Supertweeter + K-402/K-69-A...?

[Chris A]

One of the issues brought up recently in another thread is titanium-diaphragm compression driver "chatter". The K-69-A driver chatters, and so do a number of other Ti- and Al-diaphragm drivers. Beryllium diaphragms are said to be the "gold standard" presently, but command very high prices. One other approach is to entertain the idea of a "3-way Jubilee" without using the K-69-A driver as the tweeter. One such alternative is something like a Fostex T500AmkII driver, which uses "99% pure magnesium" diaphragms which exhibit high internal damping in the Mg material itself.

To start with, maybe a rank ordering desirable traits of compression drivers may be useful since the issue of polar response (i.e., the T500AmkII Fostex compression driver/horn) was raised in another thread. Separation of these into two lists may be useful: one for midrange and another for high frequency compression drivers.

I'll go first (...please feel free to disagree...)

Relative importance of high frequency compression driver attributes (IMHO):

1) freedom from ringing (i.e., 10-20 Khz--but is actually lower depending on age and gender of the listener) This is most important for clean impulse response, like cymbals, percussion, and other hf transients.

2) freedom from modulation distortion (FMD) (PWK's claim to fame: BTW, ringing looks like FMD or THD but really isn't.)

3) relatively circular SPL polars in azimuth and elevation--out to the angular design extent (e.g., 90 x 60 for midrange drivers, less for hf drivers)

4) high frequency extension to above audible frequencies (i.e., not using the device all the way to the extreme of the driver's FR performance)

5) flat FR.

6) flat or smoothly changing phase vs. freq.

Relative importance of low frequency compression driver attributes (IMHO):

0) freedom from ringing

1) freedom from FMD

2) relatively circular polars

3) low frequency extension in order to avoid having to add more horns/drivers/crossover filters

4) flat FR

5) flat or smoothly changing phase vs. freq.

The existence of coupling of these with each other in the real world is stipulated, but note that engineers tend to trade these attributes as if they're independent factors.

Note that I intentionally never talked about electrical or acoustic impedance even thought the Fostex driver/horn is pretty spectacular in that regard. "Reliability" (...actually survivability at extreme SPL output...) also isn't on my list of attributes since home use is almost always much less demanding than professional applications.

The TAD TD-4002 on a K-402 or a K-510 horn apparently hits well on all points except cost. They also chatter above 20 Khz, if that means anything since I don't know any human that can hear them at those frequencies.

Why would someone like K-402/K-69-A or K-510/K-69-A owner be interested in this type of "supertweeter" driver/horn? Because you can buy-in for less than a pair of TADs (~$3500+ US) added to the prices of a pair of K-402s or K-510s with K-69-As attached. Just adding the supertweeter with a crossover at about 10 KHz and carefully time-aligning might get you a "90% solution" to TADs on K-402s, or maybe even better depending on the quality of the crossover and time alignment.

Of course you'd have to be mindful of the size of the K-402's mouth and whether or not the relative offset of the supertweeter WRT the K-69-A is aimed directly at your listening position to get accurate time alignment with the K-69-A at 10 Khz.

From my inspection of the available data, the polars of both the Fostex T500AmkII and the K-402/K-69-A are not very far apart from 10-20 Khz, and the Fostexes go much higher and flatter in FR and phase without as accurate bore-alignment/concentricity of the K-69-A driver on the K-402 throat being required.

The data also implies to me that the Fostexes aren't chattering and would likely sound very clean.

Chris

[dtel]

1) freedom from ringing (i.e., 10-20 Khz--but is actually lower depending on age and gender of the listener) This is most important for clean impulse response, like cymbals, percussion, and other hf transients.

Yes and at my age and gender added with ship building for years, a long time ago. I would waste my time with a better tweeter, I may not even be able to tell it worked or not ! And it's not getting any better.

[DrWho]

The waterfall plots I've seen seem to indicate that mylar is even better behaved than Berrylium....and it's a whole lot cheaper too. I think the tradeoff is peak power handling, but I'm not sure that's a huge concern in the home.

[Deang]

Maybe I don't how to interpret polars properly, which is entirely possible I suppose, but when I look at the plots for the 402/69, the vertical and horizontal both appear to be collapsing pretty rapidly above 10kHz. I have trouble advocating the use of a tweeter which is also beginning to beam at the same point. The Fostex, regardless of how clean it is, is still a bullet tweeter. This tweeter has similar off-axis performance as the Beyma CP-22. If you go to the Beyma site, you can compare the polars of the CP-22 and the CP-25. Like I also said in the other thread, that's a mighty expensive tweeter. $1800 gets you almost half way to the TADs, or a pair of much better mid-drivers and tweeters with solid off-axis performance.

[Deang]

Al does not "chatter" like Ti. In fact, the paper clearly stated that Al had similar decay characteristics as Be in the last two octaves - which covers quite a bit of ground actually. No kind words for Ti at all in the distortion and sound quality departments.

[Deang]

402/69 vertical coverage, upper treble.

[Deang]

402/69 horizontal coverage, upper treble.

[Speakmeister]

I am curious about this tweeter... http://bmsspeakers.com/index.php?id=4528nd_specification

[Deang]

Beyma CP-25 horizontal coverage

[Deang]

Beyma CP-22 horizontal coverage.

[Deang]

Fostex tweeter plot can be seen in the attached PDF doc.

t500ammk2.pdf

[DrWho]

when I look at the plots for the 402/69, the vertical and horizontal both appear to be collapsing pretty rapidly above 10kHz.

