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Old 7th January 2007, 05:21 PM   #341
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Default A clarification

I'm simulating a design in MLQW and have switched to Sections for comparison purposes.
I think there is a difference in geometry. Let me state my understanding for correction, if needed.
In Sections, I think if a port is used it begins at the end of the TL.
In MLQW, a port entry is inside the enclosure.

If this is correct, does it matter where the entry of the port is situated within the MLQW?

I'm seeing a resonance around ~600 Hz whose magnitude seems to be related to port length. I'd like to understand the above before trying to solve/understand the resonance/port length issue.

I am aware I may be too picky in trying to understand this...been known to happen.

Thanks
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Old 7th January 2007, 06:59 PM   #342
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Ed,
that 600 Hz resonance stems from the port behaving as a TL- nasty, but not really incurable.
1 - lengthen the port by a factor of square root of 2. No need to go to ten digits, just make your port 1.4 times as long.

2 - drill half a dozen 8 - 10mm holes at half the port's length.

3 - have a drink to celebrate full success.

4 - if still in festive mood, repeat #3

Pit
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Old 7th January 2007, 07:24 PM   #343
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Pit,

As lengthening the port moves the resonance of the system I would have to make other adjustments. Correct?

Is there any explanation for #2? I can guess pressure relief but what effect does that have on the system?

Are 1 & 2 a combined solution?

I understand option 3 very well. #4 even better
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Old 7th January 2007, 08:06 PM   #344
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Quote:
In Sections, I think if a port is used it begins at the end of the TL.
Correct, the port would continue out of the bottom end of the TL.

Quote:
In MLQW, a port entry is inside the enclosure.
Correct, the port can be moved to different positions along the length between the end of the TL and the driver.

Quote:
If this is correct, does it matter where the entry of the port is situated within the MLQW?
The entry of the port sets the position you specify along the length. For example, if you had a ten inch long port that extends up into the enclosure from near the bottom, the position would be closer to L-10 in in even though the exit is nearer to L.

Hope that helps,

Martin
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Old 7th January 2007, 11:33 PM   #345
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Thanks Martin, that helps.

Along the way, I've found that moving the port location will remove the resonance I was seeing around ~600 Hz.

I found something PaulK suggested to be interesting. The scale of Mathcad graphs can be changed by selecting the graph, selecting the axis and then inserting new limits.
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