Isobaric subwoofer with passive radiator

[CrankyElbow]

Over the years I've employed most all subwoofer designs - generally focusing on maximum output... most recently I've come to enjoy an isobaric configuration utilizing a passive radiator.

This offers the lowest extension for a given cabinet volume while also giving the opportunity for great tune-ability (assuming an easy way to vary PR mass).

The trade-off is an enclosure that is half the size required for 1 driver and a design that is as simple to construct as a sealed enclosure for 2 woofers (if the drivers are inverted and mounted together via a mounting ring)... for a bit of PR mud (as compared to a port, though this is mitigated by the isobarik arrangement and smaller enclosure) plus the cost of 2 subwoofer drivers that will only output as much as one. The output of a PR will not match that of a properly configured port (especially flared tubes)... said proper (low tuned with sufficient surface area) port in a small enclosure very well could DOUBLE the enclosure size.

Here I have 2 10" MB Quart shallow mount woofers, ds1-254 with an earthquake SLAPS-m12 12" PR. Enclosure is ~1.25 cubic feet. This PR is EXTREMELY capable and easily tuneable.. the drivers are nothing spectacular (from a car audio setup) - being shallow and relatively light weight simply makes them easier to work with. I have Dayton HO 10's RSS265HO-4 that work extremely well in the same configuration - but the drivers stick out much farther, throwing off the balance (the enclosure would tip over if it were placed the same way), and weigh much more... I'll likely go back to them and build a more presentable cabinet with better materials (that does not have an inverted woofer sticking out - a similar driver/PR layout but with one driver mounted internally and box dimensions mod'd to accommodate) once I get the overall setup more dialed in. Mounting the second woofer internally adds some complexity and added volume to the design that I was trying to avoid with this iteration... though I can likely drop to an internal volume of ~.75cu ft and maintain extension... which will end up with a similar external volume.

I've had extremely loud with no focus on sound quality and extremely high fidelity with barely enough output to satisfy, and everything in between over my ~30 years in audio... this configuration for a home theater/leisurely listening/fun to build and tune subwoofer is by far my favorite to date.

Here is a ported box that offers similar frequency response, and much more output with the same drivers utilized... note the tremendous size difference! MUCH heavier and so much more difficult to carry... personally I love this enclosure as a 'piece of furniture', but obviously its a bit much to "hide". This enclosure has its advantages, but the added output takes the configuration further into the "knock pictures off the walls" territory I have not been interested in for some years now... side note, I've tested this with 4 of the MB quart 10's in an isobaric configuration, which yielded a fantastic overall response.

 

[sarumbear]

But isn’t the small size to do with the drivers you chose? Chose a driver with a smaller Vas and you will get the same outcome with just one driver. The resulting speaker will be easier to drive and cheaper.

 

[CrankyElbow]

But isn’t the small size to do with the drivers you chose? Chose a driver with a smaller Vas and you will get the same outcome with just one driver. The resulting speaker will be easier to drive and cheaper.

The same theory would still apply - that lower Vas driver would benefit in the same way. Having double the motor for the same cone area plus the smaller enclosure tightens up the response significantly.

You certainly could hunt for the perfect driver for a given application, and keeping things simple certainly is a great pathway... this is more for tinkering and specific applications that benefit from it.

The subs currently used here require a pretty large box to get anything under 40hz, setup this way they have a pretty solid response into the low 30's. There are drivers that could do the same in a smaller sealed enclosure - but part of the hobby is having fun, tuning a passive radiator is alot of fun and I've got a handful of subs laying around that I enjoy employing in a variety of applications

 

[sarumbear]

but part of the hobby is having fun, tuning a passive radiator is alot of fun and I've got a handful of subs laying around that I enjoy employing in a variety of applications

I agree but as the other part is learning I wanted to add my comment

 

[CrankyElbow]

I agree but as the other part is learning I wanted to add my comment

My apologies - the authority has spoken, both my original post and my response are invalidated. I should feel bad for even trying this nonsense - how dare I use what I have in a way that accomplishes the goals I have set forth (namely having fun - remember what "fun" is?)

That is.. I replied to your contrary stance, nothing personal... get over yourself.

"WANTED: Happy members who like to discuss audio and other topics related to our interest."

How about I get back to that...
And you can throw down the mic and hopefully find some joy in your life.

 

[Citizen]

Ha, I have been considering this very same project, the earthquake SLAPS-m12 12" PR is on my list, I like you have a few drivers laying about gathering dust(12" alpine type R,12" Magnat XTC 1200, 10" type S) and a few other random drivers that I just want to have a bit of fun with and see if I can get lower and louder than my pair of Rel HT1205's in half or so the size, you know just to have a bit of fun.