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]

Originally posted by BAM
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]

Originally posted by BassAwdyO
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.