Last Belle Crossover ?

[BEC]

May I refer you to some recent testing of the K-55s?

In this set, I would say that the K-55V single piece phase plug has the highest output, the K-55V two piece phase plug has the lowest output and the K-55M is right in between them. In this case, then, everyone can be right.

http://forums.klipsch.com/forums/1/772921/ShowThread.aspx#772921

As far as the K-77 is concerned, I have rebuilt and tested hundreds of them. Some K-77Ms have higher output than some K-77 alnicos. Some K-77 alnicos have higher output than some K-77Ms. In a large group of them you will see about 3 db variation. I can't make up my mind which to say is louder.

Also, Klipsch considered the two tweeters close enough that if an alnico failed after the ceramic came along, they just replaced the alnico with a ceramic under warranty, not the pair.

Bob Crites

[Hardhead]

Tom--

I regret your thinking that I was being hostile. I assure you that wasn't my intention nor did I see any hostility in what I wrote or the way I wrote it. Again, my regrets.

[Hardhead]

Bob--

Since I'm aware that you very admirably rescue blown and/or old Heritage drivers by changing their diaphragms, I wonder if any of the midrange drivers whose test results you have posted on the forum have had their drivers changed. I suspect that the vast majority of Heritage tweeters and squawkers sent to you for repair are blown and not just old, so you don't get to do "before and after" tests on them to see how a new diaphragm affects their output. The tests you do on repaired drivers are therefore almost always after your repairs.

I remember your saying that some of the diaphragms (made sometime in the 80's, if I remember correctly) were either thinner or thicker than normal, I can't remember which, and were therefore of a lesser quality than the newer ones you install. That makes me wonder if installing a newer and apparently more suitable diaphragm that would be lighter or heavier than the original may change the output somewhat, even a dB or so up or down, depending. It seems reasonable to think that it might.

Of course, I'm not saying that changing the output of the drivers by changing their diaphragms--if that happens at all--is nesessarily a bad thing, since your tests tend to show that their outputs are more uniform after the diaphragms are changed. I'm just wondering if testing drivers that have non-original diaphragms could skew the results of the tests toward more uniformity of output.

[BEC]

Bob--

Since I'm aware that you very admirably rescue blown and/or old Heritage drivers by changing their diaphragms, I wonder if any of the midrange drivers whose test results you have posted on the forum have had their drivers changed.  I suspect that the vast majority of Heritage tweeters and squawkers sent to you for repair are blown and not just old, so you don't get to do "before and after" tests on them to see how a new diaphragm affects their output.  The tests you do on repaired drivers are therefore almost always after your repairs.  

I remember your saying that some of the diaphragms (made sometime in the 80's, if I remember correctly) were either thinner or thicker than normal, I can't remember which, and were therefore of a lesser quality than the newer ones you install.  That makes me wonder if installing a newer and apparently more suitable diaphragm that would be lighter or heavier than the original may change the output somewhat, even a dB or so up or down, depending.  It seems reasonable to think that it might.

Of course, I'm not saying that changing the output of the drivers by changing their diaphragms--if that happens at all--is nesessarily a bad thing, since your tests tend to show that their outputs are more uniform after the diaphragms are changed.  I'm just wondering if testing drivers that have non-original diaphragms could skew the results of the tests toward more uniformity of output.      

None of the midrange drivers in the latest posted spate of testing had new diaphragms. As far as I know, that group were all original. I have had a few K-55s that I tested and then decided to replace the diaphragms because of poor frequency response with the old diaphragm. In each case where the K-55 performed poorly before diaphagm replacement, the problem was in the low end. Very low output below 1 khz. I have trouble understanding what could cause that, but I have seen that problem several times.

The K-77 diaphagms have been made like they are being made now for perhaps 25 years. That is that the leads are copper-beryllium and the phenolic is very uniform. The phenolic got better sometime earlier than that. On some very old tweeters, I would find that the phenolic had a different thickness in some places than in others. I can't imagine how that could have been a good thing.

You are right in that most of the tweeters I see have open diaphragms when I get them, but often I do get a pair to replace the diaphragms on with only one bad. They do match better after both diaphragms are replaced.

Now, to discuss what brought these bad tweeters to me. I have only seen a few (probably less than 5) tweeters that had bad diaphragms showing obvious damage from over power. Those all had the voice coil actually come apart and resembled a slinky. In most of those cases, the customer told me that he (or someone) got carried away at the party and turned up the amp too far.

In most cases I can see no reason the diaphragm failed. Just that it is open somewhere in its 72 inches of 40 AWG wire. Sometimes the lead wire just comes loose from the voice coil. That problem seems to be mostly solved by using the newer copper-beryllium flat leads.

Bob Crites

[Hardhead]

That's interesting. I'd never have thought the voice coil might simply come apart when driven hard.

On a similar subject do I recall, or did I dream it, that the older ( I'm not sure what date) K-77 (and its successor) tweeters had leads or voice coils rated only to 2 watts and that "newer" (date?) ones are rated to 5 watts?

In my distant memory I seem to recall that the lower rated K-77's (and successors) had very thin flat wire--the lower rating was perhaps because of the thin wire--and the higher rated ones somewhat wider flat wire (that may be the flat wire you're talking about), but I'm not sure there were two different widths and ratings of leads, either. Is that also correct? If so, have you noticed any differencies in problems with the two types of voice coils/leads other than what you mentioned above?

[BEC]

I have also heard the 2 watts for the old ones and 5 watts for the new ones and I think that change had to do with the time the copper-beryllium flat leads came along. djk may have been the source for that info. I know that the late model T-35As have a rating of 5 watts long term 4000 to 20,000 Hz pink noise. Frequency response is listed as 3,500 to 16,000 plus or minus 5 db. I have a bunch of those brand new in the box built in 1988 and that is from the spec sheets with them. I also know that the Type AA crossover limits the power to the tweeter to about 2 watts by zener diodes.

I don't have a spec sheet for the older ones. I wish I had a sheet for the alnico type Klipsch used in the 70s.

The diaphragms that Klipsch is having made now for its K-77F look more like the older ones from the 70s. At least the two of them that I installed for a customer did. They might be back to the lower power rating, but I don't have any specs on that.

Bob Crites