Diagnosing Tweaters

[mark1101]

In my last post on wire splicing I mentioned the difference in top end between my Las and Corns. The Las are from 1990, the Corns, much older vertical horns (don't have serials / at work).

Anyone know the range of years when the verts were made?

Anyhow, the Corn tweeters definitely work. Both sound about the same. But they underperform by a wide margin when compared to the Las.

Can there be such thing as "worn" tweeters? Could the crossovers be damaged?

I have to say I thought everything was decent (not great becasue they are old), until I recently got the Las.

There's probably nothing wrong, but would it hurt to replace the diaphrams? Would that improve the sound any? Can that be done in the squawkers as well? Anyone know if it's routine that this needs to be done on these models after so long?

How much????

Sorry with all the questions, but I saw the comment that one person thought his corns top end sounded better than Las. Not even close at my house. So I'm a little concerned.

Thanks for any info provided.

[formica]

The diaphragms of the tweeters can fatigue, in which case it'll play at a lower volume. They are readily available and the repair has been covered here in other threads... you can check out my step by step here:

K77-diaphragm-replacement

the diaphragm alone is about 25$ each from Simply Speakers or Bob here (BEC is his user name) also sells a pre-soldered version for 40 to 50$ each (I think)

Before replacing it, you should carefully test your Cornwalls as they do have a different midrange sound versus the LaScalas because of the mid-horn lens. I prefer it's somewhat more discreet nature. Try swapping out just one tweeter and see if the weak highs follows the driver or stays with the speaker.

I haven't heard of the squawker diaphragm fatiguing... but it to is available (about 100$ each). Again... i'd recommend testing it before replacing it.

let us know what you find...

Rob

[mark1101]

Thanks for the info.

Of course now you've generated another question. I see lots of "diaphram" replacement discussion. What other parts can fail and / or are replaceable on the tweeter and squawker. One thing I feel confident of is the woofers are performing very well.

Last question: Can crossovers cause degraded performance or do they typically quit?

Thanks again.

[BEC]

Mark,

One thing I might suggest trying is to remove one of the tweeters from the cornwalls and place it on top of one of the Lascalas. You could then disconnect the Lascala tweeter from the crossover and run a pair of wires to the tweeter you want to compare. In my experience, a tweeter on top of a Lascala sounds very close to one that is installed. This might help you figure out if your problem is the tweeter or the crossover or something else.

Bob

[WMcD]

I'd just be a bit careful about reaching a conclusion it is a problem with the output of the tweeter, independent of everything else. Of course if you can make a side by side comparison, without the different crossovers, that might be a good test.

I would suggest you do use the same crossover and rig up some improvised A-B test, if only by switching wires. Keeping the crossover in place is a good idea unless you can ensure the test signal is limited to the operating range of the tweeter. You don't want to risk burning out the tweeter in testing. I've done it and gave myself a head slap.

One guess is that if there is a real output difference under controlled conditions, it might be that the magnet, if the round Alnico, has lost some strength. However, I wonder if you're going to find a gross output difference.

Let me point out a few things that may cause the difference in the top end.

1) The tweeters in the LaScala and the Cornwall are turning on at 6 kHz and running up to 15 kHz. That is essentially the upper octave of our hearing. The output with music is going to sound very, very tinny, even scratchy. It is making a contribution to the treble heard, but not too much. My suspicion is that if you hear a lack of treble, it is not a tweeter problem. Rather, it arises from different performance of the midrange squauker (sp?) horn.

2) In view of 1) you might try listening to the CW and LS pairs with the tweeters disconnected. It is pure guesswork here but I'd bet a nickle you'll find this is what you're hearing. You can do it by connecting the LS to "A" output of an amp and the CW to "B" output. This might cause some other perceptual problems. The LS is going to be louder, the CW is going to have better deep bass. So keep that in mind.

3) We should expect that the high end of the K-400 in the LS and the K-600 (or is it a K-700) in the CW to be different. They have similar geometry, but different dimensions. The combination means that they "beam" differently. A related issue is that the vertical orientation of the mid horn in the CW (is that correct?) is going to ensure that the dispursion and beaming is going to be different between the two. The test suggested in 2) may show this up.

3.5) The point of discussing the above points is that what we hear as "treble" may well be more a matter of 3 kHz to 6 kHz. That is the domain of the midranges. It is also the octave where the horn geometry is causing beaming and compensating for the falling output of the driver. The beaming due to geometry and size, and thus overall frequency response, of the two designs, is not going to be matched even without a crossover issue.

