[darkmoebius]

Do the same rules for vertical center-to-center placement of drivers (0.5 or 1.0 highest freq. wavelength) apply to the pair of woofer lines?

I know Dr Griffin states in his white paper that horizontal distance between mid-woofer/tweeter lines is critical:

While the vertical separation of the drivers in each line of the line array plays a significant factor in the performance of an array, the horizontal spacing between the two lines needs to be minimized to reduce image shift as the sound transitions between the woofers and the tweeters. The design is essentially the same as if you designed a two drivers (woofer/tweeter) speaker that is placed horizontally.  Care must be paid to minimize horizontal lobing from the side-by-side drivers.  Some things to consider are the basic horizontal dispersion of the individual drivers that would ideally be similar and overlap to at least 30 degrees off axis.   The two lines need to be located so that their horizontal center-to-center distance is less than a one wavelength at the crossover frequency.  Finally, a higher order acoustic crossover may be necessary to minimize any
driver interaction above and below the crossover point.

I get that both woofer lines are individually close enough to the planar/ribbon line, it's the distance from each other that I am trying to understand. 

[Rick Craig]

Do the same rules for vertical center-to-center placement of drivers (0.5 or 1.0 highest freq. wavelength) apply to the pair of woofer lines?

I know Dr Griffin states in his white paper that horizontal distance between mid-woofer/tweeter lines is critical:

While the vertical separation of the drivers in each line of the line array plays a significant factor in the performance of an array, the horizontal spacing between the two lines needs to be minimized to reduce image shift as the sound transitions between the woofers and the tweeters. The design is essentially the same as if you designed a two drivers (woofer/tweeter) speaker that is placed horizontally.  Care must be paid to minimize horizontal lobing from the side-by-side drivers.  Some things to consider are the basic horizontal dispersion of the individual drivers that would ideally be similar and overlap to at least 30 degrees off axis.   The two lines need to be located so that their horizontal center-to-center distance is less than a one wavelength at the crossover frequency.  Finally, a higher order acoustic crossover may be necessary to minimize any
driver interaction above and below the crossover point.

I get that both woofer lines are individually close enough to the planar/ribbon line, it's the distance from each other that I am trying to understand.

The spacing of the two woofer lines is important because it effects how they couple around the crossover point. The wavelength rules are affected not only by the woofer diameter but also the driver's dispersion.

[darkmoebius]

The spacing of the two woofer lines is important because it effects how they couple around the crossover point. The wavelength rules are affected not only by the woofer diameter but also the driver's dispersion.

Thanks for the response Rick, would you mind elaborating - if you have time and it's doesn't impinge on any proprietary work?

I was originally going to ask if the two overlapping dispersion/radiating fields somehow sum, but couldn't even think of a way to form a question about it.

[Rick Craig]

The spacing of the two woofer lines is important because it effects how they couple around the crossover point. The wavelength rules are affected not only by the woofer diameter but also the driver's dispersion.

Thanks for the response Rick, would you mind elaborating - if you have time and it's doesn't impinge on any proprietary work?

I was originally going to ask if the two overlapping dispersion/radiating fields somehow sum, but couldn't even think of a way to form a question about it.

It's not really easy to explain - just something I've observed from building several designs.

[Rick Craig]

The spacing of the two woofer lines is important because it effects how they couple around the crossover point. The wavelength rules are affected not only by the woofer diameter but also the driver's dispersion.

Thanks for the response Rick, would you mind elaborating - if you have time and it's doesn't impinge on any proprietary work?

I was originally going to ask if the two overlapping dispersion/radiating fields somehow sum, but couldn't even think of a way to form a question about it.

Just read your other posts at another site. Sorry to sound so vague but I've spent quite a few hours in the past with phone calls / emails / online posts advising others on line arrays and been burned by a few that sucked the life out of me.

One of them is the guy who suggested that I copied his use of 3" drivers in his reply to you. The same person was booted from another forum for being a total ass to myself and others as well. Whatever he says I would take with a grain of salt - he was practically laughed off the forum by people who know how to properly design speakers. He became very hostile with me when I questioned some of his design problems and he won't engage in a civil conversation if you challenge his design. I feel sorry for anyone who has emulated his work because it's a poor design built with the cheapest parts he could find.

It is a real problem that there's a lack of good information on DIY arrays for home use but those of us who do this for a living just don't have the time to help everyone who has a question. It's not fair to my customers to delay their delivery time while I spend hours with those who never intend to buy anything. Recently I had someone who called me 3-4 times and I spent probably an hour or more each time on the phone. The guy later admitted he was interested in selling speakers and never even offered to compensate me for my time! So I decided with the next call I would ask for a consultation fee and after I made that request the conversation ended. I could go on with other examples but I don't want to sound like I'm ranting - just trying to explain how things are from my perspective.

If you want to build your own design I would take Jim Griffin's paper as a starting point, buy some good crossover design software (or a DSP active crossover), and measuring equipment. I wouldn't even attempt one without being able to measure it because you're simply pissing in the wind. By measuring you can see firsthand what things work and observe how they really function versus just going by theory.

[darkmoebius]

Thank you for the honest reply about design and I know the individual you are referring to, he's has very strong opinions about any line array design not his own. Well, strike that, he has strong opinions about his, too.

