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Old 10th June 2021, 01:08 PM   #21
martinsson is offline martinsson  Sweden
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Technically it's a OD-MLTL
Right, and the mass loading stems from the ports air mass, correct?
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Old 10th June 2021, 01:51 PM   #22
AllenB is offline AllenB  Australia
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Vented vs TL...
Quote:
Originally Posted by martinsson View Post
what designcriteras needs to met for calling it a TL,
Exploitation of box modes. A standard ported box doesn't do this.
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Old 10th June 2021, 08:25 PM   #23
GM is offline GM  United States
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Originally Posted by martinsson View Post
Right, and the mass loading stems from the ports air mass, correct?
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Old 10th June 2021, 08:30 PM   #24
GM is offline GM  United States
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Originally Posted by AllenB View Post
Exploitation of box modes. A standard ported box doesn't do this.
Right, it must be a high enough aspect ratio for 1/4 WL pipe modes to damp the vent enough to make a measurable difference to a lower Fb, so varies based on desired tuning, otherwise it's presumed to have a ~uniform particle density.

Resonances of open air columns
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Old 11th June 2021, 02:25 AM   #25
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by David McBean View Post
If you adjust for the end correction and set QL to lossless as shown in the attachments, the results become effectively identical, with the fundamental frequency being 42.4 Hz in each case.
Yup, but it does raise the question of which of those two models will more accurately predict the response of the attached system, without having to adjust any of the dimensions involved. I do know that the standard OD model did a very good job of predicting the Fb for both my POC6 and my "Boom Unit" builds.

How is the end correction calculated, btw?
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Old 11th June 2021, 02:30 AM   #26
Brian Steele is offline Brian Steele  Grenada
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I forgot to mention that the inclusion of vent losses in the ODOV model probably makes its predictions of what happens to the FR around Fb a bit more accurate than the OD model.
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Old 11th June 2021, 03:44 AM   #27
grindstone is offline grindstone  United States
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Originally Posted by Brian Steele View Post

How is the end correction calculated, btw?
dia = 2 * Sqrt(Ap / Pi) <---- Port tube diameter (m)
Lpt1 = Lpt + 0.306 * dia <---- Port tube length plus unflanged inlet end correction (m)
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Old 11th June 2021, 06:26 AM   #28
David McBean is offline David McBean  Australia
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Originally Posted by Brian Steele View Post
it does raise the question of which of those two models will more accurately predict the response of the attached system
The second (bass reflex) model will more accurately predict the results because it takes vented-box enclosure losses (default QL = 7) and the port tube internal end correction into account (the internal end of the port tube is assumed to be un-flanged).
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Old 11th June 2021, 06:41 AM   #29
David McBean is offline David McBean  Australia
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Originally Posted by grindstone View Post
Lpt1 = Lpt + 0.306 * dia <---- Port tube length plus unflanged inlet end correction (m)
Hornresp actually uses the following formula for the internal unflanged end correction length, which gives effectively the same result as the one above.

EC = 0.1952 * Pi * Rp

Where EC is the end correction length and Rp is the port tube radius.

In the previous example, Ap = 320.00 sq cm

EC = 0.1952 * Pi * Sqrt(320 / Pi) = 6.19 cm (to two decimal places)
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Old 11th June 2021, 07:49 AM   #30
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by martinsson View Post
and the mass loading stems from the ports air mass, correct?
Correct.
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