Decent midrange driver 250...1500 Hz

Ehhh, did you check the specs? And have you been able to compare it to any other system fairly? I can accept taste as a criterium, but fail to see the connection with your starting post.

Anyway, a lot of important things have been mentioned, I only could add that the Fane and Eminence drivers you picked are quite regular PA drivers, not specific for studio monitors and I'd search a bit further. For the mid, since nobody else took the trouble, I advice you to check out the 18Sound 6ND430. That unit (still) is a no-brainer, even compared to much more expensive hi-fi drivers.
 
Hi
These options I have in mind so far the horn:
B&C ME45
P.Audio PH-2370
P.Audio PH-4220
Fane FH.450
Eminence H290s
Exponentials, 90x40°. Somehow, I don't like the sharp edges of CD horns.
My ceiling is quite low, 2.3m, so I'm afraid of the top side reflection. Reason for going at 40° vertical dispersion.

I would not worry too much about your ceiling height. I have 2.4m ceilings, not that different from your 2.3 m ceilings, and over the years I have abandoned each and every tweeter with a limited vertical dispersion because they all sounded unnatural to my ears. I have tried many horns, Raal Ribbons, Beyma AMT's ESS AMT's and Raven Ribbons and abandoned them all because of this. At the moment I'm using a pair of B&C DE250 on RCF H100 constant directivity horns that don't have any sharp edges. These have 75 degrees vertical dispersion with sound much more natural, better sound stage, better integration with mids than any 40 or 60 vertical degrees horn I have ever had. Trying to limit ceiling reflection is a good goal but driver integration is a much more important factor and that is pretty hard to do with vertical limited tweeters in a home environment.
 
I think a coaxial compression driver (BMS) solves all problems:

1) Three-way fidelity
2) Two-way size (for short ceilings).
3) Easy dispersion matching to LF with similar sized horn.
4) Mid / High time alignment already taken care of inside the compression driver.
5) Money spent is worth it as we get: good SQ, less effort and time taken to bring up.
 
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Are you really sure about the 4) item ? It probably asks some passive or active crossover care for time alignment according the cut-off point and slope, no? Have someone already share impulse response of such a BMS coax ? (it has an awesome reputation btw)


I don't remember but some had good result with the BMS into a 18THSounds horn ? There was some hype as well about the Faital coaxs !
 
At the moment I'm using a pair of B&C DE250 on RCF H100 constant directivity horns that don't have any sharp edges. These have 75 degrees vertical dispersion with sound much more natural, better sound stage, better integration with mids than any 40 or 60 vertical degrees horn I have ever had. Trying to limit ceiling reflection is a good goal but driver integration is a much more important factor and that is pretty hard to do with vertical limited tweeters in a home environment.
Thanks Sjef, the 90x75 horn could be a better compromise towards the mid. I'll keep searching. If too reflecting, I could lay a diffusor panel on ceiling.

About coaxials, I'm not a fan, as they can suffer from Doppler effects and surely no time alignment. In my youth I built many budget systems with car audio speakers.
 
About coaxials, I'm not a fan, as they can suffer from Doppler effects and surely no time alignment.

Note that the tweeter diaphragm is actually behind the midrange in this *coaxial:
BMS 4594 Compression Driver How It Works - YouTube

*and remember, this is a coaxial compression driver, not a typical tweeter in front of a midrange car-type.

..still, coax. compression drivers are expensive. 😱

(..and without a VERY large horn, won't get you anywhere near 250 Hz. ..and it's particularly for this reason I think that this is not a good solution for the intended purpose.)
 
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That's alright but what is the thickness of a diaphragm anyway, I mean the error in time alignment due to the thickness of the mid diaphragm ?

And Doppler effect in a compression driver with two diaphragms, with the excursions of each being less than 1mm ? I think something's not right and there's some confusion here.

Regarding pattern matching, I think the OP can definitely match HF horn pattern with a 6-8" midrange at 2-2.5 kHz and in turn, match it with the LF (around 250Hz) where pattern itself may not matter a lot.

Without a VERY large horn, won't get you anywhere near 250 Hz.

250Hz is a bit greedy and also results in an under-utilised LF. An 18" (deep) horn may however still get to 400Hz with an LR24 crossover.
 
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A quote from the BMS datasheet..
Perfect Time Alignment without Problems of Multi-Source Interference
Here they have tacked together two factors, presumably to make an inference but to actually comment on their application rather than the absolutes.. does it say they are actually time aligned?

In reality it may not be the problem it seems, we can align by adjusting the phase of the signal in. But while we know that, some people really want to see the words "time aligned" written somewhere.
 
I wouldn't know why they would not align the mid and high driver. The motors are both on the outside, it's only a matter of moving the diaphragms closer to or further from each other and shaping the compression channels. A lot of other coaxes (Tannoy e.g.) have the problem that the motors are back to back and one has to account for the different acoustic centers.
 
Maybe what they actually mean is that the diaphragms are physically aligned, which if everything else is OK, would translate to "time aligned".

This is a coaxial compression driver, not a typical tweeter in front of a midrange car-type.

Yes, the OP seems to be confusing the BMS with coaxial car speakers. The Doppler part of it also seems to make sense now.
 
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