Need Help with DIY Subwoofer Selection

[Argroft]

Lots of great info shared here from the group Argroft!

Personally speaking for the size you are thinking I like the CSS SDX-12. It has loads of Xmax and works well in sealed or vented/PR applications.

There are a number of users of that sub both here and other places.

The Dayton Ultimax is a good comparable alternative but enclosure size will go up quite a bit.

This is the only part of speaker building I have come to hate, choosing a driver/design. I tend to research everything to death before making a decision. I was looking into the CSS SDX-12 you mentioned and it looks to be a promising contender, however, I don't have the knowledge to design an enclosure for it to fit my needs (I can be very needy!). If you could recommend a tried and tested build for the CSS SDX-12 or even send me in a direction to design my own it would be greatly appreciated!

 

[rojo]

@rojoAs far as bracing goes, how was that being implemented?

I figured 3/4" MDF for the box and brace. 19.5" external height and width would mean an 18"x18"x0.75" brace behind the sub. If I recall correctly, I was figuring just cut a 12" hole in the middle of the brace and mount it behind the driver, parallel to the front baffle.

I was using Torres Box Tuning Calculator to determine the displacement of the port. I don't recall exactly what it figured, but Wolfram Alpha says a 4" dia * 26 11/16" tube has a volume of ~0.19ft³. Of course that's not taking into account what schedule pipe you use or the added volume of the couplers on an elbow; but neither is it taking into account 3/4" of the tube being inset into the baffle. In any case, as Swerd said, there's a pretty forgiving margin of error with a vented sub build. You're not building a particle collider.

This is the only part of speaker building I have come to hate, choosing a driver/design. I tend to research everything to death before making a decision. I was looking into the CSS SDX-12 you mentioned and it looks to be a promising contender, however, I don't have the knowledge to design an enclosure for it to fit my needs (I can be very needy!). If you could recommend a tried and tested build for the CSS SDX-12 or even send me in a direction to design my own it would be greatly appreciated!

The CSS SDX12 is an excellent driver; but for vented subs, the port length tends to be unreasonably long for the necessary enclosure size. I think unless people build the SDX12 into a sealed enclosure (as I did), they usually do passive radiators. An SDX12 + a passive radiator far exceeds your requirement of staying below $200.

 

[Argroft]

Ok, assuming I'm using schedule 40 pipe for a port, the added volume of the pipe itself (not including added material in the elbow) is less than 0.014ft³. I don't see that playing any significant roll in anything. So I think I'll stick with this original plan (since it IS well within budget) and get the ball rolling on it sometime soon-ish and hopefully I'll get around to making a post as to how it turns out, that is after I clear the woodshop of all current projects (DIY kayak roof rack, speaker stands, refinishing furniture). Yeah, it's a bit hectic in there.

Also, I noticed that the SDX12 was a more expensive driver than I was looking for (not to mention a passive radiator yet) after I made a reply. I was having some difficulty locating a price on it, I'm sure it's a great driver, but it's something that will likely wait for something (much) further down the road.

@rojo Thank you for verifying the enclosure specs for me, I'm itching to get started! After all my other projects that is. I'll consider this some much needed motivation to get them done!

 

[rojo]

Excellent! I hope you'll start a build thread and post in-progress pics. Judging from the bookshelf speakers and stands you showed us, you are an exceptional craftsman!

 

[Argroft]

While I'm thinking about it, when it comes to driver and port location in the box, where are the ideal places to locate them? Should they both be facing out front or driver out front with the port in the rear or even a down-firing setup?

 

[annunaki]

Ok, assuming I'm using schedule 40 pipe for a port, the added volume of the pipe itself (not including added material in the elbow) is less than 0.014ft³. I don't see that playing any significant roll in anything. So I think I'll stick with this original plan (since it IS well within budget) and get the ball rolling on it sometime soon-ish and hopefully I'll get around to making a post as to how it turns out, that is after I clear the woodshop of all current projects (DIY kayak roof rack, speaker stands, refinishing furniture). Yeah, it's a bit hectic in there.

