Passive Radiator question(s)

[evil_lies]

So I've been planning to put an old 10" MTX sub in a sealed box in my Jeep. I'm learning about passive radiators and may want to incorporate them in my design. So if I understand it correctly I need either double my cone size or double my x-max (throw?)? So according to the spec sheet for my MTX I have 9.4mm x-max for my 10" sub. I am looking at Dayton Audio PRs and either their 10" or 12" have 10mm x-max. So I could theoretically use either in my application? My plan was to downfire the MTX in a long, thin box (across rear trunk). I would prefer not to put the PRs on the top of the box for a few reasons, can I put them on the ends or on the side of the box (90 degree from the MTX)? Also, when tuning what is used for weight? Do you use magnets like a sub, or something else that you can add/subtract to tune with?

Click to read more...

 

[gckless 5,000+ posts]

You want at least double the Vd (Sd times Xmax) in your PRs as you have in your powered drivers. So, if you have the same amount of Xmax, I would do a pair of 10" PRs on each side of the box. That way their opposing movement cancels each other out as well, and you won't have a box jumping around. Normally washers are used for weight, but it depends on the PR and what kind of mount it has. If it's just a bolt, use washers.

 

[evil_lies]

You want at least double the Vd (Sd times Xmax) in your PRs as you have in your powered drivers. So, if you have the same amount of Xmax, I would do a pair of 10" PRs on each side of the box. That way their opposing movement cancels each other out as well, and you won't have a box jumping around. Normally washers are used for weight, but it depends on the PR and what kind of mount it has. If it's just a bolt, use washers.

Thanks, I saw your build thread while I was searching. I'm actually just a little outside S.A., and thought it was cool you were local. Another question I forgot to ask, my MTX is rated at 250 watts rms. Is that too little to push it and 2 PRs? Also, do I need to mount my sub inverted as you did in your build, or can they all be inside the box?

 

[gckless 5,000+ posts]

Thanks, I saw your build thread while I was searching. I'm actually just a little outside S.A., and thought it was cool you were local. Another question I forgot to ask, my MTX is rated at 250 watts rms. Is that too little to push it and 2 PRs? Also, do I need to mount my sub inverted as you did in your build, or can they all be inside the box?

No, the sub is still going to move to it's rated amount on that power, so it's all the same. You can mount regular no problem, just need to remember to have space around the powered sub so the PRs don't hit it when they get moving.

 

[evil_lies]

So it would be smart to place my powered MTX sub as near the middle of the box to not only keep from hitting the PRs, but to also (hopefully) keep the soundwaves an equal distance to the PRs and try to eliminate any "phasing" between three speakers working on one set of soundwaves? (if that makes sense)

 

[evil_lies]

Also, are the internals of a PR box different than a sealed box? Do I need any kind of baffling or bracing (or at least on a smallish box like the one I'm planning)?

 

[gckless 5,000+ posts]

So it would be smart to place my powered MTX sub as near the middle of the box to not only keep from hitting the PRs, but to also (hopefully) keep the soundwaves an equal distance to the PRs and try to eliminate any "phasing" between three speakers working on one set of soundwaves? (if that makes sense)

Yes sir.

Also, are the internals of a PR box different than a sealed box? Do I need any kind of baffling or bracing (or at least on a smallish box like the one I'm planning)?

It will be the same net airspace as a ported box for that sub. The only space savings are from the subtraction of a traditional port. I would brace a little better than a regular ported box, gonna have a lot more vibration.

 

[T3mpest 10+ year member]

Also, are the internals of a PR box different than a sealed box? Do I need any kind of baffling or bracing (or at least on a smallish box like the one I'm planning)?

You will want extra bracing from the extra moving mass. Also, if your interested, I have a 15inch passive radiator for sale, well 3 of them actually. Very nice ones, better than what your looking at, overkill for your build, but a single would work very well for you. You'd have a 15inch cone with 35mm of xmax, so MORE than enough for your subwoofer you could probably even run a pair at some point and have enough displacement. You may want to consider it. 10mm of xmax isn't much even for a subwoofer, let alone a passive. If you upgrade those daytons will limit you to the point of unuseability. Even a single mid tier 10inch car audio woofer can max out those daytons if you put over 500 watts o ***.. You'd pay about the same for one of my used passives as a pair of those daytons, but an excellent value for what you getting and they are "future proof" so to speak, since one could handle a mid to upper tier 12 by itself.

