RL-p15 Table Sub

[Inu_Yasha]

Ok, I've finally committed myself to building me a sub. I want to make it into a table much like nick77 did with his RL-p15 project here:

https://www.htguide.com/forum/showthread.php?t=19805&page=1

But I was wondering if it would be possible to also make the sub down firing like the svs PB12-Ultra/2:

https://web.archive.org/web/20070119072525/http://www.svsound.com/products-sub-box-ultra2.cfm

My thought is to make the sub down firing with a baseplate much like the PB12. The top will be much like nick's. I hope to tune it to around 19hz and possibly have all the ports down firing as well...

1.) My first question is would this be a plausible project?
2.) How big would the sub have to be in order to reach 19hz (optimally)?
3.) My uncle has a router and is coming down Sunday, what bits would be needed to cut the hole for the sub.

Thanks all!

[cdwitmer]

You can have a down-firing sub; the only thing you should never have in a horizontal plane is a passive radiator, but that's irrelevant here because you are using ports instead. The one consideration is that depending on how high you elevate the driver off the floor, the space below the subwoofer could act as a port of sorts.

The dimensions of the subwoofer will depend on your choice of driver.

As for the choice of bit, the best way, if you have the tools, is to use a saw to make the mounting hole and then neaten it up with the router: that will save you a lot of sawdust. However, you can also cut the entire hole with only a router. There are many ways to skin this cat! Probably the easiest is to use a circle jig like the Jasper Circle Jig, or you can DIY a tool that does much the same thing. A straight bit will work fine. Depending on how you make them, you might want a roundover bit for the ports, as that can smooth the flow of air and reduce port noise. If you are going to veneer the enclosure there are also bits for trimming veneer . . .

[Inu_Yasha]

I was initally thinking of using my jigsaw to make the hole for the sub, but I wanted to make sure the hole was straight, that's why I'm thinking of using a router. The driver I'm going to use is the RL-p15 for soundsplinter.com (I'm currnently waiting on the D2's to come back in stock).

The main thing I want to achieve this weekend is to have the hole cut for the sub to sit in. The whole venner and stuff can come later as I have the tools for that. One other question though, what type of board should I use to make the sub? I want to stain the wood in the end, so I'm thinking of doing an inner box of MDF and then making the other part some type of plywood.

[steve nn]

1.) My first question is would this be a plausible project?

It would depending on your answer to question two. How much room do you have to work with? The PB12-Ultra has it's ports bent to come up with the 20 Hz tune in that amount of real estate. The RL-p is going to require more port yet, so keeping them straight and having room on the baffle is the dilemma considering you want this to be table and the ports firing down along with the driver. You can also bend the ports, but it'll take some room to do so..that is having your ports incorporated on your baffle.

3.) My uncle has a router and is comming down sunday, what bits would be needed to cut the hole for the sub.

I think you'll find the straight bit and the flush trim bit the most desirable bits to have on hand. Adding a round over bit would be nice if you plan on rounding the edges?

[ThomasW]

One other question though, what type of board should I use to make the sub? I want to stain the wood in the end, so I'm thinking of doing an inner box of MDF and then making the other part some type of plywood.

The choice here depends on the look you want. MDF takes a smooth painted finish better than ply. Ply is nice of you want a stained wood look.

You might consider a lower tuning point. Since you're going to need elbows to have downfiring ports you might as well use longer ports and tune down to 15-17Hz if the box is big enough.

[steve nn]

You might consider a lower tuning point. Since you're going to need elbows to have downfiring ports you might as well use longer ports and tune down to 15-17Hz if the box is big enough.

yes..This would give you the benefit of better SQ (sound quality) if your able to do so not to mention more SPL in the lower regions. If your going to be loading your sub NF, (near field) it would increase the benefit of doing so. It's somewhat subjective, but I think most would agree.

[Inu_Yasha]

You might consider a lower tuning point. Since you're going to need elbows to have downfiring ports you might as well use longer ports and tune down to 15-17Hz if the box is big enough.

Ok, lets say I consider a tuning point of 16hz, what box volume would I need? I currently have a 36X22X16 table in my living room that i want to replace. I am thinking of making the box 32X18X12. The table top will be 36X22 and using 3 in to separate the box from the baseplate. What do you guys think?

Also, how much harder will it be to do downfiring instead of side firing? Is it just addition of elbow joints inside of the box? And how many ports should I use?

[ThomasW]

Do you know how to model a sub using computer software?

WinISD Pro or Unibox 4.0 (use google) are freeware progams that will help you figure out what size port fits in what size box to create a specific tuning

4" spacing would be a better choice than 3".

Yes you can simply use an 90 degree elbow. Use 6" PVC for your port then you'll only need one

[Inu_Yasha]

I'm trying to model in WinISD and I have SteveCallas file as my reference. I'm still not too sure which graphs I'm supposed to be looking at (I'm mainly looking at SPL graph right now). Which ones am I supposed to be comparing is my first question.

On the ports, if I choose a larger port, it gives me a longer vent length; viceversa with smaller. Does this mean I could use a smaller port to achieve the same freq tune?

[ThomasW]

I don't use WinISD so I can't comment on specifics of that program. The problem anytime a smaller diameter port is used is the Mach number (air speed in the port ) goes up. High Mach numbers = port chuffing, so the numbers should be as low as possible. That's why we recommend a 6" port with the RL-p15.

[Inu_Yasha]

Ok, I finally have the time to restart working on my design. I ordered my ep2500 and it was supposed to be delievered today, but I missed the ups guy :cry:. I also ordered a RL-p15 D2 today as well with no idea when I will be recieving it.

