Building a Subwoofer.

[Volitions Advocate]

My Amp: HERE
The Sub that goes with it: HERE

the Subs are discontinued which means I have to build my own.  Which is okay because it'll be less than half the price.

I've tried it with a Bass guitar amp and it sounds friggen amazing.  But since most bass amps wont fit the form I need it to be to sit next to my half stack underneath my combo amp I"ll have to make one.  At first I thought I coudl just make a subwoofer like most car stereo enthusiasts do. Just make the box, but the subs in and grab one of those car stereo amps and screw it into the side of the enclosure, and somehow wire up a 1/4 inch jack to it.

But then While Jack was helping me find replacements for those speakers that I blew he directed me to Parts Express (thanks jack!) and i Found this: Subwoofer Amplifiers

Awesome! must be just what I need and more suited to what I'm planning on doing.
So I narrowed it down to THESE TWO amps to keep up with what rivera used as spec. 500W.

The Problem is neither of these have a 1/4 inch jack. I'm assuming because they're made for home theatres or something.  Does anybody know of some sub amps that have a 1/4" input?  Or would it be easy to wire one in somehow?  Or maybe just getting a little adaptor cord would be the best solution here.

And once thats figured out, what drivers do you think I should use? JBL, Eminence?  What do you think would work best?
thanks in advance for the help.

 

[Patrick from Davis]

The box works out to be a little tougher that just slapping in speakers and going.  I am guessing that you will not be building a ported cabinet.  These are tuned to a frequency with the port/speaker combo.  Generally you get into Thiele-Small (dunno if I spelled that correctly) specs to port it correctly.  If you make a sealed cabinet, and yes, you want the air not to move, you want to cover the surfaces with insulation/cotton to lower any errent noises inside the cab.  Do not make a cube, keep the Height-Width-Depth lengths all different if possible.  It tends to cut down on the rattles from vibrations and echos and such.  There are some sites that tell you some go to sizes for cabinet design out on the web.  Either that, or measure one of those Riveria cabs.  Use silicone to keep the thing from leaking at the wood joints, and use the gasket that comes with the speaker to keep that joint sealed.  If you get no gasket with the speaker, you have to make one with some rubber or gasket material that you buy from somewhere.  The cut out for the amp in the cab should also get a sealant layer.  The amp it's self appears to have banana plug audio adapters for the inputs on the high level inputs and RCA jacks on the other ones.  If you look up Banana audio jacks you will find a ton of brands.  Also, although it might kill your back moving things, high density particle board was the go to material in sub woofer cabs for cars and home audio.  It is dense hard and does not vibrate or hum when you put a lot of low frequency noise through it.  And Cheap, but it got the job done.

I worked at a place that made Sub woofers for cars for a while, hard not to pick up a few things...
Patrick

 

[-CB-]

You can effectively increase the range by one octave down, if you tune the sealed box according to the Thiele and Small parameters, box volume, speaker specs etc.  This works great, and I've seen it done on the old Dual Showman cabinets with outrageous success.

That said - subwoofer woofers are usually not suited for bass guitar.  You need a rather long throw yet fairly modest range in frequency. 

You need to impedance match the amplifier for the sub to the source... your amp.  Most amps have "line level" expecting about one volt or slightly more input, and fairly high impedance (medium high actually).  Guitar amps are very high impedance inputs.  So... you might need to do some gymnastics to get that going.

 

[Volitions Advocate]

I'm not sure about how to work around the impedance.

I know the line out for the subwoofer isn't powered, thats why the subwoofer needs its own amp, I didn't realize you'd want the impedance to match up.  My 412 cab is 8 ohm so thats why my amp is set to, so that means I need the subwoofer to be 8 ohm as well even though its not powered by the head?  I dont know about the input on my amp but if i remember correctly my sub output is something like 560 ohms. (I can't check right now its down at the rehearsal space)
As for the woofers, i'm not really using them for bass guitar.  I just tried it out with a bass guitar amp to see what it sounded like.  I'm thinking with a non-specialized subwoofer it might sound even a bit better than a bass amp.

I can also call Rivera and ask them about what they used.  I'd hope they'd be happy to help seeing as how they wont make them anymore.  And everytime I've phoned I've gotten Paul Rivera Jr. on the phone and he seems like a pretty cool guy.

EDIT:  Oh, and where can i find some literature about this Thiele and Small business?

 

[-CB-]

line out for the subwoofer

My 412 cab is 8 ohm so thats why my amp is set to, so that means I need the subwoofer to be 8 ohm as well even though its not powered by the head? 

EDIT:  Oh, and where can i find some literature about this Thiele and Small business?

a.  You said line out - ok then those amps should work, just keep in mind many amps are cheating in the rating of their wattage

b.  Once you go line out for sub, thru a sub amp... your speakers must match THAT amp, irrespective of what the speakers in the main amp are.  Apples and oranges... no correlation.  However.... you may need to reverse the phase on the speakers to get that all lined up and not self defeating.

c.  Do a google on T&S parameters.  As I'm remembering we took a piece of 2 inch PVC about oh... five or six inches long and sealed it in to the front of the cabinet (off axis).  The problem with that is... once you get this big ol wave coming out... your cones start moving like crazy.  For that reason, guitar speakers are NOT used with ported cabinets, except by derating them quite a bit (about 1/4 of the output).  Sound reproduction speakers, or speakers with huge throws should be used.  BTW... we used JBL D-120F's... but volume levels were kept in the "easy listening" range, and the bass was solid, but not cranked.  He'd have done better with a set of EV's.

 

[Volitions Advocate]

Re A: and B:

Yeah okay thats what I figured, 

as for C:

man this is confusing, I can't make much sense of it. Although i did find a calculator on a website somewhere. I suppose I'll need to figure out what woofers I'd actually be using and plug those values in.  But then I have to figure out what to do with all the values it spits back at me.  I havent seen so much Formulae since I took physics in grade 11.

 

[Patrick from Davis]

Yeah, it was way more complex than I cared for as well.  The sealed cabinet is much easier and while it doesn't have some of the tuning benefits of the ported cab, it is much easier to build and much less of a headache with the calculator.  Really, the main reason we futzed with them was to tune the sub cabinets to the freq that shook the camper shells on the trucks the things were going into.  Also, this was a good decade or more ago so things might have changed.  I went from subs to biochem in that period of time and didn't look back.
Patrick