Vendor guidelines - Vifa:

1. TD19AD-05-06, a 3/4" (19 mm.) aluminum dome tweeter. One of only a few 3/4" tweeters which made the list. This unit features exemplary FR from 3 kHz to past 20 kHz.  response   waterfall 
2. TD25AG-35-06 aluminum dome tweeter. One respondent commented that he'd never heard a Vifa metal dome tweeter that he didn't like. At under $30, this is a great value.  view   response   waterfall 
3. TD25ASG-05-06 aluminum dome tweeter. This is a shielded cousin of the D25AG-35-06 listed above. Because of the physical requirements of magnetic shielding, this driver is based on the "05" version rather than the "35" version, indicating a higher resonant frequency. It's still an excellent unit.
4. TD27TG series fabric dome tweeters. Ruler flat passband response combined with textbook-perfect LF roll off. All under $25, These units come in five variants:
    view D27TG05   view D27TG35 
   1. The D27TG-05-06 and D27TG-15-06 feature a 1 kHz resonance which improves the FR flatness in the passband. Since none of the D27TG series tweeters should really be crossed over below 2 kHz, this isn't particularly significant.
   2. The D27TG-35-06 and D27TG-45-06 spec a lower 650 Hz resonance, which should make crossover design less critical.

      Warning! My respondents tell me that the Fs of current production units consistently measures around 850-950 Hz. The difference is enough to require a completely different crossover design. These units are therefore only conditionally recommended!

   3. The D27TG-15-06 and D27TG-45-06 feature a slightly bulged face plate which provides subtle pseudo-horn loading. This doesn't improve the sensitivity or effect off-axis response, but it can help control diffraction effects.
   4. The D27TG-05-06 and D27T-35-06 feature a flat face plate.
   5. The D27SG-05-06 is a shielded version of the 1 kHz Fs design.

5. XT25TG30-04 tweeter featuring a "dual-concentric" fabric diaphragm, resembling a ring radiator with a phase plug. This is a fairly new entry which has been receiving rave reviews and several significant design-in's in high end systems. Respondents who've heard it and measured it tell me its distortion numbers could be lower and that it likes a high crossover frequency, more suited to a 3-way than a 2-way design.  view   response 
6. DX25TG05-04 fabric dome tweeter. This is an excellent unit which has been available for several years only to Vifa's OEM customers. Recently, these began making their way into the DIY market. Featuring high sensitivity, a low Fs, and roust construction, it's easy to see why the DX25 was an OEM favorite.  view   response 
7. M10MD-39-08, a 4" (13 cm.) paper cone midrange. One of Vifa's least glamorous drivers, it represents solid value in an excellent midrange. Used in many OEM designs, it's also available with an isolation cup enclosure from Human Speakers as the PRO 054.  view   response 
8. P13WH-00-08, a 5" (13 cm.) PP cone mid/bass. This driver is used in the popular Ariel and many other highly regarded DIY projects. Its ruler-flat passband response and well-controlled roll off have led many DIY'ers to declare this to be the finest midrange driver in existence.  view   response   step   waterfall 
9. P17SJ-00-08, a 6.5" (17 cm.) PP cone shielded mid/bass. Ideal for center- channel horizontal D'Appolito designs.
10. P17WJ-00-08, a 6.5" (17 cm.) PP cone mid/bass. Similar to the P17SJ, this unshielded driver features a larger diameter VC and slightly greater Xmax.  view 
11. P21WO-20-08, an 8" (21 cm.) PP cone woofer. There seems to be a consensus that his is the best of Vifa's 8" woofers. It has good, well-behaved extension on both sides of its passband.  view 
12. M26WR-09-08, a 10" (26 cm.) woofer. This driver does almost everything that can be asked of a 10" woofer. Its sole drawback is its untreated paper cone, which may cause longevity problems in some climates.  view