high frequency drivers

[Scp53]

Is there a big difference between the phenolic diaphragm compression drivers used in some of the heritage klipsch speakers vs the titanium in the reference series? I have two pair of klipsch bookshelf speakers. one has a phenolic driver mounted on the horn and the other pair has aluminum compression drivers. When I compared these to the titanium drivers in the reference line its like a night and day difference. Why would klipsch not update there bigger speakers(like the Heresy II, Klipschorn and La Scala) to better drivers? Or am i mistaken and they already have?

[TBrennan]

SCP----Phenolic diaphragms have certain advantages over metal diaphragms and metal has certain advantages over phenolic. It depends on what you're doing and how you do it.

If you want to crossover below 500hz with a 1" throat driver it's best to use phenolic; 1" throat metal diaphragm drivers have problems working lower than 500hz. But with phenolic you'll need to use a tweeter, thus a 3-way.

But if you can crossover at 500hz or higher you can use a metal diaphragm 1" throat driver and get away without a tweeter; thus a 2-way.

Then you have cost. A phenolic 1" mid driver and a tweeter can be less expensive than a single 1" aluminum driver meant to reproduce mid AND high frequencies.

Fact is that every diaphragm material has it's devotees who can make a sensible arguement for their viewpoint. For instance there are those that think phenolic gives a warmer, more realistic tonality to midrange. Talk to some RCA horn enthusiasts, talk about phenolic nuts.

Some horn enthusiasts think that aluminum sounds better than titianium and the finest drivers I've heard were aluminum. My opinion. But those drivers I like so well don't have titanium as an option. However titanium is more reliable than aluminum. Personally I think titanium sounds fine going by the titanium JBL Pro drivers I've owned and the Klipsch I've heard.

[Scp53]

TBrennan, thanks for your help

[WMcD]

It is my understanding that there are a lot of tradeoffs when you design a horn driver.

Certainly one reason the Heritage series used phonelic is that EV and Atlas did so. "Availablility" as PWK said. At the time the alternative of metal diaphragms was very expensive.

One thing that may dictate that phonelic is okay is that drivers don't work very well below their resonant frequency and I think both the K-55 series have a resonant frequency just below 400 Hz.

The resonant frequency is a function of both mass and the spring formed by the suspension. But probably mass is what is the easiest to play with. The bottom line is that a heavier diaphragm may be necessary to get the low end response reasonable. So there is no reason to not use the well understood and easy to produce phonelic. No reason to start with something lighter and then add mass to reduce resonant frequency.

The problem OTOH is that low resonance and heavy diaphrams make high frequency response difficult to achieve. The energy of the motor is used up trying to move the mass back and forth rather than pumping the air load. The motor runs out of steam.

Generally, it seems the output of the driver extends for X octaves above the resonance. So, if you have a driver with a resonance of 400 Hz and it rolls off at 6000 (with a given horn which has some on axis gain from 3000 to 6000) there is something you can do.

That something is to use a lighter diaphram with a resonance at 800 Hz. Now, octaves being what they are, the upper limit goes up to 12000 Hz. But you need aluminum or titanium to make the lighter diaphragm.

Diaphragm break and how to make the surround comes into play. E.g. the metal dome rings across its surface; and how do we make a good floppy surround out of metal, or bond it to an elastic material.

It is not even quite that easy because the diaphram assembly is not just the dome, but also the wire and the former cylinder it is wound upon. It was found that aluminum wire is ligher than copper though difficult to work with and less conductive. But balancing conductivity and mass, aluminum wire can be the optimum; for that issue.

But going back to the question. You'll note that drivers which claim high end response and which can be used without an additional tweeter cross over at 800 or 1200 Hz, or higher at the low end (like the Refs). It is all "bandwidth." Note they are not going as low as the Heritage with a K-55.

You will see the large drivers with 4 inch diaphragms, titanium diaphragms, and 2 inch throats, and claims for high end response. These can work, in part because the 4 inch driver has a larger voice coil with more wire in the gap, in part because of very strong magenets, and in part because of very sophisticated phase plugs.

None the less, getting any driver to have an unequalized, flat output over more than 3 or 4 octaves is not really accomplished.

Let's see, call it 400 Hz to 800 Hz; 800 to 1600; 1600 to 3200 Hz. That is what the K-55 is doing in 3 octaves. The horn narrows the beam to bring it up to 6000.

(It is interesting to note that the K-Horn bass driver starts at 40 Hz. You go up the octaves to 80, then 160, and 320 . . and then there is a problem. I.e. same numbers divided by 10.)

I suspect that the Ref drivers are using some equalization in the crossover to knock down the lows (which is so maintain the highs).

The same is true of the big 4 inch drivers. They are not flat to 15,000 Hz and require some equalization. I took a look at the websites for midrange manufactures some years ago. There are a lot of caviats. HF output shown is on a given horn, or power handling only well above resonance.

The bottom line is that I believe there was nothing very wrong about phonelic in the first place. It was and is good for the application. There have been some better materials which can be more effectively put together these days. None the less, the ancients knew what they were doing.

Anyone want to descibe the Western Electic 555.

Gil

[ZAKO]

JBL has taken a 4" diaphram the 2450 & redesigned its surface Drawing it a little thinner then coating it with Aquaplas (used on submarines) This smoothed out resonence problems in the audible band . Called 2450SL . It has the longivity of titanium but the smoothness of aluminum & phenolic. (400hz to 18000hz)

[djk]

The 476 was the first with aquaplas over a smooth dome.

Is the 2450SL ribbed and then coated, or is it a smooth dome and coated?

[ZAKO]

The 475 476 was born out of the K2-95000 The 2450SL I suspect is the same voicecoil/diaphram & is smooth dome.(aquaplased) I believe the smooth domed without coating is 2445...Im not shure.