Acoustics offset & BSC

[NyxOne]

Hi Everyone,

I'm considering participating in Zaph's contest but there is a few thing I'm that I can't seem to be able to do :

Setup : lspCAD with the FRD files.

First : How do I determine the acoustic offset of the woofer relative to the tweeter (I'm talking about the dZ for those who use lspCAD). I'd like to know if there is a know and proven way to extract this information without having the driver on hand?

So far, my guestimation tell me that It must be 25-26mm... I'm using the drawing of the woofer and I've measured the distance between the front of the frame to where the spider is attached to the voice coil. Is that "ok" ?

Second : I'm also having a hard time generating a new FRD file for a custom enclosure (based on the "infinte" baffle measurement). I've tried a few different programs and they all seems to give different results although I can definitively see a trend. Is there a recommended application or technique to generate a FRD file for a XYZ baffle ?

I know this sound like dumb questions but even after re-reading a few references threads and books (just some parts ) I'm still unsure! ops:

Any advices are welcome

Thanks,
Chuck

[dmalphur]

I'll take a stab at this. The acoustic offset is included in the measurements. He measured both the woofer response and the tweeter response on axis referenced to the baffle, the phase information is included in the files.

(edit: corrected mistake about measuring from the same location)

I've been able to successfully model the files using Jeff Bagby's spreadsheets, but there are tutorials around (check on the Parts Express forum) to help you better than I could.

As far as trusting the response modelers, here's an exercise. You know the baffle layout for the set of files that Zaph provided (same as ZA5.2, and infinte), model the baffle that he used (using infinite baffle as input) in one of your programs and compare the response with the file Zaph provided. Use the program that most closely matches that response.

Good luck,
David

[NyxOne]

I'll take a stab at this. The acoustic offset is included in the measurements. He measured both the woofer response and the tweeter response from the same location, the phase information is included in the files.

I've been able to successfully model the files using Jeff Bagby's spreadsheets, but there are tutorials around (check on the Parts Express forum) to help you better than I could.

Humm... I've my doubts. Zaph should detail his measurements conditions, that would clarify this topic. Ok, well I guess I'll just have to model both with and without an offset...

I'll take a stab at this. The acoustic offset is included in the measurements. He measured both
As far as trusting the response modelers, here's an exercise. You know the baffle layout for the set of files that Zaph provided (same as ZA5.2, and infinte), model the baffle that he used (using infinite baffle as input) in one of your programs and compare the response with the file Zaph provided. Use the program that most closely matches that response.

Good luck,
David

That seems like a smart idea... and beside I found something after posting, lspCAD has the KFH tool which is able to generate an FRD file with BSC applied to the infinite baffle measurement. I'll just have to validate that it correlate with Zaph's model!

Thanks dmalphur,
Chuck

[dmalphur]

from Zaph's blog:

All drivers are measured individually on axis for proper simulation. Phase is referenced to the baffle, so the acoustic centers are properly represented in these files. Levels are 2.83 V at one meter. The Soundeasy files are set to the range of 10Hz - 50kHz and are good for V14 or greater.

[NyxOne]

from Zaph's blog:

DOH!!! :E Shame on me! ops:

I better read more carefully next time!

Thanks for pointing that out dmalphur.

Chuck

[Saurav]

If you still want to enter a dZ, say for off-axis simulations in LspCAD... I *think* what you can do is:

* Take Zaph's measurements, create a 'crossover' that's just the two drivers with no filtering, note the response
* Generate minimum phase versions of both measurements, plug those into LspCAD
* Adjust dZ until the combined measurement matches what you'd noted earlier

Like I said, I *think* that will get you what you want.