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Multi-Way Conventional loudspeakers with crossovers

Both Horizontal and Vertical MTM array
Both Horizontal and Vertical MTM array
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Old Yesterday, 09:58 AM   #1
Arunkumar14_th is offline Arunkumar14_th  India
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Default Both Horizontal and Vertical MTM array

What are the effects of a custom D'Appolito array that is both vertical and horizontal?
ie, two woofers horizontally and two woofers vertically both sharing the common center tweeter.

Something like:
*M*
MTM
*M*
(Please ignore the '*'s in the above diagram, spaces at the beginning of the line were ignored)
Just wanted to explore both benefits and disadvantages of such an arrangement.
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Old Yesterday, 11:13 AM   #2
TBTL is offline TBTL  Germany
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It would result in lobing issues in both the horizontal and vertical plane. This happens because the driver spacing is not small, compared to the wavelength at the cross over frequency.
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Old Yesterday, 12:15 PM   #3
PeteMcK is offline PeteMcK
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have a look at this thread:
Midrange drivers in a circle?
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old Yesterday, 12:31 PM   #4
Daihedz is offline Daihedz  Switzerland
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This 2-Dimensional Horbach patent paper goes in depth of the question:


LOUDSPEAKER ARRAY SYSTEM


Follgott has already set up a beautiful 2-dimensional Horbach-Keele Array.
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Old Yesterday, 07:52 PM   #5
Patrick Bateman is online now Patrick Bateman  United States
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Quote:
Originally Posted by Arunkumar14_th View Post
What are the effects of a custom D'Appolito array that is both vertical and horizontal?
ie, two woofers horizontally and two woofers vertically both sharing the common center tweeter.

Something like:
*M*
MTM
*M*
(Please ignore the '*'s in the above diagram, spaces at the beginning of the line were ignored)
Just wanted to explore both benefits and disadvantages of such an arrangement.
A D'Appolito array uses a specific combination of spacing and crossover slope to narrow the vertical beamwidth of a two-way array. You can simulate it fairly quickly with xdir.

I think the work that Horbach and Keele did, as well as David Smith at Snell, was to extend the concept into a three way or even four way array. Google "horbach keele" or "snell expanding array" to learn more.

If you took a D'Appolito array, and added two more midranges horizontally, it would look a lot like the Donald North array. This one is way more obscure, but it there IS a patent on it, with all the info you need.

The North array does exactly what you would expect it to do: it makes the beamwidth symmetrical, both vertical and horizontal.

One other "neat" thing about a symmetrical D'Appolito array, is that you may be able to raise the output and the power handling a little. This is because you can bring the midranges in tighter.

For instance, a pair of four inch midbasses have about as much output as a 6" midbass, but the 4" midbasses can be packed tighter.

I've posted a bunch of articles on diyaudio about this stuff, so check my post history or use Google to dig them up.
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Old Yesterday, 07:53 PM   #6
PeteMcK is offline PeteMcK
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Patrick does an analysis of the DNA layout here:
Optimal MTM Geometry
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old Yesterday, 07:58 PM   #7
Patrick Bateman is online now Patrick Bateman  United States
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Oh, one more thing, Donald North from DNA and David Smith from Snell are members here, they might chime in.
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Old Today, 08:53 AM   #8
Arunkumar14_th is offline Arunkumar14_th  India
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Join Date: Feb 2006
Location: Bangalore
Thanks All for your valuable input!!
Now I have a bunch of info to read and comprehend .
Will come back here once i have more questions on this topic.
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Old Today, 02:12 PM   #9
TBTL is offline TBTL  Germany
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Horbach-Keele arrays require some waveguide on the tweeter, as practically sized arrays only work up to say 3 kHz. Their crossover frequencies (for a given driver diameter) are lower than that of a regular MTM.
Quote:
Originally Posted by Daihedz View Post
Follgott has already set up a beautiful 2-dimensional Horbach-Keele Array.
Yes: Pseudo-coaxial with narrow directivity (and Horbach-Keele filters)



But we are skipping the important part: why do you want to use an MTM array? Do you need the narrow directivity?

Last edited by TBTL; Today at 02:28 PM.
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Old Today, 02:43 PM   #10
Patrick Bateman is online now Patrick Bateman  United States
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TBTL makes a good point. Most of these modern MTMs use tighter spacing that the D'Appolito arrays from the 90s.

Even the Snell expanding array, from Smith, uses tighter spacing.

The Horbach Keele paper suggest a spacing of 55% a wavelength.

For instance:

Let's say we have a MTM with a xover of 2000Hz. 2000Hz is 6.75" long. 55% of that is 3.7125".

From that, you can see that a xover of 2000Hz is impossible.

So you have to keep dropping the xover point until it works.

For instance:

Let's say we have a MTM with a xover of 1350Hz. 1000Hz is 10" long. 55% of that is 5.5".

This spacing is "do-able"; you can achieve it using 3" midranges. Possible even with 4" midranges, depending on the geometry.

But you get the general idea; in order to get well behave response off-axis, the spacing has to be tight.
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