Phase Coherence or Time Alignment: Which More Imp?

Again, for anyone who doesn't know, I am a part of the current Fried loudspeaker operation. I needed to get involved because of my feelings for Bud.

Suits_me, I was also thirsting for the information you are seeking at one point. I could not read enough about the Frieds. Thankfully, a significant amount of this can be found at http://imf-electronics.com/Fried/index.html, including the C series of pyramidal, time aligned minimonitors. There are a lot of pdfs of old sales literature. Amazing how quickly and profoundly the computer has impacted this area, most everything here was typewritten and mimeographed.

I have Bud's personal pair, and sure enough, they have been tweaked and tweaked, but think that the pair Skrivis owns are probably not all that different sounding. They have an uncanny ability to produce music without so much of the resonances that we never notice until we have a pair of loudspeakers that don't produce them. Also, as someone who has been around enough audio equipment as I have, to find a pair of speakers that image as these do really leaves one impressed. I also have the matching O subwoofers that they sit on, but don't look anything like that on the website, as they switched to a design that was narrow and deep ala what is currently in vogue.

I think you'll agree with me when I first perused the site that the description of the man literally being a generation ahead of his time was accurate. Alas, there will NEVER be another...

Yes, I surely do like my C/3-Ls, and they've served me well for 15 years or so. I'm in the process of getting them upgraded to C/6 status.

Suits me:

You don't need a stepped baffle to get time-alignment. A sloped front baffle actually works better.

Bud did recommend that most of his bookshelf speakers be listened to from a certain axis.

This brings me to my next point, and it involves an earlier comment I saw about the new Monitor 7 and Studio 7 not being time-aligned.

The acoustic center of a typical tweeter is closer to the plane of the front mounting plate than in a woofer. Since you're sitting out in front of the speakers, we can say that you're closer to the tweeter (to the tweeter's acoustic center). That's a bad thing if we're looking for time-alignment.

So we need to move the tweeter farther away (or the woofer closer). Stepping the baffle can move the tweeter farther away, as can sloping the baffle.

With something like the Monitor 7s, you're meant to listen on-axis with the woofers. The tweeters are off-axis, so they're farther away from your ears. In this case, time-alignment is accomplished without sloping or stepping the baffle.

All we're really looking for is to align the _distance_ from each driver to your ear to be the same.

So Bud had designs that had sloped front baffles, and he also had designs where you were meant to listen from a certain point where the distance from the drivers to your ear was equal.

I used to listen to my Betas on stands that tilted them back. An possibly equivalent method would have been to place them on taller stands. In this case Bud recommended tilting. I can only assume that he looked at the positioning of the drivers and their respective acoustic centers and determined that placing them tilted back was correct.

He recommended that the A/3s that my brother owned be placed on taller stands, with the woofer at ear level.

As you can see, it's difficult to judge whether a speaker is time-aligned or not, unless you also know where your ears are meant to be in relation to the drivers.

BTW, I don't feel stepped-baffles are a good idea because you can get big problems with reflections and diffraction. Fried suggests another problem:

"We have developed as our first possibility three drive systems, in time proper enclosures, joined by a network that makes them “phase coherent”. These we must get to work in a “phase aligned” fashion, i.e., all providing the proper data to the listener at the proper time. The only way known to the author is to place the drivers on a sloping baffle, so that the propagating center of each driver is in vertical alignment with each of the others. If we place them on a flat board, we will be phase coherent but not phase aligned; if we place the bass units out in front, with a step back to the mid, and another step to the tweeter, we will get proper time at just one seat on axis, every other seat in the room being very out of phase; and we will have introduced severe problems in the vertical plane. The best we can do is to slope the baffle, either by designing it in; or by recommending that the speaker be used on a tilt back stand."

Note that he re-thought this later and arrived at time-alignment as done in the Monitor 7s as an alternate. (I first saw that same arrangement on the Studio IVs.)

I regret that I never got subwoofers to match my C/3-Ls. I am planning to buy a pair of Monitor 5s, which likely don't image as well, but have better bass and maybe even better midrange due to less reflections back through the cone.

The Monitor 7s evidently may have bass that's a bit better than that, but they use a tweeter that is not as good.

Perhaps a much deeper C style cabinet would help avoid reflections, but you're still dealing with pretty tight spacing. The larger cabinets of the floor-standers give you much more room for the line and its folds, but you get a larger front baffle along with it. Topping a rectangular cabinet with a truncated pyramid would help, but then your cabinet costs go way up.

Suits_me> Is there a vintage site with a picture of the C/3L?

There is a picture at: http://groups.yahoo.com/group/IM_Fried/?yguid=180415640

They appear to be of early-middle vintage, judging by the drivers. My C/3-Ls resembled these at one point, although I used a single piece of foam to cover the tweeters without a cutout for the dome. (The foam they sell for air-conditioner filters works quite well.)