A bit later, V.M.A. Peutz of Holland and some other smart people figured out that intelligibility could be designed into a system ahead of time. Peutz was a real genius, unlocking the whole intelligibility problem. While there are current “gods” of intelligibility, this is where it all came from, where it all started.

Autographing their book for an attendee.

When Peutz took one of the early TEF analyzers and programmed it to measure intelligibility, essentially - everybody objects to the term “measurement” in this regard but its an estimate taken off the data, it provided a place and explanation as to why so many systems of the time were falling short. The numbers really proved it.

Keith: I’ve also read that you were instrumental in bringing the first TEF analyzer to market.

Don: Cal Tech (university) came to us and asked if we’d take over the licensing of Time Delay Spectrometry. They had only one licensee at that point, after a decade, and we got them 120 or so licensees within a year. That was kind of an interesting experience, and when they said, ‘OK, now it’s going good and we want it back’, we gave it right back to them. We weren’t in the business to be wheeler-dealers.

Carolyn: Getting back to equalizers, in March of 1968, Don went to a convention and came back with this idea for equalizers. He went straight to Art Davis (an Altec engineer) and told him about it. Art wanted to do it a little differently, and Don said fine, I don’t really care, and he and Don were on the original patent.

Don: I spaced out what the filters had to do, and Art made a contribution I hadn’t thought about, to make frequencies combining, summing -

Carolyn: – and we had a prototype by September and went to the AES Convention that year and presented a paper on it.

Don: The chairman of the session had been involved in early equalization work as well, and when he read the title of the paper - “One-Third Octave Broadband Equalizer” - he kind of stopped and raised an eyebrow on the word “broadband”.

To him, what we were calling “broadband” was actually very narrow. Now, there’s nothing wrong with a filter being exactly the shape of whatever your problem is, but you can’t go after anything that isn’t the middle of the phase realm. There are things in there - “bumps” - that if you put an EQ on it, you only make the problem worse.

But if you put it in the minimum phase realm, then the EQ clears everything – it corrects amplitude, it corrects phase, it even corrects time. But it must precisely meet, and any divergence causes problems. There was a great deal to be said for a parametric equalizer, only nobody really knew how to make them at the time. Dr. Paul Boner was making these real narrow filter devices, trying to make the intrusion as minimal as possible. But one-third octave shaping filters could shape to the broadband nature of the problem beautifully, and they didn’t introduce any major phase anomalies as a result. You follow the general shape of the curve.

Now there might have been a little individual narrow-band anomaly, but these were so narrow that they were inside critical bandwidths, and thus they didn’t much matter.

The early days: a packed Syn-Aud-Con seminar led by Don & Carolyn.

Nowadays we have the correct parametric process and equipment, and there are also these beautiful programs that invoke the house curve and let you match to it. If you know what you’re doing you can get very refined equalization.

But in the meantime, one-third equalization dramatically improved loudspeakers of that time, and it also led to discovery of problems with signal alignment. This is still something no one has really pursued fully yet, at least that I’m aware of. I don’t think the equalization field and issues have been fully worked out yet.

Right now, with most of the current devices, you get further by improving the audible quality of sound systems with signal alignment than you ever do with anything else, particularly with the newer array concepts. It will always be a tough job to have more than one of anything in an acoustical system – nature doesn’t like that. So, you make your compromises.

The contribution that I felt like I made is that prior to this work, the acoustic environment was almost totally ignored. Yet all along that was the major tool to play with. And in fact, most rooms ought to be corrected by people doing sound systems. There’s an optimum match for every system to every room, so that you don’t add any more power than needed for maximum intelligibility and you don’t add any more absorption than necessary for maximum control of energy. This is what a good acoustical consultant should do, but it’s surprising how many of them don’t.