Advent Design Concept

[TVTed]

Last night I added to my armada for 70's speakers (AR/JBL/Klipsch), by plucking a pristine pair of Advent/1's (1st Gen) off craigslist for a great price. I'm new to Advents and am really impressed with what I heard! It's wonderfully neutral and initially appears to have a greater ability to tame harsher sounding recordings than the other speakers I have. I'll consider refreshing the crossover and internal wire, only after getting further acquainted with what is going on.

A question for you good Adventists.....

Does anyone know the design thought behind offsetting the tweeter? At first blush it would seem the image focus would be enhanced if the tweeter were centered with the woofer....but hey, who the hell am I?

Looking forward to the journey (not the band)

Teddy

[Zilch]

Does anyone know the design thought behind offsetting the tweeter? At first blush it would seem the image focus would be enhanced if the tweeter were centered with the woofer....but hey, who the hell am I?

Conceptually, it's best with respect to cabinet edge reflection and diffraction interference if the distance between the tweeter axis and cab edge is not the same in any direction(s), though this is somewhat mooted by Advent's recommendation that the grille with it's small tweeter opening be in place for listening. Still, mirror-imaged would be a better design approach, as vintage Advents do not image worth a whit; it was not a recognized priority, and largely ignored in those days. There are also distribution logistics issues associated with manufacturing and selling in pairs.

Interestingly, spaciousness is somewhat enhanced via these "bad" alignments, as the common-mode output is decorrelated between channels at crossover and above. Artificial spaciousness is very much an element in the New England loudspeaker design legacy. I have recently become aware that some Advent "fried egg" tweeters are themselves asymmetrical, indicating that somebody may have been thinking about and paying attention to this stuff.

[Or, perhaps not.... ]

[TVTed]

It's got me thinking beyond freshening the crossover, and about possibly experimenting with new cabs that center the tweeter. I assume someone else has played with this?

[Zilch]

It's got me thinking beyond freshening the crossover, and about possibly experimenting with new cabs that center the tweeter. I assume someone else has played with this?

What I do to mod Advent HF is typically more comprehensive, but looking at pictures of the early /1, it appears that plugging the hole and cutting in a new one at the desired location would be the most direct approach. I'd probably just mod one this way to mirror-image the pair....

[TVTed]

What I do to mod Advent HF is typically more comprehensive.

Zilch - I'm here to learn. What mods are typically doing to Advents?

[Zilch]

Zilch - I'm here to learn. What mods are typically doing to Advents?

Large Advents in the background here:

Smaller Advents here:

http://techtalk.parts-express.com/showthre...738#post1650738

[TVTed]

Large Advents in the background here:

Smaller Advents here:

http://techtalk.parts-express.com/showthre...738#post1650738

WOW! Incredible amount of research, experimentation, conversation and results. Congrats to all who have participated.

My question now is this...It appears the Advent/1 has the same drivers as the Large Advent, but a smaller cab. So I assume the crossover kit/plans for the Large Advent combined with the Waveguide for for the Smaller Advents would be the way to go for me? Is there something I'm missing?

[Zilch]

My question now is this...It appears the Advent/1 has the same drivers as the Large Advent, but a smaller cab. So I assume the crossover kit/plans for the Large Advent combined with the Waveguide for for the Smaller Advents would be the way to go for me? Is there something I'm missing?

What to use is a function of the available baffle space. If you have 12" in width, the larger waveguide will fit.

In detail, the crossovers vary a bit with driver/waveguide complement. I've used the 8" square waveguide successfully on both the Smaller Advent and AR4x, now. Know in advance, however, that either way, there's about $200/pair involved in these "conversions."

The main thread is on AudioKarma with 11,305 posts, 717,402 views, and nearly 100 "registered" builds, not all of them Advents, of course, but quite a few, with additional threads by others regarding several of those linked from Post #1 under "Supplements:"

http://www.audiokarma.org/forums/showthread.php?t=150939

You must be registered there to view the images; tell 'em Zilch sent you.

[This thread should probably move to Mods, Tweaks & Upgrades here on CSP if we're going to discuss this further..... ]

[Pete B]

It's got me thinking beyond freshening the crossover, and about possibly experimenting with new cabs that center the tweeter. I assume someone else has played with this?

I strongly suggest that you try BSC if you want them to image:

http://www.classicspeakerpages.net/IP.Boar...?showtopic=2692

[Zilch]

By what means do we suppose that "BSC" EQ might improve imaging?

