A technical review of the K77M and BEC CT125 tweeters

[Al Klappenberger]

Dman,

Pay no attention to the phasing. I didn't bother to look which way I hooked them up! + and - may well have been reversed! I should have paid attention to that!

EDIT (Next day): I went back and did the test again. The two were indeed both connected with the same polarity. The inversion in the output burst is probably in the mike itself.

Also, don't read anything into the fact that one output burst is earlier in time than the other. That is just because the mike got moved as I swaped the tweeters!

Al K.

[D-MAN]

Yeah, but at least you're consistant! I saw the inversion - no harm done.

If you guys think I called it bad, let me know.

DM

[PrestonTom]

I guess it is all in the eye of the beholder.

The FR measures do show a difference but what is the interpretation? The K77 has a flatter response then poops out more quickly (at about 17k). While the other has a more extended bandwidth, but it is ragged. One interpretation from the measurements would be that many of us do not have much hearing up at 17-20KHz. So we are proabaly not missing much. I won't even bother belaboring the point that any music energy up there is going to be fairly attenuated anyhow. In that case, the less ragged FR of the K77 "might" be better since that is still in an audible range and there is music in that region.

The IM distortion (which I am glad you ran) looks more similar than dis-similar between the two. Actually it does not look to bad in either case.

The impulse and the boxcar at 5KHz are difficult to interpret. First they don't look that different, since some of what you are seing are reflections. Again they seem more similar than dis-similar.

It is difficult to tease apart rise time from bandwidth. Essentially a narrow band process will always "ring" with the ring time (rise and decay) being inversely proportional to the bandwidth. But both these tweeters have enough bandwidth so I am not sure that is the difference, Additionally, the "apparent" rise and decay can be influenced by phase shifts between the components (perfectly normal in a linear device and absolutely not perceptible at these high frequencies anyway).

One other difference is the sensitivity of these two, which is clear in the first graph. Since the freq response is different between the two, a typical measure of sensitivity (or efficiency) is probably not appropriate. At a crude level, do they seem to be "equally loud" with a broad band signal?

Good Luck,

-Tom

[D-MAN]

That brings up a point about high frequencies and the limits of hearing...

It seems reasonable to me that although I may not be able to hear a pure 20KHz tone, per se, but what I can hear from a speaker capable of producing it is the SUB-MULTIPLES of it produced by various reflections and such that would give me the sense of the sound being REAL vs. not there at all.

You hear these "over-and-under" tones and resultant harmonics everyday of your life - they are part of your ability to determine distance and direction of various sounds. And when they are not there because you PURPOSELY choose or accept speakers that simply can't produce the originating frequency, you lose the sense of "real". Forget about actually hearing the tone itself - its the RESULTANT frequency effects that you CAN HEAR that matter!

That's my opinion and I'm sticking to it!

DM

[Hardhead]

Al--

Thanks for the information. So the efficiency of Bob's tweeter is slightly lower than the K-77-M. Since, according to graphs you posted some time ago, the K-77-M is a few dB's more efficient than the Alnico K-77, then the efficiency of the CT125 is somewhere between the Alnico K-77 and the K-77-M. That may help explain what some people are hearing.

It stands to reason that a more efficient tweeter like the CT125 would make the sound of cymbals stand out when contrasted with a less efficient Alnico K-77, especially an Alnico K-77 that may have lost some of its magnetism over the last 20 to 30 years. The effect would be accentuated if the CT125 were paired with an Alnico K-55-V squawker that may also have lost a little of its magnetism over the years. It also doesn't hurt that the CT125's frequency response is more extended.

I've heard the same effect when I adjusted the tweeter level up and down a couple of dB's in my Klipschorns. The same tweeter can sound brilliant or dull depending on how loud it is playing.

[Deang]

If you terminate the woofer and squawker sections of your network and play just the tweeters, the K-77-M sounds like a tinny tweeter. When you do it with the APT-50 it sounds like a "speaker". The extra extension is nice, but I think the real strength of this driver is on its low end, and it makes a tremendous difference on the first order filters where you still have a lot on energy being dumped into the tweeter an octave below the transition point.

[m8o]

Here's the results of the tone burst test. Both tweeters were fed a 3 cycle burst of 5KHz. I don't think there is much to choose between the two, but I think the K77 looks a bit more "civilized". Both of them costed for one extra cycle.

Wow, I like the attack of the CT125 ... I see now why some people might object to them. It makes me want to buy a pair.

Thanx for the work Al. I have a Terrasonde ATB-3 myself. You're inspiring me to get off my tail and do some tests.

[Bennyboy]

Dean ,

"The extra extension is nice, but I think the real strength of this driver is on its low end."

Exactly ! !

I have been waiting on mine tweeters for almost three weeks when i ordered them .
Shipping to the Netherlands is real slow.

Anyway , in the mean time i heard everybody talking about cymbals and the high end of this tweeter.
But when i heard this tweeter yesterday on Saterday 18 march for the first time ................it was powerful.

This means you can cross it earlier ............. i still like the K-400

Okey we have a difference of opinion about the AL-4 and AK-4.
It was intend to be for 4500....................?
But Dean and All , when you have a network ready for 4500 Hz i will be the first !