Also, I noticed that the SDX12 was a more expensive driver than I was looking for (not to mention a passive radiator yet) after I made a reply. I was having some difficulty locating a price on it, I'm sure it's a great driver, but it's something that will likely wait for something (much) further down the road.

@rojo Thank you for verifying the enclosure specs for me, I'm itching to get started! After all my other projects that is. I'll consider this some much needed motivation to get them done!

You must account for the volume of the vent including the air inside it when factoring for displacement of a vent. If it is not accounted for the tuning will be off. Volume of a cylinder is pi*r2*L

 

[rojo]

... Wolfram Alpha says a 4" dia * 26 11/16" tube has a volume of ~0.19ft³.

You must account for the volume of the vent including the air inside it when factoring for displacement of a vent. If it is not accounted for the tuning will be off. Volume of a cylinder is pi*r2*L

Shh! Don't get him started second guessing the dimensions again. The displacement of the vent has already been accounted for, even if OP was mistaken in his verification. It'll work out.

While I'm thinking about it, when it comes to driver and port location in the box, where are the ideal places to locate them? Should they both be facing out front or driver out front with the port in the rear or even a down-firing setup?

Driver and vent orientation aren't critical to the sub's output. If you do down-firing, you'll need to add another 4 inches of height for the legs. If you do front-firing, you might want to build a grille (just a thin wood frame {baseboard quarter-round?} with acoustic fabric stretched over it, maybe held in place with some rare earth magnets from Harbor Freight). You might also consider doubling-up on the front baffle so you can flush mount the driver.

I recommend having both the driver and the vent exit on the same baffle if you can in case you want to corner load the sub in your room. I'm not sure what the diameter of the vent cut will be after you flare your PVC pipe, though. You might need to mount the driver and the vent toward opposing corners, rather than having the driver centered. (18" H x 18" W gives ~25.5" diagonal across the front baffle internally.) Of course if you prefer, you could do what Chongdigga did and just router the flare into the wood.

 

[Argroft]

You must account for the volume of the vent including the air inside it when factoring for displacement of a vent. If it is not accounted for the tuning will be off. Volume of a cylinder is pi*r2*L

I was already incorporating the vent displacement into things, I only figured the displacement of the internal volume though. That being said, I was just curious how much space the actual vent (just the plastic) took up, which it seems is a rather negligible number. So as long as I factor in the internal volume of the port at the very least I should be close enough to obtain the results I'm looking to get.

 

[Argroft]

I recommend having both the driver and the vent exit on the same baffle if you can in case you want to corner load the sub in your room. I'm not sure what the diameter of the vent cut will be after you flare your PVC pipe, though. You might need to mount the driver and the vent toward opposing corners, rather than having the driver centered. (18" H x 18" W gives ~25.5" diagonal across the front baffle internally.) Of course if you prefer, you could do what Chongdigga did and just router the flare into the wood.

Am I correct in assuming that I can change the shape of the box to say, a rectangular prism to gain height on the front baffle as long as the internal volume stays the same? Or is it better to use a cube? Because of the way I designed my other speakers, I am against the idea of offsetting the driver and vent from center because I won't be able to keep the same pattern for all of the enclosures in the system.

That's a shot of my newly finished center channel. This is the design scheme I'm trying to keep. And before anyone asks, I built the dresser it's sitting on as well.

As far as a flare cut into the wood instead of the pipe, is there a general standard for the radius of the round over? I could do up to a 3/4" radius or anything smaller. The only thing I will have to find a workaround for is how to finish the port since it will be mounted into a piece of veneered mdf. I'll probably just end up flaring PVC then trimming it and flush mounting it to fit.

 

[rojo]

Yeah, you can make it taller and narrower if you wish as long as the net volume stays the same. It doesn't have to be a cube. You could even make it down firing and make it look like an end table if you wish. Do a Google Image search for "subwoofer end table" to see what others have done.