[Steve F]

Interestingly, spaciousness is somewhat enhanced via these "bad" alignments, as the common-mode output is decorrelated between channels at crossover and above. Artificial spaciousness is very much an element in the New England loudspeaker design legacy. I have recently become aware that some Advent "fried egg" tweeters are themselves asymmetrical, indicating that somebody may have been thinking about and paying attention to this stuff.

[Or, perhaps not.... ]

I think your "perhaps not" comment is closer to the truth. Trust me, in those days, it was the basics that counted. They were just discovering so many aspects of loudspeaker design and measurement methods that we now take for granted.

They were trying to get the FR right, they were experimenting with stuffing amount and type to squeeze another Hz or two from the low end, they were playing with x-o design, etc.

I know the head product designer at Advent (at that time) quite well. He has said to me on many occasions that "imaging" and "spaciousness" was not something they paid attention to at all, not in the slightest. In those days, the concept of 'imaging' was to make sure your speakers were in phase, you were the correct distance away, and you could hear Morello on the left and Brubeck on the right. That was it.

It was in that atmosphere that the Bose 901 came out. It was revolutionary to a degree that people not involved in the speaker business at that time can't quite grasp. I'm not coming out in favor of or opposed to the 901. That's a different discussion. I'm only reporting that in the '60's, the big three NE companies weren't concerned with "imaging" or "spaciousness." Not intentionally, anyway.

Steve F.

[Zilch]

I think your "perhaps not" comment is closer to the truth. Trust me, in those days, it was the basics that counted. They were just discovering so many aspects of loudspeaker design and measurement methods that we now take for granted.

Internal engineering docs from JBL ca. 1980 indicate they were having the same discussions there as we were in The Kitchen here recently. Even today, thirty years later, many of the issues are not fully resolved, so they still make excellent fodder for debates.

[And research.... ]

[Steve F]

Internal engineering docs from JBL ca. 1980 indicate they were having the same discussions there as we were in The Kitchen here recently. Even today, thirty years later, many of the issues are not fully resolved, so they still make excellent fodder for debates.

[And research.... ]

For some reason, 30 years after 1980 doesn't seem anywhere near as long as 15 years before 1980, does it? By 1980, some pretty advanced stuff was taking place, and a lot of really good research was going on. Today's computer-aided crossover and bass-alignment programs are far superior, and the materials/production methods are more advanced.

But by 1980, Allison had done his Boundary study, T-S had published their work, The AR-9 was 2 years old already (meaning that the research into the audibility of early baffle reflections, vertical alignment of drivers, and so forth, had already been completed, etc.). 1980 was very much in the 'modern era' of loudspeaker design and understanding.

By contrast, in the mid-60's, they were very much still in the 'discovery' stage. It definitely doesn't surprise me that JBL, et al. were discussing very advanced concepts in 1980.

But like I said, trust me, they weren't worried about driver alignment, flush-mounting, or intentional spaciality in the mid-60's.

Steve F.

[Pete B]

By what means do we suppose that "BSC" EQ might improve imaging?

psychoacoustics

Seems you still have not tried BSC?

[kkantor]

I think your "perhaps not" comment is closer to the truth. Trust me, in those days, it was the basics that counted. They were just discovering so many aspects of loudspeaker design and measurement methods that we now take for granted.

They were trying to get the FR right, they were experimenting with stuffing amount and type to squeeze another Hz or two from the low end, they were playing with x-o design, etc.

I know the head product designer at Advent (at that time) quite well. He has said to me on many occasions that "imaging" and "spaciousness" was not something they paid attention to at all, not in the slightest. In those days, the concept of 'imaging' was to make sure your speakers were in phase, you were the correct distance away, and you could hear Morello on the left and Brubeck on the right. That was it.

It was in that atmosphere that the Bose 901 came out. It was revolutionary to a degree that people not involved in the speaker business at that time can't quite grasp. I'm not coming out in favor of or opposed to the 901. That's a different discussion. I'm only reporting that in the '60's, the big three NE companies weren't concerned with "imaging" or "spaciousness." Not intentionally, anyway.

Steve F.

I'm with you on the commercial impact of Bose.

Let's also give some props to Varese, Xenakis, Stockhausen, Pink Floyd, John Lennon, ELP, LSD and the general adoption of spatialization as a compositional element in the popular music of the 60's.

