Very low budget sub.

**mgboy** · **02-01-07, 02:20 PM**

Well I already have the $25 driver, so I guess I'll have to work with what I have. And I always like to try new things and experiment. So, PR's do that job.

18*18*45 box, with the two PR's on the sides of the ED sub.

** Wait, you said 'tune' the PR's? How does that work?

**BoomieMCT** · **02-01-07, 02:24 PM**

Quote:

mgboy wrote:

Well I already have the $25 driver, so I guess I'll have to work with what I have. And I always like to try new things and experiment. So, PR's do that job.

18*18*45 box, with the two PR's on the sides of the ED sub.

** Wait, you said 'tune' the PR's? How does that work?

Instead of using a column of air as a "spring", a PR uses a column of air's equivalent mass. Each PR will have a bolt that you can remove and add washers until it is the proper weight. It is actually very easy. For tuning you just install the PR's backwards so you can easily get to the washer bolts. When you get them set right, just flip the PR's around and re-install.

PR's are neat and I'm always tempted to use them. Every time I do I end up doing cost calculations and wussing out and just using a design with a larger port.

**mgboy** · **02-01-07, 02:27 PM**

Ooh. I'd definatey need some help with that. >_> Also, would I have to buy more washers?

**BoomieMCT** · **02-01-07, 02:34 PM**

Check out this link - tuning isn't as hard as it sounds. I don't think the PR comes with washers, but the bolt is just an M5 bolt so you should be able to get washers at any hardware store.

**mgboy** · **02-01-07, 02:46 PM**

Thanks, that link helped a lot.

* Hmm, I was doing it wrong, and when I plugged in the right numbers, I get something crazy like 23 lb's on each PR. What am I doing wrong?

**BoomieMCT** · **02-01-07, 02:50 PM**

No prob. diysubwoofers.org is "da bomb".

**mgboy** · **02-01-07, 03:49 PM**

See my edit, I keep on getting some insanely large numbers.

**BoomieMCT** · **02-01-07, 03:59 PM**

Quote:

mgboy wrote:

See my edit, I keep on getting some insanely large numbers.

I don't know. To be honest, I always just use Unibox and let the computer crunch the numbers. Without seeing your work the only thing I can suggest is that you double check that all your units match up (esp. for the density of air).

**mgboy** · **02-01-07, 04:10 PM**

Well, I did it for just one PR (instead of two) and came up with 1307 grams, which is like 2.88 lbs. That has to be way too much, I mean, they sample driver they used was like 280 grams, which is less than a pound.

Can it support ~ 3 lbs on the bolt? < Dumb question. I know it can, but it still seems like a lot.

**BoomieMCT** · **02-01-07, 04:22 PM**

Quote:

mgboy wrote:

Well, I did it for just one PR (instead of two) and came up with 1307 grams, which is like 2.88 lbs. That has to be way too much, I mean, they sample driver they used was like 280 grams, which is less than a pound.

Can it support ~ 3 lbs on the bolt?

Well, according to the spec sheet the stock mass is 200 grams and the maximum moving mass is 500 grams (total, I assume). So, if the tune you are trying for requires 1307 grams then you may need three PR's, buy a 15" Dayton DVC PR or a TC-Sounds PR or change the tune of the sub.

But first let me double check my math - I'll get back to you in a few hours (since I have to wait to go home first).

BTW, what tune were you using?

**mgboy** · **02-01-07, 04:27 PM**

22Hz. >_> I really want it, but I may just stick iwth a port if I'm going to have to get multiple PR's.

**BoomieMCT** · **02-01-07, 04:35 PM**

If you really want to keep this "very low budget" I saw somewhere that someone had made their own PR's from speaker surrounds and MDF. Apparantly it worked pretty well down to 20 Hz or so (when it started flapping).

**mgboy** · **02-01-07, 04:37 PM**

lol, No that's okay. But that's pretty ingenius.

**BoomieMCT** · **02-01-07, 05:12 PM**

Okay, here is a first stab at this. First off, I made the input power 200 watts as that is the most RMS power the driver's voice coil can take (don't max out your amp). I used 170 liters (6 cubic feet) as the size of the enclosure. Here is a plot of the EHQS-12 driver with two of the cheaper Dayton 12" PR's. One has no additional mass (which results in a 30 Hz F3), the other has 300 grams extra weight on each PR (the most it can take). That one is tuned too low and results in an F3 of 43 Hz.

As a note (not included), the low mass one barely exceeds driver excursion on the active driver at 25 Hz, but the PR exceeds it at 30 Hz. The high mass one had all kinds of excursion problems starting at 50 Hz.

**BoomieMCT** · **02-01-07, 05:26 PM**

Here is what I mean. Some of these excursion problems go away by using a smaller box and/or adding a third PR. I haven't yet gotten the driver to not overexcurse below 25Hz no matter what I do (for PR or ported).

I'd almost be tempted to experiment with a sealed box with an aperiodic vent.

**mgboy** · **02-01-07, 05:26 PM**

Hm, What about a 5 ft^3 with a 22hz port? Still lots of overexcursion?

**mgboy** · **02-01-07, 05:32 PM**

What would that vent do exactly? If sealed is what I have to do to get down to the lower 20's without exploding, that's fine I guess.

**BoomieMCT** · **02-01-07, 05:35 PM**

Here's the best I can do so far: 3 PRs, 144g in washers on each, 100L box.

**BoomieMCT** · **02-01-07, 05:41 PM**

Please note that I am by no means an expert here - maybe someone else can pipe up with an idea. I have built a sub that had a similar class driver that has the same excursion pattern at about 23 Hz. It sounds fine as long as I don't feed it movies with real real low bass.

I'm just concerned about your desire to go lower then 27Hz and stay "very low budget".

Also, if anything else, this would make a decent sealed sub in a 1.8 cubic foot box.

**BoomieMCT** · **02-01-07, 05:51 PM**

Quote:

mgboy wrote:

What would that vent do exactly? If sealed is what I have to do to get down to the lower 20's without exploding, that's fine I guess.

I have heard that an aperiodic vent will give a sealed sub a bit more low end extension, but no one seems to know how to model them except with trial and error. I also doubt it would get you to the low 20's.

**BoomieMCT** · **02-01-07, 06:11 PM**

I am a moron. I was getting too hung up on the F3 and ignoring all the other stuff. Here is a 4.2 cubic foot box with three PR's with 300 grams on each (closer to what you calculated in post #34). It looks pretty good across the board and should get you close to 20Hz.

Let this be a lesson in not chasing one metric!

**mgboy** · **02-01-07, 06:18 PM**

What happens when only two are used?

** Edit: Could you model a 16*16*36 (= 4.23 ft^3 ) sealed? I can't get WinISD working for the life of me.

**BoomieMCT** · **02-01-07, 10:37 PM**

Just two would be like a higher tune. For the 4.2 cubic foot box it looks like the attached. A 6 cubic foot box is earlier. A sealed box of the same size looks like a sealed box with an F3 of 55 Hz (see post 44).

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