# Two CSS TRIO 12s ported to 15Hz



## skrap853

My original decision thread is here. I was able to find more space by integrating my subwoofer, center channel, and entertainment stand into one. I also, decided on round ports instead of slotted because of the design complexities that arose with the center channel cut out.

This is my proposed design and build:

Subs - Two CSS TRIO 12"
Box - 3/4" MDF, 14ft³ net, ext 68"x23.5"x22" (in the future I will wrap/trim in in some real wood assuming it sounds great)
Amp - Carver TFM-25, 700W ([email protected] per channel)
HPF - None
EQ - None planned
Ports - Three 30" x 4" PVC 2729 (thin wall ~.075)

?Foam - Should I be using foam or stuffing?

Please let me know if something doesn't look correct. The design is mainly final, but that doesn't mean I can't make changes. It looks like the box will take some time and require some pretty precise cuts.

Some screen shots to get an idea:
*WinISD includes a 80Hz LPF*
**All the inside edges will have a radius**


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## carmaniac13

Cool design. Definitely a bit different than the usual. One concern I see is the edge to edge joining on the top panel. Make sure those cuts, specifically, are PERFECT. The edge joint shouldn't be a problem if done well, but I feel like there's less room for error than with a standard corner joint.

Good luck, looking forward to seeing the finished product!


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## skrap853

carmaniac13 said:


> Cool design. Definitely a bit different than the usual. One concern I see is the edge to edge joining on the top panel. Make sure those cuts, specifically, are PERFECT. The edge joint shouldn't be a problem if done well, but I feel like there's less room for error than with a standard corner joint.
> 
> Good luck, looking forward to seeing the finished product!


I was thinking the same thing, considering making the top all one piece then routing/cutting out that section. It seems like it is a leak waiting to happen. I just added the section in the back where the ports come up.

I've been doing lots of modeling in WinISD and SketchUp, pretty excited to actually be able to start when this design is final. I still have to get some elbows and measure them, had to guess for my sketch.


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## carmaniac13

That would be a better bet if it's not too much trouble in the way of needing a larger piece of material. But it would also probably be faster to cut one large top piece, then just use a flush cut bit on a router once it's all glued down and remove the center section in 2 minutes, instead of having to deal with 3 separate pieces and getting them all aligned to each other.


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## Mike P.

That's an interesting design and your modeling is correct. :T


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## musikpirate

Sweet! This one I can't wait to see!


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## Mattcc22

I'll definitely be following this one. I've also thought about doing something similar.


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## GranteedEV

Hey your model looks great. _Personally_ since it doesn't look like you plan on using a high pass filter, I'd tune a smidgen lower (40" vents instead of 30" vents). Technically you lose some headroom, but IMO It would manage vent speed a bit more and probably work better with more room-functions (for tighter SQ) We're talking about 2-3db of headroom and 2hz of extension here, but it's just my opinion. Either way you'll end up with a deadly sub(s). :hsd:


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## skrap853

GranteedEV said:


> Hey your model looks great. _Personally_ since it doesn't look like you plan on using a high pass filter, I'd tune a smidgen lower (40" vents instead of 30" vents). Technically you lose some headroom, but IMO It would manage vent speed a bit more and probably work better with more room-functions (for tighter SQ) We're talking about 2-3db of headroom and 2hz of extension here, but it's just my opinion. Either way you'll end up with a deadly sub(s). :hsd:


I appreciate the advice. My room is very large so not sure how much room gain I will get. The other issue is - I would have to change the way the ports are arranged since I could not add 10" to them in their current configuration. Based on all that, I'd like to move forward with my current design if it is acceptable. I'm pretty happy with the modeling considering my criteria. 

Screen captures for the sake of comparison:


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## Mike P.

Your current plans will be fine. For making a comparison, In your graphs above you would lower the input power on the lower tuning so Xmax is the same.


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## patchesj

Your cone excusion scares me... You're going to need a HP filter no matter what, but I would consider playing with your tuning a bit to get the cones under control and lower your port speeds. 

Another option would be to divide the box in half and go with 4 ports (2 each side). I've always found that 2 drivers in the same air space can create some unintended results. 

Also your ports look a little squeezed in that small space in the back. I'd think about angling them slightly so they open up into the larger volume behind the drivers. With that much air moving 45 degree angles will give less noise than 90s.


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## skrap853

patchesj said:


> Your cone excusion scares me... You're going to need a HP filter no matter what, but I would consider playing with your tuning a bit to get the cones under control and lower your port speeds.


