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YL 75000 has heavy phase plug indeed ,  rca style (see sketch) while 1250 ( I never had one) gets a fixed metal dome equivalent  to spherical piece on 75000 and rca  plugs without conical shape pointing the exit of throat. Ironically the 1250 looks like simpler than rca style as cone is the same as every
driver we know, but throat on the oposite side like rca .




I made graphical work on this as i owned 55000 and 75000 then figured out how it could be designed. ALE P1260 looks like a big 75000 (phase plug included) .
May be Ale p160 works like  yl 1250 i suspect. P 1260 (3inch throat) crossed 80 hz while P160 (5inch Throat) goes down to horn low end.
On the other hand yl 1250 is 3inch throat(not 4inch as I said the post before)and ¡¡16 hz¡¡that is hard to believe (see the response graph)
Note the rear duct open but controlled by the cotton fiber(could be regulated)






About voice coil height I would say it gets deeper as driver grows in low end response.increasing from 5/7mm (55000) to 10/12mm (75000) reaching may be 20/25 if you look at previous phographs carefully, for YL1250. It makes a lot of sense. I always thougth that the few big drivers would work fine in midbass horn(say 80 hz).


My thoughts about low frequency drivers and how to do with it, is complicated question but i would relate things as the keys in order of influence:

1.-the suspension : diameter and length of it (excursion capability)
2-the cone diameter (response capability , efficiency at low freqs)
3-The throat diameter grows( to very low frecuencies a must be) 
4-the phase plug or abscence of it (can be only when very big diameter, but then pressure requires limitation of real throat.....so dome without conical shape is enough like yl1250,ale p160 but air exit must be reduced anyhow) as imposibility of say 15 inch driver with very light cone leads to direct radiator working as a driver(No phase plug or air exit reduction).

The driver vs direct radiator dilemma efinetly Is a matter of scale , materials , geometry.manufacturing. Always better a driver unit than direct radiator.......to the point it cant be done by "construction and materials limits" The question is to reach the limit. Seems to me that japanese guys went ahead everybody else on this , so ......let´s see.




 I will try soon the 75000 unit on 90 hz horn, but I dont trust much to be succesful.I belive that the bigger drivers (said to be 16/20Hz or whatever) will do fine at upper bass but not  the lowest end(not to mention the big horn "problem". 
There is some 1250like driver by Ale manufactured  time ago that could be an option as well. 


Eduardo, do you use or do you have listening experiences with YL1250 or with other compression bass divers?  If you can differentiate between bass tone and bass pressure then what is you feeling about the tonal capacity of compression bass divers?

As I said i never had one, so about low freq driver tone only can talk about Yl 55000 and 75000 on 200hz horn  and have to say that even
that horn alone , 6db say 500-2k, is tonally full, you can nearly forget rest of the channels.it pours low frequencies very very well but it is not bass, its upper bass, at best.
what I can feel ,though: this kind of drivers are capable of go down much more than what i have heard myself in 200 hz horn,for sure.That´s why i dont quit and will try
on 90 hz horn.I think it will work even lower than that and would be fine..... then how much lower? my thougts are that if it works to 90 80 60 hz it would be fantastic.


Regards

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