Quick bass reflex port question... - Page 2

infinia · 7th March 2009, 10:43 AM

Quote:

Originally posted by revans

Is it possible that I would be able to disregard a flare and just have 90 degree exit?

Yes, but flares always look cool.

Tip- Look at using Unibox program instead of WinISD to model them as well/

revans · 7th March 2009, 08:45 PM

Hey thanks for that suggestion infinia. I went and played around with Unibox and it seems a fair bit more in depth than WinISD.

I chucked in all the correct values and got this port speed graph which I've attached (although it wouldn't let me change the port length to the 9.2cm that I'm using).

It seems that air speed only exceeds bad levels at about 72Hz and below. Is this a problem? Would I perhaps want to put in a filter to block anything below 70Hz?

revans · 7th March 2009, 09:50 PM

What about flaring the internal end of the port? That would be better than no flare at all, correct?

infinia · 8th March 2009, 12:19 AM

Quote:

Originally posted by revans
It seems that air speed only exceeds bad levels at about 72Hz and below. Is this a problem? Would I perhaps want to put in a filter to block anything below 70Hz?

Yes.
HP filter would be advised if you plan on pushing SPL's and keeping lower distortion and/or even prevent damage.
Look at a sealed box for a 4" if using a subwoofer.

Quote:

Originally posted by revans
What about flaring the internal end of the port? That would be better than no flare at all, correct?

Yes
Unibox lets you model that as well.
Also check the box (button) for the port secondary resonance to see.

revans · 8th March 2009, 12:40 AM

OK thanks for that infinia. I checked port resonance btw, though I'm not sure what difference it made to the graphs.

Anyway though, just to summarise... will the speakers be fine with regard to port noise if I: 1) put in a high-pass filter around 70Hz; 2) flare the internal end of the port; 3) leave the other visible end of the port at a 90 degree exit?

infinia · 8th March 2009, 12:58 AM

Quote:

Originally posted by revans
OK thanks for that infinia. I checked port resonance btw, though I'm not sure what difference it made to the graphs.

Anyway though, just to summarise... will the speakers be fine with regard to port noise if I: 1) put in a high-pass filter around 70Hz; 2) flare the internal end of the port; 3) leave the other visible end of the port at a 90 degree exit?

Check the Xmax vs frequency chart at max power to decide where the filter cutoff should go.
I don't think you will have any problem with air turbulance.

revans · 8th March 2009, 03:24 AM

Wow... I looked at the "Cone Excursion vs. Frequency at 25W" [it's attached] and it seems a bit crazy. I'm guessing that according to that graph I should cut it off at about 175Hz... isn't that a little high? The Tang Bands should be able to handle at least down to 100Hz if not 80Hz, so what's up with that?

infinia · 8th March 2009, 05:09 AM

Your tunings way way off. Go back to WinISD and start with the nominal box Vb and Fb, then plug those back in Unibox these will be the lowest tuning you should use.
Now adjust Pin so the top of the graph peak just kisses the Xmax limit line. Looking the lowest point of the graph dip= fb and the area below it is were the port "unloads" the driver. Below that the graph will cross Xmax steeply.

revans · 8th March 2009, 05:14 AM

Thanks infinia. Just giving your directions a read-over I have no idea what you're talking about, but I'll have a look around WinISD and Unibox and see how I go and get back to you.

infinia · 8th March 2009, 05:36 AM

The first sentence is plain. Take what WinISD gives you and plug those numbers back in Unibox.

Second sentence say's start with 5W of power and move it up slowly untill the peak hits the line.
Now look at the graph and reread what I wrote,

8th March 2009, 05:09 AM	#18
infinia diyAudio Member Join Date: May 2005 Location: Californication	Your tunings way way off. Go back to WinISD and start with the nominal box Vb and Fb, then plug those back in Unibox these will be the lowest tuning you should use. Now adjust Pin so the top of the graph peak just kisses the Xmax limit line. Looking the lowest point of the graph dip= fb and the area below it is were the port "unloads" the driver. Below that the graph will cross Xmax steeply. __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

8th March 2009, 05:36 AM	#20
infinia diyAudio Member Join Date: May 2005 Location: Californication	The first sentence is plain. Take what WinISD gives you and plug those numbers back in Unibox. Second sentence say's start with 5W of power and move it up slowly untill the peak hits the line. Now look at the graph and reread what I wrote, __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

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7th March 2009, 09:50 PM	#13
revans diyAudio Member Join Date: Aug 2008	What about flaring the internal end of the port? That would be better than no flare at all, correct?

8th March 2009, 12:40 AM	#15
revans diyAudio Member Join Date: Aug 2008	OK thanks for that infinia. I checked port resonance btw, though I'm not sure what difference it made to the graphs. Anyway though, just to summarise... will the speakers be fine with regard to port noise if I: 1) put in a high-pass filter around 70Hz; 2) flare the internal end of the port; 3) leave the other visible end of the port at a 90 degree exit?

8th March 2009, 05:14 AM	#19
revans diyAudio Member Join Date: Aug 2008	Thanks infinia. Just giving your directions a read-over I have no idea what you're talking about, but I'll have a look around WinISD and Unibox and see how I go and get back to you.

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