Heresy differences

[Mike Lindsey]

I just picked a pair of 1976 Heresy's this past weekend and opened up the back to take a look inside. These are consecutive serial numbers and all have the same drivers (K-77 tweeter, K-55-V squawker and K-22-EF woofer) and networks (type E).

While looking at both, I noticed the tweeters are different. They both have the same drivers but the magnets look different. One has a square magnet that's 3" by 3" and is about 1/2" in depth. The other one is round and is about 2.25" in diamater and about 2" in depth.

Can someone explain to me what I have and which ones are correct? They both say K-77 on them. Also, I was thinking of rope caulking them and wanted to know if I am supposed to take the magnets off and just caulk the small driver? Does the same hold true for the squawker?

Thanks in advance,

Mike

This message has been edited by Mike Lindsey on 10-29-2001 at 06:45 PM

[JohnA]

The square tweeter is a K-77-M. It was probably a replacement for a defective K-77. The K-77-M has more and smoother VHF performance.

Only damp the back (out) side of the horns and don't remove the tweeter's magnet. It isn't supposed to come off.

John

[Mike Lindsey]

Thanks for the answer, John! Should I replace the other tweeter or will it make a difference? It looks like the tweeters are the same, only the magnets are different...

Mike

[WMcD]

FYI,

The K-77 series of tweeters came from Electro Voice. They're used in the K-Horn, Cornwall, Belle, LaScala, and Heresy.

The round magnet is made of Alnico. Aluminum, nickle, cobalt, and maybe some other things. This was used in the earliest form of the tweeter. There was even some earlier forms without the ridges on the mouth (output end) of the tweeter.

The square magnet design came later. The material is called ceramic. In the formative state it is a slurry and so it is sometimes called a mud magnet. Perhaps the reason for the M.

People have opinions over whether one or the other is significantly different in output. And if significantly different, which is better.

I've not read of anyone falling over, over the difference. So I wouldn't rush to find a replacement for one or the other to make them match. If they sound good to you, that is what is important.

I understand that people do like to dampen the midrange as a tweek. The theory is that the metal horn structure "rings" without caulk damping.

On the other hand, I have some doubts whether this is an issue with the relatively small horn on the tweeter.

Congrats on your purchase.

Gil

This message has been edited by William F. Gil McDermott on 10-29-2001 at 09:03 PM

[Mike Lindsey]

Thanks for the info, Gil! I'll caulk them and see if I like them or not...I can't wait to get these hooked up and put into action!

Mike

[JonM]

When you rope caulk your squawkers, try this. Do one, then from the front of the speaker (with the grill removed) tap the inside of the horn (not way inside toward the back - don't take a chance damaging the diaphragm!) with a small screwdriver, pencil, anything hard you can tap it with to get a "tick" sound. Then do the same with the squawker you haven't damped, and listen for the difference. I damped my Heresies (which have the plastic horn on a K53 driver), and was surprised at the difference. (I'm a natural skeptic.) The damped horn was much deader and sounded much less "plasticy" when I tapped it. I even heard a difference between two layers of caulk and just one layer - again, the one with two layers was acoustically more dead. That's what convinced me that the rope caulk really will damp out resonances that might be excited by signals from the driver.

I'd be real curious to hear your results - do the metal horns ring with a metallic quality the way the plastic ones sound plasticy? (I damped the metal horns on my K-horn squawkers, but the grill cloth kept me from doing the tap test.)