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Flared ports and rescaling an enclosure
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Foca_Dacian View Drop Down
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Joined: 05 February 2011
Location: Romania,Cluj
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Points: 118 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Foca_Dacian Quote  Post ReplyReply Direct Link To This Post Topic: Flared ports and rescaling an enclosure
    Posted: 10 June 2015 at 7:48pm
Hi,
I want to make two reflex subs following the 18 sound Kit 18 subwoofer plans.
http://wizardaudio.hu/hasznos/hangfal%20tervek/bass/bass%20reflex/pdf/18Sound%20Kit18%20B.pdf
(no longer on the 18 sound website)loading them with FaitalPro 18FH510 drivers.

But I want to slightly modify the plans.
To be more specific, I want to make the enclosure 500 mm wide(580 mm in the original plans)but to keep the same inner volume and tunning by making it taller and deeper.
To keep the original tunning I have to use the same port area by making the port taller and the depth as the original plan.

The port is flared,where do I measure the port area from?Inner lip of the flare or the outter lip of the flare?
By the flared part beeing somewhat narrower after I finish rescaling,will that affect the tuning of the box.

Never worked with flared ports before so I don't know how they react to this type of changes.
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DMorison View Drop Down
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Joined: 14 March 2007
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Points: 1649 		Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 10 June 2015 at 8:30pm
Originally posted by Foca_Dacian Foca_Dacian wrote:

Hi,
I want to make two reflex subs following the 18 sound Kit 18 subwoofer plans.
http://wizardaudio.hu/hasznos/hangfal%20tervek/bass/bass%20reflex/pdf/18Sound%20Kit18%20B.pdf
(no longer on the 18 sound website)loading them with FaitalPro 18FH510 drivers.

But I want to slightly modify the plans.
To be more specific, I want to make the enclosure 500 mm wide(580 mm in the original plans)but to keep the same inner volume and tunning by making it taller and deeper.
To keep the original tunning I have to use the same port area by making the port taller and the depth as the original plan.

The port is flared,where do I measure the port area from?Inner lip of the flare or the outter lip of the flare?
By the flared part beeing somewhat narrower after I finish rescaling,will that affect the tuning of the box.

Never worked with flared ports before so I don't know how they react to this type of changes.


I don't know for sure, but I'd think that the area at the narrowest (and consequently longest) part of the port will have the biggest effect on the tuning, so I'd work from that. There's a paper published by some JBL engineers that summarises a lot of research on flared ports here; if I've understood it correctly then one thing I note is that flaring the port only had a big effect when the ratio between the mouth height and the minimum height was quite big. As the ratio on the 18Sound plan is a medium amount, I don't think it will affect tuning much so you would probably be safe using the same amount of flaring even with your recalculated height.
HTH,
David.
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