Zaph SR71, with Aluminium or Excel Tweeter?

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Hi there, I'm new to the forum, and French so all apologies if my English is not perfect.
Well, I'm thinking about building a pair of Zaph's SR71 in a 18L cabinet, but switching the TDFC tweeter for the higher range TDFC/G (aluminum) or even for the Excel Millenium one (T28CF002). It seems they share similar characteristics to the TDFC.
The millenium got very good reviews everywhere, and seems to perform better than the TDFC in every point except for the sensitivity (89dB/W vs. 90 dB/W) but apparently it can easily be compensated by lowering the corresponding resistor on the tweeter x-over section. Especially, the millenium has a much better off-axis response. The TDFC/G doesn't have the bump at the end of the response curve, although it has a big one around 26kHz: would you think that bump at high frequencies might be responsible for listening fatigue? It has a big advantage over the TDFC: its hexagrid protecting the tweeter from the too curious small fingers...
It would be my first DIY loudspeaker kit, my initial budget was more around 1000$, but I was hooked when I read reviews of the SR71 and when I watched a video on utube comparing them to the Bifrost (surprisingly I liked the SR71 better, they sound more organic).
What do you think about it?
As you are inexperienced in speaker DIY I would strongly suggest to build the SR71 exactly as they are designed. That means same drivers, same values for crossover components, same baffle and same volume for the enclosure. If you want to modify something, on the Zaph site you'll find some options for reduced BSC,tweeter level, tweeter offset and others.

If you want to change tweeter, the TBFC/G is IMHO in the same range as the TDFC, i.e. both really good value for money. From the Seas data they seems to have similar impedance and frequency response graphs (but not equal), so switching an optimized design for a TDFC with a TBFC/G would surely require some (probably) small changes in the crossover. You are totally on your own on that, you need good ears and/or measurement equipment.

As per the millennium tweeter, I wouldn't change the TDFC with that. As it is designed the SR71 is a balanced speaker, IMHO there is no sense in using a tweeter costing more than double the woofer. And the data on Zaph site show that the millennium has higher harmonic distortion that both the TDFC and TBFC/G.

The spike at 26KHz of the TBFC/G is the breakup of the metal dome. It does propagate down in frequency as harmonics but they are very down in level, so I wouldn't bother. In fact the TBFC/G is one of the best tweeter in regards of harmonic distortion.


PS comparing speaker on a tube video doesn't make any sense.
I used the aluminum dome of the same series on my version of the SR71. It gave a nice bit of additional detail. When all was completed, the crossover wound up back to his original values. I did add a felt ring from Madisound, and the box has 3/4 radius on all 12 edges. Without those too mods, it was way too bright. It did not need any notch for the breakup. Hey, this is the third speaker ever, first of mine, that passed my wife's super sensitive hearing. Only the Sequal and 2Ce passed in the store. The distortion of the tweeter is that good.

I will caution you on the SR71. It seems to be sensitive to the baffle. Build it exactly the way John says. People who have changed the baffle or not done sufficient radius are very unhappy. I love mine. I intend to use the same woofer next time, but with the HDS tweeter. I also wrapped the port with dynamat.

BTW, I used the fabric tweeters to upgrade some Vifa D27's in another set with Dayton 140's. Much nicer. It is a very good tweeter too.
I agree with SP. Besides, when you change something, it is not a Zaph SR-71. I don't claim mine are. Studying his crossover and its relationships with the drivers,and the sensitivity of the baffle is a worthwhile exercise. You can learn something. I started with his design, and made decisions that suited me. I do some things in my box construction he does not I feel offer additional benefits. These were not my first, by about 30 years.

The ZRT is a lot larger box, and a lot more money. I also agree that u-tube is not the way to evaluate speakers. But, this is DIY. Most of us are not just after a good speaker, as it is a lot easier to go buy one you can hear first. I bought the SR71 parts kit because I had already selected those drivers and worked up an almost identical crossover. I was comparing a number of tweeters in this project. The mid range Seas are very good. I think the HDS is better. Someday I'll work up to an Revealator, OM1 or Excel. OM1 needs a midrange though.
I used the ER18RNX with the TBFC/G tweeter, a good analytical combo, but I used 24L tuned to the mid 40s & still wanted more bass. However, I didn't use any BSC in the crossover.(have a look at Mark K's version, slightly better crossover than Zaph's)
For smaller bookshelf speakers, perhaps the SB 5" would be more suitable:
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