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Old 25th December 2012, 09:59 PM   #21
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Quote:
Originally Posted by Patrick Bateman View Post

Admittedly, these are actually less of a factor in a design like the CS-30, where there's a high tuning. (Since port compression becomes a bigger problem at lower frequencies.)
The CS-30 is tuned around 34 Hz, if that is a high tuning, what do you consider low ;^)?
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Old 7th January 2013, 09:52 PM   #22
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Quote:
Originally Posted by weltersys View Post
Looking at the cabinet design, it is obviously a single ported cabinet. The port design has been described in JBL white papers, it reduces turbulence at high port velocity.

As far as the impedance response, it does look odd for a cabinet that is ported.

As you can see in the comparison of a Lab 12 in an oversized (underdamped) box and the CS-30 below, the Lab 12 Fb is higher, but they both have very similar phase and magnitude response above Fb.

Art
Do you have a link to the paper wherein they describe the math for determining the ideal dimensions for such a de Laval-style vent?
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Old 8th January 2013, 12:43 AM   #23
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Originally Posted by 454Casull View Post
Do you have a link to the paper wherein they describe the math for determining the ideal dimensions for such a de Laval-style vent?
Maximizing Performance from Loudspeaker Ports* - Audio ...
http://www.aes.org/e-lib/download.cf...94&name=harman

The paper has some math, but to quote from the article:

"The main difficulty in modeling flared loudspeaker ports is the infinite variety of profiles that will yield the same port tuning. Many loudspeaker designers choose not to experiment with flared ports because without a well- defined diameter to plug into the standard port tuning formula, they are left to design by trial and error. There are no CAD programs that incorporate the ability to design flared ports as of yet. However, there is a growing demand to take advantage of flared ports and a need for predicting their performance."

This statement was certainly reinforced by my most recent empirical quick and dirty port study, the response in post #7 surprised me, and does not fit any model I've seen, though emulates the CS-30 pretty well as far as frequency and phase response.

Art

Last edited by weltersys; 8th January 2013 at 12:51 AM.
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Old 8th January 2013, 05:09 AM   #24
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Quote:
Originally Posted by weltersys View Post
Maximizing Performance from Loudspeaker Ports* - Audio ...
http://www.aes.org/e-lib/download.cf...94&name=harman

The paper has some math, but to quote from the article:

"The main difficulty in modeling flared loudspeaker ports is the infinite variety of profiles that will yield the same port tuning. Many loudspeaker designers choose not to experiment with flared ports because without a well- defined diameter to plug into the standard port tuning formula, they are left to design by trial and error. There are no CAD programs that incorporate the ability to design flared ports as of yet. However, there is a growing demand to take advantage of flared ports and a need for predicting their performance."

This statement was certainly reinforced by my most recent empirical quick and dirty port study, the response in post #7 surprised me, and does not fit any model I've seen, though emulates the CS-30 pretty well as far as frequency and phase response.

Art
Not even Akabak?
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Old 9th January 2013, 03:16 PM   #25
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Originally Posted by 454Casull View Post
Not even Akabak?
Try it and see if it matches what you build.
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Old 10th January 2013, 12:55 AM   #26
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by weltersys View Post
Maximizing Performance from Loudspeaker Ports* - Audio ...
http://www.aes.org/e-lib/download.cf...94&name=harman

The paper has some math, but to quote from the article:

"The main difficulty in modeling flared loudspeaker ports is the infinite variety of profiles that will yield the same port tuning. Many loudspeaker designers choose not to experiment with flared ports because without a well- defined diameter to plug into the standard port tuning formula, they are left to design by trial and error. There are no CAD programs that incorporate the ability to design flared ports as of yet. However, there is a growing demand to take advantage of flared ports and a need for predicting their performance."

This statement was certainly reinforced by my most recent empirical quick and dirty port study, the response in post #7 surprised me, and does not fit any model I've seen, though emulates the CS-30 pretty well as far as frequency and phase response.

Art
Hi Art,

Just adding a few links to similar information, i.e. The 'Math' for a Nozzle ports and more, Good to have links to good 'Papers' gathered at the same location.

Vented-box geometry and low frequency reproduction: the aerodynamical approach

AES E-Library Vented-box Geometry and Low Frequency Reproduction: The Aerodynamical Approach


Sound source design in the very low frequency
domain.

AES E-Library Sound Source Design in the Very Low Frequency Domain


APPROXIMATIONS TO THE DIRECTIVITY INDEX

http://www.dtic.mil/dtic/tr/fulltext/u2/778660.pdf


b


PS: Adding my Notes (Picture):
Attached Images
File Type: jpg Slot-Nozzle-Ports-notes.JPG (871.5 KB, 247 views)
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Old 13th February 2013, 04:12 AM   #27
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Lab 12 c. Slightly higher power handling. Perfect for this CS-30!

Patrick, finalize a design and maybe I'll build / test it over the summer when I'm bored! (I have a lab 12 in a large horn now, but I can remove it and throw it into a CS30 copy for teasing)
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