10-12 watt resistors are fine in that position. I'll double them up in that spot just because the leads are stronger when braided together. It also allows fine tuning of the value. Use a multimeter/whatever to verify the value of the resistors. Generally they are very close, but it's nice to match them close, and there is the occasional 7.3 ohm resistor in a bag of 8's

I believe PE has some measurement systems so you don't have to piece things together. I use a Cross Spectrum Labs calibrated mic, the Dayton version of the ECM8000. I formerly used a Blue Icicle usb preamp for the mic, which eventually was replaced with a Behringer UMC202HD. A Behringer UCA202 DAC sends the output to an Onkyo A-9050. This was all stuff that people at the time had found to work, and it has There are many other solutions worth looking into now

Thank you for all your feedback and advice. I will keep this updated here in the near future once I get them completed.