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Old 21st November 2012, 02:06 PM   #2981
tb46 is offline tb46  United States
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Hi David,

I took a simple dual driver sealed box (modeled in Nd), and slot-loaded the front of the driver using OD. While most graphs look as expected, the displacement at the low end looks too large, e.g.: @ 15Hz it almost tripples. I don't have any way to physically verify this; but, does that seem correct to you? Additionally, the impulse response shows a stronger than expected ringing; and, why do both curves not start at the same time, I would not have thought that there should be a 5msec difference here?

I'm wondering about the correctness of the simulations.

Regards,
Attached Images
File Type: jpg DCS380_sealed_Input.jpg (35.5 KB, 181 views)
File Type: jpg DCS380_slot_Input.jpg (38.1 KB, 180 views)
File Type: jpg DCS380_sealed_v_slot_SPL.jpg (28.4 KB, 156 views)
File Type: jpg DCS380_sealed_v_slot_Impulse.jpg (22.7 KB, 155 views)
File Type: jpg DCS380_sealed_v_slot_displacement.jpg (25.7 KB, 153 views)
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Last edited by tb46; 21st November 2012 at 02:10 PM.
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Old 21st November 2012, 06:00 PM   #2982
Kolbrek is offline Kolbrek  Norway
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Quote:
Originally Posted by tb46 View Post
While most graphs look as expected, the displacement at the low end looks too large, e.g.: @ 15Hz it almost tripples.
Try using the same number of drivers for both simulations. I see that your closed box sim has two drivers in series, while the slot-loaded version has only one.

-Bjørn
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Old 21st November 2012, 11:57 PM   #2983
tb46 is offline tb46  United States
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Hi Bjorn,

Thank you so much. Sometimes I can look at something like this, and just cannot see the obvious. This fixes the displacement (I knew that could not be right), but the SPL and the impulse response still look bad, and I still don't understand why there should be a substantial difference in the first arrival time?

Regards,
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Old 22nd November 2012, 06:51 AM   #2984
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Quote:
Originally Posted by tb46 View Post
I took a simple dual driver sealed box (modeled in Nd), and slot-loaded the front of the driver using OD. While most graphs look as expected, the displacement at the low end looks too large, e.g.: @ 15Hz it almost tripples. I don't have any way to physically verify this; but, does that seem correct to you? Additionally, the impulse response shows a stronger than expected ringing; and, why do both curves not start at the same time, I would not have thought that there should be a 5msec difference here?
Hi Oliver,

As far as I can determine, the Hornresp simulation results should be valid :-).

As Bjørn has pointed out, changing to 2S drivers in the offset driver horn example will resolve the displacement issue.

The SPL response (resonances unmasked) and the impulse response ringing are what I would expect to see for the offset driver horn configuration you have specified. Sanity check - when the impulse response is exported to ARTA and transformed back to the frequency domain, the resulting SPL response is very close to the original (see attached screenprints).

As documented in the Impulse Response tool description in the Hornresp Help file, the maximum positive or negative amplitude value is normalised to 0.9 and the maximum peak is positioned by default at the 0 msec reference point. This was the presentation recommended to me by Jean-Michel (Jmmlc), the author of the impulse response calculation method used in Hornresp.

In the case of your offset driver horn example, the maximum peak is negative which is why it, rather than the first positive spike, is shown at the 0 msec point.

Hope this helps to clarify things.

Kind regards,

David
Attached Images
File Type: jpg DCS380_sealed_v_slot_SPL.jpg (28.4 KB, 30 views)
File Type: png Oliver.png (76.0 KB, 29 views)
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Old 22nd November 2012, 07:48 AM   #2985
Kolbrek is offline Kolbrek  Norway
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To confirm the simulations, I ran the same setup in my own horn simulation SW, and got the same results (but then I use the same model... ). A use a different IR calculation algorithm, and I do not change the position of the impulse based on the location of the peak. Still the results are very similar.