4) Please know the crossover in the LS has the tweeter running without attenuation. The voltage is not knocked down by the autotransformer. However, in the CW, it is attentuated by the autotransformer in the design of the crossover, probably by 3 dB. The midrange too.

5) I can't rule out damage to a voice coil, or weak magnet, causing lack of output of either the tweeter or mid. However, if both CW sound thin compared to both LS, then it would be an odd simultanious, matched degradation. I'd suggest you give some close consideration to this and some listening.

6) The caps, inductors, and autotransformers in these units should not be expected to degrade or even fail. It can't be ruled out entirely but I think it is the least likely. On the other hand, the screw down connections to the crossovers should be checked. Make sure they're clean and snug.

7) The bottom line is that I would not suggest switch diaphragms out before you have reached some solid conclusions that such is the problem.

So, tell us what you find. I'd be happy to give more free advice. It is all worth what you pay for it. Smile.

Gil

[mark1101]

Gil,

This is all great info. This weekend I will try isolating the issue and report back on what I come up with.

By the way, the corns say C-DB-15, serials 3L960 / 3L961.

Any idea what year these are? As I stated earlier they are the vert model. So I know they are pretty old.

From everything you described, I am betting that nothing is wrong. They are just being out performed by the Las. Both sound exactly the same. Not likely a matched degradation or failure as you mentioned.

But it will be fun determining what's up and doing a fair comparison on the components.

Thanks again.

[edster00]

mark1101,

Your Cornwalls are from 1973, I have a pair from the same year. Do you have any photos you can post? I'd love to see your decorator model!

[mark1101]

Hey,

Thanks for identifying my corns as '73s. I took a picture and it failed to post due to a script time out. I live in Athens, Ga. and have a piss poor dial up connection here at home. But I will work on it and try to get a compacted version of the picture up here sometime tonight.

Admittedly, the corns are a little rough. Actually, probably not bad for 30 years old. But they still sound fine (if you turn off the LaScalas they are sitting on) (also in the picture). You probably understand this coment from everything previous.

I think I just got fixated on the corn sound since I've had them for so long, then just got the Las about a month ago. Pulled off one of those drive deals up to Roanoke, Va. 13 hours to add Las to the corns.

I'll work on the picture thing. Thanks again.

[mark1101]

OK,

Here is a picture experiment. I really knocked down the res. The corns are '73 as you identifed. The Las are '90s.

Thanks

[Marvel]

Is this the way you have been listening to them, to compare the two? I would flip the Corns over, so that the mid/tweeter are lower, and more in line with your ears if this is the case. That will also put them on the outside (left/right). They would be pretty high the way they are shown. Still can't believe how huge those boxes are!

Marvel

[marksdad]

i understand your concerne about the tweets, but remember that the corns and las have very different high end, if i were to have made a comparicon while i still owned my corns i would have come to the same conclusion, the corns did sound laid back to ??? when it came to head to head tweet comparison, frankly i did not like all of the high end, on the other hand when doing low end comparisons the las seemed to lack using the same criteria, as stand alone speaks either just cant be beat, both have thier strengths, and i really would not consider either to have weaknesses, just slightly different voices. i guess in short i am trying to say listen seperatly, to the same music, is there really a dificincy? or are you just hearing 2 voices?

[hightone]

William

Good comment about the mid horn. The mid horn in a La scala is huge (mid range lazer beam) in compairson to the Cornwall. It may just be precived tweeter output.

[WMcD]

Well, I was thinking.

It might be easier to just muffle the tweeters rather than disconnecting the wiring, particularly on the CW. A folded up facecloth held in place with masking tape would be all you need. Of course you'd muffle all four. A cheap test set up none the less. As George Foreman said in the Midas commercial, "I'm not gonna spend a lot for this muffler."

It seemed like I was backpeddling a bit at the end, talking about free advice. Probably what I should have said was that I do give a lot of credance to the fellow who is there, rather than anyone giving suggestions from afar(myself included). Though I will make an exception when people say they can hear solder. So please let us know what the results of any experimentation might be.

Thanks for the photos. Both units look great. We saw some LS in a very slick piano finish at Indy. They look a bit like them. Someone got the finishing idea correct; they really do look like the fine musical instrument they are. No one would try to sell a piano in raw birch.

Though I bet it is not easy or cheap to make such a fine paint job.

Best,

Gil