Jump to content

Type AA plus K-55M/K-77M = Sibilance?


mboxler

Recommended Posts

I built an AA for fun...sounded terrible.

 

The sibilance on my K-33E/K-55M/K-77M Khorns drove me out of the room.  I couldn't find a crossover error, so I set up my mic and ran some REW sweeps.

 

Sweep One below shows a large dip between 300 and 400hz, and a large bump between 5 and 6khz.

 

In Sweep Two below, I reversed polarity on the woofer.  The blue trace shows that the dip is gone.  Is this the K-55M phase shift issue the AK-3 corrected???

 

Sweep Three below explains the bump between 5 and 6khz.  The K-55M is fairly flat to 6khz, then drops.  The AA tweeter on the K-77M crosses the K-55M around 4.5khz.

 

I have an AK type tweeter filter, so I put an 8 ohm resistor across the AA tweeter out, and connected the AK tweeter filter between the amp input and the K77-M.  As you can see, the AK filtered K77-M crosses with the K55-M perfectly at 6khz.

 

Sweep Four shows the AA (red) vs the "AAK" (blue).  Not bad!  

 

Does the K-55V drop off sooner than the K-55M?  If so, was the AA tweeter filter designed to compensate for that drop off?

 

Oh...my Type "AAK" sounds pretty good!  Still some sibilance but nothing like it was with the AA tweeter filter.

 

Thanks, Mike
 

Sweep One.jpg

Sweep Two.jpg

K55M K77M AA AK.jpg

Sweep Four.jpg

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

You’re not allowed to measure stuff anymore, lol. 
 

I was talking to JEM the other day, who mentioned that the AA was designed to work with the Alnico K- 77, and doesn’t sound particularly good with the EV 77-M. It was an interesting discussion. With that said, I don’t think I have ever seen a plot like that before.

  • Like 2
Link to comment
Share on other sites

2 hours ago, winglet said:

Here’s one of Bob’s threads showing response of various k5* drivers on a k400 horn

 

 

Thanks, I forgot about that thread.  Looks like the K55V single phase plug drops off quite differently compared to the K55M.

 

Dean's right...I gotta stop measuring stuff.

  • Haha 1
Link to comment
Share on other sites

4 hours ago, Deang said:

You’re not allowed to measure stuff anymore, lol. 
 

I was talking to JEM the other day, who mentioned that the AA was designed to work with the Alnico K- 77, and doesn’t sound particularly good with the EV 77-M. It was an interesting discussion. With that said, I don’t think I have ever seen a plot like that before.

That may explain a bit why I like my Alnico K77 more than spare K77M connected to my AA LaScala.

Link to comment
Share on other sites

@mboxler - excellent work and observations. While the midrange and tweeter issues between network and driver variations are more well known, the woofer to midrange transition in a KLIPSCHORN is less understood. Your woofer polarity swap with a gentle 6db slope network is a great example. 
 

It would be great to get Chief Bonehead’s insight on that issue.

  • Thanks 1
Link to comment
Share on other sites

30 minutes ago, BeFuddledinMn said:

@mboxler - excellent work and observations. While the midrange and tweeter issues between network and driver variations are more well known, the woofer to midrange transition in a KLIPSCHORN is less understood. Your woofer polarity swap with a gentle 6db slope network is a great example. 
 

It would be great to get Chief Bonehead’s insight on that issue.

 

Thanks for the kind words.  Your post is a great seqway to another measurement I took this morning (sorry Dean 😎).

 

Without a zobel across the K33E, there's really no way to achieve a classic first order 6db per octave low pass.  The inductance of the voice coil continuously raises the impedance of the woofer as frequency increases.  With a series 2.5mh inductor, the result electrically is a much flatter transfer function (blue plot).  Then there's the SPL itself.  Even without an inductor, the SPL drops dramatically after 180hz.  In my room, with a 2.5mh series inductor, the SPL is down around 12db at 400hz (green plot).  I believe this creates my dip in frequency response between 160 and 410hz???

 

Mike

 

 

2.5mh Inductor K33E.jpg

Link to comment
Share on other sites

The only in-network plot I have of the K-77-M with an AA is a Klipsch anechoic plot that I can't really post. Those peaks aren't there.

 

There are some out of network plots that are easy to find with google - Al did most of them. No peaks.

 

It's also odd that you would be "driven out of the room", and your initial impression that it "sounded terrible".

Link to comment
Share on other sites

1 hour ago, mark1101 said:

Something doesn't look right with the K77M having so much energy below 6K.  Sweep 3.

 

Are we sure the AA network is operating correctly?

According to ALK, the AA network is sending full power to both the squawker and tweeter between 5k-6k.

 

And the k77M is 5-6bd more sensitive than the k77F over that range...

Edited by winglet
Link to comment
Share on other sites

13 hours ago, mark1101 said:

Something doesn't look right with the K77M having so much energy below 6K.  Sweep 3.

 

Are we sure the AA network is operating correctly?

 

I believe so.  This morning I ran a few more tests to ease my mind.

 

My LTSpice model vs the REW plots come out very close.  One thing that's difficult to model is the K77, as I believe it resonances in the 4 - 5khz range.  I'm not smart enough to determine if that's why the SPL peaks sooner than the voltage.

 

I appreciate all comments.  Perhaps I'll install new diaphragms and try again.

 

Again, thanks.

 

Mike 

 

 

Type AA Voltages.jpg

Screenshot (165).png

Link to comment
Share on other sites

No.  They are both almost identical and from different measurement tools.  You can see the filter knocking back both the voltage and FR of the driver at 6K, which looks normal to me.  That sweep 3 above bothered me.  Why?  Because in my lascalas I have AA networks, K55V mid, and god forbid K77X tweeter.  My measurements never showed the tweeter with anywhere near that kind of power below 6K.  I think my combo sounds excellent and I'm getting away with it.  There is no harshness till you overdrive the room.  I know it's not the preferred setup.  😀  It's just very hard to find a good matched pair of alnico K77.  I have bought and tried many.  A bunch of mismatches and poor extension.  So at least now I have a known good pair of matched Klipsch tweeters.

Link to comment
Share on other sites

Thought I'd post my conclusions here for so I can easily find my results.

 

Like Dean said, it appears that the AA Network was designed for the K77 alnico tweeters.  Research indicates that the K77M is hotter than the K77.  I'll assume the AA was also designed for the K55V single phase plug drivers, as they are not as flat as the K55M from 4.7 to 6khz(?).  Again, I don't have these drivers, but I'll assume my AA build is correct for the K55V/K77 driver combination.

 

I am surprised how hot the K77M is.  I finally got the idea to measure the raw frequency response of the K55M (200 to 20000hz) and the K77M (4500 to 20000hz).  Around 4.7khz the K77M is actually 1db hotter than the K55M.   The tweeter circuit of the AA isn't designed to handle the K55M/K77M driver combination.  The steep slope of the AK tweeter filter, on the other hand, knocks off most of the voltage to the K77M below 6500hz.

 

Mike

 

 

AA Sibilance Results.jpg

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...