The dip at around 390Hz comes from the fact that the L12 is a quarter wavelength at that frequency, so the reflection from the blocked end is 180 degree out of phase with the driver. The front acoustical load impedance is as good as zero at this frequency.

The peak at ~160hz is at the quarter wave resonance frequency of the full length of the horn plus end correction, which is about 10cm. There is a large peak in the acoustical impedance at this frequency, raising the efficiency by around 10dB compared to the 30-100Hz range.

The model assumes the driver to be attached at a *point*, in practice it will be "distributed". That will most likely change the magnitude of the peaks and dips, especially since the slot is relatively shallow, and the driver occupies a large part of it.

A 2D BEM simulation (free field, 3m distance) gives a very similar result, but with a somewhat less pronounced peak. So the Hornresp simulation appears to be quite good

-Bjørn
Attached Images
File Type: jpg SL.jpg (356.4 KB, 43 views)
File Type: jpg SLBEM.jpg (132.9 KB, 35 views)
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Old 22nd November 2012, 02:37 PM   #2986
tb46 is offline tb46  United States
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Hi David and Bjorn,

Thank you both, your explanations are very much appreciated.

I was looking at this thread: A bench style cabinet subwoofer 2x15 closed Post #23, and wondered about this application of slot-loading.

As djk has pointed out numerous times in the PPSL thread: A Thread for those interested in PPSL enclosures e.g.: Post #6, the cavity resonances reduce a lot when one of the drivers is turned around (and even more, if the S1 area of the slot is partially filled in).

Again, Hornresp is just a wonderful tool. Save a tree - simulate. :-)

Regards,
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Old 23rd November 2012, 02:49 PM   #2987
epa is offline epa  Netherlands
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hi david
is there any sofware that you (or anybody else)now of ,that can import hr data ,to model a filter/eq .
this would be helpfull to determen a hpf.
tnx erik
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Old 23rd November 2012, 03:18 PM   #2988
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by epa View Post
hi david
is there any sofware that you (or anybody else)now of ,that can import hr data ,to model a filter/eq .
this would be helpfull to determen a hpf.
tnx erik
Hi epa,

Thats easy to do: You only need to convert the HR textfile to a format that any of these program can recognize:

FRD Consortium

PS: I usually first import the .wav files from HR to HOLMimpulse where I edit the IR/FR and then export to e.g. MPRM program where you can do all filtering/ Eq. and the back to Holmimpulse to present the resulting graphs you want to display.

b
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Old 23rd November 2012, 03:26 PM   #2989
epa is offline epa  Netherlands
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tnx bjorno
i'll look in to that.
edit/how do i export*.wav from hr?
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Last edited by epa; 23rd November 2012 at 03:54 PM.
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Old 24th November 2012, 04:27 AM   #2990
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Quote:
Originally Posted by Kolbrek View Post
The dip at around 390Hz comes from the fact that the L12 is a quarter wavelength at that frequency, so the reflection from the blocked end is 180 degree out of phase with the driver.
The effect of varying the driver offset position while maintaining a constant overall horn length can be seen by moving the L12 slider in the Loudspeaker Wizard tool. Attachment 1 refers.

Quote:
Originally Posted by Kolbrek View Post
The peak at ~160hz is at the quarter wave resonance frequency of the full length of the horn plus end correction, which is about 10cm. There is a large peak in the acoustical impedance at this frequency, raising the efficiency by around 10dB compared to the 30-100Hz range.
The effect of varying the overall horn length while maintaining a constant driver offset position can be seen by moving the L23 slider in the Loudspeaker Wizard tool. Attachment 2 refers.

Quote:
Originally Posted by Kolbrek View Post
The model assumes the driver to be attached at a *point*,
If Nd is set to 1 in the sealed box example, and in the offset driver example S1 to S3 are set to 819.40 (Sd) and L12 and L23 are set to 0.01, then the results for the two cases become effectively identical, as expected.

Kind regards,

David
Attached Images
File Type: png L12Changed.png (75.3 KB, 25 views)
File Type: png L23Changed.png (68.3 KB, 19 views)
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