Subwoofer with external port - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th February 2008, 03:03 AM   #1
Newbomb is offline Newbomb  United States
diyAudio Member
 
Join Date: Feb 2008
Default Subwoofer with external port

I am considering a sub (Dayton RSS265hf) with a large enclosure (~60 l+). The layout is such that I can - and may need to - have the vents completely external. Has anyone ran into issues with a design such as this?

Outside of not accounting for the vent volume on the enclosure size, is there anything else I should consider?

Thanks,

Todd
  Reply With Quote
Old 19th February 2008, 04:15 AM   #2
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
60+ L large?! That's a bookshelf size speaker around here! Anyway, low frequencies are way larger than 60 L, so having an external vent poses no problems and with such a small vented cab don't forget to account for the volume displaced by the driver and any bracing.

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 19th February 2008, 10:23 PM   #3
Thawach is offline Thawach  Thailand
diyAudio Member
 
Thawach's Avatar
 
Join Date: Dec 2007
Default Re: Subwoofer with external port

Quote:
Originally posted by Newbomb
vents completely external
hi

why don't i understand about these words.? is it the original vent box? if it's larger than 60 l. i think that it's not good.


bye



  Reply With Quote
Old 19th February 2008, 10:45 PM   #4
Newbomb is offline Newbomb  United States
diyAudio Member
 
Join Date: Feb 2008
Default Re: Re: Subwoofer with external port

Quote:
Originally posted by Thawach


hi

why don't i understand about these words.? is it the original vent box? if it's larger than 60 l. i think that it's not good.


bye




No. This is just a custom enclosure - I haven't decided on the size. It could be as large as 100+ liters. It is not worth necessarily explaining why, but the ports (2 of them) will not be _inside_ the enclosure. They will be completely (or perhaps mostly) outside of the enclosure.

I would imagine this is somewhat common in the event that aesthetics are not of prime concern. For example a sub built into a wall (or crawlspace) that is vented externally. For the vent size I am looking at, they are nearly 1 meter long so they would probably not fit inside the box anyway.

Just looking for any gotcha's.

Todd
  Reply With Quote
Old 20th February 2008, 05:04 AM   #5
pkm is offline pkm  New Zealand
diyAudio Member
 
Join Date: Feb 2008
Default Re: Re: Re: Subwoofer with external port

Quote:
Originally posted by Newbomb



No. This is just a custom enclosure - I haven't decided on the size. It could be as large as 100+ liters. It is not worth necessarily explaining why, but the ports (2 of them) will not be _inside_ the enclosure. They will be completely (or perhaps mostly) outside of the enclosure.

I would imagine this is somewhat common in the event that aesthetics are not of prime concern. For example a sub built into a wall (or crawlspace) that is vented externally. For the vent size I am looking at, they are nearly 1 meter long so they would probably not fit inside the box anyway.

Just looking for any gotcha's.

Todd
This is where Passive radiators come into play - tiny boxes where the ports end up 1metre + long.

Also consider vent air speed and power amplifier used.

Note that youl get a nice organ pipe effect at some low midrange frequency,so youl want to avoid that. Compare the Peerless XLS with the old adire shiva. Shiva demands large box,but no PR required.
  Reply With Quote
Old 20th February 2008, 05:17 AM   #6
Newbomb is offline Newbomb  United States
diyAudio Member
 
Join Date: Feb 2008
Default Re: Re: Re: Re: Subwoofer with external port

Quote:
Originally posted by pkm

This is where Passive radiators come into play - tiny boxes where the ports end up 1metre + long.

Also consider vent air speed and power amplifier used.

Note that youl get a nice organ pipe effect at some low midrange frequency,so youl want to avoid that. Compare the Peerless XLS with the old adire shiva. Shiva demands large box,but no PR required.

