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How big is too big for ports?
How big is too big for ports?
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Old 18th January 2019, 05:13 PM   #1
The Lord Flashheart is offline The Lord Flashheart  United Kingdom
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Default How big is too big for ports?

Assuming I can fit the port in the box, is there such a thing as too much port area?

Playing with WinISD I can see the port air velocity going down ( a good thing ), the port length going up ( a neutral thing if box size is calculated properly and size isn't an issue) and port resonance frequency going down; which I don't know about.

Assuming I high pass at 20Hz and low pass at 80Hz, would a port resonance frequency of around 240-250Hz have any strange acoustic effects?
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Old 18th January 2019, 08:10 PM   #2
trojantrow is offline trojantrow  United Kingdom
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Well as you know I have my own questions at the moment but from what I have read I think the following

There are 2 issues

1 port air velocity and
2. Resonant frequency

When you increase the port diameter the air velocity goes down (good) but the 1st resonance frequency also goes down (bad) so itís a trade off.

Apparently if you are setting a low pass filter of 80hz. Itís recommended by many that you try to keep your 1st port resonance at at least 1 octave above you high pass filter. In your case that would be 160hz. So your good to go.

Basically, what happens is, the driver plays music which exites the resonant frequency of the port. If the resonant frequency was in the range of your sub or close to it e.g 60 to 140hz or so, then it would mess drastically with your frequency response. And wouldnít blend very well with you let mains.

As you know Iím no expert but Iím trying to share the research I have read lately because no one else seems to be replying to our threads at the moment.
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Old 18th January 2019, 08:23 PM   #3
chris661 is offline chris661  United Kingdom
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^ What he said.
Worth checking in Hornresp to see where the resonances come out.

Chris
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Old 18th January 2019, 08:29 PM   #4
trojantrow is offline trojantrow  United Kingdom
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Nice to know I took it all in lol.
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Old 23rd January 2019, 06:45 PM   #5
Crashpc is offline Crashpc  Czech Republic
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I have good experience with 70-80cm ports. If you cut between 80-90hz, it's not much of an issue with some inner padding. Longer and without padding, it really creeps in, but even then, for some usage, the distortion and aggresiveness if the sound adds some interesting dynamics to it. There are bins working that way.
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Old 23rd January 2019, 07:00 PM   #6
The Lord Flashheart is offline The Lord Flashheart  United Kingdom
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Quote:
Originally Posted by trojantrow View Post
Well as you know I have my own questions at the moment but from what I have read I think the following

There are 2 issues

1 port air velocity and
2. Resonant frequency

When you increase the port diameter the air velocity goes down (good) but the 1st resonance frequency also goes down (bad) so itís a trade off.

Apparently if you are setting a low pass filter of 80hz. Itís recommended by many that you try to keep your 1st port resonance at at least 1 octave above you high pass filter. In your case that would be 160hz. So your good to go.

Basically, what happens is, the driver plays music which exites the resonant frequency of the port. If the resonant frequency was in the range of your sub or close to it e.g 60 to 140hz or so, then it would mess drastically with your frequency response. And wouldnít blend very well with you let mains.

As you know Iím no expert but Iím trying to share the research I have read lately because no one else seems to be replying to our threads at the moment.
Thanks buddy, kind of you to take the time.

I will be crosssing over at 80hz and with a port tuned to 30Hz, am looking at 112cm^2 port area and a length of around 53cm.

The resonances are several octatves higher and so my mind is at ease on that now too.

Maximum port velocity is under 30fps so all good on that front too I think.

I just hope having the port forward firing wonít prove to be a mistake.
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