Vintage Jensen Speakers

[deveng]

I have a 1955 Fender Tweed Deluxe 5E3 I've owned since I was a kid. It originally had a Jensen blue frame that I blew up in 1967. My dad took it took Fender in Fullerton and they replaced it with a C12q ribbed cone dated 1967. I have practiced, recorded and gig'd with it for too many years to count and it always sounded great with C12q. I have always wanted to get it back to original speaker type but they've been outrageously expensive. About 2 years ago I found a black frame 1955 P12q with original ribbed cone (organ pull) for under $100. Volume sweet spot was a little different due to it being close to 7.8 ohms but it sounded really good. Then recently I managed to score a 1952 P12r blue frame with bell cover and original smooth cone for $102!! The voice coil was rubbing so I had to have it re-coned. I expected it would not sound that much different than the P12q. Especially since it has a modern replacement smooth cone and new coil. The new coil DCR measures 6.7 ohms. Well here's where it takes the twist. The re-coned P12r sounds incredible and its not subtle. It's not just the bass response that's different, its everything about it. The obvious difference from the C12q is understandable but the difference between the P12q and P12r is substantial. Nothing else was fixed or changed. I'm not even close to being an expert in speakers so for those of you who are, do you believe the difference is simply the ribbed vs smooth cone? Or because the amp volume sweet spot changed? I've also heard that early P12r coil gaps were larger (not confirmed)? Or possibly the combination of smooth cone and a weaker Alnico magnet? No matter what it is, this speaker is not leaving this amp, ever.

 

[soapfoot]

P12R will be a lower-wattage speaker than P12Q (at east from the factory).

Perhaps you're getting more speaker breakup?

 

[capacitorless]

I've had a few original P12Qs and C12Rs, and have one of each here (both needing repair but not terminally so). I'll get cone material observations and report back.

Edit: the Q cone material feels different, more flexible; the R cone material feels stiffer. I can't determine if it's a thickness difference or a materials difference, but it's significant to my fingers anyways. It's also entirely possible that the C12R cone is dried out more - I'm up at altitude. Both speakers are from local organs however.

I'm definitely not a pro, but I've read that the compression properties of alnico magnets become more apparent at higher SPL, so maybe that can be mostly ruled out?

The P12Q voice coil diameter is larger than the C12R; I can't properly measure the C12R since the dust cap is still present, but the P12Q is 1 1/4", and the online C12R specs say 1".

 

[deveng]

I find my C12q is brighter, louder and has a tighter low end (at the same amp setting) than both the P12q ribbed and the P12r smooth versions. It is difficult to be objective when these speakers have been changed over long periods of time. I do know the amp sweet spot changes for each version and I was quite surprised at the volume difference between a 6.7 ohm and 7.8 ohm speaker (the P12r and P12q respectively). I had not thought about the dryness of the cone material. I've read that its difficult to duplicate the original cone material so most vintage re-cones are supposedly not a perfect representation of a P12r with an original old cone that has dried out. I used to think that some of the guitar forums that discussed these old Jensen's were a bit over the top on their opinions but now that I've experienced it, I'm convinced there is some weight to their arguments. As for breakup, yes that appears to contribute to the complexity of these comparisons. Its a bit of apples to oranges. Most of my experience is with circuit design, debug/repair and testing so this is unfamiliar territory for me. I know this has been discussed to death on some of the guitar forums but I have more faith in the analysis by the members here at Groupdiy!