I'm not sure I personally would call it rapid, but it definitely beams up top....the TADs should beam even more than the K69.

Above ~6.8kHz, the polar response on a 2" throat is going to be dominated by the compression driver / phase plug.

[Chris A]

Above ~6.8kHz, the polar response on a 2" throat is going to be dominated by the compression driver / phase plug.

That was my observation as well. My thinking is--"Why not save some bucks and just add a "supertweeter" to your K-69-As (assuming you are springing for K-402s or K-510s)?"...

For those that don't know, the K-402s and K-510s have to have a driver attached if you buy them from Klipsch, and that driver type doesn't include TADs. Adding a "supertweer" (assuming very well implemented crossover, time alignment, and physical mounting to the K-402 or bass bin) might be a way to save about $1K(US) or more and perhaps improve the polar coverage of the 7-20 KHz band, without requiring replacement of the factory K-69-A (or other Klipsch-supplied driver).

Now the only problem is to find a supertweeter that will fill the bill and whose price somewhat satisfies the "cheep skates" objecting to the cost of even the Fostex tweeter mentioned earlier.

Note that this thread isn't for me - I already own TADs: this thread is instead for those that may be thinking about investing in K-402s or K-510s with Jubilee, MWM, K-??? (midbass lookalike to the K-402), or home brew bass bins.

Chris

[Chris A]

Beyma CP-25 horizontal coverage

Quoted from here: http://www.usspeaker.com/beyma%20cp25-1.htm

"THE BEYMA CP25 COMPRESSION BULLET TWEETER IS DESIGNED FOR SOUND REINFORCEMENT AND STUDIO APPLICATIONS"

This tweeter's sensitivity is 104 dB/(W-m), with Al diaphragm, Al/Kapton edge-wound coil, and...ferrite permanent magnet.

Maybe that's why the price is so low...as well as its sensitivity? No rare earth materials on this baby...

Chris []

PS: I haven't got a clue as to which polar curve is which off-axis value (...just in case that matters..). Is it 0, 2.5, 5, 10, and 15 degrees off-axis?

[Guest " "]

In the KPT-535's a k-70-g tweeter is used with the k-69. In the MCM Grand line, the k-69 is the tweeter. are you guys sure the chatter is not on the low end? the k-69 has a recommended xover of 800hz, you k-402/k-69 folks are crossing over at 500hz. I don't think the k-1132/33 chatters, it's designed for high power output at 500hz.

[Deang]

O.K., it's a bullet tweeter with an attached horn designed to produce an even dispersion pattern instead of drilling a hole in your head.

[ClaudeJ1]

Al does not "chatter" like Ti. In fact, the paper clearly stated that Al had similar decay characteristics as Be in the last two octaves - which covers quite a bit of ground actually. No kind words for Ti at all in the distortion and sound quality departments.

But if you don't EQ up the falling response of a compression driver that uses TI, and filter it out in the network, then it has no audible effect. The problem range is up high, no down low. the Klipsch 1133 driver is titanium and performs more like a phenolic with better transients where it counts...........the midrange.

[tigerwoodKhorns]

One of the issues brought up recently in another thread is titanium-diaphragm compression driver "chatter". The K-69-A driver chatters, and so do a number of other Ti- and Al-diaphragm drivers. Beryllium diaphragms are said to be the "gold standard" presently, but command very high prices. One other approach is to entertain the idea of a "3-way Jubilee" without using the K-69-A driver as the tweeter. One such alternative is something like a Fostex T500AmkII driver, which uses "99% pure magnesium" diaphragms which exhibit high internal damping in the Mg material itself.

Interesting discussion. Is the chatter issue just related to conpression drivers?

I ask because my former speakers were B&W N and S 800 series with aluminum tweeters. My current speakers are TAD's with Beryllium tweeters. I have also heard B&W's diamond tweeters. The fancy materials and tests are interesting, but at the end of the day, you would be hard pressed to be able to pick the best of the bunch if you were blindfolded, meaning that the the plain old aluminum tweeters B&W used in their older Nautilus speakers sounded as good as any of them.

Only caveat is that none of these are compression drivers.

[Chris A]

Is the chatter issue just related to compression drivers?

Yes. The compression driver diaphragms begin to break up into complex non-pistonic modes of motion. You typically see a rise in response in the 10-20KHz region of these drivers (Titanium) - that is typically diaphragm breakup taking place.

The stiffer and lighter the diaphragm, the higher the frequency at break up. Beryllium diaphragm drivers typically start to break up above 20 Khz - an inaudible region.

Chris

[DrWho]

Is the chatter issue just related to compression drivers?

Yes. The compression driver diaphragms begin to break up into complex non-pistonic modes of motion.

???

Ummm...the exact same issue happens with a normal direct radiator too.

I suppose it's worse with a compression driver because the actual diaphragm is much larger than the throat (that's what gives you the compression). A 1" dome tweeter only needs to be rigid for 1" diameter. A 1" compression driver has a 1" throat, but behind it will be a 2-4" diameter diaphragm, which needs to be rigid for a 4" diameter, and there is greater pressure involved. However, the compression driver doesn't need to move as far as the 1" dome so I think it ends up being a wash. Maybe someone can dive through the math to know for sure?

I just know that cone breakup shows up in every tweeter measurement I've seen: both CD and DR. The fun thing about the breakup is it affects the polar response too.