My final Tempest plans!

[Brian Steeves]

I have spent many days and nights thinking and emailing back and forth about the design. I also spent a considerable amount of time playing around with LspCAD. Taking all things and advice into consideration this is what I decided on.

10.5 ft3/300l (net) internal volume, using 24"i.d. Sonotube
Tuned to 18hz
2-6" i.d. pvc vents 32.25" (actually only 31" long due to them not extending all the way through bottom endcap)
Driver and vents mounted on bottom




She said,"you're gonna put that thing WHERE!"

[ThomasW]

Brian

Looks good. You'll probably want to use some grill cloth over the ends of the ports, to tune out any possible "pipe" resonances created as a function of the long length of the ports




theAudioWorx
Klone-Audio

[Brian Steeves]

Are you kidding me? I thought this wouldn't be a problem. The reason I went with longer (bigger diameter) ports was to rule out any chuffing at high volumes. Now you're telling me I'll get pipe resonances? I just can't win!!

What would be a better solution?




She said,"you're gonna put that thing WHERE!"

[ThomasW]

Hey not to worry, this isn't a big issue and the fix IF NECESSARY is easy.

When the speakers are built I'll walk you through testing for pipe resonances, and you can do a quick fix. Things like this are just part of building a big ported sub.

Remember EVERYTHING is a compromise in speaker building trading one thing for another. You do eliminate "chuffing" with the 6" ports, but their length creates POTENTIAL of the resonances.

"Perfect ports" are big in diameter and short, hopefully less than 24". But that's generally not possible.




theAudioWorx
Klone-Audio

[Andrew Pratt]

Thomas as you likely know my ports are 73 cm long (28")...no I'm not bragging Anyway what test should I be doing to see if I've got a problem? Is it the 9 volt battery test?

[ThomasW]

Andrew

I wouldn't worry with the 28" length, and yes it is the battery test

BTW, can you find the thread where that is discussed? I can't




theAudioWorx
Klone-Audio

[Brian Steeves]

Thomas,

Someone over at HTT posted a concern about the distance between the edge of the ports and the edge of the Sonotube. He said something about it should be at least 1/2 the width of the port width. Is this a structural or some other type of concern? Do you have any idea? Because if it's only a structural thing that shouldn't be any problem as I build things like brick $h1Thouses!

Here is a bitmap of a fairly close depiction of the layout I was planning. The actual scale may be a little off but it's close.

http://images.honesty.com/imagedata/h/006/93/20069349.jpg

She said,"you're gonna put that thing WHERE!"

[ThomasW]

Brian

No, it's not structural.

Please reference pages 54-55 of "The Loudspeaker Design Cookbook". The section 2.71-Vent resonance and mutual coupling, deals with this subject.




theAudioWorx
Klone-Audio

[Brian Steeves]

Tom,

I read the pages you directed me to. It's not really clear as with much of what Vance talks about in this book. The basic idea is there but doesn't really give any solutions to the problem.

What if I used 2 90 degree elbows (make an upsidedown "U" on the inside opening) on each port? Thereby being able to do the following and avoid any possible problems due to close proximity of the ports.

1) position the inside ports so they face toward the driver.
2) make it possible to seperate the distance between the port openings from each other inside the speaker.

Something like this only spread the ports further apart from each other.


Resonances due to port length may be another problem but at least not compounded by placement.

What do you think?




She said,"you're gonna put that thing WHERE!"

[ThomasW]

Brian,

IMO using elbows and having the inherent port resistance changes they create, is more problematic than any potential issues with port resonances. I'd suggest staying with straight ports.

The distance of the ports from the tube wall in the picture, is further than that indicated in the drawing.




theAudioWorx
Klone-Audio

[Andrew Pratt]

I wouldn't use elbows if you can at all avoid it. I've used them in past and its difficult to get them solid enought that they don't rattle or come loose. Besides why add the resistance and logistics problems if you don't need to

Thomas I'll see if I can find that post

[Patrick Sun]

I think Dan Wiggins has suggested using a flexible tube that can be coiled for the correct length if the overall port is longer than the height of the tube. Email Dan on this option.




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