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Old 2nd March 2004, 09:05 PM   #1
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Location: NH, USA
Default rear port vs front port

I was going to use a rectangular port in the back of the speaker at the bottom. Instead of a round port in the front about 12 cm away from the bottom. They will have the same cross-section area and length. What are the draw backs? I can make a rectular port in the same place in the front 12 cm away from the ground if it sounds better or near the ground or anywhere.

This is the port I want to modify
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Old 2nd March 2004, 09:10 PM   #2
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I like this question. Some people hate front ports yet it shouldn't really matter. I suppose there is potential to have mid frequencies audible through a front port but I've not had that problem. I'm also understanding that having a LF source near the floor will help so a low port is good.
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Old 2nd March 2004, 09:26 PM   #3
sreten is offline sreten  United Kingdom
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A badly positioned / dimensioned port will exhibit pipe mode
resonances that simply shouldn't be there, minimal or badly
placed internal damping can contribute to the effect.

A bad port is better facing backwards.

A ports position has no influence at its bass resonant frequency,
except for a speaker designed to be up against a wall, where
postioning in the base of the speaker or the front is needed to
prevent port blocking.

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Old 2nd March 2004, 09:28 PM   #4
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children's LEGO's will rarely find their way into a rear port
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Old 2nd March 2004, 09:36 PM   #5
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Originally posted by jackinnj
children's LEGO's will rarely find their way into a rear port
But mice will

What about reinforcement from the floor?
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Old 2nd March 2004, 10:03 PM   #6
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Mice! bah thats funny, reminds me of a story I read on the web about a mouse who had camped out inside sum1 PC, made a nice little home for itself. All the wires mouse arranged to make a nest thing, I think it also got other stuff in there too to make it more coasy problem is the mouse got stuck and died Bad smell.
What the hell are you screamin' for? Every five minutes there's a bomb or somethin'! I'm leavin! bzzzz! Now with website! under construction.
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Old 2nd March 2004, 10:17 PM   #7
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I had some KEF R104/3 once. These are coupled cavity loading for the twin bass units, so the vent on the front is tuned to around 65Hz. This means that the vent was around 4" diameter and only 2 or 3" deep. I found that my cat would crawl inside and lay on the cone of the internal upward firing bass driver!!
That is until I realised that she was doing this. Then I waited for the moment I found her in there, and then I turned on some music.
She never went in again. I should say that I did not play the music loud. I would never be that cruel. Just loud enough to surprise her.


p.s. on a technical note...rear firing vents, depending on the tuning frequency will have a slightly different response than a front firing vent because of the added delay, but this won't make a huge difference in practice. It will however couple very differently into the room resonances and this can make a significant difference to the in-room response.
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Old 2nd March 2004, 10:17 PM   #8
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the mouse got stuck and died
I think I had to fix that PC
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Old 2nd March 2004, 10:22 PM   #9
Svante is offline Svante  Sweden
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I have been trying to simulate pipe resonances, but have had little success. Anyone tried this, or is there any software that does it? I'd like to learn how.
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Old 2nd March 2004, 10:47 PM   #10
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Default horns???

I have a similar question (please don't accuse of stealing the thread), but I'm curious what the difference is when the mouth is on the front or back of horns. For example the Fostex recommended enclosure for the FE103 has a mouth in front, but the Buschhorn MK2 and Ed Schilling's horn have them in the rear. Wouldn't the output from the front horns be out of phase from the driver? It seems like the rear is the logical choice for these type of designs. I could be completely wrong as my knowledge of acoustics is limited.
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