A high pass filter can be added later if there is an issue with excursion. I'm not seeing how adjusting tuning helps air speed or cone excursion for my design parameters (limited box size, and set amplifier power). Decreasing the tune frequency lowers air speed, but gives a very undesirable effect on SPL response. Increasing the tune frequency only increases air speed and again causes undesirable SPL response. Increasing the tune frequency does lower cone excursion for frequencies above the tune frequency but makes it more likely that a HPF is needed.



patchesj said:


> Another option would be to divide the box in half and go with 4 ports (2 each side). I've always found that 2 drivers in the same air space can create some unintended results.


Now that you mention it my only concern with an undivided box is that I'm using my amp in stereo. I'm feeding my amp by splitting the LFE output from my receiver. I suppose there could be a difference in the channels, although unlikely. I'll consider what happens to the design by separating the drivers.

Moving to four 4" ports decreases air speed by 8m/s at peak, but lowers first port resonance to 164Hz from 224Hz. I'm still learning in this area and have nothing real world to compare to. I was planning on using a radius on the ports to help combat air noise. I was also hoping to find a way to add a radius at the inside end of the ports.



patchesj said:


> Also your ports look a little squeezed in that small space in the back. I'd think about angling them slightly so they open up into the larger volume behind the drivers. With that much air moving 45 degree angles will give less noise than 90s.


It seems like air volume inside the box is just that - volume. It shouldn't matter that one space is smaller than another, the space is shared (seems like if it did have an effect it would lower the tune by creating a port effect, I'm just not sure). From the top of the port to the top of the box is 5", then that opens to the two larger chambers. I was also thinking of making the support that holds the end of the ports have some cut outs. I was under the impression that a box should not be one long uniform shape to avoid standing waves. If you've heard or know of a design similar to mine that sounded horrible please let me know before I move forward.

There are two types of 90° elbows, sweeping 90 and 90. From the reading I've done most people seem to think the sweeping elbows perform fine. I guessed on the radius of the elbow in my drawing. Since then I went to the lumber store and found the outside radius of their sweeping 90 is just over 6".



I appreciate your input. It caused me to look into some of my design which is good for increasing my experience. I'm not even a novice let alone an expert and can stand to learn much more. Unfortunately, I have nothing to compare modeling versus real world. ie I'd like to listen to a well built subwoofer and then look at it's WinISD model and then a poorly designed subwoofer.

Does anyone else see the things patchesj mentioned as being issues? I'm getting the garage ready and collecting materials hoping to start building in a couple weeks.


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## patchesj

skrap853 said:


> I was also hoping to find a way to add a radius at the inside end of the ports.


You can get some nice port flairs online that will greatly improve the airflow.



skrap853 said:


> It seems like air volume inside the box is just that - volume. It shouldn't matter that one space is smaller than another, the space is shared (seems like if it did have an effect it would lower the tune by creating a port effect, I'm just not sure). From the top of the port to the top of the box is 5", then that opens to the two larger chambers. I was also thinking of making the support that holds the end of the ports have some cut outs.


Yes, volume is volume. However you need to think about how the air is going to flow in and out of the port ends. The center port is going to perform a bit different than calculated because there is a limited amount of air that can flow into it without being disturbed by airflow at the mouth of the other 2 ports. It is effectively choked off by the air movement on the other 2 and will have a lot of turbulence around it.

Overall, a very nice design. I have a Trio12 and think they are great drivers for the money.


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## Mike P.

I agree on the port flairs, I did triple 4" flared ports 30" long on one of my builds.

http://www.hometheatershack.com/for...54-mach-5-audio-ixl-18-4-build.html#post72475


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## event horizon

Oh boy, do you have a huge problem with port air velocity 

I have a suggestion for you that will make this sub work & I have done the calculations for you so all you need to do is build it 

Please take a look at this thread...

There is a nice picture on there that just about explains what you need to do :T

However I had to effectively model your 14ft^2 twin trio speaker & then fit a port that got the port air velocity low enough so it won't chuff like Ivor The Engine :rofl2:

The port needed to get to just over 10m/s with 700W RMS was 32cm in diameter & nearly 2.5m long :whistling:

However, with a power port you get something much smaller & with no worries about the 1st port resonance...

So here is the equivalent power port to the 32cm x 250cm port










Going by that you need an 8" internal diameter port that is just over 16" long. You also need something of 2" diameter to act as the flow guide, which is called the "extension" (bottom row of calculation). In the pic on the other thread it runs up the centre of the 8" port tube.

