Silly question... I used a 50uF cap when measuring my tweeter with JustMLS. But...

fjhuerta · 20th September 2005, 12:37 PM

...now that I'm trying to use the data on LSPCad, I'm wondering... must I add the effect of said capacitor on the schematic?

Since I didn't model the tweeter alone, but the tweeter with a capacitor in series, how can I tell LSPCad there was a tweeter during the measurements? I have seen this is possible on the JustMLS tutorial, but it's only mentioned - nowhere does it say how can I do it. Is it necessary to add the cap to the model, or can I get away without modeling it?

Thanks a lot!

simon5 · 20th September 2005, 05:16 PM

Well the 50uF cap will do a first order highpass x-over at 375 Hz on a 8 ohms tweeter.

So unless you plan to do a very very low crossover, you can forget about it I guess! I don't think it will change the results much especially over 1 kHz.

fjhuerta · 20th September 2005, 07:08 PM

Hi Simon,

Thanks a lot for your answer!

I'm still concerned about phase shift, though. I think my measurements will be wrong if I don't consider the 90° shift.

Maybe I should bite the bullet and take the measurements again, sans cap...

Davey · 20th September 2005, 07:37 PM

You're only going to get appreciable phase-shift outside of the passband of the filter. Using the 375Hz, 8 ohm tweeter example the phase shift would only be 45 degrees at 375Hz. It'll be near zero for the area you're interested in. Your existing measurements should be fine.

Cheers,

Davey.

20th September 2005, 12:37 PM	#1
fjhuerta diyAudio Member Join Date: Apr 2005 Location: Mexico City	Silly question... I used a 50uF cap when measuring my tweeter with JustMLS. But... ...now that I'm trying to use the data on LSPCad, I'm wondering... must I add the effect of said capacitor on the schematic? Since I didn't model the tweeter alone, but the tweeter with a capacitor in series, how can I tell LSPCad there was a tweeter during the measurements? I have seen this is possible on the JustMLS tutorial, but it's only mentioned - nowhere does it say how can I do it. Is it necessary to add the cap to the model, or can I get away without modeling it? Thanks a lot!

20th September 2005, 05:16 PM	#2
simon5 diyAudio Member Join Date: Nov 2004 Location: Québec, Québec	Well the 50uF cap will do a first order highpass x-over at 375 Hz on a 8 ohms tweeter. So unless you plan to do a very very low crossover, you can forget about it I guess! I don't think it will change the results much especially over 1 kHz. __________________ DIYaudio for President !

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20th September 2005, 07:08 PM	#3
fjhuerta diyAudio Member Join Date: Apr 2005 Location: Mexico City	Hi Simon, Thanks a lot for your answer! I'm still concerned about phase shift, though. I think my measurements will be wrong if I don't consider the 90° shift. Maybe I should bite the bullet and take the measurements again, sans cap...

20th September 2005, 07:37 PM	#4
Davey diyAudio Member Join Date: Dec 2001 Location: Bremerton, WA.	You're only going to get appreciable phase-shift outside of the passband of the filter. Using the 375Hz, 8 ohm tweeter example the phase shift would only be 45 degrees at 375Hz. It'll be near zero for the area you're interested in. Your existing measurements should be fine. Cheers, Davey.

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