Port Placement

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.
 
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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.

[IMGDEAD]http://www.speakerbuilder.net/web_files/Projects/D2/wooferts.gif[/IMGDEAD]

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.

[IMGDEAD]http://www.speakerbuilder.net/web_files/Projects/D2/inboxz.gif[/IMGDEAD]
 
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Thawach

Member
2007-12-13 9:48 pm
This is a wrong advise!

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

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Thawach

Member
2007-12-13 9:48 pm
@ 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.


Helmuth i think that why u did not understand my english in thai version. the last post of sreten. the port is away from the woofer about 2-3 inch on pdf file. u meant that the port away about 2-3 km from the woofer?:confused:
 

Scott L

Member
Paid Member
2008-12-27 12:32 pm
Knoxville, TN
The better choice for placement is directly behind the tweeter. You'll want to
place sound absorbent material on the back of the cabinet wall directly behind the woofer. Ports get a baad raap because they are often too small, and placed incorrectly. The function of a port id the load the woofer at a certain frequency, but NOT allow mid range information to escape from same said port. In a little speaker box like that, it's best located on the back. If it was a larger box: a dedicated woofer/ or sub, then the best location would be on the front panel.
 

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I always thought woofer placement and port placement on say....the front of the baffle should be odd multiples.......The thinking is that even multiples makes for reinforcement/stacking of mode points within the enclosure.
Not sure how to say it.........

__________________________________________________Rick.............
 

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Scott L

Member
Paid Member
2008-12-27 12:32 pm
Knoxville, TN
not sure if I can edit, but I corrected this

The better choice for placement is directly behind the tweeter. You'll want to
place sound absorbent material on the back of the cabinet wall directly behind the woofer. Ports get a baad raap because they are often too small, and placed incorrectly. The function of a port is to the load the woofer at a certain frequency, but NOT allow mid range information to escape from same said port. In a little speaker box like that, it's best located on the back. If it was a larger box: a dedicated woofer/ or sub, then the best location would be on the front panel.
 
Ok, after getting a port education in a different thread, I've decided to port my Zaph Audio ZA-SR71 kit build. (The complete kit shows "out of stock" at Madisound because their enclosures don't have the port hole.)

Everything I've read says that one wants to stay clear of the woofer, but exact placement can vary by a small fraction of resonant wavelength. Yet Zaph's port placement is so close to the top of the speaker enclosure that one can't place a full thickness of acoustic foam between the port and the top. Move the hole down 1/2", not even to directly behind the tweeter, and there's room for 1" acoustic foam.

Enclosure drawing with baffle layout

By training I try to be very sensitive to the slightest anomaly. That is for example how impossible-to-find bugs get discovered in computer programs. Here, it disturbs me that, without explanation, Zaph notes that the port is too close to the top for full insulation, but he doesn't move it down. I can't find any supporting explanation that a half inch would matter.

Any ideas?
 
By training I try to be very sensitive to the slightest anomaly. That is for example how impossible-to-find bugs get discovered in computer programs. Here, it disturbs me that, without explanation, Zaph notes that the port is too close to the top for full insulation, but he doesn't move it down. I can't find any supporting explanation that a half inch would matter.

Any ideas?
The port is close to the top wall of the cabinet, which lowers tuning slightly compared to the same port a half inch further down.

Since the port is flared, the proximity difference would make less difference than it would with a straight tube port.

At any rate, moving the port down a half inch would probably raise the tuning by less than 1Hz, not a big deal.

The type and quantity of fill would have more affect on Fb than moving the port 1/2".

That said, 1" fill compressed a bit by the port flares won't make a bit of difference, as long as a bit of fill by the flare is removed to keep the flare clear of fill.