Crossover thoughts?

[saildoctor]

Hi folks - I'm using some Tekton 8.1's in my system which were built with Fostex FE207e full range drivers plus T-90a 'supertweeters'.  They're monitor style cabinets which measure 10.5"x17.5" and they're 13.5" but i don't know the internal volume.  It came with a crossover built on the inside - I know some basics of crossover design like the concept of BSC and whatnot, but I'm no expert.  I upgraded the resistors inside to mills non-inductive type and the caps to Obligatto gold film.  Any thoughts on possible improvements?  The inductor looks like one of those available at Madisound - no label on them so I don't know their value.  Do you think it's inclusion very necessary?  At the very least I'd like to upgrade it to something a little nicer.  

[Paul Joppa]

Use a cliplead (pack of 10, cheap, at Radio Shack. Millions of uses!) to short out the inductor and listen, to see if it's worthwhile to you.

[earwaxxer]

Hi Kerry - I dont blame you for wanting to hack around in the crossovers! I have got mucho satisfaction from the same. In the case of the maggies, they are a two way design that I feel were not being well utilized by the el-cheapo crossovers that were used by Magnepan. I ended up taking the inductor out all together. I kind of ended up doing that in stages. I first crossed the inductor over higher than stock, and went to a much higher quality air coil. In the end I removed it and did not find that the bass panel produced much in the mids/highs anyway. What made a bigger difference was in the caps. I also tried the obligatto golds. Great price in high values. Not as good IMO with the plannars as the paper/silver/oils. What was interesting was that I ended up finding I could cross the tweeter ribbon over lower to dip down more into the vocal ranges. Much better sound overall. Now I have a 22uF cap combo crossing my tweeter down to about 1700Hz.

Now I doubt your super-tweeter will enjoy going that low! You can mix and match to your driver specs. Here is a good cap/inductor calculator site to give you an idea about what you are doing. If you are talking low value caps I would look at Mundorf. My personal favorite is the silver/oil. If you cant afford them, go with a good paper/oil (AmpOhm). I have (2) 10uF AmpOhm paper/oils bypassed with a Mundorf 2.2uF silver/oil - in parallel for a total of 22uF for each tweeter. That combo sounded much better than the 22uF Obligatto (larger soundstage, better resolution, bigger more 'analog' sound). I will say that if I had the money I would probably straight away go with the high end Mundorfs!

Enjoy - Eric

[earwaxxer]

sorry I forgot to attach the address for the calculator!

http://www.bcae1.com/passxovr.htm

[saildoctor]

Thanks for the input guys. I've been really busy lately so not much time to experiment.  Im not sure how i should calculate the t-90's LF cutoff caused by the cap. Is the resistance I should use the series and parallel sum of the two resistors with the 8ohms of the speaker?

[earwaxxer]

Hey Kerry - I dont use resistors in the tweeter crossover just the cap(s). So calculate using 8ohms. You can experiment a bit with different cap values depending on your tweeter. I found that my maggie pseudo ribbon can be crossed over lower than they were from the factory. You could also damage the tweeter from crossing it over too low though. Dont worry, have fun. 'Danger Will Robinson'!

Eric

[saildoctor]

Right - I'm open to redoing the crossovers but I would like to first determine what the current cutoff to the supertweets is.  I may try putting the T-90a on its own L-pad and cap and remove the inductor and zobel/BSC? off the 207e.

[earwaxxer]

It seems you can start by removing the inductor since it blocks high frequencies to your woofer/mid. If the mids highs are muddied up then you need the inductor. I'm not sure why resistors are needed/used in crossovers at all! They dont sound as good as caps and certainly not as good as nothing at all. You have to use a cap on the tweets. Especially supper tweets. A necessary evil unless you go to an active crossover (another heated topic). Some swear to bi or tri-amping with actives. I dont. Its too complicated and I cant tell where problem lies. Control freak? Definitely.

[Grainger49]

Looking at Madisound and the spec sheet:  http://www.madisound.com/loudspeaker_specifications/t90arev.pdf

The suggested wiring is a high pass to the super tweeter and no roll off for the woofer.  In your crossover the 20 ohm and 5.6 ohm resistors are there for level matching.  That would take place of the "attenuator" in the Madisound schematic.  

I would not filter the signal to the full range driver, just augment it with the T90A.  If the highs are too much just use a very small, under an ohm, non inductive series resistor to pad the tweeter down.