edit: the ones I'm selling also have weight adjustement in the FRONT! You unscrew the dustcap to add weight, much better design than the rear weights that you have remove the passive from the box to change. Adding and subtracting weight to adjust tuning is a major advantage to passives, mine take that advantage to the next level. Also, if you buy it, I can help you design a proper box for your passive, I'm quite knowledgable about passives, and stereo systems in general. (not to be cocky, just offering)

You'd want to put the passive on one side of the box, so you'd make to make the box tall and wide enough to mount the passive, but no taller or wider. These are very shallow and come with weight.

here is a link to the passives I am a selling

http://creativesound.ca/details.php?model=APR15

 

[evil_lies]

You will want extra bracing from the extra moving mass. Also, if your interested, I have a 15inch passive radiator for sale, well 3 of them actually. Very nice ones, better than what your looking at, overkill for your build, but a single would work very well for you. You'd have a 15inch cone with 35mm of xmax, so MORE than enough for your subwoofer you could probably even run a pair at some point and have enough displacement. You may want to consider it. 10mm of xmax isn't much even for a subwoofer, let alone a passive. If you upgrade those daytons will limit you to the point of unuseability. Even a single mid tier 10inch car audio woofer can max out those daytons if you put over 500 watts o ***.. You'd pay about the same for one of my used passives as a pair of those daytons, but an excellent value for what you getting and they are "future proof" so to speak, since one could handle a mid to upper tier 12 by itself.
edit: the ones I'm selling also have weight adjustement in the FRONT! You unscrew the dustcap to add weight, much better design than the rear weights that you have remove the passive from the box to change. Adding and subtracting weight to adjust tuning is a major advantage to passives, mine take that advantage to the next level. Also, if you buy it, I can help you design a proper box for your passive, I'm quite knowledgable about passives, and stereo systems in general. (not to be cocky, just offering)

You'd want to put the passive on one side of the box, so you'd make to make the box tall and wide enough to mount the passive, but no taller or wider. These are very shallow and come with weight.

here is a link to the passives I am a selling

Creative Sound - Product Details

Thanks for the offer, but a 15" will be too large for my application (very small space in a Jeep Wrangler). I'm almost wondering if I have enough space with the 3 10's. The box is getting bigger than I meant for it to be, which is fine I guess as long as I can get it to fit. I was hoping to keep it reasonable though so I can remove the box when I need the cargo space. The single 10 in a sealed box is no problem, and I don't think the 3 10s will be too unwieldy (I'm not a complete wienie).

 

[T3mpest 10+ year member]

Thanks for the offer, but a 15" will be too large for my application (very small space in a Jeep Wrangler). I'm almost wondering if I have enough space with the 3 10's. The box is getting bigger than I meant for it to be, which is fine I guess as long as I can get it to fit. I was hoping to keep it reasonable though so I can remove the box when I need the cargo space. The single 10 in a sealed box is no problem, and I don't think the 3 10s will be too unwieldy (I'm not a complete wienie).

I'd look hard at the passive link I posted go back a page and they have a 12 inch model. Box gets a hair bigger, by like I said you'll still only need one and its upgradeable compared to the dayton. Those Daytons will work, but you'll be pushing them decently hard I bet without modelling and if you ever got a better sub you'll be SOL

 

[evil_lies]

I'd look hard at the passive link I posted go back a page and they have a 12 inch model. Box gets a hair bigger, by like I said you'll still only need one and its upgradeable compared to the dayton. Those Daytons will work, but you'll be pushing them decently hard I bet without modelling and if you ever got a better sub you'll be SOL

I'll check out the link. I think if I upgrade I'd probably just build a new box anyway, but good looking out. A single 12" firing at the tailgate may be easier to fit than the 2 10's on the side. I guess that would take the "cancellation" effect of placing the two across from each other and I would need more bracing in the box?

 

[evil_lies]

Looking at the size constraints of the box, if I wanted to keep the PRs on the sides, could I use (2) 8" PRs and (2) 3.5 PRs? I don't know if it works that way or not.

 

[gckless 5,000+ posts]

Looking at the size constraints of the box, if I wanted to keep the PRs on the sides, could I use (2) 8" PRs and (2) 3.5 PRs? I don't know if it works that way or not.

No different sizes won't work.