gar

I've been down this road, and considered an APT series driver as well as the Morel MTS-37. The Morel is a horn loaded soft dome tweeter and is supposed to be an excellent device. I haven't changed parts, but found improvement with the piezo after damping the whole rear of the tweeter with mortite. It seemed to smooth them out a bit and could be attributed to lowering the resonant frequency of the plastic horn, or the increase in mass could have just made it less excitable by the woofer interaction. Or, I'm just crazy. There are certain people around who claim to have tamed the piezo tweeters in other designs with a coat of Dammar varnish. I can't comment on the effectiveness of this, and don't intend to find out. I'd still be interested in trying the APT or Morel out. As you've heard, the Alpha 10 woofer does pretty amazing things in that cabinet. Some of the magic of this design is in it's simplicity though. When going to a different tweeter, this will be lost as either way will require a 2nd or 3rd order network, and varying degrees of attenuation. Still, at the 2 Pi's price point, Wayne has a very unique product. I know of nothing else that will "get it done" like the 2 Pi for the money. Good luck and good listening! Jerrod

The little one π's and two π's are entry-level products, and should be judged for comparison as such. However, as I said, I think the KSN 1038 tweeter is a good sounding device, particularly for their cost. It has flat response and low distortion, whereas the annoying KSN 1005 peaks in the vocal overtone region very badly, giving it a "spitty" sound which I suspect is the single biggest thing that people don't like.

I would not pair a high-efficiency 8" or 10" midwoofer with a 1" compression horn because this is to essentially have two midrange devices. If building a four-way, then a transition from 8" or 10" midrange to 1" compression horn is perfect. But if building a two-way system, I'd rather have a tweeter that is tuned a bit higher because that allows the system to deliver greater bandwidth. After all, a 1" compression horn shares over three octaves of operating range with high-efficiency 8" or 10" speaker, so pairing them together wastes a lot of bandwidth.

One of my favorite little bookshelf speakers of all time used a JBL Profesional Series 2115 - which is an 8" full range midwoofer - paired with a KSN 1038 tweeter. The only parts used were a 0.5mH coil in series with the (8 ohm) woofer and a 0.33uF capacitor in series with the tweeter. The coil tamed some rising response in the 8" driver and the capacitor attenuated the tweeter to match. Functionally, the speaker was crossoverless, like current models. This was a "Professional Series one π" speaker, and it combined a $200.00 JBL driver with a $10.00 piezoelectric tweeter, and it was probably my most popular model in the 80's. Sounded fantastic, and there are still many, many units out there, with happy, long-term owners.

Link to price & specs at Parts Express:

• Peerless Horn Tweeter

The 0.33uF cap I put in series with the tweeter last night did help a lot (And I came up with it without even know about the One-Pi Professional!). I will certainly explore other insulation material as well. BTW, going through the archives, you use to recommend the 22ohms across the speaker terminals for tube amps, but have not mentioned it in a couple of years. Is this still valid? When I did it, it did tone down the tweeter.

Thanks for the advice on the 1" compression. But just to play devil's avocate, the 12" and 15" Eminence drivers have pretty good SPL up to 3.5KHz as well. How is using a 1" compression with these guys different from the 10"?

gar.

About attenuation of the KSN 1038, this was required for matching with the JBL 2115 because the JBL part wasn't nearly as loud as the Eminence Alpha 8 or Alpha 10. The situation is reversed with the Eminence midwoofers though, and the tweeter is slightly less loud.

In all honestly, if you measure a one π or two π with Eminence Alpha 8 or 10, you'll see that the tweeter isn't as loud as the midwoofer. There is a slight shelf, caused by the tweeter's output being less loud than the midwoofer. This is followed by a rise in output from the Alpha's, which is subdued by the coil. But the point is that the tweeter is already generating less output than the midwoofer, and adding series capacitance attenuates it further.

If your room is a bit bright or you simply prefer relaxed tone, then additional attenuation of the tweeter may be perfectly suited to your tastes. But the area that is hottest in the current model is actually the 1kHz to 4kHz vocal overtone range, which is covered by the midwoofer and not the tweeter. That's what the series coil is installed to subdue.

In regards to addition of a 22 ohm shunt resistor across the speaker terminals, there is absolutely no harm and I still like the idea. My reasoning was that since the one π and two π loudspeakers become more like a purely capacitive load at high frequencies, this may cause come amplifiers a problem, and some might even oscillate.

Some SET amps are known to be pretty sensitive to their loads, and I expected that perhaps the output transformer might interact with tweeter capacitance in a peculiar way, again, possibly even setting up an oscillation. So the 22 ohm swamping resistor was suggested to damp the circuit, just in case. There certainly is no harm in doing so.

I haven't found a single case where it was needed though, and I personally cannot hear the difference on any amplifier I ever used with one π or two π loudspeakers. So I stopped actively suggesting it, for the most part. But it would be the first thing I would suggest, if one were to find high-frequency oscillations in the circuit.

I'm not sure I'd be happy with response limited to 16kHz in a tweeter of this class though. I used to use a device that generated good response out to 40kHz and I loved the way they sounded. Then again, I quickly stopped using them because they were too fragile and easily blown.

Another direction I'd look at would be the ribbon devices. The old Infinity EMIT tweeters were really something, and now days there are several manufacturers that provide robust high-efficiency models.