A bit out of the public consciousness, Blumlein in the 30's, Snow, Moir, Olson in the 50's, (and many other researchers around the world), published extensively about stereo image quality using terms very similar to those found in the popular press today.

-k

[speaker dave]

Does anyone know the design thought behind offsetting the tweeter? At first blush it would seem the image focus would be enhanced if the tweeter were centered with the woofer....but hey, who the hell am I?

Looking forward to the journey (not the band)

Teddy

Back to the original question...

In any two-way sytem you can measure polar curves around the system in horizontal and vertical directions. If the tweeter is directly above the woofer then the horizontal polars will show effects of the drivers rolling off, off axis, but little time difference between units generated by moving in that horizontal plane. I say little because there is some dependence between listening angle and phase. At the very least a woofer will roll off at wide angles and the phase response must droop with that rolloff, appearing as extra delay.

Now if we do a vertical polar around the system then in one direction we get closer to the tweeter and farther from the woofer (generally up) and in the opposite direction the opposite happens. If the sytem is well designed then the units will fall in phase with each other on axis and symetrical nulls will occur at some up and down angle.

Now if we shift the tweeter an inch or two left or right, the geometry could be considered exactly the same if we revise horizontal and vertical to "around the plane bisecting the two units" and "on the plane in line with the two units". We would expect to see the same off axis effects, the same response nulls, just in a plane that is skewed by the offset of the tweeter.

Although it is the fashion these days to stack all our units in a vertical line (to get the best horizontal response and worst vertical response) the slight shifts we are talking about will have no effect on response near the on-axis position. They may make the worst null locations a little down to the left and up to the right, but by no means would I expect the imaging to be inherently worse, especially assuming you have toed in your speakers to listen in line with the center of the baffle. Since these typical offsets seldom put the tweeter more than 30 degrees offset from the woofer, I wouldn't loose sleep over it.

On the other hand, the unequal tweeter to edge spacing might be beneficial.

(Except we all know the direct sound is inconsequential...sigh.)

David

[Zilch]

Now if we shift the tweeter an inch or two left or right, the geometry could be considered exactly the same if we revise horizontal and vertical to "around the plane bisecting the two units" and "on the plane in line with the two units". We would expect to see the same off axis effects, the same response nulls, just in a plane that is skewed by the offset of the tweeter.

I think of it as the plane of equidistance between drivers being tilted as opposed to horizontal. This does have implicit consequences when two speakers are involved -- the intersection of the planes of each becomes a line in space, whereas, if the drivers are vertical-in-line, that intersection is a plane in space which, depending upon the alignment of the acoustic centers and phase, may itself be tilted vertically.

(Except we all know the direct sound is inconsequential...sigh.)

I'm a strong believer in the direct sound dominating and power response being fairly inconsequential. Most of what I read, and believe to be on track, describes our perception of frequency response to be best modeled as a time windowed response with the window long at low frequencies and short at high frequencies. For highest frequencies this admits the direct sound only. For mids an early reflection or two.

Alas, The Kitchen is closed, and our reverberant fielder has left the site.

CBT would easily satisfy his vision of nirvana.

[2010 -- Keele trumps Allison in delivering max horizontal dispersion.... ]

http://www.jblpro.com/catalog/support/getf...0&doctype=3

http://www.jblpro.com/catalog/support/getf...&docid=1409

[Pete B]

For some reason, 30 years after 1980 doesn't seem anywhere near as long as 15 years before 1980, does it? By 1980, some pretty advanced stuff was taking place, and a lot of really good research was going on. Today's computer-aided crossover and bass-alignment programs are far superior, and the materials/production methods are more advanced.

But by 1980, Allison had done his Boundary study, T-S had published their work, The AR-9 was 2 years old already (meaning that the research into the audibility of early baffle reflections, vertical alignment of drivers, and so forth, had already been completed, etc.). 1980 was very much in the 'modern era' of loudspeaker design and understanding.

By contrast, in the mid-60's, they were very much still in the 'discovery' stage. It definitely doesn't surprise me that JBL, et al. were discussing very advanced concepts in 1980.

But like I said, trust me, they weren't worried about driver alignment, flush-mounting, or intentional spaciality in the mid-60's.

Steve F.

Good points, the 1960s are not equal to 1980s.

Blumlein's pioneering work in the 1930s is fascinating:

http://en.wikipedia.org/wiki/Alan_Blumlein#Stereo

but I think in the 1960s most speaker designers were more concerned

with getting the basics right as you point out - crossover design

and box design were not as well understood in that time period.