I'm not a speaker/cab expert, just know enough to be dangerous.
Have you had any luck with any searches with folks switching out the driver in the cab? Eminence may or may not have specific recommendations for your particular cab.
There are a series of specs for the Thiele small parameters, speakers with similar specs may or may not just drop in. The devil is in the details with smaller cabs that are expected to do big, bassy sounds. Typically, there are some key choices made for the cabinet size and port tuning. Disregarding the details can result in the speaker not having proper power handling, too much excursion, etc... that will destroy it.
If you have at least the internal dimensions for the cab, port size and depth, etc... you can then start finding the proper replacement speaker via plugging in the specs a couple different ways.
1. Via a speaker cab program, which has a cost for the convenience. This is just plug and go.
2. Via several speaker cab calculators found online for free, but will require some note taking. Being a cheapskate, an incessant tinkerer and seeing this as a learning experience, this is the route I took.
How did I get my dangerous level of knowledge? Two cabs.
The first was reloading my old 1968 Kustom TuckNRoll ported 2x12" with modern speakers for better tone and power handling. The original CTS speakers were shot, and extremely heavy. I had a Peavey 12" Scorpion, which I like for bass, and found a Hydrive 12" here on TB in the Classifieds. I just dropped the speakers in the cab, plugged it in, turned it up and it sounded great and there was no weird farting, etc... It also lost about 15 pounds with the new speakers. This one was somewhat lucky, I already knew that Scorpions were used in a wide variety of sealed and open back cabinets of various sizes, so it was most likely fine. The Hydrive speaker is used in ported cabs that were about 1/2-2/3ds the internal volume, so I just took a chance. Here we are a few years later with no issues.
The second is a homemade, closed back 1x12" cab that was purchased off of Craig'sList solely for the OEM Mesa EVM12L speaker that was in it. The speaker was destined for an older Mesa Mark IIA guitar combo that I have, but the cab was decently built, so I wanted to repurpose it. It didn't follow any specific build (like the famous TL806 design for 12" EVM as well as sounding great with other speakers), but the dimensions and such were in the ballpark for a nice 1x12" bass cab--external dimensions of 20.75"/53 cm wide x 16.5"/42cm high x 15.5"/40cm deep with an internal volume of 2.133 cubic feet/60.445 cubic liters. It had just a 3.5" vent hole cut out of the baffle, no real port. I tried just dropping another Scorpion in it, which worked fine for guitar, but it didn't work properly with bass. There was some farting on the low E and F. I do question the integrity of
that particular speaker, though. It may be half bagged or the cab in it's current configuration wasn't properly tuned for the Scorpion. Either way, it was determined that I wanted a more robust speaker anyway and looked into various other speakers and their Thiele specs.
There was a NOS Eminence Delta Pro 12A being sold for $40 on CraigsList by a pro audio company here in town. I already knew that it is a speaker designed for pro audio use-particularly monitor wedges--
hey, those are about the same size as this cab. However, it's also a popular choice for guitarists wanting an EVM type speaker. Looking at the specs on the website, and comparing to other guitar or bass specific speakers, it's specs looked good for my purposes. The cab's internal volume was right in the middle of the published vented enclosure volume range for the 12A. Plus, it's got pretty high power handling at 400W and since it's a small cab, the speaker being rather heavy (16lb/7kg) is not an issue.
I picked up the speaker and started doing a LOT of research on cab/port tuning for bass guitar (in regards to resonant frequency of the speaker and the like). Read a ton of articles and message board threads while plugging speaker and cab data into various calculators to see if the results were consistent. I finally came up with my specs (tuned the port
just barely above the 51Hz resonant frequency), ordered a proper sized port to get to my desired goal, put it together and plugged it in with my TC BH250 head. Turned it up and everything sounded great. It's a fat sounding extension guitar cab and smooth, punchy bass cab. Just what I was looking for. Here a couple years and a couple dozen gigs later, it's still going strong.
