EV35 and K-77

[digjr]

Hi,

Does anyone know where I can get four horn lenses for the above? Also, I have just purchased a pair of tweeters with "baby cheeks" lenses. The magnet assembly is twice as thick as my other rectangular K-77's. They also have push type wire connectors. Numbers are 829 0165 747. They look like EV's but are heavier. I tried to include a picture but keep getting an error message? Any thoughts on what they might be? I have hooked them up to a pair of Belles and they sound fantastic! I paid $37.00 for the pair and would like to know what I have.

Thanks alot,

Don

[djk]

Sounds like an EV ST350B. Same diaphragm as the K77, two stacked K77M magnets.

[djk]

Sounds like an EV ST350B. Same diaphragm as the K77, two stacked K77M magnets.

[digjr]

Thanks DJK,

I thought maybe that's what they were.

[WMcD]

Page one of spec. sheet.

[WMcD]

Page two of spec. sheet.

[WMcD]

Page three of spec. sheet attached.

[WMcD]

Page 4 of spec. sheet for EV ST350B attached.

Gil

[WMcD]

I scanned those at 200 dpi so that they'll print nicely. They're too large for easy viewing though.

You'll see the effect of things I talk about quite frequently. In other contexts.

Note that without equalization via a tweeter crossover filter, the lower response is quite good at 3500 Hz and it goes down to about 103 dB per watt at 15000 Hz. This shows that the motor, even with the big magnet, can't drive the mass of the diaphragm, plus the acoustic load of the horn, at high frequencies. It is a demonstration of the actual SLP at the throat as delivered by the diaphragm and motor, looking into the horn.

So, why don't we see that in other horn systems.

1) The horn here is a constant directivity type, more or less. That means it does not narrow the beam at higher frequencies. If it did, that directivity would give it some on axis gain at high frequencies. That is a type of equalization where, again on axis, the output of the horn increases.

2) Other horn designs do have this on axis gain. The T-35/ K-77 does it, I believe, because of the ribs which set up some sort of a diffraction effect which narrows it down at high frequencies on axis. But it you look at the polar response of the T-35. The off axis response at high frequency is falling off. It probably is not just the ribs, but they help.

3) Another way of getting this narrowing of the beam in the high frequencies is to use a mouth which is small in the vertical direction. Like we have with a lot of the Klipsch exponentials as they are usually oriented.

That means it is not directional at low frequencies. But as frequency increases, the vertical dimension is becoming large enough to become direction. You have to look at this in terms of wavelenghts. At high frequencies the wavelength is smaller and the vertical dimension of the mouth is, in terms of wavelength, bigger.

This is a bit contrary to what you think looking at the mouth of the exponentials when typically oriented. You might think the pattern is defined at all frequencies by the aspect ratio of the mouth, as if there is a flashlight at the throat shining through the rectangular mouth. Not so, that is only true at high frequencies. At low frequencies (long wavelengths) there is a broader vertical pattern. Again, as frequency goes up, the vertical pattern narrows, giving us some gain.

The K-55 driver has falling output above 3000 Hz. Yet the K-400 horn gives some gain. It does narrow in the vertical, this is called controlled directivity. PWK speaks of this.

4) The issue we see with the ST350 is that we do not have gain from the horn. The pattern doesn't narrow and it is called constant directivity. It takes a big mouth in both horizontal and vertical to do this. You'll note the Klipsch tratrix horns have the same large rectangular mouths. Importantly this means the constant angle will prevent off axis acoustic output in the operating range. So the sound is not sprayed toward the walls of the room. A good thing.

5) However, we now have the problem of reduced output overall. At 15000 Hz we have just about enough and going down in frequency from there, too much. The solution is to use the passive crossover circuit to knock down the lower frequencies. Which is a bit unconventional.

6) We usually think of tweeter crossover filters of turning on at a given frequecy and then being flat from there up. Not so here. The filter output is tailored by the component values of L and C to not be flat. Its output is poor at 3000 or 6000 Hz (note the two designs) to knock things down, and it doesn't fully turn on 'til about 15000.

7) You can see how this could work in the Ref series with direct radiator woofers. If the woofer out put is in the high range of the 90's dB per watt, we have more room to work with passive crossover to the treble tratrix horn.

8) It may well be that the output of the diaphragm in the Klipsch tratrix treble horn is falling of at high frequencies, particularly because it is more massive. It has to go lower too. If the raw response is falling, say to 96 dB at 15000 Hz, and higher below, we don't have to worry. A passive crossover can be designed to equalize things overall to 96 dB overall in the tratrix horn. (I'm picking 96 dB out of my hat without checking specs. Yet this is pretty much the story.)

Just in case anyone wanted to know.

Gil

[digjr]

William, thanks for the info! I have been gone for a few days so I'm sorry it took a while to respond. It's a full plate to digest, but I understand the concept. Compared to my K-77's they are not quite as sharp and crisp but I am running staight through a 3 way crossover. I'll try a few different options.

Other question, I have four K-77 drivers (the guy told me they were a pro line?? Originally two drivers into one lens. Does anyone have any old lenses that they are not using? Or any suggestions of replacements? EV says they have no more but did give me a few names of people to check with (no luck yet). It's such a shame to have the four, in great shape, but not be able to use them.

Thank you,

Don