You'll need 13" diameter discs which are spaced 3" from the ends of the rounded off port, which needs a 2.5" radius on each end & a 5.5" radius onto the discs from the extension.

It might be a bit of work with saws & car body filler, on the other hand you might know someone with a wood turning lathe.. But the result is a much smaller port with an equivalent air velocity of a much bigger one & no port resonances to worry about (which would be at about 69.7Hz with the monster 32cm port).


If you need help understanding all the above I'll attempt to help out if you have questions. If you take a good look at the other thread & the picture I feel all will become much more obvious given some time :T


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## Mike P.

His design has three 4" ports, that has 38 square inches of port area. He'll be fine, there won't be any port chuffing.


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## event horizon

Mike P. said:


> His design has three 4" ports, that has 38 square inches of port area. He'll be fine, there won't be any port chuffing.


I'm sorry but I disagree... The result of 3 x 4" ports is still over 34M per second velocity at 15Hz with 700W of input power. The deeper you go when tuning the lower velocity you need to have to avoid turbulence being generated. Not only that there is a maximum limit to the air speed which is dependant on the size of each port in question. Above this limit there will be compression & the port will start turning into a plug.

I was just looking about when I discovered a rather interesting site, which you'll find here  http://www.subwoofer-builder.com/flare-it.htm

Now if you look at that little box that looks similar to winISD, you'll see the core limit of a 4" port at 15Hz is less than 20M per second & the chuffing will start at approximately 11M per second. If the port was bigger these speeds could increase a tad.


This is why I suggested something to get the port velocity down to a more sensible level of around 10M per second..


Of course it up to the OP on what he decides to do & I wish him the best of luck


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## Mike P.

You can push a single 4" flared port to 26 m/s. Three 4" flared ports to 34 m/s is not a problem. 

Green is the modeled air speed of the OP's design. Yellow is the modeled air speed of my IXL-18 build. I've thrown test tones at it at every frequency, played movies at very high levels and have not once heard chuffing or port noise of any kind.


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## carmaniac13

I would agree with Mike P. trying to get port noise down to 10m/s is a bit unreasonable. Especially for such low frequencies that won't often be used. You'll be hearing things rattle before you'd hear port noise anyway. Low 30's seems to be a common number that most of us aim for, with good results.


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## skrap853

patchesj said:


> Yes, volume is volume. However you need to think about how the air is going to flow in and out of the port ends. The center port is going to perform a bit different than calculated because there is a limited amount of air that can flow into it without being disturbed by airflow at the mouth of the other 2 ports. It is effectively choked off by the air movement on the other 2 and will have a lot of turbulence around it.


I was wondering myself if the ports being in line would affect the tuning. I did it that way trying to keep it symmetrical.

Thanks again for your input, I'll play around with moving the side ports and leaving the center one where it is. I bought some of the materials this weekend including elbows which should allow me to model the ports better.


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## skrap853

Mike P. said:


> You can push a single 4" flared port to 26 m/s. Three 4" flared ports to 34 m/s is not a problem.
> 
> Green is the modeled air speed of the OP's design. Yellow is the modeled air speed of my IXL-18 build. I've thrown test tones at it at every frequency, played movies at very high levels and have not once heard chuffing or port noise of any kind.
> 
> View attachment 34805


Mike, thanks for the real world example. Are you using port flares on one or both ends - Nevermind, I looked at the pictures from your build and see the flared ports on both ends.



carmaniac13 said:


> I would agree with Mike P. trying to get port noise down to 10m/s is a bit unreasonable. Especially for such low frequencies that won't often be used. You'll be hearing things rattle before you'd hear port noise anyway. Low 30's seems to be a common number that most of us aim for, with good results.


Carmaniac, thanks for your input. I'm glad to be leaving my ports at three 4", specially since I bought the pvc and elbows this weekend.


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## skrap853

I've been really busy lately, but found some time to update my design based on feedback from the forum. I still have some work to do where the port meets the brace. I moved the braces off center to provide support for the end of the ports. I hope that also helps be keeping the chambers asymmetrical.

Let me know what you guys think.


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## carmaniac13

Looks Good :T

That should be a really dead box, with all the inside corners, bracing, and asymmetry going on. What's the clearance between the center port mouth and the top of the box? That's the only thing I see that looks mildly concerning.


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