Carlspeak
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Posts posted by Carlspeak
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I have a NLA and its original tan grille cloth TPI is 16X16. It also has a very open, fine mesh black backing fabric.
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Same advice as I gave over at AK regarding advantagious' post:
12x12 is an extremely coarse weave for grille cloth. However, with the black backing cloth also, I guess it will be okay.
For single cloth grilles on classic speakers, I recommend linen in the 20-30 TPI range and 4-7 osy.
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Zilch: "Parameter changes after high-power testing are common; they return to original after "resting."
Yup, I forgot to add that sentence in my last post. The Fs does go back up with rest.
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I've also noticed when checking Fs numerous time during some spider softening experiments that Fs drops after extended cycling at relatively high power. I guess the extreme flexing sort of softens up the joints in the foam like my arthritis does in my hands in the morning after waking up
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Hi Guys,
I recently re-tested (out of cabinet) a few woofers treated with Permatex last year, and it appears that fs has risen on the average of 3 to 4 hz. The Permatex has lost its tacky nature, and seems to have stiffened a bit. While still better than anything else I have used in the past, the rise in fs is a little disconcerting.
Carl, I was wondering if you still have any of your test woofers around to check out.
Roy
No, I don't Roy.
It may simply be that while we're striving to find someting like the 'original' sealant, even the original applied to the surrounds met the same fate you site above. I write this because if they did stiffen over time, it would explain why on many vintage cloth surround woofers we see numerous areas where light shines thru that resulted from the sealant hardening and falling out with flexure of the cloth during normal use.
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Hi Vern. Nice to see you back. Haven't 'heard' much from you lately.
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My first post was focused on how the job was done. This post made to simply report the customer re-installed the reconed woofer and reported yesterday he was extremely satisfied with the results.
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Attached is a blog document account of a recent Model A woofer recone job. The woofer was made by RCF, an Italian mfg. (Model L12P48).
The challenge was to salvage the original cone, install a new surround, VC and spider and properly position and align the VC without shimming it.
The document speaks for itself.
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Read thru and downloaded this thread today and was impressed with the volume of info. provided. However, many important details are no longer accessible. In particular, KK's testing of a driver provided by TT. KK's research assistant provided a few links in a few posts that now are dead ends (e.g. file no longer found).
KK: can this data be accessed again? Your fine report on the 3/4 inch tweeter testing project also is no longer accessible.
Just a suggestion here, but I've found numerous instances of dead end links to important information in threads going back a few years.
I think all important data should be embedded in a post to best preserve prosperity should the site be once again upgraded to another format by Mark.. Another thought would be for key authors to CC the library when making important posts. Perhaps that location is less vulnerable to 'evaporation' issues.
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I am fiddling with a set of unrestored, late version AR-11B (from 1978), and took out the 10 uF tweeter cap for replacement (it is the black Callins? with the red sealing in the ends). Just out of interest, I tested the value on my multi meter, and this must be a record in capacitor off value: 32 uF! I just need an 8 uF in parallel and I can use it for the midrange.
BRgds Klaus
Careful Klaus. That Calluns' ESR may also be way off. Did you test that also? Just adding the parallel cap may bring the crossover point back to spec, but the mid's potential output may suffer due to elevated impedance across the caps.
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Those are some funky resistors, Carl!
Well, I've completed ONE of the 4 xovers here. I'm doing mine with Dayton caps and Mills resistors. The Daytons fit fine and the Mills are easy to work with because of their compact size. Next: Recapping Rob's Fives with the SA Clarity Caps. That will take creativity
Just watching for the UPS guy to deliver them.........
Kent
Nice job Kent!
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Hello again Kent.
The Clarity cap size you quoted indicates you chose their SA Range which are rated at 630 Vdc. Cap size is roughly proportional to its rated voltage. Clarity's PX range cap is rated at 250 Vdc, the same as the Dayton and costs less than the SA. MPP film thickness also affects cap size. the SA uses 10 um film. PX uses 6 um film.
250V is plenty for a passive xover application.
