DiyMobileAudio.com Car Stereo Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
290 Posts
Discussion Starter #1
So, I just finished the isobaric tuned ported enclosure for my truck yesterday, and it sounds pretty darn good :) That was fun ! So now I want to try something else ? {My GF thinks I'm crazy.... but surely some of you know what its like to do this kind of stuff just for play, right ?}

So here's my thoughts; I have this pair of RSS390HO-15"s. The recommended sealed enclosure airspace for these is 1.58 cubes, or 3.16 for the pair. So now I'm thinking about building such an enclosure, and adding one of these..... "Dayton Audio RSS390-PR 15" Aluminum Cone Passive Radiator" from www.parts-express.com!.
The typical advice for passive radiators is that they should provide at least double the displacement of the subs they are being used with. Well, my 15"s only have a peak to peak X-max of 26mm's and this passive radiator can do 60mm's. Shouldn't this work fine ? Any of you ever use passive radiators ? Any advice on this type of build ???
 

·
Registered
Joined
·
41 Posts
I've built a passive design subwoofer for home and debated using the drivers for my X6 but decided to use a different driver in a sealed enclosure.

I assume you know a passive radiator design is considered to be a ported alignment with a few advantages; Adding a PR usually allows for a smaller box and no port chuffing. On the down side it will cost more than a ported design and lose a bit of max SPL assuming the same amplifier and driver.
 

·
Registered
Joined
·
290 Posts
Discussion Starter #3
Thank you Midway. Yes, and I LOVE ported enclosures 🙂
Now, I have read that using PR's can increase the DB's by at least, but maybe more than, 6 DB's. I assume this to mean, "over the same subs in a sealed enclosure. To be honest, I haven't seen PR's compared straight across with standard ported enclosures... But you say, it can lose a bit of SPL ? Hmmm.

Right now, my only pause, is how to tune it ? I read the the PR can be weighted with washers that attach to the backside center of the cone.... But I mean, can this be calculated ? Before you mount the thing in the box ? How bad would it be to have to take the PR out and put it back in the box like 6 times, while you fumbled around trying to tune it by ear ?
 

·
Registered
Joined
·
1,342 Posts
Thank you Midway. Yes, and I LOVE ported enclosures
Now, I have read that using PR's can increase the DB's by at least, but maybe more than, 6 DB's. I assume this to mean, "over the same subs in a sealed enclosure. To be honest, I haven't seen PR's compared straight across with standard ported enclosures... But you say, it can lose a bit of SPL ? Hmmm.

Right now, my only pause, is how to tune it ? I read the the PR can be weighted with washers that attach to the backside center of the cone.... But I mean, can this be calculated ? Before you mount the thing in the box ? How bad would it be to have to take the PR out and put it back in the box like 6 times, while you fumbled around trying to tune it by ear ?
I haven't done it, but you can model a passive radiator box in WinISD, you just need the T/S specs for the PR then adjust added weight as necessary.
 

·
Premium Member
Joined
·
3,532 Posts
I haven't done it, but you can model a passive radiator box in WinISD, you just need the T/S specs for the PR then adjust added weight as necessary.
Or just model it as a port and then make the PR weight match what the frequency of the port youndeifned match.

One advantage is that if one is not handy with a pencil, then the maths to compute the port volume and then add that to the box volme gets easier... ;)
 

·
Registered
Joined
·
290 Posts
Discussion Starter #6
I think my solution is going to be, to mount my passive radiator inverted, so that I can super easily add or subtract weights from it, to be able to just play with it, until I get it dialed in perfectly. In fact, I could change the weight 27 X's, until I knew exactly what I liked, and then, after all that, I could go on and flip the PA around, flush mounted. Only thing is, this will decrease the box volume just a tad.... which might actually be a good thing, as its actually hard to build an enclosure small enough to work perfectly in an isobaric setup...

It's an interesting thing... but an enclosure big enough to mount two Isobarically oriented subs on top, and still be able to mount a 15" PA on any side, needs to be a cube of at least 16" x 16" > which, is borderline too much airspace..... Very unusual issue in car audio enclosures.

In any case, I have a Dayton 15" Passive Radiator on the way. So I will be able to play with it, and figure it all out :)
 

·
Premium Member
Joined
·
3,532 Posts
One has to consider if the PR will sag hanging vertically an SPL run out of travel in the sag direction... or some bungee to counteract the mass...?
A lot require a vertical panel
 

·
Registered
Joined
·
290 Posts
Discussion Starter #8
One has to consider if the PR will sag hanging vertically an SPL run out of travel in the sag direction... or some bungee to counteract the mass...?
A lot require a vertical panel
Now that is another interesting subject. I've often wondered about this kind of thing concerning speakers themselves.
Now, for my PR build, the PR will actually be mounted on the side of the enclosure, so no gravity induced sag. But what about my subs themselves ???
 

·
Registered
Joined
·
10 Posts
Designing PR enclosures is my job. This is my experience:

If you are going to use anything close to 26mm xmax peak-peak of the active drivers the PR will not work so well for a couple of reasons.

1. The PRs can move 60mm, but it doesnt have the suspension to do it well. Count on 30mm peak to peak without too much noise/distortion.
2. 26mm movement from two fifteens is 2.26L x2. So total displacement 4.5L. To make good use of the PRs you would need ~10L of displacement. That means four of them.

Keep power and/or expectations on the low side and you should be fine with two PRs and two active drivers.
 

·
Registered
Joined
·
290 Posts
Discussion Starter #10
Designing PR enclosures is my job. This is my experience:

If you are going to use anything close to 26mm xmax peak-peak of the active drivers the PR will not work so well for a couple of reasons.

1. The PRs can move 60mm, but it doesnt have the suspension to do it well. Count on 30mm peak to peak without too much noise/distortion.
2. 26mm movement from two fifteens is 2.26L x2. So total displacement 4.5L. To make good use of the PRs you would need ~10L of displacement. That means four of them.

Keep power and/or expectations on the low side and you should be fine with two PRs and two active drivers.
Johnathan, if your still around, I'm sorry I missed this....

I was reading your whole response just now, and I was thinking, "but I only used two PR's and it worked great" ! Then I got to where you said, "with two drivers" .....
I'm only using one driver. Granted, it's a massive 18" with a pretty long throw.... But yea, the two 15" Dayton PR's are doing a great job 🙂 This box sounds fantastic !
 
1 - 10 of 10 Posts
Top