What's the average directivity range of a typical 6" cone? - diyAudio
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Old 16th September 2014, 07:07 PM   #1
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Default What's the average directivity range of a typical 6" cone?

Average baffle width flush mounted and not OB or dipole. At what point decreasing in frequency does it become Omni? Besides cardoid or dipole cancellations, what else can be done to control directivity lower in frequency? Vertically an array can help but what about horizontally?
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Old 16th September 2014, 08:34 PM   #2
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Think of three ranges. At highest frequencies the cone beams and will narrow down to less than 90 degrees, then less than 45, etc. For a 6" this may start around 4kHz, off the top of my head.

From this frequency down to a few hundred then the baffle is sufficiently large to constrain the directivity to hemispherical. i.e., 180 degrees. This is determined by the baffle size and nothing else.

Below that frequency the baffle is no longer big enough and the dispersion spreads towards Omni.

So to answer your question, the frequency is totally related to baffle size. If you use a program for determining "baffle step function" (cabinet diffraction response) such as Tolvin, "the edge", then where the response starts to shelve down is also where the polar pattern starts to spread from 180 to, ultimately, 360.

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Old 16th September 2014, 08:55 PM   #3
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Quote:
Originally Posted by mayhem13 View Post
Average baffle width flush mounted and not OB or dipole. At what point decreasing in frequency does it become Omni?
Take a look at the polar of this driver, it might give you a hint ( it begins to be directive as it approaches 1kHz, albeit only slightly, and reaches -5dB past 2kHz)

AL 170 - 8 Ohm

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Originally Posted by mayhem13 View Post
Besides cardoid or dipole cancellations, what else can be done to control directivity lower in frequency? Vertically an array can help but what about horizontally?
Huge horn or - to a certain extent as should obvious from the example above - large radiating area, either large Drivers (non-CD) or 2D Array. No free luch tho. Below 500 Hz Dipole might be the best bet.
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Old 16th September 2014, 09:49 PM   #4
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My area of comparison is a 6" midwoofer as compared to say the common 12-15" woofers often associated with waveguide two ways. I'm trying to find the advantage of the large diameter drivers over the smaller. If we assume the same wide baffle needed to accommodate the woofer in a three way, the small 6" midwoofer should remain near constantly directive lower in frequency as the larger diameter drivers?
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Old Yesterday, 12:27 AM   #5
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Your question was at what frequency the speaker goes omni. The answer is that it goes omni when the baffle is no longer large enough to support hemispherical radiation. It is down to baffle dimensions, nothing else.

Now if the question is at what frequency, going up, the driver starts to beam and narrow to less than hemispherical, then that is directly tied to driver diameter.

David
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Old Yesterday, 12:34 AM   #6
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So infinite baffle drivers can maintain directivity below 100hz?
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Old Yesterday, 05:29 AM   #7
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Quote:
Originally Posted by mayhem13 View Post
So infinite baffle drivers can maintain directivity below 100hz?
Almost, hemispherical then (180¤) It is questionable if that should be called directivity.

http://www.acs.psu.edu/drussell/demos/baffledpiston/baffledpiston.html

Click the image to open in full size.
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Old Yesterday, 07:13 AM   #8
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Could you all help me understand the baffle step? Is it correct that it lowers on-axis LF frequency response, or is it only the problem with power response? I am not exactly sure what exactly it does.
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Old Yesterday, 08:54 AM   #9
Juhazi is offline Juhazi  Finland
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Originally Posted by kenderes View Post
Could you all help me understand the baffle step? Is it correct that it lowers on-axis LF frequency response, or is it only the problem with power response? I am not exactly sure what exactly it does.
This is a good one
Baffle Diffraction Step
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Old Yesterday, 10:10 AM   #10
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Quote:
Originally Posted by kenderes View Post
Could you all help me understand the baffle step? Is it correct that it lowers on-axis LF frequency response, or is it only the problem with power response? I am not exactly sure what exactly it does.
Baffle step is actually the combination of 2 factors. At low frequencies frontal energy is allowed to bend around the cabinet edges into the back hemisphere. This is a loss in axial pressure as power escapes to the back side.

At the same time the low frequency loading is reduced and the actual system efficiency is less below baffle step than above.

Both factors contribute about 3 dB of step for a difference approaching 6dB.

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