As far as radius, there probably is a standard radius, but I don't know what that would be. Invoke the "this isn't a Hadron collider" rule and you'll be fine.

 

[annunaki]

I was already incorporating the vent displacement into things, I only figured the displacement of the internal volume though. That being said, I was just curious how much space the actual vent (just the plastic) took up, which it seems is a rather negligible number. So as long as I factor in the internal volume of the port at the very least I should be close enough to obtain the results I'm looking to get.

I see. It is usually easier to just use the outside dimensions of the vent and then factor volume. Sorry for any confusion.

 

[annunaki]

Am I correct in assuming that I can change the shape of the box to say, a rectangular prism to gain height on the front baffle as long as the internal volume stays the same? Or is it better to use a cube? Because of the way I designed my other speakers, I am against the idea of offsetting the driver and vent from center because I won't be able to keep the same pattern for all of the enclosures in the system.

That's a shot of my newly finished center channel. This is the design scheme I'm trying to keep. And before anyone asks, I built the dresser it's sitting on as well.

As far as a flare cut into the wood instead of the pipe, is there a general standard for the radius of the round over? I could do up to a 3/4" radius or anything smaller. The only thing I will have to find a workaround for is how to finish the port since it will be mounted into a piece of veneered mdf. I'll probably just end up flaring PVC then trimming it and flush mounting it to fit.

A rectangular prism is just fine. The driver need not be centered on the baffle either.

Also a 3/4 round over would work very well. Otherwise you can buy the flared ends from parts express or other sites.

 

[Argroft]

Ok, I really like the idea of essentially hiding the subwoofer in plain sight, but how does that work when it comes to placement? I am not wild about having a random end table sitting in a corner or in an odd location in order to achieve the best sound. That being said, is it possible to get a good sound if I were to say, place it next to the listening position? And I'm not sure about what would happen to things sitting on a table with a sub hiding in it, would they vibrate off or is that the idea behind building a solid, heavy duty box to keep the external walls from moving? As I said, I really like the idea of using furniture to hide the box, but then again, I like the idea of having it as a stand alone item so that I can place it where I want it. If I could guarantee good results from a downfiring sub placed anywhere in a room, I would do it in a heartbeat. On that note, is there a benefit to making 2 end tables with subs and placing them on opposite sides of the listening position. Or better yet, I could make 2 end tables, one with a sub and the other with a finished enclosure for a sub that way I have the option should the need arise (and since I will likely need 2 end tables anyway). Thanks in advance on any input on this idea, I really like where this project is headed!

 

[annunaki]

It is really your call. If you have any sub right now I would recommend doing a little testing first to help narrow down the options.Borrow one if you can if you do not have one.

As you are finding out the world of loudspeaker design and engineering is one filled with compromises. Design goals are important so that you know what compromises you can likely make and which ones you cannot.

 

[Argroft]

I don't have a sub nor do I have access to one. I'm relatively new to speaker building, but figured I'd start with a relatively decent system (for a first build) since I do have the skill to make the enclosures. Since I started this thread, I think I have a definitive list of goals: must be a down firing setup for use in an end table design, must provide adequate output for a medium/large room (I don't have a room for it yet, but was thinking something like 12'x14' as a rough estimate), preferably a ported design with tuning that will be good for bot HT and music, and an enclosure volume not to exceed 3 cubic feet. So far from the way things look, the dayton sub @rojo picked out for me seems to for the bill, so unless anyone has any input as to why it couldn't be used to meet these goals, I think it will be my design of choice at the moment. I think I can design and build a decent table enclosure to fit my needs because I really do like the idea of a functional enclosure. So if anyone has any suggestions or objections, I'm all ears. If not, then I'll proceed with this route. Thanks!

