Clearance: down-firing port to spikes?

ro9397 · 05:39 PM

On my sub enclosures the down-firing port base is flush with the enclosure, not recessed. What is minimum safe clearance from the port/enclosure base to the tip of spikes for thick carpet and pad?

10" driver faces the wall with about 3/4" clearance. If I compute correctly, and if it makes a difference, in effect the port is open about 180-degrees and closed off on the wall side.

1.1cf internal, 10" super duty 16 lb net weight, 600Wrms power handling, port about 2" x 16" moving (apparently) a lot of air, 20 Hz clean in current state of tune (four employed total, one in reverse polarity).

TIA!

infinia · 15th June 2010, 06:56 PM

Port air velocity with 2"x16" port?
I've read where one port radius is all the clearance that is required. But your port area seems to be too small for such low tuning> unless low SPLs due to Xmax limitations. Can you show us your box calculations/tuning to acheive 20Hz? What power is Xmax reached?

badman · 15th June 2010, 07:10 PM

You want to have a significant increase in area so as to have the gap between box and floor not act as a vent extension. I'd go 3" in your case.

ro9397 · 11:00 PM

Quote:

Originally Posted by infinia

Port air velocity with 2"x16" port?
I've read where one port radius is all the clearance that is required. But your port area seems to be too small for such low tuning> unless low SPLs due to Xmax limitations. Can you show us your box calculations/tuning to acheive 20Hz? What power is Xmax reached?

Sorry, a real speaker designer licensed me to build this. I double checked, and he specified to allow "60ci" for port displacement in the box, and it looks like it's closer to 2" x 20" in length. It's also tuned for reverse room gain, meaning 3 dB/octave roll off below 100 Hz. So I suppose its about -7 dB @ 20 Hz relative to 100 Hz (or -10 dB @ 20 Hz if that's the -3 dB point, which may well be the case). Xmax: 12.3mm

I must admit I'm surprised how variable are the replies.

infinia · 15th June 2010, 11:37 PM

Quote:

Originally Posted by ro9397

Sorry, a real speaker designer licensed me to build this.
I must admit I'm surprised how variable are the replies.

Well... speaker design is not an exact science. But maybe a real designer would disagree with that. LOL

If you have supersonic port velocity I would allow much more distance to the floor ...FWIW If'n I was was you I would get a second opinion about that port.

chris661 · 16th June 2010, 08:16 AM

I'd agree - that's a very small port, especially for the amount of excursion on offer.

Aucosticraft · 07:37 AM

How did Tannoy manage with Subwoofer of HTS-100 system? I am posting its pic. This system sounds very impressive at its cost.

I heard them lot of times at Cafe Coffee Day. Coffee tastes good with this.

15th June 2010, 05:34 PM	#1
ro9397 diyAudio Member Join Date: Jan 2007 Location: No. Utah	Clearance: down-firing port to spikes? On my sub enclosures the down-firing port base is flush with the enclosure, not recessed. What is minimum safe clearance from the port/enclosure base to the tip of spikes for thick carpet and pad? 10" driver faces the wall with about 3/4" clearance. If I compute correctly, and if it makes a difference, in effect the port is open about 180-degrees and closed off on the wall side. 1.1cf internal, 10" super duty 16 lb net weight, 600Wrms power handling, port about 2" x 16" moving (apparently) a lot of air, 20 Hz clean in current state of tune (four employed total, one in reverse polarity). TIA! __________________ James "Television is the poor man's whiskey." Russel Baker Last edited by ro9397; 15th June 2010 at 05:39 PM.

15th June 2010, 06:56 PM	#2
infinia diyAudio Member Join Date: May 2005 Location: Californication	Port air velocity with 2"x16" port? I've read where one port radius is all the clearance that is required. But your port area seems to be too small for such low tuning> unless low SPLs due to Xmax limitations. Can you show us your box calculations/tuning to acheive 20Hz? What power is Xmax reached? __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

15th June 2010, 07:10 PM	#3
badman diyAudio Member Join Date: Sep 2003 Location: Sunny Tustin, SoCal	You want to have a significant increase in area so as to have the gap between box and floor not act as a vent extension. I'd go 3" in your case. __________________ I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!

16th June 2010, 08:16 AM	#6
chris661 diyAudio Member Join Date: Feb 2008 Location: Sheffield Blog Entries: 8	I'd agree - that's a very small port, especially for the amount of excursion on offer. __________________ "Throwing parts at a failure is like throwing sponges at a rainstorm." - Enzo My setup: http://www.diyaudio.com/forums/multi...tang-band.html

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