Port noise problem

ernieretief · 31st July 2003, 03:25 PM

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

Guss · 1st August 2003, 12:32 AM

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

JOE DIRT® · 1st August 2003, 12:34 AM

I did post a good program on another thread for it...nobody seemed interested

Guss · 1st August 2003, 01:52 AM

Hey joe, Im interested, wich thread ?

ernieretief · 1st August 2003, 07:01 AM

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

andy_c · 1st August 2003, 07:17 AM

Okay, no jokes about a "port noise complaint" allowed

.
(Ducking...)

rossco · 1st August 2003, 11:54 AM

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

Superassbass · 3rd August 2003, 08:52 AM

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/

kelticwizard · 3rd August 2003, 02:04 PM

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.

Eul · 4th August 2003, 08:11 PM

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!

31st July 2003, 03:25 PM	#1
ernieretief diyAudio Member Join Date: Jul 2003 Location: Cape Town	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

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

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?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

1st August 2003, 12:34 AM	#3
JOE DIRT® diyAudio Member Join Date: Apr 2003 Location: Brantford, ON	I did post a good program on another thread for it...nobody seemed interested

1st August 2003, 01:52 AM	#4
Guss diyAudio Member Join Date: Jun 2003 Location: Montreal	Hey joe, Im interested, wich thread ?

1st August 2003, 07:01 AM	#5
ernieretief 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

1st August 2003, 07:17 AM	#6
andy_c Banned Join Date: Apr 2003	Okay, no jokes about a "port noise complaint" allowed . (Ducking...)

1st August 2003, 11:54 AM	#7
rossco 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

4th August 2003, 08:11 PM	#10
Eul 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!

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)