Passive Radiator

[brandinooooo 10+ year member]

I've been thinking since the trunk in my Saturn is small and I only have my hdc3 18" that a passive radiator might be a good option. Does anyone make any custom pr's? Any good companies make them?

What size would I need for an 18"? Most likely the box would be ~6 cubes walled behind the back seat firing into the cab. Has anyone used a pr in this type of application?

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[gckless 5,000+ posts]

Generally you want twice the amount of Vd in the passive radiator as you have in your powered woofer.

 

[cx-7heaven 10+ year member]

Generally you want twice the amount of Vd in the passive radiator as you have in your powered woofer.

Ya, for an 18, you want at least a pair of deep stroking 15 pr's. You can't just toss in a PR in a system and expect it to do amazing things. If you are running ported, then a pr is out of the question, it needs to be a sealed setup. Second, a pr is a great help for a box that is very small for the sub you are running. If you are running a 6 cu.ft. sealed box for that 18, I'm not sure if that is a small box for that sub, more investigation is in order. Also, you want a PR to have a wall to reflect off of, they seem to work better that way.

As far as a recommendation goes, I bought one of these about 8 months ago and it works very well for me:

Earthquake Sound SLAPS12 (SLAPS 15) 15" Audio Passive System

You can make an offer for around 105 for it and they will accept it. The downside to this particular one is that it comes with very little in the way of an owners manual, it is assumed that you already know what you are doing. I will link a thread I created in the DIYMA forum that has the spreadsheet that Earthquake created for tuning it. I had to get a hold of them, and it took a while to get it so here you go:

A tool to tune the Earthquake SLAPS PR's - DIYMA Car Audio Forum

good luck

 

[brandinooooo 10+ year member]

Ya, for an 18, you want at least a pair of deep stroking 15 pr's. You can't just toss in a PR in a system and expect it to do amazing things. If you are running ported, then a pr is out of the question, it needs to be a sealed setup. Second, a pr is a great help for a box that is very small for the sub you are running. If you are running a 6 cu.ft. sealed box for that 18, I'm not sure if that is a small box for that sub, more investigation is in order. Also, you want a PR to have a wall to reflect off of, they seem to work better that way.
As far as a recommendation goes, I bought one of these about 8 months ago and it works very well for me:

Earthquake Sound SLAPS12 (SLAPS 15) 15" Audio Passive System

You can make an offer for around 105 for it and they will accept it. The downside to this particular one is that it comes with very little in the way of an owners manual, it is assumed that you already know what you are doing. I will link a thread I created in the DIYMA forum that has the spreadsheet that Earthquake created for tuning it. I had to get a hold of them, and it took a while to get it so here you go:

A tool to tune the Earthquake SLAPS PR's - DIYMA Car Audio Forum

good luck

The passive radiator serves as the port so using one in a ported box would be pointless. And if I'm not mistaken, you still use the normal ported box size without the port and add the pr displacement. But I could be wrong, it's been a while since I read up on them. Thanks for the link, I'll take a look at it.

 

[cx-7heaven 10+ year member]

Really a pr is just a way to get more LF extension from a box that is to small. You will more than likely lose a lot of output if you are running ported now, and want to replace that with a pr. If you are looking for more output, maybe try tuning higher- say 42 or so?

 

[TaylorFade 10+ year member]

The whole "smaller box" thing stems from the fact that you don't need to account for any port displacement. PR's aren't miracle workers for boxes that are too small to begin with. Although, they are pretty damn good in boxes that are too small. But generally, you'll want them in a box around the same size as a ported.

1.5x the cone area or xmax is the general rule at a minimum.

I've been playing with a pair of 12" PR's lately. The 1cf box with a single 12" and both 12" PR's tuned to 28hz is my favorite. The amount of weight on those things in that box is retarded. Lol.

 

[Falcons 5,000+ posts]

hey taylor fade can you put up that formula you put up on caco?

 

[brandinooooo 10+ year member]

I just got the Saturn and my hdc3 is in my Tahoe back home in 6 cubes tuned to 35. I haven't measured out the trunk to see if I could fit 6+ cubes walled in there yet so I've just been looking at options incase it won't fit. Im also considering getting a couple 8's or something if it doesn't work out.

@TaylorFade how does that box sound?

 

[cx-7heaven 10+ year member]

Nice pr build there. The pr seems to resemble a Sunfire IIRC. You mention that your pr build is very heavy, that is what I like about the earthquake slaps, there is no basket on it. the pr really only weighs a couple pounds . I may have to show off my inventive pr build tomorrow, I call it my bass cube, 8 ID8's with that Earthquake PR. looks funny, sounds amazing lol.

 

[TaylorFade 10+ year member]

hey taylor fade can you put up that formula you put up on caco?

 

[gckless 5,000+ posts]

The whole "smaller box" thing stems from the fact that you don't need to account for any port displacement. PR's aren't miracle workers for boxes that are too small to begin with. Although, they are pretty damn good in boxes that are too small. But generally, you'll want them in a box around the same size as a ported.
1.5x the cone area or xmax is the general rule at a minimum.

I've been playing with a pair of 12" PR's lately. The 1cf box with a single 12" and both 12" PR's tuned to 28hz is my favorite. The amount of weight on those things in that box is retarded. Lol.

What PR's are those?

 

[TaylorFade 10+ year member]

Those are cutom Tantric PR's made with the same soft parts as the sub that I use.

It sounds awesome. But because I had to use so much weight to tune so low in such a small box, a sub without much motor has a tough time controlling the PR's at lower frequencies so the low end gets a little "muddy." I put a stronger sub in (the CF one) and it's much better. I like it becuase it's so small and it gets down low low. It's not an SPL build by any means, but I did have them in a 2cf box with (2) 12's @ ~ 30hz. That box did 145@35hz and 146@ 60hz. That's not bad from a trunk on 2k in such a small 30hz box.

 

[gckless 5,000+ posts]

Those are cutom Tantric PR's made with the same soft parts as the sub that I use.
It sounds awesome. But because I had to use so much weight to tune so low in such a small box, a sub without much motor has a tough time controlling the PR's at lower frequencies so the low end gets a little "muddy." I put a stronger sub in (the CF one) and it's much better. I like it becuase it's so small and it gets down low low. It's not an SPL build by any means, but I did have them in a 2cf box with (2) 12's @ ~ 30hz. That box did 145@35hz and 146@ 60hz. That's not bad from a trunk on 2k in such a small 30hz box.

That box had 2 powered woofers and 2 PR's? Did you notice any excursion issues with the PR's? Were they built with extra excursion capabilities?

 

[TaylorFade 10+ year member]

That box had 2 powered woofers and 2 PR's? Did you notice any excursion issues with the PR's? Were they built with extra excursion capabilities?

Yeah, (2) Tantric MD12's (750w rms/ea) in front, (2) matching PR's firing back.

When you don't have enough Sd or Xmax, you will run into PR's unloading at higher power. And I could unload these pretty quick below 35hz or so, but only at like, "demo" volume. Normal everyday listening, it was never a problem. In the single 12" box, I can't max those PR's out if I try.

They have the same excursion as the sub(s).

 

[T3mpest 10+ year member]

Best and easiest way to calculate tuning on a pr is to use a box program. Winisd alpha does pr setups and it will even model excursion to make sure you have enough cone area.. try creative sounds for passives. A lot of excursion great build quality and cheaper pricing than car audio branded passives. Plus weight on the front side is a genius idea.. makes adjusting tuning a breeze.