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Re: [regsaudioforum] Re: LS3/5a measurement

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  • Fred
    There seems little mention of tweeter adjustment by taps at L3 of the LS3/5a crossover.(See cropped attachment from BBC_1976-29.pdf below) B110 driver Bextrene
    Message 1 of 45 , Feb 2, 2010
    There seems little mention of tweeter adjustment by taps at L3 of the LS3/5a crossover.(See cropped attachment from BBC_1976-29.pdf below)

    B110 driver Bextrene cones seem to be outlasting predictions but I found this of interest -


    --- On Wed, 3/2/10, regtas43 <regonaudio@...> wrote:
    From: regtas43 <regonaudio@...>
    Subject: [regsaudioforum] Re: LS3/5a measurement
    To: regsaudioforum@yahoogroups.com
    Date: Wednesday, 3 February, 2010, 0:14

    The older production may have been peakier to begin with.
    If you look in Stereophile, there are measurements from over a period
    of time of different generations as it were of the speakers.
    What happens in addition(Derek H can illuminate this further perhaps)
    is that as I understand it the "doping" of Bextrene can migrate over time so that the drivers of Bextrene based speakers are no longer
    correctly doped for antiresonance.
    Again, I do not know the details, but my understanding is that the Bextrene drivers of the Spendor BC1s were handdoped individually to achieve the best possible performance but that this can shift with time.


    --- In regsaudioforum@ yahoogroups. com, "Edward" <Edward_Wu@. ..> wrote:
    > I believe Paul Seydor may have mentioned this tendency (of older LS3/5as to become even peakier in the treble with age) in a TAS review of the Stirling version.
    > According to this article, older Quad esl57s also become brighter and more forward:
    > http://www.quadesl org/Quad_ R_D/AgedPanels/ agedpanels. html
    > --- In regsaudioforum@ yahoogroups. com, "laurie483000" <laurie483000@ > wrote:
    > >Late 15ohm LS3/5as were known to become more peaky with age at around 1.5-2khz and it has been suggested on the Yahoo site that this be fixed periodically by fairly simple x-over modification.
  • Tom Mallin
    I believe that foam surrounds may last longer if kept in a humidity controlled environment, but that s just anecdotal from my own experience and that of
    Message 45 of 45 , Feb 3, 2010
      I believe that foam surrounds may last longer if kept in a humidity controlled environment, but that's just anecdotal from my own experience and that of others. The 1960s AR speakers' woofer surrounds made of foam have mostly all rotted by now. I have 1980s Siefert Maxim III speakers with foam surrounds and the foam is in like-new condition still. They were in service until about a year ago.

      AR made even older AR-3 and the early 3a speakers with cloth surrounds and those are in relatively fine shape--no rot at all; same goes for the AR 2-series speakers. The cloth surrounds used in those and all KLH speakers of similar vintage may need to be re-coated with some pliable substance, however, to maintain an adequate air seal. Capacitor deterioration is very common in both AR and KLH speakers.

      My theory is that many of those who are today appreciative of vintage speakers are looking for speakers with a more mellow balance than is common in modern speakers. As I noted, the aging of capacitors can cause the high end to roll off. Thus, many who have not measured the speakers may find them to be just what they are looking for. As you noted, JBLs such as the L-100 in high demand today sounded MUCH brighter than AR-3as when both were new--I frequently heard both in same-store A/B demos. Thus, any softening of the sound caused by aging caps could also bring those speakers closer to neutrality.

      I have not seen comments about speaker magnets losing their magnetism. Alnico magnets were common in older speakers and are thought by some vintage speaker collectors to be superior. Some modern brands (e.g., Alon/Nola) boast of alnico magnets in their designs.

