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Old 3rd February 2018, 02:33 AM   #11
Brian Steele is offline Brian Steele  Grenada
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Here's a comparison between measured FR and a "Lossy Le" version of the sim. There is much better correlation between the sim and the measurements at the low frequencies, but it goes out of whack above 60 Hz and the upper cutoff slope does not match.
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File Type: png 20180202-INF10-BP (lossy Le).png (59.5 KB, 82 views)
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Old 3rd February 2018, 04:04 AM   #12
anatech is offline anatech  Canada
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Redoing an old build
Hi Brian,
I wonder if the 400 Hz peak isn't coming from the back of the woofer and angled just right to come out the port.

I like your measured response better than the sim. It may not reach the predicted SPL, but trading that for some section of flat-ish response is fine.

-Chris
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Old 3rd February 2018, 05:21 AM   #13
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by Brian Steele View Post
Here's a comparison between measured FR and a "Lossy Le" version of the sim. There is much better correlation between the sim and the measurements at the low frequencies, but it goes out of whack above 60 Hz and the upper cutoff slope does not match.
Hi Brian,

Would it be possible to post a screenprint of the input parameters window or alternatively a copy of the exported record file, for the simulation? Thanks.

Kind regards,

David
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Old 3rd February 2018, 10:37 AM   #14
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by David McBean View Post
Hi Brian,

Would it be possible to post a screenprint of the input parameters window or alternatively a copy of the exported record file, for the simulation? Thanks.

Kind regards,

David
Here ya go. This is the current tweaked model that I'm working with. I've also included an image of the vented section with the access panel removed. This shows the only significant difference between the sim and the build, as the sim assumes that the vents are external to the vented section, when they're actually internal (and yes, the adjusted sim takes into consideration the volume displaced by the vents).
Attached Images
File Type: png 2018-02-03.png (15.5 KB, 68 views)
File Type: jpg 20180203_070321.jpg (179.4 KB, 74 views)
Attached Files
File Type: txt INF10-BP.txt (956 Bytes, 3 views)
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Old 3rd February 2018, 11:59 AM   #15
Ron E is offline Ron E  United States
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Quote:
Originally Posted by Brian Steele View Post
Here ya go.
An adjusted sim using (from your screenshot)
Fs 20.0 Hz
Qts 0.317
Qes 0.332
Vas 141.78 Liters
Re 6.89 Ohms
Dia 20.50 cm

Vr=21.3

Gives modified (caused by sealed side) parameters of:
Fs 55.3
Qts 0.824
Qes 0.919
Vas 18.518

Then using (guesses)
Vf=18.7
Fb=57
Ql=15
Qb=Qp=30

Gives this:
Impedance peaks at ~35 and ~90 just over 30ohms
F3l=33
F3h=102
slight droop in the passband
Attached Images
File Type: png inf10 impedance.PNG (31.0 KB, 70 views)
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Old 3rd February 2018, 05:52 PM   #16
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by Brian Steele View Post
Here ya go. This is the current tweaked model that I'm working with. I've also included an image of the vented section with the access panel removed. This shows the only significant difference between the sim and the build, as the sim assumes that the vents are external to the vented section, when they're actually internal (and yes, the adjusted sim takes into consideration the volume displaced by the vents).
Sigh, I found a minor error in the model, see corrected information below and attached....
Attached Images
File Type: png 20180203-INF10-BP (no stuffing)-FR.png (39.9 KB, 58 views)
File Type: png 20180203-INF10-BP (no stuffing)-IMP.png (53.4 KB, 17 views)
File Type: png 2018-02-03 (1).png (15.5 KB, 17 views)
Attached Files
File Type: txt INF10-BP.txt (956 Bytes, 1 views)
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Old 3rd February 2018, 06:13 PM   #17
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by Ron E View Post
An adjusted sim using (from your screenshot)
Fs 20.0 Hz
Qts 0.317
Qes 0.332
Vas 141.78 Liters
Re 6.89 Ohms
Dia 20.50 cm

Vr=21.3

Gives modified (caused by sealed side) parameters of:
Fs 55.3
Qts 0.824
Qes 0.919
Vas 18.518
Fb is actually 54 Hz when the panel is left off the vented side, so that's pretty close. I basically took the panel off, took the vents out, laid the cabinet on its side (so the holes for the vents were blocked), then measured the impedance curve and compared it to a Hornresp model of a sealed cabinet loaded with a short "horn" with the same CSA and depth of the vented section.


Quote:
Originally Posted by Ron E View Post
Then using (guesses)
Vf=18.7
Fb=57
Ql=15
Qb=Qp=30

