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Jensen speakers and acetone

Discussion in 'Amp Tech Center' started by maxvintage, Jan 5, 2017.

  1. maxvintage

    maxvintage Friend of Leo's Ad Free Member

    Age:
    58
    Mar 16, 2003
    Arlington, VA
    Over a decade ago I bought a pair of Jensen reissue C10Qs for a project that never happened. They've been sitting in boxes in the attic ever since.

    Recently I built a couple simple 1x10 cabs and decided to put the Jensens in there. Did not like the sound! Shrill, and brittle are the adjectives that came to mind.

    So I go to teh google and lo and behold, there's a treatment--brush acetone on the surround and then subject the speaker to a steady AC signal at 1/3 of rated power

    Uncle Spot process

    I don't have a variac but I do have a line 6 nine volt AV wall wart, and nine volts is just about 1/3 power for the Jensen C10Q


    So I rigged up the wall wart to the speaker, then brushed acetone on the surround and turned the speaker on. Let it run for a couple minutes, then did it again.


    The difference is completely obvious and unmistakeable--you can hear it, see it, and feel it.. The sound of the hum changes--it gets louder and deeper. There were a couple little chips of wood on the speaker when I plugged it in--at first they bounced a little, but each time I tried the acetone treatment the little chips bounced higher, and finally they bounced right out of the speaker. And finally the speaker feels noticeably different--if you push it with your fingertips, it moves much more freely.

    The sound is much much better--the shrill top end is gone, the speaker just has a more comfortable feel in the ears.

    I don't know how far you can go with this--presumably you are weakening the surround. But this really works
     
    nojazzhere and nasdak like this.

  2. screamin eagle

    screamin eagle Friend of Leo's

    Oct 9, 2008
    S. CA
    Interesting experiment Max.

    I'm on the fence about either a reissue p12q or weber 12a125a for an EH185 amp I'm having built. This muddies the waters even more. Did you do this treatment to both speakers? Or just one? Be interesting to see what the difference is if you only did one--or at least one at a time.
     
    nojazzhere likes this.

  3. Jupiter

    Jupiter Telefied Silver Supporter

    Jun 22, 2010
    Osaka, Japan
    With a title like that, I was expecting a disaster thread...:D
     

  4. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Age:
    66
    Mar 2, 2003
    Lawndale CA
    That's a long-used way to break in speakers. I generally can't stand reissue Jensen without removing the dope that is so heavily applied to most, so I no longer install them at all (they're not close to original specs anyway) - but I had 3 and decided to use them for a tweed Bandmaster build (2 C10Q's and a C10R). Spent a lot of time running an M3 player into an amp and brushing acetone on the surround to loosen them up. It would have taken *decades* to do it otherwise.

    The problem you ran into is typical of any new speaker, though. The have to break in. But that's the best way to "break in" new Jensens.

    Hoever, acetone is extremely dangerous - it's highly flammable (never use it near a gas appliance of water heater - the fumes can cause a flash fire. I've seen it happen) and you mush wear a cartridge-type respirator that's been properly fitted by a professional - or do it outside, but STILL wear a respirator..
     
    nasdak likes this.

  5. dan40

    dan40 Tele-Holic

    826
    Aug 19, 2015
    Richmond Va
    I have also used this method on several speakers with good results. I believe that I read about it on the Weber forum years ago.
     
    DavidP likes this.

  6. maxvintage

    maxvintage Friend of Leo's Ad Free Member

    Age:
    58
    Mar 16, 2003
    Arlington, VA
    Yes it's been around for a while--I just never tried it. I tried it on one speaker and loved the results, and tried it on the second and it was equally effective. The jensens are vey nice sounding speakers now.

    I wish I'd done a comparison recording. Normally I'm very skeptical of claims like this but the difference was obvious and again I could hear it when it was hooked up to 9 volts AC, and I could see it in the way the little wood chips were moving, and I could feel it very clearly in how much more easily the cone moved under finger pressure

    I did it four times, acetone, turn it on, let it run for a couple minutes, turn it off, repeat.
     

  7. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    I just played mine at moderate to loud volume for a year, and they improved quite a bit. They have potential, but it takes a long time to unlock it.
     

  8. JD0x0

    JD0x0 Poster Extraordinaire

    Age:
    28
    Feb 22, 2009
    New York
    Did you give the speakers a chance to break in before you did this treatment? Break in could've explained the difference.
     

  9. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    I played the heck out of the Jensesn in my '59 Bassman RI. I bought the amp used, but it looked brand new and the Jensens sounded brand new. Very tight, very bright. When is ay i played the heck out of it, I've been gigging it pretty regularly and up and down in volume, hitting it with dirt and fuzz, etc.

    Last week, I installed two Eminence 1028alk speakers in place of two of the Jensens... I have sung the praises of the Jensens for years now.


    But, I'm currently on the look out for another pair of Eminences.

