Edgar

Coincidentally, I am retiring the end of this week! I hope to use it as a reason to start doing something. Perhaps several somethings.

It's kind of sad; nobody on the planet knows more about Altec drivers than Bill. But the best technical people often are not the best business people. Perhaps the new owners will be more responsive to customer inquiries.

I've been trying to reach GPA for months; at least a half-dozen phone calls, email messages, and contacts through ebay. No response. I've pretty much given up on them, will probably try something like a FaitalPro HF146 instead.

Ah, that's a shame. Thanks for the info.

Thanks, I already tried that. Funny thing is, I worked with Bill Hanuschak at Altec Lansing in the 1990s ... had a desk not 20 feet from his lab. But it's obvious that he doesn't remember me.

Thank you. Now if I could just get GPA to answer email messages, phone calls, ebay contacts, or mental telepathy, I could actually purchase the drivers.

Don't forget that the narrowing polar response of a 15" direct radiator comes into play around 500-600 Hz. So the rolloff due to VC inductance is at least partially compensated on-axis by the polar response.

Dark Side of the Moon, Pink Floyd

Hanging on in quiet desperation is the English way. The time is gone, the song is over, thought I'd something more to say.

Suddenly I feel even older.

I've had pretty good results with Tidal HiFi, but lately I'm finding that more and more of their tracks are "remastered". And the quality of the remastering can vary considerably. For example, the other day I was listening to Crime of the Century and the low bass was gone. It was like everything below 60 Hz simply didn't exist.

"When everyone is out to get you, 'paranoid' is just good thinking." - Dr. Johnny Fever

I have a friend who uses several AE woofers (don't remember which model -- Dipole15 comes to mind) in an open baffle, and swears by them. The Crites and current Klipsch woofers are made by Eminence. Eminence may not be perceived as an exotic brand, but it's hard to disagree with their results. For articulation, speed, and tone, there is a huge following of Altec Lansing 416 and 515 16" woofers, now made by Great Plains Audio. But you'll pay through the nose for them.

You don't understand ... after the house purchase there is no money left. 😟

They're less than an hour's drive away from me. If I weren't in the middle of buying a new house, they'd probably be in the back of my Grand Cherokee right now.

I thought that the photos looked familiar ... Again, no affiliation. Don't blame me! 🙂

https://stlouis.craigslist.org/ele/d/union-klipsch-cornwall-4s-new/7437525535.html No affiliation.

Anybody on the Forum in contact with Don Keele? I was in an extended email conversation with him a couple of weeks ago, when he suddenly stopped replying. I'm concerned that he might have fallen ill, or worse.

I searched and found almost nothing -- a few references to copper-plated screws, but nothing in the metric size that you cited and everything in bulk quantities. However, I did find this: DIY Copper Plating. Might get you there.

That is something upon which we can both agree. I don't understand what you're trying to say and you don't understand what I'm trying to say, so there is no reason for either of us to say anything more.

I don't see how "ideally you want each driver's peaks to be time aligned when they are reproducing the same frequencies" equates to "the input of filter to output filter phase doesn't really matter it's the summed output to output that is important". Also, unless the lowpass and highpass outputs are perfectly in-phase at all frequencies, they may sum to unity at and near the crossover frequency on-axis but they won't sum to unity off-axis. Not a big problem in most living rooms, but a big problem in an auditorium.

Nope, for exactly the reason that I offered with my example of the 1st-order crossover network. The lowpass portion and the highpass portion are 90° out of phase with each other at the crossover frequency, meaning that the peak of the sinewave coming out of the highpass filter is displaced in time by ¼ wavelength relative to the peak of the sinewave coming out of the lowpass filter. Yet the two sum perfectly to the original waveform.

Here's an example of how complicated the issue of crossover phase can be. In a Linkwitz-Riley crossover network, the lowpass section and the highpass section are perfectly in-phase at all frequencies. So you would expect that a square wave, passed through the crossover network and then recombined (lowpass output and highpass output added together), would still be a square wave. The attached graphic shows what happens when you do exactly that. The weird thing is, there are numerous studies indicating that you can't hear the difference! That's right: a real square wave and the ugly mess that used to be a square wave, shown below, sound exactly the same (or so it is claimed).

Again, phase is just not a simple issue. Both drivers "reaching their peak at the same time" doesn't even explain it adequately. For example, the 1st-order crossovers cause the LF and HF drivers to be 90° out of phase with each other at the crossover frequency. Yet they sum perfectly.

I think you've identified a large part of the problem. In the context of a crossover network, the phase relationship between the two drivers that are "crossing over" is the issue here. There are many other phase issues that can be addressed, but they are not part of this discussion.