When you are a "technical" listener i think you will need a trac-horn with a Beyma.
I am a technical listener and know i miss some detail in the K-400.
But i like the sound the way it is.

Thank you,

Ben

[Al Klappenberger]

Ben,

But Dean and All , when you have a network ready for 4500 Hz i will be the first !

I have already designed the "ES4500". You can consdier it available now. It needs to be mated with one of the woofer / squawker networks though. It only provides the squawker / tweeter transition.

AL K.

[Bennyboy]

Al ,

I was thinking of a universal network or maybe a ALK junior.

I was aware you have a network for the 4500 Hz crossover.

But with the combination of a "ES 4500" and "ES 500 T" my wife would have mine suitcases ready.[]

Ben

[BEC]

Ben,

There is a very simple mod to a Type A crossover that brings the tweeter in earlier and rolls off the squawker earlier. A lot of people with the CT125 tweeter like that combination.

Bob Crites

[triode]

Ben,

There is a very simple mod to a Type A crossover that brings the tweeter in earlier and rolls off the squawker earlier. A lot of people with the CT125 tweeter like that combination.

Bob Crites

Please enlighten us Bob on this simple mod!

[BEC]

OK, first I will post a voltage vs frequency plot for a standard Type A crossover.

Bob Crites

[BEC]

Now, we can increase the value of the tweeter cap to 4 uf (instead of the standard 2 uF) and add a 500 uH inductor to the squawker output.

Note: Don't do this mod and use a K-77 tweeter. It can't take the extra power at lower frequencies!!

Bob Crites

[BEC]

Now another voltage vs frequency plot with the mod.

Bob Crites

[chops]

So you lower the crossover point on the squawker and tweeter? What is the reason for doing this?

I'm guessing the lower crossover point on the squawker would eliminate some breakup at the higher frequnecies coming from the K55? But lowering the crossover point on the CT125, eventhough it can go lower than the K77, wouldn't that just put extra strain and breakup into the tweeter then?

Note: As I just wrote in another thread, I am NOT an expert by any means when it comes to crossover designs. All I know is what they do, not why or how. Also, I do not know much if not anything about the Type B networks in my CWs, so with that in mind...

With say my CW's, the crossover point is at 6000Hz, right? Instead of changing the crossover point, wouldn't it just better to use a steeper slope on the squawker (-12dB or -16dB per octave) and a shallower slope (-6dB per octave) on the CT125?

In my mind, that would seem to be the better choice. The K55 would still play up towards 6Khz, but roll off sharper eliminating some of that breakup (if that's what's really going on up there) and the tweeter would roll off slower extending down a little closer to 4.5Khz, and not having as much extra strain put on it, and possibly blending in with the squawker at a lower frequency.

Like I said, it seems like an ok idea in my mind, but for all I know it could be causing a bunch of phase shifts and everything else. Heck, maybe it's a major no-no to have different slopes in a single network.

It's just a crude thought of mine though, as I really have no idea what I'm talking about, sort of. []

[Al Klappenberger]

Guys,

The main reason for the lower crossover is to get away from the K400 horn ASAP! The new CT125 tweeter allows the change. The mod Bob suggests is crude, but it works. I doubt if I will be offering a 4500 Hz version of my original "ALK". I thought about it, but I would rather permote the Trachorn replacement instead. It is the direct approach to getting away from the K400!

Al K.

[BEC]

Chops,

Lots of possibiltiies on how to do this. What I showed is just a simple way to try a lower frequency crossover to the tweeter since the CT125 tweeter is very robust compared to the K-77 and can stand it. Several people have tried this set-up and liked it.

Bob Crites

[Daddy Dee]

I have modded my stock Type A crossovers as Bob has described, and my Khorns have never sounded better.

Rolling off the K55 at 4500hz is a surprising improvement and the tweeter can carry the freight at all the frequencies above that.

It is the best bang for the buck tweak I've done in my system, hands down.

My wife even noticed the difference, and she is just an occasional listener to my system.

[chops]

Chops,

Lots of possibiltiies on how to do this. What I showed is just a simple way to try a lower frequency crossover to the tweeter since the CT125 tweeter is very robust compared to the K-77 and can stand it. Several people have tried this set-up and liked it.

Bob Crites

I understand this, but why is it so important to get the squawker crossed over lower? What is happening to the K55 and horn above 4.5Khz that everyone is affraid of? Is the CT125 better capable at handling the frequencies between 4.5 - 6Khz than the K55?

I thought I read somewhere (not in the Klipsch forums) that the stock CW Type B network actually allows the K55 to roll off naturally, or IOW the squawker is ONLY crossed over at 600Hz from the K33, and that the K55 driver is capable of output to around 12-15Khz on its own. Is any of this true?

I still want to buy a pair of CT125's to help out on the extreme end of things with my CW's. If lowering the crossover freq of both the K55 and CT125 will make a bigger improvement than just dropping the CT125 in on the stock network, then I'm all for it. I'm just wanting to find out why these other changes are desired, that's all. I'm not doubting or questioning anyone. []