Added inductance of even a tweeter changes amp response? - diyAudio
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Old 6th October 2009, 04:01 AM   #1
sendler is offline sendler  United States
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Default Added inductance of even a tweeter changes amp response?

Here's one of the filters I have modeled for the Sure 2X100 amp which is bridged. I actually like the sound of the one that I built using 4uH air cores much better than the filter with 13uH toroids wound on MicroMetals T106-2 cores. The air cores sound great but pollute AM reception up to 20 feet away so shouldn't be used in an on going basis. I will wind some smaller toroids to 6uH to see if that will get me closer to the sound I am getting with the forbidden air cores.
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Here's the response into 8ohms.
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It has a slight peak into 8 ohms but I like to keep the coils as small as possible and it is pretty flat into 4 ohms. Now look at the simulated response when .2mH is added in series to the 8ohm load. This would be a low amount of inductance even for a tweeter at 2k, let alone a midwoofer at 20k but is a fair demonstration just to get started.
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Down 12 volts/6db at 30k. Shouldn't we correct our filters to account for driver Le?
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Old 6th October 2009, 05:36 AM   #2
H3nry is offline H3nry  United States
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That's what the Zobel C7 & R4 are for, but I have yet to see a Zobel which is anywhere close to the right values of R and C for real speakers on an amplifier schematic. Most are calculated for a resistive test load. Worse, the required Zobel changes from speaker to speaker.

Start making C7 larger and see what happens. Usually to match a speaker, the C has to be a few MFD and R has to be small, which means it has to be able to dissipate some power.
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Old 6th October 2009, 02:55 PM   #3
sendler is offline sendler  United States
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Default I see what I did wrong

Quote:
Originally Posted by H3nry View Post
That's what the Zobel C7 & R4 are for, but I have yet to see a Zobel which is anywhere close to the right values of R and C for real speakers on an amplifier schematic. Most are calculated for a resistive test load. Worse, the required Zobel changes from speaker to speaker.

Start making C7 larger and see what happens. Usually to match a speaker, the C has to be a few MFD and R has to be small, which means it has to be able to dissipate some power.
I see what I did wrong with the model. I inserted the tweeter inductance on the wrong side of my measuring point. The new sim doesn't have the sagging response but does show that the zobel is very important to keep the filter from peaking.
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