 

[rojo]

Sounds like a plan! And if down-firing, you can stick with the 19.5" cube and add 4" legs since centering the driver on the baffle will no longer affect the aesthetics. I think 23.5" is a reasonable height for end tables. I just measured the height of my living room end tables at 23", and they're about an inch or so lower than the arms of my couch.

I'd suggest building a matched pair, then adding the second driver to the other enclosure when budget allows. Having dual subwoofers will help even out room response so you won't be so limited by placement. Besides, end tables generally come in pairs anyway.

Re: putting a lamp or something on top of the end table, just use a little cut of rubber shelf liner under the lamp. Dollar General sells rolls of it for ~ 3 bucks IIRC.

You should go ahead and jump on one of those Crown amps since they're on closeout pricing. They might not wait around for you to get ready to begin your project. BH Photo Video | Musician's Friend

 

[Argroft]

You should go ahead and jump on one of those Crown amps since they're on closeout pricing. They might not wait around for you to get ready to begin your project.

About those, what's the best/ easiest way to hook that up to a typical home AVR? I was reading somewhere that since they are professional amps they don't just plug and play with your typical consumer AVR, but I never got a clear understanding of how to hook the two together.

In other news, I think I have a design down for this thing:

I was aiming for something aesthetically pleasing that didn't have the need for false doors/drawers, but also matched my current speakers. It uses the same vinyl/mahogany/stainless steel rods to make it, so I think it will definitely have a unique look. Thoughts on it are welcome as I'm not totally sold on the vinyl and wood look since it may not be easy to match it to anything else.

 

[rojo]

Aw snap! That's pretty sharp, man. I'd probably make the top piece smooth solid wood, though, just because it'll be easier to Pledge / lemon oil, and you won't get crumbs stuck next to the steel rod you have to pick out with something pokey every week.

The Crown amps have RCA inputs. Nothing to worry about with AVR connections. The Behringer iNuke would've required a little more planning, but with the Crown, you're already golden.

 

[Argroft]

Yeah, I've considered making the top solid, I designed the top before adding the black to the sides, so I needed something to offset the wood. I think it would probably be look ok solid tho. The gap under the unit is 4.75" at the highest point and is about 14" wide. I assume this should be sufficient for air flow?

And as for the amp, I was reading that there was a leveling issue when using the output on a home avr and the rca's on the crown amp, but I may be wrong. I just have a single jack for a sub output, looks like an rca jack except it's black.

 

[rojo]

Yeah, you've got plenty of space for air flow.

Just plug a single RCA cable from the AVR into channel 1 of the Crown, then set the Crown to Bridged Mono mode. Or, use a Y cable from AVR to Crown (like this one, for example) and set the Crown to Stereo mode if using two subs and you need independent level control for each sub. Either way, leave the crossover setting bypassed and let your AVR handle the low pass filter. I haven't heard of any leveling issues, and haven't seen any complaints about the performance of these Crown amps. The only suggestion I can offer is that the knobs on the front of the amp are intended for adjusting gain, not volume. They're there to compensate for varied input voltages. Start with them at 12 o'clock and adjust as needed. Also, AVR auto correction (Denon and Marantz in particular that I know) often sets the LFE channel output too conservatively. After having my AVR run its sweeps, I generally have to go into the settings and increase the LFE volume +8dB or so. Anyway, getting a look at the manual might help you relieve a bit of anxiety and solve the mystery of how it's all going to fit together.

Hey, I was just re-reading this thread and realized I haven't shown you any pretty graphs. Here's the predicted response of the Dayton 12" DVC in a net 3 cubic foot box tuned to 19.5Hz. Keep in mind that a jackhammer is about 110dB, and there will be in-room gains added to these predictions once you get them built and playing.

SPL@1m anechoic for 300W, 150W, 75W, 37.5W, and 18.75W

Cone excursion for 300W -- Driver Xmax is 15mm, reached near 16.5Hz

Vent air velocity in meters / second at 125W

Impedance

Group delay