soundguy64
12-27-2018, 08:21 PM
Since a tweeter stopped working on one of my 601-8D "Duplex" speakers a few weeks ago, I've been doing some digging on the puppy. A couple of issues and interesting facts have surfaced:
1) The crossover issued with the speaker is the N-3000-E, which I knew already. This was billed as a 3 kHz two-way crossover. As I found out, it isn't. It's a 3 kHz high-pass filter with a level control for the tweeter. The woofer is fed straight to the speaker terminals; no filter at all. Want upper mid-range? You got it! (Too much of it, in fact.)
2) There is a center-tapped coil used in the tweeter filter, but only half of the coil is connected across the tweeter terminals (via the level control as part of the filter). The other coil half is wired in series with the tweeter! Yup, this "super tweeter"--supposedly having a useful response up to 22 kHz--has a high-cut filter on it.
3) The tweeter is wired out-of-phase with the woofer. Seems strange, since the tweeter is mounted right on the front of the woofer's center pole piece in what should be an almost perfect time-aligned position with the drivers in phase.
As mentioned, one of these tweeters is no longer working. As measured with a VOM, there is no continuity across its terminals at all, which tells me the driver may not be fried, but may just have a broken lead underneath the center dust cover. I can only hope that's what it is, because I've had no success finding a source of Altec 3000A tweeter elements. All this leaves me with questions.
1) Is there a good source of replacement elements for the tweeter, or am I gonna hafta replace the whole tweeter (assuming it is fried)?
2) I'm assuming that "3000A" is the variant used in the 601-8D. Am I correct?
3) What is the nominal impedance of the 3000A (or whatever tweeter is used in the 601-8D)?
4) Why is the tweeter wired out-of-phase with the woofer?
5) Why is that pesky half-coil wired in series with the tweeter? Somebody at Altec allergic to highs in the 1960s? (I mean sonic highs.) I am--you should pardon the expression--baffled at this. :dont-know:
Any pertinent insights offered will be much appreciated. Many thanx to all who read this.
1) The crossover issued with the speaker is the N-3000-E, which I knew already. This was billed as a 3 kHz two-way crossover. As I found out, it isn't. It's a 3 kHz high-pass filter with a level control for the tweeter. The woofer is fed straight to the speaker terminals; no filter at all. Want upper mid-range? You got it! (Too much of it, in fact.)
2) There is a center-tapped coil used in the tweeter filter, but only half of the coil is connected across the tweeter terminals (via the level control as part of the filter). The other coil half is wired in series with the tweeter! Yup, this "super tweeter"--supposedly having a useful response up to 22 kHz--has a high-cut filter on it.
3) The tweeter is wired out-of-phase with the woofer. Seems strange, since the tweeter is mounted right on the front of the woofer's center pole piece in what should be an almost perfect time-aligned position with the drivers in phase.
As mentioned, one of these tweeters is no longer working. As measured with a VOM, there is no continuity across its terminals at all, which tells me the driver may not be fried, but may just have a broken lead underneath the center dust cover. I can only hope that's what it is, because I've had no success finding a source of Altec 3000A tweeter elements. All this leaves me with questions.
1) Is there a good source of replacement elements for the tweeter, or am I gonna hafta replace the whole tweeter (assuming it is fried)?
2) I'm assuming that "3000A" is the variant used in the 601-8D. Am I correct?
3) What is the nominal impedance of the 3000A (or whatever tweeter is used in the 601-8D)?
4) Why is the tweeter wired out-of-phase with the woofer?
5) Why is that pesky half-coil wired in series with the tweeter? Somebody at Altec allergic to highs in the 1960s? (I mean sonic highs.) I am--you should pardon the expression--baffled at this. :dont-know:
Any pertinent insights offered will be much appreciated. Many thanx to all who read this.