Filter/tweeter modification problem

[wdekler]

I've decided to upgrade my Elipson speakers with new scanspeak 2904 tweeters. The old scanspeak 2010 units have different electric parameters (of course) so a modification to the old filter was necessary.

As I'm not that good at electronics I went to a loudspeaker shop where an "expert" looked into it and proposed some modifications.

The new filter had to be adjusted for two parameters to get the new tweeter to play at the same volume level.

A new filter was drawn and it shown (together with the old one) in the attached picture.

The old tweeter has a DC resistance of 5.7ohm, the new one has 3ohm. So a 2.7ohm resistor has been added to bring the tweeter up to the same impedance (DC resitance on the spec sheets).

The new tweeter has a sensitivity of 94.5db and the old one 90db. So the new filter has two extra resistors to bring the volume down. I understood that this is a very common construction, I only know the dutch word for it: rendements aanpassing, I guess it's called something like sensitivity adjustment. The values for R1 and R2 were looked up in a printed table and he decided that 3,9 (R1) and 8.2 (R2) should be a good starting point.

Next he also decided that two parts were irrelevant (!) the 33ohm and the 0.47cap. could be removed... Strange!

So last night we built the new filter and listened to it at a low volume for a short time. Well, as the subject says... it wasn't good at all. The high tones were muted and the tweeter clearly also got frequencies which where really way to low...

After thinking it through we came up with 3 possible causes:

1) This filter is connected via a cable to another filter which is used for the mid. modifying the tweeter also has consequences for this part.

2) The values for R1 and R2 seem to be VERY wrong. I've checked the table myself and a value of 2.2 and 10 should be WAY better.

3) The 33ohm resistor and the 0.47cap are relevant to the filter and should be re-applied to the new filter.

4) Is there another thing we overlooked?

I hope that someone can help me out here....

- adjusting R1 and R2 seems like a very good idea to me, but can this explain the wrong frequencies of the new filter or only the volume?

- Insert the 33ohm and 0.47cap back into the filter because they are relevant? Are they needed to get the filter working again? Do they explain the wrong frequencies? Where should I place it, before R1 R2?

- I really hope that I don't need to adjust the filter of the mid...

Any help is very much appreciated!

thanks!

Wanne.

[wdekler]

I left something out in the text and I've correct an error in the drawing.

The dealer left out 3 items not 2.

It's not only the .47cap & 8.2 ohm resistor but also the 33ohm resistor in front of the 0.22mh

This was clear from the drawing I made, but, the values of the 33 and 8.2 resistors were swapped

I've updated and included the correct schematics.