type of port for vented box - Page 2 - diyAudio
Go Back   Home > Forums > Design & Build > Construction Tips

Construction Tips Construction techniques and tips

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 29th March 2011, 03:08 PM   #11
diyAudio Member
 
Join Date: Aug 2009
Location: Sacramento
Hello,

Post #3 by Arty is dead on. Yes it about physics. You measure and calculate T/S parameters. You calculate the dimensions of the box. You calculate the dimensions of the port. You revaluate your assumptions and recalculate.

Port noise is velocity noise.

For a given quantity of moving air divided by the cross sectional area of the port gives velocity or doing it the other way about, pick your maximum velocity that gives cross sectional area.

Flared ports are not required.

BTW if a flared port is used is it flared on both ends? There is turbulence at the end inside the box as well!

Like any other recipe bake until done.

DT
All just for fun!
  Reply With Quote
Old 29th March 2011, 05:48 PM   #12
diyAudio Member
 
Join Date: Feb 2011
Quote:
Originally Posted by PaleRider View Post
You`re wrong about flared ports Arty, this is plain simple physics, no mysteries involved.
Non-flared ports makes a geat deal of turbulence and turbulence not only restricts flow but it is the main reason for unwanted port-sounds too.

About unpredictable; the final lenght of a port should not be just based on calculations, it needs to be meashured (tonesweep+ohm-meter) and tuned by trained ears.

gcguy2169:

Telescopic ports are sold from several dealers, search and you will find!
Same results can be achieved with non flared ports.
Flared ports come in singe end flared and both ends flared versions.
Drawback is that flared ones are a bit more sensitiv to where they are placed at.
Even so, port velocity is calculated -at least by me- at the given smallest cross section. I think it is logical.
Flared ports on the otherhand can sometimes behave quite intresting, sometimes You need them shorter than expected, sometimes longer.
Straight ports are a bit more predictable.

Yes, final lenght is tuned by mesurements, but it is a pain to run into the limits of what You can fit into the box
not to mention the air contained in the port is not part of nett. box volume.
Flared ports are allso a tricky one on this too.

Flared ports can pick up wider band of in-box resonances than straight ones, and so on. (well not in any case, but thats just a nother unknown, un-simulated variable to complicate things even more)

Actualy both straight, single flared, double flared, "slot", bendt, mmm.. "sticking out of the box", and who know how many other variations are out there have advantage, and disadvantage. Hence i consider eatchone as a compromise. Since it is.

Since most are going after the simulation predicted ports, i would assume the more predictable solution has a slight advantage. At least You are not getting that mutch off of what the simulation predicts.

DualTriode:
ports flared on one end only will have turbulence and velocity noise on the straight end, it is usualy the one inside the box. It just has more room to decay.

I think best is to go what Your personal taste tells You.
There is no superior one. Just different advantage traded for a different drawback.
  Reply With Quote
Old 29th March 2011, 11:05 PM   #13
diyAudio Member
 
Join Date: Aug 2009
Location: Sacramento
Hello,
Just to straighten out a couple of things.
Noise due to air velocity in a duct (in our case a tuned port) varies ~ to the 6th power of the velocity. Put another way double the velocity the noise increases by near 16 db, note that is in the straight section of the duct not the inlet or outlet. Also note the duct (tuned port) length is a small multiple of the diameter. The duct is not long enough to provide laminar flow.
The short version of this is the flow will always be turbulent and minimizing the velocity is of primary importance for controlling noise. Flared inlets and outlets will provide little benefit.
DT
All just for fun!
  Reply With Quote
Old 30th March 2011, 03:07 AM   #14
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally Posted by DualTriode View Post
You measure and calculate T/S parameters.
Keep in mind that the T/S parameters you measure will give you a point on the T/S curves and what you get are dependent on the weather and your drive.

That is one of these reasons for Arty's need to cut & try (repeat till done).

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 30th March 2011, 03:59 AM   #15
diyAudio Member
 
picowallspeaker's Avatar
 
Join Date: Apr 2007
Quote:
Originally Posted by Arty View Post
Flanged end ports are told to be better, that is what i can not confirm.
I don't have much experience (in any box design), but the theory behind the duct tells that 'flared' is an improvement over 'flat' . It's the theory of fluid motion ,and air is a light fluid . The same flared ends can be seen inside an engine ,where oil has to be 'sucked' better ,and it's called the Venturi principle
(same but different for the airbrush ) .
  Reply With Quote
Old 30th March 2011, 06:44 PM   #16
diyAudio Member
 
Join Date: Feb 2011
i know about the venturi effect, but do consider that the noise is created at the scross section where its minimal. So even if You do flare both end of the ports, the part between them is plain simply a small cross ection, and do to venturi principle the air will be faster there. that makes the noise.
So actualy the goal- as pointed out a few times- is to minimise the velocity, since it is in direct relation to the noise lvl.

That calls for a large crossectional area.
That is, if the port is not a stright pipe, the size of the smallest crossectional area will be the critical bottleneck.
Allso, do noitce, while fulids can not be compressed, air can be, an it acts like a spring.
So the engine oil is not a good example.
  Reply With Quote
Old 30th March 2011, 06:59 PM   #17
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Re the flared ports, you can throw all the theory at it you want, but in a real world experiment published in Speaker Builder/audioXpress, the gains in reduction of port noise with a flared pipe were dramatic. And to be most effective flared and terminated identically inside & out.

I approach it quite differently, using long, very high ratio, high R slot vents, purposely pushing the vents into compression. In practise it works REALLY well.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 30th March 2011, 09:03 PM   #18
diyAudio Member
 
Join Date: Feb 2011
hard to argue with that, for sure.
/but do notice i did mention reduced noise, and my point was simply: same can be achieved with a non flared one. Its godzilla rule. Bigger is better./
  Reply With Quote
Old 30th March 2011, 10:02 PM   #19
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally Posted by Arty View Post
Bigger is better
Properly attributed to the late Terry Cain.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 19th February 2012, 09:43 AM   #20
diyAudio Member
 
Join Date: Feb 2012
Default Its all about compromise

If you can keep port one diameter away from anything else... But not essential... I had to install 2 ports in the side of the box... And the only option was to fit them 2 inch seperation... Apsolutely has not compromised the sound what so ever...

Lots of myths and old wives tails in the car audio world... What is critical is vb and port dimensions and solid box build... If you get those facts right... Youll get enough bass to keep you happy until you cant drive anymore...And once you have a great box... You can put almost any sub brand into it providing its the same size sub, although 10's will go into a box made for 12's and visa versa, with a ring adapter .. But not 15's, they generally require a larger vb

Changing a sub brand or line will change the shape of the frequency response
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
In Bass reflex box (vented)-If I make smaller box than what consequences will I have? eliaselias_0 Multi-Way 6 3rd January 2011 03:49 PM
L-shaped port for vented design runethechamp Multi-Way 3 27th May 2009 05:11 AM
Flex hose as port in vented cabinet ? Jan Dupont Subwoofers 19 27th March 2007 03:53 PM
Can I mod an old labriynth box to be a vented box? MikeHunt79 Subwoofers 7 23rd May 2006 06:44 PM
Vented Enclosures - What type is this? nrgy Multi-Way 8 29th March 2004 08:21 AM


New To Site? Need Help?

All times are GMT. The time now is 04:27 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2