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Old 25th October 2006, 08:21 PM   #1
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Default Port lenght - Thick MDF Cabinet

Hello!

Im currently building John Krutke L18-27BFC/G monitors (1st proyect).
I used 1" thick MDF on cabinet construction. Zaphs original cabinet is constructed out of 3/4" thick MDF.

"The port was made up of several Parts Express 260-402. It's a flared 1.6" port which seems kind of small, but I took 4 of them and cut each one to 2.2", then taped them together for a 4.4" total length"

Since im using thicker MDF for the back panel, the internal port lenght will decrease...
Should i increase the total port lenght by 1/4" (remember im using 1" instead of 3/4" MDF for the back panel). Or should i just keep the original 4,4" total length?

In other words, is the internal port lenght what matters, or only the total port lenght regardless if its inside or not?

Thank you!!!!
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Old 25th October 2006, 09:11 PM   #2
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Default Re: Port lenght - Thick MDF Cabinet

Quote:
Originally posted by richardtextex
In other words, is the internal port lenght what matters, or only the total port lenght regardless if its inside or not?
Only the total port volume matters, BUT remember that port volume is subtracted from internal volume, and adjust internal volume accordingly.
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Old 25th October 2006, 09:13 PM   #3
hooha is offline hooha  Canada
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Hi there,

I'm not familiar with the two designs you mentioned in your post, but will comment based on the following criteria:

- you kept the internal volume the same as the original design despite using a thicker baffle

- you are in fact using a flared port and mounting it on the outside of the baffle

Based on this, you should keep the length the same.

On a lighter note, 1/4" difference in port length does not make a whole lot of difference.

Mark

Ha! Leadbelly beat me to it.
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Old 25th October 2006, 09:41 PM   #4
v-bro is offline v-bro  Netherlands
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Quote:
Originally posted by hooha

On a lighter note, 1/4" difference in port length does not make a whole lot of difference.
You're right, I don't think you'll hear the difference of 1/4" pipelength, make sure indeed that the extra wood thickness doesn't affect internal volume.

Pipe length can be adjusted to fit the room-acoustics better, mostly differences become audible when they're about 1" or more...

Generally a longer pipe decreases output + lowers deepest freq. and shortening it increases output + hightens deepest freq.
Adjust at will!
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Old 26th October 2006, 01:48 AM   #5
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Ok, thank you! Im sticking with the 4,4" length then...

Regards!
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Old 26th October 2006, 01:58 AM   #6
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Default Re: Re: Port lenght - Thick MDF Cabinet

Quote:
Originally posted by leadbelly


Only the total port volume matters, BUT remember that port volume is subtracted from internal volume, and adjust internal volume accordingly.

Do you mean i should decrease total cabinet internal volume by:

(pi)*radius^2*(1/4)" ?????

"Since total internal volume will be increasing if i mantain 4.4" and use a thicker cabinet, if you consider the port tube volume is "stealing internal volume"....

Thank you guys
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Old 26th October 2006, 06:27 PM   #7
Svante is offline Svante  Sweden
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In order of importance if you want to produce the same response as in the original design:

Keep the shape and size of the air plug inside the port the same.
Keep the baffle shape the same.
Keep the volume of air inside the box the same.

If you use thicker MDF this probably means that you should make the box slightly deeper.
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