Port noise problem - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

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 31st July 2003, 03:25 PM   #1
diyAudio Member
 
Join Date: Jul 2003
Location: Cape Town
Question Port noise problem

Hi,
I have just built my first active sub and it sound good. I'm about to fine tune the sound, but I don't understand some stuff.

Background: I'm using it for Home Theater and music in my Living room. I'm using a 15" 300W RMS driver (quoted anyway...?) with a 150Watt RMS amp. The box was supposed to be 380 liters in volume, but that was too much for me, so I changed it to 131 liters. What difference will this make?

Firstly, when designing the port length, you have to give a tuning frequency. What frequency is this, and what is best to use?
I used this app to calculate my port length, and it’s still making a noise when I play it at high volume.
http://www.linearteam.dk/default.asp...ventcalculator
I used these values:

Vb = 131 liters
Tuning frequency: 23Hz
1 vent
Vent diameter: 10.8 cm
Acoustic power of 0.72

What did I do wrong? What is the port suppose to do to the sound, and how do you know you've got the right setting?

One last question. Does anyone have a link where I can download sound files that play different low frequencies so I can test my Sub with that?

Thanks
Ernie
  Reply With Quote
Old 1st August 2003, 12:32 AM   #2
Guss is offline Guss  Canada
diyAudio Member
 
Guss's Avatar
 
Join Date: Jun 2003
Location: Montreal
Quote:
One last question. Does anyone have a link where I can download sound files that play different low frequencies so I can test my Sub with that?
Kazaa is full of em, search for subwoofer tests. If you dont have kazaa, try this one.TEST .

have fun with your sub
  Reply With Quote
Old 1st August 2003, 12:34 AM   #3
diyAudio Member
 
JOE DIRT®'s Avatar
 
Join Date: Apr 2003
Location: Brantford, ON
I did post a good program on another thread for it...nobody seemed interested
  Reply With Quote
Old 1st August 2003, 01:52 AM   #4
Guss is offline Guss  Canada
diyAudio Member
 
Guss's Avatar
 
Join Date: Jun 2003
Location: Montreal
Hey joe, Im interested, wich thread ?
  Reply With Quote
Old 1st August 2003, 07:01 AM   #5
diyAudio Member
 
Join Date: Jul 2003
Location: Cape Town
Thanks for info on files, but can anyone answer my questions about the tuning frequency and other related questions?
What can I do to reduce the port noise at high volumes?
Thanks
  Reply With Quote
Old 1st August 2003, 07:17 AM   #6
andy_c is offline andy_c  United States
Banned
 
Join Date: Apr 2003
Okay, no jokes about a "port noise complaint" allowed .
(Ducking...)
  Reply With Quote
Old 1st August 2003, 11:54 AM   #7
rossco is offline rossco  United Kingdom
diyAudio Member
 
Join Date: Jul 2003
Location: UK
Hi

This is my second post here. I'm a pro cab builder specialising in the unusual.

I've taken a look at the limited info you supplied regarding the driver and the port. The problem is the air speed in the port is reaching around 21.5m/s which is producing the noise you hear.

The solution is to fit a second port and make sure both ports are 103mm long and 108mm in diameter. The second port can be fitted anywhere, even the back of the sub it makes no difference.

Hope that helps

Rossco
  Reply With Quote
Old 3rd August 2003, 08:52 AM   #8
diyAudio Member
 
Superassbass's Avatar
 
Join Date: Jul 2003
Location: Sunny Australia
Default Re: Port noise problem

Quote:
Originally posted by ernieretief


One last question. Does anyone have a link where I can download sound files that play different low frequencies so I can test my Sub with that?

Thanks
Ernie
Not sure where these came from but here anyway:

http://www.users.bigpond.net.au/wirelinx/frequency/
  Reply With Quote
Old 3rd August 2003, 02:04 PM   #9
Wizard of Kelts
diyAudio Moderator
 
Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
Quote:
Originally posted by ernieretief
Thanks for info on files, but can anyone answer my questions about the tuning frequency and other related questions?
What can I do to reduce the port noise at high volumes?
Thanks
There seems to be agreement that flared tubes are the equivalent of a tube of twice the crosssection.

For a 4" tube, try www.partsexpress.com part# 268-352.

Those flared tubes are available other places, as well.
__________________
"A friend will help you move. A really good friend will help you move a body."
-Anonymous
  Reply With Quote
Old 4th August 2003, 08:11 PM   #10
Eul is offline Eul  Netherlands
diyAudio Member
 
Join Date: Jul 2003
Location: Netherlands
The tuning frequency is the frequency where the port will produce the most sound. This frequency is not something you can choose how you would like it but it has to fit with the rest of the speaker. A good tuning frequency is where the frequency-response curve keeps in a straight line and in the end falls off strong (24dB/O is common for a basreflex), not a bump in the curve and a long slowly lowering curve is not the best also.

A flared tube helps a bit to reduce the port noise but I strongly doubt that it is equivalent of a tube of twice the cross-section. A flared port mostly helps to reduce the port non-linearity. this is the chance of tuning frequency to a higher frequency. This happens because the turbulence at the ends of the port increases with the airspeed, this will make effective part of the port shorter, that results in a higher tuning frequency. The flared port reduces the turbulence and its noise a bit but a bigger port is most of the time the best solution, or making more ports.

I would do what Rossco suggested.

Good luck getting it better!
  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
Port noise CARTRulz Subwoofers 6 13th June 2006 12:27 PM
port noise minimise Artmaster Subwoofers 26 1st December 2004 06:08 AM
port turbulent jet noise. any advice? Artmaster Multi-Way 32 6th October 2004 06:11 AM
Port Noise, Wind Speed................. OMNIFEX Multi-Way 20 13th April 2003 04:27 PM
Port Noise Redeye Multi-Way 19 11th February 2003 09:47 PM


New To Site? Need Help?

All times are GMT. The time now is 03:20 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