Dayton CX150-8 Coaxial Project

[jhollander]

Those look good. Let me figure out what I messed up.

[4thtry]

If the Z-dip bothers you, I've noticed more than once (on a bandpass) that running the series components 1st (closest to amp) followed by the shunts, (for some reason - unknown to me as yet) the Z-min holds up higher. Not sure all softwares can handle that topo., but some of them can.

I moved the series components first (to the amplifier side), followed by the shunts, but the impedance dip remained about the same. Is this the re-arrangement of parts that you were suggesting?

[jhollander]

Here are the bended and trimmed min phase files. Other than moving tail slopes around I can't explain why the match is off on the tweeter to mid. Give it a go if you like

M blend min ph.frd
T trim min ph.frd
W blend min ph.frd

[Chris Roemer]

Yup, That's it. If I look strictly at the Xfer Fn of the bandpass, it shifts the Zmin down from 600Hz to 400Hz and adds about +1ohm to it. To better that you'd need a bit less overlap yet, or make at least 1 slope steeper (as you know).

[jhollander]

Bill here are a few ideas

[4thtry]

Here are the bended and trimmed min phase files. Other than moving tail slopes around I can't explain why the match is off on the tweeter to mid. Give it a go if you like

Thanks, John, I forgot to mention that I had a 33uF polypropylene protection capacitor in series with the tweeter for all measurements. But this shouldn't affect your ability get a good match on the tweeter to mid since the protection capacitor is on both sides of the matching equation, so to speak. The protection capacitor should only reduce the accuracy of the model a little bit compared to actual measurements of the final speaker system. It should not affect the ability to get a good modeling match. Would this be correct?

I will give your FRDs and ideas a go and see what happens.

[4thtry]

Yup, That's it. If I look strictly at the Xfer Fn of the bandpass, it shifts the Zmin down from 600Hz to 400Hz and adds about +1ohm to it. To better that you'd need a bit less overlap yet, or make at least 1 slope steeper (as you know).

Thanks, Chris.

[jhollander]

Thanks, John, I forgot to mention that I had a 33uF polypropylene protection capacitor in series with the tweeter for all measurements. But this shouldn't affect your ability get a good match on the tweeter to mid since the protection capacitor is on both sides of the matching equation, so to speak. The protection capacitor should only reduce the accuracy of the model a little bit compared to actual measurements of the final speaker system. It should not affect the ability to get a good modeling match. Would this be correct?

I will give your FRDs and ideas a go and see what happens.

The cap will shift the phase. It likely messes up the match after taking the minimum phase of each driver an then trying to match a T+Cap+ M. I need to play with the files.

[donradick]

The cap will shift the phase. It likely messes up the match after taking the minimum phase of each driver an then trying to match a T+Cap+ M. I need to play with the files.

John,

I don't want to hijack this thread, but how can (how do I) I "munge" the tweeter FRD and ZMA files if I have measured them with a cap to protect the tweeter?
My tweeter sims don't usually match my measured results, and that could be why.

[jhollander]

Chris Roemer figured it out one time. For me I measure with bass removed track in omni mic and/ or at low volumes for sensitive tweeters. Domes I'm not that carefull, but I do measure the tweeter first to set the level. I think ARTA also has the feature of limiting the sweep frequencies. I still haven't had a chance to play with the files. I should be able to add a cap in xsim to see if the match improves.

[donradick]

Chris Roemer figured it out one time. For me I measure with bass removed track in omni mic and/ or at low volumes for sensitive tweeters. Domes I'm not that carefull, but I do measure the tweeter first to set the level. I think ARTA also has the feature of limiting the sweep frequencies. I still haven't had a chance to play with the files. I should be able to add a cap in xsim to see if the match improves.

Thanks John (and Chris)

[wogg]

ARTA has a bandwidth limit for pink noise, but I didn't see one for the swept sine measurements. When I did my tweeters recently, I determined the cap to use by plugging it into xsim with the OEM FRD / ZMA files to see what value was required to avoid a visible effect on the impedance and response at and above resonance. I used 50uF on mine, but I didn't try to do the matching you guys are... so FWIW.

[jhollander]

So playing around with this, the caps are big enough where there's no change in the frequency response (as expected). So there's no change in the fit of the graphs. What does change is the offset required to get the match/ fit. This is not an issue with Bill's graphs as he's using "as measured" phase. It is an issue for me when I take the minimum phase of the drivers and then try to match the overlay T+Cap+M. The offset changes due to the cap.

I seem to recall a formula for change in phase for a single filter element so the change in offset can be calculated.

[Wolf]

Couldn't you 'un-slope' the tweeter tail in the Blender or RM?

Later,
Wolf

[jhollander]

Couldn't you 'un-slope' the tweeter tail in the Blender or RM?

Later,
Wolf

The combined response T+Cap+M also has the tweeter phase shift in it due to the cap. I don't know of anyway to get cap phase shift out to make it comparable to the tweeters minimum phase.

Seems easiest to recognize the shift and recalculate the offset by adding a cap to the tweeter's minimum phase response before adding that to the mids minimum phase response.