Attached are before and after pics of one of a pair of Polk SDA SRS crossovers I recapped and re-resistored with a mix of VERY high end Duelund caps and resistors for the tweeter section and Sonicaps and Solens for the mids and bass sections. Now that was a challenge!
The Duelund resistors are quite unusual. They look like cinnimon sticks! They were so long I had to stand them on end.
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Hi Kent.
1) No, I removed the original components that were replaced with new ones
2) I like to replace the sand cast series-wired resistors with wire wound, non-inductor types like Mills. No preference regarding resistors. You may have a tough time fitting in the Clarity caps. I believe they are bigger than the Solens. The biggest fitting problem will be in the lower left corner where the bundle of caps is and also 2 new resistors have to be crammed in there.
3) The correct cap values will be the ones you find on the boards you get to work on. I have found some minor variations as evidenced in my hand drawn vs formal schematics you referenced.
I didn't replace the 25 uF cap wired in parallel for the woofer. You can if you want.
The resistor values you listed seem correct.
p.s. If Rob has a later ser.#, you may find a different looking xover board than the one in my picture. I have recently worked on a later version which is a PC board and not hard wired like the original in the pic. Have pics of the newer one also if you need them.
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HI, IF YOUR STILL AROUND CAN YOU TELL ANYTHING ABOUT THE CAPACITORS HE USED, KENT IS REBUILDING SOME M5 CROSSOVERS FOR ME (I DONT HAVE HANDS ANYMORE) AND ANY INFORMATION IS HELPFUL, THANKS, ROB
Well, I'm still around at least. Didn't use anything fancy. Solen caps and mills resistors as shown in the attached pic.
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I may have measured the drivers but can't remember. That was 5 yrs ago. The speaker is rated at 4 ohms as noted in the copy of the Model A owner's manual which should also be in the library. Didn't note the model numbers of the drivers.
[i hope Mark reads this]
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Sure Carl, whatever you have I'd like to take a look.
I've attached some stuff IMO belongs in the library. Schematics, pictures and a chronological history by model (can't vouch for accuracy) that was available for downloading from the oroginal CSP site.
Snell_model_a_component_layout.doc
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I have my own hand drawn version made during a rebuild of the upper section. It does not include the woofer section. Anyone interested?
Was puzzled to see no reference to Snell in the Library section. I thought there was some stuff back in the old site.
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Wouldn't it be funny if we somhow found out that Permatex (or something very similar) is what was used originally to seal these classic speaker's cloth surrounds?
It behaves pretty much the same with respect to its tackiness.
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Carl,
I've been reading Villchur's original patent document for some insights.
The question of "how sealed" a cabinet needs to be is a good one, as "a small amount of air bleeding or air leakage is permitted" according to the document. It also states that "the enclosure is designed to provide an acoustic seal, that is, one which does not allow significant air leakage over a period corresponding to a half-cycle of the lowest frequency encountered". Nowhere in the document, however, does it suggest that the "acoustic seal" lowers fc, only that it provides "uniformity of frequency response at lower frequencies". According to Villchur the surround must "be substantially air-tight to confine the acoustical pressures produced by the diaphragm".
It is therefore probably prudent:
1) To make sure the old surround sealant has not stiffened to the point of compromising compliance.
2) That a satisfactory new sealant be sparingly applied to insure the integrity of the "acoustic seal".
3) Not to compromise compliance by glopping on too much sealant in an attempt to cover every tiny hole.
Roy
Vance Dickason says in the 4th Ed. of LCB that "Enclosures for closed-box speakers should be air tight........Air leakage caused by a speaker's lossy surround or porous dust cap should probably be ignored since attempts at correction can create as many problems as they solve."......
He doesn't seem too worried about some surround air leakage. The question remains, how much is too much? - at which time it may be prudent to reseal it. Can anyone shed some light on this? Is the point when a fix is needed measurable? How much air leakage is there in a 1/2 cycle at the lowest frequency encountered?