I am not sure why you consider a 100 l box tiny? The reason for the external ports is to put them in a specific location, not because they won't fit inside the box. I am actually looking to have the ports (two of them) at a distance of 6 feet from each other. I will thereby select the diameter such that they will be long enough. I should have plenty of leeway, but they will probably end up about 0.75 m each.

I am not aware of 'organ effects' at low midrange frequencies - although I suspect the vent could generate harmonics. Please explain. I will filter at 80 - 100 Hz.

Todd
  Reply With Quote
Old 20th February 2008, 06:41 AM   #7
diyAudio Member
 
Join Date: Dec 2007
There is nothing wrong with external ports
  Reply With Quote
Old 20th February 2008, 06:57 AM   #8
pkm is offline pkm  New Zealand
diyAudio Member
 
Join Date: Feb 2008
Default Re: Re: Re: Re: Re: Subwoofer with external port

Quote:
Originally posted by Newbomb



I am not sure why you consider a 100 l box tiny? The reason for the external ports is to put them in a specific location, not because they won't fit inside the box. I am actually looking to have the ports (two of them) at a distance of 6 feet from each other. I will thereby select the diameter such that they will be long enough. I should have plenty of leeway, but they will probably end up about 0.75 m each.

I am not aware of 'organ effects' at low midrange frequencies - although I suspect the vent could generate harmonics. Please explain. I will filter at 80 - 100 Hz.

Todd
I didnt mean that 100L is tiny.I was referring to small PR boxes around 50L vs 120L with an adaquate port with typical 12" HT drivers.

Well,you should be aware of PIPE RESONANCES. There is even a warning in the winisd manual from memory.


Yes,youl filter it,theyl be out of band.
But the port will make a nice narrow peak in response at 1/4wave of pipe length(www.quarter-wave.com). Youl want to look into this to make sure its inaudible.From memory,1metre is getting abit close. Ofcourse it depends on the nature of this pipe resonance, and your program material if it is audible.
  Reply With Quote
Old 20th February 2008, 05:23 PM   #9
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Default Re: Re: Re: Re: Re: Re: Subwoofer with external port

Quote:
Originally posted by pkm

Yes,youl filter it,theyl be out of band.
Only the driver's response, the vent's 1/2 WL pipe harmonics are not affected by the XO, so you may need to damp the vents to keep them from audibly comb filtering with the mains when there's significant vent output.

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 20th February 2008, 09:53 PM   #10
Newbomb is offline Newbomb  United States
diyAudio Member
 
Join Date: Feb 2008
Default Re: Re: Re: Re: Re: Re: Re: Subwoofer with external port

Quote:
Originally posted by GM


Only the driver's response, the vent's 1/2 WL pipe harmonics are not affected by the XO, so you may need to damp the vents to keep them from audibly comb filtering with the mains when there's significant vent output.

GM
I agree that vent harmonics will be generated regardless.

So why is this not a problem with shorter vents. IE, a 750 mm (30") vent has a 1/2 WL harmonic at about 226 Hz. A 10" vent has a ~680 Hz 1/2 WL harmonic. It sees to me comb filter effects would occur on either. I would be much more worried about comb filtering of frequencies higher than those dominated by room modes.

As far as damping the vent... What to do? The harmonic nodes are on the ends. Does not seem to make much sense to damp at the antinode. Line the inside ends of the tube with a thin layer of damping material?

Todd
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Passive Subwoofer, Bi-amped with Electronic External Crossover slhijb Subwoofers 9 24th January 2007 05:02 PM
long external port idea dwk123 Subwoofers 4 22nd November 2006 09:50 PM
external amp for subwoofer Dave Jones Solid State 6 29th January 2004 08:49 PM
port lenght for subwoofer ?? hilbren Subwoofers 8 5th July 2003 09:44 AM
Car Ported Subwoofer: Can the port be Outside the box? Noob-in-a-Camry Subwoofers 11 23rd May 2002 02:59 PM


New To Site? Need Help?

All times are GMT. The time now is 01:07 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2