port question for 8's

[05_ZX636 10+ year member]

a buddy of mine is building a box to go under the back seat of his 4-door colorado. He is just using some kicker or rockford 8's (1 pair). The subs will be facing down and he is wanting them tuned around 35hz. The box is close to 1.5 cubes without subs. Could he just use a 4" pvc port, or what would be easier? and how long. thanks

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[Louisiana_CRX 5,000+ posts]

two 4" pvc pipes each 19" long

 

[RAM_Designs 5,000+ posts]

two 4" pvc pipes each 19" long

That gives him nowhere near a 35hz tune in a 1.5ft^3 box. Use one 4" pipe and make it 15.5" long. If he used two they'd have to be 34" a piece. Not to mention the 1.5ft^3 is before and sub/port displacement...so it'll have to be even long than 15.5" for a single port.

20" should give you right around 35hz after taking away the .15ft^3 for the port and .15ft^3 for the subs.

 

[05_ZX636 10+ year member]

i will call him tomorrow and he can check his cubic feet. Thanks for the help

 

[Louisiana_CRX 5,000+ posts]

That gives him nowhere near a 35hz tune in a 1.5ft^3 box. Use one 4" pipe and make it 15.5" long. If he used two they'd have to be 34" a piece. Not to mention the 1.5ft^3 is before and sub/port displacement...so it'll have to be even long than 15.5" for a single port.

i always used slot ports i thought round ones worked the same i knew it would give about 25 sq inch opening....and 19" length on a slot is around 36 hZ

 

[05_ZX636 10+ year member]

Would there be a better alternative to pvc, slot port?

 

[Louisiana_CRX 5,000+ posts]

i've just always used slots easier to figure for me...i didn't know round were different

 

[RAM_Designs 5,000+ posts]

i always used slot ports i thought round ones worked the same i knew it would give about 25 sq inch opening....and 19" length on a slot is around 36 hZ

I'm very confused by this statement. 25in^2 of port 19" long equals 36hz? What size box would that have to be in to get that tuning, because with a 1.5ft^3 box it'd have to be 30" long to get that tuning. That'd actually be a 44hz tune with a 25in^2 port 19" long in a 1.5ft^3 box.

 

[Louisiana_CRX 5,000+ posts]

I'm very confused by this statement. 25in^2 of port 19" long equals 36hz? What size box would that have to be in to get that tuning, because with a 1.5ft^3 box it'd have to be 30" long to get that tuning. That'd actually be a 44hz tune with a 25in^2 port 19" long in a 1.5ft^3 box.

i'm going by the specs i've received from the DD website

 

[RAM_Designs 5,000+ posts]

i'm going by the specs i've received from the DD website

Clearly they're not going for a very musical box tuning that high //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[azimuth 5,000+ posts]

Would there be a better alternative to pvc, slot port?

pvc defeats the purpose of using round ports. with actual flared aero ports, you can get away with around 1/2 the port area as a slot or square port, in the same size box. pvc is not flared, so the advantage is lost. you could do 1 4 inch flared aero for that box.

 

[Louisiana_CRX 5,000+ posts]

Clearly they're not going for a very musical box tuning that high //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

my boxes always hit pretty low....they like 16 sq inches per cu ft and according to the charts 13" long was 45hz 16" long was 40hz..so I have assumed 19" long was about 35hz....on the website it shows the 40hz specs now....it use to show the 45hz specs....I've always heard standard box formulas don't work for DD subs

 

[azimuth 5,000+ posts]

my boxes always hit pretty low....they like 16 sq inches per cu ft and according to the charts 13" long was 45hz 16" long was 40hz..so I have assumed 19" long was about 35hz....on the website it shows the 40hz specs now....it use to show the 45hz specs....I've always heard standard box formulas don't work for DD subs

what does standard box formula mean? box volume and port length are calculated by mathmatics, which never changes.//content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

 

[Louisiana_CRX 5,000+ posts]

http://www.ddaudio.com/dd/caraudio/enclosureInfo/boxSize_hiEff.asp

 

[Louisiana_CRX 5,000+ posts]

maybe you know more than DD since they've only been making their subs for about 10 years....i'm just going on what DD claims because i figure i know less than they do.....