In reality, I am never going to actually build an array myself. I just don't have to skills, dedication, and time to do so. I've learned this lesson after failed intentions of building SS & SET amps. I bought all the testing gear and never got around to doing it. With speakers, I have zero cabinetry skills/tools, and no desire to work up that learning curve. Let alone testing individual drivers, crossovers(active vs passive, digital vs analog), etc.

Instead, I realize that I simply love doing the research. Learning everything I can about a particular approach/topology, then applying that knowledge towards picking the commercial product that best suits my needs. And finished aesthetics/workmanship means a lot to me, too.

What got me thinking about underlying design approach to the Symmetricas is that there is a demo pair for sale right now. I'd rather pay more and buy a finished, fully tested and proven, design with a furniture grade quality, than save money and going DIY. I'd rather start playing music right away than waiting 6 months, a year, or even more on doing it myself - even if it costs me more.

My current system is made up with high quality, small manufacturer, components(Art Audio, Cain & Cain, Museatex, Scheu Analog)  and that's the approach I'd like to stick with for my next system upgrade.

[Rick Craig]

Thank you for the honest reply about design and I know the individual you are referring to, he's has very strong opinions about any line array design not his own. Well, strike that, he has strong opinions about his, too.

In reality, I am never going to actually build an array myself. I just don't have to skills, dedication, and time to do so. I've learned this lesson after failed intentions of building SS & SET amps. I bought all the testing gear and never got around to doing it. With speakers, I have zero cabinetry skills/tools, and no desire to work up that learning curve. Let alone testing individual drivers, crossovers(active vs passive, digital vs analog), etc.

Instead, I realize that I simply love doing the research. Learning everything I can about a particular approach/topology, then applying that knowledge towards picking the commercial product that best suits my needs. And finished aesthetics/workmanship means a lot to me, too.

What got me thinking about underlying design approach to the Symmetricas is that there is a demo pair for sale right now. I'd rather pay more and buy a finished, fully tested and proven, design with a furniture grade quality, than save money and going DIY. I'd rather start playing music right away than waiting 6 months, a year, or even more on doing it myself - even if it costs me more.

My current system is made up with high quality, small manufacturer, components(Art Audio, Cain & Cain, Museatex, Scheu Analog)  and that's the approach I'd like to stick with for my next system upgrade.

Sorry for the confusion - I thought you were going the DIY route.

[darkmoebius]

Sorry for the confusion - I thought you were going the DIY route.

Actually, I did too, until I started reading Rod Elliot's(Elliot Sound Products) excellent DIY articles on:

• Passive Crossovers - The Design of High Quality Passive Crossover Networks
• Serial vs. Parallel Crossover Networks - Are there any real differences?
• Active Vs. Passive Crossovers - An explanation for the profound audible differences
• Benefits of Bi-Amplification - Not quite magic, but close (Part I)
• Benefits of Bi-Amplification - Crossovers, tri-amping, etc. (Part II)
• Active Filters - Active filter design guide ... topologies, component selection, slope (dB/octave), transient response, etc.
• Baffle Step Compensation - What it is and why we need to compensate for it
• Phase Correction - Myth or Magic? - Do all-pass filters really work to correct loudspeaker phase anomalies?
• Phase, Time and Distortion in Loudspeakers- Is "Time Alignment" worth the effort?
• Impedance - Effects Of Source Impedance on Loudspeaker Drivers
• Doppler Distortion in Loudspeakers- Is the effect real or imaginary when applied to loudspeakers?
• Digital Signal Processing (DSP) - What DSPs can - and cannot - do for your system

I find all of that stuff extremely interesting, but I would much rather use the knowledge to buy the best array I can afford and get on with simply enjoying music, rather than invest years in learning, testing, building towards that same result.

Perhaps I should start over again and just ask what you find is the difference between the musical presentation of a single line like the Alexandrite & the dual line of the Symmetrica (besides bass extension & need for a subwoofer)

[JohnR]

Do you really have to have such a long signature?

[Rick Craig]

Do you really have to have such a long signature?

Does that make it more difficult for you to manage the site?

[darkmoebius]

Do you really have to have such a long signature?

Fixed

Years ago when I joined, I just cut & pasted that from my Audiogon system and never really thought about it again. I rarely post, so never noticed.

[Rick Craig]

.

Perhaps I should start over again and just ask what you find is the difference between the musical presentation of a single line like the Alexandrite & the dual line of the Symmetrica (besides bass extension & need for a subwoofer)

Other than the bass extension the main difference is in the coverage which is the same on the left or right side with the symmetrical layout. Even if you have a low crossover point (850hz with a new ribbon I have on hand) a single line of woofers and ribbons will have some response differences horizontally off-axis due to the lobe of a passive crossover and the effects of the baffle itself. The symmetrical layout also is the best way to implement the small woofers and still have high output capability (thirty-two 3" woofers have the surface area of ten 5" drivers). The larger woofer arrays (5" to 7") do have more drivers to choose from so there's more flexibility in terms of cone material choices and budget.

[JohnR]

Do you really have to have such a long signature?

Does that make it more difficult for you to manage the site?

It makes it more difficult to provide everybody with the leeway for things like links in their signatures, which need characters but don't use up excessive screen real estate.