Use passive radiator in a bandpass?

[rjon17469]

If a bandpass arrangement I have is predicting a very long port, would using a passive radiator be a viable alternative?

 

[m4dm4n]

Well i've tried it on a 6th order bandpass using tangband w8-740c.

It's hard to tell how it was, but it works.

The groupdelay would be a bit higher then vented bandpass.

 

[BAM]

Yeah, you theoretically can use a passive radiator. Some Logitech computer subwoofers do it.

 

[rjon17469]

Yeah, you theoretically can use a passive radiator. Some Logitech computer subwoofers do it.

Now, to my understanding, when you build a port, the port's resonance frequency is whatever the box is tuned to. A passive radiator has a different resonance frequency. Will this affect anything?

Or will it be similar to a ported vs passive radiator system? Slightly higher cutoff, slightly higher group delay?

 

[BassAwdyO]

In a ported box you have an airspring(the air inside the box) and a mass(the air in the port). Just like a solid spring and mass they will resonate at a specific frequency depending on the spring constant and the amount of mass. A PR is already a mass and a spring with its own resonant frequency. When this is coupled to the airspring of the enclosure it will create yet another resonant frequency which is the resonant frequency of the system. When the PR's resonance is played, the PR and enclosure interact in a destructive manner and the SPL dips, but slightly above that resonance is a boost just like a port. You can use a PR instead of a port but calculate the rear chamber just like you would a seperate PR box, with the same resonant frequency and the same volume.

 

[tiroth]

Or add sufficient mass to hit your target.

 

[Cal Weldon]

My experience goes like this.

I used to use passives because they seemed like a cheap way of getting some bass, regardless of the colouring of the sound. When my ears grew up I decided to try something. I was thinking that the problem with the drone cones was that you had to make them heavy enough to not respond to the higher frequencies present in the box. This made them somewhat "slow and sloppy" and if you will : offered forth a "confused sounding" low end. So I thought why not take a 15" woofer and two 15" drones, (old converted lighwieght pulp woofers with some added white glue stiffening) put them into three separate chambers with the woof in the middle and connect them via a tuned port on each side. My thought being, that by introducing a mechanical filter before introduction of the wave to the drone, you are reducing the need for mechanical damping on the drone. This will allow for a faster, less restricted drone. It seemed to tighten up the system. Has anyone else had a similar experience?

Just my eager but uneducated thoughts and experiences on a sunny Saturday in December.

Cal

 

[BassAwdyO]

that isnt a bandpass I believe from what you described. Its an alignment that doesnt have a common name. What you described was that the driver itself was in a bass reflex box which was vented into two boxes, one on either side, which then had passive radiators to radiate into space. That is exactly the same idea I had once. Good luck on designing the box with a predicted FR though!

 

[rjon17469]

that isnt a bandpass I believe from what you described. Its an alignment that doesnt have a common name.

That actually resembles a dual/triple chamber ported system, if you think about it....

 

[BassAwdyO]

Look at the attached picture below. A is the standard dual chamber bass reflex enclosure(not bandpass). I've heard C has no advantage over a standard single chamber BR, therefore B would not really have an advantage either, but perhaps due to the PR's higher order response characteristics it might have a desireable effect.

 

[Cal Weldon]

My chambers resembled B but with front firing drones. I can see how A and C might not improve anything but B looks to be a good idea simply because you have two different means of transmission, the port and the drone. The port being used to 'set-up' the drone.

It would be interesting to hear if there is validity in these thoughts.

Cal

 

[BassAwdyO]

If you ask me I'd say B and C would probably have little if any difference in response than a standard bass reflex enclosure, but A, that would be different. A is the dual chamber ported system desribed here: http://www.diysubwoofers.org/prt/dual_chamber.htm

 

[aarvin2]

I was asking myself the same thing as the legth of the port calculated was wayyyy to long.

Are there other alternatives to passive radiators ?

How do you tune the passive radiator + front chamber to a certain frequency?

Any results of your experiments ? 🙂

 

[Ron E]

Even a zombie thread deserves an answer! Hopefully it isn't some zombie dodo seeking brainz!

Use a PR with at least twice the Vd of the driver used. Design a front chamber with a port the size of the passive radiator - you will get a very long result. Calculate the volume of air in a port that size and figure out the mass. Subtract the mass of teh PR, and what is left is the amount of mass to add. You want the resonant frequency of the PR with mass added to be lower than the frequency range your BP box will be playing.

 

[sreten]

Hi,

I've never seen a PR used for the front chamber of
a 4th order bandpass, but it can be used for the
rear instead of a port for a 6th order bandpass.

Not that you can't use a PR for the front chamber,
but it makes no sense, and is very complicated
and needs a very unusual driver, specified to
couple with the PR for the low bass alignment.

rgds, sreten.

 

[aarvin2]

Even a zombie thread deserves an answer! Hopefully it isn't some zombie dodo seeking brainz!

Use a PR with at least twice the Vd of the driver used. Design a front chamber with a port the size of the passive radiator - you will get a very long result. Calculate the volume of air in a port that size and figure out the mass. Subtract the mass of teh PR, and what is left is the amount of mass to add. You want the resonant frequency of the PR with mass added to be lower than the frequency range your BP box will be playing.

Merci beaucoup! 😀

 

[Sonce]

I was asking myself the same thing as the legth of the port calculated was wayyyy to long.

Are there other alternatives to passive radiators ?

Lenght of the port is very long because the area of the port should be big enough. But guess what - commercial subwoofers very often have not big enough area of the port, so the lenght is acceptable.
Or for DIY home subwoofer just put the pipes out of the box, upright.

 

[aarvin2]

Lenght of the port is very long because the area of the port should be big enough. But guess what - commercial subwoofers very often have not big enough area of the port, so the lenght is acceptable.
Or for DIY home subwoofer just put the pipes out of the box, upright.

I thought of placing the pipes out of the box, but something like 2 meters of piping ? That wouldn't look very nice would it

 

[lcsaszar]

I built a 6th order bandpass with PR firing downwards. The net result is a boomy confusing sound, although it goes down to 20Hz. Also the harmonics above the passband are finding their way through the passive radiator, so they should be electrically filtered.

 

[aarvin2]

I built a 6th order bandpass with PR firing downwards. The net result is a boomy confusing sound, although it goes down to 20Hz. Also the harmonics above the passband are finding their way through the passive radiator, so they should be electrically filtered.

Can I mount a passive radiator down-firing?

The PR should never be down-firing, the high Mms will cause the diaphragm to be displaced downward immediately. The spiders will eventually be stretched permanently by this treatment, and the unit will need to be rebuilt.