Guide to Sub box Design

**Danny** · **05-06-06, 01:55 AM**

Just thought I'd do a quick post about the general rules of Sub Box Design.

1. length, width and height all need to be different.

2. Angled Baffle - this is normally done on smaller boxes so the driver will fit on one surface.

3. Although it doesn't really matter where you fire the sub from it is ideal to fire it backwards or upwards ( & backward a bit though)

4. when building it use MDF at LEAST 16mm thick and build it Rock- Solid.

5. Difference between ported and sealed enclosures - Ported generally has a lower Frequency response however is more complicated to build than a sealed enclosure and really to get it to sound good you have to be as close as possible in your measurements and your design has to be good. Ported designs are also more efficient than sealed enclosures, so if you had 2 drivers that are the same and one was in a ported box and the other was in a sealed box the driver in the ported box would be louder
Sealed is easy to build and design but is just not as good as ported.

If I've forgotten anything let me know.

**Exocer** · **05-06-06, 09:11 AM**

Hey Danny,
Great post! There are some things that were left out though.

Also when building a sub box, bracing is never a bad idea,to help get rid of resonances. Window bracing takes up hardly any internal volume but greatly increases rigidity of a box. Some people will go as far as double up on all the walls, and if a beefy driver is being used, the front baffle may even be as thick as 3 layers of MDF (mine is 3 layers, 2 for mounting and 1 for the countersunk look). Sealed boxes are generally smaller than ported boxes. Reason being, the laws of physics...Ported subs just require more internal volume to hit low tuning frequencies.

(Sealed corner-loaded subs are my favorite) Any properly sealed sub will have the advantage of a 12db/octave rolloff which when corner loaded can have more of a tactile effect on bass as room gains helps boost those lower frequencies. On top of that, you get away with a smaller box. Vented allignments will have a 24db/octave roll-off belowing Fb (tuning point/enclosure resonance) and in most cases should be accompanied with a high pass filter to protect the driver below its tuning point (where the driver can easily exceed x-max and destroy itself if designed properly). So as you see, vented subs have a steeper roll-off once they hit they're tuning point.

When designing a vented allignment, the port must be placed at least its own diameter away from any internal walls to prevent conflicts. Also, the port MUST be the proper length and diameter to prevent what is called port chuffling. Port chuffling occures when air passes through the port at a speed where port velocity becomes audible during listening sessions, usually those high excursions deeper frequencies that require more air to be moved. Vented enclosures are much easier to get a desired extension from, all you do is model it in a program like unibox and select what tuning point you would like. Not all vented subs go deeper than all sealed subs though. Those with larger enclosures generally will go deeper than a sealed because of it's larger cabinet allowing it to be tuned for a low frequency.

Proper application of a vented box is when you need a more efficient louder design to fill a relatively larger space. Ported subs can also be used in smaller rooms as well. Sealed subs however must be in a smaller room to take advantage of low roll-off characteristics. Since sealed isn't as effecient it will take more amp power to get to the same DB levels as a ported which is why a smaller room would be easier for a sealed sub to fill.

People say sealed subs are more musical than ported subs. I have no way of testing this but I do know I probably will not be going back to a vented sub. Personally I prefer sealed speakers overall. Even the rest of my HT consists of sealed speakers.. I find that they have a particular tonal quality that I like.

If one wants an extremely low tuning point that will require a large diameter and long port I would suggest designing a sonosub like Steve Callas's awesome beast. They just lend themselves better to long/wide diameter ports.

**Danny** · **05-07-06, 04:59 AM**

Sealed boxes are definately way smaller that the ported designs. For my sub it was either a 59.5Lt ported box or a 28lt sealed. also one thing that I forgot to mention in my other post. For ported designs the port is generally tuned to the resonant frequency of the driver that your using.

Thanks to Exocer for pointing out those things I'd forgotten

D.

**bobgpsr** · **05-07-06, 11:40 AM**

Quote:

Danny wrote:

...length, width and height all need to be different...

This is a very good rule for normal speakers as it helps to avoid internal resonances. In fact there are certain ratios that are preferred as described in speaker building books. For subwoofers this factor is not so critical as the sound wavelengths involved are far beyond the enclosure dimensions. At least for any normal design when 15 cubic foot or under volume is used. Several of the sub building gurus have recommended cubic box dimensions (equal) for some of their plans.

Bob

**Brian Bunge** · **05-07-06, 09:32 PM**

Yep, I'm with Bob. #1 is not a concern for subwoofer design. I've built a number of perfect cube boxes, including the little 13" cube box I've got sitting in the living room right now. Which reminds me, I need to get some pics of that thing! It does look kinda funny sitting next to my 200lb. left front speaker though!

**Exocer** · **05-07-06, 11:34 PM**

hahaha Brian, I bet! I'd love to see that pic. Oh and I too am using a cube although slightly bigger than yours at 17".

**Brian Bunge** · **05-08-06, 07:36 PM**

I'll try to get those pics up in the next few days. I just finished a pair of my new Micro +'s (3" Tang Band driver and 1" Dayton tweeter) in ribbon mahogany veneer that I need to take pics of as well.

**Exocer** · **05-10-06, 02:40 PM**

ooo Ribbon Mahagony Veneer, sounds beautiful. Definitely looking forward to those pics.

**Brian Bunge** · **05-10-06, 10:22 PM**

Here are the pics of my 13" cube subwoofer. It uses the Dayton RS 10" HO drivers and the BASH 300W amp. The veneer is figured cherry with around 5-6 coats of gloss wipe-on poly (NOT Minwax!) Let me know what you think.

**Exocer** · **05-10-06, 11:55 PM**

I think you've done an outstanding job! I could only dream of getting that nice of a finish.

**Exocer** · **05-12-06, 11:50 PM**

Well another thing to think about are Materials.

MDF = Dusty and requires good dust collection to prevent any messes that will take as long to clean as the routing process lol. Cheap and can be found almost anywhere, HD, Loews, Local lumber yard etc. Easy to use.
HDF = Very nice to machine, and stronger than MDF. Good to use to add mass, to prevent cabinet resonances.
Baltic Birch ply 13 layer = If you can find it void-free would be the prefered wood to use.Beautiful layered edges. Also doesn't make the mess of MDF. Requires sharper tools to cut however.

**Brian Bunge** · **05-13-06, 12:10 AM**

I've only used BB once and it was pretty nice to work with, IMHO. The downside I found was cost and the extra time/materials it takes to layout all of your cuts. Since MDF has no grain, you don't have to worry about grain orientation when cutting your pieces. With BB (or any type of grained wood) you at least have to give it some consideration.

**Exocer** · **05-13-06, 10:48 AM**

Good to know.

The only thing holding me back from my next project is the thought of inhailing MDF dust again...(it sux)I have so much of it just laying around though Id feel guilty buying Baltic Birch for the next PJ. Must get rid of that MDF lol.

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