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Discussion Starter · #1 ·
Hi. I have a 15 inch driver and am considering building a cylinderical enclosure. Is there anything out there (like PVC) that I could use other than "sonotube?" Where does one buy sonotube anyway?

Any thoughts on the size sealed enclosure (just volume ideas) that I would need to get down to 20hz cleanly? I'll go ported if I must. I was thinking of about 5 feet of 18 inch PVC/Sonotube (~200 litres?)or similar. I saw concrete casts on the weg that might work with proper bracing, but I don't know where to buy them.
Here are some driver specs:
Free Air Res-28.94hz
Qts-.799
Qes-.880
Qms-8.773
Vas-102 L
Sen-86.38 db

I have several option for power (older amp from M&K sub, amp from CambridgeSW Cubebass 12 or sub channel in my HT amp)

THANKS!!
 

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The Sonotube has advantages over PVC or Concrete. It is relatively light, fairly "dead" acoustically, easy to work with and fairly inexpensive. Concrete was experimented with in the late 70's, early 80's (including structures cast with polystyrene beads to reduce weight) but was not very successful. I know of one user was going to use PVC but cannot say how they got on. I would try and source Sonotube.
Someone in the Greenville area should be able to help you locate it.

As for the design I get some strange results from WinISD. The grey is what the program chose for ported. :scratch: The yellow is sealed and the blue is what I got by plugging in my own size and tuning.
Text Line Font Design Parallel

Do you have the make and model of the driver?

Cheers,
Bill.
 

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Discussion Starter · #3 ·
It is a Digital Design driver; it's either an older but similar model to their current 1515a or 2515b. I pulled the specs posted here from the 1515a specs on their website:

http://www.ddaudio.com/mobile-audio/woofers.aspx

I bought the driver (used)from a friend and am currently working with the manufacturer to determine the exact model and specs. They (Digital Design) emphatically recommend a ported design for (all?) of their drivers. I know that I should listen to them (and probably will) as they designed the driver, but I plugged the specs into an online modeler, and it recommended a sealed design-

http://www.home-speaker.net/subwoofer-design.html

I have always preferred sealed designs, but I wonder if I just have not heard a well designed ported sub.:huh:


Your design certainly looks as if it superior. The sealed enclosure looks as if it rolls off sharply below 40hz, but as it's hard to read the bottom numbers on the graph so that's a guess on my part.

I'm willing to go with whatever design will sound best as long as it's not too expensive. I've made some phone calls and can not seem to find Sonotube locally...yet. I don't even have any idea how much it costs!

Thanks for the help. Which pic shows the specs (volume & tuning freq.) for your design? I am open to ANY suggestions that will make this sub sound its best. Yes, I want it to go low (20hz or so) but it must be clean, too. I guess that I want something that will shake the room for movies but sound good for music, too. If I could only afford a JL Audio Fathom...:laugh: I may scrap this driver and go with two 10s or 12s. Thanks again!!!
 

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The grey curve is what WinISD plotted, 825 Litres, 15 Hz
The blue is the figures I chose to give a reasonable response in a reasonable size, 400 Litres, 18 Hz
And the yellow is Sealed.

I have moved the items around in the graph in the first post so you can see them clearer.

Here are the sizes for an 18"and 24"Tube.

Text Line Font Parallel Screenshot


Text Line Font Parallel Screenshot


Cheers,
Bill.
 

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Discussion Starter · #7 ·
So, if I understand you, a build following one of the two cylindrical designs above should give me a response close to what is plotted by the blue line (with a -3db of ~ 17hz.)

"I believe we have a plan!" Thanks!!
 

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So, if I understand you, a build following one of the two cylindrical designs above should give me a response close to what is plotted by the blue line (with a -3db of ~ 17hz.)

"I believe we have a plan!" Thanks!!
That's right. (as long as the specs are correct.)
For movies you will need a high pass filter on the amp to prevent over-excursion below tuning.

I'm surprised no-one has suggested any local suppliers of tubing yet.

Cheers,
Bill.
 

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Discussion Starter · #9 ·
That's right. (as long as the specs are correct.)
For movies you will need a high pass filter on the amp to prevent over-excursion below tuning.

I'm surprised no-one has suggested any local suppliers of tubing yet.

Cheers,
Bill.
Shouldn't the crossover in my pre-pro take care of that? The sub will be crossed over at ~50 to 60hz with its own amp. I also have options as to what amp I'll use: one of two amps pulled from older subs OR the "subwoofer" channel on my 6 channel THX amp. I'm new to DIY, so perhaps I'm missing something. :scratch:

I contacted Sonotube directly, and they sent a list of "local" dealers. The closest dealer is in Raleigh. :unbelievable: A local supplier will order it for me, but the minimum order is 12 feet!

Thanks again; you have been incredibly helpful!
 

