Port Placement

[rockgardenlove]

Hi,
I'm building the Dayton II cabinets from speakerbuilder:
The Dayton II Project
I was wondering about placing the ports. I was thinking about placing the port directly behind the tweeter as I don't think the tweeter radiates backwards.
These are my tweeters:
DISCONTINUED Dayton DC28FS-8 1-1/8" Silk Dome Shielded Tweet | Parts-Express.com

Or should I place them halfway up the middle of the enclosure? Thoughts?


thanks!

[Thawach]

will be ok if u place it away from the woofer

[toprepairman]

Best place for a port is somewhere along the coast.
Ports have no place in a HiFi speaker.

IMHO, of course.......

[Helmuth]

Originally Posted by Thawach

will be ok if u place it away from the woofer

This is a wrong advise!


A bass reflex port functions the best if it has a good coupling with the rear radiation of the woofer cone. The port puts a acoustical load to the driver at his resonance point(BR-tuning point). So it can reproduce about a octave lower as in a closed setup.

Also it is wrong to have damping wool between the woofer cone and BR port. It will influence the function of the BR tuning the wrong way.

Placement on the back behind the woofer is good. It will influence the placement of your loudspeaker from the wall. Because the wall or corner can give 3-9dB loudness increase. The same when the port is placed near the floor it will also increase the level of the output of the BR-port.

You can play with this effect depending on the port gain of your design. And how much sub bas you prefer.


When you do not want to have increase of the level of the BR-port. Place it on the frontbaffle atleast 30cm( 1 feet ) above the floor.

[Helmuth]

Here the response of your woofer without BR-PORT LOAD. Impedance peak at 38Hz due loss of acoustical load of your cone due its diameter and maximum travel distance.
The peak is resonance of your woofer, the amplifier puts in power and the woofer can not radiate it to the air. So the woofer is like a swing it gets every time a new push on the right point. And then creating a electromotive force that we see back in the apparently resistance known as impedance. As shown in the peak at 38Hz.



And here in your enclosure with BR-port you see two impedance peaks in the middle of those peaks the port puts on a load on your driver 38Hz so were normally the -3dB point would be the box radiates this frequency on level through the BR-pipe.

[Thawach]

This is a wrong advise!

Helmut what's wrong?, i meant the port is place that's like the pic.

[Thawach]

and see this pic from the book. can place it everywhere if i want. i don't think. it will wrong.

[sreten]

Hi,

On the back somewhere around behind the tweeter will be fine. FWIW
often the best place for cored inductors is directly behind the woofer.

rgds, sreten.

[Helmuth]

@ Thawach,

As I explained earlier for a good functioning port it is important to have a good coupling with the woofer.

You can place the port any where you like, the loudspeaker will always make sound. When you want the optimal result place it near the woofer.

[sreten]

Hi, Its a small box, the port will always be near the woofer, rgds, sreten.

Typical box plans : http://www.zaphaudio.com/SR71.pdf