Port not part of the enclosure volume? - Chevy Impala SS Forum
 
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post #1 of 10 (permalink) Old 03-27-2007, 03:17 PM
sherlock9c1
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I'm running some calculations on different styles of boxes and I've got a question. In the case of a bandpass box, does the volume of the port subtract from the volume of the enclosure in the same way you'd subtract the volume of the driver? There's a bunch of calculators out there and some explain it and some don't.
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post #2 of 10 (permalink) Old 03-27-2007, 07:00 PM
UndercoverPunk
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Port volume is never a part of net volume.
post #3 of 10 (permalink) Old 03-27-2007, 10:45 PM
PIMPALA-SS
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Quote:
Originally posted by UndercoverPunk:
Port volume is never a part of net volume.
Not trying to correct you, but you shouldnt ever use the word "never" in the car audio world.


The material that the port is made from, can adversely change the internal volume of an enclosure.

To completly answer your question, the air inside of the port is considered to be also inside the enclosure, in any enclosure. the box ends, where the port ends.

So if your port is flush with the outside of the box, then you only need to subtract the material that the port is made of.

If your port sticks outside of the box (sounds strange, but in some installations, its needed) then the port volume thats outside of the box, adds to the internal volume of the enclosure.


ANY hard material (wood used for bracing, subwoofer motor structures, port material, ect ect) takes away from internal volume.
 
post #4 of 10 (permalink) Old 03-28-2007, 07:02 AM
sherlock9c1
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Thanks guys. I'm actually looking at an external port, possibly. I'm looking at putting a bandpass installation in the left rear cargo area of my wagon and depending on packaging, I may run an external port. That's why I was asking the question - this seems to be the road less traveled.

If that's true, then the nice thing about an external port is that it'll make my required box size smaller!
post #5 of 10 (permalink) Old 03-28-2007, 09:12 AM
PIMPALA-SS
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yup, you calculate the area of the external port thats "outside" of the box, and add it to your enclosure volume!
post #6 of 10 (permalink) Old 03-28-2007, 01:16 PM
kdrolt
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sherlock9c1: ask me next time. I can answer in double E-speak to make it easier for you.

Edit: the port can physically be part of the enclsoure voluem BUT it is not part of the enclosure volume when it comes to calculating the compliance (1/stiffness) of the enclosure for a Helmholtz resonator ported box. If you think about it, you'll understand why.

[ 04-03-2007, 12:48 PM: Message edited by: kdrolt ]
post #7 of 10 (permalink) Old 03-28-2007, 01:17 PM
PIMPALA-SS
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Quote:
Originally posted by kdrolt:
sherlock9c1: ask me next time. I can answer in double E-speak to make it easier for you.
did he have an issue comprehending what i wrote?
post #8 of 10 (permalink) Old 03-28-2007, 02:30 PM
sherlock9c1
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Quote:
Originally posted by PIMPALA-SS™:
did he have an issue comprehending what i wrote?
Naw, it's just that Ken and I are both fluent in nerdspeak.

This whole question may become irrelevant because I may just go with a sealed box for now (smaller and simpler!). The things of concern are: box size, construction simplicity, venting (getting the speaker output into the cabin, which may be a concern based on how I package it), low-frequency roll-off and transient response.

I know a sealed box is better at transient response, but I don't really know if transient response matters to me. The low-frequency roll-off is something I think I care about, and all the online calculators I could find showed a much improved low-frequency extension using bandpass, but again, I don't know if I'll care. Using my existing driver, the rolloff was only at -9dB at 20Hz, which was a lot better than the sealed box response curve. Up top, I'd be crossing everything over at 80Hz (head unit offers this, or 125Hz), and the front speakers I'm installing are good down to 100Hz, so the bandpass's much quicker rolloff up high wasn't a concern.

I can whip together a quick sealed box in an evening and then try it to see if it'll work where I want to put it. If I don't like it, I may pursue the bandpass box.

Oh, and Ken, I'll shoot you an email.

[ 03-28-2007, 04:02 PM: Message edited by: sherlock9c1 ]
post #9 of 10 (permalink) Old 03-28-2007, 06:58 PM
UndercoverPunk
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What is your setup going to consist of? I've had great low end roll off with low tuned ported enclosures.
post #10 of 10 (permalink) Old 03-29-2007, 11:55 AM
sherlock9c1
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Pioneer DEH-P3600 head unit (already installed)
Audiobahn 6.5 components up front, with some treatment to the doors to help them out (not yet installed)
Pioneer 6x8s (don't ask, long story) in the rear with some acoustic treatment to their mountings and surrounds (not yet installed),
and the amp/sub.

The HU allows me to HPF the fronts/rears at 125, 80 or 50, and the sub can be LPF'd at those same frequencies. With the upgraded front/rear speakers and treated speaker locations, I was thinking I'd be able to get away with them crossed over at 80, cross the sub over at 80, and be happy.

For awhile now, I've been thinking about a way to bury the sub in the left rear cargo compartment AND still have enough room to store my little roadside repair kit (5" by 7" by 10") and a few quarts of oil behind the factory door.

My thought was to remove the black plastic compartment and just use the interior panel as a cover for whatever I build, so it looks completely stock from the outside. The top storage tray I would remove and replace with a carpeted vent, like Klez did. I was thinking of a ported or bandpass enclosure because if I try to keep the compartment door for its original purpose, it gets tougher to position a 12 in this area so that the speaker can vent directly to the cabin, hence using the port from a bandpass to give me more freedom to package everything in a way that works. I'd almost definitely use fiberglass so I could make better use of all the funky curves back there and still get the volume I need.

So.. them's my thoughts.
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