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Can I install passive radiators into a speaker box with regular full-range speakers?

M

Mohammad Ali

New Member
I'm hoping to build wooden enclosures for these PC speakers I have. The drivers I'll be using will come from 2 different 2.0 PC speaker systems, and I'll be putting one driver from each into each "new" enclosure. I would also like to put passive radiators into the new enclosures. I've heard in the past that the PRs you use should be at least the same size as the woofers or drivers you're using (can't remember the exact wording tbh). The drivers I'll be using have diameters 7 cm and 4.5 cm, meaning their total area is 54 cm^2. This is the equivalent of one driver with diameter 8.3 cm. So can I put one PR of diameter 8.3 cm in each new enclosure, or is there something I'm missing?
 
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Depending on the frequency, a passive radiator can actually experience more cone excursion than the woofer. That's why it's common to have a passive radiator that is actually larger than the woofer. Having a passive radiator that is the same size as the woofer can work also. Since there is no magnet or voice coil on a passive radiator, the cone of the passive radiator is typically able to travel farther than the cone of the regular woofer.

It's hard to say how it would play out when using two active woofers in the same speaker cabinet. If they are all sharing the same internal air volume, keep in mind that the woofers will be interacting with each other in addition to the passive radiator.
 
Thank you for the swift response Chris.

I've noticed you use "woofers" to refer to the speakers. Does it make a difference to your judgment that the speakers I'm going to use are just full-range drivers, not woofers or subwoofers?

Thanks.
 
A passive radiator, in a perfect world, should have about twice the VOLUME DISPLACEMENT of the woofer.

Either a passive radiator with the same X-max as the woofer, but twice the cone area (like the 12" radiator with the 8" woofer referred to above), or a passive radiator with the same area, but twice the X-max, would both work fine...

Regards,
Gordon.
 
There is the occasional outlier defying conventional wisdom. An example from the Human Speakers site:

EPI Magnus CD 60 with 12 inch woofer having a single 10 inch PR.

epi-cd60 1.jpg

No idea how that works ...:dunno:
 
If the full-range speakers in each enclosure have diameters 4.5 cm and 7 cm, is it okay for me to use 2 PRs in each enclosure with diameters 4 cm and 8.3 cm? In case it matters, the combined area of the full-range speakers (~54 cm^2) is smaller than the combined area of the PRs (~67 cm^2)
 
I have a regular 2.0 PC speaker system and I was wanting to boost the bass on them a little, so I was wondering is it ok to install PRs into this system?

In almost all the other threads I've looked at people talk about the PR having twice the surface area of the woofer or a larger diameter than the woofer, but Idt I've come across anything confirming whether or not it's ok to put them into a box with regular full-range drivers.

Thanks
 
actually, the pr only has to be capable of moving twice the amount of air as the driver. whether that is accomplished via cone size or xmax or combination of the 2.

i don't think there is any rule saying that you can not use a passive radiator in place of a port with a full range driver as long as the driver has specs that make it suitable for a ported enclosure.

but as far as just throwing a pr into a sealed enclosure and thinking you will get better bass, that's about the same as drilling a hole in a cabinet and calling it ported.
 
Speakers aren't randomly assembled from available parts, the are actually designed for performance and price point. Meaning that the suspension, porting (if any), box size, and driver characteristics are all computed out and matched.

Changing anything will very likely result in sound quality degradation,
 
I ended up with a handful of pr's in a couple sizes to play with from all the junk I collect. I've popped them in with a few things and will agree with the others that finding a combination of all the variables that would render them an improvement in sound is kinda like intending to draw a royal flush in the first hand. I don't really know for sure, but I'd bet that adding to a sealed enclosure of any size will do the opposite of what you want - rendering the low bass less "quick" and "punchy" and more "smeared out" with less definition... not to mention allowing for greater excursion I.e. lower power handling. It will actually drop Q, right fellas? I could be backwards. Either way it will definitely affect the entire freq. bandwidth that it interacts with so, with a full range speaker, all of the music, not just the bass. You could end up dissipating alot of your upper mids.

Woofers that want a big huge enormous bass reflex are gonna be the most suitable to pr's, but even then you'll be changing the parameters for the woofer and whether it will be an improvement is something I couldn't know from numbers. I'm kind of a hack, myself. Far from professional, farther still from an engineer.

I wouldn't cut into your boxes. Not at all. I'd recommend starting from scratch and building AROUND the pr's, ideally utilizing a design that has some kind of following or history to back it up.

Possibly just adding a sub.

Possibly... Just investing in better speakers. What are they, exactly?
 
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^^ Bingo! When it comes to ports and passive radiators all the planets have to align. Driver specs, box size, port diameter and length, or passive radiator diameter and how it's weighted, etc. It take lots of math, test equipment and experimentation to get it right. With any good speaker design a lot of time and money is spent in the development stage.
 
unga-unga said:
Woofers that want a big huge enormous bass reflex are gonna be the most suitable to pr's
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not really. a driver can be optimized to work in a small ported enclosure and work fine with a pr. it's even possible that the box can be smaller because you don't have the volume that the port displaces.
 
Lavane said:
^^ Bingo! When it comes to ports and passive radiators all the planets have to align. Driver specs, box size, port diameter and length, or passive radiator diameter and how it's weighted, etc. It take lots of math, test equipment and experimentation to get it right. With any good speaker design a lot of time and money is spent in the development stage.
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but it sure is rewarding when you get a pr system right tho! i've done a couple. i'd do more but pr's cost more money than a piece of pvc or a couple extra pieces of mdf to make a slot port.
 
Smaller midbass drivers work very well in a largish box with a passive radiator.
Look at Polk speakers like the Monitor 5jr, 7, 10, etc. I have a pair of monitor 10's with two small midbass drivers and a large passive in a big box. Bass digs down into the high 20hz range. I also have a pair of the smaller 5jr's that sound pretty good with a single 5 1/2" midbass driver and a passive radiator. The 7's use a single small midbass driver also with a larger box and passive radiator and sound very good.
Here is a picture of the 10's.
 

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painttoad said:
but it sure is rewarding when you get a pr system right tho! i've done a couple. i'd do more but pr's cost more money than a piece of pvc or a couple extra pieces of mdf to make a slot port.
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Nice. I think I would give myself a headache trying to figure out a passive design. :biggrin:
 
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