Orion Xover testing & SpectraPlus question

[¿GotJazz?]

I just finished building my Orion crossovers this morning. I did the "A" test on one board, and saw some deviation outside of the allowable ranges:

- The 100 Hz W-M normalized difference signal was 0.026 (should be 0.1 +/- 0.04).
- The 1545 Hz mormalized Tweeter out was 0.43 (should be 0.42 +/- 0.02)
- The 1545 Hz M-T normalized difference signal was 0.57 (should be 0.53 +/- 0.02)

Overall, not too bad, but outside of the specifications.

So, I moved on to the Orion "B" tests. I saw the signals make it all the way through my cross-over on the 400 Hz, 40 Hz, and 4 Khz signals. But, the values were off a bit from SL's tables - about 2% to 5% errors.

Questions:

(1) I want to try out SpectraPlus to see if a transfer function plot looks like the graphs in the Orion plans. How do I connect the PC's sound card to my Orion crossover to do this? What special cables do I need to build, if any?

(2) Are there other resources on SL's site to do further debugging of the crossover build? Most of the testpoints on the board have not been touched yet during my testing.

[audiorasp]

Hello,

Did you take your measurements with the 50HP switch closed? If this is left open, the measurements will be slightly off.

Regards,
George

[¿GotJazz?]

I currently have C100 replaced by a shorting wire, so the 50 Hz HP filter has been disabled.

I actually was very lucky with this - C100 was the only part that was out-of-stock at DigiKey. When I received my order, I was wondering how I was going to replace the only missing capacitor in the crossover (backordered to almost December). Then, I read in the Orion construction plans that C100 was the only optional part! I needed to bypass C100 anyways during debugging, and C100 wasn't needed if I didn't want to use the 50 Hz HP filter.

[Zodiac]

One thing to watch for is if the woofer and tweeter adjust pots are not exactly in the centre. I had some slightly off readings as well, but slightly tweaking the pots made the readings fall within the margin of error

p.s. finished my Orions last weekend, they are superb! I was using PMC TB2's before, but these are an order of magnitude better. The bass is great and the soundstaging deep and wide, with instruments well located in space. One day I will post some piccies and comments, but I want to get the XOs into some hand built enclosures and build some amps for the woofers. At present I'm using 2*Pass Aleph 3 for the mid / tweet and 1*Nak PA7 for the bass, but I'm planning on building some monoblocks for the bass based around the Hypex UCD400 module (400W into 4 ohms) with some meaty transformer and caps as the Nak eats electric and takes up a lot of space in the living room. That way I will end up with 2 stacks of 12"*12" components behind each speaker comprising XO, bass amp and aleph 3.

[Davey]

Jazz,

Check out this link and you'll see my setup procedure for using SpectraPlus to check your crossover:

http://www.linkwitzlab.com/faq.htm#Q27

If you have any problems feel free to contact me by email and I can help you.

Cheers,

Davey.

[¿GotJazz?]

Zodiac - I tried to make sure that the pots were adjusted properly before the measurements, but it is a little hard to tell if they are exactly centered (electrically). I'll try some voltage measurements to see if I can center them better. Visually / mechanically, they were OK.

Davey - That's just what I needed! I was going to go to Fry's to pick up a couple of 3 mm stereo -> dual female RCA adapters after work tonight. I'm glad to see that I "guessed" correctly. Your very helpful wiring & setup information proveide the last pieces of the puzzle.

I'll let you guys know how it goes ...

[¿GotJazz?]

With your guys' help, I got SpectraPlus working!

Well, sort of ...

The software seems to be working fine, but here's what I'm seeing on my screen:

Woofer Transfer Function:


Midrange Transfer Function:


Tweeter Transfer Function:


It looks like some sort of noise spikes occur at approximately 70 Hz harmonics (not 60 Hz!). I measured the peaks using SpectraPlus' cursor function, and most of the spikes are very close to 70 Hz apart.

This seems an extrememly low frequency (and pretty high amplitude) for a switching power supply problem. Both crossover boards show a similar characteristic.

What the heck is going on here?

[Davey]

Jazz,

Yep, you've got some problems. The traces should be much much cleaner than that.
I can converse with you via email if you like and help you work through it.

Davey.

[catapult]

That looks like 60 Hz stuff to me. You are using a 4096 point FFT so that gives you a sample about every 10.8 Hz. There would be samples at about 54 and 65 Hz so 60 Hz noise would go in the 65 Hz bin.

[¿GotJazz?]

catapult (and others) -

I just took some frequency samples off one of my boards. Here's the frequencies where the strongest peaks occured on my Orion Crossover Tweeter output:

14.65, 59.95, 69.59, 140.12, 179.25, 209.42, 280.33, 349.43, 421.68, 492.10, 563.04, 633.55, 700.98, 775.58, 843.78, 910.27, 982.00, 1050.50, 1123.77

The red numbers indicate the strongest peaks, the black numbers were approximately 50% -> 75% of the height of the stronger peaks.

You can see from these numbers that there is a very small portion of harmonics from a 60 Hz component, but the majority is approximately 70 Hz related.

I'm still clueless!