Replacing Diaphragms

[bfish]

...I guess I've just said what you guys already did.

Perhaps Cal, but it was how you said it that piqued my interest.

You could write a book (many have) on the process of fatigue from the point of manufacture to breakdown of a particular item of cold-formed aluminum. I plucked the following applicable quote from one such effort;

"The significance of the fatigue limit is that if the material is loaded below this stress, then it will not fail, regardless of the number of times it is loaded. Material such as aluminum, copper and magnesium do not show a fatigue limit, therefor they will fail at any stress and number of cycles. Other important terms are fatigue strength and fatigue life. The stress at which failure occurs for a given number of cycles is the fatigue strength. The number of cycles required for a material to fail at a certain stress is fatigue life."

If you're willing to pay for the information, you can obtain S-N curves of fatigue parameters for any given alloy from the ASTM. I'm willing to bet that whatever alloy "Pascalite" is has a significant edge over the "other" alloy in this department.

Now while all that is very interesting for the terminally bored, what does it mean regarding our diaphragms?

The end result of fatigue is cracking. Has anyone here ever retired a tired 'fram for that reason? If so, was it in the hinge or the dome?

[magnarc]

That was just my point it isn't set in stone each diaghram has to be evaluated individually if possible.On all points mentioned.I just picked up a pair of 8-G's with 23744's NOS that I'm willing to bet have NO Fatigue and they been on the shelf for 35 years.Just because they are 35 years old doesn't mean they won't perform as intended or spec'd.You have to hunt for those treasures though.

I guess the point I was making is age has nothing to do with it as long as they are in a protected enviroment.And most importantly not A-B-U-S-E-D But already made this point in post #3 IMHO

WOW. *Drools*

[Cal Weldon]

[I]"The significance of the fatigue limit is that if the material is loaded below this stress, then it will not fail, regardless of the number of times it is loaded.

Interesting and it makes sense. I am wondering if fatigue even comes into play here. My guess is no. I think the loading would be well below the stress point in the case of the diaphragms. Aluminum fatigue is an indicator of when to retire airplanes and the such.

[bowtie427ss]

Has anyone here ever retired a tired 'fram for that reason? If so, was it in the hinge or the dome?

I think on one Altec phragm in the long past. I've encountered other fractures in altec small format phragms, but i believe they were all the result of creases, dents, or other cases of direct contact with bumbling meddlers being in there. I've never seen an altec phragm that looks like it just simply fatigued and let go, there's always been evidence of an extenuating circumstance. But, i believe that there's a definite difference in sound between well used phragms and fresh new ones, it'd be interesting to see what's measurable vs. what's placebo.

I have however destroyed a couple "other brand" phragms where the "titanium" cracked along the bend at the outer diameter of the dome. They don't sound so good after that happens.:doh:

[Altec Best]

If so, was it in the hinge or the dome?

You know (Bfish) you always make great points !!!

This question for me depends on (Large) or (Small) format diaghrams !!


Small format usually the wire leads break long before the Alum.dome or compliance.So the weak point for me is the wire leads.

Large format Alum. they tend to break where the edge of the dome meets the compliance.That is were the Diaghrams are weakest or stressed the most. IMHO

[bowtie427ss]

Large format Alum. they tend to break where the edge of the dome meets the compliance.That is were the Diaghrams are weakest or stressed the most. IMHO

The one time i've seen a broken large format phragm, this is what had happened to it. But, the dome had very evident marks where it had been in contact with the phase plug. My thought is that someone had driven it without any hi pass filter, or it had been rode really hard and left for dead.

[Cal Weldon]

When I received my 288C's the dome part was intact but the entire surround portion was shattered into wee little bits. Perhaps they had been dropped?

[Altec Best]

When I received my 288C's the dome part was intact but the entire surround portion was shattered into wee little bits. Perhaps they had been dropped?

Or Massive amounts of distortion and or lower frequencies.

With metal the weak points will always be in the bends or creases as opposed to the flat surface's when vibration is concerned.

[SOOTSHE]

A bit off topic perhaps, but I have heard that with bass drivers it's better to run them than leave them sit idle for years on end....sort of like a car engine. If you let it sit for years without starting it, the seals & other components will deteriorate & so you're better off using it. Not the perfect analogy I know....but is there any truth in the bass driver scenario?

[bowtie427ss]

A bit off topic perhaps, but I have heard that with bass drivers it's better to run them than leave them sit idle for years on end....sort of like a car engine. If you let it sit for years without starting it, the seals & other components will deteriorate & so you're better off using it. Not the perfect analogy I know....but is there any truth in the bass driver scenario?

Interesting point.

I know from experience that some bass drivers' suspensions can become very stiff over long idle periods.

If the surround becomes abnormally stiff, it seems to me that this would put stresses on the cone that it might not have been designed for. With a motor as powerful as that of something like the 515, i'd think there's the potential for it to destroy the cone in short order, at least sonically if not physically crack or break it.