My idea is this, to build the outer box out of BB ply (i think the one at Lowes is only 7 ply though), and then do the bracing and reinforcements in mdf. My outer dimensions are 32X20X16. Since I'm planning on doing downfiring, I'm thinking of using legs like those used in the sonsub projects to raise the box 4in off the ground and then having a plate on the bottom. I am planning on using a 36X24 sheet on top for the table top.

Right now, my main questions are:

1. Is the Birch going to be ok to use if I do reinforce the inner baffle (considering the birch is only 7 ply).

2. At this point, does the desgin seem like it will work? I'm trying to look for something functional since this will go into my apt.

3. Considering that I am going to have to use an elbow inside the sub, how would I go about measuring the total length of the port? I'm not too sure how that elbow will play into the length.

[dyazdani]

3. Considering that I am going to have to use an elbow inside the sub, how would I go about measuring the total length of the port? I'm not too sure how that elbow will play into the length.

The port length is the centerline distance I think so you just add the "net" length of the elbow to it...

You may want to make the baffle out of two layers of BB.

[ThomasW]

It's better to use ply for bracing, since MDF has zero compression strength.

The inner workings of the box can of course be made from OSB. It has the strength of ply and the cost of MDF. All MDF does is machine nicely and add mass.

[Inu_Yasha]

Sorry to be noobish, but what is OSB? Since it's not going to be seen anyways, I could always use a cheaper wood on the inside . Sorry, poor college student trying to get his home theatre ready.

On a side note, how hard is it to use a router with Birch? I'm not too familiar with routers as I just got my first one a couple of weeks ago. I'm thinking of making little slots for my braces so that they will hold better (like a biscuit). Also, how would I go about attaching legs to the bottom of my sub? I know Stevecallas has legs supporting his; I wanted to sorta copy that design.

[ThomasW]

OSB= oriented strand board

[dyazdani]

On a side note, how hard is it to use a router with Birch? I'm not too familiar with routers as I just got my first one a couple of weeks ago. I'm thinking of making little slots for my braces so that they will hold better (like a biscuit).

If you are doing two layers, sometimes it's easier to make "slots" by cutting the inner layer into sections.

[Inu_Yasha]

If you are doing two layers, sometimes it's easier to make "slots" by cutting the inner layer into sections.

That makes a lot of sense. I may just do that; I'm debating on whether or not I'm going to use screws and glue, or slots and glue.

After factoring in the outside box, my inside dimensions ended up being 24.5 X 20.5 X 15.5. Considering that I use a 6 in port, I think I probabbly can only run the port 24 in giving a 24HZ tuning freq. I was also looking at doing two 4 in diameter ports at 24 in a piece to give the same tuning freq. My two questions are, which would be better? And, if two ports are used, would the vent length be 24 in or would it equal to 48 in considering that there are two ports used?

[ThomasW]

With those dimensions you forget about building a ported system, sealed is the only thing that makes sense.

[Inu_Yasha]

With those dimensions you forget about building a ported system, sealed is the only thing that makes sense.

Just out of curiosity, around what internal volume should I be shooting for if I was to go ported? The main reason I was looking at a smaller enclosure is because I live in a 1 bedroom apt. So sealed would be the best to use with my enclosure size?

I was looking at the SS website and saw that "Home audio enthusiasts should shoot for 3.5 cu ft net internal volume, with a tuning frequency between 18 - 25 Hz."

[SteveCallas]

I was looking at the SS website and saw that "Home audio enthusiasts should shoot for 3.5 cu ft net internal volume, with a tuning frequency between 18 - 25 Hz."

I don't know why they make that recommendation. Let's say you use 3.5 cubic feet and tune to 20hz. How in the heck are you suposed to come up with an acceptable port solution that won't suffer from a variety of problems? I'd shoot for at least double that size if going ported, preferably more.

[ThomasW]

Mike's background and primary demographic is car audio. Overtime he's actually increased the size of his recommended enclosures given all the bandwidth larger boxes have gotten.

You have 2 choices sealed or PR's. I'd start with sealed and use EQ and amplifier power to get the job done.

[---k---]

Thomas,

What do you mean by: "given all the bandwidth larger boxes have gotten."
I'm unclear how the termbandwidth applys to subs.

Thanks

[ThomasW]

bandwidth= all the posts on various forums....

[---k---]

Ahhh. thanks.

[Inu_Yasha]

Ok, I've gotten pretty far on building my box; now I'm to the bracing. I'm making window braces and was wondering, do I need to round the edges or can I just cut them with the jigsaw and leave them as is?

I'll post pics as soon as I get to my apt. I'm in the process of moving now

[soho54]

do I need to round the edges or can I just cut them with the jigsaw and leave them as is?

That is completely up to you. It's like taking 10lbs of sound deadening out of you car to make it faster. How big of a perfectionist are you?

You don't have to, but it won't hurt. Will you be able to tell a difference? :huh:

[Inu_Yasha]

The main question is would there be an audiable difference or not. I heard that some ports sing if they aren't rounded so I figured that the braces would if I didn't round them.

Also, what is the best way to post pics to the site? I was going to upload like 3 or 4 pics?

[ThomasW]

The best way to show pics is by posting a link to a URL there the pics are hosted. If your ISP gives you free hosting that's the easiest way. Otherwise use one of the free online hosting services. Google and you'll find dozens.

Or you can simply attach pics (files) using that option when you make a post. Those those need to be fairly small (100k I think?) or our server won't accept them.