I agree as you state in point #3 above, go easy on the sealant as Dickason cautions so as not to make matters worse.
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Why would you say Fc should have dropped? If I ported the speaker would Fc necessarily rise? It's a real question, not a challenge.
The answer to your question lies in the low end natural woofer's roll off in a vented (24 dB/octave) vs an acoustic suspension (12 dB/octave).
It follows then that as a sealed box behaves more like a vented box the -3 dB point will start to creep up - assuming the rolloff's original starting point of both the vented and AS speakers is the same (see attached sketch). This is all theory of course.
In the case of cloth surrounds where the miniscule open area of a paratially deteriorated old cloth surround is further sealed a bit, does it make any measurable difference? Perhaps not as I noted earlier in my tests.
I agree will others who posted here that sealers that stiffen the surround will increase Fs.
Now, could someone demonstrate with test data the benefits of sealing an old surround whilst maintaining original Fs?
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Vern:
Having used this stuff today, I didn't find it that bad. Other adhesives I use in speaker repair are much more oderous from their VOC's.
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Well Roy, my curiosity got the best of me. Having a KLH 5 woofer in my posession prompted me to visit my local AutoZone store and pick up a can of 98H. Same stuff as yours, only in a smaller can.
I first ran a WTII scan on the woofer as is and got an Fs of about 27. Then cleaned the cloth surround with Isopropyl alcohol, dried it and applied the 98H with a small brush. During the application process I held the woofer up to the light and noticed quite a bit of light coming thru the small holes in the cloth were it had NOT been coated with the Permatex. After I finished the application and dried it, I looked again and almost all of the visible holes were gone. The technique I used was to apply light pressure to the brush to try and force the stuff into the interstices of the fabric. I did not thin it.
Next, tested Fs again and it came out the same.
Next, put the woofer back in the cabinet and tested Fc and got about 46 hz. - about the same as I got prior to sealing the surround with Permatex.
Next took the woofer out and put it in my oven at 170 deg. F for 1/2 hr. (couldn't get the oven to control any lower temp.).
Took the woofer out after the alloted time and let it cool outside. The coating wasn't as tackey then.
Next, tested Fs again and got about the same as original and treated prior to ageing/curing. Good news, the butyl coating didn't seem to harden with forced ageing.
Next, put the woofer back in the cabinet and tested Fc and again got about 46 hz.
Yes, the Permatex treatment seems to perform as you described, even after some deliberate ageing. What bothered me though was the lack of change in box Fc. I presume I was successful in sealing most of the visible holes and yet no lowering of Fc.
So, what's the point again in 're-sealing' cloth surrounds?
Hey, maybe mine were a one-off. I don't know, but thought I should share.
I can post all of the WTII test curves I generated. Just don't have time now. If anyone is interested, let me know.
Cheers!
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Thanks Roy for doing the research. I'm sure members here and visitors alike will benefit from your work. I think it's just fun researching and finding ways to improve our audio hobby. I very much injoyed doing the grill cloth, stuffing and capacitor studies.
You may want to consider artificially ageing that 10" KLH woofer to see if the Fs changes. Put it in an oven at 100 deg. F for an hour, let it cool and re-measure. That should age it somewhat without damaging the woofer.
BTW, did you measure the before and after treatment on box Fc? That's really the bottom line. If the surround was indeed sealed better, the improved seal should have lowered the Fc a bit.
Mark/Vern:
The option list print function will print all the posts. Another approach is to choose 'download the file to word' from the same options list. My M'Soft 2007 Office word program did a nice job of opening everything up, including Roy's pics. I then simply deleted all the posts except Roy's and printed it. Voi-la a nice hard copy for my records!
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Mark:
For your item 1) question, check out Wikipedia.org's Acoustic Research write up. It's not bad and probably could be edited a bit to suit your needs.
It's all about the music
Carl
Carl's Custom Loudspeakers
All Advent questions answered
in Advent
Posted
Doug/anybody: could you give us a rough range of ser. No's for the 16/16/3 types and the 16/8/3 types?
Thanks,