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I'm a newbie in need of direction on tuning sub to 20Hz...

#1
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2/7/09 at 4:19pm
  • Joined: February 2009
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Where can I find information on this site to help me build my powered sub enclosure?

I'm not only a newbie to this site but also a DIY newbie, tossing out my Sony Home Theater IN-A-BOX for a quality Yamaha receiver, and built myself a set of Hivi tower speakers (1.5" thick, dual 5" mids, 1 tweet and 1 8" ported mid bass) and a dayton MKIII 15" sub with a dayton 1000 watt (supposedly) rack amp.

I wan to build the sub enclosure ported and have it tuned to 20Hz, maybe less. I keep coming up with outrageous port lengths (even for dual 4" ports).

Any help would be greatly appreciated!
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#2
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2/8/09 at 9:47am
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Re: I'm a newbie in need of direction on tuning sub to 20Hz...

Oh, also, is there a certain size that my ports HAVE to be? Can I do two 4" ports or do I need to stick with a single 3" port? I was going to put it in a sealed easy to build box, but after reading some comments on here, it seems I can get a lot more LF bass out of the sub in a well designed ported box.

Thanks!
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#3
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2/8/09 at 7:57pm
  • Joined: August 2000
  • Location: Southaven, MS
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Re: I'm a newbie in need of direction on tuning sub to 20Hz...

Porting a subwoofer is a bunch of compromises. You are coming up with outragous port lengths because you are not making your box large enough when modeling the driver. I like 160L tuned to 18hz. Yes, the dual ports will be almost 3' long (each). To tune the sub that low you have to have a large box. You can use shorter ports if you want to tune higher (not recommended) or use smaller diameter ports (again, not recommended). Another option is to use passive radiators but that just increases the price.

-Robert
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#4
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2/8/09 at 9:27pm
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Re: I'm a newbie in need of direction on tuning sub to 20Hz...

Thanks Robert. I read older posts of yours regarding this topic. What is 160L? 160 liter?

How big would my box need to be to be able to house the 15 and two 36" ports? I don't really want the port sticking out of the box, so obviously at least a 36"i.d. long box. Is there an optimum shape that I need to go for? Also what size dual ports? 3" or 4"?

Thanks so much in advance for the info!
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#5
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2/9/09 at 6:20am
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Re: I'm a newbie in need of direction on tuning sub to 20Hz...

L = Liter
CF = cubic feet

You can make the sub as large as needed. If you want straight ports then you need at least 40" (length of port + the port diameter) in one direction. You can put elbows on the ports to curve them so that you don't need one dimension that long. This is DIY so it is entirely up to you.

Shape means nothing to subs. Cube, rectangle, cylinder, etc. Pick it.

4" ports. 3" ports will chuff like crazy. 4" is still smaller than optimum. These subs move massive ammounts of air so you need to let it flow freely.

-Robert
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#6
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2/9/09 at 2:46pm
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Re: I'm a newbie in need of direction on tuning sub to 20Hz...

Thanks a lot Robert. So, if I want to build a 160L box, tuned to 18Hz for my MKIII sub, what would be the ideal port size/length & amount of ports. I have no problem figuring the SF of the enclosure, but not too informed on how much to subtract for port volume and all that. I have 3 sheets of .75"MDF in mt garage and all the tools needed for the build. Is the 160L the area after the sub and ports are subtracted?

Thanks for the info....I'm enjoying learning a new hobby.

Chad
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#7
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2/9/09 at 10:29pm
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Re: I'm a newbie in need of direction on tuning sub to 20Hz...

When discussing any speaker enclosure, the volume is always net. You have to subtract the amount of space the driver, ports and any braces take up.

When I modeled the 160L enclosure, I was using dual 4" ports that were 34" long each. To determine how much space the ports occupy you use basic geometry. Pi*r^2*L where r is the radius to the outside of the port and L is 34. Use appropriate formulas for the bracing as well.

Finally, for proper construction techniquest take a look at this design. Very good use of bracing.

-Robert
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#8
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2/12/09 at 8:34am
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Re: I'm a newbie in need of direction on tuning sub to 20Hz...

Thanks Robert. So I think I've decided to go the "coffee table" route so I can get the 5.6CF and have enough space for the long ports and plenty of bracing. I have two more questions:
1. Is there any advantage or disadvantage of having the sub down firing opposed to a forward facing setup?

2. Would I be better off going with one 6" port 37.5" long instead of two 4"X34" ports? My calculations (if I did them right) show that the single 6 inch port displaces more volume than two 4" ports.

Thanks!

BTW, this page was a great help in doing my calculations!
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