Empty Cabinets Find

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HomeBrewCabinet (2).JPG The wife and I were at a garage sale. These were found empty of drivers. Home made and built well. Made for a Single driver 12 inch. Boxes are 3.8 cubic ft.. Tuned with twin ports to 25.5 hz. Any one know what the drivers could have been tuned that low ? Thanks for any insight you may shed on the mystery drivers.
 

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It's not obvious from the pics, are you sure these are homemade? Back in the 1950s and early 60s, before speaker building was as much of a science as it is now, it wasn't uncommon to purchase a full range or 2-way coax driver and mount it in a pre-built (or kit-built) box. A long time ago I inherited a pair of cabinets like that (I no longer have them).

Also, wouldn't the box tuning depend on the driver mounted inside?
 
well, the resonant frequency of the box depends on the volume of the box and the volume of the port & can be calculated as such; it's a Helmholz resonator (like a jugband's jug).

helm_resonator_2.gif


https://people.seas.harvard.edu/~jones/cscie129/nu_lectures/lecture3 /ho_helmholtz/ho_helmholtz.html
 
This is where whomever built them marked for drilling. They could be manufactured enclosures. They are certainly worth the price paid.
 

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It was probably originally stuffed with something like a JBL D123. I doubt any 12" speaker was capable of going down to anywhere near the mid 20 hz range back when these were made.
 
The JBL D123 seems likely. There is only a hole for the wire in the back. No cut out for a tweeter adjustment knob. The person I bought them from got them at an estate sale. He bid on them and then found they were empty.
 
I installed terminals for speaker hook up. Cut down the Betsy's open baffle to fit the cabinets. Does not sound bad at all. I do not have the room for an open baffle system. Finally have a use for the Betsy speakers.
 

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My mission wasn't to correct you, just to post an example. ;)

In some of the early lit you'll find their resonant frequency spec'd @ 32hz which would make a 25 hz tuning seem reasonable although perhaps a bit optimistic.

From experience i would opine that 30hz is probably the 3db down point which suggests the still usable 10db down point is going to be somewhere down in the 20's. Like most of the classic Altec woofers, they roll off pretty smoothly in a favorable alignment, albeit a little more steeply than their 15 inch siblings.
 
Thanks for the information. The Betsy will work for now. I will keep an eye out for something more appropriate . My main speakers are the Altec Model 15 with 412c woofers. The Empty now filled with Betsy cabinets are for the wife. She can just flip on the Yamaha and listen. When I am really listening. I can switch off the Betsy and run the Crown PS200 and the Altecs.
 
This is a slow sweep about 1 foot from speaker center. Not bad till about 4,000 hz then a drop off. If I decide to add a tweeter and crossover, this is where it would start.
 

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Don't overlook the Bozaks coaxials (sort of) as a possibility, and an excellent one at that, though the porting would not be to Rudy's satisfaction at all.
 
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