HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

Another crazy idea that may just work (or not).

Some rave on about infinite baffle speakers as being the ultimate. Large bass driver mounted in a wall for example and the rear of the driver outputting into an adjacent room or space which is extremely large when compared to the Vas of the driver concerned. You don't want to be able to hear any of the output from the rear of the driver.

Sounded like a good idea to me but i don't have any spare rooms that i can fire the rear of the driver into Then i remembered that my house has floorboards with a void underneath. I know this because of the work i have done in the past with water, CH pipes and electrical wiring going under the floorboards. I am assuming the void under the floorboards is large enough to make the idea work (volume of void about 10x the drivers Vas specification).

So the reality of this is a couple of 12" doped drivers firing upwards from floor level with a very large enclosure for the rear waves.

I can see complications here like;

*are the joists spaced far enough apart to be able to cut a 12" hole ? (I can't remember)
*there can be no messing about with positioning once the holes are cut and drivers installed
*is the under floor void acoustically separated enough from the listening room ?

From a space saving point of view it would be amazing. But what do i do with the 5" mid bass drivers ? Put them in the floor as well ? Have them in a conventional small enclosure with tweeter ? How well would the drivers integrate together (i don't have any problems with my current down firing 12", up firing 5" and front firing tweeters).

If i put the 5" mid bass in the floor as well then all i am left with above floor level is the tweeters. Mount them into the walls (brick and plaster) ?

Omg

Assuming it works if put miss and tweeter in a cube or a vertical infinite baffle

Latteman wrote: ↑Wed Oct 16, 2019 1:24 pmOmg

Indeed.

It's not just a matter of cutting the holes, dropping the drivers in and off you go. Void behind the baffle (flooring board in this case) needs to be at least 10x the Vas of the driver( Measured in litres (L), is a measure of the free air 'stiffness' of the suspension - the driver must be mounted in free air. It represents the volume of air that has the same stiffness as the driver's suspension when acted on by a piston of the same area (Sd) as the cone. Larger values mean lower stiffness, and generally require larger enclosures).

Suitable drivers are said to have a Qts between 0.5 and 0.7. The driver's Doc used are over 0.4 in their raw state. As i think doping increases Qts then maybe that makes them even more suitable for infinite baffle use. I have no way of measuring them without sending them off to someone who has (£cost).

It's a difficult thing to "suck and see" as Doc would say as it involves making holes in the bloody floor. Anyway, enough of these T&S parameters, Doc will be having a fit up there.

Well Stu............ you've fikin baffled me..!!!

What about sympathetic vibration from the floor itself? (Probably balanced by furniture placement).
How about an approximation by putting the driver in a board with legs and shuffling it around the room. Standard spacing of floor joists is 16 inch centres. Just a few thoughts.

What about......Spin the chamber and pass the revolver.

People have done this with cinema systems. 24" drivers with the rears facing into an attic or under-floor space.

It works well. And all you need to undo it is a few floorboard sections.

You can even have the drivers forward facing with a box around them that vents the rear sound though a large hole in the floor.

Seriously.?

terrybooth wrote: ↑Wed Oct 16, 2019 7:05 pm What about sympathetic vibration from the floor itself? (Probably balanced by furniture placement).
How about an approximation by putting the driver in a board with legs and shuffling it around the room. Standard spacing of floor joists is 16 inch centres. Just a few thoughts.

Well yes Terry, vibration of the floor must be taken in to consideration. Thanks for the standard joist spacing, i should get away with a 12 incher in there .