Subwoofer with external port

[Newbomb]

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

 

[GM]

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

 

[Thawach]

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

 

[Newbomb]

Re: Re: Subwoofer with external port

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

 

[pkm]

Re: Re: Re: Subwoofer with external port

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.

 

[Newbomb]

Re: Re: Re: Re: Subwoofer with external port

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

 

[aznboi3644]

There is nothing wrong with external ports

 

[pkm]

Re: Re: Re: Re: Re: Subwoofer with external port

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.

 

[GM]

Re: Re: Re: Re: Re: Re: Subwoofer with external port

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

 

[Newbomb]

Re: Re: Re: Re: Re: Re: Re: Subwoofer with external port

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

 

[hooha]

There you go.

 

[AKN]

Looks nice

 

[pkm]

Re: Re: Re: Re: Re: Re: Re: Re: Subwoofer with external port

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

If you look at any properly measured bass reflex subwoofer,youl see little series of wiggles in response.Ofcourse BP6 bandpass would have two sets.I vaguely remember seeing some on stereophile,because they measure the port output and splice it with the rest.

 

[bjorno]

FYI, Compare See:

http://www.diyaudio.com/forums/showthread.php?threadid=117933

b

1(3)

 

[bjorno]

2(3)

 

[bjorno]

3(3)

 

[Warmon]

Originally posted by hooha

Nice job! What do you call it...the sled sub? The copper metallic painted ports are so cool. I like it...

 

[Alex from Oz]

Re: Re: Re: Re: Re: Re: Re: Re: Subwoofer with external port

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

G'day Todd,

I have a killer port treatment. Ground breaking stuff.

Read these two posts.
http://www.diyaudio.com/forums/showthread.php?s=&postid=1438104#post1438104

http://www.diyaudio.com/forums/showthread.php?s=&postid=1442990#post1442990

When you stop laughing at how ridiculous this is, if you are looking for a serious solution I'll explain the 'how to' so you can try it for yourself.

Cheers,

Alex