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Old 6th January 2012, 03:15 PM   #2521
blo06 is offline blo06  France
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thx David,

that's clear now.

Cheers.
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Old 6th January 2012, 03:46 PM   #2522
tb46 is offline tb46  United States
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Default Multiple Speaker SPL - Post #2520

Hi David,

I hope that in evaluating the multiple speaker SPL output level you will not loose the radiator size and frequency dependent relationship of the acoustic radiation resistance.

Regards,
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Old 7th January 2012, 01:46 AM   #2523
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Quote:
Originally Posted by tb46 View Post
I hope that in evaluating the multiple speaker SPL output level you will not loose the radiator size and frequency dependent relationship of the acoustic radiation resistance.
Hi Oliver,

Please see my reply on the other thread :-).

Single sheet TH challenge

Kind regards,

David
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Old 9th January 2012, 08:28 AM   #2524
NEO Dan is offline NEO Dan  United States
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Hi David,
I see 2890-120101 but no update here. Is this the one with auto tune?
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Old 25th January 2012, 12:44 PM   #2525
Xoc1 is offline Xoc1  United Kingdom
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Default Vented Box Enclosures & Multiple Ports?

Hi David
I am re-tuning some direct radiator vented box enclosures.
I was using Hornresp and checking the results with WinISD alpha.
(WinISD makes it possible to add a filter so I can set the hipass on my DSP crossover)
When I set WinISD to use a single round port with one flanged end, the results for port length and tuning agree with the Hornresp data.

To Quote the WinISD Alpha Help file

'End correction factor is analytically or empirically determined factor, how much port extends beyond its physical ends. For free end, end correction is 0.30665 times port effective diameter. For flanged end, more analytical expression is available, 4/(3·pi) ~= 0.42441 times port effective diameter. Flanged end is calculated assuming that tube terminates to infinite baffle. Which is not exactly true, but.. Following table summarizes various port configuration types and their total end correction factors

Summary of end correction values Port configuration end correction 1 end correction 2 Total end correction
Two free ends 0.30665 0.30665 = 0.6133
One flanged and one free end 0.42441 0.30665 = 0.7311
Two flanged ends 0.42441 0.42441 = 0.8488

Physical port length is obtained by subtracting port effective diameter multiplied by suitable end correction value from port's acoustical length.'


My problem is that I want to use multiple ports. In this case I have 2 ports of 10.3cm diameter. If I use Winisd I get a different physical port length for 2 ports.
Ap is 166.65 sq cm = 1 port 14.56 cm dia = 2 ports 10.3cm dia
For a resonant frequency of 50Hz
Single port - length is quoted as 6.4cm WinISD and Hornresp
2 ports - WinISD quotes 9.55 cm

End Comensation Calc..
14.56 X 0.732 = 10.66cm
10.3 x 0.732 = 7.54cm
Difference is 3.12cm
6.4 + 3.12 = 9.52cm nearly the quoted length in WinISD.

In the first instance could you confirm that my assumption that Hornresp is assuming a single round port with one flanged end (as shown in the Schematic), and as such it is using a end correction value of 0.731 x the effective port diameter?

I would like to be able to calculate the length for multiple ports.
In this case I am retuning an old speaker - and the ports are too small at Xmax levels.
To increase the size of the ports I would need to be able to calculate a effective length for 2 ports shaped like right angled triangles.
Any insights into how to calculate the port lengths would be appreciated.
Kind Regards
Martin (Xoc1)
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Old 25th January 2012, 02:15 PM   #2526
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Quote:
Originally Posted by Xoc1 View Post
I would like to be able to calculate the length for multiple ports.
In this case I am retuning an old speaker - and the ports are too small at Xmax levels.
To increase the size of the ports I would need to be able to calculate a effective length for 2 ports shaped like right angled triangles.
Any insights into how to calculate the port lengths would be appreciated.
Kind Regards
Martin (Xoc1)
Martin,

The triangular corner ports will tune lower than round ducts of the same area and length, there are various calculators on line showing differences between “slot ports” and round ducts.
By putting an "L" on the inside end of the port, it will tune lower yet, allowing for less cabinet space being reduced by the larger port.

I have measured differences in Fb between various types of port termination, but can’t help with the math.

My approach since discovering some gross errors between predicted and actual Fb (not using Hornresp) has been to simply make the ports a bit long, check the Fb visually, then reduce port length if Fb is too low.

Art
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Old 25th January 2012, 05:41 PM   #2527
AndrewT is online now AndrewT  Scotland
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win isd pro has this error corrected.
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Old 25th January 2012, 08:14 PM   #2528
Xoc1 is offline Xoc1  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
win isd pro has this error corrected.
Could you be more specific?
Is Hornresp correct, and WinISD Alpha wrong with multiple ports!????
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Old 26th January 2012, 04:33 AM   #2529
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Quote:
Originally Posted by NEO Dan View Post
I see 2890-120101 but no update here.
Hi Dan,

The 2890-120101 release fixed a very subtle bug in the Loudspeaker Wizard. It had no bearing on the accuracy of the results so I didn't bother to announce the change.

I have just fixed another similar low-impact bug associated with the main input parameters screen. Product Number 2890-120126 refers.

Kind regards,

David
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Old 26th January 2012, 05:18 AM   #2530
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Hi Martin,

Quote:
Originally Posted by Xoc1 View Post
In the first instance could you confirm that my assumption that Hornresp is assuming a single round port with one flanged end (as shown in the Schematic), and as such it is using a end correction value of 0.731 x the effective port diameter?
Hornresp assumes a single circular port tube, but not as shown in the schematic. In practice the port tube is normally positioned internally, so for the purposes of the simulation model the unflanged end is considered to be inside the enclosure and the flanged end is considered to the port opening in the enclosure baffle.

Hornresp adds a length correction of 8 / (3 x Pi) x (0.5 ^ 0.5) times the port effective radius to the unflanged end inside the enclosure. No length correction is necessary at the flanged end because unlike WinISD, the actual acoustical impedance load on the port is used in the calculations.

Quote:
Originally Posted by Xoc1 View Post
Any insights into how to calculate the port lengths would be appreciated.
Sorry, but I have no suggestions as to how the end corrections for multiple triangular ports could be calculated.

Kind regards,

David
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