After getting a prototype crossover working pretty well I spent some time listening to the speaker. The purpose was to see if the LPG38T midrange worked well as a tweeter for the system. The conclusion - a resounding NO. Here's a chart of the frequency response with the crossover.

This chart is smoothed 1/16 octave just to remove some of the "fuzzies". Also this response is inaccurate below about 400Hz due to room effects. Still, as you can see it's not a bad response chart (other than minimal high end response due to the midrange and a broad dip at 3KHz). It's +-3dB through the range, but with listening tests it became clear that the LPG was ringing badly in the mid-tweeter area. I listened to a cut with lots of Irish Harp on it - the first cut on Narada's Celtic Odyssey CD [Carolan's Ramble to Cashel by Northern Lights]. Every time the harp string was plucked the tweeter rang noticeably. [Note: In retrospect I may be too harsh here; I had changed the crossover and taken out some of the circuit that compensated for the resonant hump - so I may have been feeding too much energy to the tweeter near its resonance - but I don't think that was it].

If you look at the impedance chart for the LPG you see a noticeable hump at around 1.5KHz. This is an undamped resonance (perhaps not enough ferrofluid).

For comparison I have two speaker systems I built in the last few years. Both were written up in Speaker Builder magazine. The first system is my computer speakers (two vifa drivers with bucking magnets) and the second is a pair of speakers I slaved over for two years using LEAP (a sine wave system) and manual crossover evaluation. The second system uses a Focal woofer and a dynaudio tweeter and a very hand-tuned crossover. The current prototype took me about 1 hour of proto and listening using Speaker Workshop - which is why Speaker Workshop was created.

In any case, I've decided to switch to my favorite tweeter, a Vifa D25AG-35. This is a 1" aluminum tweeter with a phase ring. I spent about 30 minutes building a simple crossover for the tweeter (written up on the following pages) and it sounded great by comparison. It's too bad but out with the old and in with the new. The picture of the tweeter is in the upper left of this page.

At this point, it will be some time before the project continues because the next step is to build the final enclosures and then retest everything and carefully do the crossover. Until then...