Should I bother bringing these back to life? - diyAudio
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Old 14th March 2009, 03:10 AM   #1
lowpoke is offline lowpoke  Australia
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Default Should I bother bringing these back to life?

I've inherited some vintage PA cabinets my father (who was a violinist) had custom made in the 1970's. Each cabinet houses a 12" JBL K120 and an RCF TW25 horn tweeter.

I know the K120's are popular with guitarists and are a well respected driver. Although I can't find much info on the horns, RCF seem to make a respectable product and like JBL, have been at it for many years.

So I'm wondering whether I could repurpose these for use in my home set up by building new cabinets that will give me a little more frequency response in the lower end. I understand this might involve fairly large cabinets, but my wife's been looking at these beat up relics in our living room for a few years now, so anything would be an improvement in her eyes.

Any help or suggestions would be appreciated.
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Old 14th March 2009, 05:30 PM   #2
lowpoke is offline lowpoke  Australia
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OK, so I've had a little look around on the Lansing Heritage forum and found the Thiele Small parameters for the K120 as follows:

FS; 50
QTS; 0.2
QMS; 4
QES; 0.21
VAS; 121.8
EFF; 6.9
PE; 100
XMAX; 1.52
RE; 6.3
LE; 0.6
SD; 0.053
BI; 18
MMS; 35
FLUX; 1.2

I don't understand any of this, so need some assistance. From what I read over there, this driver's not really ideal in the hi fi environment, instead being more at home in a guitar amp.
Would some sort of folded horn enclosure assist in beefing up the bass response or will it all be in vain? I'm no expert in this area and need some feedback from those in the know. I did like the idea of using my father's equipment, but not at the expense of achieving a decent result.
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Old 14th March 2009, 06:40 PM   #3
badman is offline badman  United States
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A good start would be to model that driver in various enclosures via program like winisd. That'll let you play with box size and tuning. Older AlNiCo drivers don't necessarily have the same Thiele-Smalls as when new, but that's a little harder to test. Your project really could use some measurement and expertise, you're starting with what seem like decent drivers.

Any forumites near this fellow?
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Old 14th March 2009, 06:47 PM   #4
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Default Suitable??

Lowpoke:
Ran some numbers thru the calculator with your TS parameters & found..Yeah its' not looking good. The EBP (Efficiency Bandwidth Product) is WAY up there at Appx. 238....this value should "ideally" be at 50-100 for a ported enclosure. A sealed system should be shy of 50..
So it really isn't for Hi-fi. However......it might be doable for a mid-range driver. It would need some brainstorming for a crossover, but I think it would fit in OK . Finding a driver for the bottom end once you decipher(sp?) your cross-over should fall into place.
Do you have some SPL ratings for this driver? Need some F range & SPLs' for the horn too.
Check out www.partsexpress.com. of the "pro-sound" drivers at 15" will probably do OK for this project.
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Old 15th March 2009, 12:37 PM   #5
lowpoke is offline lowpoke  Australia
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Hey guys,

Thanks for your input so far. It looks like trying to make this work well could be being a little ambitious. I need to do some more reading!
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