      >>> Fred <glenndriech@...> 2/2/2010 8:24 PM >>>
      Hi Tom,

      Foam rot is certainly a universal plague isn't it?!
      I had to import a re-foaming kit from Florida for my JBL L50 bass drivers and delighted at the result. Crossover capacitor values were close enough to spec to retain and the mid-tweet pots were dismantled for cleaning and burnishing. Other attention as required and refinishing with Scandinavian oil. They retain their relatively un-JBL neutral sound and in any case, I've long known that JBLs tend to need their pots well backed off so as not to scare Banshees!

      Tweeters can have a surprisingly low rating - many less than 10 Watts so your comment is well taken.

      What had got me thinking to ask for observations is my own and how many times I've seen comments about undamaged vintage speakers performing exceptionally well. Could it be that drivers "free off" and stabilise for the long term to become more easily driven and compensate for lowering crossover capacitor values? What of actual capacitor life or magnet types and retention? Is there confirmation that speakers in active use will outlast those even carefully stored?
      - ETC -
      These were seeds of thought into a partly rhetoric question (returning some interesting answers).



      --- On Tue, 2/2/10, Tom Mallin <tmallin@...> wrote:

      From: Tom Mallin <tmallin@...>
      Subject: Re: [regsaudioforum] Re: LS3/5a measurement
      To: regsaudioforum@yahoogroups.com
      Date: Tuesday, 2 February, 2010, 17:36

      In the case of American-made vintage speakers for the 1960s and early 1970s, the typical problems encountered due to aging are:

      1. Acoustic suspension sealed cabinets lose their seal due to driver surround deterioration. Foam surrounds rot; treated cloth becomes more porous. Bass becomes softer/less impactful, less extended, and more distorted.

      2. Tweeters fail. Before the later 1970s, most tweeters were not ferro-fluid cooled and when subjected to modern CD program material with its stronger highs and higher powered modern amps, the tweeter can easily fail if driven to SPLs not within the intended range. This can lead to higher distortion, or just no sound from the tweeter, usually the latter. This makes sound duller, not brighter.

      Note that this is actually one reason AR speakers of that era may sound rolled off on top to modern ears. The delicate tweeters were intentionally reduced in volume relative to midrange and bass to protect them. This can be seen in AR's publish response graphs of its speakers of the time; the tweeters are fully extended but shelved down in level. The AR LST models combated this by adding extra tweeters and angling them outward. Those models did not roll off as much in their high-frequency power response. Later, when ferro-fluid- cooled tweeters were developed, AR further brightened the balance of its speakers (beginning with the 10 pi successor to the 3a and continuing with the big AR9). Those speakers were objectively better measuring in the highs, but many think that the old verisimilitude to concert hall-like balance was lost or at least diminished from then on.

      3. Midrange and tweeter level potentiometer controls fail or get noisy. Usually either the controlled driver produces no sound if the control is in a "dead spot," or the sound is distorted with crackling and raspiness. No added brightness is produced. (But "fixing" the problem by replacing the noisy pots with modern L-pads can brighten the high-frequency balance of these speakers if the crossover is not modified to compensate for the L-pad's different electrical characteristics. )

      4. Capacitors in the crossover fail. This causes the sound to be duller than intended. I have never heard of a capacitor failure or aging problem producing brighter sound.

      5. Driver suspensions in midrange and tweeter domes stiffen up with age, even with new old stock units which have never been used. Forty-year-old new-in-box parts still exist, but probably don't sound the same as they did years ago. Most collectors describe the sonic result of such problems as decreased clarity and reduced brightness and extension, never added brightness. Thus, if replacements are needed these days, many restorers are now preferring to use more recently made parts and altering the crossover to compensate for the differing driver characteristics. Note that without crossover modifications, the result of substituting modern drivers for the old ones is almost always added brightness.

      >>> Fred <glenndriech@ yahoo.co. uk> 2/2/2010 10:56 AM >>>
      The other day I was set to wondering by how much component, driver and overall ageing could affect speaker sound. Would the effect be necessarily negative?

      Any observations or comments?

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