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WinISD accurate predictor of port noise?


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sedate 
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Joined: July 03, 2004
Location: Colorado, United States
Posted: August 24, 2005 at 8:15 AM / IP Logged  
Heh guys:
So this ported enclosure I'm building is a wee-bit small... so here's the thing, I can only fit really small ports...
Now, according to WinISD, 4 x 1.25" round ports will give me a 'Vent Mach' of .11, whereas the program says anything under .16 is satisfactory for port noise purposes...
This is pretty much the only port solution I'll be able to construct and still have the ability to get this box into my trunk.
So yea... someone tell me little ports like this 'ill work like the numbers say eh?
Like uhh.. I've never seen such small ports but on the other hand I dunno anyone else that actually uses WinISD so..
Thanks guys.
"I'm finished!" - Daniel Plainview
haemphyst 
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Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: August 24, 2005 at 8:35 AM / IP Logged  
That's about a 50% buffer - should be good. I say "Do It".
.16 seems a bit low. Port noise (from all I recall) won't become a factor till around .25. Before you use that number as Gospel, let me talk with my EE friend at Harman. "I'll get to the bottom of this." LOL
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
stevdart 
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Posted: August 24, 2005 at 8:37 AM / IP Logged  

Double-check with some other calculators like this one.  Most often, when you're in a situation where one large port won't fit, a slotted opening is used instead.  That will allow you a larger opening with less port wall area.

This is the design formula for calculating port noise.  It's what WinISD uses as well as the calculator above that I linked you to.  It's more often user error than program error if a calculation comes out wrong.  Generally, as long as the air speed is less than 10% of Mach, it is acceptable as not having too much port noise.  RMS power should be used for the power input to figure it, and the WinISD graph should be changed from "peak" to "RMS" to get the reading (if you're using the newest version).  Change from meters to feet per second, or vise versa, whatever unit you're working with.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
sedate 
Silver - Posts: 1,173
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Joined: July 03, 2004
Location: Colorado, United States
Posted: August 24, 2005 at 8:40 AM / IP Logged  
Ahh hamfist, trust you to get back in less time than it takes me to leave for Home Depot.
You sir, are the man.
WinISD  accurate predictor of port noise? -- posted image.
"I'm finished!" - Daniel Plainview
sedate 
Silver - Posts: 1,173
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Joined: July 03, 2004
Location: Colorado, United States
Posted: August 24, 2005 at 8:57 AM / IP Logged  
*ARG*
stevdart, I don't like that calculator!
It tells me that I need a port that's like 8" in diameter to run that configuration ... that can't be right...?!.. I'd need a port length like 5 feet long.
.. I don't think I'm using it wrong... kinda self-explanatory and all....
What's the deal?
I just use WinISDbeta that I downloaded like a year ago.. how's the newest version stack up?
"I'm finished!" - Daniel Plainview
sedate 
Silver - Posts: 1,173
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Joined: July 03, 2004
Location: Colorado, United States
Posted: August 24, 2005 at 9:10 AM / IP Logged  
That calculator has got to be wrong stevdart...
Okay... strictly from experience..
A 13w6 in a 1.8cft box and a 3" port with a tune of 28hz produced exactly zero port noise. No chuffing, no whistling, just bass.
A 3" PVC pipe has an area of all of ... letssee.. 7 square inches... Now if I plug those numbers (using either the 12" or 15" driver button from that site) I get either a MINIMUM port area of 33 or 64 square inches.
That is absolutely not right.
?!
"I'm finished!" - Daniel Plainview
stevdart 
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Posted: August 24, 2005 at 9:29 AM / IP Logged  

Okay... strictly from experience..

A 13w6 in a 1.8cft box and a 3" port with a tune of 28hz produced exactly zero port noise. No chuffing, no whistling, just bass.

You've got to realize in your example here that your findings were strictly arbitrary.  No program or calculator will allow a 3" round port opening for a 13W6  at 28 Hz  tuning with nominal RMS power input.

See why it's good to check a few calculators before doing the build?

Why don't you post up info on what you're using, link to parameters, net air volume and desired tuning frequency.  Some of us can take a look at it.  I do comparisons with Unibox, WinISDPro (alpha), and a couple calculators....and I've never used any previous versions of WinISD so I couldn't compare them.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
sedate 
Silver - Posts: 1,173
Silver spacespace
Joined: July 03, 2004
Location: Colorado, United States
Posted: August 24, 2005 at 10:01 AM / IP Logged  
stevdart wrote:
You've got to realize in your example here that your findings were strictly arbitrary. No program or calculator will allow a 3" round port opening for a 13W6 at 28 Hz tuning with nominal RMS power input.
Huh?
WinISD's little "vents" tab doesn't seem to have a problem with it..? I designed the box (for the w6) in WinISD, got a great curve and actually a higher vent mach than I'm supposed to... anyway... okay okay "arbitary" findings.
WinISD  accurate predictor of port noise? -- posted image.
Now.... ya wanna know what'd I'm doing eh?
I'm building a 2.25 - 2.4 (final will depend on port volume) net internal vented enclosure for 2 12's....
these guys.
Here's the thing, I'm underrunning them a bit, about 250watts/sub, so I wanted to vent the thing and make the box a bit larger, to bring down the power handling and what not.
It looks to me like a 28 - 32hz tune for those subs produces the flattest curve... nice little 2db hump at 60hz or so... drops off a little more than i'd like under 40hz, but thats okay. I look at 30 - 80hz.
So this box in WinISD looks like 4 ports, each 1.25" in size, would do the trick...
The box is 30" wide, 14.5" tall, 17" deep on the bottom and 6" deep on the top with an 18" long hypotenuse. (Or whatever you call the slanted side).
"I'm finished!" - Daniel Plainview
stevdart 
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Posted: August 25, 2005 at 8:57 AM / IP Logged  

WinISD accurate predictor of port noise?

Yes, that checks out ok in another program, given the input power these speakers will receive.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
haemphyst 
Platinum - Posts: 5,053
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: August 26, 2005 at 12:29 AM / IP Logged  
OK... I just spoke with Charles, and boy was I WAAAAAYYYYY off! When they design a ported enclosure, they aim for Mach .05! When they hit anything even much above that, even in a flared port (like .07M - that's a quoted number) the air stream is completely turbulent - to quote Charles again - CHUFF CITY!
So, here's the deal... "I don't know what I am talking about, when it comes to vented enclosures." Anyway. Just needed to get that out there! WinISD  accurate predictor of port noise? -- posted image.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
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