Matching driver with vintage BLH
;y question is that can I find out from just the impedance curves how the horn and driver is matching or i frequency measurements and listening that is needed?
I have this set of drivers (and two more not shown)
And this horn. The horn is built in 20mm/ 3/4" soft board and then covered with chipboard. I crawled into the horn (partly) and knocked/tapped at the various internal baffles, they do ring but is is high in pitch.
The horn is flat on its back and the legs up against a wall in a corner. It is so practical when testing many drivers to just let gravity seal the rubber gasket. The Beyma, Fane and Isophon had to be revers mounted with the magnet facing out as the Fane and Beyma had larger chassis diameter than the other ones and the Isophon has to be rear mounted.
The "general wisdom" is that you should use high Fr low Q driver with that horn...
To not inundate you with graphs I have piled them together.
First row is drivers with a Fr of about 30 Hz and a Q of 0.3-0.4
Note that the first peak is larger than the other two major peaks. The first impedance dip is at 35 Hz
Gamma LA1231 and Philips AD12250
Second row is drivers with a Fr of about 50-60 Hz and a Q of 0.4-0.6
Note that the first peak is about the same size as the other two major peaks. The first impedance dip is at 40 Hz
Two vintage drivers Seas 30FA and Isophon 30/37A and two PA drivers and older Fane Cresendo and a modern Eminence Delta 12A driver.
Third row is drivers with a Fr of about above 60 Hz Hz and a Q of 0.3
Note that the first peak is smaller than the other two major peaks. The second peak has a double peak not present on the other drivers. The second The first impedance dip is at 45 Hz
I've buit a couple of these 1972 using the 'Klinger' book I still possess.
The horn has a cut-off at ~35 Hz and was meant for a 12" driver(here 28 cm baffle cutout= membrane diameter) I used the very first 12" Gamma LA1231? drivers that were found found at HiFi-Kit.You could easily simulate the Horn in HR or AKAback if you put in some DIY effort.:D..Or consult: Linnar at:
I'm not sure if he have done work on this design..
I believe that Gammas first driver in Sweden was called BK 3011, alnico magnet and gray chassi as opposed to the later LA 1231 and 1232 that had black chassis and later also switched to ceramic magnets.
In red measuring best and sounding best on the NAD test record is the Beyma, I was surprised that a 80 Hz Qes= 0.3 had the deepest bass.
In yellow is the Fane, Isophon 30/37A and Eminence
In black the Philips and Gamma
I was surprised that the measured differences were so small. It sounded good but did not have the slam of Kuben.
Response in horn mouth using Omnimic. This is my very first run of measurements with Omnimic so there is much more to find out on how to use and tweak the system
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