K77-M Tweeters (difference)

[squawker]

I know there has been a million posts comparing parts but I have another curious one. I have 1979 La Scalas with bronze coloured square back K77-Ms that work great. I replaced one with a later (1985?) silver coloured K77-M back for an AB comparison. I noticed a drop in level on the silver back K77-M (maybe 3 dB). I replaced it with another silver back and got the same results. Is there a consistent differece between the the two vintages (bronze or silver back) or have my 1985 silver backs (which look new) lost some magnetism - they sound fine otherwise.

Mark

[Guest " "]

3db. thats quite a bit of difference.

[DrWho]

3dB could be explained by a doubling of the driver impedance (like 8ohm to 16ohm), but I doubt that's the case...who knows. I'm interested to learn what you find out though.

[BEC]

I have been repairing and testing K-77Ms for years. There is a variation of as much as 3 db between them. Interestingly, if you have a pair of them that have always been a pair, they match very closely. If you have one and try to find another to match it, you might have to go through several to find a match. I don't know if that pair match is the result of indivual speaker testing at the factory (which would catch a variation) or, (more likely I think) individual tweeters from a batch of tweeters match each other very well.

The reason that I think the matching is related to the batch of tweeters is based on a group of 12 new old stock T-35As (same as the K-77M before Klipsch relabeled them) that I had. In fact still have 8 of those. The ones from that batch all match each other very closely.

To take this a bit further, in trying to match up 2 of these K-77Ms, sometimes they get close enough when the diaphragms are replaced in both. Sometimes, that does not do it. Sometimes replacing the plastic diaphragm housing on one or the other will match them up. Sometimes nothing I have tried will match them up.

Bob Crites

[squawker]

Bob,

Thanks for the insight based on your experience. I don't have the means to conduct extensive experiments such as yours. I didn't think about acquiring them in pairs. It sounds like there may be multiple variables involved.

[Groomlakearea51]

I had also noticed that between bronze and silver. The only possible explanation I can think of is that EV changed the composition of the ceramic magnet. They did, in fact, do that on the K-55-M which replaced the K-55-V in 1983. That's about when the "silver" K-77's began to appear. They were also used extensively in later Heresy-I's as they began the transition to the Heresy-II ('83 with the K53/701 horn, and by 1984 with the K-24 woofers) Hard to say and I cannot find any further information on the K-77's.

[Don Richard]

Are there output differences between the round magnet K-77s and the square magnet ones? When I replaced round with square there was significantly more output (type AA xover). Or is this the output variation described previously between T-35s?

Don

[squawker]

It's nice to know someone else has noticed the same thing - your theory sounds like a good one to me. My first guess is variation in magnetic force. My second guess is other multiple variables based on Bob's experience.

[squawker]

>>Are there output differences between the round magnet K-77s and the square magnet ones? When I replaced round with square there was significantly >>more output (type AA xover). Or is this the output variation described previously between T-35s?

>>Don

The original question was the variation in output between different vintage ceramic square magnets but your point is true about the difference in output between round and square magnet K77s. There's quite a bit on this topic if you search for it here. My 74 cornwalls had a silver back square and a round magnet and the difference was huge in favour of the square magnet - about 180 degrees on the treble knob. The next step is to compare every loose K77 I have - 4 square bronze, 2 square silver and 2 round - if I ever get time. A small sample size to be sure but fun.