Slot port calculation

 

Bronze Member
Username: Alonzoub

Post Number: 50
Registered: Apr-10
Every box designing website/calculator I find seems to ask for a Port Diameter when designing a ported box. I gotta say im not a huge fan of round ports, the Slot design looks much cleaner to me. So, would it be okay to say:
Upload
h = height of slot port
w = width of slot port
d = diameter of equivalent round port

so to compute the "diameter" of the port as a function of the slot height and width i would use:
Upload (using the + obviously)

This makes sense to me because given any port length L, the total volume of the port will be the same. But im not sure how this goes with actual box building.

If im wrong someone please point me in the right direction.
 

Platinum Member
Username: Glasswolf

Post Number: 14019
Registered: Dec-03
http://www.bcae1.com/spboxnew2.htm
 

Bronze Member
Username: Alonzoub

Post Number: 51
Registered: Apr-10
Thanks.
 

Bronze Member
Username: Alonzoub

Post Number: 52
Registered: Apr-10
Another question about slot ports.

How important is the h:w ratio of the slot port. I read on some other forums that you shouldnt exceed a 9:1 ratio or else port noise will become an issue.

I just wanted to know if anyone has experienced this problem. because Im having alot of trouble designing a box using a wall as part of the slot. The internal height of the box im designing has to be at least 13.5" so my port width ends up being very thin.

Here is what I came up with:
Upload
Upload
Upload

The small peice in the middle of the port is only ~5 inches long and I only put it in to protect from port rattle.

Im designing this box for a single IDQ 12 v3 tuned to 28 Hz.
Unfortunatly the ratio of h:w of the port on this box is 10.8:1 ... well above the recommended limit of 9:1.
 

Platinum Member
Username: Glasswolf

Post Number: 14041
Registered: Dec-03
Widen the port, and just add length internally to compensate?
 

Bronze Member
Username: Alonzoub

Post Number: 53
Registered: Apr-10
Making the port just 1/4 an inch wider to 1.5 x 13.5 (exactly 9:1) would force me to extend the port by ~8 inches to retain a 28Hz tuning, That takes away ~.15 cuft from Vb; im not sure how that would effect the sound. That would also make the end of the port about 2 inches from the right wall,

That brings up another few questions. How many turns in a port is too many? Does having turns in the port effect sound quality negatively? And are U-shaped bends a bad idea?

Back to the original question though, I want to get some opinions on my current box design, is that port width too small? Should I just scrap this design and start over?

Sorry about all the questions but I have never designed a ported box before and I'm just looking to learn from the fine members of this board.
 

Bronze Member
Username: Canaanwhite

Monroe, Louisiana USA

Post Number: 25
Registered: Nov-10
RE has the best box calculator out there...thats what I use on all my boxes
 

Bronze Member
Username: Alonzoub

Post Number: 60
Registered: Apr-10
yea I actually discovered that calculator after I redesigned this enclosure, it does help alot, but it doesnt work 100% for me because of the way I do the baffle.

Since I got no answers on my other questions, I just assumed 2 turns is okay. Heres what I came up with:
Upload

Vb ~ 1.8 ft^3
Fb ~ 28hz
Vent mach ~ .07
 

Platinum Member
Username: Glasswolf

Post Number: 14084
Registered: Dec-03
sorry I missed the thread. two turns is fine, and the box looks good in the drawing.

Ever see how many turns some more complex enclosures have, like transmission lines? They call some boxes "snail shells" for a reason.
 

Bronze Member
Username: Canaanwhite

Monroe, Louisiana USA

Post Number: 66
Registered: Nov-10
I like snail shell boxes
 

Platinum Member
Username: Glasswolf

Post Number: 14087
Registered: Dec-03
they are pretty awesome
 

Bronze Member
Username: Alonzoub

Post Number: 62
Registered: Apr-10
alright cool, im still learning alot. I just got into car audio like 3 months ago and im pretty much addicted.

so I was doing some googling about some crazy enclosures, and i stumbled on this pic:
Upload

the area of this port is changing in steps, is there any rules or formulas to follow when making a port that gets larger?
 

Platinum Member
Username: Glasswolf

Post Number: 14088
Registered: Dec-03
It's a wave guide. Do a bit or research on waveguides, and you'll find what you're looking for.
 

Bronze Member
Username: Lord_huggington

Ontario Canada

Post Number: 53
Registered: Oct-10
That's one crazy box. Correct me if I'm wrong!

It sounds like TL's are used for accuracy among very long port lengths for the desired very low tuning because as the port area increases, the sound propagates (the wave developes more, becoming more pronounced), and so that by the end of the very long port, the force isn't diminished, and you get a nice "sound" instead of just lots of air being moved. It should be able to reproduce a very wide frequency range because as the box plays a high frequency, the port isn't being used all that much (and it would be tuned pretty damn high too - like 60 HZ), yet when a low frequency is played the box doesn't roll off at -24dB/octave like normal ported box, it could be damn near flat.

I'd say that box is tuned to 60 HZ but can also touch 20 HZ at the same levels. Something like that. I really don't know LOLZ!
 

Platinum Member
Username: Glasswolf

Post Number: 14102
Registered: Dec-03
yup, transmission line works in a way, similarly to a bandpass enclosure. It masks harmonic distortion and extends bottom octave output. great design for smaller drivers in home audio cabinets.
Jump to: Home Audio Forum | Home Video Forum | Home Theater Forum | Car Audio Forum