MtnBob Posted April 9, 2005 Report Share Posted April 9, 2005 I picked up a pair of 48Bs today at the thrift store for $5. Of course the foam surrounds on the woofers was shot. (Actually I'm assuming here, since only one had woofer remains in it.)I'm just looking to use these as shop speakers anyway, since I figure it would be too expensive to restore them. So, does anyone know where I might find the T/s parameters on the originals so I could find suitable replacements?Just in case, here's what is on the woofer carcase:200040-0561 8429Made in the USATIAMB Link to comment Share on other sites More sharing options...
Guest bocoogto Posted April 10, 2005 Report Share Posted April 10, 2005 It would be much cheaper to refoam the woofers than to replace them. Why not do that? If you do it yourself, less than $25 total. If you have it done, about $50. Link to comment Share on other sites More sharing options...
MtnBob Posted April 10, 2005 Author Report Share Posted April 10, 2005 Guess I didn't make it clear in my post, there's only one woofer, so I would have to buy another one. Pretty sure that's not cost effective for some shop speakers.I realize that not restoring them is heretical to an AR lover, but I just want to get some decent sound out of them on a limited budget.Anyone wonder why manufacters don't give any info with the speakers, or label the drivers? Seems like their attitude is "Hey, these will last forever, if they don't, junk 'em and buy new ones."Surely AR knew those foam surrounds would crap out in a few years, and it's not like that was their only choice - My KLH 20s that I bought in '69 are still going strong.MB Link to comment Share on other sites More sharing options...
tysontom Posted April 11, 2005 Report Share Posted April 11, 2005 >Guess I didn't make it clear in my post, there's only one>woofer, so I would have to buy another one. Pretty sure that's>not cost effective for some shop speakers.>I realize that not restoring them is heretical to an AR lover,>but I just want to get some decent sound out of them on a>limited budget.>Anyone wonder why manufacters don't give any info with the>speakers, or label the drivers? Seems like their attitude is>"Hey, these will last forever, if they don't, junk 'em and buy>new ones.">Surely AR knew those foam surrounds would crap out in a few>years, and it's not like that was their only choice - My KLH>20s that I bought in '69 are still going strong.>>MBDear MB,First of all, the AR-48Bs were very good speakers. No one here says that you have to restore them to their original glory, and it is certainly not heresy to “modify” an AR speaker, contrary to popular belief. Yes, AR historians and purists (myself included) bemoan the thought of modifying one of the classic ARs such as the AR-3a, AR-LST, AR-9 and so forth, but no one cares in the least what you do to your own speakers. The AR-48 was not considered one of the classics anyway, so even the purists won’t mind if you go in and change it. AR did not intentionally deceive people about the half-life of the urethane-foam surrounds, as you suggest. After 1968 virtually all speaker manufacturers began to use the foam surrounds without the knowledge that they would oxidize as quickly as they did (10-17 years on average). Your KLH 20s, incidentally, didn’t use foam surrounds anyway, but an impregnated cloth surround much like the early AR speakers. These surrounds do go bad, but they do not oxidize, crumble and disintegrate like the foam versions; on the other hand, the cloth surrounds can introduce noises of their own, leak air and have greater distortion than their urethane-foam counterparts. Cloth surrounds do little to dampen unwanted oscillations down the cone at higher frequencies as in the case of the foam surrounds. These are all trade-offs, but the foam surrounds gave superior performance in every respect except longevity.The 10-inch woofer used in the AR-48 has a free-air resonance (fs) of 26 Hz, +/-15%, and mounted in the 1.3 cu. ft. AR-48 enclosure, a system resonance (fc) of approximately 52-55 Hz., and the crossover frequency was around 400 Hz, fairly low for a 10-inch woofer. Sensitivity was 87 dB. The Qtc for this speaker was 1.15, I believe. The Xmas is approximately 3/8-inches, but I do not know the Vas, Sd, Cas or other parameters of this woofer, as none of this was published or made public. Virtually no manufacturer publishes all that information except for the raw-driver purveyors. Therefore, if you search for a generic 10-inch acoustic-suspension woofer with those approximate characteristics, it would probably work with some experimenting with the speaker stuffing material to “optimize” the resonance peak. The other parameters were not published, but are found on factory blue-line drawings and so forth. Some individuals, such as Pete B and others on this forum, might help you select an appropriate woofer (you might consider replacing both woofers at the same time), and you could purchase such a woofer through partsexpress, below:http://www.partsexpress.com/index.cfm?did=7--Tom Tyson Link to comment Share on other sites More sharing options...
MtnBob Posted April 11, 2005 Author Report Share Posted April 11, 2005 Thanks for the info, Tom. Sorry if it came across that I thought AR tried to deceive people, I just didn't realize they didn't know about the problems with foam. Oh well, I just get a little frustrated that it is so hard to get any info about speaker parts. It wouldn't be that hard to put technical specs in the owners manual, even if most people didn't have a clue what they mean, at least the info would be there for those that need it. One more page of paper couldn't cost that much!Anyway, thanks again.MB Link to comment Share on other sites More sharing options...
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