Aurum Cantus AC120/50CK Enclosure

[joekool]

Hey guys,

Working on replacing / upgrading the midrange drivers in my Cerwin Vega D9's. The AC120/50CK's fit perfectly in the cabinet and have a decent frequency range as a mid. The issue is they are not sealed backs. I think I have a plan to create enclosures inside the cabinet, but I want to make sure I am not missing the boat.

I have some 5" diameter cardboard tubes (heavy duty). I believe I can cut these to the right length to get the right volume, cap the ends, and then glue them to the inside of the cabinet, thus creating my sealed mids. What I am unsure of is exactly what length to make these tubes.

Vas = 0.42 ft(3) fs = 43 Qts = 0.18 If using a Qtc of 0.707, it seems the volume needs to be 0.03 ft(3) or 51.84 in(3). for a f3 and fb of ~168 Hz

I assume the displacement of the driver would be around 40 in(3), do I need to add this to the tube volume for a total of 90 in(3) ?

If I am calculating this right, tube length will be around 4.625".

The crossover point between the woofer and mid is ~ 333.

Am I on the right track?

Joe

[joekool]

I would not say anything is "wrong" with them. I bought the D9's back in 1986, and they have been sitting in my basement for the last 10 years. Last summer I decided to pull them out. Man, they were not in good shape so I decided to rehab them. Once I got started I was all in.

To be honest, I was never super happy how these sounded. They are loud and OK, but not quite what you want when you fast forward 35 years and sit back with a glass of bourbon and try to listen to some Pink Floyd.

So, like a lot of people, during the pandemic I decided to take on a project, I wanted to try and make these D9's "better". I have been working on redesigning the crossover, I have a pair of Morel 338's, 2 pair of the AC120/50CK's. The woofers have been reconed. I bought some testing gear to see what these drivers are really doing, bought a copy of X-Over Pro, and quite frankly am having a lot of fun. I have learned a lot, read a lot, and done lots of trial and error.

The self imposed rules of this project have been, replace anything, but dont damage the cabinet to the point where I cant put the original parts back in.

Anyways, I think I am pretty close to what I am looking for, I am only working on one cabinet so I can compare to the original. But I truly believe I need to seal those mids as I am certain I am getting distortion for the woofer.

I am going to have some more questions real soon, I am sure.

Ohh, and yes, I know I would probably be better off if I had just started fresh from scratch..........

Joe

[Billet]

I think you are on the right track by having the enclosed midrange driver Fs around 2x lower than your planned crossover point. That should give some "distance" above the resonant frequency and hopefully it will not be too noticeable. I wouldn't go any smaller...

[djg]

I deleted an earlier comment, kind of snarky. I looked at the D9, I would change the tweeter also. You might end up with a very nice speaker.

[Chris Roemer]

Your logic (and use of maybe WinISD?) seems sound, but ...
I've seen SOME AC drivers measure W-A-A-Y different from the mfr's claims.
One guy here on PETT measured some of those drivers and got a Qts much closer to .50 (than 0.18), w/an Fs around 55Hz, and a Vas near 0.34 cu.ft.
THOSE specs would multiply your cab volume by over 10 times ! ??

Do you have any way to measure the T/S parms of YOUR actual drivers?
Also, I'd plan on stuffing any mid cab used this way w/either polyfill or fiberglass.