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Multi-Way Conventional loudspeakers with crossovers

Sealed enclosure -- golden ratio?
Sealed enclosure -- golden ratio?
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Old 19th September 2017, 10:10 PM   #111
33Polkhigh is offline 33Polkhigh  United States
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Quote:
Originally Posted by Juhazi View Post
Tall boxes might have internal standing waves (multiple order) in the passband of woofer(s). One example is Cerwin-Wega CLS-215, which was measured by Soundstage. Look at response and impedance around 150Hz!
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Click the image to open in full size.

The revised version XLS-15 has a divider in bass compartment that should help. I couldn't find measurements, sorry.
You can plug the internal box measurements into this calculator to see where the standing waves would be.

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Old 20th September 2017, 02:10 AM   #112
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by keantoken View Post
If you have a tall speaker with a driver at the top, can a standing wave inside the enclosure cause the cone to twist in the pressure gradient? Could internal reflections cause early cone breakup this way?
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Originally Posted by 33Polkhigh View Post
I don't think so. I think it would just raise the q slightly of the system by putting more air pressure on the cone, like using a smaller sealed box.
I'm reluctant to answer this as I haven't demonstrated it but I think Polk's comment may be reasonable in the first order (overall), and keantoken may have a point at higher orders.

I can't say I've worried too much about it because these modes are being dealt with anyway and I haven't found these affects to be a problem.
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Old 20th September 2017, 02:10 PM   #113
Patrick Bateman is offline Patrick Bateman  United States
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Originally Posted by gedlee View Post
Shape and placement of the sound absorbing material will have a big effect on its effectiveness. This is because sound is absorbed only when there is particle velocity. At the walls the particle velocity goes to zero so absorption on the walls does little. I always place the absorption in the middle of the box, not on the walls. The box shape will affect the mode shape and move the locations of maximum particle velocity around. A long tube with absorption on the walls won't see so much sound attenuation because the wave motion is normal to the walls. Place it in the middle of the tube and it becomes very effective. So shape is a factor, but any shape can be optimized if you know what you are looking for - hence no shape is any better than any other. Only the implementations vary.
Interesting. Kef puts a lump of foam in the center of the port of the LS50. IIRC, it's there to absorb high frequency resonances being radiated by the port.
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Old 21st September 2017, 04:07 PM   #114
gedlee is offline gedlee  United States
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Do you mean "center" along the duct, but across it, or center in the duct along it but not across it? Each technique would do different things.
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Old 21st November 2017, 06:50 PM   #115
33Polkhigh is offline 33Polkhigh  United States
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I'm happy to say that the issue I was reporting earlier about how my speakers sounded "stuffy" or lacking in openess was not due to the stuffing or box.

It was just that the drivers weren't yet broken in. The problem went away on its own. Sealed box filled with fiberglass works great. You do want some space around drivers and an adequately sized box.
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