Gives this:
Impedance peaks at ~35 and ~90 just over 30ohms
F3l=33
F3h=102
slight droop in the passband
Vf looks a little small there (I worked it out to be 22 l), and Fb a bit lower than measured. Depending on whether you use the minimum impedance or the zero-phase crossing to determine Fb, it lies between 59 Hz and 62 Hz.
Attached Images
File Type: png 20180203-INF10-BP (open)-IMP.png (43.4 KB, 15 views)
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Old 3rd February 2018, 11:17 PM   #18
Ron E is offline Ron E  United States
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f Port Zin
5.0 46.1 6.9
5.2 46.7 6.9
5.4 47.4 7.0
5.5 48.0 7.0
5.7 48.6 7.0
5.9 49.2 7.0
6.2 49.8 7.0
6.4 50.4 7.0
6.6 51.0 7.0
6.8 51.7 7.0
7.1 52.3 7.0
7.3 52.9 7.0
7.6 53.5 7.0
7.8 54.1 7.0
8.1 54.8 7.0
8.4 55.4 7.1
8.7 56.0 7.1
9.0 56.7 7.1
9.3 57.3 7.1
9.7 57.9 7.1
10.0 58.6 7.1
10.4 59.2 7.1
10.7 59.8 7.2
11.1 60.5 7.2
11.5 61.1 7.2
11.9 61.8 7.2
12.3 62.4 7.3
12.7 63.1 7.3
13.2 63.7 7.3
13.7 64.4 7.4
14.1 65.1 7.4
14.6 65.7 7.5
15.2 66.4 7.5
15.7 67.1 7.6
16.2 67.8 7.6
16.8 68.5 7.7
17.4 69.2 7.8
18.0 69.9 7.9
18.7 70.6 7.9
19.3 71.3 8.1
20.0 72.1 8.2
20.7 72.8 8.3
21.4 73.6 8.5
22.2 74.3 8.7
23.0 75.1 8.9
23.8 75.8 9.2
24.6 76.6 9.5
25.5 77.4 9.8
26.4 78.2 10.3
27.3 79.0 10.8
28.3 79.8 11.5
29.3 80.5 12.4
30.3 81.3 13.5
31.4 82.1 15.0
32.5 82.8 16.9
33.6 83.5 19.5
34.8 84.2 22.8
36.1 84.8 26.2
37.3 85.3 27.9
38.6 85.8 26.2
40.0 86.3 22.4
41.4 86.6 18.7
42.9 86.9 15.8
44.4 87.2 13.7
45.9 87.3 12.2
47.6 87.5 11.1
49.2 87.6 10.3
51.0 87.7 9.8
52.8 87.8 9.5
54.6 87.8 9.3
56.6 87.9 9.2
58.6 87.9 9.2
60.6 88.0 9.4
62.8 88.0 9.7
65.0 88.1 10.1
67.3 88.1 10.6
69.6 88.0 11.4
72.1 88.0 12.5
74.6 87.8 14.0
77.3 87.7 16.0
80.0 87.4 18.7
82.8 87.0 21.7
85.7 86.6 23.8
88.8 86.0 23.5
91.9 85.4 20.9
95.1 84.7 17.7
98.5 84.0 15.1
102.0 83.2 13.1
105.6 82.4 11.6
109.3 81.6 10.6
113.1 80.7 9.7
117.1 79.9 9.1
121.3 79.1 8.6
125.5 78.2 8.3
130.0 77.4 8.0
134.5 76.6 7.8
139.3 75.8 7.6
144.2 75.0 7.4
149.3 74.3 7.3
154.5 73.5 7.2
160.0 72.7 7.2
165.6 72.0 7.1
171.5 71.3 7.1
177.5 70.5 7.1
183.8 69.8 7.1
190.3 69.1 7.1
197.0 68.4 7.1
203.9 67.7 7.2
211.1 67.0 7.2
218.6 66.3 7.3
226.3 65.7 7.3
234.3 65.0 7.4
242.5 64.3 7.5
251.1 63.7 7.6
259.9 63.0 7.6
269.1 62.4 7.7
278.6 61.8 7.8
288.4 61.1 8.0
298.6 60.5 8.1
309.1 59.9 8.2
320.0 59.2 8.4
331.3 58.6 8.5
343.0 58.0 8.7
355.1 57.4 8.8
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Old 4th February 2018, 05:46 AM   #19
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by Brian Steele View Post
see corrected information below and attached....
Hi Brian,

Thanks for the information. Because the port tube is simulated using a horn segment rather than Ap and Lpt, no end correction is being added to the internal end. Attachment 1 may be a more accurate model, with segment 1 accounting for the internal end correction (0.1952 * Pi * Rp, where Rp is the port tube radius). The predicted system resonance frequency becomes 61.49 Hz.

Kind regards,

David
Attached Images
File Type: png Attach_1.png (53.8 KB, 20 views)
File Type: png Attach_2.png (61.8 KB, 19 views)
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Old 6th February 2018, 06:31 AM   #20
Brian Steele is offline Brian Steele  Grenada
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Join Date: Nov 2007
Quote:
Originally Posted by David McBean View Post
Hi Brian,

Thanks for the information. Because the port tube is simulated using a horn segment rather than Ap and Lpt, no end correction is being added to the internal end. Attachment 1 may be a more accurate model, with segment 1 accounting for the internal end correction (0.1952 * Pi * Rp, where Rp is the port tube radius). The predicted system resonance frequency becomes 61.49 Hz.

Kind regards,

David
Hi David, I'd actually accounted for the end-correction in my sim. The vents are flared at both ends, and inside the box they terminate pretty close to the access panel and the sides (which are within 1 diameter of the vent opening), so I thought that the best way to work out the effective vent length was to measure Fb, and then work backwards to see what combination of S1-S2 and effective vent length (L34) would give a similar Fb. The actual "length" of the vents (minus part of the flare) is about 20cm each.

The build is actually in pieces at the moment, as I'm repainting the box (it is about 14 years old and the white paint had yellowed). but when I have it back in one piece again, I'm going to rerun the test with even shorter vents to see if I can at least flatten the passband. I would really like to know however where the up to 6dB of theoretical output in the passband has disappeared to.
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