# First Sub: LLT, SDX-15, Slot port



## sirfifer

This is my first sub build!

It has been a great pleasure reading through this wonderful resource for the past few months.

I already have an SDX-15 (Christmas Present!)

I'm not providing much info on the room as It may change. The room will be between 14'x16' - 22'x20'

Use will be about 70/30 HT/Music. I'm a huge movie nut and LOVE subsonics, but I'm a musician and music lover so while I'm definitely going to do a ported design, I want to do everything I can to improve the audio quality.

While I'm looking at doing a slot port, I plan on making it as long as it needs to be, flaring both ends, softening the bends, and even softening the sharp corners along the port lengths. i was thinking of doing the last by just using some small molding material.

The rough dimensions I'm looking at so far are 24"x26"x34"

I'm planning on using 3/4" MDF or Plywood, maybe a mix, one for shell, the other bracing
I plan on heavily and carefully bracing the box.

I'm wavering between using a 500-1000w Plate amp or an EP2500.

Regardless I'm thinking of getting a BFD, EC8000 and using REW.

I plan on using Google Sketchup to do the design so if anyone can recommend an existing Sketchup design that might be a good starting point that would be great!!

Any and all tips, ideas, and pointers are VERY welcome.

A special shout out to anyone in the general Portland, OR area who is at all interested in the project, is working on or has completed such a project and would not mind sharing!

Thanks!!


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## Mike P.

24"x26"x34" will give you a net volume of about 9 cu.ft. Tuned to 18 hz with a slot port 3" x 12" x 28" long would definitely give you the low end output for movies.


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## looneybomber

If you want the SDX ported and tuned below 20hz, anywhere from 8-13.5ft works with a tuning from 18-14hz. So if you want to go bigger, you certainly can. Otherwise 9ft will work fine.

About the power, the ep2500 will do a good job powering it, but with all that power on tap, you'll want a subsonic filter. Rarely will you see me recommend one, but that's quite a bit of power (over 1600w with <1% THD at 20hz) for an SDX in an LLT. If you ended up with a 500w plate amp, I wouldn't worry about an SSF.

For bracing, you don't have to go crazy with a dense 3-axis matrix. They say 8-12" gaps between window braces are just fine, but bracing all three axes is best.


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## sirfifer

I was aware that if I'm really trying to nail a good LLT design and to go especially low that I need to plan on using a High pass filter.

Is this something the BFD can handle?

In many ways I would prefer a plate amp as long as it is not truly a compromise. Are there any good 500-100w plate amps that have a HPF? How hard would it be to incorporate one into a plate amp that did not already have one like the OAudio or a parts-express?


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## sirfifer

While I do want good SPL I'm especially interested in maximizing my use of the SDX-15, especially with regard to sound quality and low frequency. I would like to go as low as I can while not sacrificing too much SPL and not increasing the size that much. Adding as much as another foot in one direction is not a problem, I mainly have size constraints in 1-2 of the 3 dimensions.

How low have people gotten the SDX-15?

I will pose this question in more detail in the CSS forum.

Thanks!!!


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## Mike P.

Thread moved to the CSS forum. Box size, amp power and Hi-Pass filter will determine what output levels can be achieved. Let's start with the cabinet. What is the maximum size you are willing to live with?


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## sirfifer

Mike P. said:


> Thread moved to the CSS forum.


Mike, I had intended this to be my official project thread which is why I started it in what I understood to be the proper location. It is understandable that any project thread will get product specific at times as every project contains products. 

I was going to start a new thread in CSS to ask about extra low success with the SDX-15. 

If this makes sense please move this back to the appropriate location. 

Thanks for the help!!


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## sirfifer

Mike P. said:


> Box size, amp power and Hi-Pass filter will determine what output levels can be achieved. Let's start with the cabinet. What is the maximum size you are willing to live with?


I think that the maximum for two dimensions are 24"x26" The third was at 32" but can go to as much as 50-60".

How does fill fit into this? I have read some indication that it has the effect of making the volume act like it is larger, but at a cost?

Sound Quality is a big priority to me with in the context of maximizing a slot port LLT design.

Thanks!


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## lsiberian

There are 2 options that I recommend for what I'd consider your best sound. I recommend sealed for this one actually. 

1. a sealed 4 ft^3 build(using a Behringer Feedback Destroyer to shape the response you want)

2. a port 7.132 ft^3 19.32 hz tuned build(using a 2nd order subsonic filter at 20hz) 

I think your best option is actually the first one given your love for music and the simplicity of a sealed build. 6db is all you gain from the ported design once you employ the subsonic filter at 20hz over the sealed sub and below 15 hz the sealed will beat the ported. 

I think sometimes people don't realize how powerful a great driver can be in a good sealed box. This thing is around twice as loud as a jackhammer at 20hz in that sealed box. 

With a folded slot port you could get large enough to make port compression a non issue, but it will be a pretty large box for most folks.


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## Mike P.

> I think that the maximum for two dimensions are 24"x26" The third was at 32" but can go to as much as 50-60".


That is more then enough volume for a proper LLT. In 14 cu. ft. tuned to 15 hz you would need a 8" port 37" long. Since the cabinet is tuned to 15 hz there is no need for a Hi-Pass filter according to the design criteria. Also shown is 4 cu.ft sealed, both models are with 1000 watts input power and no Hi-Pass filter







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## sirfifer

Mike P. said:


> That is more then enough volume for a proper LLT. In 14 cu. ft. tuned to 15 hz you would need a 8" port 37" long. Since the cabinet is tuned to 15 hz there is no need for a Hi-Pass filter according to the design criteria. Also shown is 4 cu.ft sealed, both models are with 1000 watts input power and no Hi-Pass filter.
> 
> 
> 
> 
> ​


Mike, that looks fantastic! 

