Passive Radiator and Ports.

[Evyn1]

How the (hack) can you tune a passive radiator and ports to the same frequency?

I have 6.75 Cubic ft.
(2) 6” Ports 33HZ.

Looking to put a Passive Radiator for the situation because adding more ports means more length and I can’t. So I might just switch to a 18” passive radiator.

But was wondering if I could keep the ports and use both to the same 33HZ?

How can I calculate this because it might change the length of the 6” ports in order to synchronize with the passive radiator. @33HZ

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[Firewalker]

@SlugButter @Buck

Both those guys know their stuff with boxes. I know slugbutter has done a couple maybe a few with those passive radiators.

 

[Evyn1]

@SlugButter @Buck

Both those guys know their stuff with boxes. I know slugbutter has done a couple maybe a few with those passive radiators.

It would be cool to have both. Thinking realistically I’ll need to replace the ports with a inverted 18” passive radiator.

I’m cuffing at volume 44.

But 36-39 is really deep and clean . So I’m managing nicely

 

[Evyn1]

A. Try inverted 18” Passive Radiator and the Ports.
B. (1) Single 18” Passive Radiator.

C. (2) Dual 18” Passive Radiators. Normal mount.

 

[SlugButter]

This isn’t going to work very well unless you’re very experienced at designing and building. If you were to try it, you’d have to match the amount of air the ports displace exactly to the amount of air the radiator displaces. VD. You’d have to design the box as if it has 3 ports of exactly the same size and length. The 2 ports would have to be sized exactly to the amount of air the radiator moves and tuned as if there are 3 ports in the box. The radiator would then be weighted and tuned to match the ports tuning exactly. It’s not that it can’t be tried, but I’m not really seeing a reason to do it. The 2 ports are already taking up space in the box, so the space saving benefit of using radiators is already moot. You’d also need to start from scratch and build an entirely new box. Modifying an old box with a radiator is not going to work.

 

[Buck 5,000+ posts]

I think if you could even get it tuned correctly, you’ll have cancellation issues, because the radiator and ports are going to reproduce frequencies differently even while tuned the same. I would stick with one type or the other.

 

[hispls 5,000+ posts]

Why would you consider using ports and passive radiator? Just pick one and work with it.

Determining passive radiator mass is quite simple. Model your box with port area equal to the piston area of your passive radiator. Determine the volume of that port, then determine the mass of air in that volume. That will be the mass you're aiming to get on your passive radiator. Or you could simply guess and test if you had easily changeable masses and some test tones or tool(s) to measure impedance and just watch where your Z-min lands.

 

[Evyn1]

Cool.

 

[Evyn1]

Why would you consider using ports and passive radiator? Just pick one and work with it.

Determining passive radiator mass is quite simple. Model your box with port area equal to the piston area of your passive radiator. Determine the volume of that port, then determine the mass of air in that volume. That will be the mass you're aiming to get on your passive radiator. Or you could simply guess and test if you had easily changeable masses and some test tones or tool(s) to measure impedance and just watch where your Z-min lands.

Will the Ports still be 33HZ if I match the Passive Radiator to a single port air mass?

Yeah might just use (1) 18” Passive Radiator high excursion.
A single PR 18” 4th order bandpass was kinda my plan.

I could just possibly optimize with the 18” PR (and both ports). Not counting on it.

Will experiment first then conclude.

 

[Evyn1]

If the Ports stay 33HZ at the same size volume of air with the PR. That would be ideal.

The weight of air volume in both ports is .003. Ounces.

 

[SlugButter]

If the Ports stay 33HZ at the same size volume of air with the PR. That would be ideal.

The weight of air volume in both ports is .003. Ounces.

Yeah, but you are essentially adding a 3rd port with the radiator introduced. Now the port tuning will no longer be 33 HZ, not to mention fact that you can’t control fhe size of the radiator to match the air volume the ports displace. The ports would have to be matched exactly in size and length, and be designed around the radiator.to displace the exact same amount of air while maintaining exact tuning frequency. This would take a few pieces of notebook sized scratch paper to do all the calculations involved and design it into a box.

 

[Evyn1]

Agh 3:1 experiment. Wasn’t counting on anything.

I’ll stick with the Bass Reflex 33 HZ for now.

 

[hispls 5,000+ posts]

The weight of air volume in both ports is .003. Ounces.

You're not trying to figure out the mass of air in your 3" port or whatever, you're trying to figure out the mass of air that you would need in an 18" round port for your desired tuning since an 18" port tunes by vibrating a column of air of that mass.

Start over by entering 18" round port into your box software and determining the port length required to get down to your desired tuning. Your mass is going to be closer to a pound assuming your box volume is 6 to 7 cubes or thereabouts.