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[lindsay Dean]

ivan do you have time to explain this term?

[Lee Buckalew]

ivan do you have time to explain this term?

What are your specific questions?

It is a coaxial design or, more realistically it is a dual concentric although I believe that phrase is trademarked so....

The Differential Dispersion portion indicates that it has a different dispersion characteristic at one portion of the horn than at another.  The horizontal coverage varies/tapers through the vertical coverage. 

The goal is to create a speaker that has a coverage pattern that is more even in SPL and frequency response with a dispersion characteristic that allows for fewer speakers to be utilized than would be required if more traditional speakers were utilized.  The hot spot in the pattern is 5 degrees (or so, a few models have slightly different coverage) below the top of the coverage so your speaker aiming can now focus the hot spot at the farthest seats while not spraying HF above that coverage point and wasting a significant portion of your horn coverage angle.  Meanwhile the HF decreases in level because it increases in horizontal angle as you move down through the vertical coverage angle.  When placed properly this makes the relative SPL far more even throughout the listening area than would be achieved with a standard speaker design.

Here is a link to the brochure where there is a simplified marketing explanation.

https://static.martin-audio.com/downloads/brochures/MartinAudioCDDbrochure.pdf

Each model has EASE data available on the website so that you can plug it in and look at the coverage at various frequencies, model by model.

Lee

[Ivan Beaver]

ivan do you have time to explain this term?

I have never heard of the term.  It is manufacturer specific for their product.

Lee would know more about it than me.

The only comment I will make about horns that have different patterns in one part vs another is the same as usual.

It all "depends" on the physical size of the horn and the freq of interest.

As with any other device, the pattern is NOT what it is rated at-for all freq.

The actual radiation pattern will vary with freq-depending on how large the horn is.

This goes for ALL loudspeakers from all manufacturers.

You MUST look at various freq to see how well the pattern is "controlled".

SIZE MATTERS, and small horns simply don't control much of the freq spectrum, just the top octave or two-depending on the pattern.

Narrower horns have to be LARGER to have the same control as wide horns.

[lindsay Dean]

so lets use as an example 500 to 10 k how large would the "horn" have to be to get decent pattern contol ?

[lindsay Dean]

it seems a lot of brands have virtual " audio spray bottle" control except for a limited range, correct ?

[Lee Buckalew]

so lets use as an example 500 to 10 k how large would the "horn" have to be to get decent pattern contol ?

Use the EASE data that is available and check.  It is very accurate.
Yes, you lose pattern control the lower in frequency that you get but there is effective control down lower than might be thought by many.

Lee

[Nathan Riddle]

From what I read the whole concept for the CDD "Coaxial Differential Dispersion" isn't to control low freq radiation; it is to widen the HF radiation to match the low freq pattern for up close.

Then, in addition to that, as Lee said; 'throw' the HF better because of the 5* 'hot spot' in the pattern (vertically).

Example:
K12 75* pattern, really its more like: 30* from 12k up (getting narrower as freq raises), and 50* from 8k up (getting narrower as freq raises) and 75* from 4k up (getting narrower as freq raises)...

Whereas the Martin CDD's pattern "control" is more of a widening of the HF response so that even up at 12kHz the pattern is still 60* as stated in the brochure.

Disclaimer: values are arbitrary.

Someone correct me if I'm wrong.

[Lee Buckalew]

it seems a lot of brands have virtual " audio spray bottle" control except for a limited range, correct ?

I am not sure what you are meaning by "audio spray bottle". 

I will give you an example of a use with a CDD LIVE 12.  I have a client that is a Grammy winning Symphony Orchetsra.  They were testing some CDD LIVE 12's for various uses.  They often have meetings, gatherings, etc. in the 3 story tall marble grand entry of their building.  They have typically used standard self powered aa x bb coverage angle speakers on sticks for this.  It is always either too loud up front or too quiet in the back and there is always too much reflection back off the opposition wall. 

They used a single CDD LIVE 12 on a stand exactly per the manuals suggested placement.  It was not too loud for people in the front, it was not too quiet for people in the back, it did not drop off at the sides in the front, there was not noticeable/distracting slap from the wall opposite the speaker.

Beyond stories of use are there specific questions?

No, I don't work for Martin Audio.  Yes, I design quite a bit with them, but also with many other brands.

Lee

[Lee Buckalew]

From what I read the whole concept for the CDD "Coaxial Differential Dispersion" isn't to control low freq radiation; it is to widen the HF radiation to match the low freq pattern for up close.

Then, in addition to that, as Lee said; 'throw' the HF better because of the 5* 'hot spot' in the pattern (vertically).

Example:
K12 75* pattern, really its more like: 30* from 12k up (getting narrower as freq raises), and 50* from 8k up (getting narrower as freq raises) and 75* from 4k up (getting narrower as freq raises)...

Whereas the Martin CDD's pattern "control" is more of a widening of the HF response so that even up at 12kHz the pattern is still 60* as stated in the brochure.

Disclaimer: values are arbitrary.

Someone correct me if I'm wrong.

This is very much the correct thought process. 
With smaller boxes, and even the 15" is not that large, you won't get a horn large enough for LF pattern control so the focus is on creating a better HF coverage for a broader range of applications.
There is a downside.  You can't array these speakers in a typical fashion and achieve anything pleasant.

Lee

[Ivan Beaver]

so lets use as an example 500 to 10 k how large would the "horn" have to be to get decent pattern contol ?

You need to supply more information.

The rated pattern of the horn matters quite a bit.

The narrower the pattern, the larger the horn has to be.

Here is the basic formula.

I suggest you put a couple of numbers into it to get a feel for it.

freq of control=1,000,000/ (size of horn (not including the flange) in inches x rated pattern)

Lets say you have a 10* vertical horn (as common in line arrays) and it is 12" tall.

