D'apollito crossover

[mr2racer]

Hey Everyone,

I want to use a Peerless dome tweeter and a pair of Peerless 6.5 midwoofers in a D'Appolito array with a 12 woofer. Is there an easy crossover design to use in this case as a starting point? The tweeter I have is 8ohm and the mids are 4ohm. I haven't got a woofer yet but it will probably be an 8ohm also. If I run the mids in series that will make them 8ohm but won't that put them 90 degrees out of phase?

I read on another thread here that the D'appolito array is supposed to be 90 deg out of phase. If that is true which driver is out of phase the upper or lower?

Kevin

[Inductor]

May I ask a question, at what frequency is there the phase shift you mention? I don't think there is a difference in phase between series and parallel, per se. Now, if you have an inductor and drivers in series is going to affect both drivers. With mids probably there is none.

[mr2racer]

A friend told me that when an AC voltage passes through either a capacitor or an inductor its phase is shifted 90 degrees. Is that not correct? This would be at all frequencies. I also read on another thread that "..if the phase isn't shifted 90 at the crossover point its not a D'Appollito its an MTM." I wanted to put the midranges in series to match the impedence of the tweeter and increase the power handling.

A tech at Parts Express told me that when in series speakers don't shift phase because the energy is converted to mechanical energy and heat. I.E. its not the same as an inductor coil.

[Inductor]

I don't know what you mean by,

Originally Posted by mr2racer

"..if the phase isn't shifted 90 at the crossover point its not a D'Appollito its an MTM."

A D'Appollito is basically an MTM (with an exception more like a 3-way).

[Artie]

Originally Posted by Inductor

I don't know what you mean by,

A D'Appollito is basically an MTM (with an exception more like a 3-way).

Take what I say with a big grain 'o salt, because I'm just starting to learn about this myself, but I believe the essence of the D'Appolito design is the interaction of the wave fronts from the woofers and tweeter. The spacing of the drivers must be set according to the xover frequency and vice-versa, using the formula - speed-of-sound / xover-freq = center-to-center spacing.

If you don't adhere to that design principal, then its just a tweeter mounted between to woofers.

[Inductor]

Originally Posted by Artie

Take what I say with a big grain 'o salt, because I'm just starting to learn about this myself, but I believe the essence of the D'Appolito design is the interaction of the wave fronts from the woofers and tweeter. The spacing of the drivers must be set according to the xover frequency and vice-versa, using the formula - speed-of-sound / xover-freq = center-to-center spacing.

If you don't adhere to that design principal, then its just a tweeter mounted between to woofers.

Some ideas, to spend time reading, http://www.zoominfo.com/people/D'App...ce=page&page=2

The following is an excerpt from the Snell Illusion Whitepaper that illustrates the design philosophy behind the Illusion, and the MTM array of the “D”Appolito Configuration” that has been adopted by many other speaker companies:

“The Configuration

What was fixed from the beginning was the basic configuration. The Illusion was to be a 3-way loudspeaker. It is our strong belief that the critical midrange and its lower overtones should be reproduced in a single driver or driver pair. In the Illusion this is the frequency range between 250Hz and 2500Hz. This is also the frequency range of maximum human hearing acuity. A single driver will provide excellent coherence with no spatial ambiguity. By contrast, a 4-way system will invariably involve transitioning from a lower frequency midrange driver to an upper frequency midrange driver. Typical crossover frequencies are in the range of 600Hz to 800Hz. It is extremely difficult to make a seamless crossover in this frequency range. Furthermore, the quality of the midrange drivers in the Illusion makes such a crossover unnecessary.

Also fixed form the start was the use of our signature MTM driver array to reproduce all frequencies above 250Hz. This array comprises a pair of midrange drivers, one above and one below a central tweeter. This arrangement of drivers, popularly known as the “D’Appolito Configuration”, was developed by our Chief Engineer, Dr. Joseph D’Appolito in the early 80’s. Over the past 20 years countless loudspeakers produced with vertical mid-high-mid driver layouts have claimed D’Appolito status without any particular technical (or legal) legitimacy. A true D’Appolito array is a far more sophisticated entity, whose transducer parameters and dimensions, geometric relationships, and time-domain characteristics of crossover-filter circuits must all be meticulously calibrated to produce the intended result.”

[Artie]

Originally Posted by Inductor

Please give me back more than just the smiley faces. If what I said is out in left field, tell me so. I'm beyond the point in my life where I'll go cry in my Wheaties.

Be direct. Tell me where I'm off base. I come here to learn.

[Inductor]

Originally Posted by Artie

Please give me back more than just the smiley faces. If what I said is out in left field, tell me so. I'm beyond the point in my life where I'll go cry in my Wheaties.

Be direct. Tell me where I'm off base. I come here to learn.

There's no need to cry. Do you mean a front wave of woofer and tweeter? at what frequency? And the center to center design you mention is it fixed or max.?

[kevinkr]

Originally Posted by mr2racer

A friend told me that when an AC voltage passes through either a capacitor or an inductor its phase is shifted 90 degrees. Is that not correct? This would be at all frequencies. I also read on another thread that "..if the phase isn't shifted 90 at the crossover point its not a D'Appollito its an MTM." I wanted to put the midranges in series to match the impedence of the tweeter and increase the power handling.

A tech at Parts Express told me that when in series speakers don't shift phase because the energy is converted to mechanical energy and heat. I.E. its not the same as an inductor coil.

From an electrical standpoint I think you can still look at them basically as two inductors in series, you only get phase shift when the circuit elements in series are dissimilar such as a inductor in series with a resistor or capacitor. Driven by an X-O the phase shift relative to each driver will be identical (i.e. there is no phase shift between two identical drivers) as long as the impedance of the two drivers in series are identical at any given frequency. (vc inductance, stray capacitance and dcr)

Note that the typical first order butterworth X-O are typically 45 degrees and -3dB, second order 90 degrees and -6dB so I am not sure I understand what you are getting at, the rule applies with higher order even and odd order X-O and is the phase and amplitude relationship required to get things to sum to a flat amplitude response in the cross-over region. Your comment would seem to imply that D'Appolito configurations would have to have 2nd or fourth order X-O. My understanding of the D'Appolito configuration was that it was intended to have a very specific radiation pattern. (Controlled directivity, specifically IIRC in the vertical plane)

I believe one legitimate user of the D'Appolito configuration was Swans Speakers (originally based in Maine) which IIRC was a collaboration between James Bock (+ others) and D'Appolito back in the late 1980s - early 1990s..

[DRNB]

Originally Posted by Inductor

There's no need to cry. Do you mean a front wave of woofer and tweeter? at what frequency? And the center to center design you mention is it fixed or max.?

What Artie is saying is that the centre to centre distance should be equal to the wavelenghts at x-over frequency. Which is 100% correct for D'Appolito. That is to get a good vertical polar reponse.

I would personally take it one step further and say for the midranges to act as one source the distance measured from bottom cone edge of lowe mid to upeer cone egde of upper diver should be equal to x-over frequency. But thats just my opinion