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Old 3rd July 2019, 06:05 PM   #2201
jmrathbun is offline jmrathbun
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Default How Much Torque?

OK, I got a couple of new panels for my 2+2s and need to correctly install a replacement for the one that's apparently kaput. Not sure what went wrong with the old one but the connections have been checked and the thing intermittently emits severely distorted sound. I noticed there were a couple of places where the panel's plastic frame had buckled, presumably because somebody over-tightened the bolts that hold it in the wood frame.


So now those bolts are torqued to 1 ft-lb with my electric screwdriver, which is about where the matching bolts were on the other side. Before I close it up, I'd like some advice on how much torque to apply so I keep the thing from rattling in its frame without risk of breaking the plastic. The replacement panel is not new, so I assume the plastic may be brittle.



Any opinions?
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Old 3rd July 2019, 07:06 PM   #2202
CineDave59 is offline CineDave59
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As for tightened bolts, I have found hand tight is quite sufficient. In fact, I had once overtightened a panel, leading to increased rattle, which in turn caused me to buy a replacement panel. It was during the swap that I came to realize that "too tight" was an issue.
What does concern me in your situation is what exactly you mean by "buckled". Id imagine a scenario does exist that if the louver is cracked on both sides in a similar location the ability of the mylar to remain taut could be compromised and thus rattle.I certainly have a few minor chips in the louvers, but in no instance are there fissures through the frames entirity.
Have you tried or know of the hair dryer or heat gun treatment? Loosened mylar from constant common-use excursion does cause a rattling to creep in during heavy bass passages and the fix-all has always been a heat treatment. I do this biannually.
Another possibility is a lifted "spacer bridge" (my term). On the tops and bottoms of the pannels there is a t-shaped run of plastic that extends the width of the panel. Seems its a cap and spacer all-in-one. On 2 occasions the glue has ceased working and bridge/cap has lifted causing a pronounced rattling in that locale. In these instances i reglued and used halved wooden clothespins as wedges force the plastic back down and into place.
Rattling can also be due to loosened stator wires. Here i once again reglued by placing a dab of glue in that particular louver "square" and used a splintered popsicle stick to push the glue between stator and louver for reattachment.
Hope this helps
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Old 3rd July 2019, 07:37 PM   #2203
jmrathbun is offline jmrathbun
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Default Fragile Framing

Here are some pictures to clarify what I mean by buckled. 01 and 02 show different instances where pressure from the plastic collar on the screw has collapsed part of the frame. In 03, the view is of the side of the frame that's against the wood, so I don't think it's significant as a source of noise; note the wrinkled appearance of the softer plastic inside the frame, however. I don't see anything like that on the others. Possible source of distortion? Fixable?
Attached Images
File Type: jpg Panel01.jpg (277.6 KB, 164 views)
File Type: jpg Panel02.jpg (241.2 KB, 192 views)
File Type: jpg Panel03.jpg (324.1 KB, 162 views)
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Old 3rd July 2019, 09:16 PM   #2204
CineDave59 is offline CineDave59
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You can confirm source of the rattle by using a paper towel roll to localize what you're hearing durring a heavy bass passage. Minus a screw in that position one should expect rattle due to friction between wood frame and louver. Then again, you could have the missing screw scenario while at the same time be experiencing rattle due to loose stator. These things are quite deceptive and tedious to track down. You should be able to reinsert bolt w plastic collar and use paper towel roll to locate position. I determine general area of rattle and then proceed to use a splintered popsicle stick to check for loose stators in that area by gently flicking the stator to see if it moves at all. A single loose stator can create an unfathomable amount of rattle. I'd also confirm that all bolts are just hand-tight and not torqued before proceeding with stator wire check technique.
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Old 6th July 2019, 01:01 AM   #2205
jmrathbun is offline jmrathbun
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Default Success!

I hope that will be the last time I ever have to strip one of those things down and replace one of the transducer panels, but the results have been beyond expectations! The sound is better than I can recall. It must have been damaged in our last move, which was 13 years ago. Anyway, thanks for all the encouragement.
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Old 8th July 2019, 11:07 AM   #2206
stevetennant is offline stevetennant
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Hi all If one compares a Sepctra 44 to a Spectra 66 how much louder will a 66 be given the same power amps (valve 400w)?
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Old 9th July 2019, 11:07 PM   #2207
Mike Beck is offline Mike Beck  United States
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20log6/4=3.5dB if only considering area.
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Old 10th July 2019, 04:57 AM   #2208
kazap is offline kazap
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Resonance issues?

Stereophile measured the Spectra 11 and 1100 waterfall plots. Theres resonance in the midrange around 2-3kHz. I cant see what's causing that. Is it the Spectra model frames or the actual panels or ....?

Click the image to open in full size.

Click the image to open in full size.

Last edited by kazap; 10th July 2019 at 05:04 AM.
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Old 12th July 2019, 05:54 PM   #2209
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by kazap View Post
Resonance issues?

Stereophile measured the Spectra 11 and 1100 waterfall plots. Theres resonance in the midrange around 2-3kHz. I cant see what's causing that. Is it the Spectra model frames or the actual panels or ....?

Click the image to open in full size.

Click the image to open in full size.



During development of the Spectra 11, we did find a distinct midrange peak. This was traced to the cavity on either side of the panel within the frame (necessitated by the frame being wider than the panel). The peak was considerably reduced by “opening up” the cavity by using smaller flanges to attach the panel to the frame, rather than full-length flanges as used on early prototypes. No doubt the plots fromStereophile still show some traces of that peak. Since the panel & frame structure for theSpectra 1100 is very similar, I would expect it to exhibit similar behavior.


So, to answer your question, I believe this behavior to be unique to the Spectra 11 and 1100 and is caused by how the panel is mounted in the frame. It’s not a characteristic of the panel itself (which is used in all Spectra models), nor a characteristic of the interface system.

Last edited by AcoustatAnswerMan; 12th July 2019 at 05:56 PM. Reason: fix typos
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Old 12th July 2019, 10:28 PM   #2210
CineDave59 is offline CineDave59
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If I'm recalling correctly, I believe the frames are hollow-Is that the case?
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