So you have 1,000,000/(10x12)=8333Hz.  So basically below 8.3KHz the horn will start to lose control and it will be wider.

If the same size horn was rated at 90* you would have 1,000,000/(90x12)=926 Hz.

[Lee Buckalew]

So you have 1,000,000/(10x12)=8333Hz.  So basically below 8.3KHz the horn will start to lose control and it will be wider.

Ivan,
Do you mean it will be taller rather than it will be wider?
10 degrees would be a common vertical while 90 degrees or greater would be a more common width for line arrays.

Lee

[Ivan Beaver]

Ivan,
Do you mean it will be taller rather than it will be wider?
10 degrees would be a common vertical while 90 degrees or greater would be a more common width for line arrays.

Lee

Yes.  Most horns are the wrong size.  Typically they need to be taller than wider.
EV was the first company (that I remember) to start offering this proper ratio-back in the 80s

Many people thought they were being stupid and thought they were "wrong"-because everything they knew was opposite.

But yet THEY were ones who were wrong.

The reason for the proper size relationship is to avoid "pattern flip" in which the pattern is actually 90* off for what you think that it "should be".

Of course the ratio of the horizontal to vertical affects how severe the pattern flip is.  The greater the ratio, the worse the effects of pattern flip.  The closer the patterns are, the lower the effect of pattern flip.

I believe Renkus Heinz was the first to start publicizing this effect back around the turn of the century.

YES-size matters, and often not in the way people have been "taught".

[Ivan Beaver]

There is a downside.  You can't array these speakers in a typical fashion and achieve anything pleasant.

Lee

Totally agreed.

But that does not keep people (and even some manufacturers) from doing so and stating/showing in their brochures how to do it.

You will have some serious interactions in various parts of the patterns as they overlap.

[Lee Buckalew]

Yes.  Most horns are the wrong size.  Typically they need to be taller than wider.
EV was the first company (that I remember) to start offering this proper ratio-back in the 80s

Many people thought they were being stupid and thought they were "wrong"-because everything they knew was opposite.

But yet THEY were ones who were wrong.

The reason for the proper size relationship is to avoid "pattern flip" in which the pattern is actually 90* off for what you think that it "should be".

Of course the ratio of the horizontal to vertical affects how severe the pattern flip is.  The greater the ratio, the worse the effects of pattern flip.  The closer the patterns are, the lower the effect of pattern flip.

I believe Renkus Heinz was the first to start publicizing this effect back around the turn of the century.

YES-size matters, and often not in the way people have been "taught".

This did not answer my question.

Are you saying that the dimension of horn height and the dispersion angle for vertical dispersion are used in a formula that determines the lowest frequency of control for the horns dispersion width? 

I am asking because you referenced the height and the vertical dispersion angle and then used the word "wider" which I would take to mean increase the horizontal angle.

Also, is this true for all waveguides or is this formula for CD horns?

Lee

[Ivan Beaver]

This did not answer my question.

Are you saying that the dimension of horn height and the dispersion angle for vertical dispersion are used in a formula that determines the lowest frequency of control for the horns dispersion width? 

I am asking because you referenced the height and the vertical dispersion angle and then used the word "wider" which I would take to mean increase the horizontal angle.

Also, is this true for all waveguides or is this formula for CD horns?

Lee

Yeah-maybe I wasn't clear.  I was giving 2 examples.

Basically each part of the horn (horizontal and vertical) are figured out separately. 

The thing that causes pattern flip is when one side (vertical or horizontal) starts to lose pattern control before the other.

In the perfect world, they should both lose it at the same time so the pattern expands the same in all directions the same.

The formula is Don Keeles from many years back.

It is basically the mouth exit size.

But there is a "wrinkle" (isn't there always?).

In many horns the last part of the horn is wider than the actual rated pattern.

This is done to "ease" the horn transition and help reduce edge reflections.

So the "effective size" of the horn is not the actual outside edge, but somewhere between where the horn used for pattern control ends and the actual final exit of the horn.

And the number that is derived from the formula is a "basic" number.

As with most things audio, it does not start and stop there-but that number is in the "grey area" or area of transistion, but it does give a good idea.

The problem with the different types of horns is that some horns have VERY different patterns at different freq.

The old exponential horns would get REAL beamy higher in freq, and at that freq the actual coverage pattern was not even close to the rated pattern (that the horn had at lower freq).  But there was more gain up high because of that.

The formula "assumes" that the horn will have the same coverage pattern for all freq, until the horn starts to lose control.

And while it does not apply to every horn, it can be a really good "rule of thumb" or starting point to figure out approx where the horn will have pattern control down to.

Of course the ACTUAL best thing is to measure the horn and look at the polar patterns.  THAT is reality.

But I highly doubt (I could be wrong) that any horn would have pattern control any lower than the number indicates.

[lindsay Dean]

Great explanation Ivan,
Lee , what I meant by "spray bottle" is the pattern control for most horn frequencies are out of control except a limited amount of the bandwidth.

[Lee Buckalew]

Great explanation Ivan,
Lee , what I meant by "spray bottle" is the pattern control for most horn frequencies are out of control except a limited amount of the bandwidth.

Yes, most speakers, even with well designed horns, do not exhibit full frequency range control of directivity.

For CDD the pattern control extends much lower than most would think but you must keep in mind that CDD is a front loaded LF with a horn/waveguide fitted HF.  The CDD driver is unique and patented so. 
Of course the pattern and the degree of control vary by model/size. 

The new XE series stage monitors, which have an additional unique waveguide added that is a fixed part of the cabinet extending out over the LF driver, exhibit pattern control down to about 500Hz. 

Lee

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