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K-77M Impedance vs SPL


geoff.
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I just measured a couple of K-77Ms I have sitting on the “project shelf”.

 

One measures 6.1 and the other 6.6 ohms.

 

My question is, in decibels, how much of a difference in sound pressure level will one have over the other?

 

Is there a rule of thumb for this?

 

Much obliged,

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5 hours ago, geoff. said:

I just measured a couple of K-77Ms I have sitting on the “project shelf”.

 

One measures 6.1 and the other 6.6 ohms.

 

My question is, in decibels, how much of a difference in sound pressure level will one have over the other?

 

Is there a rule of thumb for this?

 

Much obliged,

If you had a UMike and REW couldn't you measure this yourself? REW is free and a UMike is $100 and then many answers are at your fingertips.

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20 times the LOG of ( 6.1 / 6.6 ) equals -0.68 dB. (+0.68 for 6.6 / 6.1).  You can express most anything in "dB".  Whether it's correct to do so or not is another matter.  And whether it's correct to use DC resistance versus actual impedance is also another matter.

 

You've compared DC resistance of the voice coils.  How about the specific magnet strengths, and the concentricity of the parts forming the voice coil gaps and the coils within them?

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21 minutes ago, glens said:

20 times the LOG of ( 6.1 / 6.6 ) equals -0.68 dB. (+0.68 for 6.6 / 6.1).  You can express most anything in "dB".  Whether it's correct to do so or not is another matter.  And whether it's correct to use DC resistance versus actual impedance is also another matter.

 

You've compared DC resistance of the voice coils.  How about the specific magnet strengths, and the concentricity of the parts forming the voice coil gaps and the coils within them?

Run a curve and a db test and figure out what is going on audibly. All that other stuff might have a part to play but why in the world would I try and figure all that out? Measure results and the heck with the rest of it.

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1 minute ago, glens said:

Kind of my off-handed point...

OK now I understand. I have found that K-77 to be a weak point in all the systems I have fiddled with and even if they are in perfect shape I pull them and sell them off.

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20 minutes ago, geoff. said:

Thank you all for your responses, detailed and qualified, as always!

 

All things being equal, the difference would be insignificant outside of an anechoic chamber.

 

Good to know.

 

 

You would think sound would be an exact science by now subject to measuring and analysis with predictable numbers but where would one go to find this holy grail?

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13 hours ago, geoff. said:

I just measured a couple of K-77Ms I have sitting on the “project shelf”.

 

One measures 6.1 and the other 6.6 ohms.

 

 

are your tweeters rebuilt with newer diaphragms or stock EV- -the Chinese aftermarkets are not expensive

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8 hours ago, DizRotus said:

My guess is any difference would be negligible, but it’s merely a guess.  It will be interesting to see responses from those with answers based on science and/or experience.

i  have a new-unused set of EV T35  ---when I opened the boxes  -DCR ---1 was 5,9 -6ohms , the second was 6.1 ------I spoke with Bob Crites , he said not to worry about it -

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6 hours ago, RANDYH said:

are your tweeters rebuilt with newer diaphragms or stock EV- -the Chinese aftermarkets are not expensive

 

I am not sure what I’ve accumulated after years of substitutions.

 

You see, if something stops working (aka gets fried) I replace it with the flavour of the day rather than try the same old, same old again. So there is always a one-off left over.

 

A couple of Cornwall turned Chorus-walls and a LaScala or two later and I’ve amassed more replacements than I’ll have any need for in the foreseeable future.

 

Thought maybe I’d keep the only matching pair

 

 

1F3192FE-6E82-4445-B74C-E4051864E128.jpeg

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28 minutes ago, geoff. said:

 

I am not sure what I’ve accumulated after years of substitutions.

 

You see, if something stops working (aka gets fried) I replace it with the flavour of the day rather than try the same old, same old again. So there is always a one-off left over.

 

A couple of Cornwall turned Chorus-walls and a LaScala or two later and I’ve amassed more replacements than I’ll have any need for in the foreseeable future.

 

Thought maybe I’d keep the only matching pair

 

 

1F3192FE-6E82-4445-B74C-E4051864E128.jpeg

these look like LSI industrial speakers , the right  round  k77 is Alnico ,1970's  ,  the bottom left K77 is 79-80, the other 4 silver ones are 80's k77 , they are not tagged as K77M  --------but all square magnets are ferrite magnets  -    all aftermarket k77 diaphragms fit -5$ each ,  for all these tweeters -and it takes a 15 minutes to solder -screw-test per unit

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6 hours ago, RANDYH said:

these look like LSI industrial speakers , the right  round  k77 is Alnico ,1970's  ,  the bottom left K77 is 79-80, the other 4 silver ones are 80's k77 , they are not tagged as K77M  --------but all square magnets are ferrite magnets  -    all aftermarket k77 diaphragms fit -5$ each ,  for all these tweeters -and it takes a 15 minutes to solder -screw-test per unit

OK where are you finding diaphragms for $5 each?

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1 hour ago, DizRotus said:

 

Who cares?

The idly curious with nothing immediate to do care.

 

1 hour ago, glens said:

'You get what you pay for.'

I imagine in this case that's true. I just wanted to see one to have a look at what $5 would buy.

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