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I haven't visited the audio asylum in what seems like a decade! Wow, almost forgot I had a membership.
I cam home with pair of pristine Electro-Voice Sentry IV-B from an estate sale last week. My current speakers are highly modified Klipsch LaScalas, so I know what I'm getting into. The speakers themselves are in great condition, one owner who left them in his basement for their entire lives.
The woofers have evidently been repaired at one point, as there was a service sticker form the shop on one of them. I presume he replaced the foam surrounds which, by all accounts, have a tendency to rot. These are all in good condition from what I could tell. Haven't actually taken the drivers off to inspect as they were pretty firmly stuck to the enclosure and I didn't want to break the seals.
I'd like to try a different compression driver in the SM120A horn and have a pair of Allen A-55-G which replaced the K55Vs in my LaScalas.
Can I use the 16ohm A-55-G in lieu of the 8ohm 1823M that are currently in the mid horn without altering the crossover?
Thanks
Follow Ups:
In the crossover diagram you posted - C2 and T1 is your "second order" filter. These values need to change for 16 ohm drivers.
R3 and R4 are a fixed L-pad for driver level. These values also need to be adjusted appropriately.
If you choose R3 and R4 appropriately, it looks to me like no other changes are needed. Unless I'm missing something?
I get R3=2.0 ohms, R4=10 ohms
Your John Allen A55G has a nominal impedance of 16 ohms. The measured DCR may be around 12 ohms.
My bad, the A55G is 12ohm rather than 16. In any case, I installed them and will have a listen this evening. Thanks all for responding!
Running a 12 Ohm driver on an 8 Ohm crossover is going to lower the X-over frequency of the driver, meaning the woofer and the mid driver will have some overlap, causing a hump in the response.
I calculated that you will need a 24 Ohm parallel resistor to bring it down to 8 Ohms.
Running a 12 Ohm driver on an 8 Ohm crossover is going to lower the X-over frequency of the driver if it's a first order high pass, ie., just a capacitor. With s higher order filter the transfer function is AFU.
nt
That would be the 'G' rated version.
P
Thanks for the response and calculations. Very helpful! Shouldn't be a very difficult fix to ensure that everything is running properly.
Besides lowering the x-over frequency to the driver, there are no other concerns about using the 12ohm in said x-over?
Crossovers are specific to the driver impedance, and if well designed they're specific to the drivers.
I use the couple SM120 + A55G as midrange in my system, and they are a fantastic match. I use mine from 500Hz to 6KHz.You need to modify your crossover in order to use 16ohms drivers... or maybe a simple 16ohms resistor in parallel with the diver would work? I'll let others chime in for a definite answer.
Edits: 02/23/21
That's exactly what I do with my Altec components.
The X-overs are for 8 Ohm drivers, but I have 16 Ohm drivers with an additional 16 Ohm resistor paralleled to maintain an 8 Ohm load at the X-over.
It's a simple way to get a little attenuation as well.
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