    I'll soon have a quad of Jensen P10Rs for sale. Maybe more (I have one in my '63 Vibroverb RI as well). I can throw in a can of acetone, if it'll help the sale! LOL

    Seriously, the Jensen get a beating on forums. But, for the most part I've been happy with the ones I own.
     
    Wally likes this.

  10. R.S.Fraser Sr.

    R.S.Fraser Sr. Tele-Meister

    267
    Jun 6, 2010
    canada
    OP
    What am I missing here?
    The wall wart would be DC.
    The speaker would not vibrate with a steady state voltage .
    The Variac is an AC device, it would cause vibrations.
     
    nojazzhere likes this.

  11. maxvintage

    maxvintage Friend of Leo's Ad Free Member

    Age:
    58
    Mar 16, 2003
    Arlington, VA

    You are missing the fact that the wall wart I was using puts OUT nine volts AC
     
    codamedia likes this.

  12. maxvintage

    maxvintage Friend of Leo's Ad Free Member

    Age:
    58
    Mar 16, 2003
    Arlington, VA

    No these were just out of the box
     

  13. alnicopu

    alnicopu Friend of Leo's

    Oct 3, 2009
    georgia
    Same here. That's the problem with the Internet. Some "guru" bashes on something and you're supposed to automatically Hate it. I love a p8r reissue in a champ and a p10q in a non Reverb Princeton.
     

  14. klobasa

    klobasa Tele-Meister

    392
    Jul 20, 2011
    Europe
    Bump.

    Any more comments on aging speakers with acetone? Any experiment that didn't go well?
     

  15. JD0x0

    JD0x0 Poster Extraordinaire

    Age:
    28
    Feb 22, 2009
    New York
    FWIW, I believe the idea is to remove some 'doping' from the speaker surround. Doping actually has a pretty large effect on tone.

    Generally more 'dope' gives a smoother tone, but it can constrict and compress highs a bit and make the speaker sound kind of lifeless. Removing dope can open up the high end, but you run the risk of causing 'cone cry' when the speaker is pushed hard. The dope dampens the cone excursions a bit. Lots of dope dampens the cone, and too much gives a lifeless sound. Remove too much, you'll get nasty 'cone cry' when playing loud, high up on the neck

    It's probably best to 'break in' a speaker for a bit before doing this treatment, as normal 'break in' could loosen things up enough for an improvement in sound. I notice many speakers within first 30 minutes of their life, sound like garbage. Dead, lifeless, overly compressed sounding, weak lows. Once the cone loosens up, all that tends to improve dramatically.
     

  16. klobasa

    klobasa Tele-Meister

    392
    Jul 20, 2011
    Europe
    Acetone is used for removing the doping, but also for softening/aging the cone elsewhere (but not at the dustcap).
     
    Last edited: Feb 6, 2018

  17. ndcaster

    ndcaster Poster Extraordinaire

    Nov 14, 2013
    Indiana

  18. klobasa

    klobasa Tele-Meister

    392
    Jul 20, 2011
    Europe
    I was writing this elsewhere already, but I have to mention it here also. Today, I got the confirmation that acetone treatment really can do wonders.

    I bought a brand new reissue Jensen C12Q a few days ago. Straightly out of box I did about one hour of the acetone treatment (with 9VAC). At 50min mark, the bass got deeper and smoother. It was very obvious. I gave the speaker on my Princeton reverb. The treble was nice when dialed 0-2, but quite piercing if given higher. In the next to days I gave a total of 2-3 hours of more 9VAC (no acetone) and loud playing for a couple of hours. Then it suddenly happened: the piercing highs were gone! Suddenly, I could open the treble more. Up to 6-7. That was yesterday. Today I tried the amp (and same guitars) once again. The piercing highs ares still gone. I can actually dial the treble anywhere between 2-10. If less, the sound becomes already a little bit jazzy muffled.

    Super happy with this experiment. For 70€ (speaker, 9VAC, acetone) I got a fantastic sounding speaker. I have a strong feeling that reissue Jensen bashing is mostly because of people not breaking them in. Supposedly it takes much longer than with other brand of speakers. Acetone treatment greatly speeds that process.
     

  19. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Age:
    66
    Mar 2, 2003
    Lawndale CA
    Many of these speakers take an extremely long time to break in. The acetone treatment is simply an accelerated break-in method. It's not complete - it doesn't soften the paper cone itself - but it does soften the surround enough to significantly improve tone & response.

    However - this method and normal break-in don't turn them into the same speakers as original C12Q's, P10Q's etc. They're different designs made by an Italian company that bought the rights to the Jensen name and part numbers.

    i have yet to hear any modern Jensen that I consider to be the best of its type - even in the top 3 or 4. Overall, probably my least favorite modern, name-brand speaker line.
     

  20. klobasa

    klobasa Tele-Meister

    392
    Jul 20, 2011
    Europe
    True, but other speakers from other brands are also not like old Jensens, even if they often try to emulate them...
     

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