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Old 13th August 2020, 09:09 PM   #10991
bolserst is offline bolserst  United States
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Regarding the QL parameter…this dates back to 1973 and the first Small paper on vented enclosures. The advice given was that losses in a normal vented enclosure may be adequately approximated by a QL~7. But if you read the paper in detail, you will find that Small determined the apparent measured leakage (QL) was not real, but an indication that losses from different sources in the vented enclosure system varied with frequency. More recent papers by Claus Futtrup suggest that using a constant leakage loss in an essentially leak-free enclosure is providing an approximation for the woofer mechanical losses that increase with falling frequency, and enclosure absorption losses that increase with increasing frequency. The attached post-AES convention presentation at the Munich High End Show provides a brief description. There is also a link below to the *.mp3 audio from the actual presentation. A bit more background and detail are included in his chapter on vented enclosures, also attached. His AES paper is the best source, but is not currently available for free download.

Using a QL value in the 5 – 10 range does provide better agreement with measurements of “normal” vented enclosures. But, may(will?) deviate if your system parameters are outside the norm. (ie unusually large enclosure, unusually long port, unusual amounts of damping material or thin enclosure walls...etc). If the option is included in Hornresp, it may be good to add a note, or description in the help file that it provides an approximation of total system losses as recommended by Richard Small for “normal” vented systems. Making QL adjustable in the Wizard between, say, 3 to 20 should cover the range of response for how the vast majority of vented enclosure builds would actually measure.

Links to documents:
Vented-Box-Loudspeaker-Systems--Part-1
http://www.cfuttrup.com/about/15-Scan_Speak.pdf
http://www.cfuttrup.com/about/scan_speak.mp3
http://www.cfuttrup.com/blogspot/Book_05_Futtrup.pdf
AES E-Library >> Losses in Loudspeaker Enclosures
Attached Images
File Type: png Vented_QL_Small.png (150.2 KB, 71 views)
File Type: png Vented_QL_Futtrup.png (26.0 KB, 70 views)
Attached Files
File Type: pdf JAES_1973_Vented_Enclosures_Part1-Small.pdf (694.4 KB, 2 views)
File Type: pdf 15-Scan_Speak_Losses_in_LS_Enclosures.pdf (431.1 KB, 6 views)
File Type: pdf Book_05_Futtrup.pdf (880.3 KB, 5 views)

Last edited by bolserst; 13th August 2020 at 09:26 PM.
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Old Yesterday, 03:05 AM   #10992
Giri is offline Giri
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Default Feature Request - Particle velocity display in wizard

Hello David,

One of the last things I check for, in designing a Transmission Line, is the port particle velocity. Based on which I decide the minimum possible TL end cross-section and final taper. Particle velocity is a useful feature to have within the wizard itself. Of course, if it's feasible to do

Thanks for the wonderful work, as always.
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Old Yesterday, 07:07 AM   #10993
David McBean is offline David McBean  Australia
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Hi bolserst,

Quote:
Originally Posted by bolserst View Post
Regarding the QL parameter…
Many thanks for posting this information, it is very interesting indeed.

Quote:
Originally Posted by bolserst View Post
If the option is included in Hornresp, it may be good to add a note, or description in the help file that it provides an approximation of total system losses as recommended by Richard Small for “normal” vented systems.
Noted, thanks.

Quote:
Originally Posted by bolserst View Post
Making QL adjustable in the Wizard between, say, 3 to 20 should cover the range of response for how the vast majority of vented enclosure builds would actually measure.
My plan was to include a QL slider having the range 1 to 99, with the default value being 7. Moving the slider control to the very end (just past 99) would select the current lossless model instead.

Kind regards,

David
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Old Yesterday, 07:19 AM   #10994
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by Giri View Post
Particle velocity is a useful feature to have within the wizard itself.
Hi Giri,

When the QL slider is added I intend also including a port particle velocity chart for vented-box designs. I will have a look at how much extra work would be required to provide a particle velocity chart for transmission line designs as well.

Kind regards,

David
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Old Today, 06:29 AM   #10995
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by David McBean View Post
I will have a look at how much extra work would be required to provide a particle velocity chart for transmission line designs as well.
Will be in the next update.
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Old Today, 08:11 AM   #10996
David McBean is offline David McBean  Australia
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An added advantage of including the particle velocity chart in the transmission line wizard is that the effect of absorbent filling material on velocity can then also be seen.
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