tweeter selection for D'Appolito M-T-M

[reynolds532]

I plan on building my second set of speakers. First pair was 25 yrs ago with bass port tuning and crossover done all by ear, no science--funny process for an engineer like me. This year I'm going to build an inexpensive pair of d'Appolito Midwoofer-Tweeter-Midwoofer speakers using the recommended 12 db/octave crossover at 2500 hz and the 2 4-ohm midwoofers in series. Any advice on tweeter selection? I'm leaning toward a pair of 1" silk domes--Northcreek d25-065, $36/pair. I think that the -1.5 db shelf from 1.5 K to 3 K is marketing crap, but the North Creeks do appear on paper to be a good value. Is there a better tweeter option for <$50/pair?

Are their any issues with putting 2 4 ohm midwoofers in series for 8 ohm? I picked up 4 Isophon's P170/30 cheap (<$10 each delivered) on Ebay.

If this project works well, I'll build some higher end speakers. If it's crap I'm only out $100.

[kexodusc]

The North Creek tweeter is the same on I have in one of my speaker models...the PeeCreek from speakerbuilder.net.
It is a very competent little tweeter for the price. I find it's a little on the bright side, and not as detailed or smooth as the Peerless 812687 used in another set of speakers I have (ar.com DIY's), but it is more money ($20 each from parts express) but that could be an unfair comparison since the crossovers are different.

Normally, I'd recommend you build an existing speaker design (there's hundreds out there) but since you already have the drivers, go for it!

The xo point on my PeeCreeks is 2 kHz, but it's a 4th order slope, which made it an easier blend with the choice of woofer (Peerless 850122).

I'd have to see some parameters on the Isophon woofers you have to recommend a better tweeter, and really, you'd probably be better off to reconsider using a "stock" crossover at 2500 Hz, the woofer may have some peaks or dips that makes that a bit impractical...you can probably get away with it.

The boys at the parts express forum are far more competent in this stuff than I am though, I'd advise you to look over there for some better advice from some amazing DIY nuts.

[reynolds532]

I plan to mount the crossovers externally. I'll start with the Isophon recommendation and modify with filters and attenuators or even change the order if I don't get the sound I want. I prefer to get flat Freq response from the drivers so that a simple crossover will work and I won't have to apply fixes, but if anyone ever invented the perfect driver it would take the fun out of this.

From what I've read the Isophons have a flat FR and a flat impendence curve up to 6000 hz, so the recommended crossover should be good. Now I need a tweeter with good dispersion, a flat response down to at least 1250 hz (1 octave below crossover), and a flat impedence curve. The impedence curve is the easiest thing to fix, and the dispersion is the hardest, so my priorities for tweeter selection are 1. dispersion. 2. FR. 3. impedence curve.