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Multi-Way Conventional loudspeakers with crossovers

Port Sizes and Effects???
Port Sizes and Effects???
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Old 29th August 2002, 07:32 AM   #11
Xyberz is offline Xyberz
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So how do you tune the ports? I've seen people just use PVC pipe in thier speaker systems. Also is there any easier way or some example on what size and length should a port be for a speaker? Like a 12" Sub should take a 3" dia x 6" long port. Something like that. Also is the formula different for different type of speakers? Or can I just use the same basic formula and just change a few measurements around?
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Old 29th August 2002, 10:16 AM   #12
ppl is offline ppl  United States
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The lenght as well as the port Area are tuned to the frequency you need the Enclosure to resonate at. this resonent frequency is determond by the Thiele small parameters of the Woofer you want to use. Computor Programs are available that allow you to play with Box volume and Vent area and lenght and get a Frequency response graph of the complete system a free program is http://www.geocities.com/sdecaudio/boxport/ Also other for sale programs that i have used and work good are LEAP sorry can't remember the url on that..
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Old 29th August 2002, 12:51 PM   #13
FrankDIY is offline FrankDIY  Canada
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Thumbs down small port

I always try to put the largest port diameter since this reduce the port noise. It is very easy to ruin a design with a small port even if winisd gives you a good feeling. I will always remember another bad experience with a 10'' subwoofer and a 1.5'' port!!
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Old 29th August 2002, 04:15 PM   #14
kelticwizard is offline kelticwizard  United States
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Port Sizes and Effects???
Just thought that I would add that flared ports give the port noise of a straight port of twice it's cross-sectional area. The larger the cross-sectional area, the less the noise.

So a 2" flared port has the noise of a 3" straight port, but the shorter length of a 2" straight port.

Other members have said that, when using a flared port, add one inch extra to the straight port length to make up for the flare. So a 10" flared port will tune a box the same as a 9" straight port of equal diameter.

Programs will calculate the length of multiple straight ports of any crossection. WinISD is one of the easiest.
http://www.linearteam.dk/
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Old 29th August 2002, 04:16 PM   #15
electricashman is offline electricashman
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Default Re: Re: Port Sizes and Effects???

Quote:
Originally posted by electricashman


So if you go with a "large port diamater" around 1/2 the diamater of your speaker, you will need it longer as mentioned. The increased port width will reduce port noise, or reduce the sound of air passing through the port.

LV=(1.463*10^7*R^2)/(Fb^2*Vb)

Edit: Lv is the port length needed in inches
R= port radius in Inches
Fb = port reequency like 30hzish
Fb= tuned resonance of box.

Fb=0.42*Fs/(Qts^(.9))

Fs and Qts are the Thiele/Small paramaters you will need....
Sorry guys I left out the last correction conatant term in the LV equation:
-(1.46*R)

Claus: Im trying to convert your multi port equation to inches and cuft,

I got a new constant of 41384.5.

(cm^2)/(in^2) =.062in^2
(cuft)/(leters)= 28.32 cuft
1cm>in= .39in

.062*28.32=1.755

so 1.755* 23562.5=41384.5

and the new constant k should change to inches

.39*.732=.285

so .285=k

Is that correct?

thanks guys...
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Old 29th August 2002, 07:34 PM   #16
Claus is offline Claus  Denmark
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Hi electricashman

Make it easy, do like the rest of world. Use millimeters. What is 250 million people compare to 5 billions.


Claus
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Old 29th August 2002, 08:51 PM   #17
Xyberz is offline Xyberz
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Thanks for all the help! You guys are really helpful. I'm going to use your suggestions, and if I should have any problems, I'll post up a reply. Until then, thanks again for all the incredible help.
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Old 29th August 2002, 08:53 PM   #18
electricashman is offline electricashman
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Quote:
Originally posted by Claus
Hi electricashman

Make it easy, do like the rest of world. Use millimeters. What is 250 million people compare to 5 billions.


Claus
Yea Ill never figure out us americans,

We use Inches because we hate fractions?
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Old 29th August 2002, 11:54 PM   #19
pinkmouse is offline pinkmouse  Europe
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Port Sizes and Effects???
I was brought up when England was changing to metric, so I can use either system, but I have to say, doing the maths in metric is a hell of a lot easier!!
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Old 30th August 2002, 01:28 AM   #20
Variac is offline Variac  Costa Rica
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Port Sizes and Effects???
The rule of thumb of making the port an inch longer if it is flared seems a little too easy, but is probably close. I was forced to use metric when doing a drawing for the DIY turntable thread. Boy is that EASY. I couldn't believe how much less hassle it was.
I'm an architect and spend all day worrying about fractions and adding them up!
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