I guess one thing I am misunderstanding is when a Hi-pass filter is needed. Is it something like you can avoid using one if your box is large enough AND your port is long enough to avoid an issue that could cause max excursion due to ultra low frequencies?

It just seemed that every other post I read and thought I understood talked about the need for a Hi-Pass filter when you are doing an LLT.

Also, do most people stuff an LLT sub and/or add treatment to the interior walls?

Ah, such a newbe I am lol

Thanks!!


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## Mike P.

If the box is big enough and tuned to 15 or lower you usually don't need a HPF. No stuffing needed in a LLT or most ported designs. Lining the walls is supposed to damp the backwave, some say it works, some say it doesn't. Many a unlined sub has been built with no reports of issues.


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## sirfifer

Mike P. said:


> That is more then enough volume for a proper LLT. In 14 cu. ft. tuned to 15 hz you would need a 8" port 37" long. Since the cabinet is tuned to 15 hz there is no need for a Hi-Pass filter according to the design criteria. Also shown is 4 cu.ft sealed, both models are with 1000 watts input power and no Hi-Pass filter
> 
> 
> ​


I'm looking at doing a slot port. I was planning on letting the port be the width of the front so if the box is 24" the slot width would be 22.5" and I was thinking of a slot hight of 3".
I'm not sure how to model this in WinISD Pro as when I try to duplicate what you did it does not look at all the same. Since my settings are the same as yours that I can see, I'm assuming it is what I have on the vents tab that is incorrect. In WinISD Pro would I just put in 22.5 x 3 for the "Vent diameter with a square shape? Then do I just set the port tuning and let it calculate the length? When I try that I get a length of 49.6"


I have also seen many slot port designs that did not have the port the width of the box. Are there any particular reasons one is better over the other?

I'm also planning on trying to flare the ports.

Thanks!!


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## Mike P.

2" high x 22.5 wide x 32.75 is all you need for this sub. With 1000 watts input and no Hi-Pass filter the maximum air speed is 34 m/s at 14 hz.


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## sirfifer

I'm definitely thinking of flaring at least the outside of my slot port, maybe the inside as well.

Here is an example of the kind of thing I'm looking to do:
Fi Bl 12" Double Flared Port build

If I understand right, a change in the density of the port wall material should not matter at all, it is primarily just a conduit for air movement.

I'm thinking of just flaring one direction for the inside.

Thoughts?


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## Mike P.

"Pound That Sound" does beautiful work, I've followed his builds on SSA.


> I'm thinking of just flaring one direction for the inside.


I don't follow you.


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## Binary

I've got mine in roughly 16 cubes with light stuffing and a 15~16 hz slot port (stuffing throws off the tuning ever so slightly.) It sounds amazing! My significant other hates it. lol. Its running on a QSC RMX 2450. i was running it in stereo (4 ohm) roughly 750w per channel off the amp. but i feel it likes the power enough to run it on full bridged mono mode, "2400w rms rated @ 4 ohm". I havent managed to bottom the sub out, but have managed to clip the qsc on some music sessions. No HPF required on this beast. at least i havent heard/seen a need for one.


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## sirfifer

Mike P. said:


> "Pound That Sound" does beautiful work, I've followed his builds on SSA.
> 
> 
> I don't follow you.


I will flare the inside end of the port by curving the inside wall of the port away from the box wall.
_Posted via Mobile Device_


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## Mike P.

Ok, understood.


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## sirfifer

Here is an update on my working design:

CSS SDX-15
LLT W22 D24 H68
3/4" Plywood for outside, Inside may be MDF
14Hz tuning
Slot port 20.5"x3" 53" Long
port velocity 21.4 m/s at 14Hz, Peak 23.8 m/s at 12.7 Hz
Port will be flared two ways on the outside (Flared Slot Port Example)
and the inside will be flared at least one direction. I will also be smoothing out both the slot corners along the length, and the single bend.



I have an ECM8000 on the way and will be getting a DSP1124 soon as well.

I'm most likely going to get either an EP2500, EP2000, or EP4000. I'm keeping a close eye on Craigslist and EBay!!

I'm trying to find a good Sketchup example to use as a design base. As soon as I have something roughed out I will post an update.

Let me know your thoughts!!

Thanks for all the help so far!!!


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## sirfifer

Does anyone know of a Google Sketchup design that would be a good starting point for this sub?

I know it is often easier to start from something in the ballpark then try to go from scratch.

Any other comments on the plans so far?


Thanks!


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## sirfifer

Another point I'm trying to come to a decision on is the amp.

I'm looking at a ep1500/2000 or ep2500/4000. I do not have any plans to build a second sub any time soon so I can easily run the amp in bridged mode. Even counting the difference in rms vs peak for the EP2000, it looks like it can easily put out 500-1000w with headroom to spare.

That said, I'm not sure how power hungry this design will be or how to figure that out. I don't want to limit the setup. While my room is not that large at the moment, that could change, or I may need to temporarily use the sub in another location.

The EP2000 can be had for $280 right now at Amazon while the EP4000 is $349 everywhere. I'm trying to figure out if waiting to come up with the additional $70 is clearly worth it.


Thanks!


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## Binary

I'd grab the EP4000, its beefier so you won't have to worry about running 4 ohm bridge or 2 ohm stereo on it, not only that, what are the chances you're done with your system. lol. Us DIY guys never are done. We can always go bigger. No sense in buying another amp down the road if you don't have to.


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