[aceinc]

I want to build a simple (temporary) crossover for speakers I am building. It is a 2 way 2nd order butterworth xover. The woofer & tweeter have a nominal impedance of 4 ohms each, the crossover frequency is 900hz.

I have checked 3 different online xover design tools. They all say I need;

2 -1.0 MH inductors
2 - 31.25 uf capacitors.

I asked both ChatGPT & Gemini, and they both say I need;

2 - 1.0 MH inductors
2 - 62.5 uf capacitors.

When asked why they disagree with the online calculators they say it's because the online calculators are using 8 ohms instead of 4 ohms for the drivers.

Who is right?

[newzooreview]

Grok is currently performing better than ChatGPT and Gemini in electrical engineering tasks (and on most things), and on Expert mode, it confirmed the 31.25 µf capacitor value. Here's the reply as an image to preserve the formatting:

[aceinc]

Grok is currently performing better than ChatGPT and Gemini in electrical engineering tasks (and on most things), and on Expert mode, it confirmed the 31.25 µf capacitor value. Here's the reply as an image to preserve the formatting:

Thanks for the confirmation. I just wanted to order some parts. My thought is to build a simple xover, put it in place during testing to protect the mid/tweeters and give a sense of what the speakers should sound like. Once I have everything together, I will take a stab at designing a proper xover.

[wushuliu]

900mhz seems pretty low for a tweeter, even if only testing, unless it's one of the few very robust like a DA25TX/DA32TX.

[FullRangeMan]

Correct. 900Hz is too low for a tweeter; it will burn the VC.
Tweeters are typically specified to start at 1500Hz and have recommended crossover frequency above 2000Hz.
https://www.usspeaker.com/beyma%20t25S-1.htm

[aceinc]

Correct. 900Hz is too low for a tweeter; it will burn the VC.
Tweeters are typically specified to start at 1500Hz and have recommended crossover frequency above 2000Hz.
https://www.usspeaker.com/beyma%20t25S-1.htm

Thanks for your concern, it will be an array of https://www.parts-express.com/GRS-PT6816-8-8-Planar-Slim-Tweeter-8-Ohm-272-128?quantity=1 Which are technically mid/tweeters.

[Speedskater]

But what are the real impedances of the drivers at the crossover frequency?

[S Clark]

But what are the real impedances of the drivers at the crossover frequency?

Looking at it's impedance graph, it looks about 6 1/2 ohms at 900Hz.  But when he starts putting them in parallel and series groups, those figures will be way different.  He's going to need a good measuring program/device and a lot of patience.  Parts Express sells the Pocket Clio for
~$800 that is a quality system.  I've got one that I've used a couple of times.  Without something like that, you are really flying blind. 
https://www.parts-express.com/pedocs/specs/272-128--grs-pt6816-8-spec-sheet.pdf