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Discussion Starter · #10 ·
Do I need a high-pass filter/crossover even though I am:
1) Using a pre-pro with a adjustable x-over for the sub output?
2) Using a dedicated amp (or amp channel) for the sub?
If so, what frequency do I need? (I will be using the sub for about 50hz and down)
Thanks
 

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I am not sure what a pre-pro is, do you have a model/brand I can look up?

You will need a high pass filter for playing movies as they have content below 18 Hz which could cause it to exceed Xmax. I think you set the filter the same as the port tuning which in this case is 18 Hz.
Also most receivers cross the sub/mains at around 80 Hz.

Cheers,
Bill.
 

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Discussion Starter · #12 ·
"Pre-pro" is short for "preamp processor;" think of it as an AVR without the amps*. It has an adjustable crossover for the sub output, but I don't think that's the issue here anyway. :gulp:

If I understand the statement about a high pass filter, it is (in this case) used to limit the low end response of the sub and keep the woofer from "bottoming out." It would be a high pass filter that would only allow 18hz and ABOVE to play through the sub; the pre-pro's (or AVR's) on-board crossover would limit it to ~80hz and below. Between the two filters would be the frequencies that the sub would cover. In this case 18hz to 80hz (I use a lower crossover point for my subs, but I know that 80hz is the most common point and the THX standard.)

I would need a high pass filter set at 18hz and up...is this something that I'd get at partsexpress.com? Any brands that you'd recommend? IF I used a subwoofer amp (I have two: an old M&K and a Cambridge Soundworks Basscube12 amp) would I still need it?

THANKS

* Here's an example of a pre-pro. It's an older 5.1 unit, but the review describes what it does. This is one that I used to own; my new one is a 7.1 model:

http://www.stereophile.com/solidpreamps/301lexi/index.html
 

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Discussion Starter · #13 ·
One other note, does anyone have a link to a down-loadable (pdf) overview of subwoofer design? I'm looking for something that will help me understand not so much "how" but "why" a subwoofer design works. I belive that if I understand the basic science behind design it will help me come-up with ideas for the enclosure and may lead to other designs. Thanks
 

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A ported sub works by tuning the port and air mass to a low frequency to gain a bit more bass extension. As the bass approaches the tuning frequency the cone is almost motionless and the port is supplying the sound. (See Helmholtz Resonator in Wiki)
The port itself can be a tube, a slot or even a passive radiator.

For design ideas try looking in the members database of builds located here:- http://www.hometheatershack.com/index.php?page=diysubwooferprojects
 

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Discussion Starter · #15 ·
What do you think about using an isobaric (band pass) enclosure with this speaker? What do I need to look for in this design? I believe that the tuning frequency is very important with these enclosures.
 

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I modeled these in WinISD (but I haven't tried to optimise them yet) and here are the initial results.
Both definitely look ok. The yellow is relatively flat from 20 Hz to 50 Hz and the apricot is flat from about 23 Hz to 60 Hz

Text Line Font Pattern Design


All the best,
Bill
 

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Discussion Starter · #17 ·
Thanks (again!) The bandpass designs look pretty flat, but the ported design still looks like the winner.

I think that I will download WinISD and try to figure it out. The designs that you've posted have been quite helpful; it would be nice to have access to the same tools that you use to try out several designs on my own. Since the only component that I have is the driver (and I may try a combo of different driver sizes/numbers) I could try different designs before I spend more money. I was thinking of using 4 10s in Sonotubes and using the enclosures as legs for a "table." I wouldn't use the table for anything except to quiet my girlfriend's comments about how ugly the equipment is.
Thanks again!
 

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Discussion Starter · #19 ·
Are you using the Pro version? I downloaded both and although I admit that I have spent less than 30 minutes with them, I can only seem to get regular box designs. How did you get the cylindrical designs, and is there a way to enter the volume of the enclosure directly?

The new design does look impressive! I found a used bandpass enclosure in town for $80. I haven't bough it as I'm not sure how to tell if it meets my needs. It WAS built for a DD driver, and I can figure out simple things like its volume. I'd have no idea how to figure out the tuning frequency, though. I'm tempted to buy it based on the design above, but the chances that it's the same design are slim at best. I should probably stick with the Sonotube design.

EVERY box calculator that I use recommends a sealed box based on the driver's EBP. Is there a way that I can calculate the volume of the enclosure that I would need to get to 20hz within 3db? I have to buy 12 feet and can get 16, 18 or 20 inch diameter, so I have A LOT of volume at hand.

Thanks again!!
Thanks
 

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I'm using WinISD Pro alpha.

Choose your Driver.

Text Font Line Technology Electronic device


Select normal or isobaric

Text Font Line Technology Parallel


Select Sealed, Vented or Bandpass,

Text Font Line Screenshot Technology


Then it will calculate it's design based on your selection.

Text Line Font Technology Parallel


Once you have your design you can then change the size and tuning as you see fit.

Download a copy of Sonosub as well and plug the figures in it to work out what size you want - height vs diameter.

Cheers,
Bill.
 
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