DIY Subwoofers - General Discussion

**robh** · **09-13-09, 11:05 AM**

I've never heard of transmission line. I'm just starting to get into a lot of this stuff.

Basically, the plan at this point seems to be 4 big vented enclosures with 18s. I do plan on using a sub management system, because if for no other reason, I need something to control the phase since I will have a sub on each of 4 walls.

I have considered that the room might not be capable of it, but I'm also starting room treatment and hope that I can find a way to make it work. If nothing else, the size of the room won't change, and I would at least be able to get a solid 12-14 happening, which will be good enough for the vast majority of music as well as doing pretty well for HT. I'm already seeing semi-useful extension down to 16 Hz (-6 db point) just by using REW, an FBD 1124, a pair of M&K V-125s, and a lot of patience from my wife while I move subs around the room, but no room treatment as of yet. And those subs are spec'ed as having a -3 db point of 20 Hz, which matches up with that I see in REW pretty well.

**chadcummings** · **09-13-09, 11:14 AM**

Since you have all the extra room for the subs, I would look at going with an IB and multiple drivers like the DPL15. For 8 of them you get more SPL and sensitivity than going with 4 18" subs.

**robh** · **09-13-09, 11:22 AM**

**chadcummings** · **09-13-09, 11:31 AM**

Infinite Baffle.

There is another section on the board which discusses it and there are many people who are hard line for and against them.

I myself like the IB and have designed my theater to incorporate one that is much larger than I really need, my addiction.

If you do a google search for the words Cult Infinite Baffle you will find a web site which is dedicated to the topic.

You just need to read and make up your own mind.

**noeffred** · **09-13-09, 01:37 PM**

Putting one woofer into each corner is quite a good idea. Have you thought of building a triangular enclosure to put into the corners? Looks really nice cause it blends into the wall and is pretty simple to build.
Your woman will love this, 'cause there are no boxes standing around!

Take a look at this calculator, it's in German (so it's metric!), but you'll get the gist of it without understanding the words. Basically you enter the width, length and height of your room into the three fields above and the modes for your room will be shown. Click on the checkboxes to select the frequency and look at the simulation on the right. The darker the shade, the louder the bass will be. It'll be clear when you see it.

**chadcummings** · **09-13-09, 01:44 PM**

It may have high WAF appeal but you will lose the capability of putting bass traps in the corners and may find some bad nulls in the room because of this positioning.

**StereoClarity** · **09-13-09, 03:06 PM**

Quote:

chadcummings wrote:

It may have high WAF appeal but you will lose the capability of putting bass traps in the corners and may find some bad nulls in the room because of this positioning.

Even if he's just using these below 50hz with movies? If he had one in each corner he should be able to excite multiple room nodes. I'd imagine the gain from the corners would be substantial as well. He stated that "4 refrigerator size subs probably wont work" so I think integrating them into the corners might be a good idea.

IB might be a good option but he logistics of it might inhibit the actual application. He'd need substantial space behind the woofer and 18" holes would require a severe amount of room alteration. Not to mention the bracing required to support such a thing.

Rob, are you going to be building this on your own? Sounds like a fun project!

**chadcummings** · **09-13-09, 03:10 PM**

If I remember correctly, you gain +3db off each wall so each corner give you +6db per sub.

**StereoClarity** · **09-13-09, 03:24 PM**

Quote:

chadcummings wrote:

If I remember correctly, you gain +3db off each wall so each corner give you +6db per sub.

It's a little more complicated than that but as a general rule I think that's alright. It's also frequency dependent.

**chadcummings** · **09-13-09, 03:31 PM**

Quote:

ItalynStylion wrote:

It's a little more complicated than that but as a general rule I think that's alright. It's also frequency dependent.

You are correct. It is a function of frequency along with the absorption rate of the material around, the temperature and a whole slew of other things.

That is why I stated it as simplistic as I did. It is a general rule of thumb.

Other things to consider is the size, shape and volume of the room. There are many factors that go into the SQ of any system and until you REW it you never know exactly how it will behave.

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