Passive Radiator question.

[Evyn1]

Looking at building a passive radiator 18”. Powered by a DD712.

Could it push (2) 18” Passive Radiators?

Cheerz

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[1aespinoza 10+ year member]

Looking at building a passive radiator 18”. Powered by a DD712.

Could it push (2) 18” Passive Radiators?

Cheerz

This video should give you an answer.

 

[SlugButter]

you can design a PR setup with either 1 or 2 radiators. You can do a sealed box air space with a single radiator or a ported box air space with 2 radiators. The most efficient use of space would probably be the smaller box with the single radiator, which will be tuned really low (25 HZ box tuning). The larger box with dual radiators could also be tuned low by adding a ton of weight to the radiators, but I’ve found that tuning dual radiator boxes to a traditional 30-35 HZ box tuning works really well. Changing air space inside the box changes how much weight you’ll need to add on the radiators to get the desired box tuning. You’ll definitely need to software model this if you want to get it right. Some passive radiators don’t have the xmax to do a single. The Earthquake sounds radiators have a ton of xmax, but the Dayton audio PRs I’ve used have alot less xmax.

 

[SlugButter]

This little 10 inch setup had great SQ. It wasn’t quite as loud as the same sub in a traditional ported box, but I can tune it as low or as high as I want.

 

[SlugButter]

The guy in the video made a better boom box than I made for the sound advice boom box build off. I used the same sub and amp he used, but I didn’t do passive radiators. I went with plain ported. That Tang Band 5.25 inch subwoofer is awesome for low bass output on low power. It rattles the hell out of my shop.

 

[Jimi77 5,000+ posts]

Imho, there are 2 pros to PRs. They don't require the space that the port would occupy. By adding/subtracting mass you can adjust the tuning frequency.

The downside is PRs unload faster than ports requiring a tighter hpf to prevent damage to the driver & PR.

 

[Evyn1]

Is it going to add a 18” subwoofer?
If the radiator is 18”.

I want the 18” sound difference. Basically I’d rather have an 18” then a port.

 

[Jimi77 5,000+ posts]

Is it going to add a 18” subwoofer?
If the radiator is 18”.

I want the 18” sound difference. Basically I’d rather have an 18” then a port.

Adding a PR is like adding a port. Same advantages and disadvantages of having a port. It will sound like a ported enclosure. Assuming your PR(s) have enough displacement, then you'll gain the output advantage of a ported enclosure.

 

[Evyn1]

Adding a PR is like adding a port. Same advantages and disadvantages of having a port. It will sound like a ported enclosure. Assuming your PR(s) have enough displacement, then you'll gain the output advantage of a ported enclosure.

Currently it’s in a ported bass reflex.

I’m almost sure it sounds different.

Different spectrum and more cone?

 

[Jimi77 5,000+ posts]

Currently it’s in a ported bass reflex.

I’m almost sure it sounds different.

Different spectrum and more cone?

A PR does the same thing as a port; it reinforces the low end by using the motion from the back of the cone and introducing a delay. They're both helmholtz resonators. The only way you'll know if they sound subjectively different is to build the PR enclosure.

 

[Evyn1]

Currently it’s in a ported bass reflex.

But I’m almost sure it sounds different?

A PR does the same thing as a port; it reinforces the low end by using the motion from the back of the cone and introducing a delay. They're both helmholtz resonators. The only way you'll know if they sound subjectively different is to build the PR enclosure.

Yeah there’s a significant difference in the curve.

Maybe the 18” PR will sound better to me than the port.

 

[Jimi77 5,000+ posts]

As I said PRs unload faster, which is what you're seeing in the graph. If you want the frequency response to roll off a few hertz earlier, then by all means go with a PR.

 

[Evyn1]

As I said PRs unload faster, which is what you're seeing in the graph. If you want the frequency response to roll off a few hertz earlier, then by all means go with a PR.

Today I learned about enclosure orders.

A standard bass reflex is considered a 4th order.

I learned that the bass roll off arguably defines the order of the enclosure.

Would this passive radiator represent a higher order enclosure? Because of its steeper roll off?

 

[SlugButter]

Today I learned about enclosure orders.

A standard bass reflex is considered a 4th order.

I learned that the bass roll off arguably defines the order of the enclosure.

Would this passive radiator represent a higher order enclosure? Because of its steeper roll off?

The “order” is describing the energy storage. its like a spring with a weight on the end (2 orders of stored energy), or a piston with a push/pull component. The coil(spring) is stored energy and the mass of the cone is stored energy, so a sub in a sealed box is a 2nd order (2 components of stored energy). Adding a port acts like adding a second “piston” with a push/pull effect, making it a 4th order. A PR is the same as a port essentially, having a spring and a mass(the cone) it adds 2 orders of energy storage, making a PR enclosure a 4th order. Adding 2 PRs to a single sub would make it a 6th order bass reflex enclosure, not to be confused with a 6th order bandpass enclosure.

 

[winkychevelle 10+ year member]

Short answer is yea it would work, long answer is that you would lose definition at higher frequencies due to the heavy moving mass. This can make the upper bass to midbass region sound muddy. Cross to over low and you will likely be fine but you might need a front sub or 8 inch mids in the kick ls to make up for the lost bandwidth