Geting Proper Port Area

[Jeffdachef 5,000+ posts]

Quoted from quentin jarrel, owner of dss

"So basically the 12-16 port area thing is just a simple guideline, The real method is to find the minimum square inches of port area.

Thiele Small's formula

dv = 39.37 (fb x Vd)^1/2

dv= minimum port diameter of vent in inches

fb= box tuninf frequency in hertz

vd= cone displacement in cubic meters (one way xmax in meters times cone area(SD) in meters)

for one BL 15

xmax= .018 meters

sd= .081 meters^2

tuning= 32 hertz (per you)

dv= 39.37 (32 x .018 x .081) ^1/2 (^1/2 means square root)

dv= 39.37 (.046656)^1/2

dv= 39.37 (.216)

dv=8.5 inch diameter port per sub

dv=56.72 square inches

for two BL 15's you need (2)dv. So you need 113.44 square inches of port or more."

Click to read more...

 

[Jeffdachef 5,000+ posts]

Just looking for good discussions here. A definitive answer would be nice for once though.

So you know the minimum, but how do you know whats optimal and when to stop going too far?

Do you just forget about those port area per cubic feet ratios completely or do you just match how many cubic feet with how much power you are running along with the frequency response you are going for and keep the same minimum(or higher) port area?

Does port area really impact sound quality? AKA too much = sloppy and narrow bandwidth, too little = port compression, poor low end performance etc..
@hispls @keep_hope_alive @TaylorFade

Sometimes with some woofers on Winisd, they require unreasonable amounts of port area just to keep the M/s under 30 sometimes. Sometimes they turn out to be over 20+ sq inches of port area per cubic foot in their max recommended box size, which is fking trippy.

 

[keep_hope_alive Premium Member]

When I get back to a computer I can forward some links and papers on the discussion port sizing and flares sizing. your port is based on frequency response of the enclosure and excursion of the driver. what we care about is port velocity. once we know it we can predict chuffing or other noises. that is what determines the minimum port size. the size of the enclosure has nothing to do with port velocity. Frequency response matters because lower frequencies move for air. the lower your enclosure is expected to play, the larger your port needs to be.

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---------- Post added at 08:06 AM ---------- Previous post was at 08:05 AM ----------

 

I have found port noise and port size and port velocity calculators that are a great resource. You can probably find them yourself with a few searches

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[garychurch84 10+ year member]

I've never found a straight answer for this myself,I use a combination of Torres and winisd.tweak this a bit until I get the results I want. Tuned in to see where this goes. Thanks for posting

loudspeaker design cookbook would be a great investment also!

 

[tc300 10+ year member]

this has potential for a sticky!!!

 

[psych0ticnemes1 5,000+ posts]

I was never able to get a good answer on this either. According to this calculator, I'd need 69" of port area at 35 hertz for a single HDC3 12". I'm guessing that's because of it's high xmax. That port would be enormous.

Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

 

[Jeffdachef 5,000+ posts]

I've never found a straight answer for this myself,I use a combination of Torres and winisd.tweak this a bit until I get the results I want. Tuned in to see where this goes. Thanks for posting
loudspeaker design cookbook would be a great investment also!

Did someone say loud speaker design and cookbook?!

https://docs.google.com/file/d/0B_l73GVBBlIUNTc2YTc2YTktNTNmYi00YWNmLTlmY2ItZTU0MTRhMzdkYTAy/edit?pli=1

free read lol.

 

[wew lad 5,000+ posts]

good stuff, it's great to see some real calculation based on aerodynamics instead of guesstimation lol i guess those classes on aerodynamics and fluid dynamics are actually useful

wish more people would use references for books and whatnot like you have, sometimes i like to read up on topics in depth - even if ill personally never use it

 

[garychurch84 10+ year member]

Very good read!!

 

[Jeffdachef 5,000+ posts]

I've been actually working on sound quality part of my system now, manual T/A, soundstage, new mosconi 4 channel etc... Been thinking of redoing the sub stage and was wondering about the port area and if my current one could be reduced for better SQ and maybe tune a little bit lower too. Lol funny how Sound quality led to a question asked by a lot of SPL guys.

 

[tc300 10+ year member]

i remember back in the day soundstream had book FULL of box designs...... for there woofer of coarse. lol

 

[LosIsATool 5,000+ posts]

I've been actually working on sound quality part of my system now, manual T/A, soundstage, new mosconi 4 channel etc... Been thinking of redoing the sub stage and was wondering about the port area and if my current one could be reduced for better SQ and maybe tune a little bit lower too. Lol funny how Sound quality led to a question asked by a lot of SPL guys.

For me SPL got old. It became only about how much money you spent. SQ takes way more understanding and ability to apply what you learn.

 

[gckless 5,000+ posts]

For me SPL got old. It became only about how much money you spent. SQ takes way more understanding and ability to apply what you learn.

Not once you get into the real high numbers. Or not if you actually attempt to experiment and stay in one class and do what you can. This is an old argument that I probably shouldn't have replied to, but I think we can both agree you can be successful without spending a lot to almost the same degree in either SPL or SQ.

 

[LosIsATool 5,000+ posts]

Not once you get into the real high numbers. Or not if you actually attempt to experiment and stay in one class and do what you can. This is an old argument that I probably shouldn't have replied to, but I think we can both agree you can be successful without spending a lot to almost the same degree in either SPL or SQ.

You can if you do as you said but then daily enjoyment goes out the window.

You can nail SQ but not have much out put cheap.

You can nail SPL but not have much daily use cheap.

Depending on your idea of cheap

 

[keep_hope_alive Premium Member]

Poet area can be reduced if you have inner and outer flares. Radius determines area.

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